The International Journal of Oral & Maxillofacial Implants, 06/2015

Purpose: To investigate whether the presence of bony septum, thickness of sinus membrane (schneiderian membrane), and residual alveolar bone height affects membrane perforation and the duration of sinus augmentation. Materials and Methods: Preoperative cone beam computed tomography (CBCT) images obtained from patients undergoing lateral sinus augmentation were evaluated for the presence of bony septum, thickness of sinus membrane, and residual alveolar bone height. During the operation, membrane perforation and duration of surgery were noted. The Student t test was used to compare descriptive statistics (mean, standard error) and quantitative variables between groups. The Fisher exact χ² test was used to compare the qualitative data, and Pearson correlation test was used to evaluate the correlation between data. P .05 was considered significant. Results: Data from 57 patients were evaluated. Membrane perforation occurred in 14 patients included in the study and in 8 patients with sinus septum. A significant relationship was found between the presence of septum and membrane perforation during sinus augmentation (P = .014). However, the relationship among other CBCT and intraoperative findings was not significant. Conclusion: Presence of septum in the maxillary sinus increases the risk of membrane perforation, but does not extend the duration of the sinus augmentation. Keywords: CBCT, perforation, sinus augmentation, sinus membrane

Purpose: The aim of this study was to measure the thickness of bone labial and palatal to maxillary anterior teeth on cone beam computed tomographic (CBCT) images and to compare these measurements with direct clinical measurements to determine the reliability and accuracy of CBCT. Materials and Methods: Eighteen healthy subjects were randomly selected from among candidates for immediate implant placement in the anterior maxilla. After extraction, labial bone thickness was measured at 1, 4, and 8 mm from the bone crest. Palatal bone thickness was also measured at 1 and 4 mm from the bone crest. The same measurements were performed on presurgical CBCT images. The CBCT measurements were compared to the direct measurements, and their accuracy and reliability were assessed by Pearson correlation coefficients and intraclass correlation coefficients, respectively. Results: The mean width of labial bone was 0.50 ± 0.32 mm and 0.76 ± 0.37 mm for direct and CBCT measurements, respectively. Average thickness of the palatal bone was 1.16 ± 0.53 mm and 1.41 ± 0.51 mm for direct and CBCT measurements, respectively. The mean absolute error and mean relative error of CBCT measurements compared to direct measurements were 0.28 ± 0.29 mm and 0.60 ± 0.84 mm, respectively. The Pearson correlation between CBCT and direct measurements was 0.795 (P .001) and the intraclass correlation coefficient between direct and CBCT measurements was 0.840. The correlation between the measurement series increased significantly when the measured bone was more than 1 mm thick. Conclusion: CBCT measurements of labial bone mostly overestimated bone thickness. CBCT has relatively good accuracy and reliability for measurement of labial bone thickness when the alveolar bone is thicker than 1 mm. However, most subjects have labial bone thinner than 1 mm; therefore, CBCT could result in large errors in many patients. Keywords: alveolar bone, cone beam computed tomography, dental implants, esthetic zone, reproducibility of results

Purpose: The aim of this study was to compare 3.8- and 4.8-mm abutments submitted to simulations of masticatory cycles to examine whether abutment diameter and cemented vs screw-retained crowns affect torque loss of the abutments and crowns. Materials and Methods: Forty implant/abutment sets were divided into the following groups (n = 10 in each group): (1) G4.8S included 4.8-mm abutment with screwretained crown; (2) G4.8C included 4.8-mm abutment with cemented crown; (3) G3.8S included 3.8-mm abutment with screw-retained crown; and (4) G3.8C included 3.8-mm abutment with cemented crown. All abutments were tightened with torque values of 20 Ncm, and 10 Ncm for screw-retained crowns. Torque loss was measured before and after cycling loading (300,000 cycles). Results: Torque loss of screwretained crowns significantly increased after cycling in abutments of groups G3.8S (P ≤ .05) and G4.8S (P = .001). No difference was noted between the abutments before cycling (P = .735), but G3.8S abutments presented greater torque loss than the other groups after cycling (P = .008). Significant differences were noted in the abutment torque loss before and after cycling loading only for the G3.8C group (P ≤ .05). Conclusion: The abutment diameter affects torque loss of screw-retained crowns and leads to failure during the test; mechanical cycling increases torque loss of abutment screw and screw-retained crowns. Keywords: abutment, cycling loading, dental implants, torque

