Dental Implant Summaries++++

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Vol.17 / No.1 Jul-Aug 2008

Dental Implant Summaries
and related areas of research

17/1

www.dentalsummaries.com

Dental Implant Summaries
1 Titanium allergy in dental
implant patients: A clinical study on 1500 consecutive patients

Vol. 17 / No. 1 Jul-Aug 2008

2 The implant-abutment

interface of alumina and zirconia abutments
Clinical Implant Dentistry and Related Research May 2008. Yüzügüllü B, Avçi M.

3 Immediate functional loading
of implants in single tooth replacement: A prospective clinical multicenter study
Clinical Oral Implants Research August 2008. Donati M, La Scala V, Billi M, Di Dino B, Torrisi P, Berglundh T.

Clinical Oral Implants Research August 2008. Sicilia A, Cuesta S, Gerardo C, Arregui I, Guisasola C, Ruiz E, Maestro A.

4 Sinus bone grafting procedures 5 The mucosal barrier at implant
using ultrasonic bone surgery: 5-year experience
Int. J. of Periodontics and Restorative Dentistry June 2008. Blus C, Szmukler-Moncler S, Salama M, Salama H, Garber D.

abutments of different materials

6 Evaluation of immediate bonecell viability and of drill wear after implant osteotomies: Immunohistochemistry and scanning electron microscopy

Clinical Oral Implants Research July 2008. Welander M, Abrahamsson I, Berglundh T.

Journal of Oral and Maxillofacial Surgery June 2008. Queiroz P, Souza F, Okamoto R, Margonar R, Pereira-Filho V, Garcia I Jnr, Vieira E.

7 Histopathological observations
of a polylactic acid-based device intended for guided bone/tissue regeneration

8 A photoelastic and strain-

gauge analysis of interface force transmission of internal cone implants
Int. J. of Periodontics and Restorative Dentistry August 2008. Akça K, Çehreli M.

9 Treatment outcome of

Clinical Implant Dentistry and Related Research June 2008. Koo K, Pringel G, Agelan A, Safadi F, Wikesj U.

immediately loaded implants installed in edentulous jaws following computer-assisted virtual treatment planning and flapless surgery
Clinical Oral Implants Research July 2008. Komiyama A, Klinge B, Hultin M.

10 The effects of laser

microtextured collars upon bone levels of dental implants
Implant Dentistry June 2008. Weiner S, Simon J, Ehrenberg D, Zweig B, Ricci J.

11 Preoperative radiographs

for dental implants – Are selection criteria being followed?
British Dental Journal June 2008. McCrea S.

12 Sinus floor elevation using
an osteotome technique without grafting materials or membranes

Int. J. of Periodontics and Restorative Dentistry May 2008. Schmidlin P, Müller J, Bindl A, Imfeld T.

13 Evaluation of peri-implant
bone loss around platform switched implants
Int. J. of Periodontics and Restorative Dentistry May 2008. Cappiello M, Luongo R, Di Lorio D, Bugea C, Cocchetto R, Celletti R.

14 Prophylactic antibiotic

regimens in oral implantology: Rationale and protocol
Implant Dentistry June 2008. Resnik R, Misch C.

Managing Editors: Dr. Mark Atkinson, Dr. Michael Norton Editorial Consultants: Dr. Koray Feran, Dr. Stephen Jacobs, Dr. Zaki Kanaan, Dr. Kia Rezavandi, Dr. Max Suleiman, Dr. Nadeem Zafar Dental Implant Summaries (ISSN 0967-375X) Produced bi-monthly by Specialist Dental Summaries Ltd, 104 Harley Street, London, W1G 7JD, United Kingdom. Tel +44 (0)20 7935-8687, Fax +44 (0)20 7855-0282 Email [email protected]

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1

Titanium allergy in dental implant patients: A clinical study on 1500 consecutive patients
Titanium is widely accepted as the material of choice for intraosseous applications. Although in general metals have the potential to corrode and may release metal ions with a potential to induce allergic response, titanium is known for its high resistance to corrosion and its exceptional biocompatibility. Nonetheless there are reports of symptoms ranging from skin rashes to implant failure and even non-specific immune suppression, although these cases are mainly reported from the orthopedic literature. It is not known whether these findings can be extrapolated to dental implants. Indeed very little importance has been placed on this phenomenon. The purpose of this study was to establish the prevalence of titanium allergy and to determine possible indicators for this, with a view to evaluating in which cases allergy tests should be recommended.

Sicilia A. Cuesta S. Gerardo C. Arregui I. Guisasola C. Ruiz E. Maestro A. August 2008 Clinical Oral Implants Research Vol. 19 No. 8 pp 823-835 Correspondence to: Professor Dr. Alberto Sicilia Clinica Sicilia Uria 5 Oviedo 33003 SPAIN

Materials and Methods  35 out of 1500 patients requiring implant treatment or surgery
for peri-implant related issues, were enrolled for allergy analysis. 16 were placed into the allergic group (AG) as they exhibited allergic symptoms after implant placement, dekeratinized hyperplastic peri-implant soft tissues or unknown failure (such as spontaneous exfoliation), while the remaining 19 were placed in the predisposing factors group (PG), as they had a history of allergies, 3 or more implant surgical procedures or had an implant failure of known etiology. A further 800 patients were evaluated with 35 randomly selected to form a third group to act as control (CON). Cutaneous Prick testing was performed with oxide titanium (0.1% and 5% in a vaseline carrier), titanium oxide (5% in vaseline) and metallic titanium (0.1% and 5% in an aqueous solution). Readings were taken at 10, 20 and 30 minute intervals. Epicutaneous tests were assessed using the same test substances and carriers but were placed on the back and covered with a waterproof dressing. Readings were taken at 24, 48 and 72 hours. One blind examiner graded all readings into a four tier scale: mild, moderate, significant or intense. Statistical analysis was performed at the 95% confidence interval (CI). The relative risk of titanium allergy was also given for each group.

Results  0.6% of all patients tested exhibited an allergic reaction to titanium (9 out of 1500) even at 0.1% concentration, representing 26% of all test group patients. 8 of these were in AG, 1 in PG, and none in CON. There was no significant difference between PG and CON, but differences between AG and the other groups were significant, P=0.009. This indicated that titanium allergy was 10 times more likely to occur in the AG group than in the PG group. When the various clinical indicators were compared with CON, they showed that of the 6 patients included due to allergy after implant placement, 3 tested positive. Of the 8 included for unexplained implant failure, 5 were positive. Of the 10 patients with multiple allergies only 1 tested positive. Readings were negative when failures could be explained, for high titanium exposure, and for hyperplastic soft tissue lesions. Discussion and Conclusion  The results here are broadly in agreement with findings from other studies. The prevalence of titanium allergy in the current study ranged between 0.2%-1%, with other studies showing prevalence rates between 1%-3%. The reduced rates may be partly due to the relatively short follow-up, as some hypersensitivity reactions develop over a longer period. Although it is clear that the risk of allergy to titanium is very small, it cannot be disregarded. One patient in this study required admission to the emergency department for glottis edema, with 2 exhibiting spontaneous implant exfoliation. These are important outcomes with health implications that may lead to legal considerations for the practitioner. It can be concluded that although these results should be treated with caution, titanium allergy does occur in dental implant patients at a prevalence of around 0.6%. It is suggested that patients who are suspected of titanium allergy should be considered for allergy testing. Further experimental studies are needed to confirm these findings.
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Vol.17/ No.1 Jul-Aug 2008

2

The implant-abutment interface of alumina and zirconia abutments
Until the introduction of ceramic implant abutments in the 1990’s, implant abutments were made of titanium with varying machining tolerances at the implant/abutment interface (IAI). This could lead to the establishment of a microgap of up to 100µm with a significant associated bacterial microleakage, aesthetic problems, peri-implantitis, bone or implant loss. Non-axial loading could exaggerate this microgap leading to fatigue fractures or interfacial wear. Ceramic abutments have superior esthetics and are considered to be more tissue-friendly than titanium. This scanning electron microscopy (SEM) study was designed to compare changes at the IAI using titanium, alumina and zirconia abutments secured to Brånemark implants (Nobel Biocare AB) undergoing dynamic loading.

