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Recent Advances in Restorative Materials

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RECENT ADVANCES IN RESTORATIVE MATERIALS

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CONTENTS
INTRODUCTION
RECENT ADVANCES IN AMALGAM -bonded amalgam -silver-based mercury-free restorative alloys -nanocrystalline melt spun ag-sn-cu alloy ribbons -powder coated technology RECENT ADVANCES IN GLASS IONOMER CEMENTS -Variations in Basic Glass Composition -Modifications in powder -Modifications in liquid
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-Anhydrous cement
-Metal modified glass ionomer cement -Resin modified glass ionomers -Condensable glass-ionomer cements -Compomer (polyacid modified composite resins) -Giomer (pre-reacted glass-ionomer) - Ketac™ N100 light curing nano-ionomer restorative - NVP modified glass-ionomer cements -Nanobioceramics modified GICs -Zirconia–glass ionomer cement

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-Reactive fibre reinforced glass ionomer cements
- Casein Phosphopeptide-Amorphous Calcium Phosphate into a Glass-ionomer Cement -Chlorhexidine containing GICs

- Bioactive glass containing GIC
RECENT ADVANCES IN COMPOSITES Ceromers

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Ormocers
Composite inserts Fibre reinforced composites Nanocomposites
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RECENT ADVANCES IN BONDING SYSTEMS RECENT ADVANCES IN CERAMICS SMART MATERIALS SUMMARY CONCLUSION REFERENCES

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INTRODUCTION
Different types of restorative materials and luting cements are currently used in daily dental practice
The most common are amalgam, composite resins, glass ionomer cements, ceramics etc Each material has several advantages and disadvantages To overcome the drawbacks of various materials, there has been a continuous research for the advent of newer and better restorative materials

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RECENT ADVANCES IN AMALGAM

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BONDED AMALGAM RESTORATION
Despite all the advantages, amalgam has its own limitations as a restorative material

It lacks adhesion to the tooth structure and thereby requires considerable removal of more intact tooth structure to provide long term retention.
Accordingly, amalgam weakens remaining tooth structure rather than strengthening it. This is the main reason of cuspal fracture in long standing silver amalgam restorations.
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Other limitations of amalgam restoration are: Increased microleakage under amalgam restorations. Decreased tensile strength under complex amalgam restorations.

Corrosion.

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To combat the above mentioned limitations, adhesive systems designed to bond amalgam to enamel and dentin have been introduced in an effort to compensate for the "disadvantages particularly marginal microleakage and need for additional retentive devices.

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ADVANTAGES:

The advantages of adhesive amalgam restoration over nonadhesive treatment alternatives are : It is a treatment option for extensively carious posterior teeth, with a lower cost than either cast metal restoration or metalceramic crowns. It allows use of amalgam in teeth with low gingivo-occlusal height which is not possible in conventional amalgam, amalgam with pins, inlays, onlays, complete cast crown restoration. It permits more conservative cavity preparations, as it does not require additional retention in form of groove, pins etc.
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It can eliminate use of retention pins and inherent risk involved with it such as periodontal perforation, pulp exposure, stress patterns, cracking, crazing etc.
It reduces marginal leakage to minimal. It reinforces the tooth structure weakened by caries and cavity preparation, which is not with pin amalgam. It reduces incidence of post-operative sensitivity commonly observed with amalgam restorations.

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“Six year evaluation of bonded and pin retained complex amalgam restorations.”

J.B.Summit . JO Burgess . TG Berry

Op dent 2004, 29-3, 261-268.

A bonded restoration

1A –pre –op view
1B – preparation ,showing gingivally deep extension in mesial aspect 1C -- restoration immediately after completion 1D – restoration after six years

A pin retained restoration 2A – preop view

2B – preparation after pin placement
2C – at base line evaluation 2D – restoration after six years

It reduces incidence of marginal fracture and recurrent caries.
It allows biologic sealing of P-D complex by formation of hybrid layer. It can be done in single sitting. It allows for amalgam repairs.

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AMALGAM BONDING AGENTS:
Some bonding agents which are able to bond amalgam to tooth structure are:

Amalgam bond plus
All Bond 2 and AU Bond Liner F Panavia Ex .

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Chemical composition:
Amalgam bond plus: Activator/Conditioner: 10% citric acid, 3% ferric chloride. Adhesive: HEMA (Hydroxyethyl methacrylate). Catalyst: TBB(Tri-N-Butyl-Borane oxide).

Base: 4META(4-Methacryloxyethyl trimellitate anhydride).

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MECHANISM OF BONDING

First the dentin and enamel are treated with an acid conditioner i.e. 10% citric acid, 3% ferric chloride for 10 seconds.

This causes the removal of smear layer and partial demineralization of collagen with removal of only apatite mineral and preserving the integrity of dentinal protein molecules. These open pores are now penetrable by 4 META/MMA-TBB monomer.
Monomer penetration can be improved by treating the surface with application of HEMA.

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Once polymerized, the resin formed not only entangles and envelops collagen but also encapsulates hydroxyapatite crystals, creating the acid-resistant, insoluble transitional zone, hybrid layer.

The width of hybrid layer in 5 m and is sandwiched between cured resin and dentin.

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TECHNIQUE:

Due to bonding system available, minimal retention form is required during cavity preparation. However, cavity preparation still requires adequate resistance form. Fragile cusps and walls should be reduced.

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After proper isolating and anesthesia, all carious tooth structure is removed. Surface is etched with 10% phosphoric acid gel.

Then washed for 15 seconds and dried with air jet.
After drying, conditioned enamel has dull white appearance. Three coats of primer A and primer B are applied till shiny aspect caused by hydrophilic resin incorporated in primers is obtained. The dentin-enamel bonding agent is applied with brush and freshly triturated amalgam is condensed into cavity before the auto curing bonding agent is polymerized.
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Bonded amalgam – clinical procedure

Upper second premolar with a fractured disto occlusal amalgam restoration

Rubber dam placed with interproximal wedging , and showing the fractured amalgam has been removed along with any caries

After etching and priming a thin layer of bonding resin is applied to the cavity using a disposable brush

Wax coated stainless steel matrix band placed and wedged

Bonded amalgam – clinical procedure

Amalgam placed and heavily burnished

A gel is placed occlusally and interproximally to allow complete anaerobic setting of adhesive resin

Initial carving and removal of matrix

After removal of the rubber dam, occlusal adjustment , final carving and polishing

LIMITATIONS OF BONDED AMALGAM:

Time consuming and may be technique sensitive due to bonding agents used.
Requires practitioner to adapt to new technique.

Increases cost of amalgam restorations.

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“The effect of amalgam bonding on the stiffness of teeth weakened by cavity preparation”
Omar Zidan , Usama abdul-kareim

Dent materials 2003 Nov ;19(7) : 680-5

Cavity preparation reduced the stiffness & weakened the tooth. Restoring the prepared tooth with unbonded amalgam did not restore the lost tooth stiffness. It was concluded that bonding amalgam to tooth structure could partly restore the strength & rigidity lost by the cavity preparation. This might lead to a reduction in cuspal flexure & the incidence of tooth fracture due to fatigue.

Bonded amalgam sealants and adhesive resin sealants:Five-year clinical results (Quintessence Int 2004;35 )

Bonded amalgams were used as pit-and-fissure sealants without mechanical preparation.

They were compared with resin-based pit-and-fissure sealants for retention over a 5-year period.
Clinical examinations at 6 months, 1 year, 2 years, and 5 years revealed no difference between the two techniques.

They can be used to seal pits and fissures surrounding very conservative preparations, in the “preventive amalgam restoration.”
Conventional amalgam retentive features and 90-degree cavosurface margins may not be necessary when bonding is used with amalgam.

Effect of surface roughness on amalgam repair using adhesive systems (Braz. Dent. J. vol.13 no.3,2002) Result

The use of adhesives has been suggested for repairing amalgam restorations associated with the roughening of an old amalgam surface . The application of an adhesive system could improve bonding between old and new amalgam through mechanical interlocking between the adhesive system and freshly condensed amalgam . The irregular surfaces are micromechanical retentions for bonding of primer to old amalgam and can be created with a carbide bur, diamond bur or aluminum oxide particle abrasion

Development of silver-based mercury-free restorative alloys
Although, amalgam remains the most inexpensive, reliable and popular restorative material for posterior teeth.

Recent controversy surrounding mercury has renewed interest in developing a mercury free restorative material with physical properties comparable to dental amalgam Mercury free metallic restorative materials proposed as substitute for mercury containing amalgam are gallium containing materials and pure silver and/or silver based alloys.

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GALLIUM ALLOYS
Puttkammer suggested the use of gallium in dental restoration in 1928. However, attempts to develop satisfactory gallium restorative materials were unsuccessful until Smith and others in 1956, showed that improved Pd-Ga and Ag-Ga materials has physical and mechanical properties that were similar to or even better than those of silver amalgam.

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ADVANTAGES OF GALLIUM BASED ALLOYS:

Rapid solidification. Good marginal seal by expanding on solidification.

Heat resistant.
The compressive and tensile strength increases with time comparable with silver amalgam

Creep value are as low as 0.09%
It sets early so polishing can be carried out the same day They expand after setting therefore provides better marginal seal
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Reaction

The alloy and liquid are mixed as usual. The structure of gallium alloy resembles that of amalgam. The reaction between AgSn particles and liquid Gallium involves the formation of AgGa phase and a pure tin phase. AgSn + Ga  AgGa + Sn.

After mixing, the alloy tends to adhere to the walls of capsule, thus difficult to handle. Moreover, by adding few drops of alcohol, the problem of sticking can be minimized

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Properties of gallium:

MP: 24.78ºc ; BP : 1983ºc
Density : 5.90 gm/cm3 Has the property of wetting many materials including tooth structure Sets in a reasonable time and possess the strength , diametrical stability and corrosion resistance equal to or even greater than silver amalgam
(dental materials 2000,vol 16,97-102)

Composition: Recent gallium alloys have following composition:

Alloy:
silver -- 60% tin -- 25%

copper -- 13%
palladium – 20% Liquid: gallium -- 62% iridium tin -- 25% -- 25%

Physical properties of high copper silver amalgam and gallium alloys Alloy Creep% Compressive strength (after 6hrs) 370MPa Setting contraction /expansion (%) -0.05

Silver alloy (high copper)

1.04 ± 0.06

Gallium alloy (Galloy) Enamel Dentin

0.09 ±0.03

350MPa

+0.39

384 MPa 297 MPa

Biologic considerations

In early gallium alloys, surface roughness, marginal discoloration and fracture were reported. With improvement in composition, these defects were reduced but not eliminated The gallium alloys could not be used in larger restorations as the considerable setting amount of expansion leads to fracture of cusps and post operative sensitivity.

The cleaning of instruments tips is also difficult
It is also less popular because it is costlier than amalgam.

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POWDER COATED TECHNOLOGY
A technology has been developed recently at the National Institute of Technology (Gaithersburg, Maryland, USA) that allows the formation of two types of condensable metallic composites One approach consists of cold-welding silver that is based on a powder technology and transforming it from an extremely plastic mixture to a solid within the prepared tooth at oral temperature. The second approach is to condense a mixture of two intermetallic compounds, Ag4Sn (beta phase) and Ag3Sn (gamma phase), or similar alloy particles that have been silver coated and which have undergone an appropriate treatment in a surface-activating solution
International Dental Journal (1998) Vol. 48/No.1

This technology involves electrochemical powder treatment and a condensation technique which is similar to that used for direct filling gold foil.
During consolidation, the adherence of silver surfaces is enhanced after immersion of the silver-based particles in a solution of 10 per cent fluoroboric acid (HBF4). The metal segments must be stored in this special acid solution prior to use to remove surface oxides and to enhance cold welding. Thus, this product may be more technique sensitive than dental amalgam and may require more time for proper condensation.

Advantages

Flexure strength as that of amalgam Smooth surface and hardening was obtained More resistant to wear because of work hardening

A silver-tin alternative to dental amalgams (journal of material research 1995)

A novel technology for a mercury-free metallic direct filling material, a substitute to dental amalgams. A dilute acid is used for removing the surface silver oxide layers, thereby promoting the cold-welding process. The condensability, namely the ability of a loose powder to undergo consolidation within a short time duration, at body temperature and under moderate pressure has been investigated for a variety of mixtures of silver, tin, and prealloyed silver-coated intermetallic powders. The resulting metallic composite material displays transverse rupture strength values higher than those of amalgams and somewhat lower values of compressive strength and Knoop hardness.

A NEW DENTAL POWDER FROM NANOCRYSTALLINE MELT SPUN Ag-Sn-Cu ALLOY RIBBONS

A new non-gamma-two dental powder has been developed from nanocrystalline melt-spun Ag-Sn-Cu alloy ribbons.

