The International Journal of Oral & Maxillofacial Implants, 03/2013

Purpose: The purpose of this experiment was to analyze the mechanics of the ceramic abutment-implant joint and the dimensional changes in the abutment screws from cyclic loading. Materials and Methods: Two groups of experimental assemblies were used, one with zirconia abutments and the other with titanium abutments (n = 10). Each specimen consisted of an implant, an abutment, and a metal crown affixed in an acrylic resin base. The specimens were subjected to cyclic loading of 200 N for 1 million cycles at 10 Hz. After loading, a torque-angle signature analysis was done, the dimensions of the screws were measured, and the implant-abutment interfaces were examined with scanning electron microscopy. Results: There was a statistically significant increase in the total length of the screws: 121 µm in the titanium group versus 88 µm in the zirconia group (P .004). Microscopic analysis showed collected debris on the zirconia abutment undersurface and the screws. A statistically similar decrease in torque was observed: 18% for zirconia versus 13.5% for titanium. Radiographic microanalysis revealed that the debris collected in the zirconia assemblies was essentially a collection of titanium, vanadium, and aluminum, with traces of zirconium. Conclusions: While there was a loss of torque in both types of abutments, the stability of the zirconia abutment-implant joint was not affected by the loading. The study provides a better understanding of zirconia abutments, screw designs, and the mechanism holding together the implant-abutment assembly.

Purpose: The aim of the present study was to evaluate bone formation and survival rates for implants after nasal cavity grafting using exclusively anorganic bovine bone (ABB) by means of clinical, radiographic, and histologic/histomorphometric examinations. Materials and Methods: Twelve subjects with edentulous atrophic maxillae were screened for the study; four required bilateral and eight required unilateral nasal cavity grafting. A full-thickness flap was raised to determine the position for the nasal window between the anterior wall of the sinus and the lateral wall of the piriform aperture. A window, 5 to 6 mm wide and 10 to 13 mm high, was created. The window was infractured into the nasal cavity to allow the ABB to be pushed inside and was then covered with a collagen membrane. Cone beam computed tomography (CBCT) was performed before grafting (during screening), after grafting, and 6 months later. Eight months after grafting, from the 16 sites grafted, biopsy cores were taken from three patients using a 2.5-mm trephine and processed to evaluate the percentages of new bone, marrow space, and residual ABB. One screw-form implant was placed in each grafted site and loaded after 3 months. After at least 6 months of loading, the fixed prostheses were removed and all implants placed in grafted areas were tested for mobility. Results: The 6-month CBCTs clearly showed the radiopaque material inside the nasal cavity. The histomorphometric measurements showed 33.34% new bone, 30.30% marrow space, and 36.52% remaining ABB. All implants were osseointegrated and free of pain, infection, and mobility. All implants remained stable at a mean of 13 months after loading (range, 6 to 24 months). Conclusions: The clinical, radiographic, and histomorphometric results showed that nasal cavity grafting with ABB can be an excellent alternative in patients with extensively atrophic maxillae.

Purpose: The purpose of this study was to compare the osseointegration of dental implants placed in canine mandibular bone and in regenerated bone produced by bone transport distraction osteogenesis. Materials and Methods: Ten adult foxhounds were divided into two groups of five animals each. In all animals, a 40-mm defect was created on one side of the mandible. A bone transport reconstruction plate was used to stabilize the mandible and regenerate bone. Six weeks after the distraction period was finished, dental implants were placed in regenerated and native mandibular bone. The animals were sacrificed after another 6 and 12 weeks of healing, respectively. Results: Microcomputed tomographic evaluation showed that bone volume fraction (BV/TV) was greater at the coronal regions of the implants and decreased toward the apical regions. There was an increase in BV/TV around implants placed in regenerated bone from 6 to 12 weeks of healing. The regenerated group showed lower BV/TV at 6 weeks versus implants placed in native bone but had reached the same levels as the native bone at 12 weeks. Histology showed that direct bone-to-implant contact was greater for implants placed in native bone than for those placed in regenerated bone for both time periods. The removal torque of the implants placed in native bone was higher at 6 weeks than that of implants placed in regenerated bone. At 12 weeks, there were no statistically significant differences in removal torque between the groups. Conclusions: Bone was successfully regenerated in all animals. The implants placed entirely in regenerated bone were osseointegrated. The regenerated bone around the implants became denser over time. This finding suggests that implants placed entirely in regenerated bone will be as well integrated as implants in native mandibular bone by 12 weeks after placement.

Purpose: The purpose of this study was to investigate the marginal precision of computer numeric control- milled frameworks fabricated of grade 4 commercially pure titanium or cobalt-chrome alloy through digital technology and to compare them with conventional cast frameworks. Material and Methods: A titanium cast of a mandibular arch with six implant analogs was used as a master. The master cast was measured with a coordinate measuring machine. Fifteen rigid anatomic frameworks were created on the master cast in cast gold alloy and milled in titanium or cobalt-chrome material. The fifteen anatomic frameworks were measured in the same manner as the master cast. While the milled frameworks were measured once, at the end of the milling process, the cast anatomic frameworks were measured twice: immediately after the casting and divesting procedures and again after a technical adaptation procedure. Each anatomic framework was weighed. To compare the measurements obtained from each group of frameworks, descriptive statistics were calculated and one-way analysis of variance was performed, with values considered statistically significant at P .05. Results: The mean weight of the cast frameworks was 33.41 g, the cobalt-chrome frameworks weighed 18.12 g on average, and the titanium frameworks averaged 8.7 g. The mean values for three-dimensional deviation of the center point position for each group of frameworks were 261 µm (cast frameworks before adaptation), 49 µm (cast frameworks after adaptation), 26 µm (milled frameworks in cobalt-chrome), and 26 µm (milled frameworks in titanium). Conclusions: Within the limitations of this in vitro study, absolute passive fit cannot be achieved, regardless of material and fabrication technique. Anatomic milled frameworks fabricated in titanium or cobalt-chrome presented reduced center point deviation compared to cast frameworks. Titanium frameworks weighed less than cobalt-chrome and cast gold alloy frameworks.

Purpose: The present study was conducted to determine whether biomechanical and histologic parameters would differ between implant surfaces blasted with bioactive ceramic resorbable media (biologic blasting) and blasted with alumina and acid-etched. Materials and Methods: Fourteen beagle dogs were used. Eight animals received two implants of each surface per limb, and each limb provided samples that remained in vivo for 3 and 6 weeks. The other six animals received two implants of each surface in one limb, which remained in vivo for 1 week. After euthanization, half of the implants were subjected to torque-to-interface fracture; the other half of the implants were processed for nondecalcified histology to calculate bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). Statistical analysis was performed with the Kruskal-Wallis test (95% level of significance). Results: While no significant differences were observed for BIC and BAFO between surfaces at all three times in vivo and for torque levels at 1 and 3 weeks, a significantly higher torque was observed for the biologic blasting group after 6 weeks in vivo. Bone morphology was similar between groups at all times. Conclusion: A significant increase in early biomechanical fixation was observed for implants with the biologic blasting surface. However, no significant differences were observed for BIC and BAFO at any observation point.

