The International Journal of Oral & Maxillofacial Implants, 01/2013

Purpose: To investigate the association between interleukin-6 (IL-6) G174C polymorphism and susceptibility to peri-implant disease (PID) and/or chronic periodontitis (CP), in Brazilian subjects. Materials and Methods: A total of 103 Brazilian patients were submitted to peri-implant and periodontal examination. According to their peri-implant characteristics, patients were divided into: group A (healthy, n = 52), group B (peri-implant mucositis, n = 20), and group C (peri-implantitis, n = 31). All patients (n = 103) were also characterized as healthy periodontium patients without CP (HP, n = 60) or CP patients (CP, n = 43). DNA was extracted from buccal cells, and the IL-6 G174C polymorphism was genotyped by polymerase chain reaction-restriction fragment length polymorphism. Differences in the prevalence of genotypes and alleles between healthy and ill patients were analyzed by chi-square test (P .05), considering PID, CP, and PID+CP. Results: Results considered the presence of PID and/or CP in all patients. The CC genotype was the least common in all groups. The chi-square test showed no significant correlation between genotypes. However, the odds ratio showed that individuals with GG genotype and allele G were 1.53 and 1.43 times more susceptible to PID, respectively. The risk of presenting CP was increased in patients with GG genotype and allele G 1.35 and 1.24 times, respectively. When both diseases were evaluated together, patients with GG genotypes and allele G were 1.75 and 1.50 times more likely to present PID and CP together. When PID was evaluated without CP, patients with allele G were 2.08 times more susceptible to PID. Conclusions: The frequency of the genotype IL-6 174GG and allele G was different between healthy and ill groups. Therefore, this genotype may be a common risk factor for both CP and PID in Brazilian populations. Keywords: genetic polymorphism; peri-implantitis; chronic periodontitis; diagnosis

Purpose: The implant-abutment connection of a two-piece dental implant exhibits complex micromechanical behavior. A microgap is evident at the implant-abutment interface, even in the virgin state, and its width varies when an external mechanical load is applied. Materials and Methods: This study used high-resolution synchrotron-based radiography in combination with hard x-ray phase-contrast mode to visualize this gap and estimate its size. Commercially available implants with different internal conical implant-abutment connections were imaged. Pairs of implants were imaged as manufactured (new) and after fatigue loading (5 million cycles up to 120 N). Then, different static loads were applied at different angles relative to the implant-abutment assemblies, and the implant-abutment microgaps were measured and compared. Results: Microgaps existed in all systems. Fatigue loading extended the size of the microgap and increased the possibility of micromovement of the implant-abutment complex. The cone angle of the connection also influenced the stability of the abutment, with flatter cones appearing to be more stable. Conclusion: Cyclic loading at medium force (120 N) induces plastic deformation of titanium implants and abutments. Keywords: dental implants, digital radiography, phase-contrast microscopy, synchrotron radiography, titanium

Purpose: To evaluate the clinical and histologic aspects of bone formation in maxillary sinus augmentation using macroporous biphasic calcium phosphate (MBCP) comprising hydroxyapatite/tricalcium phosphate (HA/TCP) 60/40 as bone-grafting material. Materials and Methods: A total of 10 patients and 12 sinuses grafted with MBCP in two-stage sinus augmentation were included in the present study. After a healing period of 6 months, bone core biopsies were harvested during implant insertion and evaluated under light microscopy. Results: The histologic examination showed that the MBCP particles were in close contact with new bone in all biopsies. Histomorphometric evaluation demonstrated that newly formed bone constituted 28.3% ± 2.7%, residual grafted material 27.3% ± 1.2%, and marrow spaces 45.9% ± 1.9%. Conclusions: Histologic investigation showed that the MBCP grafted particles were embedded and integrated in the newly formed bone; this bone was in close and tight contact with the biomaterial particles. Data from the preliminary results demonstrated that MBCP is a biocompatible and osteoconductive material that can be successfully used as a grafting material for sinus floor augmentation. Keywords: bone regeneration, biphasic calcium phosphate, human histology, sinus augmentation

Purpose: After placement, titanium dental implants are conditioned by blood and tissue fluid. These initial processes are affected by the hydrophilicity of the implant. The hydrophilicity of titanium dioxide (TiO2) can be increased by ultraviolet (UV)-C irradiation. Anodic oxidation is an electrochemical treatment used to form TiO2 layers that are characterized by their thickness, roughness, and porosity on the surface of titanium implants. These oxide layers increase implant durability and performance. Therefore, the aim of this study was to investigate the effect of UV-C irradiation on the anodized titanium surface and the resultant tissue response. Materials and Methods: Twenty-five titanium disks and 56 screw-type implants were fabricated of commercially pure titanium and anodized. The samples were divided into a control group (anodized) and a test group (anodized and UV-C irradiated with a bactericidal UV sterilizer for 24 hours just prior to experimentation). The surface characteristics of the disks, including roughness, crystal phase of the oxide layer, chemical composition, and water contact angle, were then evaluated. Implants were placed into rabbit tibiae, and histomorphometric analysis was performed after healing periods of 4 and 12 weeks. The results were compared between groups. Results: The surface topography and phase of the oxide layer were not significantly different between test and control groups. Carbon surface impurities were noticeably decreased after UV-C irradiation, and water contact angle measurements were significantly lower (P .001). After a healing period of 4 weeks, test implants showed higher values for both bone-to-implant contact and the amount of bone in the thread area of the implant (P .01). No significant differences between groups were found for either histomorphometric measurement after 12 weeks. Conclusions: UV-C irradiation of an anodized titanium implant, accomplished via a bactericidal UV sterilizer, promoted an early bone response in rabbit tibiae. Keywords: anodic oxidation, histomorphometry, titanium irradiation, ultraviolet-C irradiation

Purpose: It is currently a challenge to determine the biomechanical properties of the hard tissue-dental implant interface. Recent advances in intraoral imaging and tomographic methods, such as microcomputed tomography (micro-CT), provide three-dimensional details, offering significant potential to evaluate the boneimplant interface, but yield limited information regarding osseointegration because of physical scattering effects emanating from metallic implant surfaces. In the present study, it was hypothesized that functional apparent moduli (FAM), generated from functional incorporation of the peri-implant structure, would eliminate the radiographic artifact-affected layer and serve as a feasible means to evaluate the biomechanical dynamics of tissue-implant integration in vivo. Materials and Methods: Cylindric titanium mini-implants were placed in osteotomies and osteotomies with defects in rodent maxillae. The layers affected by radiographic artifacts were identified, and the pattern of tissue-implant integration was evaluated from histology and micro-CT images over a 21-day observation period. Analyses of structural information, FAM, and the relationship between FAM and interfacial stiffness (IS) were done before and after eliminating artifacts. Results: Physical artifacts were present within a zone of about 100 to 150 µm around the implant in both experimental defect situations (osteotomy alone and osteotomy + defect). All correlations were evaluated before and after eliminating the artifact-affected layers, most notably during the maturation period of osseointegration. A strong correlation existed between functional bone apparent modulus and IS within 300 µm at the osteotomy defects (r > 0.9) and functional composite tissue apparent modulus in the osteotomy defects (r > 0.75). Conclusion: Micro-CT imaging and FAM were of value in measuring the temporal process of tissue-implant integration in vivo. This approach will be useful to complement imaging technologies for longitudinal monitoring of osseointegration. Keywords: biomechanics, dental implants, finite element analysis, microcomputed tomography

