The International Journal of Oral & Maxillofacial Implants, 05/2009

Purpose: To investigate the peri-implant stress fields generated from four different implant-abutment interfaces under axial loading applied at the center of the implant and several millimeters away from the implant center via photoelastic analysis. Materials and Methods: Similar unthreaded and cylindric implants and abutments were fabricated and embedded in photoelastic resin with four different implant-abutment interfaces: external hex, internal hex, internal taper (11.5 degrees), and solid connection to the abutment (one piece). The samples were submitted to vertical compressive loads; one was applied at the implant center (1.5 kg; centered load), and the other was applied 6.5 mm away from the center, 4.4 mm from the outside of the outer aspect of the implant (0.75 kg; off-centered load). The maximum shear stresses were determined and observed at 46 points around the implants under the centered load and at 61 points under the off-center load in the photoelastic models. Graphics describing the maximum shear stress (y-axis) and the analyzed points (x-axis) were obtained, and areas under the curves were calculated. Results: The centered loading (all points) resulted in small differences. The lowest amounts of stress were observed for the internal-taper implants, and values were minimally greater (0.4% to 3.3%) for the other implants. No statistically significant differences were found between groups for the centered load in any area. Under an off-center load, the internal-hex implants presented the least stress (all points). For off-center loading, the internal-hexagon implants differed significantly from the external-hex and one-piece implants and displayed the lowest stress levels. Conclusion: Under an off-center load, the internal-hex interfaces presented the lowest stress concentrations, internal-taper interfaces presented intermediate results, and one-piece and external-hex implants resulted in high stress levels. Centralized axial loads produced similar results. Keywords: abutments, biomechanics, bone loss, connections, dental implant, photoelasticity, stress analysis

Purpose: The aim of this study was to evaluate the effect of an electrochemically deposited nanohydroxyapatite (EDHA) coating on the bone bonding of sandblasted and dual acid-etched titanium implants. Materials and Methods: One hundred EDHA-coated and uncoated sandblasted/dual acidetched implants (3 mm in diameter, 10 mm long) were inserted into the femoral condyles of 50 rabbits. The osteotomy sites were enlarged to 3 mm in diameter via a sequence of drills. After 2, 4, 6, 8, and 12 weeks of bone healing, removal torque testing was performed to evaluate the interfacial shear strength of each implant type. The removed implants were prepared and observed with an electron microscope equipped with an energy dispersive electron probe x-ray microanalyzer. Results: The mean removal torque values for the EDHA-coated implants were 39.6 Ncm at 2 weeks and 40.4 Ncm at 4 weeks; corresponding values for the control implants were 21.1 Ncm and 24.1 Ncm. Removal torque values of the EDHA-coated implants were 87% higher than those of control implants after 2 weeks of healing (P = .015). However, the mean removal torque values for both types of implants were similar after 6, 8, or 12 weeks of healing (no significant differences between the implant surfaces; P > .05). Conclusions: The EDHA nanocrystal coating had a beneficial effect on interfacial shear strength during the early stages of bone healing. Keywords: electrochemistry, hydroxyapatite, implants, nanomaterials, rabbits, removal torque

Purpose: This study presents a new rat oral implant model for assessing histologic changes in the mechanical environment surrounding loaded and unloaded dental implants. Materials and Methods: The maxillary left first molar from retired breeder rats was extracted, and the site was allowed to heal for 1 month. A titanium miniscrew implant was then placed into the site and allowed to heal for 21 days. The mandibular left first molars in one group of rats were extracted to create an unloaded condition; in a second group of rats the mandibular left first molars were left in occlusion with the opposing screw head to simulate loading. Radiographs were taken on the day of placement and again at 7 days, 14 days, and 21 days after placement and were used to estimate the bone-implant contact ratio. The rats were sacrificed after 21 days. Peri-implant tissue samples from day 21 were processed for histology and immunohistochemistry with antibodies to osteocalcin and matrix metalloproteinase 13 (MMP- 13). Two-dimensional finite element models were created from images of the histologic sections and immunohistochemical samples to observe tissue changes. Results: Areas of high shear stress adjacent to the helical threads of loaded implants were associated with osteocalcin localization and bone formation but only minimal localization of MMP-13. Bone adjacent to unloaded implants showed fibrous tissue and extensive MMP-13 localization surrounding the apical two-thirds of each implant. These results agree with estimated bone-implant contact ratios, which showed a steady decrease in contact ratio for the unloaded implant group but a significantly higher contact ratio in the loaded group between 14 and 21 days. Conclusion: The rat oral implant model is useful for studies of the mechanical and physiologic environment affecting osseointegration in loaded and unloaded implants. Keywords: animal study, finite element analysis, implant, osseointegration, rat model

