The International Journal of Oral & Maxillofacial Implants, 04/2009

Purpose: This study evaluated the effect of external hexagon height and commonly applied surface treatments on the fatigue life of titanium dental implants. Materials and Methods: Electropolished commercially pure titanium dental implants (seven implants per group) with three different external hexagon heights (0.6, 1.2, and 1.8 mm) and implants with the highest external hexagon height (1.8 mm) and different surface treatments (electropolishing, grit blasting with aluminium oxide, and acid etching with sulfuric acid) were tested to evaluate their mechanical fatigue life. To do so, 10-Hz triangular flexural load cycles were applied at 37°C in artificial saliva, and the number of load cycles until implant fracture was determined. Tolerances of the hexagon/abutment fit and implant surface roughness were analyzed by scanning electron microscopy and light interferometry. Transmission electron microscopy and electron diffraction analyses of titanium hydrides were performed. Results: First, the fatigue life of implants with the highest hexagon (8,683 ± 978 load cycles) was more than double that of the implants with the shortest hexagons (3,654 ± 789 load cycles) (P .02). Second, the grit-blasted implants had the longest fatigue life of the tested materials (21,393 ± 2,356 load cycles), which was significantly greater than that of the other surfaces (P .001). The compressive surface residual stresses induced when blasting titanium are responsible for this superior mechanical response. Third, precipitation of titanium hydrides in grain boundaries of titanium caused by hydrogen adsorption from the acid solution deteriorates the fatigue life of acid-etched titanium dental implants. These implants had the shortest fatigue life (P .05). Conclusions: The fatigue life of threaded root-form dental implants varies with the height of the external hexagon and/or the surface treatment of the implant. An external hexagon height of 1.8 mm and/or a blasting treatment appear to significantly increase fatigue life of dental implants. Keywords: acid etching, dental implants, fatigue, grit blasting, mechanical properties, titanium

Purpose: Ultrasound therapy induces clinical healing of irradiated avascular mandibular bone and fractures. In vitro ultrasound in tissue culture has been shown to stimulate bone formation synthesis and bone remodeling factors and to stimulate osteoblast proliferation. Therefore, the aim of the present study was to investigate the effect of short-wave (1-MHz) and long-wave (45-kHz) ultrasound on the vascularity of the chorioallantoic membrane (CAM) of a fertilized egg. Materials and Methods: The nature of the angiogenic effect was investigated using the CAM of a fertilized egg by: (1) application of sonicated fibroblast media incorporated into methylcellulose disks onto the CAM and (2) direct application of the ultrasound, using both long-wave (45-kHz) and short-wave (1-MHz) frequencies at a range of intensities, to the surface of the egg. Angiogenesis was assessed quantitatively by three independent observers. Results: Both ultrasound methods showed evidence of an angiogenic effect compared to controls. The most effective results were seen with direct application of a 45-kHz wave at an intensity of 15 mW/cm2 and indirect application of the media of fibroblasts ultrasonicated at 1 MHz with an intensity of 0.4 W/cm2. Conclusion: This model confirms that ultrasound can induce neoangiogenesis in vivo. Keywords: angiogenesis, bone, chorioallantoic membrane culture, osteogenesis, ultrasound