Yüzügüllü B. Avçi M. May 2008 Clinical Implant Dentistry and Related Research Vol. 10 No. 2 pp 113-121 Reprint requests to: Dr. Bulem Yüzügüllü Dept of Prosthodontics Faculty of Dentistry Hacettepe University 06100 Sihhiye Ankara TURKEY

Material and Methods  15 Procera abutments comprising 5 alumina, 5 zirconia test
abutments, and 5 titanium control abutments were secured to regular platform Brånemark implants by applying 32Ncm of torque to the abutment screw. A standardized central incisor crown preparation was modeled in hard wax and scanned with a Procera scanner to produce standardized zirconia copings with a 3mm2 palatal loading area to correspond with the loading tip of the test apparatus. Alumina abutments were sandblasted with 50µm alumina powder and then steam cleaned. Copings were fixed to the abutments using dual cure adhesive resin cement (Bifix DC, Voco). The copings were seated by hand but allowed to cure under standardized conditions. Prior to the SEM imaging gold sputtering was not used so as not to introduce a thickness at the interface that may influence measurements. The gap at the IAI was measured at x 4000 magnification and at 90° to the IAI axis. The microgap was measured at 4 paired sites around the circumference of the IAI starting from the labial aspect. Rounded component margins were not included in the measurement. The implants were mounted into a customized jig using a methyl methacrylate resin to approximate trabecular bone elastic modulus (1.95GPa). The specimens were loaded at 30° to the loading stylus to mimic the angle of incisal force application. The specimens were mounted in an Instron testing device and cyclically loaded with a sinusoidal masticationlike 1Hz cycle for 47,250 cycles (45 days) at between 20-200N of force applied to the 3mm2 loading area on the coping. The force was increased uniformly between the lower and upper values. All test data for within and intergroup variation was subject to stastistical analysis at the p=0.05 level of confidence.

Abutment

Implant

Results  No component failures were seen in any of the samples. Within group and
The microgap between implant and abutment was measured by SEM before and after non-axial cyclic loading to determine any change

intergroup measurements for unloaded specimens showed no significant differences (p>0.05) in microgap sizes. No significant differences were seen after loading in any of the specimens (p>0.05) apart from the palatal aspect of the titanium abutments (3.47µm) c.f. zirconia (1.45µm) and alumina (1.82µm). There was no significant difference between the microgap on zirconium abutments when compared to alumina and titanium abutments.

Discussion and Conclusions  Differences in machining tolerances exist between implant components. Higher forces are expected to be applied to labial and palatal surfaces in function due to the angle of loading and in the current study this resulted in a significant difference in the palatal microgap of titanium abutments. However, the degree of differential wear is determined by the intimacy of fit and the preload applied to the abutment screw. The treatment of the samples before SEM analysis may have removed abraded particles caused by wear of the implant and abutment at the IAI. Since no analysis of screw wear, deformation or loosening was conducted, the effect of the abutment screw on microgap could not be evaluated. Within the limits of this study, alumina, zirconia and titanium abutments appeared to demonstrate no statistically significant differences in the measured microgaps of pre- and post loaded assemblies, although titanium abutments developed a significantly increased palatal microgap after cyclical loading, p<0.05.
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3

Immediate functional loading of implants in single tooth replacement: A prospective clinical multicenter study
The long-term success of single-tooth implants following a delayed loading protocol is well established. However, tooth loss in the aesthetic zone leads to the desirability of immediate provisionalization for patient satisfaction. Most studies, however, describe the placement of an immediate provisional crown that does not conform to the consensus conference definition of actual immediate loading since the implant is not directly loaded until a further healing time has elapsed. This study looked at the success of implants placed in conventional drill-prepared and osteotome-prepared sites and immediately functionally loaded.

Donati M. La Scala V. Billi M. Di Dino B. Torrisi P. Berglundh T. August 2008 Clinical Oral Implants Research Vol. 19 No. 8 pp 740-748

Material and Methods  151 subjects (70 male, 81 female, mean age 45 years) attended for treatment in 8 separate clinics. 11.3% smoked ≥10 cigarettes per day and 11.9% smoked <10 cigarettes per day. The smokers were distributed between three groups, a control (C, n=57) Reprint requests to: Dr. Mauro Donati and 2 test groups (T1 n=50 and T2 n=54) into which patients were randomly allocated. All Dept. of Periodontology were systemically healthy with stable occlusion and a single edentulous space anterior to The Sahlgrenska Academy at the first molars which had healed for at least 3 months and had no missing walls. Göteborg University Implants used were 4.0 or 4.5mm ø and 8 to 13mm in length (OsseoSpeed™, Astra Tech). PO Box 450 SE 405 30 Göteborg In group C, implants were conventionally placed in accordance with the manufacturer’s Sweden protocol and submerged for 3 months prior to abutment connection and loading. In T1, implants were conventionally placed and immediately loaded, while in T2 implants were placed using an osteotome site preparation technique (Osteotome TM, Astra Tech Dental) and immediately loaded. All implants required a primary stability ≥20Ncm for inclusion. At the end of surgery for groups T1 and T2, the implant position was transferred to a prepared cast using a pick up impression coping resin-cured to a prefabricated surgical template. A healing abutment was placed and the flaps sutured. A provisional abutment and crown were prepared and delivered within 24 hours, with abutments torqued to 20Ncm and crowns cemented with temporary cement in full functional contact in the intercuspal position. After 6 months, a ceramometal crown was delivered following new impressions for all patients in all groups. The treated sites were examined clinically and radiographically at baseline and at 3 and 12 months. Soft-tissue dimensions including papilla heights and keratinized tissue width were recorded along with plaque score, inflammation and probing levels all recorded at 4 locations around the crown. Radiography was standardized using custom holders and analyzed by a blinded experienced radiologist to record bone level in relation to implant abutment junction mesially and distally at x7 magnification to the nearest 0.10mm. Statistical analysis was carried out for each parameter measured using multiple tests to determine differences in outcome between groups, implant diameter or a combination of both. Results  Sites treated were upper premolars 70% > lower premolars (15%) > upper incisors (9%) > upper canines (4%) and lower incisors (2%). 2 implants in T2 were excluded when dehiscences occurred during placement. 2 patients were excluded at 1 year due to medical problems. 3 implants from T2 (5.5%) and one from T1 (2%) failed to integrate and were removed. No significant inter-group differences in soft tissues parameters were found other than distal probing levels in group C which were significantly greater than in group T2. Mesial and distal bone loss ≥ 1mm was significantly more frequent for implants in group C (24.2%) compared to T1 (11%) and T2 (11.6%) at the 1 year follow-up, P=0.01. The 4.5mm ø implants showed significantly more bone loss ≥ 1mm at 1 year than the 4mm ø in group C, p<0.01. Mean marginal bone loss was similar at 3 and 12 months indicating most remodelling occurred in the first quarter. Discussion and Conclusions  This study suggests that immediate functional loading (as
opposed to just provisionalization) of a single tooth implant placed with good primary stability may be a predictable protocol for implant success. Osteotome preparation may be associated with a lower success rate.
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4

Sinus bone grafting procedures using ultrasonic bone surgery: 5-year experience
Grafting the maxillary sinus to increase bone volume via a lateral window approach has historically been undertaken with rotary instruments which can easily damage the sinus membrane, blood vessels and nerves. Ultrasonic bone cutting (UBC), though reported 30 years ago, has regained attention due to new dedicated devices available for the surgeon to utilize during osseous surgery. Such devices are especially useful when making a lateral cortical window entry into the sinus for grafting. The objective of this retrospective report was to analyze the use of UBC in sinus surgery over a 5 year period.