Purpose: This study evaluated the biologic effect in vivo of hydroxyapatite (HA) nanoparticle surface modification on commercially pure titanium or titanium alloy (Ti-6Al-4V) implants. Materials and Methods: Miniature cylindric titanium and Ti-6Al-4V implants were pretreated with dual acid etching (DAE), and a subset was further modified with HA nanoparticles using discrete crystalline deposition (DCD). The resultant implant surface topography was characterized by interferometry and scanning electron microscopy. Miniature implants of DAE titanium, DAE Ti-6Al-4V, DCD titanium, and DCD Ti-6Al-4V were surgically placed in the femora of rats. After 4 days, 1 week, and 2 weeks of healing, osseointegration was evaluated by implant push-in tests or microcomputed tomography (microCT). Ti-6Al-4V samples were harvested at week 2 and prepared for nondecalcified histology and subjected to bone-to-implant contact (BIC) measurement. Results: DCD treatment generated a complex surface morphology via the bonded HA nanoparticles. However, the amplitude and spatial, hybrid, and functional surface roughness parameters measured at the micron and submicron levels did not depict topographic differences between the DAE and the DCD-modified implants. DAE titanium and DAE Ti-6Al-4V implants showed a sharp increase in push-in values at week 1, followed by a plateau at week 2. DCD titanium and DCD Ti-6Al-4V implants showed similar sharp increases at week 1, but the push-in values continued to increase at week 2. The surrounding bone architecture evaluated by microCT and the BIC ratio did not correlate with the biomechanical implant osseointegration measurement. Conclusions: DCD-derived surface modification with HA nanoparticles on titanium and Ti-6Al-4V implants resulted in progressive osseointegration profiles that were distinctively different from those of DAE controls. Surrogate measurements such as surface roughness parameters and BIC did not predict the biologic effect of the DCD treatment. The data indicate that early osseointegration may be more sensitively regulated by nanoscale surface characteristics. Keywords: crystalline hydroxyapatite, nanosurface topography, nanotechnology, osseointegration, titanium alloy

Purpose: To evaluate a novel surgical technique for flapless transcrestal elevation of the maxillary sinus floor via surgical templates using gel pressure. Materials and Methods: Computed tomographic scans of fresh human cadaver maxillae and three-dimensional treatment planning software were used to design surgical templates. Access to the maxillary sinus was gained by guided transcrestal osteotomies to puncture the bony sinus floor. By injection of radiopaque gel, the maxillary sinus membrane was elevated to attain a postoperative bone height of 15 mm. Results: The gel-pressure technique was performed in 10 atrophic maxillary sites with a mean residual bone height of the alveolar crest of 4.7 ± 1.6 mm. The sinus membrane was successfully elevated in all sites without causing iatrogenic perforation (mean elevation height, 10.6 ± 1.6 mm). Conclusions: The gel-pressure technique may provide a new option for minimally invasive transcrestal sinus surgery and may represent a safe method to increase bone volume in the atrophic posterior maxilla. Keywords: bone augmentation, dental implants, maxillary sinus, minimally invasive surgery, surgical templates

Purpose: This study evaluated the accuracy of four implant-level impression techniques with optical microscopy on two angulated conical internal-connection implants. Materials and Methods: A master cast with two internal-connection implant analogs angulated 10 degrees from each other and a master framework were fabricated. Four impression techniques were examined: octagonal transfer impression coping, nonoctagonal transfer impression coping, nonoctagonal pickup impression coping, and nonoctagonal pickup impression copings joined together with autopolymerizing acrylic resin. Experimental casts were fabricated from 40 polyether impressions divided into four groups. After the master framework was seated on each of the casts, one abutment screw was tightened and marginal gap measurements between analog and abutment were recorded on the other side with an optical microscope. Results: The casts produced from nonoctagonal pickup impression techniques were more accurate than those produced using transfer impression techniques (P < .05). However, there was no statistically significant difference in the accuracy between the unsplinted and splinted methods in pickup impression techniques (P > .05) or between the use of octagonal coping and nonoctagonal coping in transfer impression techniques (P > .05). Conclusion: The casts produced from nonoctagonal pickup impression techniques were more accurate than those produced by transfer impression techniques, regardless of whether they were splinted, for angulated conical internal-connection implants. Keywords: implant impression, implant-level impression, impression accuracy, internal connection