Purpose: The objective of this study was to investigate the time-dependent biomechanics of marginal bone around osseointegrated dental implants within physiologic loading conditions. Materials and Methods: The remodeling of marginal bone around a 4.1-mm-diameter, 10-mm-long implant was studied by implementing the Stanford theory into axisymmetric mathematical models simulating different bone support at the implant neck: 1-mm-thick cortical bone (model 1), 0.5-mm-thick cortical bone (model 2), absence of cortical bone (model 3), and absence of cortical bone with 0.5 mm of resorption of marginal trabecular bone (model 4). The results were examined separately for all models at five time intervals: the first loading after osseointegration and 3, 6, 9, and 12 months after osseointegration. Minimum principal stress, maximum principal stress, strain energy, total equivalent strain, displacement, average elastic modulus, and bone density were evaluated. Results: In models 1 and 2, the magnitude of the stresses increased during the 1-year period. The distributions of stresses in models 3 and 4 were less variable and lower than models with cortical bone. The region of high stresses enlarged during the first 3 months and then decreased over time. There was a time-dependent increase in strain energy density around the neck of the implant in models 1 and 2. The time-dependent displacement values of implants were almost constant over time (maximum 1 µm change). The lowest implant displacement values were observed in model 1. There was a slight increase in the elastic modulus of cortical bone and a decrease in trabecular bone (maximum 1% change). Conclusion: The time-dependent increase in stresses in the marginal zone of the implants with cortical bone support was higher than that of the implants supported solely by trabecular bone in the first year of function. Higher strain energy density around the implants with cortical bone support might indicate apposition and increase in interface stiffness, whereas lower strain energy density around implants supported solely by trabecular bone could be associated with skeletal tissue loss. Keywords: bone density, bone remodeling, dental implants, elastic modulus, finite element analysis, strain energy, total equivalent strain

Purpose: Bovine-derived bone xenograft and mineralized cancellous bone allograft have been successfully used as bone substitutes in dental surgery, but few clinical studies in humans have been reported. The objective of this study was to compare the osteoconductive effects of deproteinized bovine bone mineral (DBBM), irradiated cancellous allograft (ICA), and solvent-dehydrated allograft (SDA) when used to preserve extraction sockets. Materials and Methods: Twenty patients received bone grafting in extraction sockets with DBBM (n = 7), ICA (n = 8), or SDA (n = 5). Core biopsies were taken from each graft site 4 to 6 months after grafting and were evaluated histomorphometrically. One-way analysis of variance was used to compare each variable. P values less than .05 were considered significant. Results: DBBM induced more new bone deposition in the periphery of the native bone particles than ICA or SDA, whereas ICA and SDA were more frequently surrounded by fibrous tissue than DBBM. In addition, DBBM retained more residual graft bony particles than ICA or SDA. Conclusions: Based on these findings, the DBBM showed more of an osteoconductive effect than ICA or SDA, producing a more rigid bony structure. It is therefore suggested that DBBM may be more favorable for the preservation of extraction sockets than allogeneic graft materials. Keywords: bovine xenograft, histomorphometry, mineralized cancellous bone allograft, socket preservation

Purpose: The aim of this article was to review the current literature with regard to biofilm formation on dental implants and the influence of surface characteristics (chemistry, surface free energy, and roughness) of dental implant and abutment materials and their design features on biofilm formation and its sequelae. Materials and Methods: An electronic MEDLINE literature search was conducted of studies published between 1966 and June 2007. The following search terms were used: biofilm and dental implants, biofilm formation/plaque bacterial adhesion and implants, plaque/biofilm and surface characteristics/roughness/surface free energy of titanium dental implants, implant-abutment interface and plaque/biofilm, biofilm and supragingival/subgingival plaque microbiology, biofilm/plaque and implant infection, antibacterial/bacteriostatic titanium, titanium nanocoating/nanopatterning, antimicrobial drug/titanium implant. Both in vitro and in vivo studies were included in this review. Results: Fifty-three articles were identified in this review process. The articles were categorized with respect to their context on biofilm formation on teeth and dental implant surfaces and with regard to the influence of surface characteristics of implant biomaterials (especially titanium) and design features of implant and abutment components on biofilm formation. The current state of literature is more descriptive, rather than providing strong data that could be analyzed through meta-analysis. Basic research articles on surface modification of titanium were also included in the review to analyze the applications of such studies on the fabrication of implant surfaces that could possibly decrease early bacterial colonization and biofilm formation. Conclusions: Increase in surface roughness and surface free energy facilitates biofilm formation on dental implant and abutment surfaces, although this conclusion is derived from largely descriptive literature. Surface chemistry and the design features of the implant-abutment configuration also play a significant role in biofilm formation. Keywords: biofilm, dental implants, literature review, plaque microbiology, surface characteristics, surface free energy, surface roughness