Purpose: Lateral maxillary sinus floor elevation (LMSFE) is a predictable preprosthetic surgical procedure that is used to overcome the limitations of the atrophied alveolar ridge for the placement of oral implants. Techniques using piezoelectric devices (PEDs) and conventional rotary instruments have been described for LMSFE in the literature, with little information regarding their efficiency in terms of membrane perforation, operating time, and implant outcomes. The aim of this systematic review was to examine the intra- and postoperative events associated with the use of PEDs and conventional rotary instruments for LMSFE. Materials and Methods: This systematic review was prepared according to the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The literature was searched for studies comparing the use of PEDs with conventional rotary instruments for LMSFE. The Cochrane Collaboration risk of bias tool was used to assess the studies selected, and meta-analyses were performed using statistical software. Results: A total of 124 citations were identified. Of these, four studies with 178 LMSFEs in 120 participants were included. The pooled estimates for the risk of sinus membrane perforation did not show any significant difference between the two surgical techniques (risk ratio, 0.87; 95% confidence interval, 0.40-1.91; P = .73). Similarly, no significant difference in implant failure was found after 1 year of functional loading. The overall meta-analysis showed a statistically significant difference in the operating time between the two techniques with more time required for PED. Conclusion: The intra- and postoperative events associated with the use of PEDs and conventional rotary instruments for LMSFE are comparable. Keywords: dental implants, maxillary sinus floor elevation, meta-analysis, piezosurgery, review

Purpose: The objective of this study was to evaluate stiffness, strength, and failure modes of monolithic crowns produced using computer-aided design/computer-assisted manufacture, which are connected to diverse titanium and zirconia abutments on an implant system with tapered, internal connections. Materials and Methods: Twenty monolithic lithium disilicate (LS2) crowns were constructed and loaded on bone level-type implants in a universal testing machine under quasistatic conditions according to DIN ISO 14801. Comparative analysis included a 2 × 2 format: prefabricated titanium abutments using proprietary bonding bases (group A) vs nonproprietary bonding bases (group B), and customized zirconia abutments using proprietary Straumann CARES (group C) vs nonproprietary Astra Atlantis (group D) material. Stiffness and strength were assessed and calculated statistically with the Wilcoxon rank sum test. Crosssections of each tested group were inspected microscopically. Results: Loaded LS2 crowns, implants, and abutment screws in all tested specimens (groups A, B, C, and D) did not show any visible fractures. For an analysis of titanium abutments (groups A and B), stiffness and strength showed equally high stability. In contrast, proprietary and nonproprietary customized zirconia abutments exhibited statistically significant differences with a mean strength of 366 N (Astra) and 541 N (CARES) (P .05); as well as a mean stiffness of 884 N/mm (Astra) and 1,751 N/mm (CARES) (P .05), respectively. Microscopic cross-sections revealed cracks in all zirconia abutments (groups C and D) below the implant shoulder. Conclusion: Depending on the abutment design, prefabricated titanium abutment and proprietary customized zirconia implant-abutment connections in conjunction with monolithic LS2 crowns had the best results in this laboratory investigation. Keywords: abutment connection, dental implants, DIN ISO 14801, failure mode, lithium-disilicate (LS2), stiffness, strength, titanium, zirconia

Purpose: The aim of this study was to compare the osteoconductive potential and bone-healing pattern of biphasic calcium phosphates (BCPs) with varying compositions produced using different processing methods. Materials and Methods: Ten male New Zealand white rabbits were used. Four circular defects with a diameter of 8 mm were made in the rabbit calvarium. Each defect was assigned to one of the following BCP groups: control; BCP1, 70% hydroxyapatite (HA)/30% β-tricalcium phosphate (β-TCP); BCP2, 30% HA/70% β-TCP; and BCP3, 20% HA/80% β-TCP. The rabbits were killed either 2 (n = 5) or 8 weeks (n = 5) before surgery. Histologic and histomorphometric analyses were conducted. Results: The total amount of augmentation was significantly greater in the BCP groups than in the control group (P .05). The amount of new bone formation did not differ significantly among the groups at either 2 or 8 weeks. The resorption of BCPs was significantly greater in the BCP3 group than in the BCP1 and BCP2 groups at 2 weeks, but the difference became insignificant compared with the BCP2 group at 8 weeks. The patterns of new bone formation and material resorption varied markedly among the BCP groups. New bone lined the residual particles in the BCP1 group, but filopodia-shaped new bone was observed in the BCP2 group, and collagen fragments were scattered inside the residual particles in the BCP3 group. Multiple cracklike lines were observed on the particles in the BCP3 group. Conclusion: The specific HA-β-TCP ratios in the present study did not significantly influence new bone formation and space maintenance. The observed differences in healing patterns between the groups may be attributable to different physicochemical properties conferred upon the BCPs by the different processing methods used to produce them. Keywords: bone regeneration, bone substitutes, calcium phosphates