Blus C. Szmukler-Moncler S. Salama M. Salama H. Garber D. June 2008 Int. J. of Periodontics and Restorative Dentistry Vol. 28 No. 3 pp 221-229

Material and Methods  Patients were included in the study if implant therapy was indicated, residual bone height (RBH) to the sinus floor was less than 6mm on a DPT and Reprint requests to: bone width at the proposed site allowed placement of 3.75-5.0mm implants. Dr. Cornelio Blus Corso Francia 7 The lateral wall of the sinus was exposed via a full thickness flap. An ultrasonic (Resista) I-10138 and a piezoelectric (Mectron) device were used to perform UBC. The Resista unit induces a Torino vibration at a frequency of 20-32KHz and generates 90W power and was used with a round ITALY 2.8mm diameter titanium alloy working tip. The Mectron induces a vibration at a frequency of 24-29KHz and generates a power of 5-16 W and was used with a 2.2mm diamond coated round stainless steel working tip. Delineation of the lateral window was executed with light movements and the cut extended deeper into bone (thickness 0.5-6mm) until the sinus membrane was reached. The window was in-fractured and membrane and bone window elevation into the sinus was carried out by hand. Suitably shaped tips were then used for harvesting bone and decorticating surfaces for grafting. Autogenous bone was harvested from intra-oral sites as required. Lateral grafting with bovine xenograft (BX) and platelet poor plasma (PPP) was used if ridge width required increasing and the bone surface decorticated with UBC in these sites. As the study progressed, the graft material changed from purely autogenous (18.8%), to autogenous/BX mix (24.8%) to pure BX (56.4%) and mixed with platelet-rich plasma (PRP) before packing into the sinus. The lateral window was covered using a PPP/BX combination membrane. RBH was measured pre-operatively and 6 months post grafting before implant placement to the nearest half millimeter on DPT’s from the same equipment. 34 patients (16 male, 18 female, mean age 55±8.5 years) underwent 53 sinus lifts and 117 implant placements over a 5-year period. 46 fixed bridges and 8 single crowns were provided. 41/53 (77.4%) of the lifts were prepared with the Resista device, the remainder with the Mectron unit. RBHinitial was a mean of 3.7mm. All implant placements were undertaken between 6-8 months (mean 7.3 months). Survival criteria were fulfilled if there was no membrane tear, good implant stability at insertion and exposure, and after loading, with quarterly follow-up for the first A typical lateral window entry into the maxillary sinus created year and each subsequent year thereafter, with an absence of peri-implant mucositis or using piezo-surgery continuing radiographic peri-implant radiolucency. Results  Two out of 54(3.8%) membranes were perforated due to excessive force and
presence of a septum in the Mectron group. PPP was used to seal perforations and contain the graft with no post operative complications. RBHfinal was a mean of 16.4mm with approximately 50% being 10-15mm and the remainder being >15mm in height. 4 implants did not integrate in 3 patients where RBHinitial was <4mm and RBHfinal was <15mm. Implant survival rate was 96.6%. 113 implants remained loaded for >1 year, 94% >2 years. There were no post-loading failures.

Discussion and Conclusions  UBC resulted in a membrane perforation rate of 3.8%,
which was low compared to other studies (mean 28.6%). This was typically associated with the presence of a septum. UBC resulted in a relatively blood free field, better visibility and less soft tissue morbidity in donor sites. The Resista unit’s higher power and longer tips were noted to improve access and cutting efficiency over the Mectron.

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Vol.17/ No.1 Jul-Aug 2008

5

The mucosal barrier at implant abutments of different materials
Abutments made of different materials have been used in implant dentistry and choice in any given clinical situation is based on technical and aesthetic reasons. Although a good attachment is seen between soft-tissues and titanium, there are conflicting reports regarding gold-alloys and limited information on the use of zirconium. The aim of this study was to assess the soft-tissue barrier formed to implant abutments made of different materials.

Welander M. Abrahamsson I. Berglundh T. July 2008 Clinical Oral Implants Research Vol. 19. No. 7 pp 635-641 Correspondence to: Dr. M. Welander Dept. of Periodontology The Sahlgrenska Academy at Göteborg University, Box 450 450 30 Göteborg SWEDEN

Materials and Methods  The mandibular premolars, maxillary first, second and third
premolars were removed three months prior to the insertion of four implants (OsseoSpeed™, Astra Tech Dental) in one side of the mandible. Titanium healing abutments were connected for transmucosal healing. One month after surgery, healing abutments were removed and four abutments placed randomly. These comprised of two titanium abutments (Ti), one AuPt-alloy abutment (GA), and one ceramic ZrO2 abutment (CR). Three months later the same procedure was repeated on the contra-lateral side. Throughout the healing phase good oral hygiene was maintained. The animals were sacrificed after a further two months for histomorphometric analysis of block sections including implants and surrounding tissues. Measurements included: the margin of the peri-implant mucosa (PM), the apical extension of the junctional epithelium (aJE), the marginal bone level (B), and the implant- abutment junction (IAJ). All measurements were carried out parallel to the long axis of the implant. The proportions of the connective tissue comprising of collagen, fibroblasts, vascular tissue, leukocytes, and other matrix components was calculated from an area 80µm lateral to the implant-abutment interface. In addition the volume of leukocytes infiltrating the epithelium was determined. Statistical analysis was performed using the two-way analysis of variance (ANOVA) and the Student-Newman-Keuls tests.

Results  Evaluation of tissue alteration during the 2 and 5 months of healing indicated that in the CR and Ti sections the peri-implant mucosa and marginal bone levels remained stable. However, in the GA sections an apical migration of both the epithelium and the marginal bone occurred at most sites. Thus the distance between PM and aJE increased PM from 1.56mm at 2 months to 2.07mm at 5 months. The distance between IAJ and B were Histology 1.05mm to 1.71mm for the 2 and 5 months of healing respectively. Assessment of the connective tissue revealed that the amount of collagen and fibroblasts aJE IAJ were significantly smaller in the GA sections than that found in the Ti and CR sections, p < 0.05. In addition the proportion of leukocytes and residual tissue were greater at GA sites. B These findings were observed in both the 2 and 5 month specimens. However, a statistically significant difference was only seen in the 2 month sections (p<0.05), since data from only Zr AuPt Ti Ti 2 of the GA sites was assessed at 5 months. This was due to the apical migration of the epithelium beyond the IAJ reference in the other 4 sites. It was therefore not possible to Marginal soft-tissue reaction to analyze these sections. Furthermore a significant difference was found in the percentage of different abutments was tested leukocytes that had infiltrated the epithelium in the GA and Ti sites (6.7-6.8%) compared to (Ti) Titanium, (Zr) Zirconium and (AuPt) Gold/Platinum Alloy the CR sites (5.2%) at 2 months, p<0.05. These differences were not observed after 5 months of healing. Discussion and Conclusions  The results from this study show that soft-tissue healing around Ti and CR abutments is different to that at GA abutments. The tissue reaction that caused an apical migration of the epithelium in the GA abutment group resulted in the formation of a mucosal seal by achieving contact with the titanium surface of the implant. In addition the smaller amounts of collagen and fibroblasts at GA abutments may contribute to bone loss and apical migration as a result of poor mucosal adaptation. These findings are similar to previous reports in the literature. The differences in leukocyte infiltration of the barrier epithelium observed at 2 months may be related to differences in bacterial colonization of the abutment surface. Previous studies have shown a greater level of bacterial colonization of titanium than zirconium in the in vivo model.
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6