Purpose: Human mesenchymal stem cells (hMSCs) are primary cells capable of differentiating to osteocytic lineage when stimulated under appropriate conditions. This study examined changes in hMSC morphology, proliferation, and gene expression after growth on machined or dual acid-etched (AE) titanium surfaces. Materials and Methods: hMSCs, isolated from adult human bone marrow, were cultured on titanium surfaces. The two specimens of titanium surfaces in this study included machined and AE titanium disks. Cell morphology was evaluated by scanning electron microscopy, and cell proliferation and collagen synthesis were estimated by measuring the amount of 3H-thymidine incorporation into DNA and 3H-proline incorporation into collagen fibers. Alkaline phosphatase (ALP) activity was determined by measuring the release of p-nitrophenol from disodium p-nitrophenyl phosphate. Changes in gene expression for bone morphogenetic protein-2 (BMP-2), Runx2 type II, Osterix (Osx), osteopontin, type I collagen, ALP, osteocalcin, and bone sialoprotein were determined by reverse-transcriptase polymerase chain reaction after 22 days of in vitro culture in osteogenic medium. Results: The two substrates had no significant effects on cell adhesion and proliferation. Morphologic characteristics were observed by scanning electron microscopy. hMSCs on the machined surface spread more and were flatter than cells cultured on the AE surface. Osteopontin mRNA expression was similar on all surfaces, and the other mRNA transcripts were increased in hMSC cultured on AE surface. In particular, BMP-2, Runx2, and Osx, three osteogenic factors that induce the progressive differentiation of multipotent mesenchymal cells into osteoblasts, were expressed more on AE titanium than on machined titanium. Collagen and ALP assays confirmed the highest level of mRNA transcripts correlated with increases in these proteins. Conclusion: These results showed that an AE titanium surface stimulated the expression of markers of osteoblastic phenotype more than a machined titanium surface. Keywords: gene expression, human mesenchymal stem cells, proliferation, surface properties, titanium

Purpose: The mechanical properties and functional load performance of implant restorations coupled with metal abutments have been studied widely. However, the fatigue performance of the newly introduced ceramic implant abutments has not been reported. This study investigated the load fatigue performance of four implant systems and their corresponding zirconia ceramic abutments at the manufacturers' recommended torque levels. Materials and Methods: Three different diameters (narrow, regular, and wide) of the Replace Select and Brånemark systems and two different diameters (4.1 mm and 5.0 mm) of the Osseotite NT and Osseotite NT Certain systems provided 10 implant-abutment test groups. The abutments tested were Procera zirconia, Zireal posts, and Certain ZiReal posts. Each group had a sample size of five. A rotational load fatigue machine applied a 21-N load to the specimens at an angle of 45 degrees to produce an effective bending moment of 35 Ncm at a test frequency of 10 Hz. The number of cycles to failure was recorded. Results: Twenty-nine of the 50 implant-abutment combinations tested failed. Eighteen abutments fractured. Seven implant fractures and 16 abutment screw fractures were seen, along with some damage to the implant platform in some specimens. No significant difference was seen between the implant systems, but significant differences were observed between the implant diameters. A subsequent one-way analysis of variance revealed statistically significant differences between the 10 implant-abutment test groups. Conclusions: Rotational load fatigue testing performance of zirconia abutments is dependent on the abutment diameter. Failure modes varied according to system design characteristics. Keywords: abutment, abutment screw failure, dental implants, fracture, interfaces, load fatigue