Purpose: This study evaluated the biomechanical properties of periosteum-derived mineralized culture on different surface topographies of titanium. Materials and Methods: Titanium surfaces modified by machining or by acid etching were analyzed using scanning electron microscopy (SEM). Rat mandibular periosteum-derived cells were cultured on either of the titanium surfaces. Cell proliferation was evaluated by cell counts, and gene expression was analyzed using a reverse-transcriptase polymerase chain reaction. Alkaline phosphatase (ALP) stain assay was employed to evaluate osteoblastic activity. Matrix mineralization was examined via von Kossa stain assay, total calcium deposition, and SEM. The hardness and elastic modulus of mineralized cultures were measured using a nano-indenter. Results: The machined surface demonstrated a flat topographic configuration, while the acid-etched surface revealed a uniform micron-scale roughness. Both cell density and ALP activity were significantly higher on the machined surface than on the acid-etched surface. The expression of bone-related genes was up-regulated or enhanced on the acid-etched surface compared to the machined surface. Von Kossa stain showed significantly greater positive areas for the machined surface compared to the acid-etched surface, while total calcium deposition was statistically similar. Mineralized culture on the acid-etched surface was characterized by denser calcium deposition, more mature collagen deposition on the superficial layer, and larger and denser globular matrices inside the matrix than the culture on the machined surface. The mineralized matrix on the acid-etched surface was two times harder than on the machined surface, whereas the elastic modulus was comparable between the two surfaces. Conclusions: The design of this study can be used as a model to evaluate the effect of implant surface topography on the biomechanical properties of periosteum-derived mineralized culture. The results suggest that mandibular periosteal cells respond to different titanium surface topographies differently enough to produce mineralized matrices with different biomechanical qualities. Keywords: acid etching, machined surface, mineralized tissue, periosteal cells, titanium

Purpose: The recent use of microcomputed tomography (microCT) has made it possible to analyze qualitative bone morphology at the implant surface and in the peri-implant region. The purpose of this study was to evaluate histomorphometric changes around the implant-bone interface after placement of miniimplants using three-dimensional microCT analysis and to compare the stability of the implants after immediate and early loads were applied. Materials and Methods: Forty-eight orthodontic mini-implants (ORLUS, Ortholution) were placed in the mandibular buccal jawbone of eight beagle dogs. Force was applied immediately (immediate loading group) and 3 weeks (early loading group) after implant placement; control implants received no loading. An orthodontic force (250 to 300 g) was applied to the experimental implants for 3, 6, or 12 weeks before sacrifice. Results: The bone-implant contact in both experimental groups was not significantly different for any loading period except for after 12 weeks of loading. The immediate loading group had higher bone volume percentages compared with the early loading group after 6 weeks, but there was no significant difference between groups after 12 weeks. This was in accordance with the results of the three-dimensional microCT analysis. Conclusion: Histologic and microCT analysis showed that immediate loading of mini-implants in the dog model is possible for orthodontic applications with a high bone-implant contact and 100% survival rate. Keywords: histomorphometry, microcomputed tomography, mini-implant

