Biomechanics of Dental Implants

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Biomechanics of implants Contents:



Introduction.



Loads applied to dental implants.



Mass, force and weight.



Types of forces.



Stress, strain relationship.



Force delivery and failure mechanisms.



Fatigue failure.



Scientific rationale for dental implant i mplant design.



Single tooth implant and biomechanics.



Cantilever prosthesis and biomechanics.



iomechanics of frame wor!s and misfit.



Treatment planning based on biomechanical ris! factors.



Conclusion.



"eferences.

Page #

Biomechanics of implants

INTRODUCTION:

iomechanics comprises of all !inds of interactions between tissues and organs of the body and forces acting on them. It$s the response of the  biologic tissues to the the applied loads. %ental implants function to transfer load to surrounding biological tiss tissue ues. s. Thus Thus the the prim primar ary y func functi tion onal al desi design gn ob&e ob&ect ctiv ivee is to mana manage ge 'dissipate and distribute( biomechanical loads to optimi)e the implant supported prosthesis function. Definition

*rocess of analysis and determination of loading and deformation of  bone in a biological biological system.  +atural tooth s ImplantImplant-

 +atural tooth #. +atural tooth is anchored in to

Implant #. Impl Implan antt is rigi rigidl dly y fie fied d by

the bone by fleible periodontal

functional an!ylosis.

ligament. /.

The

around

perio riodont dontaal the

natural

lig ligamen amentt tooth

significantly reduces the amount of stress transmitted to the bone

/. The concentration of stresses mainl inly occu occurs rs at the the cres cresttal region.

Page /

Biomechanics of implants

and

facilitates

even

force

distribution. 0. The The pdl pdl acts acts as visc viscoe oela last stic ic shoc!

absorber

serving

to

0. The implant is fied and rigid.

decrease the magnitude of stress to the bone. 1. The precursor signs of a  premature contact or occlusal traum raumaa

on

natural ral

teeth

are

usua usuall lly y reve reversi rsibl blee and and incl includ udee

1. These initial reversible signs and symptoms of trauma donot occur with implants.

sign signss of cold cold sens sensit itiv ivit ity, y, wear wear facets, pits, drift away and tooth mobility. 2. This condition often helps in

2. The magnitude of stress may

the patien patientt see!in see!ing g profes professio sional nal

cause bone microfractu microfracture, re, bone

treatment by occlusal ad&ustment

loss loss

and

mech mechan anic ical al fail failur uree of impl implan antt

a

reduction

in

force

magn magnit itud udee in force force magn magnit itud udee

which which ultim ultimate ately ly leads leads to to

components.

which further reduces the stress magnitude. 3. The elastic modulus of a tooth is closer to the bone than any of

3. The implant materials differs by

the the

24#5 24#5 time timess from from the the surr surrou ound ndin ing g

curr curren entl tly y

avai availa labl blee

dent dental al

implant implant biomaterial biomaterial.. The greater greater

 bone structure. Page 0

Biomechanics of implants

the fleibility difference between the two materials, the greater the  potential

relative

generated

between

motion the

two

surfaces at the endosteal region. 6. Implants deliver a slow dull 6. The proprioceptive information

 pain that triggers a delayed

relayed by teeth and implants also

reaction if any.

differs differs in 7ualit 7uality. y. +atura +aturall teeth teeth deliver

a

 pressure

rapid,

sharp, rp,

that

high

triggers

 proprioceptive mechanism. mechanism. 8.

The

surrou rounding

bone

8. ;he ;here as the bon bone load loadiing around an implant is performed by

of

natural teeth is developed slowly

the dentist in a much more rapid and intense fashion.

and and grad radual ually in resp respo onse nse to  biomechanical loads. loads. 9. Late Latera rall forc forces es in impl implan ants ts 9. : lateral force on natural tooth is dissip dissipate ated d rapidl rapidly y away away from

concentrat rates

at

the

crestal

region.

the crest of bone toward toward the ape of the tooth.