Purpose: The aim of the study was to evaluate whether resonance frequency analysis (RFA) using a wireless transducer can be used to assess the primary stability of orthodontic mini-implants. Materials and Methods: Fifteen orthodontic mini-implants were placed in three ilium bone segments of country pigs. The wireless resonance frequency transducer was bonded to the head of the mini-implants, and RFA values of the mini-implants in bone were detected and converted into implant stability quotient (ISQ) values by the RFA monitor. In addition, the percussion test value, peri-implant radiographic bone density, and cortical bone thickness were measured. Results: The ISQ values of mini-implants correlated linearly with peri-implant radiographic bone density (r = 0.92, P .0001), cortical bone thickness (r = 0.90, P .0001), and percussion test values (r = -0.91, P .0001), respectively. In addition, by means of the calculation of 99% confidence intervals, the absolute values of the three correlation coefficients ranged from 0.61 to 0.98. Conclusion: This in vitro animal study showed that the presented RFA method using a wireless transducer might have potential to provide an alternative noninvasive assessment of the primary stability of an orthodontic mini-implant. Keywords: biomechanics, bone screws, dental implants, orthodontic appliance, torque

Purpose: The purpose of this study was to evaluate differences in the healing of cortical and cancellous bone around titanium implants with two different surfaces (machined or anodized) in rabbit tibiae. Materials and Methods: Screw-shaped commercially pure titanium implants of two different surface types were fabricated: machined implants (control) and anodized implants; each had two transverse canals that served as sites for bone ingrowth. In the tibiae of six New Zealand white rabbits, a total of 24 implants (12 implants of each surface) were surgically placed in a randomized arrangement. The upper transverse canal was positioned in the cortical bone region, and the lower transverse canal was positioned in the cancellous bone region. After a 1-month healing period, undecalcified ground sections were subjected to histologic and histomorphometric analyses. A mixed-model analysis of variance was used to compare the two types of implants and to control for the random effect of animals. Results: The percentage of bone-to-implant contact (BIC) inside the upper canals was 16.45% ± 4.05% for controls (machined surface) and 24.85% ± 4.86% for anodized implants. BIC inside the lower canals was 7.01% ± 2.34% for controls and 11.35% ± 2.67% for anodized implants. The percentage of bone area inside the upper canals was 10.94% ± 4.06% for controls and 27.95% ± 12.38% for anodized implants. The percentage of bone area inside the lower canals was 3.16% ± 1.08% for controls and 4.66% ± 1.53% for anodized implants. For all measures, the anodized implants had higher values than the controls (P .0001). Conclusion: The results suggest that anodized surface modification of titanium implants is beneficial to both cortical and cancellous bone healing. Keywords: anodic oxidation, cancellous bone, cortical bone, healing, histomorphometric analysis, titanium implant

Purpose: The All-on-Four concept advocates immediate loading and the placement of distal implants at an angle. The purpose of this study was to do a qualitative descriptive analysis of stress patterns around the distal angled implant of the All-on-Four concept. Materials and Methods: Four photoelastic acrylic resin models, each with four implants simulating the All-on-Four configuration, were prepared. The two central implants were placed vertically and parallel in each model, and the distal implant on each side was placed at an increasing angle (0, 15, 30, and 45 degrees) in each model. The four implants were splinted by means of a cast metal bar. The photoelastic models were placed between two parallel anvils. Pairs of abutments were systematically subjected to a load by suspending 5-, 10-, and 15-kg weights from one of the anvils. Photoelastic analysis was accomplished using a circular polariscope. The fringe patterns produced in the photoelastic resin for each implant and load were photographed with a digital camera. Fringe concentrations and the highest fringe order were recorded and described for the apical, central, and coronal regions of the distal angled implant for each load scenario. Results: For the implants placed at 15- and 30-degree angles, little difference in stress patterns was observed between the central straight implant and the distal angled implant. For every load scenario and for all angulations, the lowest fringe order was recorded at the central region of the implant. The highest fringe order for the apical region was always higher than the highest fringe order for the coronal region of the implant. Markedly increased isochromatic fringe concentrations were observed in model 4, which had the distal implants placed at a 45-degree angle. Conclusion: Periimplant bone surrounding the 45-degree-angled distal abutment may be more prone to occlusal overload than bone surrounding implants with lesser tilts. Keywords: angled implants, nonaxial loading, photoelastic analysis