The amalgam made from this powder exhibits excellent properties for dental filling.
The nanocrystalline microstructure was found for the first time in as-spun and heat treated Ag, Sn, Cu alloy ribbons, using X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy.

As-spun ribbons exhibited a multi-phase microstructure with preferred existence of (Ag4Sn) phase formed during rapid solidification (RS) due to supersaturating of copper (Cu) atoms and homogenous nanostructure with subgrain size of about (40-50) mn, which seems to be developed during RS process and can be caused by eutectic reaction of the Ag3Sn/Ag4Sn-Cu3Sn system.

In heat treated ribbons the clustering of Cu atoms was always favored and stable in an ageing temperature and time interval determined by Cu content.
The heat treatment led to essential changes of subgrain morphology, resulted in the appearance of large-angle boundaries with fine Cu3Sn precipitates and forming typical recrystallization twins.

Such a microstructure variation in melt-spun ribbons could eventually yield enhanced technological, clinical and physical properties of the dental products, controlled by the ADA Specification NO.1 and reported before. Thus, using the rapid solidification technique a new nongamma-two dental material of high quality, nanocrystalline ribbon powder, can be produced

RECENT ADVANCES IN GLASS IONOMER CEMENTS

Glass ionomer is the generic name of a group of materials that use silicate glass powder and an aqueous solution of polyacrylic acid The severe pulp irritation caused by silicate and zinc phosphate cements led to the replacement of phosphoric acid by polyacrylic acid resulting in zinc polycarboxylate first and GIC later.

Though, glass-ionomer was originally aimed to be restorative material, soon it was modified as luting cement also. The early cement was a slow setting and highly technique sensitive. But since its introduction, it has undergone many changes
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CLASSIFICATION FOR GLASS IONOMER CEMENT

A. According to Wilson and McLean in 1988

1. Type I 2. Type II

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Luting cements Restorative cements a. Restorative aesthetic b. Restorative reinforced

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B. According to application

1. Type I
2. Type II

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Luting cements
Restorative cements a. Aesthetic filling materials b. Reinforced materials (Fuji IX, Fuji II LC) Lining or base cement

3. Type III -

4. Type IV 5. Type V -

Fissure Sealant
Orthodontic cement Core build up cement
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6. Type VI 4 May, 2012

C. According to characteristics specified by the manufacturer
1. Type I - Luting cement (e.g.) Fuji I, Ketac 2. Type II - Restorative material (e.g.) Ketacfil, Fuji II, Fuji IX etc

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3. Type III

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a. Bases & Liners

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Weak with less acidic
(eg.) GC lining cement, Shofu liner

b. Bases & Liners bond, Shofu base

Stronger but more acidic eg Ketac

c. Bases & liners cure (vitrabond) 4. Type IV Mix
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Strong even in thin layer (eg.) Light

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Admixtures (eg) Ketac Silver, Miracle

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D. Newer classification

1. Traditional Glass Ionomer a. Type I b. Type II c. Type III Luting cement Restorative cements Liners & Bases

2. Metal modified Glass Ionomer a. Miracle Mix b. Cermet Cement

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3. Light Cure Glass Ionomer
HEMA added to liquid

4. Hybrid Glass Ionomer / Resin modified Glass Ionomer
a. Composite resin in which fillers substituted with glass ionomer particles

b. Pre-cured glasses blended into composites

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E. According to McLean et al in 1994

a. Glass Ionomer Cements (Traditional) b. Resin modified Glass Ionomer cements

c. Poly acid modified composite resins

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Composition
Traditional glass ionomer

Powder
Constituent Silica (SiO2) Alumina (Al2O3) Aluminum fluoride (AlF3) % by weight 35 – 50 20 -30 1.5 – 2.5

Calcium fluoride (CaF2)

15 – 20

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Sodium fluoride (NaF)

3.0 – 6.0

Aluminum phosphate (AlPO4)
Canthanum, Strontium, Barium

4.0 – 12
Traces (for radiopacity)

Liquid Polyacrylic acid Itaconic acid Maleic acid 5% (Decreases viscosity) 45%

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Tricarballylic acid Tartaric acid Traces (Increases working time and decreases setting time) Water 50% (Hydrates reaction product)

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Cement ASPA I

Class Conventional

Type Filling

Powder G-200

Liquid 50% PA-1

ASPA II

Conventional

Filling

G-200

47.5% PA-1, 5%

TTA
ASPA III Conventional Filling G-200 45% PA-1, 5% TTA, 5% CH 3 OH ASPA IV Conventional Filling G-200 47.5% 5% TTA ASPA IV a Conventional Luting G-200A 47.5% 5% TTA ASPA V Water– hardening ASPA V a Waterhardening ASPA X
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PA-48,

PA-48,

Filling

G-200:PA2(5:1)

10% TTA

Luting

G-200a: PA-2

10% TTA

Conventional

Filling
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G-338

47.5% 5% TTA

PA-48,
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Variations in Basic Glass Composition:

Calcium may be replaced wholly by strontium, partly replaced by barium , both being alkaline earth metals ,or lanthanum a rare earth metal that gives radio-opacity

Glasses may be modified by incorporating alumina fibers, amalgam alloys and metals. These modifications were made to improve the flexural strength.

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Modifications in powder

The modifications were to improve upon the existing property in the manipulation and the area of clinical use. Some of the modifications are: Direct polyacrylic acid (anhydrous GIC)

Silver – Tin alloy (Miracle Mix)
Silver – Palladium / Titanium (Cermet cement) BISGMA, TEGDMA and HEMA (light /dual cure GIC) NVP, CPP-ACP, Zirconia etc

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Modifications in liquid

Only water and tartaric acid (anhydrous cement)

HEMA (Light cure components)
Polyvinyl phosphoric acid

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In 1992, polyvinyl phosphoric acid was found to form cements with a wide range of metal oxides in aqueous forms. It has a structure similar to poly (acrylic acid) but contains pendant phosphoric acid P (O) (OH) 2, groups in place of the carboxylic acid -COOH groups of the zinc polycarboxylate and glass polyalkenoate cements. It is stronger acid than polyacrylic acid with a greatly increased reactivity towards metal oxides.

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The physical and mechanical properties of a number of metal oxide PVPA cements were studied and compared with those of zinc polycarboxylate cements. The faster acting of the metal oxide PVPA cements seems to produce cement that is less susceptible to early hydrolysis.

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Diamond Carve: Diamond carve (Associated Dental Products. Ltd; Swindon, UK) is a GIC that has been modified by addition of small percentage of poly vinyl phosphoric acid (PVPA), phosphorous analogue to PAA. PVPA is a stronger acid than PAA and hence more reactive

Chemically- more hydrolytically stable

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Anhydrous cement

Termed ASPA V by Prosser et. al. 1984. Anhydrous means that the acid has been freeze dried and included in the powder. The polyacrylic acid can be vacuum dried and incorporated with the glass powder.

The liquid then used being either water or a dilute aqueous solution of tartaric acid.

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Advantages:

1) Low viscosity in early mixing stages.
2) Rapid set at minimum temperature. 3) Easy manipulation. 4) Excellent shelf life.

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METAL MODIFIED GLASS IONOMER CEMENT
Metal modified cements are two types:
Silver alloy admix - amalgam alloys are interpreted into the glass powder.

Cermet ionomer cement - precious metals like silver, gold, titanium, palladium etc incorporate in glass powder. Silver is commonly used Glass is generally brittle and addition of silver was expected to improve the toughness of the cement as silver acts as stress absorber and also improves the abrasive resistance of cement.
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GLASS CERMETS This was introduced by Mclean and Gasser in 1985. Glass and metal powders were sintered at high temperature. This was attempted to improve the wear resistance, flexural strength and at the same time maintains the aesthetics

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CERMET CEMENT
The main disadvantages of conventional glass ionomers are brittleness, poor surface polish, porosity and surface wear. Improvements in these areas are essential if the clinical use of glass ionomer cements is extended to high stress bearing areas. Cermet was introduced in 1984 under the trade name Ketacsilver.

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The incorporation of a disperse-phase such as corundum (Al2O3) into the glass can double the flexural strength of the glass ionomer cement. However, little improvement in wear resistance was obtained. The incorporation of alumina fibers also increased the flexural strength of the cement but resulted in decreased abrasion resistance.

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Sced and Wilson investigated the effect of incorporating metal fibers or powders into the glass ionomer powder. Flexural strengths were increased but abrasion resistance was poor, because of lack of strong bonding between the metal filler and the polyacrylate matrix The problem of obtaining strong bonding of metal fillers to glass ionomer powder was solved by sintering the metal powder into the glass powder

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Strong bonding of the metal glass composite resulted in the formation of a cermet in which, unlike simple mixtures of metal and glass powder, the metal became part of the glass powder, and the strength of the bond was comparable to that of fusing porcelain to gold.

Currently, two types of silver cermet ionomers are available. One for hand mixing (Chelon - Silver ESPE) and other for automatic mixing in capsules. (Ketac-Silver, ESPE).

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Properties: Ketac - silver has better resistance to abrasion than regular glass ionomer Occlusal wear resistance was also close to that of amalgam alloy and microfilled composite resin (improved wear resistance could be caused by the lubricating effect of the silver). Flexural strength of the cermet ionomers is better than most commercial glass ionomer cements. Table 6.1

Fracture toughness is better than conventional glass ionomer cements.
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CLINICAL USES: As a restorative material for Class III; Class V lesions. Core Build Up: Linings Fissure fillings Restoration of primary teeth:

Restoration of class II lesions (Tunnel Preparation)
Defective margins
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SILVER-ALLOY POWDER AND GLASS IONOMER CEMENT: (MIRACLE MIX) Adding silver alloy powder to a type II restorative glass cement powder and mixing this powder admixture with polyacrylic acid liquid was intended to make this first metal reinforced glass ionomer cement radio opaque and harder.

Addition of this spherical silver alloy powder to the pure hydrous restorative type II glass ionomer cement is termed as "Miracle Mix".

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Properties: Adding silver alloy powder to glass ionomer improves Compressive strength Tensile strength

Creep resistance
Less microleakage Increased dynamic flexural strength.

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RESIN MODIFIED GLASS IONOMERS
They were introduced to overcome the problems associated with the conventional glass ionomers and at the same time preserving the clinical advantages of the conventional materials.

These combined the technologies of resin composites and conventional glass ionomers.
In general, the resin modified glass ionomer materials are the hybrid of a glass ionomer and resin composites.

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In 1988(Autonucci et al) introduced the first light curable glass ionomer cement. And this was formed a combination of a conventional glass ionomer cement with a light cured resin composites The advantages include immediate stabilization of the water balance following the light initiation as well as enhanced translucency in the ultimate restoration.

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The main disadvantage appears to be the need for incremental build up for a restoration deeper than 3-4mm, because the light penetration is limited to that depth.

However, there is a safety factor in as much as acid/base reaction will continue, even in the absence of light activation. In addition, the presence of a redox reaction in the resin component ensures complete setting of the entire restoration under all circumstances.

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Classification of Resin Reinforced glass ionomers
Depends on the curing mechanism Dual cure: Visible light cure free-radical polymerization and glass ionomer setting mechanism (Acid-base reaction). E.g. Geristore. Tri-cure: Visible light free radical methacrylate polymerization. -Chemical cure of free radical methacrylate polymerization of composite resin.
- Conventional acid base reaction. E.g. Vitremer, Fuji II LC.
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Photocure: Visible light cure only. E.g. Polyacid modified composite resins, variglass, compoglass,Dyract, Hytac. Autocure: Chemical cure of the radical methacrylate polymerization only autocure. E.g. Prosthodont.

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Once activated by intense visible light, they set rapidly. The reaction is dual setting. The normal glass ionomer cement acid-base reaction.

Free radical or photochemical polymerization process similar to that used in composite resin.

Acid-base reaction: Calcium alumino silicate + polyacrylic acid= calcium and aluminum polysalt hydrogel.
Polymerization reaction: HEMA + Photochemical initiator/ activator poly HEMA matrix.

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Advantages of resin modified glass ionomer cement’s over conventional glass ionomer cements: Sufficiently long working time controlled in command to a snap set by photocuring. Improved setting characteristics. Protects the acid base reaction from problems of water balance. Rapid development of early strength. Can be finished and polished immediately after set.

Repairs can be easily carried out, as the bond between old and new material is very strong.
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Exhibits increased adhesion to composite when used as a base. Ideal under composite as it can be etched immediately. Fluoride release is greater than conventional glass ionomer cement and compomers. Diametral strength is high (20Mpa).