Purpose: The aim of this study was to investigate the accuracy of linear measurements from cone beam computed tomography (CBCT) images and digital panoramic radiographs at various implant sites. Materials and Methods: Fifty implant sites from six skulls were marked with gutta-percha and subjected to CBCT with five different voxel protocols: 0.125 mm, 0.160 mm, and 0.250 mm with the 3D Accuitomo 170 CBCT machine and 0.200 mm and 0.300 mm with the CS 9500 CBCT machine. Images were also taken with the CS 9000 panoramic machine with three protocols: normal head, chin-up, and chin-down positions. Electronic linear measurement of bone height using the corresponding machine's software was recorded by two observers. Physical measurement using a digital caliper with ± 0.02-mm accuracy was directly recorded at the corresponding regions as the gold standard. All image measurements were compared with the physical measurements. The paired sample correlations for physical measurement, mean difference, standard deviation, absolute error, absolute percentage error, and inter- and intraobserver reliability were calculated. Results: Intraobserver and interobserver reliability was more than 0.99. Paired sample correlation between all image measurements and physical measurements was considered statistically significant at P .05. All image measurements were underestimated by less than 2 mm, except for the chin-down position of the maxilla in the panoramic radiograph. The absolute error and absolute percentage error in the mandible were less than those in the maxilla, and values obtained with CBCT were less than those from panoramic radiographs. Conclusion: CBCT images using the 3D Accuitomo 170 and CS 9500 machines and digital panoramic radiographs via a picture archiving and communication system are sufficiently accurate for vertical linear measurements in dental implant treatment planning. Keywords: CBCT, cone beam CT, dental implant, digital panoramic radiography, linear measurement accuracy, PACS

Purpose: To evaluate the host β-globin gene fragment lengths in the cell-free peri-implant crevicular fluid (PICF) during the wound healing process. Materials and Methods: Nineteen patients (25 implants) were recruited into this study. As part of the control group, gingival crevicular fluids (GCF) from healthy teeth were collected before implant placement. PICF specimens from each implant were collected during weeks 2 to 12 after implant placement. All GCF and PICF specimens were centrifuged to collect the supernatant as cell-free DNA. Five primer pairs specific to the β-globin gene for amplifying 110-base pair (bp), 325-bp, 408-bp, 536-bp, and 2-kilo-base pair (kb) amplicons were used to evaluate DNA fragment lengths with conventional polymerase chain reaction (PCR). The longest PCR amplicon of each specimen was recorded. Results: The number of 536-bp amplicons (10 of 25 implant specimens) and 2-kb amplicons (8 of 25 implant specimens) in week 2 was higher than at the other visits. In the study, the mucositis group showed the highest number of 536-bp amplicons (22 of 34 implant specimens) and 2-kb amplicons (12 of 34 implant specimens), whereas the healthy implant group showed a low number of 536-bp amplicons (3 of 66 implant specimens), and the cell-free PICF specimens had no 2-kb amplicons. Furthermore, 325-bp and 110-bp amplicons were similar in number in the control teeth and healthy implants. Conclusion: There was a difference in the number of the longest amplicons of cell-free PICF specimens between the mucositis and healthy implant groups. This pilot study suggests that the PCR amplicon lengths of β-globin gene fragments in cell-free PICF specimens might be used as a biomarker to monitor soft tissue inflammation around implants. Keywords: cell-free DNA, DNA fragment lengths, mucositis, peri-implant crevicular fluid

Purpose: The purpose of this pilot study was to evaluate the behavior of stresses surrounding orbital model implants subjected to a load of a silicone oculo-palpebral prosthesis. Materials and Methods: A photoelastic model was constructed mimicking the orbital cavity of an adult patient who underwent left orbital resection. Two 3.75 × 5-mm extraoral implants with 3.75 × 5.25-mm magnetic connectors were placed in the model to anchor a silicone oculo-palpebral prosthesis. The stress generated by prosthesis retention was evaluated using photoelasticity at 15, 30, and 60 minutes. The polariscope images were analyzed qualitatively at five areas surrounding the implants. These same areas were analyzed quantitatively using Matlab software based on the RGB color pattern. Data were compared with the Wilcoxon test. Results: Using fringe localization, the qualitative analysis demonstrated that the area between the implants had the greatest stress. The quantitative analysis showed that the peri-implant stress increased significantly in proportion to the increase in prosthesis retention time. Conclusion: The oculo-palpebral prosthesis generated stress around the implants, and the stress intensity was directly proportional to the duration of use. Keywords: extraoral implant, oculo-palpebral prosthesis, photoelasticity, stress analysis