Purpose: Various materials have been used to make guided bone regeneration membranes. The purpose of this study was to create a novel osteogenic membrane without synthetic material. The osteogenic potential of the membrane was evaluated by both in vitro and in vivo testing. Materials and Methods: The membrane was obtained by continuous culture of marrow stromal cells. The structure of the membrane was characterized by staining with hematoxylin-eosin, von Kossa, and carboxyfluorescein diacetate; immunohistochemical staining against collagen type I; electron microscopy; and energy-dispersive spectrometry. The osteogenic potential and bone augmentation effect of the membrane were investigated by implantation of the membrane and a membrane/natural coral composite into nude mice, respectively. Results: The membrane was composed of living cells and a dense matrix of collagen type I. Mineral deposition was apparent through electronic microscopic observation and von Kossa staining. Energy-dispersive spectrometry indicated that the calcium:phosphorus ratio of mineral was 1.71 in the membrane. The membrane had formed a thin layer of bone 2 months after implantation subcutaneously. In the bone augmentation specimens, new bone was observed histologically on the surface and in the pores of natural coral in all specimens of membrane-coral composite. Conclusions: This study developed a novel strategy to produce a vital guided bone regeneration membrane without synthetic material. Membrane derived from marrow stromal cells was osteogenic and had an optimizing bone augmentation effect. Keywords: bone marrow stromal cell, coral, guided bone regeneration, membrane

Purpose: Excessive heat at the implant-bone interface may compromise osseointegration. This study examined the heat generated at the implant surface during preparation of a zirconia/alumina abutment in vitro. Materials and Methods: Sixty zirconia/alumina abutments were randomized into 12 experimental groups. The abutments were connected to implants and embedded in an acrylic resin block in a 37°C water bath. The abutments were reduced by 1 mm in height over a period of 1 minute with a high-speed handpiece and then polished for 30 seconds with a low-speed handpiece, both with and without an air/water coolant. Temperatures were recorded via thermocouples at the cervical, middle, and apical part of the implant surfaces. The Mann-Whitney rank-sum test was used to assess the statistical significance of the difference in temperature between the abutment/implant complexes altered with and without coolant. Results: The 1-mm reduction with the high-speed handpiece without coolant resulted in a maximum temperature of 41.22°C at the cervical portion of the implant. Three of four temperatures above 40°C were observed at the cervical part of the implant following use of the high-speed handpiece without coolant. The temperature difference between "with coolant" and "without coolant" during both low-speed polishing and high-speed reduction was statistically significant at the cervical portion of the implant (P = .009). In contrast, the temperature difference between "with coolant" and "without coolant" during both low-speed polishing and high-speed reduction was not statistically significant at the middle and apical parts of the implant (P > .05). Conclusions: Preparation of a zirconia/alumina abutment caused an increase in temperature within the implant, but this temperature increase did not reach the critical levels described in the implant literature. Keywords: heat generation, implant abutment preparation, zirconia/alumina abutment

Purpose: Implant stability has been identified as a factor that may influence the achievement of osseointegration. The aim of this study was to compare the stability of titanium dioxide grit-blasted (TB) dental implants, with fluoride treatment (FTB) and without, over the first 24 weeks following implant placement. Materials and Methods: Subjects were edentulous patients visiting a university prosthodontics department over a 6-month period seeking mandibular overdentures retained by two implants. Each patient received two implants in the mandible: one TB and one FTB. All implants were placed by the same surgeon. TB implants were placed in the right canine region and FTB implants were placed in the left canine region. Resonance frequency analysis (RFA) was performed at the time of implant placement and at 1, 2, 3, 4, 5, 6, 12, and 24 weeks postplacement. Results: Twenty-seven patients were enrolled. TB implants showed fluctuations in RFA values during the first 6 weeks, whereas the RFA values of FTB implants remained stable throughout the study period. Conclusions: FTB implants did not exhibit the early decreases in RFA values seen in TB implants. Larger studies are necessary to confirm this finding and determine whether this will affect clinical loading protocols. Keywords: fluoride, implant stability, implant surfaces, resonance frequency analysis