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Resin-modified glass ionomer cements: a comparison of water sorption characteristics The purpose of this study was to quantify and compare the amount of water absorbed by six commercially available resinmodified glass ionomer cements and to investigate the possible influence of time and resin content on water sorption. The materials evaluated included Variglass used as a restoration, base and liner; Fuji II LC; Fuji Liner; Vitrebond; Vitremer and Photac-Bond. Z100, a composite resin, was used as control Variglass when used as a base or restorative had the least water sorption after both 1 week and 1 month storage in water. The degree of water sorption was product dependent and appeared to be influenced by the resin (HEMA) content

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Disadvantages:

Biocompatibility is controversial.
Setting shrinkage is higher microleakage is more, marginal adaptation is poor.

Low wear resistance compared to composite.
Poor fracture toughness. Color that cannot compare to composite in its ability to match natural tooth coloration (Theodore P Croll, 1991).

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Uses: Used for luting stainless steel crowns, space maintainers, bands in pedo cases. Used as a liner and base. Pit and fissure sealant. E.g. Fuji II LC (Bases- GC), Photacfil- ESPE, Vitrebond3M,Vitremer - 3M

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Core build up material.

Repair material for damaged amalgam cores or cusps.
Retrograde filling material.

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FUJI II LC IMPROVED This is a light cured resin reinforced glass ionomer restorative introduced by GC corporation. Tokyo, Japan. Fuji II LC improved has all the advantages of a traditional glass ionomer along with important advances including triple curing, immediate finishing, outstanding esthetics, simplified technique and significant time savings. Fuji II L.C improved has smaller particle sizes for greatly improved polishability and a conditioner which provides enhanced bond strength.

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FUJI BOND LC This is a resin reinforced light cure glass ionomer for bonding composites. Fuji bond LC is a bonding agent that protects and seals against microleakage and eliminates sensitivity.

This requires simple and very easy application.
The Co-efficient of thermal expansion of this material is closer to that of tooth structure.

It provides all the benefits of a true glass ionomer in the composite restoration

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Working time – 2 minutes. Light cured in 20 seconds Conditioning the tooth surface is done before applying this glass ionomer bond. The bond can be co-cured with composite resin. The advantage is composite resin will cure faster than the glass ionomer bond. The polymerization shrinkage will occur in the composite prior to complete setting of glass ionomer bond. This allows the glass ionomer bond to absorb the polymerization shrinkage forces helping to reduce the internal stress created.

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TRI CURE CEMENT

Primer – consisting of the Vitrebond copolymer, HEMA (2hydroxyethylmethacrylate), ethanol and photo-curing agents.
Glass powder – consisting of fluoroaluminosilicate glass particles. Liquid – consisting of an “aqueous solution of polyacrylic acid modified with pendant methacrylate groups” (Internal communication, 3 M dental products division). Also in the liquid solution are the Vitrebond copolymer, HEMA, water and photoinitiators for the visible light curing reaction. Resin glass – consisting of a clear, BIS-GMA/TEGDMA visiblelight polymerizing, dental bonding resin liquid.

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These materials are termed “tricure” as the resin modified glass ionomer cement sets by three phenomena.

Acid base reaction between the components of conventional glass ionomer cement.
Light cure reaction stimulated by light application – activates the initiator catalyst resin cure system. Autocure reaction – When the powder and liquid components are mixed together, the initiator catalyst system of resin gets activated and ensures that over time there will be a complete cure throughout the entire restoration with no free resin remaining.

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Modification of the glass-ionomer formulation with a visible light curing resin component improves the physical properties of the cement, simplifies clinical handling of the material, and significantly reduces operating time. The resin component allows for “on command” initial hardening, and the set cement has all the beneficial properties of traditional glass polyalkenoate formulations such as
Biocompatibility Forming a chemical bond to tooth structure Fluoride ion release with uptake by adjacent tooth structure Coefficient of thermal expansion quite similar to tooth structure
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Hydrophilic nature Tooth shades Injectability for easy handling Low solubility in the oral environment

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CONDENSABLE GLASS-IONOMER CEMENTS
Condensable glass ionomer cements more properly termed as high viscosity glass ionomer cements According to J Leirskar et al, 2001, the higher viscosity occurs to the material by the addition of polyacrylic acid to the powder and finger grain size distribution. There is no need to place a sealant over a Fuji IX restoration unless it requires protection from dehydration. It can therefore be contoured and polished under air/water spray immediately after it is set

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Advantages over conventional glass ionomer cement’s (A Castro & R F Feigal, 2001)

Packable + condensable

Easy placement
Non – sticky Early moisture sensitivity is reduced

Rapid finishing can be carried out
Improved wear resistance Solubility in oral fluids is very low
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Indications As a final restorative material in class I and II primary teeth Geriatric restorative for class I, II, III, V cavities and cervical erosion Final restorative material in class I and II permanent teeth in non stress bearing areas

Intermediate restorative material class I and II cavities
Sandwich restoration Core build up material Fissure sealing material for permanent teeth
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Compressive strength (After one week)

-

23 MPa

Modular of elasticity
(After one day) Diametral tensile strength (One day)

-

8.3 GPa

22 MPa

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Benefits of Fuji IX
Specially developed for ART Technique High viscosity offers excellent bonding properties

High compressive strength and increased wear resistance enables placement in posterior restorations
Chemical bond to tooth structure Fluoride release lowers chance of recurrent caries No shrinkage and coefficient of thermal expansion similar to tooth.

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COMPOMER (POLYACID MODIFIED COMPOSITE RESINS)

Compomers are the combination of composites (‘comp’) and glass ionomers (‘omer’).
Compomers contain dimethacrylate monomer and two carboxylic groups along with ion leachable glass. There is no water in the composition of these materials and the glass particles are partially silanated to ensure some bonding with the matrix.

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These materials set via free radical polymerization reaction and do not bond to hard tooth tissues. There is insignificant acid-base reaction between the glass particles not silanated and sparse carboxylic groups (McLean JW, 1996).

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Indications
Sealing and filling of occlusal pits and fissures Restoration of deciduous teeth

Minimal cavity preparation or tunnel preparation
Lining of all types of cavities where a biological seal and cariostatic action is required Core-build up Replacement of carious dentine for the attachment of composite resins Repair of defective margins in restorations
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Advantages

Superior working characteristics to resin modified glass ionomer cement
Ease of use

Easily adapts to the tooth
Good esthetics Good fluoride release

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CONTRAINDICATIONS Class IV carious lesions Lesion involving large areas of labial surface where esthetics if of prime concern Class II carious lesions where conventional cavities are prepared replacements of old amalgam restorations. E.g. Compomer, Dyract (Dentsply), compoglass (Ivoclar), Hytac (Espe). Lost cusp areas

Underneath metal/PFM crowns where light cannot penetrate

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GIOMER (PRE-REACTED GLASS-IONOMER)

Giomers are a relatively new type of restorative material. The name ‘giomer’ is a hybrid of the words ‘glass ionomers’ and ‘composite’. They have the properties of both glass ionomers (fluoride release, fluoride recharge) and resin composites (excellent esthetics, easy polishability, and biocompatibility). According to Ikemura K et al 2003, giomers are distinguished by the fact that, while they are resin based, they contain prereacted glass ionomer (PRG) particles

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The particles are made of fluorosilicate glass that has been reacted with polyacrylic acid prior to being incorporated into the resin.

The pre-reaction can involve only the surface of the glass particles (called surface pre-reacted glass ionomer or S-PRG) or almost the entire particle (termed fully reacted glass ionomer or F-PRG).

Giomers are similar to compomers and resin composites in being light activated and requiring the use of a bonding agent to adhere to the tooth surface E.g. Shofu’s Beautiful.

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Indications: Restoration of Class I. II. III. IV, & V Restoration of cervical erosion and root caries Laminate veneers and core build-up

Ideal for pedodontic restorations
Other dental applications such as repair of fractured porcelain and composite restoration

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Luting agent FUJI ORTHO L.C. GLASS IONOMER

In 1994 Fuji Ortho L.C was introduced by G.C Corporation, Tokyo Japan, & Light cured resin reinforced glass ionomer reported to be useful for bonding orthodontic brackets (Silverman et al, 1995).

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Composition

Powder consists of fluor-aluminosilicate glass.
Liquid consists of co-polymer of acrylic acid & maleic acid, HEMA (2 hydroxyethyl methacrylate), water, camphoroquinone and activator. P/L ratio for the cement is 3 gm /l gm

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Setting Mechanism The setting mechanism of Fuji Ortho L.C is the result of 3 reactions. When powder and liquid are mixed an acid base reaction similar to that of conventional Glass lonomer cement is initiated. In addition this is cured quickly by light irradiation (470 nm wavelength) from visible light curing device.

The light irradiation activates free radical polymerization of HEMA and other 2 monomers to form a poly HEMA and other ionomers to form a poly HEMA matrix & thus hardens the material.
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The 3rd reaction is a self cure of the reason monomers.

It is the light initiated reaction that allow for early placement of arch wires while the acid base reaction occurs simultaneously continues for a period of time after the mass has been cured by light irradiation

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Advantages of Fuji Ortho L.C over composite

1. Saves a significant amount of chair time. 2. Eliminates the need for working in the dry field. 3. Eliminates the need for etching and priming the enamel surfaces 4. Fluoride release protects teeth against decalcification 5. Repairs are quick & easy 6. Increased patient & operator comfort
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G.C. DENTIN CONDITIONER This is the polyacrylic acid solution designed to remove the smear layer from dentin for improved bonding of GI restorative lining and build up materials. Its deep blue tint & thin viscosity allow for easy placement and visibility on the tooth surface

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CHEMFLEX

It is a high strength glass ionomer restorative material. It is a fast setting glass ionomer restorative material which can be mixed to a condensable consistency offering very high strength It is available in six shades

Composition: Powder: Strontium, alumina fIuro silicate glass, polyacrylicacid,

tartaric acid, pigments Liquid: Poly acrylic acid

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Indications: Restoration of class V lesions and cavities.

Restoration of class III lesions.
Restoration of class I & II lesions of deciduous tooth. Long term temporary restoration of class I, II cavities in permanent teeth. Fissure fillings (minimal class I cavities).

Base and core bailed up
Atraumatic Restorative Treatment (ART) technique

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It should not be used as a permanent restoration of occlusal stress bearing areas. When used as a core build up, 2/3 of the remaining coronal dentine or atleast 2 mm of circumferential coronal dentine should be left for retention

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Ketac™ N100 Light Curing Nano-Ionomer Restorative A nano-ionomer is an aesthetic, fluoride-releasing restorative solution

Easy to create a high initial gloss and achieve a smooth final surface
Saving time in difficult to polish situations such as Class V’s Reduces waste, quick delivery of the material and the right mix every time

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The indications for Ketac Nano Light Curing Glass Ionomer Restorative are:

• Primary teeth restorations
• Small Class I restorations • Class III and V restorations • Transitional restorations • Filling defects and undercuts

• Laminate/Sandwich technique
• Core build-up where at least 50% of coronal tooth structure is remaining for support
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After polishing Ketac™ N100 Light Curing Nano-Ionomer Restorative showed higher gloss and smoother surfaces than resin modified glass ionomer restoratives footer materials. 4 May, 2012 Sample

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COMPOSITION

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The filler loading is approximately 69% by weight of which the relative proportions of the two filler types are approximately 2/5 and 3/5 respectively. All of the nano fillers are further surface modified with methacrylate silane coupling agents to provide covalent bond formation into the free radically polymerized matrix. The FAS glass is radiopaque, has an approximate particle size of less than 3 microns (average particle size approximately 1 micron), and provides the basis for the glass ionomer reaction and extended fluoride release in the presence of water and a polycarboxylic acid functional polymer.

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Contains combination of two types of surface treated nanofillers (approximately 5-25 nm) and nanoclusters (approximately 1.0 to 1.6 microns). Nanofillers are discrete nonagglomerated and nonaggregated fillers of 5-25 nms in size. The methacrylate functionalized nanofillers in this composition include those chemically derived from both silica and zirconia. The nanocluster fillers are loosely bound agglomerates of nano-sized zirconia/silica that appear as a single unit enabling higher filler loading, radioapacity, and strength

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Vitremer™ Core Buildup/Restorative

Ketac™ Nano Light Curing Glass Ionomer Restorative

Fuji II™ LC Resin Modified Glass Ionomer Restorative
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Ketac™ Nano Primer Ketac Nano primer is a one part, visible light-cure liquid specifically designed for use with Ketac Nano restorative.

It is comprised of the Vitrebond™ copolymer, HEMA, water, and photoinitiators.
The primer is acidic in nature.