Purpose: The objective of this study was to evaluate sinus floor augmentation with simultaneous implant placement using platelet-rich fibrin (PRF) as the only grafting material. Materials and Methods: This study included patients who underwent sinus floor augmentation with simultaneous implant placement using PRF as the sole filling material between July 2009 and January 2011 at the Department of Oral and Maxillofacial Surgery, Nagasaki University Hospital. For each patient, presurgical and postsurgical (6 months after the surgery) radiography and computed tomographic scanning were performed to assess bone formation at the implant sites. The density (in Hounsfield units [HU]) of the newly formed bone and the bone height from the sinus floor to the alveolar crest where implants were inserted were measured using implant planning software (Simplant, Materialise Dental). Results: Nine sinus floor augmentations were performed, and 17 implants were placed in six patients. The mean residual bone height between the sinus floor and alveolar crest was 4.28 ± 1.00 mm (range, 1.9 to 6.1 mm) prior to surgery and 11.8 ± 1.67 mm (range, 9.1 to 14.1 mm) after surgery. The alveolar bone ridge was wide enough for implant placement in all cases. The mean density of the newly gained bone around the implants was 323 ± 156.2 HU (range, 185 to 713 HU). All implants were clinically stable at the time of abutment insertion, 6 months after sinus augmentation. Conclusion: Sinus elevation with simultaneous implant placement using PRF as the only filling material may promote natural bone regeneration. Keywords: bone regeneration, dental implants, Hounsfield index, maxillary sinus, platelet-rich fibrin, resonance frequency analysis, sinus grafting

Purpose: To assess the primary stability of a hybrid self-tapping implant and a cylindric non-self-tapping implant in an in vitro test model using polyurethane foam. Materials and Methods: Eighty standardized blocks of cellular rigid polyurethane foam, 2 cm long and 1 cm wide, with different thicknesses of 2, 4, 6, and 9 mm (n = 10 per group) were cut. Two implant systems-a hybrid self-tapping (Tapered Effect [TE], Straumann) and a cylindric non-self-tapping (Standard Plus [SP] Wide Neck, Straumann) were placed in the block specimens. Subsequently, resonance frequency analysis (RFA) was performed. The RFA measurements were made in triplicate on four aspects of each implant (mesial, distal, buccal, and oral), and the mean RFA value was calculated. Subsequently, the tensile load of the implants was determined by pull-out tests. The data were analyzed using one-way and two-way analysis of variance followed by a post hoc Scheffé test and a t test (α = .05). Additionally, the simple linear correlation between the RFA and tensile load values was evaluated. Results: No statistically significant differences were found between TE and SP in terms of RFA at different bone thicknesses. Starting from a bone thickness of 4 mm, TE implants showed significantly higher tensile load compared to SP implants (P = .016 to .040). A correlation was found between the RFA measurements and tensile load. Conclusions: Mechanically stable placement is possible with TE and SP implants in a trabecular bone model. RFA and tensile load increased with greater bone thickness. Keywords: bone density, dental implants, resonance frequency analysis, tensile load measurement

Purpose: There is no quantitative gold standard instrumentation to assess the quality of implant osseointegration. The purpose of this exploratory study was to evaluate the response of two devices (one based on resonance frequency analysis, the Osstell device, and another that analyzes the percussion energy response, the Periometer) to assess the primary stability of implants embedded in artificial bone models. Materials and Methods: Standard implants were placed into polyurethane blocks of varying densities, and the two mechanical devices were challenged to test the specimen block series. Both analysis of variance and regression analysis were used to examine the output from each device over each series of specimen blocks as well as to directly compare outputs between the two devices. Results: The stability of the implants increased with the foam density for solid block specimens. Linear regression analysis showed significant correlation between the two instruments for testing with monolithic blocks ( r2 = 0.984). Both devices also indicated that a hybrid block with the greatest density at the top provided the best implant stability versus a hybrid block with relatively low density at the top of the block. However, resonance frequency analysis readings seemed to be more dependent on the density of the top layer of the hybrid blocks. Conclusion: Osstell and Periometer readings were in good agreement for monolithic blocks, and they were reasonably consistent when blocks of hybrid density were tested. Keywords: bone density, dental implant, implant stability, osseointegration

Purpose: The host response to infection differs between peri-implantitis and periodontitis, but the mechanisms underlying these differences are not understood. In this study, the distribution of dendritic cell subpopulations in healthy peri-implant mucosa (HPIM) was compared to that of healthy gingiva (HG). Materials and Methods: HPIM and HG specimens were obtained from nonsmoking, systemically healthy subjects. Immunohistochemistry was used to quantify the number of Langerhans cells (LCs) (CD1a+) and interstitial dendritic cells (IDCs) (factor XIIIa+) in the oral epithelium, sulcular/junctional epithelia, and lamina propria without inflammatory infiltration and with inflammatory infiltration. Results: Fourteen HPIM and 13 HG specimens were obtained from subjects aged 29 to 55 years. The lamina propria of the HPIM had fewer LCs than that of the HG (HPIM: 7.99 ± 10.76, HG: 25.68 ± 16.98; P = .003). There was no significant difference in the number of CD1a+ cells in the oral epithelium or the sulcular/junctional epithelia between the HPIM and the HG (P >= .23). A greater number of IDCs was observed in the lamina propria with inflammatory infiltration of the HPIM compared to the HG (HPIM: 57.02 ± 35.70, HG: 33.89 ± 26.98; P = .06). Conclusions: In the lamina propria of HPIM, fewer LCs and more IDCs were observed. These differences may be associated with reduced stimulation of the innate and acquired immune responses initiated by LCs and the greater matrix remodeling of peri-implant tissue associated with IDCs. Keywords: dendritic cells, peri-implant mucosa, periodontal tissue, titanium implants