Purpose: To determine the effect of maintaining torque after mechanical cycling of abutment screws that are coated with diamondlike carbon and coated with diamondlike carbon doped with diamond nanoparticles, with external and internal hex connections. Materials and Methods: Sixty implants were divided into six groups according to the type of connection (external or internal hex) and the type of abutment screw (uncoated, coated with diamondlike carbon, and coated with diamondlike carbon doped with diamond nanoparticles). The implants were inserted into polyurethane resin and crowns of nickel chrome were cemented on the implants. The crowns had a hole for access to the screw. The initial torque and the torque after mechanical cycling were measured. The torque values maintained (in percentages) were evaluated. Statistical analysis was performed using one-way analysis of variance and the Tukey test, with a significance level of 5%. Results: The largest torque value was maintained in uncoated screws with external hex connections, a finding that was statistically significant (P = .0001). No statistically significant differences were seen between the groups with and without coating in maintaining torque for screws with internal hex connections (P = .5476). Conclusion: After mechanical cycling, the diamondlike carbon with and without diamond doping on the abutment screws showed no improvement in maintaining torque in external and internal hex connections. Keywords: dental implant, implant screw, torque

Purpose: Whereas bone is anisotropic, nearly all previous mechanical analyses of implants assumed bone as an isotropic material. Another means to simplify a simulation of the biomechanics of the implant-bone interface is the assumption of complete or no osseointegration; in clinical reality, an implant never achieves 100% contact with the surrounding bone. This study evaluated different thread profiles while not taking into account these two common simplifications. This study sought to (1) investigate the effects of various implant thread designs on stress distribution in the peri-implant bone, (2) appraise previous efforts in this area, and (3) find an optimum basic thread-form design. Materials and Methods: Through finite element analysis, four different basic commercial thread-form configurations for a solid screw-type implant were modeled: buttress, reverse buttress, V, and square. Bone was assumed to be transversely isotropic, and various degrees of osseointegration were simulated. Results: Simulations showed that von Mises stresses were more distributed in the mesiodistal direction. Additionally, maximum stresses were concentrated at the cervical cortical bone region and the first thread. Moreover, in most of the models, von Mises stresses gradually increased in the supporting structure when the degree of osseointegration increased. Conclusion: The use of different thread designs and various osseointegration conditions did not affect the stress distribution patterns in the supporting bone. In this study, square threads showed the most favorable results according to the predicted values of von Mises equivalent stress, pressure, different shear stresses, and micromotion. Keywords: bone anisotropy, dental implants, finite element analysis, osseointegration, thread design

Purpose: The purpose of this study was to examine the influence of reinforcement of an embedded cast on the strains within maxillary implant overdentures. Materials and Methods: A maxillary edentulous model with implants placed bilaterally in the canine positions, dome-shaped copings, and experimental overdentures was fabricated. Rosette-type strain gauges were attached in the canine positions and at three points along the midline of the polished surface of the denture and connected to the sensor interface controlled by a personal computer. Experimental dentures with five different reinforcements were tested: without reinforcement; with a cast cobalt-chrome reinforcement over the residual ridge and the tops of the copings; with the same reinforcement from first molar to first molar, over the residual ridge and the tops of the copings; with the same reinforcement over the residual ridge and the sides of the copings; and with the same reinforcement from first molar to first molar, over the residual ridge and the sides of the copings. A vertical occlusal load of 49 N was applied to the first premolar and then to the first molar, and the strains were measured and compared by analysis of variance. Results: In both loading situations, significantly less strain was recorded in dentures with reinforcement than in those without reinforcement. When the first premolar was loaded on dentures with and without palatal reinforcement at the first premolars, the strains on the denture with reinforcement over the tops of the copings were significantly lower than on the denture with reinforcement over the sides of the copings at the canine position. Conclusion: Cast reinforcement over the residual ridge and the top of copings embedded in an acrylic base reduced the strain from occlusal stress on maxillary implant overdentures. Keywords: load, maxillary implant overdenture, reinforcement, strain

Purpose: To evaluate whether resonance frequency (RF) analysis combined with modal damping factor (MDF) analysis provides additional information on dental implant healing status. Materials and Methods: In in vitro tests, epoxy resin was used to simulate the implant healing process. The RF and MDF values of the implants were measured during the entire polymerization process. Implant stability quotient (ISQ) and Periotest values (PTVs) from Ostell and Periotest devices were used to validate the apparatus. In in vivo experiments, vibrational analysis was performed on 17 dental implants in 12 patients. The RF and MDF values of the tested implants were recorded during the first 10 weeks after surgery. The effects of jaw types and primary stability on MDF healing curves were analyzed. Results: In the in vitro model, the RF values obtained from the apparatus used in this study were similar to those obtained from the Osstell device. Unlike the Periotest healing curve, the MDF curve showed a 1.8-fold increase during the early phase. In clinical experiments, the mean RF values were unchanged during the first 2 weeks and increased continuously until 6 weeks. The corresponding mean MDF value decreased over time and reached 0.045 ± 0.011 at 10 weeks, which is approximately 50% lower than the initial value. Although the RF values of the implants with higher initial frequency remained unchanged during the healing period, the MDF values decreased significantly. Conclusion: Analysis of RF combined with MDF provides additional information on dental implant healing status. MDF analysis can detect changes in the implant/bone complex during the healing period even in implants with higher RF values. Keywords: implant, modal damping factor, osseointegration, vibration analysis