Its function is to modify the smear layer and adequately wet the tooth surface to facilitate adhesion of Ketac Nano restorative to the hard tissue.
Ketac Nano primer is applied to the surface for 15 seconds, and air dried. The primer is then light cured for 10 seconds. Adequately air drying followed by light curing of the primer before placement of Ketac Nano restorative provides adhesion to tooth structure.

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COMPRESSIVE STRENGTH

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C UMULATIVE FLOURIDE RELEASE
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Modification of conventional glass-ionomer cements with Nvinylpyrrolidone containing polyacids, nano-hydroxy and fluoroapatite to improve mechanical properties

Dental Materials, Volume 24, Issue 10, Pages 1381-1390 A. Moshaverinia, S. Ansari, Z. Movasaghi, R. Billington, J. Darr, I. Rehman

After 24h setting, the NVP modified glass-ionomer cements exhibited higher compressive strength (163–167MPa), higher diametral tensile strength (DTS) (13–17MPa) and much higher biaxial flexural strength (23–26MPa) in comparison to Fuji II GIC (160MPa in CS, 12MPa in DTS and 15MPa in biaxial flexural strength).

The nano-hydroxyapatite/fluoroapatite added cements also exhibited higher CS (177–179MPa), higher DTS (19–20MPa) and much higher biaxial flexural strength (28–30MPa) as compared to the control group.

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The highest values for CS, DTS and BFS were found for NVP-nanoceramic powder modified cements (184MPa for CS, 22MPa for DTS and 33MPa for BFS)

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Effects of incorporation of hydroxyapatite and fluoroapatite nanobioceramics into conventional glass ionomer cements (GIC)

The nanohydroxyapatite/fluoroapatite added cements exhibited higher compressive strength (177–179 MPa), higher diametral tensile strength (19–20 MPa) and higher biaxial flexural strength (26–28 MPa) as compared with the control group (160 MPa in CS, 14 MPa in DTS and 18 MPa in biaxial flexural strength). The experimental cements also exhibited higher bond strength to dentin after 7 and 30 days of storage in distilled water.
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Zirconia–glass ionomer cement––a potential substitute for Miracle Mix Scripta Materialia, Volume 52, Issue 2, January 2005, Pages 113-116 Y.W. Gu, A.U.J. Yap, P. Cheang, K.A. Khor The mechanical properties of YSZ–glass ionomer cements were investigated after 1 day, 1 week and 1 month storage in distilled water. Miracle Mix was used as a control and Fuji IX GP acted as standards for comparison No significant differences in hardness and compressive strength were observed for the three types of glass ionomers at different time intervals
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.

The diametral tensile strength of YSZ–glass ionomer was, however, significantly greater than that of Miracle Mix due to the better interfacial bonding between the particles and the matrix.
The YSZ–glass ionomer also showed comparable mechanical properties to the Fuji IX samples. YSZ–glass ionomer may serve as a potential substitute for Miracle Mix because it is tooth-colored and it has better mechanical properties.

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Reactive fibre reinforced glass ionomer cements Ulrich Lohbauer , , a, Jürgen Walkerb, c, Sergej Nikolaenkoa, Jan Wernerc, Alexis Clareb, Anselm Petschelta and Peter Greilc

The mechanical properties of glass ionomer cements used in restorative dentistry reinforced by chopped glass fibres were investigated. Reactive glass fibres with a composition in the system SiO2– Al2O3–CaF2–Na3AlF6 and a thickness of 26 μm were drawn by a bushing process.
The highest flexural strength of the reinforced cement (15.6 MPa) was found by compounding 20 vol% reactive fibres and extending the initial dry gelation period up to 30 min. Microscopic examination of the fractured cements indicated a distinct reactive layer at the fibre surface
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Spheroidization of glass powders for glass ionomer cements The effects of spherical glass powders on the mechanical properties of glass ionomer cements (GICs) were investigated. Results showed that the particle size distribution of the glass powders had a significant influence on the mechanical properties of GICs. Powders with a bimodal particle size distribution ensured a high packing density of glass ionomer cements, giving relatively high mechanical properties of GICs.

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GICs prepared by flame-spheroidized powders showed low strength values due to the loss of fine particles during flame spraying, leading to a low packing density and few metal ions reacting with polyacrylic acid to form cross-linking. GICs prepared by the nano-sized powders showed low strength because of the low bulk density of the nano-sized powders and hence low powder/liquid ratio of GICs.

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The effect of particle size distribution on an experimental glassionomer cement Dental Materials, Volume 21, Issue 6, Pages 505-510 L.Prentice, M.Tyas, M.Burrow

Large- (mean size 9.60μm) and small-particle (3.34μm) glass powders were blended in various proportions and mixed with powdered polyacrylic acid to make a range of glass-ionomer powders. These powders were mixed with a glass-ionomer liquid (SDI Ltd, Australia) at powder to liquid ratios of 2:1, 2.5:1, and 3:1, and the resultant cements evaluated for working time, setting time, clinical handling, and compressive strength. Results were analysed by ANOVA.

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Results An increased proportion of smaller particles corresponded to higher strengths, and an increased proportion of larger particles with a decrease in viscosity of the unset cement.

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Incorporation of Casein Phosphopeptide-Amorphous Calcium Phosphate into a Glass-ionomer Cement S.A. Mazzaoui1,2, M.F. Burrow1, M.J. Tyas1, S.G. Dashper1, D. Eakins1 and E.C. Reynolds1 Incorporation of 1.56% w/w CPP-ACP into the GIC significantly increased microtensile bond strength (33%) and compressive strength (23%) and significantly enhanced the release of calcium, phosphate, and fluoride ions at neutral and acidic pH.

MALDI mass spectrometry also showed casein phosphopeptides from the CPP-ACP nanocomplexes to be released. The release of CPP-ACP and fluoride from the CPPACP-containing GIC was associated with enhanced protection of the adjacent dentin during acid challenge in vitro.

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Novel resin modified glass-ionomer cements with improved flexural strength and ease of handling Dong Xie , , a, Wei Wub, Aaron Puckettc, Brandon Farmerd and Jimmy W. Maysd Poly(acrylic acid-co-itaconic acid) copolymers containing pendent methacrylates were synthesized and used to formulate redox-initiated in situ cured glass-ionomer cements (GICs) by mixing with reactive glass fillers (Fuji II LC). The results show that the in situ cured GICs demonstrated higher FS (89.6–123.2 MPa), as compared to commercial Fuji II LC GIC (57.1 MPa).

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BONDING SYSTEMS

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• Historically, microleakage and post-treatment sensitivity have been persistent problems when composite resin is bonded to tooth structure. • These problems are particularly common when bonding to dentin.

 Dentin: hydrophilic; composite resin: hydrophobic

 To overcome this problem, DBAs were developed

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Evolution of Dentin Bonding Agents
First-Generation Dentin Bonding Systems
• These products ignored the smear layer. • They included NPG-GMA (N-phenylglycine glycidyl methacrylate), the polyurethanes, and the cyanoacrylates.

E.g S.S. White's Cervident which became available in 1965
 The bond strength : 2 to 3 MPa.  Failure rate of 50%.

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Additional problems with them included:




Loss in bond strength over time
Lack of stability of individual components during storage.

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Second-Generation Dentin Bonding Systems

• Developed and marketed in the late 1970s and early 1980s

• These systems leave the smear layer largely, if not wholly, intact when used.
• They performed better than first-generation bonding agents.

 Bond strengths: 4.5 to 6 Mpa

 Clinical failure rates of 30% at one year.

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Clearfil Bond system F (Kuraray) introduced in 1978: first 2nd generation adhesive system

They were based on phosphorous esters of methacrylate derivatives
Used analogs of BIS-GMA with attached phosphate esters

The phosphate group of the dentin bonding agent bonded with calcium in the tooth structure and the methacrylate end of the molecule bonded to the composite resin
E.g Bondlite (SDS/Kerr), Creation Bond (Den-Mat), Prisma Universal Bond (Caulk), and Scotchbond(3M)

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Clinical failure was due to:

Inadequate hydrolytic stability in oral environment
Primary bonding to the smear layer rather than to the underlying dentin: smear layer prevents intimate resin-dentin contact

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Third-Generation Dentin Bonding Systems

• These systems alter or remove the smear layer prior to bonding



Bond strengths ranging from 16 to 26 Mpa

• Clearfil New Bond (Kuraray) was introduced in 1984

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Acids or chelating agents were used to remove smear layere.g Gluma

But, this reduces the availability of Ca ions for interaction with chelating surface active comonomers
So, use of acidic solution of 6.8% ferric oxalate supplement Ca ions But, an insoluble precipitate was formed  sealed the dentinal tubules However, subsequent application of an acetone solution of NPG-GMA etc improved bonding Problems: precipitate interfered with bonding; ferric oxalate caused black interfacial staining

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Other methods to remove smear layer included: Aqueous solution of 10 % citric acid and 3 % ferric chloride followed by application of an aqueous solution og 35% HEMA e.g C & B Metabond (Sun Medical) Aqueous solution of 2.5 % maleic acid and 55% HEMA followed by application of application of unfilled bis-GMA/HEMA adhesive resin e.g Scotchprep( 3M)

Main drawback was retention decreased with time

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Fourth Generation Dentin Bonding Systems
• Nakabayashi in 1991 proposed the concept of hybridization according to which diffusion & impregnation of resin into partially decalcified dentin followed by polymerization created a resin reinforced layer or ‘Hybrid layer’.

• 4th generation adhesives were based on this concept of hybridization and had the ability to bond as strongly to dentin as to enamel.

Mechanism of action – 3 steps – Conditioning of enamel & dentin

- Priming
- Adhesive resin application

Eg : All bond 2 , Panavia 21 (Kuraray) , Scotchbond Multipurpose (3M ESPE) , Imperva bond (Shofu)

Disadvantages:

• Multiple steps
• Technique sensitive • Possibility of overetching dentin with phosphoric acid

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Fifth Generation Dentin Bonding Agents
Also based on the concept of hybridization but differ in that the number of clinical steps are reduced i.e. after conditioning of enamel & dentin, steps of priming & bonding are combined. Also called Single Bottle adhesives.  Prime & Bond (Dentsply) was the 1st to be marketed.  High bond strength & time saving

Disadvantages:
• Multiple steps • Technique sensitive • Possibility of overetching dentin with phosphoric acid

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Sixth Generation Dentin Bonding Agents

 2 types - Self etching Primers & Self etching Adhesives • These bonding agents dissolve the smear layer instead of removing it completely. • It is a mixture of a mild acid + hydrophilic primer. The acid causes etching of enamel & dentin while the primer molecule penetrates the dentinal tubules to the depth of etching & polymerizes with the collagen fibrils.

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Advantages : • Simultaneous demineralization & resin infiltration • No post conditioning required • Time saving procedure • Less post-operative sensitivity

Eg: Clearfill SE Bond , Clearfill Liner Bond (Kuraray) , Xeno III (Dentsply)

Disadvantages:
• Longer etching time required for enamel • Does not bond well to enamel if not etched well

Seventh generation bonding systems:
• Mild or strong one step self etch • Least technique sensitive, less post-operative sensitivity Disadvantages:

• A difficult mixture of hydrophilic and hydrophobic components
• Prone to phase separation, formation of droplets within their adhesive layer • Lower bond strengths compared to 4th and 5th generation adhesives  E.g Clearfil S 3 Bond( Kuraray), G-Bond( GC), i- B ond( Dentsply)
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An in vitro evaluation of microleakage in class I preparations using 5th, 6th and 7th generation composite bonding agents
Journal of Clinical Pediatric Dentistry Vol 29, No 4 2005

The 5th generation bonding system (Optibond Solo), the 6th generation bonding system (Prompt-L-Pop) and the 7th generation bonding system (iBond)  5th generation outperformed both the 6th and 7th generation bonding systems.

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The evolution of dentin bonding from

No-etch

Total-etch

Self-etch

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NANOFILLED Dentin Bonding Agents
Prime & Bond NT (Dentsply/Caulk) and Excite (Ivoclar Vivadent). Prime & Bond NT contains 7- nanometer fillers Has a greater concentration of resin and a smaller molecular weight resin that have been added.