Purpose: This study evaluated the reliability and failure modes of anterior implants with internal-hexagon (IH), external-hexagon (EH), or Morse taper (MT) implant-abutment interface designs. The postulated hypothesis was that the different implant-abutment connections would result in different reliability and failure modes when subjected to step-stress accelerated life testing (SSALT) in water. Materials and Methods: Sixty-three dental implants (4 × 10 mm) were divided into three groups (n = 21 each) according to connection type: EH, IH, or MT. Commercially pure titanium abutments were screwed to the implants, and standardized maxillary central incisor metallic crowns were cemented and subjected to SSALT in water. The probability of failure versus number of cycles (95% two-sided confidence intervals) was calculated and plotted using a power-law relationship for damage accumulation. Reliability for a mission of 50,000 cycles at 150 N (90% two-sided confidence intervals) was calculated. Polarized-light and scanning electron microscopes were used for failure analyses. Results: The beta values (confidence intervals) derived from use-level probability Weibull calculation were 3.34 (2.22 to 5.00), 1.72 (1.14 to 2.58), and 1.05 (0.60 to 1.83) for groups EH, IH, and MT, respectively, indicating that fatigue was an accelerating factor for all groups. Reliability was significantly different between groups: 99% for MT, 96% for IH, and 31% for EH. Failure modes differed; EH presented abutment screw fracture, IH showed abutment screw and implant fractures, and MT displayed abutment and abutment screw bending or fracture. Conclusions: The postulated hypothesis that different implant-abutment connections to support anterior single-unit replacements would result in different reliability and failure modes when subjected to SSALT was accepted. Keywords: cementation, dental implants, fractography, implant-supported prostheses, reliability, step-stress accelerated life testing

Purpose: Although the recent success rates of dental implants are quite high, it is still true that loading during the bone healing period may be more likely to discourage osseointegration and that occlusal overloading might result in implant failure, even after osseointegration is established. The purposes of this study were to establish an appropriate experimental animal model and to histologically assess degenerative changes in established osseointegration under early and excessive occlusal loading. Materials and Methods: Forty rats were divided into control and experimental groups. The maxillary first and second molars on both sides were extracted, and machined-surface titanium implants were placed. In the experimental group, 2 or 4 weeks after implant placement, abutments that were designed to overload the implants were attached. Control group implants did not receive abutments and remained in situ 2 or 4 weeks. Sections were prepared and observed histologically. Results: Attrition of occluding opposite teeth and shiny spots on the abutments indicated that this model was useful for histologic investigation of the remodeling and bone changes around implants. Specimens showed remarkable bone loss and deterioration of osseointegration when overloading began at 2 weeks. Overloading applied after 4 weeks of healing induced active bone resorption in remote areas of the implants after 15 days of occlusion, while bone resorption at the interface was limited. Conclusion: The authors successfully established an implant occlusion model using rats. This model revealed degenerative changes in osseointegration and/or in the bone around implants upon excessive occlusal loading. These results emphasize the risks associated with immediate loading and overloading. This is the first study to reveal the possibility of bone loss around overloaded implants in the absence of infection using a small animal model. Keywords: animal experiments, bone remodeling, dental implants, histology, occlusal overload, osseointegration

Purpose: Often during implant surgery in the mandibular symphysis area, little attention is given to the mandibular incisive canal. Although it is true that intraoperative and postoperative complications with implants in the incisive mandibular canal are rare, they are more common when harvesting bone from the chin area. Loss of tooth sensation is a rather frequent consequence. The present study used cone beam computed tomography (CBCT) to identify and measure variations in the dimensions of the incisive canal and its spatial relationship to various anatomical landmarks of the mandible to reduce the number of postoperative complications after selective procedures in the symphysis area. Materials and Methods: One hundred two patients scanned for a variety of clinical indications were included in this retrospective study. The dimensions of the incisive mandibular canal were assessed, and the distances from the various mandibular landmarks were measured using the multiplanar capabilities of the CBCT device's software. Results: The results show that a mandibular incisive canal was identified by CBCT in 93% of the cases and had a mean length of 8.9 mm (range, 0 to 24.6 mm). The mean distances of the canal from the root tips of the premolars, canines, and incisors were 6.9 mm, 7.3 mm, and 10.4 mm, respectively. The mean distances from the canal to the buccal cortical border in the same tooth positions were 2.8 mm, 4.4 mm, and 4.8 mm, respectively. Conclusions: In a large majority of the sample, a mandibular incisive canal was identified by CBCT. The large variation in the spatial relationships of the canal mandates a case-by-case preoperative radiographic evaluation of the canal, and CBCT seems able to fulfill the task. Keywords: cone beam computed tomography, dental implants, incisive canal, incisive nerve

Purpose: Accurate and passive fit between a prosthesis and its supporting implants has been considered a prerequisite for successful long-term osseointegration. The objective of this in vitro study was to evaluate the strain development during tightening of a five-unit screw-retained superstructure constructed using five different methods. Materials and Methods: Five-unit screw-retained fixed partial prostheses (n = 25) were fabricated on three implants embedded in an epoxy resin block using five different methods: (1) cobalt-chromium (Co-Cr), plastic cylinders, one-piece cast; (2) Co-Cr, plastic cylinders, framework sectioned, preceramic laser-welding soldering; (3) gold-platinum (Au-Pt), gold cylinders, one-piece cast; (4) Au-Pt, gold cylinders, framework sectioned, preceramic laser-welding soldering; (5) Co-Cr, one-piece cast, and cementation to "passive abutments" (Southern Implants) after final finishing and polishing. Strain gauges (SG) were attached to the fixed partial prosthesis (FPP) and to the resin block to measure the stress created during screw tightening. Results: The combination of Co-Cr alloy and plastic cylinders in a one-piece cast showed such an inadequate fit among the fabricated methods that this group was excluded from the remainder of the experiment. Specimens of Au-Pt cast on gold cylinders in one piece showed higher strain development than the other groups used in this study, with strains ranging from 223.1 to 2,198.1 µm/m. Sectioning and soldering significantly improved the overall fit. FPPs of Co-Cr in a one-piece cast cemented to "passive abutments" produced the best level of fit, with the least strain development in the prosthesis and the resin block (59 to 204.6 µm/m). Conclusion: Absolute fit of superstructures on implants is not possible using conventional laboratory procedures. Cementing FPPs onto prefabricated cylinders directly onto the implants significantly reduces strain development compared to the other fabrication methods. Keywords: implant prosthesis, laser welding, passive abutments, passive fit, soldering, strain gauges

Purpose: Modifications in implant surface topography and chemistry may alter the early bone response at different levels. This study characterized four implant surfaces and evaluated the biomechanical fixation and histologic response at early implantation times in a canine radius model. Materials and Methods: Externalhexagon Brånemark-type implants were used with four experimental surfaces: microblasted (MI), acid-etched and microblasted (AAM), anodized (A), and discrete crystalline deposition (DCD). Surface topography was assessed by scanning electron microscopy, interferometry, and x-ray photoelectron spectroscopy. The implants were placed in the central region of the radii of eight beagle dogs and remained in vivo for 10 or 30 days. The implants were torqued to interface failure, and a general linear statistical model with torque as the dependent variable and implant surface and time in vivo as independent variables was used. Results: All surfaces presented were textured, and different surface chemistries were observed. No significant differences between implant surfaces were observed for torque at 10 days. However, at 30 days, the AAM surface presented significantly higher torque values compared to the DCD and A surfaces. Significantly higher torque values were observed at 30 days compared to 10 days (P .001). Conclusions: Significantly different biomechanical fixation dependent on surface preparation was observed after 30 days, and all surfaces were biocompatible and osteoconductive. Keywords: dental implant, histology, in vivo, osseointegration, surface properties