Purpose: Passive fit of implant-supported superstructures cannot currently be achieved. The aim of this investigation was to create a methodology that can be used to study the effects of prosthesis misfit in humans. Materials and Methods: An edentulous patient received two interforaminal implants and a screw-retained bar for the retention of the mandibular denture. A corresponding in vitro model with strain gauges placed mesially and distally, adjacent to the implants, was fabricated to serve as a standardizing control. Over a period of 6 months, a total of 10 measurements on both the in vitro model and in the patient's mouth were conducted with newly fixed strain gauges on the bar. Results: The in vitro experiments showed that no component wear at the abutment-bar interface had occurred and that repositioning of the strain gauges on the bar caused deviations in strain measurements up to 10.55%. In vivo, a reduction in strain development, from 445 to 383 µm/m, was observed in the initial phase up to 12 weeks after bar insertion. Subsequently, the measurement values increased, and after a period of 24 weeks, they nearly reached the initial strain level (443 µm/m). Only minor changes in strain development of the bar could be detected; these might be a result of limited dynamic loading and the cortical architecture of the surrounding bone. Deviations in measurement accuracy caused by repositioning of the bar strain gauge are a limitation of this technique and should be eliminated in future studies. Conclusions: The present methodology can be applied to study changes in static implant loading over time in humans. Keywords: bone remodeling, passive fit, static implant loading, strain gauge technique, stress development

Purpose: This article discusses a 3-year retrospective survey of implant clinical survival and computerized tomographic analysis of bone remodeling in atrophic alveolar crests reconstructed via various autogenous bone grafting procedures and in similar regions of native bone. Materials and Methods: The retrospective chart review included consecutive edentulous patients with severe alveolar crest atrophy treated between 2000 and 2002 with onlay autogenous bone grafts in the mandible and anterior maxilla (as needed) and implant insertion. Implant recipients were followed for 3 years. Defective areas were reconstructed by bone graft harvested from the chin or iliac crest. Implants in reconstructed areas were divided into two groups according to graft source. Implants in corresponding native areas served as controls. Cumulative survival rate (CSR), survival rate, and confidence interval (CI) were calculated, and linear measurements of bone remodeling around implants were assessed on computerized tomographic scans. Results were compared for statistically significant differences by Wilcoxon signed-rank test with a significance level α = .05. Results: Forty patients were treated with 109 screw-type, root-form, rough-surfaced implants inserted in 48 onlay grafts; 88 implants were placed in native bone. The implant 3-year CSRs were 98.9% (CI 96.7% to 100%) in native bone and 99.1% (CI 97.3% to 100%) in onlay grafts, irrespective of bone source. Mean resorption in the maxilla was 4.6 ± 0.9 mm buccally and 3.8 ± 0.8 mm palatally in areas reconstructed with chin grafts, 3.4 ± 1.7 mm buccally and 2.6 ± 1.4 mm palatally in areas reconstructed with iliac crest grafts, and 3.2 ± 1.2 mm buccally and 2.1 ± 0.9 mm palatally in native areas. Conclusions: Similar implant CSRs were seen in native and grafted sites. Maximal implant CSR was observed in onlay grafts from the chin despite more marked linear bone remodeling in this group as compared to iliac crest grafts or native bone. Keywords: atrophic mandible, atrophic maxilla, autogenous bone graft, dental implants, onlay bone graft, osseointegration