Page 1

Biomechanics of implants CHARACTER OF FORCES APPLIED TO DENTAL IMPLANTS -

<cess loads on an osseointegrated implant may result in mobility of supporting device and ecessive loads also may fracture an implant compon component ent or body. body. The intern internal al stress stresses es that that develo develop p in an implan implantt system and surrounding biological tissues under imposed load may have a significant influence on the long term longevity of the implants in vivo. : goal of treatment planning should be to minimi)e and evenly distribute mechanical stress in implant system and contiguous bone. LOADS APPLIED TO DENTAL IMPLANTS: o

In function = occlusal loads

o

:bsence of function = *erioral forces



>ori)ontal loads

o

Mechanics help to understand such physiologic and non physiologic loads and can determine which t?t renders more ris!. MASS, FORCE AND WEIGHT: Mass – : property of matter, is the degree of gravitational attraction the

 body of matter eperiences. eperiences.  @nit = !gs - 'lbm( FORCE (SIR ISAAC NEWTON !"#$: 

 +ewton$s II law of motion

Page 2

Biomechanics of implants F A ma ;here a A 9.8 m?s/ 

Mass = %etermines magnitude of static load



Force = Bilograms of force

WEIGHT:

Is simply a term for the gravitational force acting on an ob&ect at a specified location. FORCES AND FORCE COMPONENTS: 

Magnitude, duration, direction, type and magnification



ector 7uantities$



%irection = dramatic influence MOMENT % TOR&UE:

The force which which tends to rotate a body. @nits = +.mD +.cm, +.cm, lb.ft D o).in In addition addition to aial force, force, there there is a moment moment on the implant implant which which is e7ual e7ual to magnit magnitude ude of force force times times 'multi 'multipli plied ed by( the perpen perpendic dicula ularr distance 'd( between the line of action of the F and center of the implant.

Page 3

Biomechanics of implants

FORCES ACTING ON THE IMPLANTS: T'ee t)*es of fo+es a+tin on t'e -enta. i/*.ants 

Co/*essi0e



Tensi.e



s'ea

Compressivei(

Tend to push masses towards each other.

ii(

Maintains in integrit rity of of bo bone = implant in interfa rface.

iii(

:ccommodated best.

iv(

Cortical bone is stron rongest in compressi ssion.

v(

Cemen ementts, ret retent ention ion sc screw rews, implan plantt com comp ponen onents ts and and bo bone = im impla plant interfaces can accommodate greater compressive forces than tensile or shear forces. Page 6

Biomechanics of implants vi(

>ence compressive forces should be %ominant in implant

 prosthetic occlusion. occlusion.

TENSILE FORCES

SHEAR FORCES





*ull ob&ects apart

Sliding

 %istract ? disrupt bone implant interface.

Shear  She

forc forces es are most ost dest destru ruct ctiv ivee, cort cortic ical al bone bone is wea! ea!est est to

accommodate shear forces. Cylinder implants implants =in particula particularr are  Cylinder

highest highest ris! for for shear forces forces at

the implant tissue interface unless an occlusal load directed along the long ais of the implant body.  They re7uire a coating to manage the shear forces to manage the shear

forces through a more uniform bone attachment.  Threaded ? finned implants impart a combination of all three types of

forces forces at the interfac interfacee under under the the action action of single single occlus occlusal al load. load. This This Page 8

Biomechanics of implants conversion of a single force in to three types of forces is controlled by the implant geometry. STRESS:

The manner in which a force is distributed over a surface is referred as mechanical stress. 1 F%A

The magnitude of stress depends on two variables4

force magnitude.

4

cros crosss sec secti tion onal al area area over over whic which h the the forc forcee is is dis dissi sipa pate ted. d. Fo+e /anit2-e may be decreased by reducing magnifiers of force that

are#.

Cantilever le length

/.

Crown height

0.

+ight guards

1.

Ecclusal material

2.

Ever dentures F2n+tiona. F2n+tiona. +oss se+tiona. aea may be optimi)ed by-

 #. increased by +umber of implants /. Selecting Selecting an Implant Implant geometry geometry that has has been designed designed carefull carefully y to maimi)e the functional cross sectional area.

Page 9

Biomechanics of implants DEFORMATION 3 STRAIN:  : load applied to a dental implant may induce deformation of the implant

and surrounding tissues  %eformation and stiffness of implant material may influence

 A.

Implant tissue Interface Interface

 B.

Ease of implant manufacture manufacture

C.

Clinical longevity

STRESS – STRAIN RELATIONSHIP:



: relationship is needed between the applied stress that is imposed on the implant and surrounding tissues and the subse7uent deformation.



The load values by the surface area over which they act and the strain eperienced by the ob&ect produces a stress strain curve. Page #5

Biomechanics of implants 

The slope of the linear portion of the curve is referred to as the modulus of elasticity and its value indicates the stiffness of the material.