Make the DBA tougher, stronger, and able to cover adequately with a single coat;
Penetrate dentin better, provide improved marginal integrity, and have a low film thickness

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Composites

Traditional Composites
 Developed during 1970’s
 Conventional or macrofilled composites  No longer widely used  Finely ground amorphous silica or quartz  Wide distribution in particle size  Average size 8-12 microns; up to 100 microns can also be present

Relation between inorganic filler and resin matrix in 1st generation composites

Early materials with large particles included: Adaptic, Concise, Clearfil F ,Smile, Simulate, Nuva-Fil

Properties of traditional composites
 Filler loading: 70-80% by wt.  Compressive strength: 250-300 Mpa

 Tensile strength:50-65 Mpa
 Elastic modulus:8-15 Gpa  Coefficient of thermal expansion:25-35ppm/deg C  Water sorption:0.5-0.7 mg/cm2  Knoop hardness :55 KHN  Radiopacity:2-3 mm Al

 C.S. is greater than that of unfilled acrylics because of transfer of stress from matrix to filler particles

 T.S. and elastic modulus and hardness is also increased

 Increase in hardness is due to filler reinforcement and crosslinked resin structure

 Water sorption ,polymerization shrinkage and thermal expansion are reduced

 More resistant to abrasion than unfilled acrylics

 Roughening of surface->selective abrasion of softer resin matrix surrounding the harder filler particles

 Also,they are radiolucent

Clinical considerations:  Rough surface  Discoloration

 Poor resistance to occlusal wear

Small Particle Filled Composites
Evolved to improve surface smoothness and physical and mechanical properties of traditional composites
Inorganic fillers are ground to size of 0.5-3 microns

Inorganic filler:80-90% by wt.
C.S.:350-400 Mpa T.S:75-90 Mpa Elastic modulus:15-20 Gpa Thermal expansion coefficient:19-26 ppm/deg C Water sorption :0.5-0.6 mg/cm2

Amorphous silica as filler

Glasses that contain heavy metals for radiopacity
Increase in surface smoothness Greater wear resistance

But,heavy metal glass fillers are softer and more prone to hydrolyze and leach in water than amorphous silica and quartz

Clinical considerations:
• Higher strength and other physical properties • Indicated for high stress and abrasion prone areas e.g : Class IV sites • Provide reasonably smooth surface for anterior restorations but not more than microfilled composites

Microfilled composites
Problems of surface roughening and low translucency associated with traditional and small particle composites is overcome by the use of microfilled composites Colloidal silica particles Filler particle size:0.04-0.4 microns Reinforcement of resin with filler as well as surface smoothness  Inorganic filler:35-67% by wt.

C.S.:250-350 Mpa
T.S:30-50 Mpa

• Elastic modulus:3-6 Gpa
• Thermal expansion coefficient:50-60 ppm/deg C • Water sorption :1.4-1.7 mg/cm2

• Physical and mechanical properties inferior to those of traditional composites

They remain wear resistant for several years but in the longer term, if placed in wear prone areas, will eventually break down

Clinical considerations:
Preferred for restoring teeth in with carious lesions in smooth surfaces i.e classes III, IV

The inorganic filler particles are smaller than the abrasive particles used for finishing the restoration.
The silica filler is removed along with the resin in which it is embedded leaving a smooth polished surface

• Not preferred for class II and class IV sites

• Debonding of prepolymerized composite filler

• Chipping at margins of restorations

• e,.g Renamel Microfill(Cosmedent), Durafill(Heraeus Kulzer), Matrixx Anterior microfill

Hybrid Composites
• They were developed to obtain esthetics better than SPF, while maintaining the desirable properties of the latter
 Contain 2 kinds of filler particles:

• Colloidal silica
• Ground particles of glasses containing heavy metals:0.4-1.0 microns

 Filler content:75-80 wt%
 Physical properties range between those of traditional and SPF composites

• But superior to microfilled composites

• Radiopacity greater than that of enamel

Clinical considerations:
• Class IV restorations : surface smoothness and reasonably good strength

• Stress bearing posterior restorations

• The 1st submicron hybrid introduced: Herculite (Kerr) in 1975 • Charisma( Kulzer) in 1980s • Synergy (Coltene), Vitalescence (Ultradent), P60

Flowable Composites
• A modification of SPF and hybrid composites results in flowable composites • Introduced in late 1996

• Reduced filler content
• Adapts intimately to a cavity form • But has poor wear resistance • Used as a cavity base or liner • Where access is difficult

• Minimal class I restorations, as fissure sealants

Examples include:
• Esthet X Flow, Aelite , FlowRite • Durafill Flow, FloRestore, Flow-It, Nexus2, Revolution etc

Packable Composites
• Also called condensable composites
• Introduced in 1990’s • To enable clinicians to apply techniques similar to those used for amalgam restorations • Contain elongated, fibrous, filler particles, around 100 microns in length

• Textured surfaces that interlock and resist flow
• Causes uncured resin resistant to be stiff and resistant to slumping

Desirable characteristics

• Nonsticky, wets tooth surfaces, easily transferable and packable. • Moisture tolerant • Should not show much elastic recovery

• High critical shear strength for flow (to hold the proximal contact of matrix band)

• No access problems for cure (uses bulk cure, chemical cure, or has excellent visible light depth of cure)

• Cures rapidly to final hardness but with minimal residual stress • Little or no shrinkage on curing • Easily carved, burnished or Smoothened

COMPOSITE INSERTS
Preformed shapes & sizes of glass ceramic whose surfaces have been silane treated. Available in different shapes L, T, round, conical, cylindrical size 0.5-2mm (mega fillers). Application Used to minimize the marginal contraction gaps in composite fillings. Properties Low coefficient of thermal expansion

Wear resistant

Reduces polymerization shrinkage by upto 75% & stiffness of the filling.
Radiopaque

Manipulation Pressed into a cavity preparation that is already filled with unpolymerized composite - restoration is then contoured using diamond rotary instruments & polished.

Cavity is prepared → Thin layer of composite is placed

→ above this glass fillers are placed → rest of the cavity is filled with composite resin →contouring done → cured→ finishing and polishing

J O Canad Dent Assoc March 2003

Fibre-reinforced Composites
First described in 1960s by Smith when glass fibers were used to reinforce polymethyl methacrylate

Contain fibers aimed at enhancing the physical properties

This group of materials is very heterogenous; depending on the- nature of the fiber - geometrical arrangement of fibers - overlying resin used

Fibers within the composite matrix are bonded to the resin via an adhesive interface

Fibers increase the structural properties by acting as crack stoppers

The resin matrix acts to protect the fibers and fix their geometrical arrangement, holding them at predetermined positions to provide optimal reinforcement

The interface plays the vital role of allowing the loads to be transferred from the matrix to the fibers

Fibers are classified based on:  Material composition  Fiber architecture within the restoration

 Surface impregnation status
 Product designed for chairside or laboratory use

Based on material used:
 Glass  Ultra-high mole. Wt. polyethylene fibers

 Kevlar fibers

Based on fiber architecture:

 Unidirectional
 Weave  Mesh  Braid  Leno weave

Based on impregnation status:
 Preimpregnated to resin  Impregnation required prior to bonding

Factors influencing the physical properties of FRCs are:

 Fibre loading -fracture resistance increases with the increase in quantity of fibers in the polymer matrix

 Fiber-matrix interphase -large differences between the elastic properties of matrix and fibers have to be communicated through this interface

-wetting of fibers by resin is very important

 Fiber architecture and orientation -unidirectional fibers give anisotropic mechanical properties (in a single direction)

-suitable when the direction of highest stress is predictable

-fiber weave in two directions allows for multi-directional reinforcement of restoration

Clinical applications of FRC’s  Reinforced resin based composite

 Single Individual restorations (Inlay, Onlay, partial/full veneer crowns)

 Periodontal splinting/Post trauma splint

 Immediate replacement transitional and long term provisional bridges

 Fixed bridgework – Ant and Post
Single Cantilever Fixed-fixed

Implant supported


Reinforcement or repairing dentures Fixed orthodontic retainers



Advantages
 Low treatment costs
 Single visit immediate tooth replacement  Suitable for transitional and long term provisional restoration  Readily repaired

 Suitable for young patients (developing dentin) and elderly (time saving).

 Metal free restorations
 Improved esthetics  Can be produced in simple manner in laboratory without need for waxing, investing and casting  Can frequently be used with minimal / no tooth preparation.  Wear to opposing teeth much reduced in comparison to traditional PFM.

Disadvantages
 Wear of overlaying veneering composite especially in patients with significant parafunction.

 May lack sufficient rigidity for long span bridges.

 Excellent moisture control required for adhesive technique.

 Space requirements are greater in posterior occlusal situations in comparison to metal occlusal surfaces (to allow sufficient room for fibers and adequate bulk for veneering composite overlay).

 Uncertain longevity in comparison to traditional technique.

LABORATORY BASED, PREIMPREGNATED FIBER REINFORCED SYSTEMS

Introduced in 1998
TARGIS/VECTRIS
• Highly filled Targis Ceromer (ceramic optimized polymer) composition, along with Vectris, a fiber reinforcing composite framework

Consist of 2 major components 1. Targis - forms the bulk of the restoration 2. Vectris - fiber framework. Various types of fibers

For metal-free posterior bridges, crowns, inlays and onlays.

 SCULPTURE/FIBREKOR

Involves veneering a composite resin (Sculpture) to a
resin preimpregnated glass fiber network (Fibrekor)

Fibers available in 15 cm lengths of various widths.
Sculpture is polycarbonate based composite resin.

 RIBBOND

It is a cross-linked leno stitch weave of polyethylene fibers.  Can be used chair side or in laboratory to fabricate composite resin bridges .

ORMOCERS
Dr. Herbert Wolters from Fraunhofer Institute for Silicate Research introduced this class of material in 1994. Acronym of Organically Modified Ceramic Represents a novel inorganic-organic copolymers in the formulation -allows for modification of its mechanical parameters. Eg., DEFINITE

Inorganic condensing molecule segment is used to build inorganic network. An inorganic Si-O-Si network is developed through targeted hydrolysis and inorganic polycondensation in a sol-gel process.

The organically polymerizing molecular segment has (meth) acrylate groups which form an additional cross-linked network matrix after induction of a radical based polymerization.

The inorganic poly condensation and organic polymerization result in formation of an inorganic –organic co-polymer.

 Fillers 1-1.5 m in size & contains 77% weight and 61 % by volume.

 Matrix - low molecular monomer components, mainly Bis – GMA.  On light activation DC 60-70% - they can be eluted.

 Silicon oxide, a filler, serves as a basic substance for the ormocer.

 Modified by adding polymerisable side chains in the form of methacrylate groups.

 Methacrylate molecules can no longer be eluted during incomplete polymerization.

 ORMOCER has a biocompatible polysiloxane net with low shrinkage

Physical properties as given by Wolter are

Bending strength (3 point bending test): 100-160 MPa Modulus of elasticity :10-17 GPa

Coefficient of thermal expansion
Water uptake Solubility in water Shrinkage

:17- 25 x 10-6 K-1
:< 1.2% :Not detectable :1.7 – 2.5 vol%

Advantages Biocompatibility- will not release any detectable residual substance . Reduced polymerization shrinkage

Lasting esthetics ( available in 16 shades )
Anticariogenic property

CEROMER
Ceramic Optimized Polymer was introduced by Ivoclar

Composition • Composed of specially developed & conditioned fine particle ceramic fillers of submicron size ( 0.04 & 1.0 μm ), which are closely packed ( 75 – 85 weight %) & embedded in an advanced temperable organic polymer matrix. • Properties of ceromers = composites & they exhibit fluoride release lower than conventional glass-ionomers or compomers.

Uses  used for veneers, inlay/onlay without a metal framework.

 can be used with Fiber Reinforced composite framework for inlays/onlay, crowns and bridges (3 unit) and for crown and bridges including implant restorations on a metal framework.

Ceromers combine the advantages of ceramics and composites

 Durable esthetics  High abrasion resistance  High stability

 Ease of final adjustment
 Excellent polishability  Effective bond with luting composite  Low degree of brittleness  Conservation of tooth structure

NANOCOMPOSITES
Nanotechnology refers to the deliberate placement, manipulation and measurement of sub-100 nanometre scale matter

The first nanocomposite introduced was Filtek Supreme (3M ESPE)

With its nanosized particles and another ew technology called “clustering”, it provided more polishability without sacrificing strength

Clustering is a process by which numerous nanoparticles are combined to form larger particles

30 different shades in 4 opacities (dentin, body, enamel and translucent).

Filtek Supreme:

nanomer nanocluster

Discrete nonagglomerated and nonaggregated particles of 20-75 nm in size

Loosely bound agglomerates of nanosized particles nanotube

Nanotubes have remarkable tensile strength

Advantages  Superior translucency and esthetic appeal, excellent colour, high polish and polish retention.

 Superior hardness, flexural strength and modulus of elasticity.

 About fifty percent reduction in polymerization shrinkage.