Purpose: The aim of this study was to compare two different forms of bovine-derived hydroxyapatite (HA) in sinus augmentation and simultaneous implant placement. Materials and Methods: The schneiderian membranes of 12 domestic pigs were elevated bilaterally through an extraoral approach. One sinus of each pig was grafted with bovine-derived granular HA (GHA) and the other was grafted with bovine-derived spongiosa block HA (BHA) (Unilab Surgibone). One dental implant was placed simultaneously into each grafted sinus. Animals were sacrificed after 6 months of healing. Primary implant stability (ISQi) and secondary implant stability (ISQf) were measured by resonance frequency analysis. Undecalcified sections were prepared for histomorphometric analysis. Results: Mean ISQi values for implants placed in sinuses grafted with BHA and GHA were 68.8 ± 5.0 and 68.2 ± 3.7, respectively (P > .05). The mean ISQf value for implants in GHA increased to 72.0 ± 5.1 and for implants in BHA decreased to 52.3 ± 8.8 (P .01). There was a statistically significant difference between ISQi and ISQf values for implants placed in BHA (P = .03) and GHA (P = .037). Mean boneimplant contact (BIC) in residual bone was 61.3% ± 2.1% for BHA and 61.2% ± 1.7% for GHA (P > .05). In augmented bone, mean BIC percentages were 20.6% ± 2.1% and 35.6% ± 1.8% for BHA and GHA, respectively (P = .002). Mean percentages of connective tissue were 61.9% ± 9.5% and 48.4% ± 10.7% (P = .036), new bone formation percentages were 12.8% ± 5.5% and 27.9% ± 4.6% (P = .012), and percentages of graft material around the implants were 25.3% ± 5.8% and 22.4% ± 6.2% (P > .05) for BHA and GHA, respectively. Conclusion: The form of graft material affects the osseointegration of implants in sinus augmentation and simultaneous implant placement. Keywords: bovine-derived hydroxyapatite, dental implants, histomorphometry, resonance frequency analysis, sinus augmentation

Purpose: The aim of this clinical trial was to evaluate the influence of gingival tissue thickness on crestal bone loss around dental implants after a 1-year follow-up. Materials and Methods: Forty-six implants (23 test and 23 control) were placed in 19 patients. The test implants were placed about 2 mm supracrestally, whereas the control implants were positioned at the bone level. Before implant placement, the tissue thickness at implant sites was measured with a periodontal probe. After healing, metal-ceramic cement-retained prostheses were constructed. According to tissue thickness, the test implants were divided into A (thin) and B (thick) groups. Intraoral radiographs were performed and crestal bone changes were measured at implant placement and after 1 year. Results: Mean bone loss around the test implants in group A (thin mucosa) was 1.61 ± 0.24 mm (SE; range, 0.9 to 3.3 mm) on the mesial and 1.28 ± 0.167 mm (range, 0.8 to 2.1 mm) on the distal. Mean bone loss in test group B (thick mucosa) implants was 0.26 ± 0.08 mm (range, 0.2 to 0.9 mm) on the mesial aspect and 0.09 ± 0.05 mm (range, 0.2 to 0.6 mm) on the distal aspect. Mean bone loss around control implants was 1.8 ± 0.164 mm (range, 0.6 to 4.0 mm) and 1.87 ± 0.166 mm (range, 0.0 to 4.1 mm) on the mesial and distal aspects, respectively. Analysis of variance revealed a significant difference in terms of bone loss between test A (thin) and B (thick) groups on both the mesial and the distal. Conclusion: Initial gingival tissue thickness at the crest may be considered as a significant influence on marginal bone stability around implants. If the tissue thickness is 2.0 mm or less, crestal bone loss up to 1.45 mm may occur, despite a supracrestal position of the implant-abutment interface. Keywords: biologic width, crestal bone loss, dental implants, microgap, mucosal thickness

Purpose: The aim of this study was to evaluate the success rate of implants placed in the pterygomaxillary region using drills and osteotomes with a minimum of 12 months' follow-up. Bone loss after 1 year of loading and patient satisfaction with the prosthesis were evaluated. Material and Methods: A retrospective case study was made. The sample was composed of patients rehabilitated with pterygoid implants between January 2000 and January 2006. The inclusion criteria were patients in good general health with severe atrophy of the posterior maxilla who had been rehabilitated with one or two pterygoid implants inserted using drills and osteotomes and had been followed for 12 months after implant loading. Implant success was defined according to the criteria of Albrektsson et al. Bone loss was measured on panoramic radiographs on the mesial and distal of each implant, and the largest value (whether mesial or distal) was selected as the bone loss for the implant in question. Subjects indicated satisfaction with the new prosthesis on a visual analogue scale. Results: Forty-five patients were treated with 268 implants (200 anterior and 68 pterygoid). The success rate of pterygoid implants was 97.05%. The mean bone loss around implants in the pterygomaxillary region after 1 year of loading was 0.71 mm (range, 0 to 3.20). All prostheses were stable at the end of the observation period. Patients were satisfied with comfort and stability, ability to speak, ease of cleaning, and esthetics and functionality of the prosthesis. Conclusion: Placement of implants in the posterior pterygomaxillary region using drills and osteotomes is a viable alternative treatment modality for rehabilitation of atrophic posterior maxilla. Patients were satisfied with a prosthesis supported by pterygoid implants. Keywords: anatomic buttress, maxillary atrophy, pterygoid implants, pterygomaxillary region