Purpose: To clarify the antimicrobial efficacy of zinc chloride (ZnCl2) and cetylpyridinium chloride (CPC) by testing their impact on the growth of seven bacterial strains known to be involved in the pathophysiology of both peri-implant disease and halitosis-Staphylococcus aureus, Streptococcus mutans, Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum, Treponema denticola, and Tannerella forsythia. Materials and Methods: A time-response growth curve was obtained. Commercial mouthrinses with CPC, ZnCl2, or both were added to the media in a final concentration of 0.25% CPC, 2.5% ZnCl2, and 2.5% ZnCl2 with 0.25% CPC. Results: Both CPC and ZnCl2 effectively inhibited the growth of almost all bacterial strains tested except T denticola. ZnCl2 was generally more effective in suppressing bacterial growth than CPC. ZnCl2 with CPC showed the greatest inhibitory activities on almost all strains of bacterial growth except for P gingivalis and T denticola, followed by ZnCl2, then CPC, thus suggesting the possibility of a synergistic effect of the two agents. P gingivalis exhibited a different pattern because ZnCl2 showed the most significant inhibitory effect. CPC did not show growth inhibitory effects on T denticola, but ZnCl2 did. Conclusion: Zinc and CPC effectively inhibit bacterial growth that causes both halitosis and peri-implant disease. The effect is even more powerful when applied in combination. Keywords: bacterial growth, cetylpyridinium chloride, halitosis, peri-implant disease, zinc chloride

Purpose: To retrospectively analyze the survival rate of endosseous dental implants placed in the edentulous or partially edentulous mandible over a long-term follow-up period of 10 years or more. Materials and Methods: The charts of patients who underwent mandibular implant placement at a private prosthodontic practice and received follow-up care for 10 years or more were included in this study. Implants were examined according to the following study variables: patient sex, patient age, degree of edentulism (fully vs partially edentulous), implant location, time of loading (delayed vs immediate), implant size and type, bone quality, prosthesis type, and the presence of other implants during placement. Results: The study sample was composed of 2,394 implants placed in 470 patients with 10 to 27 years of follow-up. Of these 2,394 implants, 176 failed, resulting in an overall cumulative survival rate (CSR) of 92.6%. A total of 1,482 implants were placed in edentulous mandibles, and 912 implants were placed in partially edentulous mandibles, with CSRs of 92.6% and 92.7%, respectively. Comparisons of the study variables with respect to CSR were largely nonsignificant. However, there were significant differences in CSRs between anterior vs posterior locations and rough- vs smooth-surfaced implants in addition to some prosthesis types, ages, and bone qualities. The overall CSR of 92.6% in the present study is high and comparable to survival rates observed in previous long-term analyses of mandibular implants. The significant differences observed between implant locations, patient age groups, bone qualities, and prostheses were not suggestive of any remarkable trends. Conclusion: Patient sex, age, degree of edentulism, implant location, time of loading, implant size and type, bone quality, prosthesis type, and the presence of multiple implants did not result in any significant effect on long-term implant survival. The CSR observed after 10 to 27 years of follow-up in a single private prosthodontic center was high (92.6%) and supports the use of endosseous dental implants as a long-term treatment option for the rehabilitation of the edentulous and partially edentulous mandible. Keywords: dental implants, life-history analysis, long-term study, mandibular rehabilitation, osseointegration, survival rates

Purpose: Cementation of implant-supported restorations poses two major challenges: (1) minimizing excess cement (reducing the risk of peri-implantitis), and (2) establishing sufficient retention (reducing the risk of decementation). This study presents the first data on a clinical cementation technique that might address both problems. Materials and Methods: Between 2011 and 2013, 39 patients were provided with 52 implants supporting 52 single crowns (SCs). All restorations were cemented extraorally using replicas made of pattern resin and zinc oxide cement. All decementation events and the peri-implant soft tissue status were assessed and compared with those from a group of 29 patients with 40 conventionally cemented SCs (control). Results: In the experimental group, after 12 months, decementation was recorded in three individuals (7.69%) with 3 SCs (5.77%). In the control group, after 12 months, no case of decementation was recorded. No cases of peri-implantitis were detected in either group. Conclusion: Within the limitations of this study, the authors conclude that the use of zinc oxide cement initially establishes sufficient retention of implant-supported fixed restorations independent of conventional or replica cementation techniques. Keywords: decementation, dental implant, excess cement, single crowns, zinc oxide-noneugenol cement