Purpose: To evaluate the biomechanical effects of platform switching on external- and internal-connection implants with regard to strain around the implants under loading. Materials and Methods: Implant analogs (5.0 × 12 mm) with external (EX) and internal (IN) connections were embedded into an acrylic resin block that simulated an edentulous ridge. Abutments with diameters of 5.0, 4.2, and 3.7 mm were attached to EX and IN analogs. A 100-N lateral load was applied to each abutment at an angle of 30 degrees, and the experiments were repeated 10 times. Strain gauges were attached to the implant surface at 1 mm (neck area) and 8 mm (apex area) below the platform to measure the strain around the implant under loading. Statistical analyses were performed by one-way analysis of variance and Steel-Dwass test. P .05 was considered statistically significant. Results: Significantly higher strain values were found around the neck area in both analogs (EX, -682.8 µε; IN,-582.1 µε) with conventional matching 5-mm-diameter abutments, followed by the analogs with 4.2-mm-diameter (EX, -184.1 µε; IN, -229.1 µε) and 3.7-mm-diameter (EX, -150.5 µε; IN, -129.7 µε) platform-switched abutments; this was statistically significant for EX (P .05). In the apex area, a mild increase in strain was found with a decrease in abutment diameter, but no significant difference was found between 4.2- and 3.7-mm-diameter abutments for IN (P > .05). Conclusion: Within the limitations of this study, platform switching reduced strain surrounding the implant neck area in both EX and IN during loading. However, the decreases in strain values were greater with EX than with IN. Keywords: external-connection implant, internal-connection implant, platform switching, strain

Purpose: The effects of implant angulation, impression material, and variation in width of the arch curvature on transfer models were evaluated. Materials and Methods: Three edentulous maxillary epoxy resin models were fabricated, and six internal-connection implant analogs were placed in different locations and different angulations in each model. In the first model, implants were positioned in the canine, first premolar, and first molar regions, and all analogs were positioned parallel to each other and perpendicular to the horizontal crestal plane (parallel model). In the second model, analogs were positioned in same regions (canine, first premolar, and first molar), but three of them were positioned with 10-degree buccal angulations (versus the horizontal crestal plane) (angular model). In the third model, analogs were inserted in the lateral incisor, canine, and second molar regions and parallel to each other (wide-arch model). Eighteen impressions of each model were made with each of the three materials-condensation silicone, polyvinyl siloxane, and polyether-and impressions were poured and kept at room temperature for 24 hours. They were then observed under a toolmaker's microscope, with epoxy resin models of each group used as references. Distance deformations between implants in each model in the x- and y-axes were recorded separately. Implant angulation deformations were recorded in the x-z plane. Statistical evaluations were performed with analysis of variance and the least significant difference post hoc test. Results: Angular model measurements showed the greatest deformation values (P .05). All impression materials showed deformation, and the polyether impression models showed statistically significantly less deformation in angular measurements (P .05). Conclusions: The models with implants placed parallel to each other exhibited greater accuracy than a model with implants placed at angles to each other. Keywords: implant angulation, impression accuracy, impression material, impression technique

Purpose: To report 20 cases with implant periapical pathology diagnosed during the osseointegration phase, evaluating retrospectively the efficacy of the treatment with implant periapical surgery. Materials and Methods: A retrospective chart review was conducted of all patients in whom implant periapical surgery was performed between 1996 and 2010. The criteria for diagnosing implant periapical pathology and, accordingly, performing implant periapical surgery were: (1) acute pain during the osseointegration period (8 weeks after implant placement) located in the area of the affected implant or presence of mucous fistula in relation with the implant apex; (2) absence of implant mobility; (3) non-dull percussion of nonsubmerged implants; and (4) presence or absence of implant periapical radiolucency. Results: Twenty-two implants were diagnosed with periapical pathology in 20 patients (13 women and 7 men) with a mean age of 54.3 years (range, 32 to 70 years) and were consecutively treated by a surgical approach. In 19 implants, the diagnosis was acute apical peri-implantitis (nonsuppurated in 7 cases and suppurated in 12), as based on the symptoms and radiographic sign, and in 3 cases it was subacute apical peri-implantitis, as based on the presence of a fistula. After a minimum follow-up of 1 year, 20 implants remained functional, with no clinical or radiologic alterations; the survival rate of the treated implants was 91%. Conclusion: The early diagnosis of inflammatory implant periapical lesions during the osseintegration phase, and their prompt surgical treatment, led to a survival rate of the treated implants of 91%. Keywords: implant periapical lesion, retrograde peri-implantitis, apical surgery, dental implants

Purpose: The sequence of observations presented is intended to alert the dental profession to complications that may occur when teeth and implants co-exist and subtle adult craniofacial growth occurs. Materials and Methods: The authors' observations of partially edentulous implant restorations with more than 20 years of follow-up included some observed changes relative to patients' remaining teeth and jaw structures. These changes, which were not easily explained and appeared to be random deviations from expected implantrestorative stability, conformed with research findings of craniofacial growth continuing into adulthood. The authors identified several distinct areas in which such adult craniofacial growth could potentially influence the relationship of implant restorations to the remaining teeth and jaw structure. Results: Potential esthetic, occlusal, and periodontal ramifications of continued adult craniofacial growth were found to include changes in occlusion, opened contact as a result of teeth migration, and changes in anterior esthetic results. The latter may include labialization of the anterior implant restoration and a progressive discrepancy of the cervical gingival margin of the implant restoration relative to the adjacent teeth. Cases are presented showing poor sequellae of treatment due to growth occurring after the assumption was made that a stable jaw dimension had been reached. While continued adult craniofacial growth sufficient to cause clinical problems is not common, it is also presently not predictable. Conclusion: When changes in tooth position relative to implant restorations secondary to long-term adult growth occur, they can cause problems that are difficult or even impossible to correct. Future research will ideally enable identification of patients at risk for developing such problems. Keywords: implant, growth, esthetics, occlusion, maintenance, complication