Purpose: To determine whether zirconia abutments with an internal connection exhibit similar fracture load as zirconia abutments with an external connection. Materials and Methods: The following zirconia abutments were divided into four groups of 20 each: StraumannCARES abutments on Straumann implants (group A), Procera abutments on Brånemark implants (group B), Procera abutments on Nobel- Replace implants (group C), and Zirabut SynOcta prototype abutments on Straumann implants (group D). The abutments were fixed on their respective implants either internally via a secondary abutment (A) or a metallic coupling (C) (two-piece) or directly externally (B) and internally (D) (one-piece). In each group, 10 abutments were left unrestored (A1 to D1). Ten received glass-ceramic crowns (A2 to D2). Static loading was performed according to the ISO norm 14801 until failure. The bending moment was calculated for comparison of the groups and subjected to statistical analysis (Student t test). Results: The mean bending moments of the unrestored abutments were 371.5 ± 142.3 Ncm (A1), 276.5 ± 47.6 Ncm (B1), 434.9 ± 124.8 Ncm (C1), and 182.5 ± 136.5 Ncm (D1). Two-piece internally connected abutments exhibited higher bending moments than one-piece internally (C1 versus D1 P = .003, A1 versus D1 P = .03) or externally (C1 versus B1 P = .004) connected abutments. The groups with restorations did not show different bending moments than those without restorations. The mean bending moments of the restored abutments were 283.3 ± 44.8 Ncm (A2), 291.5 ± 31.7 Ncm (B2), 351.5 ± 58 Ncm (C2), and 184.3 ± 77.7 Ncm (D2). Group C2 exhibited the highest bending moment (P < .05). Internally connected one-piece abutments (D2) were weaker than all other groups (D2 versus A2 P = .002; D2 versus B2 P = .001; D2 versus C2 P = .0003). Conclusions: The type of connection significantly influenced the strength of zirconia abutments. Superior strength was achieved by means of internal connection via a secondary metallic component. Keywords: ceramic abutments, connection, fixation, implant reconstructions, stability, zirconia

Purpose: The present study assessed damage to the inferior alveolar nerve (IAN) following nerve lateralization and implant placement surgery through optical and transmission electron microscopy (TEM). Materials and Methods: IAN lateralization was performed in 16 adult female rabbits (Oryctolagus cuniculus). During the nerve lateralization procedure, one implant was placed through the mandibular canal, and the IAN was replaced in direct contact with the implant. The implant was placed in the right mandible, and the left side was used as a control (no surgical procedure). After 8 weeks, the animals were sacrificed and samples were prepared for optical and TEM analysis of IAN structural damage. Histomorphometric analysis was performed to determine the number and cross-sectional dimensions of nerve fascicles and myelin sheath thickness between experimental and control groups. The different parameters were compared by one-way analysis of variance at the 95% significance level. Results: Alterations in the perineural and endoneural regions of the IAN, with higher degrees of vascularization, were observed in the experimental group. TEM showed that the majority of the myelinated nerve fibers were not affected in the experimental samples. No significant variation in the number of fascicles was observed, significantly larger fascicle height and width were observed in the control group, and significantly thicker myelin sheaths were observed in the experimental samples. Conclusion: IAN lateralization resulted in substantial degrees of tissue disorganization at the microstructural level because of the presence of edema. However, at the ultrastructural level, small amounts of fiber degeneration were observed. Keywords: dental implants, inferior alveolar nerve lateralization, light microscopy, nerve regeneration, titanium, transmission electron microscopy

Purpose: The complicated relationships between mandibular bone components and dental implants have attracted the attention of structural mechanics researchers as well as dental practitioners. Using the finite element method, the present study evaluated various bone and implant parameters for their influence on the distribution of von Mises stresses within the mandible. Materials and Methods: Various parameters were considered, including Young's modulus of cancellous bone, which varies from 1 to 4 GPa, and that of cortical bone, which is between 7 and 20 GPa. Implant length (7, 9, 11, 13, and 15 mm), implant diameter (3.5, 4.0, 4.5, and 5.5 mm), and cortical bone thickness (0.3 to 2.1 mm) were also considered as parameters. Assumptions made in the analysis were: modeling of the complex material and geometric properties of the bone and implant using two-dimensional triangular and quadrilateral plane strain elements, 50% osseointegration between bone and implant, and linear relationships between the stress value and Young's modulus of both cancellous and cortical bone at any specific point. Results: An increase in Young's modulus and a decrease in the cortical bone thickness resulted in elevated stresses within both cancellous and cortical bone. Increases in the implant length led to greater surface contact between the bone and implant, thereby reducing the magnitude of stress. Conclusions: The applied masticatory force was demonstrated to be the most influential, in terms of differences between minimum and maximum stress values, versus all other parameters. Therefore loading should be considered of vital importance when planning implant placement. Keywords: cancellous bone, cortical bone, dental implants, finite element technique, stress distribution characteristics