The closer the modulus of elasticity of the implant to the biological tissues, the less the relative motion at the implant tissue interface. Ence a particular implant system is selected the only way for an operator to control the strain eperienced by the tissues is to control the applied stress or change the density of bone around ar ound the implant.



reater the strength stiffer the bone



%ifference in stiffness is less for CpTi G %# bone but more for %1 bone



Stress reduction in such softer bone



To reduce resultant tissue strain



Lower @ltimate strength



>oo!$s law Stress A Modulus of elasticity  strain  A <.ε γ  A 4ITING FORCES:

 :ial component of biting force- '#55 = /255 +( ? '/6 = 225 lbs(  It tends to increase as one moves distally  Lateral component 4 /5 + 'appro.(

time per meal A 125 sec   +et chewing time Page ##

Biomechanics of implants



Chewing forces will act on teeth for A 9 min?day



If includes swallowing A #6.2 min?day



Further be increased by parafunction FORCE DELI5ER6 AND FAILURE MECHANISM:

 The manner in which forces are applied to the dental implant restorations

within the oral environment dictates the li!elihood of system failure.  :n understanding of force delivery and failure mechanisms is critically

impo import rtan antt to the the impl implan antt pract ractit itio ione nerr to avoi avoid d cost costly ly and and pain painfu full complications. 

The moment moment or tor7ue tor7ue is the the product product of the force force

magnitude magnitude multipl multiplied ied by the perpendicu perpendicular lar distance distance from the point point of interest to the line of the action of the force.

 Moment loads are destructive in nature and may result in-

Interface brea!down one resorption Page #/

Biomechanics of implants Screw loosening ar ? bridge fracture : total of si moments may develop about the three clinical coordinate aes4 occlusoapical 4 faciolingual 4 mesiodistal  These moment loads induce microrotations and stress concentrations at the crest of the alveolar alveolar ridge at the implant implant to tissue tissue interface interface , which lead lead inev inevit itab ably ly to cres cresta tall bone bone loss loss.. Thre Threee clin clinic ical al mome moment nt arms arms in implant dentistry 4 occlusal height 4 cantilever length 4 occlusal width

Page #0

Biomechanics of implants Minimi)ation of each of these moment arms is necessary to prevent unreta unretaine ined d restor restorati ations ons,, fractu fracture re of compon component ents, s, cresta crestall bone bone loss loss or complete implant system failure. $ O++.2sa. 'ei't:

4 Ecclusal height serves as the moment arm for force components directed along the faciolingual ais4 wor!in wor!ing g or balanc balancing ing occlusal occlusal contac contacts, ts, tongue tongue thrus thrusts ts or peri peri oral oral musculature, and the force components directed along the mesiodistal ais. 4 force components components along the vertical vertical ais is not affected affected by the occlusal occlusal height because there is no effective moment arm. 4 in division : bone initial moment load at the crest is less than in division C or % bone because the crown height is greater in Cand %. 7$ Canti.e0e .ent': 

Large Large moment momentss may develo develop p from vertic vertical al ais ais force force compon component entss in  prosthetic environments designed with cantilever etensions or offset loads from rigidly fied implants.



: Lingual force component may also induce a twisting moment about the implant nec! ais if applied through a cantilever length.



Force applied directly over the implant does not induce a moment load or tor7ue because no rotational forces are applied through an offset distance.

Page #1

Biomechanics of implants 

:ntero posterior spread is the distance to the center of the most anterior implant and the most distal aspect of the posterior implants.



The greater the :4* spread the smaller the resultant loads on the implant system from cantilevered forced because of the stabili)ing effect of the antero4posterior distance. :ccording to  MISCH



Cantilever length is determined by the amount of stress applied to system



enerally =%istal cantilever = not be H /.2 times of :4* spread



*atients with parafunction = not to be restored by cantilever.



S7uare arch form involves smaller :4* spreads between splited implants and should have smaller length cantilever.



Tapered arch form = largest :4* spread = larger cantilever design. 8$9 O++.2sa. i-t':

;ide ;ide occlus occlusal al tables tables increa increase se the moment moment arm for any offset offset occlusal loads. Faciolingual tipping 'rotation( can be reduced significantly  by narrowing the occlusal tables or ad&usting the occlusion to provide more centric contacts. : vicious destructive cycle can develop with moment loads and result in crestal bone loss.

Page #2

Biomechanics of implants

Mo/ent .oa-s

Cesta. ;one .oss

In+eases o++.2sa. 'ei't Fai.2e if ;io/e+'ani+a. ;io/e+'ani+a. en0ion/ent is not +oe+teO++.2sa. 't9 /o/ent a/

Moe +esta. ;one .oss

Fa+io.in2a. Fa+io.in2a. /i+o otation o o+<in

FATIGUE FAILURE:

Fatigue failure is characteri)ed by %ynamic cyclic loading conditions, four factors significantly influence the fatigue failure.