Purpose: Short implants are an alternative to bone augmentation procedures for patients with reduced bone height. This study evaluated the success of short implants in posterior locations prior to loading. Materials and Methods: Eighteen patients received at least four Astra Tech implants in symmetric posterior locations. Implants (n = 82) ranged from 6 to 11 mm with 70 implants = 9 mm and 38 implants = 6 mm. Placement was planned virtually using software and cone beam computed tomography (CBCT) scans. Computer-generated guides were ordered for all patients; however, lack of interarch distance precluded their use for five patients. In these situations, guides were used to communicate pilot drill position only. Osteotomies were prepared using the guides and accompanying drill sequence following a two-stage surgical approach. Degree of bone mineralization (DBM) parameters for implant osteotomy sites were measured using three-dimensional CBCT images taken before and after implant placement. A paired t test was performed to compare the DBM parameters between failed and successful implantation sites. Results: Early failure occurred for 7 out of 82 implants or 8.5%. All of the failed implants were 6 mm in length and placed using computer-aided design/ computer-assisted manufacture (CAD/CAM) surgical guides. Three failures occurred in one patient. Bone grafting was done for failed implant sites, and after healing, new implants were placed using conventional surgical guides. No further failures occurred. The most frequent value (peak) for DBM was significantly higher for failed implant sites than for successful ones (paired t test, P = .043). Conclusion: Current failures suggest that CAD/CAM guides used with external irrigation may pose a greater risk for the success of 6-mm implants placed in posterior areas with advanced bone loss. This may be due to the bone density in these highly resorbed areas combined with limited irrigation reaching the osteotomy sites. Keywords: short implants, failure, bone density

Purpose: The aims of this study were to evaluate the incidence of maxillary sinusitis associated with the sinus elevation procedure and to analyze the influence of maxillary sinusitis on the prognosis of dental implants. Materials and Methods: Data were collected from medical records and dental radiographic findings of patients who received dental implant therapy along with a sinus elevation procedure at Seoul National University Bundang Hospital from June 2003 to December 2008. Results: A total of 338 sinus elevation cases (643 implants) were included in this study, out of which maxillary sinusitis was reported in 33 cases (9.8%). The type of surgical approach used and the occurrence of sinus membrane perforation could be considered factors affecting maxillary sinusitis associated with the sinus elevation procedure. The implants at the site of the maxillary sinusitis associated with the sinus elevation procedure showed lower survival rates in male patients. Better clinical outcomes were achieved in the group receiving combined medical and surgical therapy for sinusitis associated with the sinus elevation procedure. Conclusions: Postoperative maxillary sinusitis decreased the survival rates of implants, whereas early diagnosis and combined medical and surgical therapy had the opposite effect. Keywords: maxillary sinusitis, sinus elevation, dental implants, prognosis

Purpose: Implants placed into the pterygomaxillary region allow for increased posterior support and a full complement of teeth without the need for distal cantilevers. With advancements in research and technology, implant delivery has evolved from the traditional two-stage procedure to immediate loading freehand and guided surgical template protocols. The purpose of this retrospective study is to determine if there is a significant difference in implant survival rates between these protocols. Materials and Methods: All pterygomaxillary implants placed in a single private practice from September 1985 to July 2011 were categorized into three separate classifications (two-stage freehand, single-stage freehand, or single-stage guided) by retrospective chart review. Life tables were constructed to determine the cumulative survival rates (CSR), and ANOVA was used to identify statistical significance. Results: A total of 981 patients comprising 371 males and 610 females were included in the study. Of all pterygomaxillary implants, 1,460 of 1,608 implants osseointegrated for a CSR of 90.80%. Seven hundred nine of the 825 two-stage, 624 of the 647 single-stage, and 127 of the 136 guided surgery implants osseointegrated for CSRs of 85.94%, 96.45%, and 93.38%, respectively. The comparison between two-stage and single-stage protocols was statistically significant, (P .05) while the difference between single-stage guided versus freehand protocols was found to be statistically insignificant (P > .05). Conclusion: The results from this retrospective study reinforce that immediate loading of pterygomaxillary implants with a provisional prosthesis is beneficial to both doctor and patient. The lower CSR for the guided surgery protocol compared with the single-stage freehand procedure is statistically insignificant, suggesting guided surgery is still a viable and recommended option for qualified patients. Keywords: dental implants, immediate loading, guided surgery, tuberosity, osseointegration

Purpose: Simultaneous insertion of multiple implants may exhibit suboptimal positions, especially in edentulous jaws considered for a fixed restoration. The aim of this study was to compare the incidence of and confounding factors in implant positioning errors related to the use of freehand and computer-aided treatment methods. Materials and Methods: A total of 353 implants were placed in 54 patients with at least one edentulous jaw using freehand and computer-aided methods involving 16 mucosa- and 12 bonesupported single- and multiple-type stereolithographic surgical guides. At the stage of prosthesis delivery, a blinded examiner evaluated seven positioning error criteria. Results were analyzed by chi-square test and logistic regression. Results: Interproximal emergence (OR = 2.82, P .0001), insufficient interimplant distance (OR = 1.42, P .0001), and improper parallelism (OR = 1.24, P = .001) errors were significantly higher in implants placed by the freehand method. The highest probability of positioning error (88%) was associated with the use of the freehand method, whereas the lowest (6%) was associated with single-type, mucosa-supported guides with other significant confounding factors. Conclusion: Utilizing computer-aided methods may alleviate the occurrence of implant positioning errors that are frequently associated with the freehand method. The use of software planning with enhanced viewing capabilities and single-type, mucosasupported stereolithographic surgical guides in suitable patients minimizes errors. Keywords: implant position; positioning error; malposition; guided surgery; implant prosthodontics; stereolithography

Purpose: The number of clinical reports giving detailed information on clinical outcomes with guided surgery is rather scarce despite its large-scale introduction over the last decade. The aim of this report was to determine implant survival and success in terms of peri-implant bone loss and evaluate whether smoking affects the outcome. Materials and Methods: A total of 26 cases with a partially or totally edentulous maxilla were selected for implant treatment using the Facilitate software system (Astra Tech). In totally edentulous cases, six fluoride-modified OsseoSpeed implants (Astra Tech) were inserted. Immediately after implantation, abutments were screwed onto the implants. Within 8 hours, a provisional screw-retained fiber-reinforced acrylic fixed dental prosthesis was screwed on the abutments. For the partial cases, the surgical guide rested on the remaining teeth and implants were not immediately loaded. Results: In total 13 out of 114 implants were lost within 12 months after surgery, resulting in 88.6% survival at 1 year. Twelve of those failures occurred in smokers, leading to 69.2% implant survival compared to 98.7% in nonsmokers. Implants were lost in 7 out of 26 (26.9%) patients; only 1 out of 17 nonsmokers (5.9%) compared to 6 out of 9 (66.7%) smokers lost one or more implants. In total, 38.5% of the subjects with a full immediately loaded fixed dental prosthesis experienced implant failures compared with 15.4% of the partially delayed loaded cases. The overall mean bone loss based on all implants was 0.47 mm (SD, 0.94). Mean bone loss was 0.36 mm for nonsmokers and 0.62 mm for smokers. Conclusions: On the basis of the current case control study, it is tempting to suggest that smoking is an exclusion factor when placing implants using stereolithographic guided surgery in conjunction with immediate loading. There is still not enough scientific evidence to show if this method is as safe and predictable as the traditional method. Keywords: dental implants, stereolithography, guided surgery, smoking, clinical outcome