Purpose: Soft and hard tissue responses to experimental peri-implantitis around thin sputter hydroxyapatite (HA)-coated implants were evaluated and compared to the responses to implants with other surface treatments. Materials and Methods: Forty-eight dental implants with four different surfaces-machined (M), sandblasted/acid-etched (SA), 1-µm thin sputter HA-coated (S), and plasma-sprayed HA-coated (P)-were inserted into the mandibles of six beagle dogs. Three months later, experimental peri-implantitis was induced with ligatures to allow plaque accumulation. After a 4-month period of active breakdown, the ligatures were removed, and plaque accumulation continued for 5 additional months (progression period). Radiographic marginal bone levels, probing depths, clinical attachment levels, and modified Gingival Index were evaluated at baseline, after the active breakdown period, and after the progression period. Results: Significant increases in mean probing depths and clinical attachment levels were seen around all implants after active breakdown, but no significant differences were found during the progression period. Radiographic analysis revealed marginal bone loss of 1 to 1.7 mm during the active breakdown period. Additional bone loss occurred during the progression period (M 0.2 mm, SA 0.3 mm, S 0.2 mm, P 0.4 mm). Conclusion: Comparable tissue behavior was demonstrated around dental implants with all four surfaces under peri-implantitis conditions. Thin sputter HA-coated implants possess the favorable osteoconductive properties of calcium phosphate coatings without exacerbating further peri-implant tissue breakdown during the progression of peri-implantitis.

Purpose: While the ability of various grafting materials to preserve extraction socket morphology has been adequately reviewed, the quality of the grafted bone in the socket is not as well understood. This systematic review aimed to compare the proportion of vital bone and connective tissue between grafted and naturally healed sockets. Materials and Methods: An electronic search of five databases (from 1965 to November 2011) and a hand search of peer-reviewed journals for relevant articles were performed. Human clinical trials that compared histologic components of soft and hard tissues in augmented sockets and naturally healed sites, with at least five samples per group, were included. Results: Eight studies (five randomized controlled trials and three controlled clinical trials) were included. The mean percentages of vital bone and connective tissue in natural healing sockets were 38.5% ± 13.4% and 58.3% ± 10.6%, respectively. Limited evidence (one to two articles for each material) implied that vital bone fraction was not different with demineralized allografts and autografts and increased by 6.2% to 23.5% with alloplasts in comparison to nongrafted sites. Four studies investigating the effect of xenografts were available, with equivocal results. The difference in the mean percentage of vital bone ranged from -22.2% (decrease) to 9.8% (increase). Connective tissue content decreased with the use of the aforementioned bone substitutes. Considerable residual hydroxyapatite and xenograft particles (15% to 36%) remained at a mean of 5.6 months after socket augmentation procedures. Conclusions: Based on a limited number of prospective comparative studies, the use of grafting materials for socket augmentation might change the proportion of vital bone in comparison to sockets allowed to heal without grafting. Whether these changes in bone quality will influence implant success and peri-implant tissue stability remains unknown.

Purpose: The aim of this study was to assess bone ingrowth into porous titanium granules used for maxillary sinus augmentation. Materials and Methods: Eighteen biopsy specimens from 17 patients participating in a clinical trial on sinus augmentation using porous titanium granules (PTG) were received in the laboratory. The specimens (trephine cores of 4.5 mm) were obtained 6 months after PTG placement. After being embedded in methacrylate, the samples were scanned in a microcomputed tomography (micro-CT) scanner. Specimens were then cut along the long axis and central slices were ground to 70 µm before staining with hematoxylin and eosin. Results: The micro-CT analysis demonstrated an average bone fill of 19% (standard deviation [SD] 5.8%), whereas the graft material occupied 22.7% (SD 4.7%). The volume of newly formed bone decreased with the distance from the residual bone of the sinus floor. Two-dimensional histomorphometric analysis demonstrated a mean area of new bone of 16.1% (SD 9.4%). The PTG alone occupied 25.9% of the total mean area (SD 6.1%). The newly formed bone consisted mainly of woven bone growing in close contact with the granules and bridging the intergranular space. The remaining area was occupied predominantly by nonmineralized connective tissue. There were no signs of inflammation in any of the biopsy specimens. Conclusions: After 6 months, new bone had formed at a similar rate and quality as has been reported for other well-recognized bone graft substitutes. The new bone formed in close contact with the PTG, suggesting that the material is osteoconductive.

Purpose: The crestal bone level around a dental implant may influence its strength characteristics by offering protection against mechanical failures. Therefore, the present study investigated the effect of simulated bone loss on modes, loads, and cycles to failure in an in vitro model. Materials and Methods: Different amounts of bone loss were simulated: 0, 1.5, 3.0, and 4.5 mm from the implant head. Forty narrow-diameter (3.0-mm) implant-abutment assemblies were tested using compressive bending and cyclic fatigue testing. Weibull and accelerated life testing analysis were used to assess reliability and functional life. Statistical analyses were performed using the Fisher-Exact test and the Spearman ranked correlation. Results: Compressive bending tests showed that the level of bone loss influenced the load-bearing capacity of implant-abutment assemblies. Fatigue testing showed that the modes, loads, and cycles to failure had a statistically significant relationship with the level of bone loss. All 16 samples with bone loss of 3.0 mm or more experienced horizontal implant body fractures. In contrast, 14 of 16 samples with 0 and 1.5 mm of bone loss showed abutment and screw fractures. Weibull and accelerated life testing analysis indicated a two-group distribution: the 0- and 1.5-mm bone loss samples had better functional life and reliability than the 3.0- and 4.5-mm samples. Conclusion: Progressive bone loss had a significant effect on modes, loads, and cycles to failure. In addition, bone loss influenced the functional life and reliability of the implant-abutment assemblies. Maintaining crestal bone levels is important in ensuring biomechanical sustainability and predictable long-term function of dental implant assemblies.

Purpose: Hyperbaric oxygen (HBO) has been recommended to enhance implant osseointegration in irradiated bone. The aim of this study was to further investigate the effects of HBO on implant integration in irradiated bone tissue. Materials and Methods: The present study was an experimental intraindividual study in 16 rats. A single fraction of 20 Gy external irradiation was applied to one rat hind leg, while the other served as a nonirradiated control. Three days after radiation, two implants were inserted in each tibial tuberosity. The rats were divided into two groups: non-HBO treated (group 1) and HBO treated (group 2). Five weeks after radiation, removal torque tests were performed. Implants with surrounding tissue were processed to undecalcified cut and ground sections for histomorphometric evaluations of bone-to-implant contact and bone area. Retrieved bones were also investigated with dual-energy x-ray absorptiometry. Results: The non-HBO treated rats (group 1) demonstrated higher, but not statistically significantly higher, values in the nonirradiated leg for all investigated parameters compared to the HBO-treated rats (group 2). However, the mean value for bone area was significantly higher in the irradiated sides compared to the nonirradiated control sides. Conclusions: In the present study, HBO treatment did not have a significant impact on osseointegration of implants in irradiated bone.