#( iomaterials /( eometry 0( Force magnitude 1( Loading cycles $ 4io /ateia.s: 

Fatigue behaviour of biomaterials is characteri)ed to a plot of applied stress vs no. of loading cycles



>igh stress = few loading cycles



Low stress = infinite loading cycles

Page #3

Biomechanics of implants 

Ti

alloys

ehibits

a

higher

enduran rance

limit

compared

with

commercially pure titanium 'Cp Ti( 7$ Ma+o eo/et): 

The geometry of an implant influences the degree to which it can "esists bending and tor7ue



Lateral loads also causes fatigue fracture



The fatigue failure is related as 1th power of the thic!ness difference



 :lso affected by the difference in Inner and outer diameter of screw and abutment screw space 8$ Fo+e /anit2-e:

The magnit magnitude ude of loads loads on dental dental implan implants ts reduce reduced d by carefu carefull consideration of arch position 

>igher loads on posteriors



Limitation of Moment loads



eometry for functional area



Increasing the +o. of implants

 =$ Loa-in +)+.es 

"educing the +o. of loading cycles



<limination of parafunction



"educing the occlusal contacts SCIENTIFIC RATIONALE FOR DENTAL IMPLANT DESIGN Page #6

Biomechanics of implants %ental implan implants ts functi function on to transf transfer er of load load to surrou surroundi nding ng biolog biologic ic  %ental tissues.  Thus the primary functional design ob&ective is to manage 'dissipate and

dist distrib ribut ute( e( biom biomec echa hani nica call load loadss to opti optimi mi)e )e the the impl implan antt supp support orted ed  prosthesis function.  iomechanical load management depends on two factors that are

#( Character of applied load.

/( Functional surface area

 Forces applied to dental implant characteri)ed in terms of Magnitude,

duration, type, direction and magnification. FORCE MAGNITUDE

The The magn magnit itud udee of biti biting ng forc forcee varie variess as a func functi tion on of anatomic anatomic region and state of dentition dentition.. The magnitude magnitude of force is greater greater in molar region and lesser in canine region.



>igher >igher magnit magnitude ude demand demandss increa increased sed bone bone densit density y and Influence the selection of biomaterials.



Materials such as silicon hydroyapatite and carbon are characteri)ed by lesser ultimate strengths even though they are highly compatible with the biological tissues.



In

cont contem emp porar orary y

appl appliicat cation ions,

the these

materi teriaals

are

considered for use as coatings applied to stronger substrate materials. 

Silicone, >:, carbon has4 >igh biocompatibility 4 Low ultimate strength



Titanium and its alloy = <cellent biocompatibility Page #8

Biomechanics of implants 4 Corrosion resistance 4 ood ultimate strength 4 Closest appro. to stiffness of bone FORCE DURATION: 

The duration of bite forces on dentition has a wide range under ideal conditionsD the total time of those brief episodes is less than 05 minutes  per day.



*atients who ehibit bruism, clenching or other parafunctional habits may have their teeth in contact several hours each day.



The enduranc endurancee limit limit or fatigu fatiguee streng strength th is the level of highes highestt stress stress through whish a material may be cycled repetitively without failure. The endurance limit of a material is often less than one half its ultimate tensile strength. 

The ability of implants and abutment screws to resist fracture from  bending loads is related directly to the moment of inertia of the component.



This parameter is a function of the cross sectional geometry of the component.



Implant bodies are particularly susceptible to fatigue fracture at the apical etension of the abutment screw within the implant body or at the crest module around abutment 'eg- with an internal heagon(



The formula for the bending fracture resistance in these conditions is related to the outer diameter radius to the fourth power minus the inner diameter radius to the fourth power.

Page #9

Biomechanics of implants 

The wall thic!n thic!ness ess of the implant implant body body in this this region region controls controls the resistance to fatigue failure. <ven a small increase in wall thic!ness results in a significant increase in bending fracture resistance because the dimension is multiplied to a power of four.