 Excellent handling properties.

marginal staining

microleakage

secondary caries

enamel micro-cracks

debonding

post-operative sensitivity

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Types of monomers added to composites

 SPIRO-ORTHO-CARBONATES-1970’S(SOC)

-SOC with dimethacrylate resins -SOC with epoxy (oxirane) resins

-SOC with epoxy + polyol in the proportion of 4:8

Advantage:

-shrinkage was half of that of bis-GMA /TEGDMA

Disadvantage:
-less reactivity -decreased cross-linking; hence poor mechanical properties

 Polyol with oxirane

-shrinkage of 0.6% at 60 min -shrinkage of 1.6% at 24 hrs -contraction sress lesser than conventional composites -slower rate of polymerization allows for relaxation of stresses

 VINYLCYCLOPROPANES (VCP) -1997
-Replaces TEGDMA in BIS-GMA /UDMA resin -Shrinkage is 2/3rd of BIS-GMA/UDMA resin

 POLYBUTADIENE RUBBER POLYMER (1999) -20 µm of this polymer is absorbed into fumed silica & added BIS-GMA /TEGDMA -Reduce shrinkage by 25%

 Methacrylated styrene allyl alcohol (MSAA)-1997

-Added to replace 20% BIS-GMA /TEGDMA with 62
vol% filler -Reduces shrinkage by 20%

 Silorane -combination of siloxanes and oxiranes . -Polymerizes by a cationic ring opening process -Shrinkage values less than 1 vol % -E- modulus and flexural strength comparable to those of methacrylate based composites.

As silorane-based composite polymerizes, “ring-opening” monomers connect by opening, flattening and EXTENDING toward each other. The result is significantly less volumetric shrinkage compared to methacrylate-based composites

As methacrylate-based composites cure, the molecules of these “linear monomers” connect by actually SHIFTING closer together in a linear response. The result is a loss of volume
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Tris[4-(2′-hydroxy-3′-methacryloyloxypropoxy) phenyl]methane (TTEMA)

-synthesized by reacting triphenylolmethane triglycidyl
ether (TTE) with methacrylic acid in the presence of 4 -(dimethylamino)pyridine.

-very low photopolymerization shrinkage of 2.09%

-3:2 TTEMA–TEGDMA unfilled resin revealed 10% lower shrinkage than a conventional bis-GMA system containing the same amount of TEGDMA.

- The flexural strength of a light-activated composite resin formulated with TTEMA is comparable to that of a bis-GMA composite resin under the same conditions.

 Inorganic-organic hybrids
- created by means of sol-gel processing of hydrolytically condensable, organically modified trialkoxysilanes, which contain radically polymerisable methacrylate groups or cyclic groups capable of ring-opening polymerisation.

- Improved polymerization shrinkage, wear resistance and biocompatibility

 Cyclopolymerizable Monomers -reaction of conventional monofunctional acrylate monomers with paraformaldehyde.

-The external position of the acrylate esters means that these pendant groups can be varied for alteration of the physical properties of the monomers and the corresponding polymers.

-The polymers exhibit high degrees of conversion and significantly reduced polymerization shrinkage, compared with polymers obtained from conventional diacrylate or dimethacrylate monomers.

Antibacterial Monomer MDPB
Imazato et al 1994 incorporated a non releasing newly synthesized monomer MDPB with antibacterial properties into resin composites.

 MDPB is methacryloxy decyl pyridinium bromide

Chemically bound

It was found to be effective against various Streptococci.

However, its activity against other important species in plaque formation like Actinomyces,, Neisseria and Veillonella still needs to be investigated.

After curing – No Elution of antibacterial components from material.

Comparable to triclosan.

 BIOACTIVE FORMULATIONS
ACP (amorphous calcium phosphate)-2000 -ACP + BIS-GMA /TEGDMA/HEMA with Zirconyl methacrylate

 Fluorinated Bis-GMA analogues:
 Liquid crystalline monomers

CERAMICS

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Composition of ceramics :
1. Feldspar :

-when mixed with metal oxides and fired, it forms a glass phase that is able to soften and flow slightly
-This softening of glass allows porcelain particles to coalesce together. This is called sintering - Seen in concentration of 75-85 %. 2. Kaolin / clay : -it acts as the binder. -When mixed with water , it forms a sticky mass which allows unfired porcelain to be easily worked and molded.

-On heating it reacts with feldspar and gives rigidity. -Its white in color and reduces translucency .so its added only in concentration of 4-5 %.

3. Quartz : -It imparts more strength, firmness and translucency. -It gives stability of mass during heating by providing a frame work. - 13-14%

GLAZES: • It decreases pores on the surface of fired porcelain. • This increases strength by decreasing the crack propagation. if glaze is removed by grinding, the transverse strength is half of glazed porcelain.

Self glazing :
-External glaze layer is not applied here. -the completed restorations is subjected to glazing here.

Add on glazes: -external glaze layer is applied here. -They are uncolored glasses whose fusing temperature is lowered by the addition of glass modifiers. -Disadvantages : low chemical durability, difficulty to apply evenly, difficult to get exact surface characteristics.

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Colouring agents :
-These coloring pigments are produced by fusing metallic oxides together with fine glass and feldspar - Ex : iron / nickel oxides- brown , copper oxides-green, titanium oxide –yellowish brown,

cobalt oxide – blue.
Opacifying agents:

-Opacifying agents consists of a metal oxide ground to a very fine particle size .
ex :cerium oxide, titanium oxide, zirconium oxide –most popular.

Stains: -This powder is mixed with water and the wet mix is applied with brush to the surface of porcelain before glazing. -Internal staining is preferred as it gives life like results and prevents direct damage to stains by surrounding environment. Glass former : Glass formers are silica. 1.crystalline quartz 2.crystalline cristobalite 3.crystalline tridymite 4.non crystalline fused silica

Glass modifiers
- Potassium oxide , Sodium oxide , Calcium oxide -> used as glass modifiers - they act as fluxes by lowering the softening temperature of a glass Intermediate oxides :

-Glass modifiers reduces the viscosity of porcelain .
-It needs a high viscosity as well as low firing temperature. This is done by the addition of AL 2 O3 and B2O3 .

ADVANCES IN METAL CERAMICS
COLLARLESS PORCELAIN
This was introduced to overcome the disadvantage of metal being exposed and giving unesthetic appearance. Here the collar of metal is absent in the gingival area. They can be made with platinum foil or refractory die

ALL CERAMICS

CLASSIFICATION: 1.CONVENTIONAL POWDER & SLURRY CERAMICS
1. HI-CERAM ( ALUMINA REINFORCED) 2.OPTEC HSP(LEUCITE REINFORCED) 3.DUCERAM LFC

2. CASTABLE ALL CERAMIC RESTORATIONS 1. DICOR 2.CERAPEARL 3.PRESSABLE ALL CERAMIC RESTORATIONS 1.IPS EMPRESS 2.OPTEC PRESSABLE CERAMIC 4.INFILTRATED ALL CERAMIC RESTORATIONS 1.IN- CERAM 5. MACHINABLE ALL CERAMIC RESTORATIONS 1.CAD- CAM,

CONVENTIONAL POWDER AND SLURRY TECHNIQUE

PORCELAIN JACKET CROWNS:
- they were very brittle and fractured easily. -they also showed poor marginal adaptation. Processing : - PJC are made using platinum foil technique -a platinum foil is first adapted to the dye. The foil acts as a matrix and supports the porcelain during firing.

ALUMINOUS PORCELAIN JACKET CROWN ( HI–CERAM)

-McLean and Hughes in 1965, introduced porcelain jacket crown with aluminous core to improve the strength of traditional PJC.

-Increased content of alumina ( 40-50%) in the core strengthened the porcelain by interruption of crack propagation.

Factors affecting strength & opacity of aluminous porcelain:

1. Finer the grain size, greater the strength.
2.coarse grains are less opaque. -so there is a compromise between strength and esthetics.

3.size of glass powder is less than 40 µm as this sized powder softens and flows more easily around alumina grains producing high sintered densities.

4.Rounded grains are preferred over angular ones, since angular ones interfere with the flow of glass phase producing flaws around the grains and reducing the strength.

5.Alumina concentration should be around 40-50% by weight . Concentration higher than this would prevent complete flow and wetting by glass matrix. PROPERTIES : Compressive strength: 3,16000 psi Transverse strength : 20000 psi Shear strength : 21 000 psi Modulus of rupture : 15000 psi

Uses : - Due to reduced translucency , aluminous porcelain is limited to forming refractory framework capable of supporting weaker but more translucent dentin and enamel porcelains

LEUCITE REINFORCED PORCELAIN :

OPTEC HSP :
Leucite were used as reinforcing fillers because of their increased tensile strength.

- Leucite is potassium alumino silicate crystals.
Processing:

- Leucite and glassy components are fused together during baking process at 1020ºC .
-Build up, condensation all are done by powder and water slurry technique. Leucite porcelain can be used for both body and incisal portions as leucite doesn’t need employment of translucent porcelain. Leucite crystals amount to 50.6% wt of Optec Hsp

-ADVANTAGES ;
-Lack of metal or opaque substructure -Good translucency -Moderate flexural strength DISADVANTAGES: -Potential fracture of posterior teeth -Increased leucite content leads to high in-vitro wear of teeth

DUCERAM LFC

DUCERAM LFC : -Also called hydrothermal low fusing porcelain -Its composed of an amorphous glass containing hydroxyl ions -Due to the absence of leucite crystals, the hardness of the material and its ability to abrade the opposing teeth is reduced . Processing ; -Restoration is made in 2 layers -Base layer is duceram metal ceramic ( leucite porcelain ) which is placed one refractory die using powder slurry technique and baked at 930ºc. -Second layer Duceram LFC is added on the base layer , using powder and slurry technique at 660ºc

DUCERAM LFC

CASTABLE CERAMICS OR GLASS CERAMICS

1. A metal stable glass is first formed after casting. 2. during subsequent heat treatment controlled crystallization occurs with nucleation and growth of internal crystals. 3. this conversion process of a glass to a partially crystalline glass is called ceramming.

Thus a glass ceramic is a multiphase solid containing residual glass phase with a finely dispersed crystalline phase
- It decreasing the crack propagation .

DICOR
It is composed of Sio2, K2o,Mgo, Mgf2 Alo2, Zro2.added for durability

Flourescing agent for esthetics

Flouride acts as a nucleating agent and improve fluidity of molten glass.

After ceramming material is 55% crystalline

Fabrication : -wax pattern made
-invested in phosphate bonded refractory material. -molten glass (1358ºc)is then cast to the heated mold after dewaxing. -cast restoration is then freed from investment , covered by protective embedment material and made to ceramming. - It takes 114 minutes to reach casting temperature of 1075ºc and maintain this for 1 hour. embedment tray is then removed.

- cerammed glass is then build up with enamel and dentin

Properties : compressive strength : 120000 psi modulus of elasticity : 10.2 ×106ps Esthetics : - Esthetic due to their translucency which matches that of natural tooth enamel - Its made entirely of 1 material , and so no opaque substructure - It gives a chameleon effect in which the restoration acquires part of color from adjacent teeth -Precision fit is seen with dicor

-Durability: it can withstand 20 years of tooth brush abrasion
without any changes

-Tissue acceptance : it is high to periodontal tissues because ,
1. there is no need for opaque porcelain to cover metal substructure 2.absence of opaque layer helps clinician to obtain natural translucency in gingival area little discomfort occurs on contact with hot or cold foods because of its extreme low thermal conductivity

Advantages : -excellent marginal fit -high strength -surface hardness & occlusal wear similar to enamel -can reproduce wax pattern precisely with lost wax technique -excellent esthetics inherent resistance to plaque accumulation disadvantages : -chance of losing the low fusing feldspathic shading porcelain, which have been applied for good colour matching

CASTABLE APATITE CERAMIC (CERAPEARL)

-Developed by hobo & bio ceram group as Cao – P2O5 – Sio 2Glass Ceramic
-This material once cast has an amorphous structure, but when subjected to ceramming ,forms crystalline oxylapatite , Ca 10 ( po 4 ) 6o . -Compared to normal enamel, crystals of cerapearl show irregular arrangement and this difference in arrangement accounts for its increased mechanical properties. -cao (45%),p2o5(15%) are main ingredients essential for formation of hydroxyl apatite crystal

PRESSABLE CERAMICS

-Also called injection molded glass ceramic, leucite reinforced hot
pressed glass ceramic -This system was first introduced by wohlwend et.al in 1989 came as ips empress and optec opc - it is less susceptible to fracture than conventional porcelain -it shows lower compressive strength than metal ceramics IPS EMPRESS: -this also uses lost wax technique but here the material is pressed into the mold under pressure and not centrifugally driven. -wax pattern is first fabricated and then invested in phosphate bonded investment material

CAD – CAM RESTORATIONS

STAGES IN CAD- CAM FABRICATION ;
1.computerized surface digitization 2.computer aided design 3.computer assisted manufacturing 4.computer aided esthetics 5.computer aided finishing

Mormann and Brandestini was the first ones to use cad- cam device in 1988.the first model which came was called cerec I. -CEREC I (1988) -cannot prepare the occlusal anatomy of the preparation . -camera not good -CEREC –II: ( 1994) -They had better image processing systems . -it also has a cylindrical diamond stone which is able to finish off undercuts at buccal extensions -occlusal anatomy could be produced here disadvantage- has many parts ,so the operator had to move around -impression not good -marginal fit not good.