Evaluation of immediate bone-cell viability and of drill wear after implant osteotomies: Immunohistochemistry and scanning electron microscopy analysis
The process of bone repair is dependent on the cellular and vascular status of the bone, for which the presence of extra-cellular–matrix proteins is important. These proteins include osteoprotegerin (OPG) involved in tissue remodelling, RANK ligant (RANKL) a tumourrelated necrosis factor, and osteocalcin (OC) essential in the activity of osteoblasts. It is the relative balance of these proteins which guides tissue healing. Heat generated by drills in the placing of implants can have adverse effects on tissue healing and consequently on implant integration, with repeated drilling, using progressively less sharp instruments, causing greater temperature rise. In an attempt to quantify these effects, the influence of using implant drills repeatedly and the consequent immediate bone cell viability were assessed by measuring the three bone matrix proteins named above.

Queiroz P. Souza F. Okamoto R. Margonar R. Pereira-Filho V. Garcia I Jnr. Vieira E. June 2008 Journal of Oral and Maxillofacial Surgery Vol. 66 No. 6 pp 1233-1240 Reprint requests to: Dr. R. Okamoto: Rua José Bonifácio 1193, Vila Mendonça, Araçatuba, São Paulo, CEP 16015-050 São Paulo, BRAZIL

Material and Methods  Ten rabbits, each of which received 10 osteotomy sequences for
implants in the superior cortical layer of their tibias, were divided into five groups in which drills of varying previous usage were employed. These ranged from new and hence previously unused drills through those used 10, 20, 30 and 40 times for the corresponding number of osteotomies. After sacrificing the animals and dissecting the treated tibia, bone samples were prepared to enable analysis of the levels of the three proteins under scrutiny, produced within osteocytes in the cortical bone adjacent to the experimental perforations. For the second part of the study the drills used in creating the experimental defects were evaluated by assessing photomicrographs obtained from a scanning electron microscope. The tips of the drills were compared for wear and plastic deformation before and after use for the respective number of times; at x35 and x100 magnification.

Results  Protein analysis showed that OPG, RANKL and OC were present in a balanced and dynamic manner which was compatible with bone viability and hence potentially good healing in the 10 and 20 times used drill groups. However, in the 30 and 40 times used groups, an increase was recorded in the expression of RANKL compared to OPG which through statistical analysis indicated changes in the protein balance. Comparison of photomicrographs of the drill tips showed a progressive trend towards plastic deformation with increased use ranging from those not previously used to the greatest wear in those used 30 and 40 times. At x35 magnification, wear was noted on the cutting tips’ lateral surfaces together with abrasion of the metal surfaces. Areas of metal release were observed with subtraction of material in some parts and addition in others. Although present in all drills, these effects were most pronounced in those used 30 and 40 times. In these latter drills, at a magnification of x100, damage was more clearly seen with a tendency of edges to curl and with discontinuity and grooving to the metal surfaces.
After using 30-40 times, drill tips showed marked damage to their cutting edges

Discussion and Conclusions  The standardized protocol utilizing the superior cortical layer of bone of similar type and thickness in rabbits enabled comparison of the results in a way that had not been previously possible. Bone heating during active preparation of implants is known to affect the turnover activity of bone tissue during osteotomies and this study sought to analyze the influence of repeated use of implant drills and immediate cell viability by measuring protein expression. The balance of OPG and RANKL observed in the 10 and 20 times used drill groups confirmed the cell viability after these osteotomies and suggested the characteristics of bone tissue in the physiological state commensurate with tissue healing. Since the frictional heat generated is related to the force used, drill size, form and drilling time, by use of the methodology employed in this study the authors conclude that bone cell viability is preserved when a less traumatic surgical protocol is adopted. This technique includes appropriate irrigation, drilling speed, and movement variability during drilling. The repeated use of drills in this study indicated an altered protein balance in relation to the thirtieth preparation and above.
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7

Histopathological observations of a polylactic acid-based device intended for guided bone/tissue regeneration
Guided bone regeneration (GBR) and guided tissue regeneration (GTR) are widely used tissue engineering techniques aimed at increasing bone volume in implant and periodontal surgery. The use of occlusive barrier membranes allows for cell occlusivity, space maintenance and tissue integration. Polylactic acid (PLA) has been used to produce various resorbable products such as membranes, pins and plates for use in orthopedic surgery and for use in dental surgery. However reports on PLA have included episodes of adverse tissue reactions, osteolysis and sterile abscesses although few studies have focused on the biologic processes immediately associated with the biomaterial used. The aim of this animal study was to evaluate the short- and long-term tissue and biomaterial response following the implantation of a PLA-based carrier device for GBR/GTR.

Koo K. Pringel G. Agelan A. Safadi F. Wikesj U. June 2008 Clinical Implant Dentistry and Related Research Vol. 10 No. 2 pp 99-105 Reprint requests: Dr. Ulf M.E. Wikesjő Laboratory for Applied Periodontal & Craniofacial Regeneration, Department of Periodontics, Oral Biology & Maxillofacial Pathology, Medical College of Georgia School of Dentistry #1430, 1120 Fifteenth St. Augusta, GA 30912 USA

Materials and Methods  Twenty-one Sprague-Dawley rats were divided into three
groups. 15 animals formed the test group (TG) receiving the PLA device (Atrisorb), 5 animals were subjected to sham surgery (SG) and the one remaining animal acted as the control (CG) with no surgical procedure carried out. Calvarial bone was exposed via a full thickness incision along the mid-sagittal suture and reflection of the skin, underlying tissue and temporal muscle. The PLA device was tucked under the soft tissues and lay in direct contact with the bone. Tissues were reapproximated and the wound closed with metal staples. Animals in the SG underwent identical surgery without implantation of the PLA device. Animals in the TG were sacrificed at 3, 5, 7 and 12 months to provide longitudinal observations while the animals in the SG and CG were all sacrificed at 3 months. In each case the cranial bone was removed en bloc and fixed in formalin. Specimens underwent standard preparation for histological analysis of 5 x 7μm central step-serial sections stained with hematoxylin and eosin. Each sample was assessed for the presence of residual biomaterials, inflammatory reactions within the associated bone and soft tissue.