Purpose: To determine the level of bacterial contamination in immediate implantation or augmentation sites vs pristine bone, before and after saline rinses. Materials and Methods: Bacterial samples were taken from fresh extraction sites (17 patients) and pristine bone (15 patients) before performing implant dentistry surgical procedures. Levels of bacterial contamination were estimated before and after saline rinses. Samples from the socket were placed on an agar plate for total bacterial account and on selective plates for Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis counts. Results: The level of bacterial contamination before saline rinse was 1.2 × 104 units of bacterial colony (CFU)/mL in fresh extraction sites (study group) and 5 × 102 CFU/mL in pristine bone sites (control group). After a saline rinse, the bacterial level was lowered significantly to 5.2 × 103 CFU/mL in the study group and to zero in the control group (P .05). Levels of bacterial contamination were higher in the mandibular sockets (7.5 × 103 CFU/ml) than in the maxillary sockets (5.6 × 103 CFU/mL), and the difference was statistically significant (P = .034). All implanted/augmented fresh or pristine sites survived in the followup period. Conclusion: Fresh extraction sockets with clinical signs of infection show bacterial presence. Pristine bone shows a lower bacterial level. Saline rinse in addition to a decontamination protocol may reduce the level of bacterial contamination significantly both in fresh extraction sites and pristine bone. Keywords: bacterial contamination, immediate implantation and augmentation sites, pristine bone sites

Purpose: To evaluate crestal bone changes around implants with platform-switched abutments placed 1 mm subcrestally in a prospective clinical investigation. Materials and Methods: Forty consecutive systemically healthy patients (mean age ± standard deviation [SD], 55.2 ± 8.7 years) with one or more missing teeth were consecutively treated with 1-mm subcrestally positioned, platform-switched, tapered, full treated implants restored with coded abutments. A total of 58 implants were placed. Final restorations were delivered 4 to 8 months after implant insertion. Digital standardized periapical radiographs using customized film holders were obtained at the time of implant insertion, and at 12 and 24 months after final prosthesis placement. Marginal peri-implant bone levels were measured at the mesial and distal surfaces of each implant using digital image software. Results: All implants osseointegrated and were clinically stable at the 2-year followup. The cumulative survival rate was 100%. From implant insertion to the 2-year follow-up, the mean bone loss was 0.32 ± 0.37 mm. No significant differences related to sex, implant site, and bone density were observed. The mean midbuccal and interproximal soft tissue margin positions were 1.13 ± 0.5 mm and 1.15 ± 0.6 mm coronal to the prosthetic finish line, respectively. Conclusion: There is limited clinical information regarding the amount of marginal bone loss around two-piece platform-switched implants placed at subcrestal positions. Results of this study suggest that platform switching and subcrestal location of the implant-abutment interface may be effective in reducing bone loss and in preserving esthetics around dental implants. Keywords: bone preservation, crestal bone level, dental implant, platform switching

Purpose: It has been suggested that functional loading and light irritative stimuli could lead to changes in bone architecture, shape, and volume, and that by placing implants in the edentulous mandible and subsequently loading them, functional conditions could be created to limit bone resorption or even stimulate bone apposition (the latter was reported only for fixed implant-supported prosthetic reconstructions) in the distal area of the mandibular osseous crest. The aim of this study was to radiographically assess the bone height changes in the posterior area of the mandible after implant placement and loading with an overdenture on two or four implants over a mean follow-up period of 10.5 years. Materials and Methods: Panoramic radiographs were taken of 82 totally edentulous patients before implant placement and at repeated follow-up intervals spread over a mean observation time of 10.5 years. All patients received an implant-supported overdenture as prosthetic treatment. The mandibular bone height in the distal part of the mandible was measured on each of the available radiographs and the initial, intermediate, and final values were compared. Results: A mean mandibular bone height reduction of 0.5 mm was measured. Conclusion: No clinically relevant difference was found between the posterior mandible height before implant placement and at follow-up after functional loading with an implant-supported mandibular overdenture. Keywords: bone height changes, implant-supported overdenture, radiographic assessment