Purpose: To evaluate the osteogenic activity of a novel synthetic peptide, PEP7, derived from bone morphogenetic protein 2 (BMP-2) on MG-63, a human osteoblast-like cell line, and on new bone formation in vivo. Materials and Methods: The novel synthetic peptide was synthesized by a standard Fmoc method and purified to 98% purity. Cell adhesion, proliferation, and differentiation of MG-63 were observed in the presence of different concentrations of PEP7. Eight micropigs were used to evaluate new bone formation in a supra-alveolar peri-implant defect model. The PEP7-coated implants were randomly allocated to mandible defect sites. The animals were sacrificed after 8 weeks for histologic analysis. Results: PEP7 affected an early stage of adhesion and dose-dependently stimulated differentiation of MG-63 cells. The cell adhesion rate in the group coated with 1 µM PEP7 increased approximately 47% compared to the uncoated group and 32% compared to the group coated with recombinant human bone morphogenetic protein 2 (rhBMP-2) (P .05). The alkaline phosphatase activities of groups treated with 50 µM of PEP7 were higher than for the other groups. PEP7 induced production of osteoblast-specific proteins in MG-63 cells. The largest effect was caused by 50 µM PEP7, followed by the groups treated with 20 µM synthetic peptide and 10 ng/mL rhBMP-2 (P .05). Conclusions: A novel synthetic peptide derived from BMP-2 has osteoinductivity and new bone formation effects, including vertical augmentation of the alveolar ridge.

Purpose: To evaluate the alterations of the buccolingual width of the alveolar ridge after immediate implant placement using a fully synthetic biphasic calcium phosphate (BCP) consisting of a mixture of 60% hydroxyapatite and 40% ß-tricalcium phosphate in esthetic regions. Materials and Methods: The buccolingual widths of the alveolar ridge in 20 extraction sites in 20 patients were assessed using computed tomography. Measurements were performed before and 6 months after extractions and immediate implant placement. In group 1 (11 patients), BCP was in the space between the buccal wall of the alveolar ridge and implant. In group 2 (9 patients), the same evaluations and procedures were performed but without using BCP. Results: The buccolingual dimensions of the alveolar ridge in group 1 (BCP) showed no significant preoperative differences (8.49 ± 1.1 mm) during the 6-month period after surgery (8.82 ± 0.9 mm) (P = .14). In group 2, the differences in buccolingual dimensions of the alveolar ridge were statistically significant (P = .01) with reduction in dimensions from 8.12 ± 0.7 mm during the preoperative period to 7.01 ± 0.4 mm 6-months after surgery. Conclusion: The use of BCP was effective in preserving buccolingual dimensions of alveolar ridges in immediate implant surgeries.

Purpose: To compare bone augmentation on pure titanium-machined surfaces and surfaces that have been modified by microarc oxidation (MAO) using titanium caps. Materials and Methods: Twenty caps were manufactured from rods of commercially pure titanium. The control group (CG) consisted of 10 titanium caps with machined inner walls. The test group (TG) consisted of 10 titanium caps that were modified by MAO in an electrolyte solution containing calcium phosphate ions. The two types of titanium caps were fixed on the calvaria of 10 New Zealand rabbits. Each rabbit received two different caps. Although each cap was unfilled, the marrow and blood from the wound of the rabbit skulls could penetrate into the caps. After 4 weeks, the rabbits were sacrificed, and the skulls were removed for observation. The zenith of new bone was measured directly after the caps were removed from the skulls; subsequently, the bone volume was calculated by microcomputed tomography. Results: Little bone augmentation could be observed in the CG caps, and the new bone height of the CG group was inconspicuous. In contrast, the new bone extended along the inner walls of the TG caps. The mean height of new bone of the TG group was 2.3 ± 0.28 mm. The mean volume of new bone in the TG group was 18.63 ± 3.80 mm3. Conclusions: New bone formation in a titanium cap surface modified by MAO was greater than that of a nonmodified cap. A titanium cap allowed new bone formation on the MAO surface to be observed and is a promising device for bone augmentation. Additionally, this finding suggests that observation through a titanium cap is a feasible method for biomaterial testing in hard tissue.

Purpose: To compare the osseointegration of a laser-etched (LE) implant with a magnesium-incorporated oxidized (MgO) implant, evaluating their ability to enhance the bond strength between a titanium substrate and rabbit femur. Materials and Methods: Two type of dental implants, LE (test, commercially pure [CP] titanium grade 4) and MgO (control, CP titanium grade 4) (length, 8 mm; diameter, 3.3 mm), were evaluated for the surface characteristics using a field emission scanning electron microscope (FE-SEM), an energy dispersive spectrometer (EDS), and an optical three-dimensional profiling system. After that, two types of dental implants were implanted at the right and left distal femoral metaphysis of 10 adult rabbits weighing approximately 3.0 kg. After 6 weeks, histomorphometric analysis, removal torque tests, and surface analysis of the torque-tested implants were performed. Results: After surgery, the LE group showed thick bonelike materials within the pores observed using FE-SEM (magnifications ×500 and ×900). The mean removal torque was 40.72 ± 13.3 Ncm for the test (LE) implant and 22.26 ± 6.4 Ncm for the control (MgO) implant, respectively (P = .041). The mean bone-implant contact in the three best consecutive threads in the cortical region was 63.35% ± 16.44% in the LE group and 51.63% ± 5.09% in the MgO. Conclusions: In the beginning stage of cancellous bone healing, biomechanical properties of the LE implant could influence a more favorable bone response than that of MgO.

Purpose: This 15-year prospective study evaluated the success rate and preservation of the gingival margin of single implants placed in a flapless procedure loaded immediately after extraction or after a healing period. Materials and Methods: Immediate flapless implant placement was performed in patients who fulfilled specified inclusion criteria. Implants were either immediately restored with a provisional crown or left unloaded (received healing abutment only). Impant success and gingival margin levels were evaluated after implant placement and after 1 to 15 years. Results: A total of 305 healthy nonsmoking subjects (90 men, 215 women) were treated with 430 immediate implants during a 15-year period (December 1994 to December 2009) and monitored for 1 to 15 years. Two hundred seventy-five implants received an immediate provisional crown, and 155 received a healing abutment. The implant survival rate was 93.03% (± 3.74%). The immediate provisional helped to maintain the original gingival margin, although the implant survival rate was higher for implants that were not immediately restored (96.78%) than for the implants that were immediately restored with a provisional (90.9%). Conclusions: This 15-year prospective study showed a favorable implant success rate related to the flapless immediate implant placement protocol with healing abutment placement or an immediate provisional crown to replace a single missing tooth.