Purpose: To investigate the interactions of implant diameter, insertion depth, and loading angle on stress/strain fields in a three-dimensional finite element implant/jawbone system and to determine the influence of the loading angle on stress/strain fields while varying the implant diameter and insertion depth. Materials and Methods: Four finite element models were created, which corresponded to two implant diameters and two insertion depths. The jawbone was composed of cortical and cancellous bone and modeled as a linearly elastic medium; the implant had a detailed screw structure and was modeled as an elastic-plastic medium. Static loading was applied to the coronal surface of the implant with a maximum load of 200 N for all the models. Loading directions were varied, with buccolingually applied loading angles ranging from 0 to 85 degrees. Results: Increases in the angle of force application caused not only increased maximum stress/strain values but worsened stress/strain distribution patterns in the bone and implant. The maximum stress in the bone always occurred at the upper edge of the cortical bone on the lingual side adjacent to the implant. The use of a larger-diameter implant or an increased insertion depth significantly reduced the maximum stress/strain values, improved the stress/strain distribution patterns and, in particular, decreased the stress/strain sensitivity to loading angle. Conclusions: A narrow-diameter implant, when inserted into jawbone with a shallow insertion depth and loaded with an oblique loading angle, is most unfavorable for stress distribution in both bone and implant. An optimized design of the neck region of an implant, in combination with a carefully controlled implant insertion depth that sets the threads of the implant neck well below the upper edge of the cortical bone, should be especially effective in improving the biomechanical environment for the maintenance of bone in implant/bone systems. Keywords: biomechanics, dental implant, finite element analysis, jawbone, stress analysis

Purpose: This article reports preliminary results of a single-cohort prospective study that sought to evaluate a new surgical protocol for the immediate rehabilitation of edentulous maxilla without using bone grafting. Materials and Methods: Twenty consecutive patients in need of a full-arch maxillary rehabilitation were included in the study. Each patient received four tilted implants that engaged the posterior and the anterior sinus wall and two axial implants in the anterior maxilla. A total of 120 implants (30 Brånemark System MK IV and 90 NobelSpeedy Groovy) was inserted. Acrylic resin provisional prostheses were delivered within 4 hours of implant placement, and definitive restorations were placed 4 to 6 months later. Follow-up visits were scheduled every 6 months for the first 2 years and yearly thereafter. At each follow-up appointment, plaque and bleeding indexes were scored, periapical radiographs were obtained to assess marginal bone level changes, and patient satisfaction was recorded by means of a questionnaire. Results: The follow-up ranged between 18 and 42 months (average, 27.2 months). No implants failed. All prostheses were stable and functional. No adverse events occurred. At 1 year, mean marginal bone loss around axial and tilted implants was similar: 0.8 mm for axial implants (SD 0.4, n = 30) and 0.9 mm for tilted implants (SD 0.5 mm, n = 60) (P > .05). Plaque and bleeding scores decreased over time, and patient satisfaction with both esthetics and function increased. Conclusions: This technique can be considered a viable treatment modality for the immediate rehabilitation of the edentulous maxilla, as it provides optimal support in the posterior region, minimizes distal cantilevers, and avoids bone grafting or sinus augmentation. Keywords: dental implants, edentulous maxilla, immediate function, immediate loading, tilted implants

Purpose: A high clinical and radiographic level of osseointegration has been reported for early and immediately loaded (IL) implants. The aim of this study was to analyze, histologically and histomorphometrically, the bone-titanium interface of IL and submerged titanium implants that were retrieved at 4 and 8 weeks after placement. Materials and Methods: Four patients underwent rehabilitation of the posterior mandible with fixed prostheses, and an additional implant was inserted distally in the mandible. In two patients, the additional implants were put into nonfunctional immediate loading with a fixed provisional prosthesis on the same day of the implant surgery, whereas in the other two patients, the implants were left submerged. The implant stability quotients at implant insertion were 70 and 67 for the submerged implants and 69 and 77 for the IL implants. Before retrieval, the IL implants were clinically osseointegrated and were not mobile. After 4 and 8 weeks, the four implants (two IL and two submerged) were retrieved with a 5-mm trephine and processed for histologic examination. Results: After 4 weeks, the IL implant showed a bone-implant contact percentage (BIC) of 65.6%, while the BIC for the submerged implant was 54.7%. After 8 weeks, the BIC was 76.2% for the IL implant, while for the submerged implant it was 62.3%. Conclusions: Very high BICs were present after 4 and 8 weeks around both submerged and IL implants, with the latter showing a higher quantity of bone. IL did not impede bone formation in the early healing periods. Keywords: histology, immediate loading, implant surfaces, loading conditions, retrieved dental implants