Purpose: Achieving implant primary stability in poor-density bone is difficult when the available bone height is less than 6 mm. This study assesses the 1-year clinical performance of tapered implants in sites of reduced height in combination with osteotome sinus floor elevation without bone grafting material. Materials and Methods: An osteotome sinus floor elevation procedure without grafting material was performed in the atrophic posterior maxilla. Tapered implants were placed in maxillary sites with residual bone height of 1 to 6 mm. Implant primary stability was assessed by finger pressure exerted on the implant. Bone gain in the elevated sinus and crestal bone loss were evaluated at 1 year via radiographs. Results: Fifty-four tapered implants were placed in 32 patients and were loaded after a mean of 4.2 ± 1.6 months. The mean maxillary residual bone height was 3.8 ± 1.2 mm. All implants achieved primary stability, and all were successfully loaded. At the 1-year radiographic control, the mean bone gain within the sinus was 2.5 ± 1.7 mm and the mean crestal bone loss was 0.2 ± 0.8 mm. Conclusions: In the atrophic posterior maxilla, primary stability can readily be achieved with tapered implants, even when the mean residual bone height is 3.8 mm. Despite limited bone support and lack of grafting material, all loaded implants were clinically stable, and crestal bone loss was limited. A net bone gain of 2.3 ± 1.8 mm was observed. Survival and success rates were 100% and 94.4%, respectively. Elevation of the sinus membrane without the addition of bone grafting material led to bone formation beyond the original limit of the sinus floor. Keywords: atrophic posterior maxilla, crestal bone loss, dental implants, grafting material, osteotome, sinus lift, tapered implants

Human biopsy of immediately loaded implants is the most definitive means to determine the occurrence of osseointegration. This case report discusses the histologic and histomorphometric analysis of the bone-titanium interface in immediately restored implants with and without occlusal contact, retrieved after a healing period of 5 weeks. The two implants had been inserted in the posterior mandible; both were freestanding. One implant had been put into functional loading (in occlusal contact) with a fixed provisional prosthesis on the day of implant surgery (implant A), whereas the other implant was restored without occlusal contact (implant B). Both implants were retrieved with a 5-mm trephine after 5 weeks. Before retrieval, both implants appeared to be clinically osseointegrated, and no mobility was present. Both implants were surrounded by newly formed bone lamellae. In both implants about 0.5 to 1 mm of pre-existing and newly formed bone was found coronal to the implant shoulder, with no resorption of the pre-existing coronal bone. The bone-implant contact percentage in implant A was 51.2% ± 4.5%, whereas in implant B it was 55.1% ± 2.3%. Within the limitations of this study, the histologic findings indicated that no differences were found in the histologic response around immediately restored implants with and without occlusal contact. Keywords: histology, immediate loading, immediate provisionalization, implant surfaces, loading conditions, occlusal loading, retrieved dental implants

In some patients the size and location of the incisive canal may affect treatment planning in the mandible. This case report addresses management of a patient with a large incisive canal, which prevented placement of a dental implant in the intraforaminal area of the mandible. Relevant anatomy is reviewed, treatment considerations are outlined, and potential consequences of inappropriate therapy in similar patients are discussed. Keywords: dental implants, incisive canal, incisive nerve