Purpose: The aim of this study was to evaluate the effectiveness of a calcium phosphate (CaPO4)-coated and anodized titanium surface in vitro and in vivo. Materials and Methods: A turned surface was employed as a negative control. A sandblasted/acid-etched surface and an anodized surface were used as positive controls, and a CaPO4-coated and anodized (CPA) surface was investigated as the experimental group. Surface characteristics were analyzed with field emission scanning electron microscopy, energy dispersive spectroscopy, and confocal laser scanning microscopy. In vitro osteoblastic differentiation was evaluated by alkaline phosphatase assay. In vivo bone response was analyzed using bone-to-implant contact (BIC) ratios and bone area (BA) of 2- and 4-week specimens obtained from six rabbits. Results: The means and standard deviations for average height deviation (Sa) and developed surface area ratio (Sdr) were 0.32 ± 0.03 µm and 3.6% ± 1.5% for the turned group, 1.36 ± 0.11 µm and 56.7% ± 16.1% for the sandblasted/acid-etched group, 0.68 ± 0.02 µm and 50.9% ± 2.9% for the anodized group, and 0.67 ± 0.11 µm and 50.0% ± 16.9% for the CPA group. There were no significant differences in alkaline phosphatase activity among the groups at 7 and 14 days. In the in vivo experiment, the CPA group exhibited a significantly higher BIC ratio than the turned group, and the anodized and CPA groups showed significantly higher BA values than the others after 2 weeks. At 4 weeks, there was no significance in either BIC ratios or BA values among the groups. Conclusion: A CaPO4 coating on an anodized surface may induce rapid osseointegration at the bone-implant interface and more bone formation near the implant surface.

Purpose: The aim of this retrospective study was to evaluate the predictors of peri-implant bone loss in a sample of patients treated with 10-mm implants and single crowns who underwent periodontal/periimplant maintenance (PM) in a Mexican private periodontal practice. Materials and Methods: Outcomes of a group of systemically healthy, partially edentulous patients attended up to July 2012 were assessed. Patient data were considered for inclusion if they involved treatment of partially edentulous sites with 10-mm-long implants and single crown restorations, as well as at least 3 years of regular PM following implant placement. Peri-implant bone loss was evaluated from data recorded at the most recent examination. Logistic regression analysis was performed to investigate associations between peri-implant bone loss and sex, duration of PM, location and number of implants placed per patient, region of the mouth, smoking status, type of implant, and retention of restoration. Results: A sample of 104 subjects who had been treated with four different types of dental implants and maintained for at least 3 years was selected. Of the 148 implants placed and followed for an average period of continuing PM of 6 years (range, 3 to 15 years), only one implant (1.8%) was lost. The outcomes of logistic regression analysis showed that the independent variables smoking, retention of restoration (cemented vs screw-retained), and type of implant (internal- or external-hex) were found to be correlated with peri-implant bone loss, with odds ratios of 39.64, 4.85, and 0.04, respectively. Conclusions: Peri-implant bone loss was significantly associated with smoking status, the type of implant (ie, externally hexed), and type of retention (ie, cemented). Overall, all patients maintained low rates of bone loss.

Purpose: Internal conical implant-abutment connections without platforms may lead to axial displacement of crowns during screw tightening. This displacement may affect proximal contacts, incisal edge position, or occlusion. This study aimed to measure the displacement of screw-retained single crowns into an implant in three dimensions during screw tightening by hand or via torque driver. Material and Methods: A stereolithic acrylic resin cast was created using computed tomography data from a patient missing the maxillary right central incisor. A 4.0- × 11-mm implant was placed in the edentulous site. Five porcelain-fused-to-metal single crowns were made using "cast-to" abutments. Crowns were tried on the stereolithic model, representing the patient, and hand tightened. The spatial relationship of crowns to the model after hand tightening was determined using three-dimensional digital image correlation (3D DIC), an optical measurement technique. The crowns were then tightened using a torque driver to 20 Ncm and the relative crown positions were again recorded. Testing was repeated three times for each crown, and displacement of the crowns was compared between the hand-tightened and torqued states. Commercial image correlation software was used to analyze the data. Mean vertical and horizontal crown displacement values were calculated after torqueing. The interproximal contacts were evaluated before and after torquing using an 8-µm aluminum foil shim. Results: There were vertical and horizontal differences in crown positions between hand tightening and torqueing. Although these were small in magnitude, detectable displacements occurred in both apical and facial directions. After hand tightening, the 8-µm shim could be dragged without tearing. However, after torque tightening, the interproximal contacts were too tight and the 8-µm shim could not be dragged without tearing. Conclusion: Differences between hand tightening and torque tightening should be taken into consideration during laboratory and clinical adjustments to prevent esthetic and functional complications.

Purpose: It has been reported that multiple abutment disconnections and reconnections following implant placement may compromise the peri-implant mucosal seal and may lead to increased marginal bone loss. Thus, the aim of this study was to evaluate the effect of healing abutment disconnection and reconnection on soft and hard peri-implant tissues. Materials and Methods: Sixteen patients were included in this prospective randomized controlled clinical trial. Following one-stage implant placement, test group implants (n = 10) received a permanent abutment and control group implants (n = 11) received a healing abutment. After 2 months of healing, control group implants underwent a prosthetic protocol involving implant-level impressions and a two-time abutment disconnection and reconnection process prior to delivery of the definitive prosthesis. Test group implants underwent a prosthetic protocol involving abutment-level impressions without any abutment disconnection. Clinical parameters were recorded at 2 weeks, 2 months, 3 months, and 6 months, and marginal bone levels were assessed radiographically at implant placement, 3 months, and 6 months. Results: The overall survival rate from implant placement to the last follow-up visit was 100% for both groups. The mean marginal bone loss at the 6-month examination was 0.13 mm for test group implants and 0.28 mm for control group implants. There were no significant differences regarding changes in periimplant mucosal dimensions between the two groups. Conclusion: The present study indicates that implants receiving a final abutment at the time of implant placement exhibited minimal marginal bone loss and were similar to implants subjected to abutment disconnection and reconnection two times. Disconnection and reconnection of the abutment two times did not cause negative dimensional changes in the peri-implant mucosa.

Purpose: The aim of this prospective clinical trial was to compare the three-dimensional marginal bone level, implant stability, and peri-implant health of two types of submerged dental implants that were restored with matching or platform-switched abutments. Materials and Methods: Twenty-five subjects were recruited (test group: 43 implants with internal conical connection and back-tapered collar carrying a platformswitched abutment; control group: 50 implants carrying a matched-platform abutment). Implant uncovering and conventional loading were performed after 3 months of healing, and the total observation time was 15 months. Marginal bone levels, resonance frequency analysis, insertion torque, and peri-implant health indices were recorded and analyzed statistically. Results: The cumulative implant survival rate was 100%. At the second-stage surgery, bone levels were similar between groups. One year after loading, mean crestal bone loss was 0.35 ± 0.13 mm for test implants and 0.83 ± 0.16 mm for control implants, a significant difference. Primary stability was significantly higher in the test group than in the control group, but this difference disappeared after 3 months of healing prior to loading. Between-group differences for periimplant health indices were negligible. Conclusions: Both implant systems had the same survival rates. Implants with a built-in platform switch and conical connection with back-tapered collar design achieved higher primary stability at insertion and less bone resorption after 15 months.