PLA Biomaterial

Calvarial bone

PLA devices were implanted above the external calvarial bone, which after only a few months was being resorbed in a manner suggestive of a foreign body reaction

Results  There were no notable differences in the histopathological observations between the SG and CG. In both groups there were no signs of bone turnover nor was there any evidence of inflammation in the soft tissues, with no discernible inflammatory cells. For the TG specimens, the picture was in stark contrast and differences were also noted at the different time intervals. At 3 months, the PLA device showed fibrous encapsulation that included periosteum with evidence of multinucleated giant cells, macrophages and lymphocytes indicative of a foreign body reaction. At this time interval the external calvarial cortex showed some signs of resorption while some bone deposition was evident lateral to the biomaterial. The same features were seen at 5 months but were more pronounced especially the resorption of the external calvarium. At 7 months, the majority of the PLA device was still intact and the specimens continued to exhibit an infiltrate suggestive of a foreign body reaction with features not significantly different from the previous time intervals. Two (n=3) of the rats showed extensive bone turnover with evidence of a progressive dystrophic calcification within the biomaterial although there were no signs of any cellular activity. However, this observation did not fulfill the histological definition of new bone formation. Residual amounts of the PLA device were still present at the 12-month interval and still surrounded by an even thicker fibrous capsule with the presence of the same inflammatory infiltrate. Discussion and Conclusion  The current study confirmed previous accounts of an inflammatory response and slow resorption of the PLA device which remained largely intact over a 12-month period. The presence of the device appeared to be associated with evidence of a foreign body reaction with unusual calcification but not bone formation. Previous studies have identified a risk for the development of a sterile abscess in such cases. This study would appear to suggest that PLA devices negatively influence the regeneration processes in GBR/GTR procedures.
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A photoelastic and strain-gauge analysis of interface force transmission of internal cone implants
It is known that the design of the implant-abutment connection can have a bearing on mechanical strength and may have a bearing on the force transfer within marginal bone. The aim of this current study was to investigate the force transmission of implants with different internal-cone connections with that of a one-piece implant.

Akça K. Çehreli M. August 2008 Int. J. of Periodontics and Restorative Dentistry Vol. 28 No. 4 pp 391-399 Correspondence to: Dr. K. Akça Çetin Emeç Blv, 6, cadde, 54/3 06450 Öveçler, Ankara TURKEY

Materials and Methods  Four implant designs were studied. A Straumann one-piece
(OP), Straumann solid screw (SS) with an 8-degree cone, Astra Tech cylindrical (AT) with an 11-degree cone and a Bicon (BI) implant with a 1.5-degree friction-grip cone connection. Following abutment connection, photoelastic resin was cast around each implant. All models were inspected within a circular polariscope to ensure a stress free state and were subsequently loaded. One set was loaded axially using a static force of 75N. The other models were positioned so that the same load could be applied at an angulation of 20-degrees. The loaded models were analyzed using a quasi-three-dimensional technique whereby the photoelastic material when subjected to load produces colorful contours (fringes), which are directly proportional to the stresses and strains in the material. The fringe patterns were digitally photographed and then transferred to a computer for quantification. A separate strain gauge study was also undertaken. Two, three-element-120-degree stacked rosette strain gauges were bonded onto the superior surface of the photoelastic blocks approximately 2mm from each side of the implant. Strain-gauge signals were digitized for data-acquisition at a sample rate of 10kHz with subsequent computer calculation to determine the principal strains. Results were statistically analyzed using the Kruskal-Wallis test with a Bonferroni correction at a 95% confidence interval.

The implants tested in this study were from left to right - Bicon, Astra, ITI solid screw and the ITI monoblock

Results  For vertical loads, a concentration of fringe orders was seen at the neck and apical region for all implants. The BI implant showed lower stresses at the collar when compared to the OP, SS and AT. The OP and SS implants showed lower fringe orders around the apex relative to the BI and AT implants. Lower stresses were observed at the microthread region of the AT implant when compared to a similar location around the OP, SS and BI implants. For oblique loads, the lowest stresses were seen around the BI and the highest around the OP implant. The AT implant again showed lower stresses around the thread region than the other implants tested. Comparison of the microstrains under axial loading revealed the highest compressive strains at the AT implant (287μξ) with the BI implant showing the lowest (120μξ), p<0.05. Both OP and SS implants showed similar strains (OP-234.25μξ, SS-246.25μξ). Under angled loading, the highest strains both on the tension and compression sides were recorded for the Straumann implants, p<0.05. The AT and BI implants exhibited comparable strains on the compression side but the BI implant showed a lower strain when compared to the AT implant, p<0.05 on the tension side. Discussion and Conclusions  Comparison of the different internal cone connections showed comparable stresses between all the two-piece implants and the one-piece implant. Similar stress levels were noted around both Straumann implants and the Astra Tech implant. The Bicon implant showed lower compressive and tensile stresses. However this may be due more to the diameter of the BI than the design. A lower magnitude of force was seen around the microthread portion of the AT implant possibly due to the increased surface area presented by this design. Although statistical differences were seen within the strain gauge data: no clinical relevance was placed on these findings. It is possible that these results reflect the limitations of the photoelastic method or that negligible difference exists at marginal bone level between the different internal cone connections. The overall findings would imply that increasing the diameter of an implant might have a greater role than implant design in reducing the force magnitude at crestal bone level.
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Treatment outcome of immediately loaded implants installed in edentulous jaws following computer-assisted virtual treatment planning and flapless surgery
Dental implants are used routinely in the rehabilitation of partially and completely edentulous patients. New concepts such immediate loading using 3-D image planning software are supported by only a few studies but appear to be favorable. The study aim was to evaluate treatment outcomes of immediately loaded implants in edentulous jaws using computer-assisted virtual treatment planning and flapless surgery.

Komiyama A. Klinge B. Hultin M. July 2008 Clinical Oral Implants Research Vol. 19 No. 7 pp 677-685 Correspondence to: Dr. Margareta Hultin Dept. of Periodontology Institute of Odontology Karolinska Institutet PO Box 4064 SE-141 04 Huddinge SWEDEN

Materials and Methods  29 edentulous patients including 5 smokers were treated using
the Nobel Guide 3D planning software and Teeth in an Hour (TIH) concept (Nobel Biocare AB). All patients were CT scanned for presurgical preparation of both the surgical guide and the final prosthesis using Nobel Guide software. Frameworks were constructed from either carbon or titanium using CAD-CAM technology. The surgical guide was anchored using horizontal titanium pins, and a flapless technique was used to place 176 Brånemark TiUnite implants into 21 maxillae and 10 mandibles. Abutments were torqued to 35Ncm and then immediately loaded. The first 5 cases were completed using a carbon-fibre bridge, while the remaining 26 were completed using acrylic on titanium. Post operative panoramic radiographs were taken to ensure abutments were seated correctly and again at the 1 year follow up. Oral hygiene instruction was given and patients were told to maintain a soft diet for the 1st week. Patients were followed up at 1 day, 1 month, 3 months, 6 months and 12 months and thereafter for up to 44 months.

Results  Surgical and technical complications occurred in 42% of cases. 3 surgical templates fractured, 1 before surgery and the other 2 after implant insertion. Bone defects were identified on radiographs in 3 cases. 2 were related to the anchor-pins used to stabilize the surgical guides in the maxilla which were successfully treated using systemic antibiotics. Five implants failed in a severely resorbed mandible despite not loading the implants. In one maxilla a fistula required open debridement and systemic antibiotics. 89% of the implants survived, with a 92% survival rate in the maxilla and 84% in the mandible. In 79% of patients implants were stable and successful, whereas 19 implants were lost in just 6 patients (21%). 31% of implants placed in smokers failed compared to 5% in non-smokers, although this was not statistically significant (P=0.08). Misfit of the abutment-bridge occurred in 5 cases. In 2 of these cases the implants were left to heal unloaded. Extensive occlusal adjustments were carried out in 3 cases, 2 of which had the opposing denture realigned, and in the other case the prosthesis was removed and remade 6 months after healing. 84% of prosthetic superstructures were functional and clinically stable up to the 44-month follow up. The 5 failed superstructures (16%) all occurred within the first 6 months. 2 were lost due to implant loss, 2 due to misfit and 1 was due to a combination of the implant loss and misfit. Two other patients had also lost implants (1 and 2 implants respectively) but their prostheses were still functional. Discussion and Conclusion  The classic protocol has shown long-term implant survival rates of >90% for both maxilla and mandible which contrasts that achieved in the current study of 92% and 84% respectively. The TIH protocol present a number of risk factors, such as potential for deviation in the transfer of data resulting in template/prosthesis misfit, which itself can lead to implant failure due to functional overload or unfavorable occlusion. Indeed all prostheses in the current study needed some occlusal adjustments and in 3 cases this was extensive. This is in contrast to the Brånemark Novum technique in which registrations for prosthesis fit and occlusion are taken after and not before implant insertion. The current study would also suggest there is a reduced ability to irrigate osteotomies leading to high rates of osteonecrosis especially in denser mandibular bone. Nonetheless successful osseointegration could be achieved when using a flapless surgical technique, with a much reduced surgery time (30–45 minutes) with minimal post operative morbidity, and a quick aesthetic result.
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The effects of laser microtextured collars upon bone levels of dental implants
New developments have enhanced osseointegration along the threaded portion of the implant, but crestal bone loss is still problematic. This study compared crestal bone response between a laser microtextured and a smooth, machined implant collar in a dog model.