Purpose: To compare survival and peri-implant bone loss around immediately loaded surface-enhanced implants in the maxilla supporting single crowns (SCs), fixed partial dentures (FPDs), and fixed full-arch dentures (FFDs). Materials and Methods: The study included all subjects referred for implant treatment in the maxilla followed by immediate loading between November 2004 and 2007 with at least 2 years of follow-up. Smokers were excluded. Implant survival and bone loss were assessed by a calibrated external examiner who compared digital periapical radiographs taken during recall visits with baseline radiographs (day of loading = day after implant placement). An implant was considered successful when bone loss did not exceed 1 mm. Survival of implants supporting SCs, FPDs, and FFDs was compared using the log-rank test. A linear mixedeffect model analysis was used to evaluate bone loss because of clustering of implants in patients. Results: Three hundred six implants were placed in 55 patients (31 women, 24 men; mean age, 57.5 ± 11.4 years; range, 19 to 77 years) and followed for a mean of 35 ± 10.2 months (range, 24 to 58 months). One implant failed, resulting in an overall survival rate of 99.7% on the implant level and 98.2% on the patient level. No statistically significant differences were observed in the survival rates for SCs (100%), FPDs (98%), and FFDs (100%). The overall mean bone loss was 0.27 ± 0.37 mm (range, 0.00 to 2.55 mm) and was not influenced by the prosthetic reconstruction. Conclusion: Immediate loading of fluoride-modified implants in the maxilla is a predictable and reliable treatment option with high survival rates and limited peri-implant bone loss after 2 years. No statistically significant differences were found between implants supporting SCs, FPDs, and FFDs. Keywords: bone loss, dental implant, immediate loading, implant survival

Purpose: To compare the donor site complication rate and length of hospital stay following the harvest of bone from the iliac crest, calvarium, or mandibular ramus. Materials and Methods: Ninety-nine consecutively treated patients were included in this retrospective observational single-center study. Results: Iliac crest bone was harvested in 55 patients, calvarial bone in 26 patients, and mandibular ramus bone in 18 patients. Harvesting of mandibular ramus bone was associated with the lowest percentages of major complications (5.6%), minor complications (22.2%), and total complications (27.8%). Harvesting of iliac crest bone was related to the highest percentages of minor complications (56.4%) and total complications (63.6%), whereas harvesting of calvarial bone induced the highest percentage of major complications (19.2%). The length of the hospital stay was significantly influenced by the choice of donor site (P = .003) and age (P = .009); young patients with the mandibular ramus as the donor site had the shortest hospital stay. Conclusions: Harvesting of mandibular ramus bone was associated with the lowest percentage of complications and the shortest hospital stay. When the amount of bone to be obtained is deemed sufficient, mandibular ramus bone should be the first choice for the reconstruction of maxillofacial defects. Keywords: atrophy, bone graft, calvarium, complications, defects, donor site, iliac crest, mandible, mandibular ramus, maxilla, reconstruction

Purpose: To compare the accuracy of implant master casts fabricated using Robocast Technology (Biomet 3i) with that of master casts fabricated using traditional transfer (closed-tray) and pick-up (open-tray) techniques. Materials and Methods: A stereolithographic replica of a Kennedy Class I human mandible was fabricated for use as the master model. Implants were placed into both posterior quadrants (both second premolars and second molars) and set parallel (P) on one side and divergent (nonparallel, NP) on the opposite side. Impressions were made of the master model (patient replica model) with Encode Healing Abutments, open-tray, and closed-tray impression copings. Identical metallic spheres were placed onto each implant analog in the stone master casts, and the casts/spheres were scanned using a digital scanner. Measurements were made between the center points of the spheres and compared to the master model. Data were divided into P, NP, and individual sites, and the differences were analyzed statistically (α = .05). Results: Encode master casts were less accurate than the open-tray casts in NP sites. Encode master casts were less accurate than the open-tray and closed-tray casts in P sites. NP sites demonstrated less accuracy than P sites within the Encode group. Encode master casts were less accurate than the open- and closed-tray casts at the mandibular right second premolar site. The mandibular left second premolar was less accurate than the mandibular right second molar in the Encode group. Conclusions: Within the limitations of this lab-based study and analysis, the Encode technique resulted in master casts that were less accurate than master casts made from traditional open- and closed-tray impression techniques. Further research is necessary before specific clinical judgments can be made. Keywords: digital scanning, Encode, implant impressions, Robocasts

Purpose: To perform a preliminary validation with cone beam computed tomography (CBCT) of the combined use of intraoral bone blocks and biomaterials for total reconstruction of the atrophic maxilla. Materials and Methods: Consecutive cases of total edentulism of the maxilla (Cawood and Howell classes IV or V) treated with bilateral sinus floor elevation, mandibular bone block grafts, and biomaterials were evaluated prospectively. Implants were placed 14 to 16 weeks after grafting. Each patient received a CBCT scan preoperatively, immediately after bone augmentation, and at reentry. A three-dimensional reconstruction of the maxilla with volumetric calculations was obtained at each stage. Results: Fourteen patients participated. Successful graft integration occurred in all cases, with no major complications. Mean preoperative volume was 11,312 mm3. Mean postoperative volume was 19,997 mm3 immediately after surgery and 19,042 mm3 before implant insertion. The average percentage volumetric increase between the preoperative condition and the situation at reentry was 71.99%. One hundred eight implants were inserted. Immediate loading was possible with 81 implants in 10 patients. Conclusions: The rehabilitation of the severely resorbed maxilla remains a formidable challenge. The results of this study suggest that the use of mandibular bone blocks in combination with biomaterials is an effective, reliable procedure for the rehabilitation of the severely resorbed maxilla. Significant volume increases and adequate stability of the augmented areas at reentry were found with CBCT analysis. The grafted bone provided sufficient mechanical support to permit provisionalization and immediate loading. This technique enabled the restoration of function and esthetics with a fixed rehabilitation at 4 months. Keywords: atrophic maxilla, bone grafting, bone substitutes, bone resorption, total reconstruction