Purpose: To compare the biologic and prosthetic outcomes of implants loaded early to retain mandibular overdentures by means of two different attachment systems. Materials and Methods: Patients were screened according to specific inclusion/exclusion criteria and randomly allocated to treatment groups involving two-implant-supported early loaded mandibular overdentures retained by ball attachments or Locator attachments. Marginal bone loss, Plaque Index, peri-implant infection, Bleeding Index, prosthetic complications, and Kaplan-Meier survival estimates of the groups were assessed at the 5-year recall. Results: Among the 29 patients (58 implants) who completed the study, one implant was lost during healing; all implants survived after prosthesis delivery. Bone loss in the ball attachment group (0.77 ± 0.05 mm) was significantly greater than that in the Locator group (0.59 ± 0.03 mm). The Plaque and Bleeding indices of both groups were comparable, and peri-implant inflammation scores in both groups were zero for all implants. The frequencies of activation of the matrix, replacement of the matrix, and denture reline in the ball attachment group were significantly higher than those observed in the Locator group. While assessments for the absence of any complication showed that the 1- and 3-year Kaplan-Meier survival probabilities of both groups were comparable, when activation of the retainer was excluded, survival probabilities of the ball attachment group were higher. Conclusions: The biologic outcomes of early loaded mandibular overdentures retained by ball attachments or Locators were comparable. Although the frequency of prosthetic complications with ball attachments was higher, this did not decrease the survival probability for the treatment.

Purpose: This retrospective study evaluated implant and prosthodontic survival/success rates of four-implant- supported distal cantilevered mandibular fixed prostheses over more than 5 years of clinical use. Materials and Methods: Patients with mandibular edentulism treated with four-implant mandibular prostheses with distal extensions were evaluated. Cumulative implant survival/success rates, peri-implant conditions, and prosthodontic maintenance efforts were assessed. Relationships between the degree of distal implant tilting, length of cantilevers, and implant-generated supporting zone were evaluated. Results: Thirty-eight patients with 152 implants (90.5% of the original sample) were available for follow-up after 5 to 7 years (mean follow-up, 66.5 ± 3.1 months). The cumulative survival and success rates for included implants were 100% and 98.6%, respectively. Denture cantilever length (mean, 14.7 ± 2.3 mm; range, 9 to 20 mm) and implant-generated supporting zone (mean, 318.9 ± 48.1 mm2; range, 225 to 410 mm2) showed significant positive and negative correlations, respectively, with the inclination of tilted distal implants toward the occlusal plane (76 ± 7.2 degrees; range, 65 to 90 degrees). Peri-implant marginal bone resorption (1.5 ± 0.4 mm) and pocket depths (1.8 ± 0.8 mm) were similar for anterior and posterior implants and were not influenced by degree of tilting or cantilever length. Plaque and calculus conditions were poorer for anterior implants than for posterior implants. No dentures fractured; however, fractures of resin tooth veneer material, denture rebasing, and a strong need for cleaning as a result of resin discoloration were seen. Conclusion: Fixed four-implant rehabilitations with distal cantilevers of a defined length with or without distally tilted implants showed high success rates. Inferior hygiene in the anterior mandible regions may be a result of reduced cleansability and variations in anatomical landmarks. Resin veneering proved advantageous for repair or modification but disadvantageous for discoloration.

Purpose: Few studies have compared the effects of immediate loading on implant prognoses in smokers and nonsmokers. The aim of this prospective study was to evaluate the long-term success of immediately loaded platform-switched implants placed in smokers and nonsmokers with edentulous jaws. Materials and Methods: Platform-switched implants were placed using the same treatment protocol in the healed edentulous jaws of two groups of patients: group A patients had smoked at least 20 cigarettes a day for more than 10 years, and group B consisted of nonsmokers. All implants were loaded immediately with provisional fixed prostheses, and definitive cement-retained restorations were delivered 4 to 6 weeks later without removing the abutments. In a standardized follow-up protocol, the implants were evaluated clinically and radiographically at the start of loading, 4 to 6 weeks later, and annually thereafter. Results: Sixty-six implants (36 in the maxilla and 30 in the mandible) were placed in eight smokers. Twelve nonsmokers received 97 implants (55 in the maxilla and 42 in the mandible). During an average loading period of 62.53 (± 44.13) months for the smokers and 98.20 (± 19.53) months for the nonsmokers, three implants failed. Two failed in group A (one because of overloading and one because of peri-implanitis) and one failed in group B (overloading), resulting in implant survival rates of 97% and 99%, respectively. No significant differences were found between groups regarding plaque, bleeding, probing pocket depths, or crestal bone loss, either mesially or distally, resulting in success rates of 92.42% for group A and 98.00% for group B. Conclusions: Long-term clinical outcomes for immediately loaded platform-shifted implants placed in heavy smokers appear to be comparable to those for nonsmokers if the abutments are placed on the day of surgery and never removed.

Purpose: To retrospectively evaluate the 1-year outcome of implant therapy involving localized lateral alveolar ridge augmentation with block bone grafts, and to compare outcomes of implants inserted simultaneously with grafting or after a healing period. Materials and Methods: Consecutively treated patients undergoing alveolar ridge augmentation with autogenous intraoral block grafts before or simultaneous with implant placement between 2005 and 2010 in the Oral Surgery Unit of the University of Valencia were included. The selection of procedure (simultaneous vs delayed implant placement, donor site) was based upon the criterion of the surgeon and thorough evaluation of each patient. All grafts were obtained with piezosurgery. Complications related to augmentation, implant survival, implant success, and peri-implant marginal bone loss were assessed. Results: Forty-two patients were included; 45 sites were augmented and 71 implants were inserted (33 delayed and 38 simultaneously). Complications (temporary paresthesia, wound dehiscence with bone graft exposure, and exposure of osteosynthesis screw) occurred after bone harvesting in nine patients; four were in the simultaneous group and five were in the delayed group. Six grafts were not successful; four were lost and two provided insufficient bone (after resorption) for ideal implant placement. The implant survival rate was 98.5% (100% for simultaneous and 96.9% for delayed implants) and the implant success rate was 92.9% (89.5% for simultaneous and 96.9% for delayed implants). Average marginal bone loss 1 year after loading was significantly higher for simultaneously placed implants (0.69 ± 0.67 mm) than for delayed implants (0.20 ± 0.50 mm). Conclusions: In lateral bone atrophy, block bone grafts provided sufficient bone for implant therapy, with few complications. Both simultaneous and delayed implant placement yielded high implant survival and success rates. Average marginal bone loss was significantly higher around simultaneously inserted implants.

Purpose: The aims of this study were (1) to evaluate long-term changes in bone height beneath mandibular screw-retained implant-supported prostheses with distal cantilevers and (2) to determine whether the reversal of residual ridge resorption in the posterior mandible is temporary or continues over the long term. Materials and Methods: Panoramic radiographs, obtained at surgery and at two follow-up visits, of 81 patients rehabilitated with mandibular screw-retained implant-supported prostheses with distal cantilevers supported by four, five, or six implants were followed for 5 to 19 years (overall mean follow-up, 9.00 years. Changes and trends in bone height adjacent to the most distal implant were evaluated between each followup visit as well as from time of surgery (baseline) to the final visit using two-way analysis of variance, a twosample t test, and piecewise linear regression. Results: Average bone height distal to the distalmost implant at placement was 10.34 ± 6.87 mm. From baseline to the first follow-up exam, a mean bone gain of 0.68 mm was noticed, and a mean gain of 0.26 mm was observed from baseline to the second follow-up exam. A statistically significant bone gain (0.92 mm) was noticed in women (n = 49) between the first and second exams, compared to 0.33 mm in men (n = 32). Individuals experienced both bone gain and loss during the study, with an overall gain. Patients with lower initial bone height experienced greater growth, but this was not statistically significant. Conclusion: Bone growth is associated with mandibular screw-retained implantsupported prostheses with distal cantilevers, and both bone loss and bone growth may occur in the same patient over time. Within the diverse population of this study, women experienced 2.5 times more gain in bone height than men. No correlation could be established between initial bone height and overall bone height changes.