Weiner S. Simon J. Ehrenberg D. Zweig B. Ricci J. June 2008 Implant Dentistry Vol. 17 No. 2 pp 217-228 Reprint requests to: Dr. Saul Weiner Dept. of Restorative Dentistry, New Jersey Dental School 110 Bergen Street PO Box 1709, Newark NJ 07101-1709 USA

Materials and Methods  Two months post-extraction, 6 mongrel dogs had 3 tapered,
surface textured, screw type LaserLok Silhouette implants Ø3.75x8mm (BioLok International) placed on each side of the mandible using a submerged 2-stage technique. On one side the laser micro-textured collared implants (MC) were placed and on the other the unmodified smooth machined collar implants (SC) were used. Both collars were 2mm. The MC implant collar was created using an Excimer laser, which was divided into 3 zones: The lower 0.8mm was textured with 12µm micro-grooves, the middle 0.7mm with 8µm micro-grooves, and the upper 0.5mm was left machined. The implants were exposed and impressions taken 3 months after implant placement for 5 of the 6 dogs. A further 2 weeks later 1 dog was sacrificed and 4 dogs were fitted with a bar prosthesis on each side. 2 dogs were sacrificed after 3 months loading, and 3 dogs (including the 6th dog, which was the negative control with uncovered implants) were sacrificed 6 months after loading. Specimens were harvested en bloc for histomorphometric analysis using scanning electron as well as light microscopy. Histological sections were analyzed for: osteoclast activity; saucerization; bone upgrowth and soft tissue downgrowth. Multiple histologic samples were processed for many of the implants, representing different boneimplant interfaces from buccal to lingual, and the data was averaged to give a single value for each implant. No statistical analysis was performed due to the small sample size.

Results  Three months after implant placement both SC and MC implants exhibited early osseointegration with significant bone-to-implant contact (BIC). The MC collar had some regions with direct bone attachment with mineralizing bone evident within the microgrooves, whereas the SC collar had few areas of direct BIC. All implants exhibited signs of soft tissue invasion between the bone-implant interface (BII). 3-6 months after loading the implants exhibited mature bone apposition at the implant interface. The MC collar had direct bone attachment with bone penetrating the depth of the grooves, and a mature soft tissue interface at the upper smooth machine part of the collar. The epithelial layer stopped below the smooth surface of the MC implants similar to the junctional epithelium on natural teeth. In contrast the SC collar exhibited extensive soft-tissue migration at the BII. Histological specimens showed greater osteoclastic activity and saucerization around the SC collar, with the difference being even greater at 6 months than at 3 months. Histomorphometric analysis indicated almost the same increase in bone height along the Image showing an implant with collars for both SC and MC implants. However, it appeared to occur quicker for the MC a laser micro-etched region group, with the difference between the 2 groups being greater at 3 months and minimal at consisting of 12µm grooves 6 months. Soft-tissue downgrowth around the collars was greater for SC implants with the difference increasing with time. Discussion and Conclusion  Many factors such as excessive stress, surgical trauma, stress shielding, the microgap and the establishment of the biological width have been identified as possible contributors to crestal bone loss. It has been suggested that microtexturing may help maintain the bone by controlling cell attachment, proliferation and differentiation. It is thought that the behavior of fibroblast and osteoblast cells can be controlled by creating an optimal surface. Studies have shown that 12µm grooves inhibit soft tissue growth relative to bone growth, and that 8µm grooves inhibit epithelial cell migration across the grooves. The results from this study show that the MC collars appear to maintain crestal bone as well as control the level of soft tissue integration. In contrast the SC collars exhibited saucerization, soft tissue invasion and relatively slower osseointegration. Further studies are needed to investigate these tissue-engineered surfaces.
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Preoperative radiographs for dental implants – Are selection criteria being followed?
It is generally agreed that prior to implant placement, visual and clinical examinations should take place, together with appropriate radiographic assessment. The latter should be accurate enough to provide details of anatomic structures, the morphology of the implant site and its bone density, together with information on abnormalities and disease. ‘Selection criteria’ have been developed in the UK by the Faculty of General Dental Practice (UK) (Selection criteria for dental radiography, 2004) and by European and US bodies in recent years to guide practitioners and to protect patients from unnecessary radiation exposure. However, there has not been any indication of how widely these criteria are adhered to. The aim of this postal survey was therefore to systematically assess compliance with selection criteria for the radiographic assessment of prospective implant sites.

McCrea S. June 2008 British Dental Journal Vol. 204 No. 12 pp 675-682 Reprint requests to: Dr. S McCrea The Dental Implant and Gingival-Plastic Surgery Centre, 717 Christchurch Road Bournemouth BH7 6AF UK

Material and Methods  A survey was sent by post to all current members of the British
Periodontal Society (BPS) who were professionally active (n=560) in July 2005, with a reminder two months later as a follow up. Comprising of a questionnaire on pre-implant radiographic assessment, the survey used closed questions with tick-box options. These sought to discover the extent of the respondents’ use of, placement and/or restoration of implants per year and their years of clinical experience, together with their formal (or otherwise) implant training. In terms of radiographic procedures respondents were asked about their routine methods for pre-operative examination including clinical assessment. The availability of more advanced two- and three- dimensional imaging techniques was also elicited. The intention of the study was to use the information to test relationships between years of experience and implant treatment activity as well as to establish surgical expertise and whether or not this had a bearing on radiographic assessment used. Additionally, it was anticipated that the data would allow a systematic analysis of those clinicians who either did or did not utilise the selection criteria.