T6PE OF FORCE: 

Three types types of forces may be imposed imposed on dental dental implants implants within within the oral environment  

4Compression

 

4Tension 4Shear 



one one is stronge strongest st when when loaded loaded in compre compressi ssion. on. 05 wea!er wea!er when when sub&ected to tensile forces and 32 wea!er when loaded in shear 



: smooth sided implant may be called a cylinder design, and this cylinder implant body result in essentially a shear type of force at the imp implan lant to bone bone inte interf rfaace. ce. Thus Thus this his body ody geom eometry etry mus must use a microscopic retention system by coating the implant with titanium plasma spray or hydroyl apatite



If the hydroyapatite resorbs from infection or bone remodeling, the remaining remaining smooth sided cylinder cylinder is severely severely compromised compromised for healthy healthy load transfer to the surrounding tissues



: thread threaded ed implan implantt may use micros microscop copic ic and macros macroscop copic ic design design features to load the bone in compression and tensile loads



Threa Threade ded d impl implan ants ts have have the the abil abilit ity y to tran transf sfor orm m the the type type of forc forcee impo impose sed d at the the bone bone inte interfa rface ce thro throug ugh h care carefu full cont contro roll of the the thre thread ad Page /5

Biomechanics of implants geometry. Thread shape is particularly important in changing force type at the bone interface 

Thread shapes in dental implant design include s7uare, v shape and  buttress



@nde @nderr aia aiall load loadss to a dent dental al impl implan antt a v thre thread ad face face 'typ 'typic ical al of  paragon, 0i and +obel iocana( is comparable to the buttress thread and has a #5 times greater shear component of force than a s7uare or a power thread



: reduction in shear load at the thread to bone interface reduces the ris! of overloadD which is particularly important in compromised %0 and %1  bone. : threaded implant also may have a surface condition such as hydroyapatite, T*S or other roughed surface.

FORCE DIRECTION: 

The anatomy of the mandible and mailla places significant constraints on the ability to surgically place root form implant suitable for loading along their long ais.



ony ony unde undercu rcuts ts furt furthe herr cons constr trai ain n impl implan antt plac placem emen entt thus thus forc forcee direction. Most of all undercuts occur on the facial aspects of the bone, with the eception of the submandibular fossa in posteroior mandible. >ence implant bodies often are angled to the lingual to avoid penetrating the facial undercut during insertion.



:s the angle of the load increases, the stresses around the implant increases, particularly in the vulnerable crestal bone region. :s a result all implants are designed for placement perpendicular to the occlusal plane.

Page /#

Biomechanics of implants This placement allows a more aial load to the implant body and reduces the amount of crestal loss. FORCE MAGNIFICATION-

Ther Theree are are vari variou ouss fact factor orss whic which h can can magn magnif ifie iess the the force forcess on dent dental al implants 

Surgical placement resulting in etreme angulation of the implant



*ara functional habits



Cantilever and crown height



Increase in functional area



Increased density of the bone



Increase in implant number decreases cantilever length and limits the force magnifier.

FUNCTIONAL SURFACE AREA: 

Functional surface area is defined as the area that actively serves to dissipate compressive and tensile non shear bonds through the implant to  bone interface and provides initial stability of the implant following surgical placement.



The The tota totall surf surfac acee area area may may incl includ udee a pass passiv ivee area area that that does does not not  participate in load transfer.



Func Functi tion onal al surf surfac acee area area also also play playss a ma&o ma&orr role role in addr addres essi sing ng the the variable implant to bone contact )ones related to bone density.

Page //

Biomechanics of implants 

%# bone, is the densest bone found in the &aws is also the strongest  bone and provides an intimate contact with a threaded root form implant at initial implant loading.



%1 bone has the wea!est biomechanical strength and the lowest contact area to dissipate the load at the implant to bone interface.



Thus an improved functional surface area per unit length of the implant is needed to reduce the mechanical stress to this wea! bone.



Implant macrogeometry and implant width are two important design variables for optimi)ing surface area.

IMPLANT MACROGEOMETR6

The The macr macro o desi design gn or shap shapee of an impl implan antt has has an impo import rtan antt  bearing on the bone bone response.



rowing bone concentrates preferentially on protruding elements of the implant surface, such as ridges, crests, teeth, ribs or the edge of threaded surface.



The shape of the implant determines the surface area available for stress transfer and governs the initial stability of the implant.



Smoo Smooth th side sided d cyli cylind ndri rica call impl implan ants ts prov provid idee ease ease in surg surgic ical al  placement, however the bone to implant interface is sub&ected to significantly larger shear conditions.



: smooth sided tapered implant allows for a component load to  be delivered to the bone implant interface, depending on the degree of taper, however the greater the taper of smooth sided implant the less the overall surface area of the implant body.

Page /0

Biomechanics of implants 

Threaded implants with circular cross sections provide for ease of surg surgic ical al plac placem emen entt and and allo allow w for for great greater er func functi tion onal al surfa surface ce area area optimi)ation to transmit compressive loads to bone implant interface.