Purpose: To report the complications encountered during 100 consecutive maxillary sinus augmentations via the lateral window approach and to propose solutions to manage these complications. Materials and Methods: Pretreatment residual bone heights and the presence of septa were recorded. The incidences of any intraoperative or postoperative sinus complications such as excessive bleeding, membrane perforation, infection, wound dehiscence, sinusitis, loss of bone graft, and implant success were reported. Results: This study evaluated 42 men and 44 women requiring 100 consecutive sinus elevation procedures between March 2008 and February 2011. Five intraoperative membrane perforations were noted, and one subsequently developed an active infection (2 weeks after surgery). Eight instances of suppuration were noted, while 10 sites presented with wound dehiscence 1 to 2 weeks after surgery. One example of partial loss of the bone graft 6 months after surgery was identified. Of a total of 151 implants placed in 97 sinuses (one patient with bilateral sinuses and one with unilateral sinus did not complete implant placement), 2 implants presented excessive bone loss prior to uncovering. One implant was removed and one was left submerged. Conclusions: Sinus floor elevation utilizing the lateral window approach is a predictable approach to manage bone volume deficiency in the posterior maxilla for patients seeking dental implant-based treatment. However, complications may include membrane tear, infection, wound dehiscence, loss of graft, and implant failure. It is vital for the clinician to understand how to recognize and solve these complications.

Purpose: To report the application of an electrical mallet (magnetic mallet) in osteotome-assisted surgery for sinus floor elevation with implants placed in fresh sockets and 2-year follow-up. Materials and Methods: A total of 32 patients (70 implants, 36 in the molar and 34 in the premolar regions) requiring extractions of maxillary premolars and molars were included in this prospective study. In all cases, implants were positioned immediately after tooth extraction. The implant site was prepared with osteotomes pushed by a magnetic mallet. Intraoral digital radiographic measurements were reported at 70 days and 1 and 2 years. Initial alveolar bone height and mean gained alveolar bone height were calculated for each implant over time. All implants were followed for 2 years. Results: One of 70 implants failed 1 month after surgery. This implant was successfully replaced 6 months later. The cumulative survival rate at 2 years was 98.57%. After surgery, no membrane perforation was reported, and no patient experienced vertigo, distress, nausea, and vomiting. Radiographic results were reported at 70 days and 1 and 2 years from implant placement. The alveolar bone gain following 70 days of healing resulted in a mean value of 2.63 ± 1.01 mm and, at 2 years from implant placement, was stable at 4.08 ± 1.25 mm. Statistically significant differences (P .05) between values at 70 days and 1 year were reported, whereas there were no statistically significant differences (P > .05) between 1 and 2 years. Conclusions: The electrical mallet represents a fast and accurate instrument for placing bone expanders in fresh socket implants and simultaneous sinus floor elevation to avoid patient distress.

Purpose: To assess the long-term behavior of wedge-shaped implants and evaluate the influence of the associated risk factors on implant survival rates. Materials and Methods: A retrospective review of clinical records of patients treated with wedge-shaped implants between 1992 and 2011 was conducted. Data on patient sex, age, smoking habits, and history of periodontitis; details of implant length, diameter, angle, and location; and data on surgical, reconstructive, and prosthetic procedures, and systemic disease were selected for analysis. Results: A total of 1,169 implants placed in 154 patients (mean age 55.17 ± 11.33 years) were evaluated. Women received 637 implants, and men received 532 implants; 60.4% were placed in patients who were undergoing periodontal maintenance care, 17.9% in smokers, 17.7% in hypertensive patients, 5.7% in diabetic patients, and 4.4% in cardiac patients. The mean overall survival for implants was 194.26 ± 9.91 months. Seventy-three implants were lost: 3 before implant loading and 70 after loading. The cumulative survival rates at 5 and 10 years were 96.6% (confidence interval [CI]: 95.5% to 97.7%) and 91.8% (CI: 90.1% to 94.1%), respectively. Univariate analysis indicated tobacco smoking (P = .014) and implant location (P .001) as significant risk factors for implant failure. The multivariate analysis showed tobacco smoking (P = .016), location (P = .001), and male sex (P = .038) as significant, and the latter factor was associated with previous periodontal disease. Conclusions: Overall survival of the wedge-shaped implant showed good long-term results. Male sex, tobacco smoking, and posterior maxillary location were associated with a greater risk of implant failure.

Purpose: To analyze the clinical, microbiologic, and host response characteristics (interleukins 1ß and 6) in the peri-implant sulcus fluid (PISF) of patients with healthy dental implants and with peri-implant mucositis. Materials and Methods: Clinical parameters (modified Gingival Index [mGI], modified Plaque Index [mPI], probing pocket depth [PPD], and absence or presence of radiologic bone loss) were recorded, and PISF samples were obtained from peri-implant sites showing mucositis as well as healthy sites. The periodontopathogenic bacteria Tannerella forsythia (Tf), Treponema denticola (Td), and Porphyromonas gingivalis (Pg) were evaluated, together with the total bacterial load (TBL) and the interleukin (IL) 1ß and IL-6 values. Results: The study population consisted of 34 individuals, and 77 dental implants were evaluated during the study (23 mucositis and 54 healthy peri-implant sites). The mGI, mPI, and PPD scores of the peri-implant mucositis group were significantly greater than in the healthy group. No differences in detection frequency were found for putative periodontal pathogens and TBL between the healthy peri-implant sites and mucositis sites. The mucositis group showed a significantly greater expression of IL-6 than the healthy group (P .05). Although IL-1ß was increased in the mucositis group, there was no statistically significant difference versus the healthy implant group. Conclusions: An analysis was made of the clinical, microbiologic, and host response characteristics in implants with peri-implant mucositis, establishing comparisons with healthy implants. In the patients studied, bacterial plaque induced an inflammatory response that can lead to the development of peri-implant mucositis. Adequate plaque control is therefore able to increase peri-implant health, avoiding the risk of future complications. No specific association to the studied bacterial species was established.