FGDP(UK) guidelines 1. Clinical and visual examination including palpation and study model assessment. 2. An initial intra-oral two-dimensional periapical radiograph for single site assessment. 3. A panoramic radiograph for multiple implant sites – this being dependant upon dose implications and the wish to investigate anatomical sites. 4. The use of cross-sectional imaging will be dependant on the individual case and on the availability of the resource, the preferred choice being computed tomography (CT) AAOMR(USA) guidelines 1. Clinical and visual examination including palpation and study model assessment. 2. A two-dimensional radiographic examination of either panoramic and/or periapical films. 3. In all cases a cross-sectional image of the site, using preferentially, conventional tomography

Results  The response rate was 81.5%, represented by 459 completed questionnaires. Of these, 179 indicated that the respondents were not involved in treatment which included either placing dental implants or restoring them. These responses were excluded from the analysis. The remaining 280 (61%) could be subdivided into three categories of clinicians, those who were involved only in placing implants (15, 5%), those involved only in restoring implants (85, 30%) and those who undertook both activities (181, 65%). The UK selection criteria were not being followed by 80.8% for single implant sites nor by 77.5% for multiple sites, while 94.0% failed to follow the recommendations established by the American Academy of Oral & Maxillofacial Radiology. No statistically significant differences were detected in compliance related to clinical experience or the quantity of implants placed. However, a difference at the same level of statistical significance was found in greater compliance by clinicians who had undertaken formal training, p<0.05. Discussion and Conclusions  An 81.5% response rate suggested that the target group regarded the questionnaire as relevant and important. However, the results indicated that a large majority were failing to comply with published guidelines, which calls into question the deference with which they regard them. Since the only significant difference was found to be between compliance and formal training, it is speculated that radiographic selection criteria may not be part of manufacturers’ courses or day courses for general practitioners. It can be concluded that with over 80% of the respondents not following published guidelines from the UK and elsewhere for pre-implant assessment, this calls into question not only the clinicians’ awareness of the guidelines, but also the relevance of their content. One can further postulate that their lack of use may be a reflection of a lack of supporting evidence for the criteria and suggests that further research be undertaken which matches implant success with the pre-operative radiographs recorded to provide a stronger evidence base with greater credence.
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Sinus floor elevation using an osteotome technique without grafting materials or membranes
It has been well established that implants may be compromised in the posterior maxilla where inferior bone quality coupled with bone atrophy and pneumatization of the maxillary sinus become complicating factors. Two techniques have been advocated in the management of this problem; the lateral window approach and the osteotome technique as first described by Summers, with the height of pre-operative bone often being the deciding factor. The latter method involves the in-fracture of the alveolar bone at the sinus floor, with or without the use of various grafting materials to help stabilize the Schneiderian membrane and implant. However, there is limited data on the adaptation of this method where no graft is used and where the implant alone supports the Schneiderian membrane. The aim of this study was to evaluate implants that have been placed according to this modified approach.

Schmidlin P Müller J. Bindl A. Imfeld T. August 2008 Int. J. of Periodontics and Restorative Dentistry Vol. 28 No. 4 pp 401-409 Correspondence to: Dr. Patrick Schmidlin Clinic for Preventive Dentistry, Periodontology and Cariology, Center for Dental and Oral Medicine, University of Zürich Plattenstrasse 11 8032 Zürich SWITZERLAND

Materials and Methods  A search was undertaken amongst the clinical records of patients
treated in the University of Zurich, for patients who had received one implant in the posterior maxilla between 2001 and 2004. Only patients who had the implant placed by the modified osteotome method, with no grafting materials, were selected and 24 patients were identified of which 22 accepted the invitation to be re-evaluated. Where patients had received two implants, the one showing the highest radiographic projection into the sinus was assessed. The pre-surgical alveolar bone height was measured using digital radiographs and the osteotomies prepared first by drill to within 1mm of the sinus floor and then by using a 2.2mm osteotome tapped to the final implant depth, with the resultant in-fracture of the sinus floor. The preparation was completed by using an osteotome corresponding to the final drill size for the implant to be placed. The integrity of the Schneiderian membrane was checked throughout. The implants (Straumann) were placed in either a one- or two-stage protocol, allowed to osseointegrate for six months and then restored. Radiographic examination was performed after an average of 17.6 months (±8.4), and measurements were taken of mesial and distal bone heights as measured from a straight line drawn just below the rounded apex to the implant shoulder. Bone gain was also measured above this line around the apex of the implants. Data analysis was performed using the Wilcoxon signed rank test.

Results  All implants successfully integrated, including two that had perforated the
Schneiderian membrane, and there was only one post-operative complication, being an epistaxis. The average pre-operative bone height was 5.0±1.5mm with the average implant length being 8.6±1.3mm and the average sinus elevation measured at 3.6±1.4mm. The percentage of newly formed bone was calculated to be 86%±22% (P<0.001) mesially and 90%±13% distally (P<0.0001). Apically, there was less bone formation, ranging from 0% to 100%, with a mean of 45%±32%.

Radiographic measurements were taken to determine the gain in bone height when no augmentation materials were used to support the Schneiderian membrane

Discussion and Conclusion  Previous studies have tested implant performance in sinus
elevations without the use of bone grafts or membranes, and have also shown impressive bone formation and implant survival. Carrying out this technique without using any type of biomaterial has the benefit of eliminating the risk of pushing debris into the sinus space and causing an inflammatory response that may require further treatment. In this study, of the two implants that did perforate the sinus, one that projected more than 5mm did suffer reduced bone formation compared with the others. Previous studies have advocated a minimum implant length of 8.5mm, and another researcher has suggested a formula of 2x-2, where x is the pre-operative bone height. The mean ratio for 8mm implants in this study was 3.1:1. Decreasing this ratio would mean placing even shorter implants and there is no good evidence for doing this. In conclusion, despite the limitations of this study, this technique does produce good implant survival rates and also promotes new bone to form around the implant apex.
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Evaluation of peri-implant bone loss around platform switched implants
The principle of biologic width (BW) around both teeth and implants has been well established in the literature. With a tooth, there exists approximately 1mm each of sulcus, epithelium and connective tissue providing a physiological seal, whilst with an implant, once it has been exposed into the oral cavity, there exists a 1.5 to 2.0mm band of tissue from the implant-abutment connection (IAC) to the level of the bone. This initial bone remodeling takes place during the first several months and following this, any further change should be limited to less than 0.2mm per year. Several studies have looked at the IAC and found that a microgap (MG) exists which creates a chronic inflammatory response thus causing bone remodeling. One method of reducing this response has been demonstrated by placing the MG above the alveolar crest in a supra-crestal placement. More recently another method has been introduced which has been termed platform switching (PS). PS is a phenomenon where, in a two-piece implant system, prosthetic components that are narrower than the implant platform are connected together. This has the effect of moving the IAC medially towards the center of the implant and thereby shifting the MG further from the bone which seems to result in reduced crestal bone remodeling. Other studies, looking at distances between adjacent implants, have also suggested that the lateral component of the BW influences crestal bone changes. The purpose of this study was therefore to evaluate, clinically and radiographically, the effectiveness of PS implants in the human.

Cappiello M. Luongo R. Di Lorio D. Bugea C. Cocchetto R. Celletti R. August 2008 Int. J. of Periodontics and Restorative Dentistry Vol. 28 No. 4 pp 347-355 Correspondence to: Prof Renato Celletti Via Cola di Rienzo 217 00192 Rome ITALY

Materials and Methods  45 patients with good dental health received 131 implants. 56
were placed in a control group and 75 in a test group. The test implants had a 4.8mm restorative platform that used 4mm components (Osseotite Certain Prevail, Biomet 3i) thus creating a PS. Control implants had a 4.1mm restorative platform and matching restorative components (Osseotite Certain, Biomet 3i). The implants were of varying lengths, and were placed subcrestally and allowed to heal transmucosally for an average of 8 weeks when provisional restorations were placed followed by the final restorations 8 weeks later. Standardized, pixel calibrated radiographs were taken pre-operatively, immediately post-operatively, 8 weeks after placement, at provisional and definitive restoration and finally 12 months post loading. Measurements were taken from the platform of the implants to the first contact of bone with implant, both mesially and distally, and analyzed using the t-test at the 95% confidence level.