Purpose: The aim of this investigation was to evaluate whether the placement of medical-grade calcium sulfate hemihydrate (MGCSH) in fresh extraction sockets might affect the quality of newly formed bone and influence crestal bone changes. Materials and Methods: Forty patients who needed maxillary single- tooth extraction followed by implant insertion were enrolled in the study. Alveoli were required to have four remaining intact walls. After tooth extraction, 22 patients received MGCSH in the extraction sockets (test group), and 18 received no grafting material (control group). At the time of extraction and 3 months later (at implant placement surgery), vertical and horizontal socket dimensions were measured. In addition, during implant placement, tissue specimens were harvested for histologic and immunohistochemical evaluations. Comparisons of test and control tissues were performed with the unpaired Student t test. Results: Vertical resorption of the buccal socket walls and reduction of the buccopalatal width were more pronounced at control sites than at MGCSH sites (1.2 mm versus 0.5 mm, and 3.2 mm versus 2.0 mm, respectively). Formation of 100% living trabecular bone with woven and lamellar arrangements was found in both test and control sections. The average trabecular bone area fraction was greater in the grafted specimens than in control specimens (58.8% versus 47.2%). In the test group, the average percentage of lamellar bone increased from 16.4% to 43.6% from the crestal to the apical region and was greater than in unfilled specimens (11.1% coronally, 22.2% apically; P < .0001). Conclusions: MGCSH seems to be effective in accelerating the bone healing process and minimizing alveolar ridge resorption in intact fresh extraction sockets. Keywords: bone healing, calcium sulfate, dental implant, human histology, socket preservation

Purpose: To evaluate the effects of implant geometry and collar macrostructure and microstructure on crestal bone height, mobility values, and attachment levels using two different types of radiographic analysis. Materials and Methods: Subjects included in this study were those who had single-tooth implants restored in the maxillary esthetic zone. Bone levels were measured from the implant-abutment (IA) interface on standardized radiographs at baseline and after 5 years using digital and standard methods. The digital method converted the radiographs into three-dimensional models based on radiodensity so that bone levels could be measured. Clinical attachment levels and Periotest values were recorded and all data were analyzed statistically. Results: The bone position from the IA interface for the rough-collar implant group was a mean of -0.61 ± 0.08 mm and it was -1.55 ± 0.10 mm for the smooth-collar implant group (-1.96 ± 0.16 mm for implants with a stepped collar and -0.85 ± 0.19 mm for implants with a straight collar). The mean bone level change over the 5-year period for the rough implants was -0.19 ± 0.09 mm and it was -0.36 ± 0.06 mm for the smooth implants. The crestal bone position relative to the implant at the time of surgery influenced mean bone level changes significantly. There were statistically significant differences in clinical attachment levels depending on implant location and on implant group and length. Conclusions: Implants with straight collars had less bone loss at the 5-year interval than implants with stepped collars. Bone level changes were greater when the implant was placed further subcrestal. The digitally converted radiographic method was significantly more precise for evaluating changes in bone levels. These findings suggest that implant geometry and implant surface roughness may play a significant role in bone level changes in the esthetic zone. Keywords: bone loss, dental implants, implant geometry, radiographic analysis, single tooth, surface roughness

Purpose: The aim of this clinical study was to assess the marginal bone around two different types of implant-abutment junctions-a so-called platform-switched assembly and a conventional externalhexagon connection-after 24 months. Materials and Methods: Forty-five patients were included in this prospective study. All selected patients required the extraction of one or two hopeless teeth in maxillary and mandibular region monoradicular and second premolar teeth, and were randomly assigned to one of two groups. The first group received 34 implants with an external-hexagon junction with the abutment and the second group received 30 implants with platform-switched abutments. Implants were positioned immediately after tooth extraction and were loaded immediately. Results: After 24 months, a cumulative survival rate of 100% was reported for all implants. The platformswitching group showed a mean bone loss of 0.78 ± 0.49 mm and the external-hexagon group showed a mean bone loss of 0.73 ± 0.52 mm (no statistically significant difference between groups). Conclusion: The results of this study indicate that implants placed immediately in fresh extraction sockets and loaded immediately represent a predictable procedure, with no differences in bone level changes between "platform-switched" and conventional external-hexagon implants after 24 months. Keywords: dental implants, immediate loading, implant-abutment junction, marginal bone loss, platform switching