Purpose: To present clinical results with 9 years of follow-up of a protocol of immediately loaded implants with two different surfaces. Materials and Methods: A total of 44 patients received 66 Brånemark System TiUnite and 55 Brånemark machined implants, all immediately loaded. Control examinations were performed on the day of surgery and at 1-, 3-, and 9-year follow-up visits. Results: All implant sites had intact buccal and lingual bone walls. The prefabricated provisional restorations showed an excellent fit. Three TiUnite and 8 machined implants failed within 7 weeks of loading, resulting in a cumulative survival rate of 95.5% and 85.5% respectively after 9 years of load. The survival rate for implants in a partial prosthesis was 98.8% and 92.2% for single restorations in the TiUnite group, and 87.8% and 83.2%, respectively, for partial and single resorations in the control group. The marginal bone resorption in the first year was on average 0.9 mm in the TiUnite group and 1.0 mm in the machined group; at the third year it was 0.4 and 0.5 mm, respectively. On examination at 9 years, there was a general settlement of the bone, with a negligible further loss in height. Conclusions: The unchanged survival rate and the low bone loss after 9 years confirm the feasibility of an immediate loading protocol in the mandible, which included flapless surgery. TiUnite implants obtained a 10% higher success rate compared with machined fixtures.

Purpose: The clinical evaluation of one-piece zirconia dental implants with different diameters to determine survival rate and type of implant failure. Materials and Methods: Information concerning implant surgery (number, diameter, length, and position of inserted implants; patient age, sex, risk factors, and bone quality) was extracted from the clinical records. All treated patients were then recalled for a follow-up examination to check the current clinical parameters concerning soft tissue, implants, and prosthetic reconstructions. Results: A total of 79 patients received 170 implants (diameter-reduced 3.25 mm: n = 59; diameter 4.0 mm: n = 82; diameter 5.0 mm: n = 29). The clinical examination showed no signs of gingival inflammation. Prosthetic information was available for 119 implants restored with single crowns (87 implants), fixed partial dentures (25 implants), and removable hybrid dentures (7 implants). Overall, 30 implants were lost due to lack of osseointegration (n = 17) or fracture (n = 13). The diameter-reduced implants showed the lowest survival rate (59.5%) compared to the implants with a diameter of 4.0 mm (90.6%) and 5.0 mm (73.9%). The survival rate for diameters of 3.25 mm was significantly lower than that for diameters of 4.0 mm. The estimated cumulative survival rate up to 3 years demonstrated a survival probability of 82.4% for all types of implant diameters and failure. Conclusions: Based on these results, diameter-reduced zirconia dental implants cannot be recommended for clinical use. The overall survival rate of 82.4% is not acceptable in comparison to the well-established survival rate of titanium implants.

Purpose: The penetration of dental implants into the maxillary sinus is becoming more common as a result of the use of new techniques to rehabilitate edentulous jaws. This complication requires the removal of the foreign body, even in asymptomatic patients, to prevent inflammatory disease. This article reports the authors' experience with the surgical removal of dental implants from the maxillary sinus with an endoscopic approach via middle meatotomy. Materials and Methods: A 10-year (2001 to 2011) retrospective analysis was performed in the authors' departments to identify all patients who underwent endoscopic removal of a dental implant from the maxillary sinus. Results: Sixteen patients (seven women and nine men, mean age 50.7 years) underwent endoscopic removal of the implant from the maxillary sinus via a middle meatotomy. Seven patients (43.8%) received general anesthesia for the surgery, and nine (56.2%) were treated with local anesthesia. No intraoperative or postoperative complications were observed. The mean follow-up period was 62 months. Conclusion: In the authors' experience, endoscopic transnasal removal of dental implants from the maxillary sinus via a middle meatotomy is a successful, rapid, safe, and minimally invasive procedure.

Dental implants may be successfully placed immediately into fresh extraction sockets when primary implant stability can be attained. This article presents a new classification system for molar extraction sites that describes extraction sockets based upon the bone available within the socket for stabilization of an immediately placed implant. Three categories-types A, B, and C-are employed: the type A socket, which allows for the implant to be placed completely within the septal bone, leaving no gaps between the implant and the socket walls; the type B socket, which has enough septal bone to stabilize but not completely surround the implant, leaving gaps between one or more surfaces of the implant and the socket walls; and the type C socket, which has little to no septal bone, thus requiring that the implant engage the periphery of the socket. Treatment protocols and relevant clinical examples are presented based upon the characterization of the socket according to this classification system.

The aim of the present study was a light and scanning electron microscopy (SEM) evaluation of the peri-implant tissues around sandblasted, acid-etched implants, retrieved from man, after a loading period of 5 and 10 years, respectively. Two implants (Leone Implant System) had been retrieved for a fracture of the prosthetic superstructure respectively after 5 and 10 years of loading. Both implants were stable before retrieval and had been retrieved using a 5-mm trephine bur. One implant was treated to obtain thin ground sections, while the other underwent evaluation under SEM. Compact, mature lamellar bone was present over most of the implant perimeter in close contact with the implant surface and with many remodeling areas. Under SEM, small concavities, completely filled by mineralized bone, were present on the implant surface. The present histologic results showed that these implants were well integrated over the long term, and the peri-implant bone was undergoing continuous remodeling at the interface.

Purpose: Three-dimensional finite element analysis was conducted to evaluate and compare the stress distribution in the abutment and retention screw of implant-supported single crowns with platform switching and with a conventional platform under vertical and oblique loading. Materials and Methods: Two finite element models were created simulating an osseointegrated implant (4 × 10 mm, platform 4.1 mm) embedded in jawbone. One model simulated a 4-mm-diameter abutment connection (conventional model) and the other represented a 3.8-mm-diameter abutment connection (platform-switched model). A crown with a cobalt-chromium framework and feldspathic porcelain veneering was applied to the titanium abutment. Static vertical and oblique loads were applied to the crown, with a maximum load of 150 N. Results: In both models, the highest stress values occurred in the abutment during vertical and oblique loading. Nevertheless, the von Mises stresses in the abutment and the retention screw were lower in the platform-switched model than in the conventional model. During axial loading, the abutment and screw supported slightly less stress in the conventional model than in the platform-switched model. Increases in the angle of force application caused a progressive increase in stresses in the abutment and screw in both models. The maximum stress was distributed at the margin and transgingival area of the abutment and on two-thirds of the flat area and the first threads of the retention screw in both models. Conclusions: Platform switching reduced the stress values on the abutment and retention screw of a single-unit prosthesis during oblique loading. Regardless of whether platform switching was employed, the stress on the abutment and screw gradually increased as the loading direction changed from vertical to 45 degrees oblique. The locations and distributions of stresses were similar in both models.

Purpose: The aim of the present study was to investigate the stress distribution in the bone around a platformswitched implant with marginal bone loss. Materials and Methods: Finite element models of an implantsupported crown on a mandibular first molar were constructed and included an osseointegrated implant, a metal crown, and cancellous and cortical bone. Two kinds of abutments, conventional and platformswitched, were imported into the model. A variety of different levels of conical marginal bone resorption, from 0 to 2.0 mm in height and width, was created around the implant neck. The stresses generated in the peri-implant bone tissue were analyzed under 200 N of vertical or oblique loading. Results: The location of stress concentration extended from the implant neck toward the apex in association with increases in bone resorption depth. In the bone-resorbed models, the platform-switched implant showed lower maximum equivalent stresses in the peri-implant bone than the conventional abutment. The difference between the two implant models decreased as bone resorption increased. Conclusion: Within the limitations of this study, the results suggest a biomechanical advantage for platform switching in a condition of marginal bone resorption, but this advantage may be weakened when bone resorption is dramatic. Additional animal or clinical studies are necessary to better clarify the effects of peri-implant bone defects on the biomechanical features of a platform-switched configuration.