Purpose: The aim of this study is to assess the long-term outcome of a single-stage approach for implant placement and maxillary sinus floor elevation (MSFE) that used a combined scaffold of laminated calvarial bone, platelet-rich plasma (PRP), and beta-tricalcium phosphate. Materials and Methods: Thirty consecutive patients who required MSFE to allow rehabilitation with implant-supported prosthesis entered this survival study. All patients received their dental implants at the time of sinus elevation, and prosthetic loads were applied 4 to 6 months after implant insertion. Clinical outcomes used for evaluation included residual bone height at the subsinus area (height of subsinus bone [HSB], assessment of surgical morbidity, and implant success and survival rates. Results: Simultaneous insertion of 86 implants, either 10 mm long (n = 76) or 12 mm long (n = 10), took place in a total of 22 bilateral and 8 unilateral sinus elevations. Loading was initiated a mean of 3.8 ± 1.5 months after the first surgery. A mean HSB of 4.9 ± 1.7 mm was present before surgery, with 50% of the sample displaying HSBs of less than 4.4 mm. The mean implant survival time was 33.1 months (95% confidence interval, 31.7 to 34.5 months), with high rates of success (94.2%) and survival (96.5%). When patients were classified by their HSB (HSB >= 5 mm vs HSB 5 mm), no differences were seen with regard to age, sex, healing time, or follow-up in terms of implant survival rates (P > .05). Conclusions: Sinus floor elevation using mainly laminated calvarial bone, PRP, beta-tricalcium phosphate, and simultaneous stable implant placement is a predictable technique with low surgical morbidity that allows shorter healing times in patients with reduced bone height. Keywords: calvaria, endoscopic surgery, implant success rate, implant survival rate, platelet-rich plasma, sinus floor elevation, subsinus bone height

Purpose: To evaluate the success and survival of immediately placed tapered implants to support fixed restorations in the maxilla and mandible. Materials and Methods: The study was a prospective, multicenter, non-interventional study of patients requiring tooth extraction who requested an implant-supported restoration in the maxilla or mandible. Patients received at least one tapered implant (either immediately after tooth extraction or at a later time point). Abutments were placed 42 to 56 days after surgery, and prostheses were placed after a further 14 days. Treatment and implant success were the primary effectiveness criteria, and secondary parameters included radiographic bone loss, patient satisfaction, and gingival health. Results: A total of 436 patients were enrolled, of whom 376 were included in the safety analysis. Single implants were placed in 77% of patients, two implants in 16%, and three or more implants in the remainder. The cumulative implant survival rates for immediately placed implants were 98.3% after 1 year and 97.7% from 2 to 5 years. Patient satisfaction was good or excellent in most patients and the majority of implants showed no or 1-mm change in bone level for up to 5 years. Conclusions: The survival rate of immediately placed tapered implants was comparable to that found in other studies. Immediate implant placement with tapered implants can allow rapid rehabilitation with no adverse impact on implant survival. Keywords: dental implants, extraction socket, healing, immediate implants

Purpose: The aim of this prospective study was to evaluate the hard and soft tissue stability and esthetic outcomes of single-tooth implants placed in the anterior atrophic maxilla, following augmentation with mandibular block grafts covered with bovine hydroxyapatite and a resorbable collagen membrane, over a 5-year period. Materials and Methods: Patients with a bony deficiency of >= 3 mm horizontally and = 3 mm vertically were treated consecutively with reconstructive procedures and implant placement 6 months afterward. Alveolar ridge dimensions were measured before and after augmentation using computed tomography. Clinical and radiographic measurements of soft and hard tissue levels and esthetic parameters (pink esthetic score [PES]) were performed annually to assess treatment outcomes. Results: Twenty-nine patients were treated. One patient had partial graft exposure after 1 month that required regrafting at the time of implant placement. Mean bone gain was 4.23 ± 0.69 mm horizontally and 1.71 ± 0.75 mm vertically. The implant cumulative success rate was 100%, according to the criteria of Albrektsson et al. Mean crestal bone resorption after 5 years was low (0.61 ± 0.33 mm). Moderate recession of the facial mucosa (-1.12 ± 0.4 mm) was observed during the study period, while mesial and distal papilla heights increased slightly (0.13 ± 0.17 and 0.19 ± 0.37 mm, respectively). Mean PES ratings remained stable, varying from 9.07 ± 1.49 at the moment of definitive crown delivery to 8.61 ± 1.55 at 5 years. Only two cases (7%) were considered slightly below the defined threshold (PES = 8) of marginal esthetic acceptability. Conclusions: This study demonstrated that implants placed in anterior atrophic maxillae augmented with mandibular block grafts showed stable hard and soft tissue levels and reasonable esthetic outcomes over the medium term, although ongoing recession of the facial mucosa was observed. Keywords: alveolar ridge augmentation, block graft, bone regeneration, esthetics, peri-implant soft tissue, single-tooth implant

Purpose: To verify, in a medium-term follow-up, whether or not zirconia (Zr) abutments show similar survival outcomes as titanium (Ti) abutments in posterior areas. Materials and Methods: A two-stage surgical protocol was used. Each patient was followed for 5 years after the definitive prosthesis insertion. Clinical and radiographic parameters were assessed at the yearly follow-up visit, and prosthetic complications were recorded. Statistical analysis (Wilcoxon signed rank test) was used to compare any difference in biologic and radiographic parameters between implants and the natural contralateral teeth. Descriptive statistics were used to analyze the changes over time (from baseline to the last follow-up) of clinical and radiographic parameters. Results: A total of 85 patients with a single posterior tooth gap were treated with 85 implants supporting 47 Ti and 38 Zr abutments, respectively. All-ceramic (38) and metal-ceramic (47) single crowns were fabricated. Four patients were classified as dropouts. Eighty-one implants supporting 44 Ti and 37 Zr abutments completed the 5-year follow-up examination. No implant, reconstruction, or abutment failures were recorded. Therefore, the prosthetic survival after 5 years of function was 100% for all the abutments and restorations. No significant differences in biologic and radiographic indexes were found between Ti and Zr abutments when compared with each other and with the natural teeth after 5 years. No significant marginal bone loss was found between the baseline and the last follow-up, both for Zr and Ti abutments. Conclusions: The medium-term survival of Zr abutments in posterior regions was comparable with that of Ti abutments. Long-term evaluations are needed to confirm this finding. Keywords: zirconia abutments, titanium abutments, single-tooth fixed prostheses, survival rate

Purpose: To evaluate the biomechanics of a novel implant placement distribution and compare it with that of conventional maxillary overdenture support using three-dimensional finite element analysis (FEA). The application of zirconia implants in the context of this novel design was also evaluated. Materials and Methods: Detailed FEA models were created to analyze the loading responses of two different distributions of implants to support maxillary overdentures. The two implant distributions were as follows: the conventional design (D1) included four unsplinted implants in the premolar regions, whereas the novel design (D2) included one midpalatal implant, bilateral canine/premolar implants, and one anterior off-center crestal implant. Anatomical models were created with computed tomographic data and static loads were applied axially and obliquely. Von Mises stresses and equivalent strains generated in peri-implant bone and first principal stresses in the implants were calculated, including any denture displacement. Results: Comparable stress and strain values were seen in the peri-implant bone for both designs. A significant decrease in the first principal stresses of D2 implants was observed with oblique loads. The maximum equivalent strain produced in the peri-implant region was mostly within the range for bone augmentation. D2 displayed lower maximum displacement values than D1. Maximum tensile stresses in the zirconia implants for either design were well below their fracture strength. Conclusions: A novel four-implant distribution involving midpalatal and crestal implants may be an alternative to the conventional design used for maxillary overdentures. This is particularly relevant when anatomical considerations prevent the placement of four anterior crestal implants. Zirconia implants may also be a valid option for a selected group of patients or for those requesting metal-free restorations. Prospective clinical studies are required to confirm these in vitro results.