:

smooth

surface

cylinder

depends

on

a

coating

or

microstructure for load transfer to bone. IMPLANT WIDTH: 

:n increase in implant width ade7uately increases the area over which occlusal forces may be dissipated.



;ider root form designs ehibit a greater area of bone contact than narrow row implants

of

similar

design because

of

an

increase

in

circumferential bone contact. 

The The larg larger er the widt idth of the the imp implan lant the more ore it rese resem mbles les the the emergence profile of the natural tooth.



The increased width of implants 34#/ mm also enhances the bending fracture resistance. ut the crestal bone anatomy most often constrains implant width to less than 2.2mm.

THREAD GEOMETR6

Threads are designed to maimi)e initial contact enhance surface area and facilitate dissipation of stresses at the bone4 implant interface. Functional surface area per unit length of the implant may be modified by varying three thread geometry parameters 4

thread pitch

4

thread shape Page /1

Biomechanics of implants 4

thread depth

THREAD PITCH:



Thread pitch is defined as the distance measured parallel with its ais  between ad&acent thread forms or the number of threads per unit length in the same aial plane or on the same side of the ais.



The smaller the pitch 'finer( the more threads on the implant body for a given unit length, and thus the greater surface area per unit length of the implant body.



If force magnitude increase or bone density decreases one may decrease the thread pitch to increase the functional surface area.



Some of the current popular designs which have different pitches.



The distance between pitches-

Page /2

Biomechanics of implants ITI Implant = #.2mm Sterioss

4 5.8mm

+obel biocare,)immer, 0i G life core = 5.3mm iohori)ons 4 5.1mm 4the fewer the threads , the easier to bond or insert the implant. THREAD SHAPE-



Thread shapes in implant geometry 'dental implant designs include s7uare, shape and buttress.



The  shape thread design is called a fiture and is primarily used for fiating metal parts together not load transfer.



The buttress thread shape was designed initially for and is optimi)ed for pullout loads.



The s7uare or power threaded provides an optimi)ed surface area for intrusive, compressive load transmission.



The shear force on a  threaded face 'typical of Jimmer, 0i and  +obel biocare( is about #5 time greater than the shear force on a s7uare thread. Page /3

Biomechanics of implants T>"<:% %<*T>

The threaded depth refers to the distance between the ma&or and minor diameter of the thread.



the greater the thread depth, the grater the surface area of the implant if all the other factors are e7ual.

IM*L:+T L<+T>

:s the length of an implant increases so does the overall total surface area.



%# bone is the strongest and densest bone of the oral environment. The stre streng ngth th of the the bone bone and and the the inti intima mate te cont contac actt betw betwee een n the the bone bone and and implant provide resistance to lateral loading. icortical stabili)ation is not needed in %# bone because it is already a homogenous cortical bone.



: long implant in %/ or %0 bone in the anterior mandible may cause increased surgical ris!, since attempting to engage the opposing cortical  plate and preparing a longer osteotomy may result in overloading of the  bone.



In poor poor 7ual 7ualit ity y %0 and and %1 bone bone func functi tion onal al surf surfac acee area area must must be maimi)ed to distribute occlusal loads optimally, the placement of longer implants implants in posterior posterior regions re7uire surgical surgical modificat modifications ions li!e nerve repositioning, placement of sinus grafts in maillary posterior regions.



The shorter and smaller diameter implants had lower survival rates than their longer or wider counter parts.

CREST MODULE CONSIDERATIONS CONSIDERATIONS-

Page /6

Biomechanics of implants  Crest module of an implant body is the transosteal region from the

implan implantt body body and charac character teri)e i)ed d as a region region of highl highly y concen concentra trated ted mechanical stress. 

Slightly larger than outer diameter, thus the crest module seats fully over the implant body osteotomy, providing a deterrent for the ingress of  bacteria or fibrous tissue. tissue.



The seal created by the larger crest module also provides for greater initial stability of the implant following placement.



*olished collar '5.2 mm( = perigingival area, provides for a desirable smooth surface close to the perigingival area.



Longer polished collar = shear loading = crestal bone loss



one is often lost to first thread, because the first thread changes the shear force of the crest module to a component of compressive force in which bone is strongest.