Purpose: To demonstrate the degree of stability decrease and subsequent increase of dental implants at early implantation times in a beagle model. Materials and Methods: The mandibular premolars and first molars of eight beagle dogs were extracted and the ridges allowed to heal for 8 weeks. Thirty-two (n = 16 each group) implants were placed bilaterally, and remained in vivo for 1 and 3 weeks. The implants with comparable dimensions were divided as follows: group 1, Straumann Bone Level with SLActive surface; group 2, Nobel Speedy Replace RP with TiUnite surface. During insertion and following sacrifice, the implants were torqued to determine insertion and interface failure values. Histologic sections were prepared for microscopy. Statistical analysis was performed using Kruskal-Wallis and multiple paired and non-paired t tests considering unequal variances at a 95% level of significance. Results: High insertion torque values were observed along with a significant decrease at 1 week in vivo (P = .003). At 3 weeks, the biomechanical fixation levels increased and were comparable to the insertion torque value. Histology showed that interfacial bone remodeling and initial woven bone formation was observed around both implant groups at 1 and 3 weeks. Conclusions: As time elapsed early after implantation, the biomechanical stability of dental implants initially decreased and subsequently increased.

Purpose: To compare the stress in bone around zirconia and titanium implants under loading. Materials and Methods: A one-piece zirconia implant and a replica of the same implant made of commercially pure titanium were embedded in two self-curing acrylic resin blocks. To measure strain, a strain gauge was applied on the surface of the two samples. Loads of 50, 100, and 150 N, with orientations of 30, 45, and 60 degrees with respect to the implant axis were applied on the implant. Strain under all loading conditions on both samples was measured. Three-dimensional virtual replicas of both the implants were reproduced using the finite element method and inserted into a virtual acrylic resin block. All the materials were considered isotropic, linear, and elastic. The same geometry and loading conditions of the experimental setup were used to realize two new models, with the implants embedded within a virtual bone block. Results: Very close values of strain in the two implants embedded in acrylic resin were obtained both experimentally and numerically. The stress states generated by the implants embedded in virtual bone were also very similar, even if the two implants moved differently. Moreover, the stress levels were higher on cortical bone than on trabecular bone. Conclusions: The stress levels in bone, generated by the two implants, appeared to be very similar. From a mechanical point of view, zirconia is a feasible substitute for titanium.

Purpose: The aim of this study was to evaluate the effect of cantilevered bar length on strain produced around two implants supporting a mandibular overdenture. Materials and Methods: Two root-form implants were placed bilaterally in the canine region of an edentulous acrylic resin mandibular cast and connected with a resilient bar/clip attachment. Four linear strain gauges were bonded to the acrylic resin at the mesial and distal surfaces of each implant. Each gauge was wired separately into a 1/4 Wheatstone bridge of a multichannel digital bridge amplifier. Strains were measured without cantilevered bar extensions (control group) and with the following lengths of cantilevered bars: 11 mm (group 1), 9 mm (group 2), and 7 mm (group 3). For each cantilevered bar length, strains were measured using clips placed on the cantilevers and attached to the overdenture (bar-clip contact) and without clips (bar-acrylic resin contact). Strain measurements were performed under central and unilateral loading using a loading device. Results: The bar with cantilevers (either with or without clips) demonstrated a significant increase in strain compared to the bar without cantilevers. The 11-mm cantilever length generated the highest peri-implant strain values, while the 7-mm length recorded the lowest. For all cantilevered bar lengths, the strains significantly decreased with bar-clip contact compared to bar-acrylic resin contact. Under central loading, distal and mesial peri-implant strains were the highest and the lowest values, respectively, while under unilateral loading, the highest strain was recorded at distal sites of the loading side and the lowest was recorded at distal sites of the nonloading side. A positive correlation was found between the recorded strain and the cantilevered bar length. Conclusion: The 7-mm cantilevered bar with clips placed on the cantilevers was recommended when two implants were used to support mandibular overdentures, as it demonstrated the lowest magnitude of strains with no significant differences between periimplant sites.

Purpose: To compare the extramaxillary approach with the widely used intrasinus approach via finite element method. Materials and Methods: A unilateral three-dimensional model of the craniofacial area surrounding the region of interest was developed using computed tomography image datasets. The zygomatic implants were modeled using three-dimensional computer-aided design software and virtually placed according to the described techniques together with one conventional implant and a prosthesis. The bone was assumed to be linear isotropic with a stiffness of 13.4 GPa, while the implants were of titanium alloy with a stiffness of 110 GPa. Masseter forces were applied at the zygomatic arch, and occlusal loads were applied to the surface of the prosthesis. The stresses and displacements generated on the surrounding bone and within the implant due to the simulated loading configuration were analyzed. Results: The bone-implant interface and zygomatic implant body for the intrasinus approach produced 1.41- and 4.27-fold higher stress, respectively, compared with the extramaxillary approach under vertical loading. However, under lateral loading, the extramaxillary approach generated 2.48-fold higher stress than the intrasinus at the bone-implant interface. The zygomatic implant in the extramaxillary approach had twofold higher micromotion than those with intrasinus approach under lateral loading. Conclusions: No one technique was found to be superior; however, if lateral loading is used, the intrasinus approach is the most favorable for the rehabilitation of severely atrophic maxillae.

Purpose: To evaluate the effectiveness of three types of abutments in the maintenance of screw joint preload before and after cyclic loading as well as to observe possible microdamage in the structure of the components using a scanning electron microscope (SEM). Materials and Methods: Forty-five external-hex implants were embedded in epoxy resin, received their respective abutments, and were randomly divided into three experimental groups (n = 15): (1) machined titanium (Ti) abutments; (2) pre-machined gold (Au) abutments; and (3) machined zirconia (ZrO2) abutments. The abutment screws were tightened according to the manufacturer's recommended torque. Initially, a static bending test was performed using five specimens of each group to determine the load applied in the cyclic loading test. Thus, 10 specimens of each group were used to measure the reverse torque value (preload) of the abutment screw before and after loading. A cyclic loading (0.5 × 106 cycles; 15 Hz) between 11 and 211 N was applied at an angle of 30 degrees to the long axis of the implants. The group means were compared using analysis of variance and the Tukey test (α = .05). Results: The reverse torque analysis before cyclic loading showed no significant difference among the groups (P > .05). After cyclic loading, all preload means decreased significantly. The lowest decrease in preload was observed in the Ti group, whereas the highest decrease was observed in the ZrO2 group, with a significant difference noted between them (P = .010). The Au group presented an intermediate decrease, with no significant difference compared to the other groups (P > .05). SEM images showed structural changes in the mating surfaces of the abutments after cyclic loading. Conclusion: The load application reduced the preload means significantly in all groups, and more significantly in the ZrO2 group.