Image showing the extent of the platform switch (PS) investigated in this study

Results  From the 131 implants placed, 1 failed to integrate and 2 (in one patient) were not available for review. After 12 months function, the test implants recorded 0.95±0.32mm of peri-implant bone loss, whilst for the control group, the readings were 1.67±0.37mm, and the difference was statistically significant (P=0.001) Discussion and Conclusion  Various studies have demonstrated the principle of bone remodeling following exposure of implants into the oral environment and the establishment of the BW occurs around all two-piece implants. The peri-implant bone loss varies from 0.5 to nearly 3mm depending on the study, with the data from this study being consistent with the others for non-platform switched implants. The results of this study corroborate the view that by moving the IAC towards the implant center, away from the crestal bone, reduces bone loss. Clinically this can be advantageous when shorter implants are indicated such as to avoid anatomical structures. In addition the maintenance will aid the preservation of the interdental papilla thereby improving soft tissue esthetics. In summary, PS can reduce peri-implant bone loss, however histological evidence and longer term follow ups are required to corroborate these findings.
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Prophylactic antibiotic regimens in oral implantology: Rationale and protocol
Using aseptic protocols, careful patient selection and a good surgical technique are of paramount importance during implant and bone grafting procedures. This may help reduce the occurrence of postoperative wound infections that may adversely affect the outcome of these procedures. There are many studies showing that the use of antimicrobials can lead to a significant reduction in postoperative wound infections. There are several factors (local, systemic and surgical) that need to be considered when deciding on a prophylactic antimicrobial regime for various surgical procedures, as well as the timing and dosage of the chosen antibiotics, to ensure their efficacy. Currently, there are no widely accepted protocols or indications for the use of prophylactic antimicrobials in dental implant therapy. The purpose of this paper is to give an overview of the pharmacokinetics and pharmacodynamics of various antimicrobials and offer a classification system that can be used by the practitioner to determine the most appropriate antibiotic regime for specific cases. The most commonly used antimicrobials in implant dentistry are antibiotics and antimicrobial rinses, such as 0.12% Chlorhexidine Gluconate (CG).

Resnik R. Misch C. June 2008 Implant Dentistry Vol. 17 No. 2 pp 142-150 Correspondence to: Dr. Randolph R. Resnik 1082 Bower Hill Road Pittsburgh PA 15243 USA

Antimicrobial rinses  CG has bactericidal characteristics which cause lysis after binding
to bacterial cell membranes. It has been shown to be slowly released from oral tissues and is widely accepted as the rinse of choice during the healing phase.

Prophylactic antibiotics  Previous studies have demonstrated a significant difference in failure rates between using preoperative antibiotics (4.6% failure) compared to without (10% failure). It is thought that the improved aseptic local environment achieved with preoperative antibiotics may be the reason for this difference. The disadvantages of routinely using antibiotics are well known and include: side effects such as nausea, development of resistant bacteria, secondary infections, toxicity of antibiotics, allergic reactions (and anaphylaxis) and their use to overcome poor surgical technique. It is thought that 6-7% of patients taking antibiotics suffer an adverse reaction. 1-3% of patients taking Penicillin will show signs of allergy, but only 0.04-0.011% will be true anaphylaxis and of these 10% will be fatal. Incidence of infection  The American College of Surgeons Committee on Control of Surgical Infections classified all surgical interventions and placed surgical dental procedures into the class 2 category (clean-contaminated), where an infection rate of 10-15% is expected. However, it is suggested that with preoperative antibiotics and good surgical technique, this is reduced to 1%. The duration of surgery is also a factor with studies showing that procedures lasting less than an hour have an infection rate almost one quarter of those lasting 3 hours. This may be the reason for inexperienced surgeons having an increased failure rate compared to more experienced surgeons, since it may take them longer to perform the procedure. Appropriate antibiotic  The ratio of anaerobic to aerobic bacteria in the oral environment
is usually 2:1, and it is therefore important that the chosen antibiotic is effective against both pathogens, it is also preferable it be bactericidal rather than bacteriostatic and exhibits the least side effects.

Tissue concentrations  It is recommended that plasma levels should reach 3-4 times the
minimum inhibitory concentration needed to kill specific bacteria. Generally this dose needs to be given at least 1 hour prior to surgery for this level to be reached. If given after bacterial contamination, results will be as if no preoperative antibiotics have been given.

Antibiotic exposure  A single dose of antibiotics in healthy patients is sufficient.
Prolonged use after surgery is not indicated except for treatments in category 3 or above.

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Prophylactic Antibiotics Penicillin V:  Well absorbed within 30 minutes but detectable levels only last for 4
hours. The main disadvantage is the frequent dosing needed to maintain blood levels and development of resistant bacteria. Amoxicillin:  Better absorption and bioavailability (diffusion into infected tissues) than Penicillin V, with very low toxicity. Used in preference for the non-allergic patient. Augmentin:  (Amoxicillin/Clavulanic acid). Recommended for sinus augmentation as it inactivates resistant bacteria in cases where penicillinases are thought to be present Cephalexin:  First generation cephalosporins are used in penicillin allergic patients as their spectrum is similar but are less prone to beta-lactamase destruction. Cefuroxime axetil (Ceftin):  2nd and 3rd generation cephalosporins have lower crossreactivity, broader spectrum and an improved resistance to beta-lactamase destruction. Erythromycin (a macrolide):  It has great absorption, is not affected by food, has a low toxicity but has a high incidence of nausea. Since it is bacteriostatic it is not recommended as a first choice antibiotic and is usually used in penicillin allergic patients. Clindamycin:  More effective against anaerobic bacteria but also targets aerobic pathogens especially bacteroides. Disadvantages include high toxicity, a high prevalence of diarrhea (20-30%), and pseudomembranous colitis (if taken over a long period). The drug is only bacteriostatic (unless given in high concentrations). It can be mixed with a chosen graft material in its aqueous form of 300mg/2ml. Ciprofloxacin (1st generation quinolone):  A broad spectrum bactericidal antibiotic used orally or parenterally. Levaquin (3rd or 4th generation quinolone):  Useful against resistant and anaerobic bacteria and mainly used in sinus augmentation procedures.

Prophylactic Protocol (Misch) Category 1:  Low risk of infection. Simple extractions without grafting and second stage surgery in healthy patients. No antibiotics required. 0.12% Chlorhexidine rinse is recommended pre- and postoperatively. Category 2:  Moderate risk of infection. Traumatic extractions, socket grafting procedures and immediate implant placements. A recommended preoperative loading dose of antibiotics and a single postoperative dose. 0.12% Chlorhexidine rinse twice a day until suture removal. Category 3:  Moderate to high risk of infection. Multiple implants with extensive soft tissue reflection or multiple immediate implants and bone grafts requiring membranes. A preoperative loading dose of antibiotics followed by 3 postoperative doses per day for 3 days. A 0.12% Chlorhexidine rinse twice a day until suture removal is also recommended. Category 4:  High risk of infection. Implant placements with sinus floor lifts, autogenous block bone grafts and the same procedures as category 2 and 3 but on medically compromised patients. Suggested regime is as category 3 but postoperative antibiotics should be continued for 5 days. Category 5:  High risk. All sinus augmentation procedures. Loading dose of antibiotics a day before the procedure (ensuring adequate levels in sinus tissues before surgery) and a beta-lactamase (Augmentin) antibiotic continued for 5 days. This is due to the high incidence of beta-lactamase pathogens in maxillary sinus infections. Chlorhexidine rinse 0.12% twice a day is also recommended, until suture removal. Discussion and Conclusions  It is clear from this review that the prophylactic use of antibiotics in dental implant and bone grafting procedures is effective at reducing postoperative infections. However, it is recommended that their use should follow a protocol, such as the one suggested, which takes into account local, systemic, surgical and procedural factors.

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Vol.17/ No.1 Jul-Aug 2008