:*IC:L %<SI+ CE+SI%<":TIE+S"ound "ound cross sectional sectional implants implants do not resist torsional torsional shear forces when abutment screws are tightened hence anti rotational feature is incorporated usually in the apical region of the implant body, with a hole or vent. one can grow through the apical hole and resist torsional loads applied to the implant. The apical hole region may increase the surface area available to transmit compressive loads on the bone. The disadvantage of the apical hole occurs occurs when the implant is placed through the sinus floor or becomes eposed through a cortical  plate. The apical hole may fill with mucous and become a source of Page /8

Biomechanics of implants retrograde contamination. :nother anti rotational feature of implant body may be flat sides or grooves along the body or apical region of the implant body. The apical end of each implant should be flat rather than  pointed, this allows for the entire length of the implant to incorporate design features that maimi)e desired strain profiles. Poessi0e Loa-in Mis+' (>"?$ proposed that

radual increase in occlusal load separated by a time interval to allow  bone to accommodate. accommodate. Softer the bone à increase in progressive loading period. Poto+o. In+.2-es, 

 

Time



 

%iet



Ecclusal Contacts and occlusal material



*rosthesis %esign

Ti/e:

Page /9

Biomechanics of implants Two surgical appointments between initial implant placement and stage II uncovery may vary on density. 

%#

4

0 Months



%/

4

1 Months



%0

4

2 Months



%1

4

3 Months

Diet:  

Limited to soft diet = #5 pounds Initial delivery of final prosthesis4/# pounds O++.2sa. Mateia.:

Initial step = no occlusal material placed over implant *rovisional = :crylic = lower impact force Final 4 Metal ? *orcelain *orcelain O++.2sion: 

Initial

4



*rovisional 4

Eut of occlusion



Final

:t occlusion

4

+o occlusal contact

Post'esis Desin:

First First tran transit sititi itiona onall = +o occl occlusa usall conta contact ct

Page 05

Biomechanics of implants +o cantilever  Seco Second nd tran transi siti titi tion onal al 4

Eccl Ecclus usal al cont contac actt ;ith no cantilever

Final restoration

4 narrow occlusal table and cantilever with implant

 protective occlusion occlusion guidelines.

SINGLE TOOTH IMPLANTS

Single Single tooth tooth impla implants nts re7uir re7uiree good good bone bone suppor supportt and contro controll of harmful effects of occlusal levers that are not parallel to the long ais of the implant.



The prosthesis must be designed to allow good oral hygiene, with easy access to inter proimal surfaces and the retaining screw.



: molar can be replaced with two standard diameter implants or one wide implant.



This type implant is contraindicated for larger spaces because the masticato masticatory ry and occlusal forces to the most distal distal or mesial mesial portions portions will  be harmful.



To avoi avoid d ece ecess ssiv ivee load loads, s, the the impl implan antt must must be cent centere ered d in the the edentulous space during placement.

Page 0#

Biomechanics of implants

ANTERIOR SINGLE TOOTH RESTORATIONS: RESTORATIONS: 

The anterio anteriorr

single single tooth tooth restor restorati ation on is achiev achieved ed using a standa standard rd

diameter implant, which is preferred over a narrow implant because it  provides a larger surface for osseo integration integration 

enerally the use of wide implants in this area is not advocated because it may compromise good esthetic results.



To avoid levers that may be produced during parafunction in centric and eccent eccentric ric positi positions ons,, its recomm recommend ended ed that that the implan implantt suppor supported ted restoration be left out of occlusion. S>E"T S*:+ FIK<% *:"TI:L %<+T@"<The construction of a 0 unit particularly cantilever fied  partial dentures re7uire a posterior triangular )one of occlusal surface  between the supporting supporting implants. The chances of overloading the implants are far less and this this provid provides es a better better long long term

progno prognosis sis,, becaus becausee it offers offers a wider wider

active )one while also achieving good occlusal load in relationship to the aes of the implants. the use of wide implants to support cantilever fied  partial dentures improves the prognosis further, especially in those cases where only two wide implants are needed compared compared to three of standard diameter. wide implants allow for an increased occlusal surfaces in these circumstances. Page 0/

Biomechanics of implants The proimity proimity of anatomica anatomicall features features such as the mandibular canal or the maillary sinus limit the use of long implants. In the presence of ade7uate bucco lingual bone width these limitations ca be managed with the use of wide implants. C:+TIL<<" FIK<% *:"TI:L %<+T@"<

It results in greater tor7ue with distal abutment as fulcrum.



May be compared with Class I lever arm.



May etend anterior than posterior to reduce the amount of force It depends on stress factors



*arafunction



Crown height



Impact width



Implant +umber The The desi design gn of cant cantil ilev ever er fie fied d part partia iall dent dentur ures es is depe depend nden entt on the the occlusal forces that can be elicited at the free end of the denture and the length and width of the implants selected.