Purpose: To analyze the axial displacement of external and internal implant-abutment connection after cyclic loading. Materials and Methods: Three groups of external abutments (Ext group), an internal tapered one-piece-type abutment (Int-1 group), and an internal tapered two-piece-type abutment (Int-2 group) were prepared. Cyclic loading was applied to implant-abutment assemblies at 150 N with a frequency of 3 Hz. The amount of axial displacement, the Periotest values (PTVs), and the removal torque values (RTVs) were measured. Both a repeated measures analysis of variance and pattern analysis based on the linear mixed model were used for statistical analysis. Scanning electron microscopy (SEM) was used to evaluate the surface of the implant-abutment connection. Results: The mean axial displacements after 1,000,000 cycles were 0.6 μm in the Ext group, 3.7 μm in the Int-1 group, and 9.0 μm in the Int-2 group. Pattern analysis revealed a breakpoint at 171 cycles. The Ext group showed no declining pattern, and the Int-1 group showed no declining pattern after the breakpoint (171 cycles). However, the Int-2 group experienced continuous axial displacement. After cyclic loading, the PTV decreased in the Int-2 group, and the RTV decreased in all groups. SEM imaging revealed surface wear in all groups. Conclusion: Axial displacement and surface wear occurred in all groups. The PTVs remained stable, but the RTVs decreased after cyclic loading. Based on linear mixed model analysis, the Ext and Int-1 groups' axial displacements plateaued after little cyclic loading. The Int-2 group's rate of axial displacement slowed after 100,000 cycles. Keywords: axial displacement, cyclic loading, dental implant-abutment connection, linear mixed model, settling effect

Purpose: To determine the range of vertical cantilever (VC), real cantilever (RC), and height of the imaginary triangle (h) formed by the bases of the three implant cylinders in full-arch mandibular prostheses supported by three implants. Materials and Methods: The sample comprised 203 patients (147 women, 56 men; mean age, 58 years, range, 37 to 79 years) with full-arch mandibular rehabilitations. Their prostheses were measured in relation to implant placement to characterize numerical values for VC, force arm of the lever system (represented by the distal cantilever or RC), and resistance arm of the system (represented by the height of the imaginary triangle formed by the bases of the three implants). Data were tabulated and means and standard deviations calculated for all measurements. The range of each of the three measurements was then divided into quintiles for characterizing data distribution. Results: The mean (standard deviation) values found were as follows: VC1 = 17.11 (3.39) mm; VC2 = 17.46 (2.89) mm; VC3 = 16.68 (3.16) mm; RC1 = 14.67 (3.90) mm; RC3 = 15.02 (4.15) mm; h = 8.27 (2.96) mm. Conclusion: VC ranged from 7.37 to 26.44 mm, RC ranged from 4.00 to 26.93 mm, and the height of the imaginary triangle formed by the bases of the three implant cylinders ranged from 0.37 to 15.33 mm. Keywords: biomechanics, Brånemark protocol, dental implants, dental prosthesis, implant-supported, mandibular prosthesis

This case report describes the rehabilitation of a patient who had been treated with a hemimaxillectomy, reconstruction with a latissimus dorsi vascularized free flap, and radiotherapy for carcinoma of the sinus some years previously. Limited jaw opening, difficult access through the flap to the bony site, and the very small amount of bone available in which to anchor the implant inspired the development and use of a new "reverse zygomatic" implant. For this treatment, site preparation and implant insertion were accomplished using an extraoral approach. The implant was used along with two other conventional zygomatic implants to provide support for a milled titanium bar and overdenture to rehabilitate the maxilla. Two years later, the patient continues to enjoy a healthy reconstruction. The reverse zygomatic implant appears to show promise as a useful addition to the implant armamentarium for the treatment of the patient undergoing maxillectomy. Keywords: 3D printing, atrophic maxilla, hemimaxillectomy, reverse zygomatic, zygomatic implants

During autogenous mandibular bone harvesting, there is a risk of damage to anatomical structures, as the surgeon has no three-dimensional control of the osteotomy planes. The aim of this proof-of-principle case report is to describe a procedure for harvesting a mandibular bone block that applies a computer-guided surgery concept. A partially dentate patient who presented with two vertical defects (one in the maxilla and one in the mandible) was selected for an autogenous mandibular bone block graft. The bone block was planned using a computer-aided design process, with ideal bone osteotomy planes defined beforehand to prevent damage to anatomical structures (nerves, dental roots, etc) and to generate a surgical guide, which defined the working directions in three dimensions for the bone-cutting instrument. Bone block dimensions were planned so that both defects could be repaired. The projected bone block was 37.5 mm in length, 10 mm in height, and 5.7 mm in thickness, and it was grafted in two vertical bone augmentations: an 8 × 21-mm mandibular defect and a 6.5 × 18-mm defect in the maxilla. Supraimposition of the preoperative and postoperative computed tomographic images revealed a procedure accuracy of 0.25 mm. This computerguided bone harvesting technique enables clinicians to obtain sufficient autogenous bone to manage multiple defects safely. Keywords: bone block, computer-guided surgery, mandibular bone harvesting