Purpose: This preliminary study was performed to evaluate a proposed maxillary expansion treatment method for adults with fused intermaxillary sutures. Materials and Methods: This study was performed in three Thiel-fixed skulls from older female cadavers with a microimplant-supported expansion screw. This modified expansion screw was mounted on the palatine process with microimplants and activated every 15 to 20 seconds with an activation key until the intermaxillary suture ruptured. A strain gauge was bonded to the expansion screw and calibrated so it could be used as a force sensor device. Rupture of the intermaxillary suture was indicated by a sudden drop in the registered force, through visible opening of the suture, and via computed tomographic data. Finite element simulations were performed, which led to the experimental testing. Results: Rupture of the intermaxillary suture was achieved in all three experiments with the microimplantsupported screw. The strain measurement on one of the expansion screws resulted in an expansion force of 86 N. Finite element simulations showed a high tensile stress concentration exerted by the microimplantsupported expansion screw on the intermaxillary suture. Conclusion: The applied expansion force led to high tensile stress concentrations, mainly on the intermaxillary sutures, resulting in the opening of fused intermaxillary sutures. This method may help adults to be treated by an orthodontist, thereby avoiding surgical intervention.

Purpose: To evaluate the mechanical properties and behavior of a self-locking taper connection with three different techniques: three-dimensional finite element analysis (FEA), ultimate failure loading, and cyclic loading analysis. Materials and Methods: The implant-abutment complex was embedded vertically in the center of an acrylic resin support block (Young's modulus > 3 GPa). All materials used in this study were assumed to be homogenous and isotropic, but while the resin was assumed to be linearly elastic, the titanium was assumed to have a multilinear behavior to better represent the implant system in its plastic phase and to compare as closely as possible the numeric simulation with the experimental tests. An 800-N 30-degree off-axis load was applied to the occlusal surface of the abutment. In addition to the FEA, static and dynamic tests were carried out. Results: The greatest von Mises stresses were concentrated in the coronal portion of the abutment's tapered connection, while at the implant neck they were lower and less extensive than the abutment ones. Experimental results confirmed the FEA findings, in which the structural limit of the system was reached, with permanent deformation of the abutment that exceeded a predefined limit, rather than fracture. Conclusion: Within the limitations of the reported analyses, these static and dynamic tests appear to supply congruent results, thus allowing evaluation of the mechanical behavior of a self-locking taperedconnection implant system. High resistance to an off-axis load was exhibited, exceeding that usually offered by screw-retained implant systems, thus indicating good stability of the implant-abutment connection.

Purpose: The aim of the present study was to evaluate the effect of splinting titanium (Ti) or zirconia (Zr) implants supporting maxillary anterior fixed prostheses on the stress levels and patterns in the implants, prostheses, and the surrounding bone; and to compare the effects of Zr and Ti implant materials on the stress distribution in splinted and nonsplinted designs via finite element modeling. Materials and Methods: Zr and Ti dental implants and the anterior maxilla were modeled. In the nonsplinted design (D1), implants were placed into the maxillary left central incisor and canine regions, and a three-unit zirconia fixed prosthesis was modeled. In the splinted design (D2), a symmetric model of D1 was generated and the two prostheses were splinted together to creat a six-unit prosthesis. Loading was applied horizontally and obliquely. Von Mises, tensile, and compressive stresses were evaluated in the implants, prostheses, and surrounding bone. Results: Under both loading conditions, the stresses on the D2 implants were lower than those in the D1 implants. Stresses were concentrated on the neck of the implant and decreased through the apex. All of the stress values in cortical bone in D1 were slightly higher than in D2 for both implant materials under both loading conditions. Conclusion: When the implants were splinted together, stresses were reduced in the supporting bone and implants in both loading conditions, but increased stress was observed in the prostheses under oblique loading. Intense stress concentrations were found in the connector of the splinted prosthesis and the cervical region of the nonsplinted prosthesis. Zr and Ti implants showed very similar stress distributions in all materials. Under oblique loading, lower stresses occurred in implants and the prosthesis core material when Ti implants were used.

Purpose: There is a variety of implant/abutment (I/A) junctions for the connection of implant-supported prostheses. The aim of this work was to compare the shear stress distribution in three types of I/A interfaces after application of oblique loading on the abutments, simulating loading on an anterior tooth. Materials and Methods: Similar wide unthreaded and cylindric implants (13.0 mm in length and 5.0 mm in diameter) and abutments were fabricated and embedded in photoelastic acrylic resin. The I/A assemblies featured three different I/A interfaces: external hex, internal hex, and internal taper. The samples were submitted to a compressive load of 0.6 kgf, which was applied to the abutment at an angle of 135 degrees. The maximum shear stresses were determined and observed at 21 points around the implants in the photoelastic models (n = 4). Graphics describing the maximum shear stress (y-axis) and the analyzed points (x-axis) were created, and the curve areas were calculated. The Kruskal-Wallis test was applied to analyze the results (P .05). Results: There were no statistically significant differences between the groups (P = .058). Conclusion: All of the wide-diameter I/A junctions presented similar behavior under oblique loading and appeared to be suitable to support prostheses that could receive this type of loading.

The removal of nonretrievable implant components represents a challenge in implant dentistry. The mechanical approach involves the risk of damaging the implant connection or the bone-to-implant interface. This case report describes a cryo-mechanical approach for the safe removal of a nonretrievable implant component. A patient had an implant surgically placed in a private practice. When the patient returned to the restorative dentist to make a definitive impression, the healing abutment could not be loosened. The patient was referred to the Division of Fixed Prosthodontics (University of Bern, Switzerland), where the stripped screw hole was enlarged with a special drill from a service kit of the implant provider. Although an extraction bolt was screwed into the opening and the torque ratchet was activated, the healing abutment would not loosen. A novel approach was attempted whereby the healing abutment was cooled with dry ice (CO2). The cooling effect seemingly caused shrinkage of the healing abutment and a reduction of the connection forces between the implant and the nonretrievable component. The approach of creating an access hole for the application of reverse torque via the extraction bolt in combination with the thermal effect led to the successful removal of the blocked component. Neither the implant connection nor the bone-to-implant interface was damaged. The combined cryo-mechanical procedure allowed the implant to be successfully restored.