Purpose: The purpose of this retrospective study was to review and assess the outcomes of subjects treated with dental implants at the University of Washington Graduate Prosthodontic Program from 1988 to 2000. Materials and Methods: A retrospective review and an outcomes assessment were conducted of patients treated with osseointegrated implants between 1988 and 2000 at the University of Washington Graduate Prosthodontic Program. Patients were treated by graduate students. All included patients had a prosthesis that had been in service for at least 5 years. Implants and prostheses were assessed by chart review, phone survey, and clinical review. Clinical review consisted of mobility testing, soft tissue evaluation, and occlusal evaluation. Specific success criteria were used and life table analyses of implants and prostheses were performed. Results: Of a total of 114 patients treated, 69 subjects (60.5% of those treated) participated in the assessment; 103 prostheses supported by 273 implants were reviewed clinically. The estimated cumulative survival rate was 96.3% for all implants and 85.4% for all prostheses. Conclusions: A retrospective review of 69 subjects who were treated in the University of Washington Graduate Prosthodontic Program between the years 1988 and 2000 showed an implant survival rate of 96.3% and a prosthesis survival rate of 85.4%. Prostheses showed higher failure rates than implants. Keywords: cumulative survival rate, dental implants, implant prostheses, osseointegration

Purpose: The aim of this study was to present an alternative treatment concept for the rehabilitation of the atrophic maxilla that used the nasopalatine canal as an anatomic buttress for dental implant insertion and to assess patient satisfaction with this treatment. Materials and Methods: The inclusion criterion for the study consisted of the presence of severe resorption of the edentulous maxilla (Class V according to the Cawood and Howell classification). In each patient, one implant was positioned in the nasopalatine canal. Additional implants were also placed in the remaining maxillary bone. The patients were followed for a minimum of 2 years after prosthesis connection. Satisfaction with the prosthesis was evaluated after 12 months using a visual analog scale. Results: Seven patients with severely resorbed edentulous maxillae received a total of seven implants in the nasopalatine buttress and 29 implants posterior to this structure. One of the seven implants in the nasopalatine canal was lost during the osseointegration phase. All patients had stable prostheses at the end of the observation period. Patients were satisfied with comfort and stability, ability to speak, ease of cleaning, and esthetics and function of the prosthesis. Five patients experienced minor sensory alterations during the first weeks after surgery. At the final examination, which took place after a mean of 5 years (range, 3 to 7 years), all patients expressed the presence of normal sensation. Conclusions: It appears that implants in the nasopalatine canal may be a viable treatment approach for the rehabilitation of the severely atrophied maxilla. Patients were satisfied with a prosthesis supported by implants in the nasopalatine canal. Keywords: anatomic buttress, dental implants, maxillary atrophy, nasopalatine canal

Facial defects can result from trauma, treatment of neoplasms, or congenital malformations, and their restoration is still a challenge for both surgeon and prosthodontists. Craniofacial implants can provide many benefits for prosthetic rehabilitation of facial defects; however, accurate placement of extraoral implants is vital for clinical success. Three-dimensional modeling is a novel technique that not only helps the surgeon to evaluate potential bone sites and adjacent structures, but also facilitates planning of the extraoral implant treatment by the prosthodontist. This technical report describes the use of three-dimensional modeling and planning for craniofacial implant placement. Keywords: computer-guided implant dentistry, craniofacial implants, extraoral implants, facial defect, maxillofacial rehabilitation, software technology, three-dimensional modeling

The efficacy of transantral endoscopy for the removal of a foreign material from the maxillary sinus has been reported previously. Endoscopy has also been used for removal of dental implants after their displacement into the maxillary sinus either during implant placement or subsequently, during implant integration or loading. This case report describes the removal of a dental implant from the maxillary sinus using a modified transantral endoscopic approach combined with simultaneous grafting of the sinus cavity. Keywords: displaced implant, endoscopic implant removal, implant migration, sinus grafting, sinus membrane perforation, transantral endoscopy