CEREC 3 : -different parts could be magnified in detail
more finer details noted disadvantage: not capable of producing margins of restoration

CEREC 3-D

marginal fit good
contacts can be chosen 3 dimensionally movable camera

CEREC II

CEREC III

CAVITY CONSIDERATION FOR CAD- CAM :
- No convexities should be present on the pulpal and gingival walls . -The occlusal step should be 1.5mm – 2mm in depth - Isthmus should be at least 1.5mm wide to decrease the possibility of fracture of the restoration. -Buccal and lingual walls of the preparation may converge towards the occlusal. -This feature is unique to cerec systems as it can automatically block out any undercuts during optical impression.

-axial walls should be straight and not follow the convex contour of
the proximal surface of the tooth -no cavo surface or marginal bevels should be given.

VARIOUS INGOTS USED FOR MACHINABLE CERAMICS ARE :
1.cerec vitablocks mark I :its composition strength are similar to that of feldspathic porcelain. Used first with cerec system. 2. Cerec vita blocks mark II: high strength feldspathic porcelain with grain size finer than that of mark I composition. -less abrasive wear of the opposing tooth

3.Dicor Mgc: glass ceramic with fluorosilicate mica crystals in a glass matrix. flexural strength higher than castable dicor and cerec systems. softer and less abrasive than cerec vitablocks mark I ,but not as much as cerec vita blocks mark II.

PROCERA

PROCERA CONCEPT
Procera system uses CAD - CAM Has densly sintered aluminium oxide coping and low fusing all ceramic veneering porcelain Procedure -Scanner is used to take impression of the teeth -The scanner probe is made to contact the surface of the dye as it revolves around the vertical axis.

-By the end of it around 50,000 lines will be mapped.
-And once its scanned, the procera software will design the restoration. -Then it is send to the procera lab for making the ceramic

SHRINK FREE CERAMICS

CERESTORE COPING & ALCERAM
Aluminous porcelain jacket crown, had firing shrinkage problem Shrink free ceramics were introduced to over come these defects The unfired ceramic is made to undergo a lengthy heat treatment by adding aluminium and magnesium oxide. This results in magnesium aluminate spinel. This produce increase in volume which decreases sintering shrinkage

Captek System
Developed by Davis Schottlander and Davis, U.K.

Captek 3 Unit Bridge

Captek is a reinforced high noble gold coping Consists of approximately 88% gold, 4% platinum, 4% palladium, 3% silver, and 1% iridium and ruthenium The copings are fabricated utilizing replicated master dies composed of a proprietary refractory material. Captek P and Captek G A thin sheet of wax (Captek P) impregnated with platinum/palladium/gold particles is uniformly contoured to the refractory die

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The die is then placed in a porcelain oven and during this cycle, the alloy particles undergo a fusing process that creates a strong skeleton of these particles, while the wax is eliminated Upon removal from the oven, the platinum/ palladium/gold coping is attached to the refractory die, after which another thin layer of wax (Captek G) containing 97% pure gold particles is placed over it. During the next firing cycle the wax is again eliminated, while the gold particles melt and infiltrate the pores in the underlying coping. During the melt/infiltration the gold penetrates the entire width of the coping, which produces an internal and external gold surface
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A thin layer of Captek P wax is intimately contoured to the refractory die.

The first firing cycle creates a skeleton of platinum, palladium and gold particles

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Captek G is added to the coping, and when fired results in an internally reinforced gold coping

External view of the completed 22 karat Captek coping. Note the absence of black metal oxides
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Clinically, this internal and external gold surface is of tremendous benefit. Internally, the gold surface contacts the preparation and due to its high nobility, eliminates any potential for allergic or adverse reactions Captek crowns exhibit less bacterial accumulation than either porcelain to high noble, high-noble full-cast crowns, and even natural enamel

Another clinical benefit of the Captek coping material is the ability to prepare the tooth in a conservative fashion

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With an overall reduction of .5 mm to 1.0 mm reduction at the margin, the coping promotes natural esthetics and eliminates overcontoured restorations. Since the Captek coping is 88% non-oxidizing gold, the resultant hue is a warm yellow color.

Consequently, less opaque can be used, resulting in a more lifelike restoration.
The coping can even be cut short to the internal line angle of the margin, allowing the technician to build a true porcelain margin, for the ultimate in esthetics.

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Estheti Glass
Available : 45 Distinctive shades (including 3 bleached shades)
EsthetiGlass low fusing porcelain crowns are made with the latest generation of ceramics from Vita. Contains more yellow-orange glass to provide warmer tones and higher translucency in the oral environment.

Gingival toned ceramics

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SMART MATERIALS

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SMART COMPOSITES
• Introduced as the product Ariston pHc in 1998 • Smart Composites are active dental polymers that contain bioactive amorphous calcium phosphate (ACP) filler capable of responding to environmental pH changes by releasing calcium and phosphate ions and thus become adaptable to the surroundings.

• These are also called as Intelligent composites.

 This phenomenon is based on a newly developed alkaline glass filler and is expected to reduce the formation of secondary caries at the margins of the restorations due to an inhibition of bacterial growth, a reduced demineralization and a buffering of acids produced by cariogenic micro-organisms

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• It releases functional ions - fluoride, hydroxyl, and calcium ions as the pH drops in the area immediately adjacent to the restorative materials, as a result of active plaque .

Composition Paste contains Ba, Al, and F silicate glass filler (1m) with Ytterium trifluoride, silicon dioxide and alkaline glass (1.6 m) in dimethacrylate monomers.

Filler Content: 80% by weight & 60% by volume.

Properties

 Fluoride release is lower than glass ionomers but more than that of compomers.
Flexural strength Flexural modulus Mean wear rate : : : 118 MPa 7.3 GPa 7194 m

SUMMARY

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SUMMARY
RECENT ADVANCES IN AMALGAM

 Bonded amalgam
• To compensate for the disadvantages particularly marginal microleakage and need for additional retentive devices. • Time consuming and may be technique sensitive • Cost

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Mercury-free restorative alloys
To overcome the problems of mercury toxicity

 Gallium alloys:
• Sets in a reasonable time and possess the strength , diametrical stability and corrosion resistance equal to or even greater than silver amalgam

• Surface roughness, marginal discoloration and fracture
• Alloys could not be used in larger restorations ; expansion  leads to fracture of cusps and post operative sensitivity

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POWDER COATED TECHNOLOGY
Flexure strength as that of amalgam Smooth surface and hardening was obtained

More resistant to wear
 More technique sensitive than dental amalgam and may require more time for proper condensation.

DENTAL POWDER FROM NANOCRYSTALLINE MELT SPUN AgSn-Cu ALLOY RIBBONS
• Experimental powder

• Better clinical and physical properties

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RECENT ADVANCES IN GLASS IONOMER CEMENTS
Cement ASPA I ASPA II Class Conventional Conventional Type Filling Filling Powder G-200 G-200 Liquid 50% PA-1 47.5% PA-1, 5% TTA

ASPA III

Conventional

Filling

G-200

45%
TTA,

PA-1,

5%

5% CH 3 OH ASPA IV Conventional Filling G-200 47.5% PA-48, 5% TTA ASPA IV a Conventional Luting G-200A 47.5% PA-48, 5% TTA ASPA V ASPA V a ASPA X Water–hardening Water-hardening Conventional Filling Luting Filling G-200:PA-2(5:1) G-200a: PA-2 G-338 10% TTA 10% TTA 47.5% PA-48, 5% TTA
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Variations in Basic Glass Composition
• Barium • Lanthanum

Modifications in powder
• Direct polyacrylic acid (anhydrous GIC) • Silver – Tin alloy (Miracle Mix) • Silver – Palladium / Titanium (Cermet cement) • BISGMA, TEGDMA and HEMA (light /dual cure GIC)

• NVP, CPP-ACP, Zirconia etc
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Modifications in liquid
• Only water and tartaric acid (anhydrous cement) • HEMA (Light cure components) • Polyvinyl phosphoric acid

 SILVER-ALLOY POWDER AND GLASS IONOMER CEMENT: (MIRACLE MIX) • Flexural strengths were increased but abrasion resistance was poor, because of lack of strong bonding between the metal filler and the polyacrylate matrix

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 CERMET • The problem of obtaining strong bonding of metal fillers to glass ionomer powder was solved by sintering the metal powder into the glass powder • Water sensitivity (acid-base reaction)

 RESIN MODIFIED GLASS IONOMERS
• Immediate stabilization of the water balance following the light initiation, enhanced translucency • Need for incremental build up for a restoration deeper than 34mm, Setting shrinkage

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 COMPOMER (POLYACID MODIFIED COMPOSITE RESINS)
Superior working characteristics to resin modified glass ionomer cement, Better esthetics Cannot be use in Class II carious lesions etc

 CONDENSABLE GLASS-IONOMER CEMENTS
Packable + condensable ,Early moisture sensitivity is reduced, Rapid finishing can be carried out, Improved wear resistance, Solubility in oral fluids is very low Final restorative material in class I and II primary teeth Geriatric restorative for class I, II, III, V cavities and cervical erosion Final restorative material in class I and II permanent teeth in non stress bearing area
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 GIOMER (PRE-REACTED GLASS-IONOMER)
Are resin based, they contain pre-reacted glass ionomer (PRG) particles

 Ketac™ N100 Light Curing Nano-Ionomer Restorative
Enhanced surface smoothness, better strength and fluoride release

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BONDING SYSTEMS
 First-Generation Dentin Bonding Systems
• These products ignored the smear layer.



NPG-GMA (N-phenylglycine glycidyl methacrylate), the polyurethanes, and the cyanoacrylates

• Low bond strengths

 Second-Generation Dentin Bonding Systems
• Based on phosphorous esters of methacrylate derivatives Inadequate hydrolytic stability in oral environment • Primary bonding to the smear layer rather than to the underlying dentin
4 May, 2012 Sample footer 308

 Third-Generation Dentin Bonding Systems
• These systems alter or remove the smear layer prior to bonding • Acids or chelating agents were used to remove smear layer
• Retention decreased with time

 Fourth Generation Dentin Bonding Systems
• Based on concept of hybridization • Conditioning ,Priming, Adhesive resin application

• Multiple steps, technique sensitivity

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 Fifth Generation Dentin Bonding Agents
• Number of clinical steps are reduced • Technique sensitive

 Sixth Generation Dentin Bonding Agents
• • • Self etching Primers a mild acid + hydrophilic primer Longer etching time required for enamel

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 Seventh generation bonding systems:
• Mild or strong one step self etch • Least technique sensitive • Prone to phase separation, formation of droplets within their adhesive layer • Lower bond strengths compared to 4th and 5th generation adhesives

 NANOFILLED Dentin Bonding Agents
• • • Has a greater concentration of resin and a smaller molecular weight resin Make the DBA tougher, stronger, and able to cover adequately with a single coat; Penetrate dentin better
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COMPOSITES
 Traditional Composites
 Rough surface

 Discoloration
 Poor resistance to occlusal wear

 Small Particle Filled Composites
 Improved surface smoothness and physical and mechanical properties of traditional composites
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 Microfilled composites
• Problems of surface roughening and low translucency associated with traditional and small particle composites is overcome by the use of microfilled composites • Not preferred for class II and class IV sites; Debonding of prepolymerized composite filler Chipping at margins of restorations

 Hybrid Composites
• They were developed to obtain esthetics better than SPF, while maintaining the desirable properties of the latter • Class IV restorations

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 Flowable Composites
• A modification of SPF and hybrid composites results in flowable composites • Adapts intimately to a cavity form • But has poor wear resistance • Used as a cavity base or liner; Where access is difficult

 Packable Composites
• Condensable composites • To enable clinicians to apply techniques similar to those used for amalgam restorations

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 COMPOSITE INSERTS
• Preformed shapes & sizes of glass ceramic whose surfaces have been silane treated. • Used to minimize the marginal contraction gaps

 FIBRE-REINFORCED COMPOSITES
• Fibers within the composite matrix are bonded to the resin via an adhesive interface
• Fibers increase the structural properties by acting as crack stoppers

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 ORMOCERS
Biocompatibility- will not release any detectable residual substance . Reduced polymerization shrinkage Lasting esthetics ( available in 16 shades )

Anticariogenic property

 CEROMER
Ceromers combine the advantages of ceramics and composites  Durable esthetics, High abrasion resistance, High stability

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 NANOCOMPOSITES


More polishability without sacrificing strength; fifty percent reduction in polymerization shrinkage.