C:S< #

: case with two implants placed for the lateral incisor and the canine with a free end central incisor.



Two implants of ade7uate length are re7uired.



The cantil cantileve everr tooth tooth should should avoid avoid contac contacts ts on the centra centrall inciso incisors rs during protrusion, lateral ecursions and maimum intercuspation. Page 00

Biomechanics of implants

C:S< II

;hen the implants serve as support for the central and lateral incisors with a free end canine, the occlusal configuration should provide group function during lateral movements and avoids loading of canine.



If it$s not possible lateral guidance may be provided by the central and lateral incisors avoiding any contact with the canine.

C:S< IIIplaced unilaterally unilaterally at the site of two maillary maillary  ;hen two implants are placed  premolars, the free end canine must must be left out of occlusion. occlusion.

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Biomechanics of implants C:S< I

Molar replacements achieve best results with a three Implant supported fied prosthesis providing premolar morphology to the restorations.



The length of the implants influences the outcome of treatment



%ue to the enormous occlusal loads in the second molar area the use of a free end fied prosthesis is contra indicated.

4IOMECHANICS OF FRAMEWOR@S AND MISFIT Fa/eo<s: 

Metal framewor! for full arch prosthesis can fracture



More towards the cantilever section

Reasons: $ Everload of cantilever 

@nli!ely to occur = typical prosthetic alloy. /( Metallurgic fatigue under cyclic loads *revention = substantial cross sectional area Page 02

Biomechanics of implants = 043 mm

TREATMENT PLANNING 4ASED ON 4IOMECHANICAL RIS@ FACTORS 

%esign of final prosthetic reconstruction



:natomical limitation

Geo/eti+ is< fa+to

#( +o. of implants less than no. of root support 

Ene implant replacing a molar = ris!. 



# wide = plat form implant ? / regular implants Two implants supporting 0 roots or more = ris! 



/ wide = platform implants

/( ;ide = platform implants 

"is! = if used in very dense bone

0( Implant connected to natural teeth 1( Implants placed in a tripod configuration 

%esired à counteract lateral loads

Page 03

Biomechanics of implants 2( *resence of prosthetic etension 3( Impl Implan ants ts plac placed ed offs offset et to the the cent center er of the the pros prosth thes esis is à in tripod tripod arrangement, offset is favorable. 6( <cessive height of the restoration

OCCLUSAL RIS@ FACTORS: 

Force intensity and parafunctional habit



*resence of lateral occlusal contact



Centric contact in light occlusion



Lateral contact in heavy occlusion



Contact at central fossa



Low inclination of cusp



"educed si)e of occlusal table

4ONE IMPLANT RIS@ FACTORS 

%ependence on newly formed bone



:bsence of good initial stability



Smaller implant diameter 



*roper healing time before loading



1 mm diameter minimum = posteriors

Te+'no.oi+a. is< fa+tos

Page 06

Biomechanics of implants 

Lac! of prosthetic fit and cemented prostheses



*roven and standardi)ed protocols



*remachined components



Instrument with stable and predefined tightening tor7ue

WARNING SIGNS:

 =

"epeated loosening of prosthetic prosthetic ? abutment screw

 =

"epeated fracture of veneering material material

 =

Fracture of prosthetic ? abutment abutment screws

 =

one resorption below the the first thread

CONCLUSION:

iomechan iomechanics ics is one of the most important important consideration affecting the design of the frame wor! for an implant bone  prosthesis. It must be analy)ed during during diagnosis and treatment treatment planning as it may influence the decision ma!ing process which ultimately reflect on the implant supported prosthesis.

REFERENCES

#.

%ental implant prosthetics = Carl <. Misch

Page 08

Biomechanics of implants /.

*ri *rinci nciple ples an and pra pract ctic icee of of im implan lant den denttist istry = Cha Charl rlees ;ei ;eiss ss,, :d :dam ;eiss.

0.

Tiss Tissue ue = int integ egra rate ted d pro prost sthe hesi sis. s. Esse Esseoi oint nteg egra rati tion on in clin clinic ical al dent dentis istr try y  = ranemar!, )arb, :lbre!tsson :lbre!tsson

1.

Eral ral reh rehaabil bilita itatio tion wit with h im impla plant sup support porteed pro prost sth hesis esis 4i 4in ncen cente

2.

ITI dental implants4 Thomas .;ilson

Page 09

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