Purpose: In spite of their osteoconductive potential, the biomaterials used as substitutes for an autologous graft do not show osteoinductive or osteogenic potential. This study evaluated the association of adult mesenchymal stem cells derived from adipose tissue with xenogenic bone graft in bone regeneration in rabbit calvaria. Materials and Methods: Mesenchymal stem cells were harvested from adipose tissue from 12 animals. These cells, combined with hydroxyapatite, were implanted in 12-mm bilateral bone defects created in the calvaria of six rabbits (test group [TG]), whereas only hydroxyapatite was implanted in the defects created in another group of six animals (control group [CG]). One grafted side of each animal was covered by a collagen membrane. After 8 weeks, the animals were sacrificed, and the region of the bone defects was removed and evaluated using histomorphometry and immunohistochemistry. Results: The TG showed higher amounts (P .05) of vital mineralized tissue and nonvital mineralized tissue, 28.24% ± 6.17% and 27.79% ± 2.72%, respectively, compared with the CG, 13.06% ± 5.24% and 13.52% ± 3.00%, respectively. In TG, no difference was observed (P > .05) in the amount of mineralized tissue between the side that was covered by the membrane vs the side without membrane coverage. On the other hand, a statistically significant difference (P .05) was observed in the CG with regard to the amount of mineralized tissue between the sides with and without membrane coverage. Conclusion: These observations suggest that the association of mesenchymal stem cells derived from adipose tissue with a xenogenic bone graft was capable of promoting better bone regeneration compared with the use of a xenograft alone. Use of a membrane did not produce an increase in the regenerative potential for the TG, in contrast to the CG. Keywords: bone healing, bone marrow, cell transplantation, osteogenesis, stem cells

Purpose: The effectiveness of rapid maxillary expansion is adversely affected by failure and relapse. It is important to identify key factors that increase new bone formation and improve bone remodeling of midpalatal sutures to improve the stability and effectiveness of this commonly used orthodontic procedure. Peroxisome proliferator-activated receptor gamma (PPARγ) plays an important role in modulating osteogenesis and bone resorption in long bones. This study was designed to explore the function of PPARγ in bone remodeling and tissue engineering of midpalatal sutures. Materials and Methods: Pioglitazone, a PPARγ agonist, and osteoclast PPARγ knockout mice were used to explore the impact of PPARγ activation and inactivation, respectively, on bone remodeling in a mouse model of midpalatal suture expansion (MSE). Histologic analysis including staining with hematoxylin-eosin, tartrate-resistant acid phosphatase, and alkaline phosphatase was used to evaluate tissue remodeling. Reverse-transcriptase quantitative polymerase chain reaction was used to measure gene expression. Results: Pioglitazone decreased new bone formation after MSE. This was accompanied by an increased amount of osteoclasts and expression of genes promoting osteoclastogenesis, as well as a decreased amount of osteoblasts and expression of genes promoting osteoblastogenesis in midpalatal sutures. Conversely, osteoclast PPARγ knockout mice increased new bone formation and decreased the amount of osteoclasts and expression of genes promoting osteoclastogenesis. Conclusion: In the process of bone remodeling after MSE, PPARγ, particularly in osteoclasts, is an important regulator of osteoblast and osteoclast homeostasis and bone remodeling in midpalatal sutures. Blockade of PPARγ might be an effective strategy to improve stability and decrease relapse in the practice of rapid maxillary expansion. Keywords: bone remodeling, midpalatal suture expansion, osteoblast, osteoclast, peroxisome proliferator-activated receptor gamma

Purpose: The aim of this prospective controlled study was to evaluate the influence of osteopenia on the levels of osteoclastogenesis-related factors in the peri-implant crevicular fluid (PICF) and on the clinical parameters of immediately loaded implants. Materials and Methods: This study included 24 patients who received at least two implants in the mandible, with restorations delivered 48 hours after implant placement. Patients were divided into control (n = 11) and osteopenia (n = 13) groups. Seven days after implant placement (baseline) and 4 months after implant placement, PICF samples were obtained, and clinical parameters (Plaque Index, Gingival Index, bleeding on probing, suppuration, probing depths, clinical attachment levels) were measured. A commercially available enzyme-linked immunosorbent assay was used to analyze PICF samples for levels of soluble receptor activator of nuclear factor of κB ligand (sRANKL) and osteoprotegerin (OPG). At the 4-month follow-up visit, the implant-supported restorations were removed and periapical radiographs were acquired to evaluate bone loss around the implants. Results: Eighty-eight immediately loaded implants were included in this study (38 in the control group, 50 in the osteopenia group). The RANKL and OPG levels, the RANKL/OPG ratio, and the clinical parameters were similar between the groups at both time points. However, the levels of these factors in PICF differed significantly between baseline and 4 months after surgery. Conclusion: Within the limitations of this short-term study, it can be concluded that osteopenia does not influence the PICF levels of osteoclastogenesis-related factors in immediately loaded implants after 4 months of loading. Keywords: dental implants, dental implant loading, immediate loading, osteopenia, osteoporosis, osteoprotegerin, RANK ligand, receptor activator of nuclear factor-kappa B