Types of monomers added to composites
• Spiro-ortho-carbonates , vinylcyclopropanes, siloranes, cyclopolymerizable monomers, antibacterial MDPB, Fluorinated Bis-GMA analogues, Bioactive formulations

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ADVANCES IN METAL CERAMICS
COLLARLESS PORCELAIN This was introduced to overcome the disadvantage of metal being exposed and giving unesthetic appearance

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ALL CERAMICS
PORCELAIN JACKET CROWNS:
- they were very brittle and fractured easily.

ALUMINOUS PORCELAIN JACKET CROWN ( HI–CERAM)
-Increased content of alumina ( 40-50%) in the core strengthened the porcelain by interruption of crack propagation. Reduced translucency

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LEUCITE REINFORCED PORCELAIN
Lack of metal or opaque substructure -Good translucency -Moderate flexural strength -Potential fracture of posterior teeth -Increased leucite content leads to high in-vitro wear of teeth DUCERAM LFC : -Due to the absence of leucite crystals, the hardness of the material and its ability to abrade the opposing teeth is reduced .

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CAD – CAM RESTORATIONS
CEREC I (1988)

CEREC –II: ( 1994) CEREC 3 :

CEREC 3-D 3.

Dicor Mgc:
Glass ceramic with fluorosilicate mica crystals in a glass matrix.

flexural strength higher than castable dicor and cerec systems

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 SHRINK FREE CERAMICS
CERESTORE COPING & ALCERAM
• Aluminous porcelain jacket crown, had firing shrinkage problem • Shrink free ceramics were introduced to over come these defects

 Captek System

 Estheti Glass
 Gingival toned ceramics

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 SMART MATERIALS

Smart composites

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CONCLUSION
These recent advancements which have introduced a true revolution in the field of restorative dentistry have enabled the dental clinicians to perform better and to present high quality service for their patients

 And the technology is still going on ……..

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REFERENCES
• Art and Science of operative dentistry-Sturdevant 5th ed
• Dental materials-Phillips 11th ed • Restorative materials- Craig 12th ed • Recent advances in Glass ionomer cements- Davidson • Textbook of operative dentistry- Summit • DCNA 2007; Dental materials • Contemporary fixed prosthodontics—Rosenstiel, Land and Fujimoto • Fundamentals of fixed prosthodontic—Shillingberg III ed.
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Thank you!

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SMART MATERIALS

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Smart composites
Introduced as the product Ariston pHc in 1998

Smart Composites are active dental polymers that contain bioactive amorphous calcium phosphate (ACP) filler capable of responding to environmental pH changes by releasing calcium and phosphate ions and thus become adaptable to the surroundings.
These are also called as Intelligent composites. This phenomenon is based on a newly developed alkaline glass filler and is expected to reduce the formation of secondary caries at the margins of the restorations due to an inhibition of bacterial growth, a reduced demineralization and a buffering of acids produced by cariogenic microorganisms

It releases functional ions - fluoride, hydroxyl, and calcium ions as the pH drops in the area immediately adjacent to the restorative materials, as a result of active

plaque .

Composition Paste contains Ba, Al, and F silicate glass filler (1m) with Ytterium trifluoride, silicon dioxide and alkaline glass (1.6 m) in dimethacrylate monomers.

Filler Content: 80% by weight & 60% by volume

Properties

Fluoride release is lower than glass ionomers but more than that of compomers.

Flexural strength
Flexural modulus Mean wear rate

:
: :

118 MPa
7.3 GPa 7194 m

Summary
RECENT ADVANCES IN AMALGAM

Bonded amalgam
To compensate for the "disadvantages particularly marginal microleakage and need for additional retentive devices. Time consuming and may be technique sensitive Cost

Mercury-free restorative alloys To overcome the problems of mercury toxicity

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Sets in a reasonable time and possess the strength , diametrical stability and corrosion resistance equal to or even greater than silver amalgam

Surface roughness, marginal discoloration and fracture Alloys could not be used in larger restorations ; expansion  leads to fracture of cusps and post operative sensitivity POWDER COATED TECHNOLOGY
Flexure strength as that of amalgam Smooth surface and hardening was obtained More resistant to wear
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More technique sensitive than dental amalgam and may require more time for proper condensation.

• DENTAL POWDER FROM NANOCRYSTALLINE MELT SPUN Ag-Sn-Cu ALLOY RIBBONS

• Experimental powder
• Better clinical and physical properties

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RECENT ADVANCES IN GLASS IONOMER CEMENTS
Cement ASPA I Class Conventional Type Filling Powder G-200 Liquid 50% PA-1

ASPA II

Conventional

Filling

G-200

47.5% PA-1, 5%
TTA

ASPA III

Conventional

Filling

G-200

45% TTA,

PA-1,

5%

5% CH 3 OH ASPA IV Conventional Filling G-200 47.5% PA-48, 5% TTA ASPA IV a Conventional Luting G-200A 47.5% PA-48, 5% TTA

ASPA V
ASPA V a ASPA X

Water–hardening
Water-hardening Conventional

Filling
Luting Filling

G-200:PA-2(5:1)
G-200a: PA-2 G-338

10% TTA
10% TTA 47.5% PA-48, 5% TTA

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Variations in Basic Glass Composition Barium Lanthanum Modifications in powder
Direct polyacrylic acid (anhydrous GIC) Silver – Tin alloy (Miracle Mix) Silver – Palladium / Titanium (Cermet cement)

BISGMA, TEGDMA and HEMA (light /dual cure GIC)
NVP, CPP-ACP, Zirconia etc

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Modifications in liquid

Only water and tartaric acid (anhydrous cement)

HEMA (Light cure components)
Polyvinyl phosphoric acid
SILVER-ALLOY POWDER AND GLASS IONOMER CEMENT: (MIRACLE MIX) Flexural strengths were increased but abrasion resistance was poor, because of lack of strong bonding between the metal filler and the polyacrylate matrix

4 May, 2012

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336

Cermet The problem of obtaining strong bonding of metal fillers to glass ionomer powder was solved by sintering the metal powder into the glass powder Water sensitivity(acid-base reaction)

RESIN MODIFIED GLASS IONOMERS Immediate stabilization of the water balance following the light initiation, enhanced translucency Need for incremental build up for a restoration deeper than 3-4mm, Setting shrinkage
4 May, 2012 Sample footer 337

COMPOMER (POLYACID MODIFIED COMPOSITE RESINS)

Superior working characteristics to resin modified glass ionomer cement, Better esthetics
Cannot be use in Class II carious lesions etc

CONDENSABLE GLASS-IONOMER CEMENTS
Packable + condensable ,Early moisture sensitivity is reduced, Rapid finishing can be carried out,Improved wear resistance, Solubility in oral fluids is very low Final restorative material in class I and II primary teeth Geriatric restorative for class I, II, III, V cavities and cervical erosion Final restorative material in class I and II permanent teeth in non stress bearing areas
4 May, 2012 Sample footer 338

GIOMER (PRE-REACTED GLASS-IONOMER)
are resin based, they contain pre-reacted glass ionomer (PRG) particles

Ketac™ N100 Light Curing Nano-Ionomer Restorative Enhanced surface smoothness, better strength and fluoride release

4 May, 2012

Sample footer

339

BONDING SYSTEMS

First-Generation Dentin Bonding Systems
• These products ignored the smear layer.



NPG-GMA (N-phenylglycine glycidyl methacrylate), the polyurethanes, and the cyanoacrylates

• Low bond strengths

Second-Generation Dentin Bonding Systems
Based on phosphorous esters of methacrylate derivatives Inadequate hydrolytic stability in oral environment

Primary bonding to the smear layer rather than to the underlying dentin
4 May, 2012 Sample footer 340

Third-Generation Dentin Bonding Systems
• These systems alter or remove the smear layer prior to bonding • Acids or chelating agents were used to remove smear layer
• Retention decreased with time



Fourth Generation Dentin Bonding Systems

Based on concept of hybridization Conditioning ,Priming, Adhesive resin application Multiple steps, technique sensitivity

4 May, 2012

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341

Fifth Generation Dentin Bonding Agents

number of clinical steps are reduced Technique sensitive

Sixth Generation Dentin Bonding Agents
Self etching Primers
a mild acid + hydrophilic primer Longer etching time required for enamel

Seventh generation bonding systems:
• Mild or strong one step self etch

• Least technique sensitive
4 May, 2012 Sample footer 342

• Prone to phase separation, formation of droplets within their adhesive layer
• Lower bond strengths compared to 4th and 5th generation adhesives

NANOFILLED Dentin Bonding Agents
Has a greater concentration of resin and a smaller molecular weight resin Make the DBA tougher, stronger, and able to cover adequately with a single coat; Penetrate dentin better

4 May, 2012

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343

Composites  Traditional Composites
 Rough surface  Discoloration

 Poor resistance to occlusal wear

 Small Particle Filled Composites
 improve surface smoothness and physical and mechanical properties of traditional composites

4 May, 2012

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344

Microfilled composites
• Problems of surface roughening and low translucency associated with traditional and small particle composites is overcome by the use of microfilled composites • Not preferred for class II and class IV sites;Debonding of prepolymerized composite filler Chipping at margins of restorations

• Hybrid Composites
• They were developed to obtain esthetics better than SPF, while maintaining the desirable properties of the latter • Class IV restorations

4 May, 2012

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345

• Flowable Composites
• A modification of SPF and hybrid composites results in flowable composites • Adapts intimately to a cavity form • But has poor wear resistance • Used as a cavity base or liner; Where access is difficult

• Packable Composites
• condensable composites • To enable clinicians to apply techniques similar to those used for amalgam restorations

4 May, 2012

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346

COMPOSITE INSERTS
Preformed shapes & sizes of glass ceramic whose surfaces have been silane treated. Used to minimize the marginal contraction gaps Fibre-reinforced Composites Fibers within the composite matrix are bonded to the resin via an adhesive interface Fibers increase the structural properties by acting as crack stoppers

4 May, 2012

Sample footer

347

ORMOCERS
Biocompatibility- will not release any detectable residual substance . Reduced polymerization shrinkage Lasting esthetics ( available in 16 shades ) Anticariogenic property

CEROMER
Ceromers combine the advantages of ceramics and composites  Durable esthetics, High abrasion resistance, High stability

4 May, 2012

Sample footer

348

NANOCOMPOSITES
More polishability without sacrificing strength; fifty percent reduction in polymerization shrinkage.

Types of monomers added to composites
 Spiro-ortho-carbonates , vinylcyclopropanes, siloranes, cyclopolymerizable monomers, antibacterial MDPB, Fluorinated BisGMA analogues, Bioactive formulations

4 May, 2012

Sample footer

349

ADVANCES IN METAL CERAMICS COLLARLESS PORCELAIN
This was introduced to overcome the disadvantage of metal being exposed and giving unesthetic appearance ALL CERAMICS

PORCELAIN JACKET CROWNS:
- they were very brittle and fractured easily.

ALUMINOUS PORCELAIN JACKET CROWN ( HI–CERAM)

-Increased content of alumina ( 40-50%) in the core strengthened the porcelain by interruption of crack propagation.

reduced translucency

4 May, 2012

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350

LEUCITE REINFORCED PORCELAIN
Lack of metal or opaque substructure -Good translucency -Moderate flexural strength -Potential fracture of posterior teeth -Increased leucite content leads to high in-vitro wear of teeth
DUCERAM LFC : -Due to the absence of leucite crystals, the hardness of the material and its ability to abrade the opposing teeth is reduced .

4 May, 2012

Sample footer

351

CAD – CAM RESTORATIONS
CEREC I (1988)

CEREC –II: ( 1994) CEREC 3 :

CEREC 3-D 3.

Dicor Mgc:
glass ceramic with fluorosilicate mica crystals in a glass matrix.flexural strength higher than castable dicor and cerec systems

4 May, 2012

Sample footer

352

SHRINK FREE CERAMICS
CERESTORE COPING & ALCERAM Aluminous porcelain jacket crown, had firing shrinkage problem Shrink free ceramics were introduced to over come these defects

Captek System

Gingival toned ceramics

4 May, 2012

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353

SMART MATERIALS
Smart composites

4 May, 2012

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354

Conclusion

And the technology is still going on ……..

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References

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356

Thank you!

4 May, 2012

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357

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