The International Journal of Oral & Maxillofacial Implants, 02/2019

Purpose: Good cell adhesion is an important prerequisite for soft tissue attachment on implant abutment or crown surfaces. The aim of this study was to evaluate the adhesion and proliferation of human epithelial cells on sol-gel-derived TiO₂-coated and noncoated zirconia. Materials and Methods: Altogether, 56 zirconia disks (Z-CAD, Metoxit) were fabricated for this study. Half of the disks were coated with a sol-gel-derived TiO₂ coating (MetAlive, ID Creations). The rest of the disks were noncoated and formed the control group. Surface properties of the disks were characterized by contact angle measurements and surface free energy (SFE) calculation. The cell adhesion was tested by cultivating epithelial cells (20,000 cells/cm²) on the experimental disks for 1, 3, 6, and 24 hours, after which the fluorescence of the samples was measured (BioTek synergy HT). The amount of cells was detected by comparing the fluorescence value to the standard curve. In addition, the proliferation was studied by growing epithelial cells (25,000 cells/cm²) for 1, 3, and 7 days. The number of cells was calculated by defining the absorbance of the samples (Multiskan EX, Thermo Labsystems), followed by a comparison with the standard curve. Finally, the samples were processed for light microscopy. Results: TiO₂-coated disks were significantly more hydrophilic with higher total SFE than noncoated disks (P .05). The amount of epithelial cells was greater on TiO₂-coated disks than on controls after 24 hours (P .05). Regarding cell proliferation, the difference was statistically significant (P .05) on days 3 and 7. Light microscope evaluation confirmed viable cells, which were in immediate close contact with both substrate surfaces. The cell layers on the coated disks appeared to be more uniform and cell rich than the layers on noncoated disks. Conclusion: This study indicated that TiO₂ coating improves epithelial cell attachment and proliferation on zirconia surfaces. This has good potential to enhance formation of the epithelial junction to the coated zirconia surfaces. Keywords: abutment, epithelial cell, hydrophilicity, implant, sol-gel coating, TiO2

Purpose: To evaluate the effect of misfit at implant-level fixed partial dentures (ILFPDs) and marginal bone support on the generation of implant cracks. Materials and Methods: This in vitro study included a mechanical fatigue test and finite element analysis. A mechanical cycling loading test was performed using 16 experimental models, each consisting of two parallel implants subdivided into four groups based on the misfit and the supporting bone condition. The framework, firmly seated at implants, was dynamically loaded vertically with a force of 1,600/160 N and 15 Hz for 1 × 10⁶ cycles. Optical microscope, scanning electron microscope (SEM), and computed tomography three-dimensional (CT-3D) analyses were performed to detect impairments. Finite element models, representing the setups in the mechanical fatigue test, were used to represent the fatigue life. Results: None of the mechanical components presented distortion or fracture at the macroscopic level during the test. In a microscopy evaluation, the fatigue test revealed scratches visible in the inner part of the conical portion of the implants regardless of the groups. SEM and CT-3D analysis revealed one implant from the misfit/no bone loss group with a microfracture in the inner part of the conical interface. The simulated effective stress levels in the coronal body were higher in the misfit groups compared with the no misfit groups. The misfit groups presented effective stress levels, above 375 MPa, that penetrated the entire wall thickness. The no bone loss group presented an effective stress level above 375 MPa along its axial direction. In the no misfit group, the area presenting effective stress levels above 375 MPa in the conical connection was larger for the bone loss group compared with the no bone loss group. Conclusion: This study confirmed that implant fracture is an unlikely adverse event. A clear pattern of effective distribution greater than fatigue limit stresses could be noticed when the misfit was present. The dynamic load simulation demonstrated that the crack is more likely to occur when implants are fully supported by marginal bone compared with a bone loss scenario. Within the limitations of this study, it is speculated that marginal bone loss might follow the appearance of an undetected crack. Further research is needed to develop safe clinical protocols with regard to ILFPD. Keywords: CAD/CAM, finite element analysis, implant fracture, implant level, misfit

Purpose: To compare the influence of ultraviolet (UV) irradiation and cold atmospheric pressure plasma (CAP) treatment on surface structure, surface chemistry, cytocompatibility, and cell behavior on zirconia in vitro. Materials and Methods: Zirconia samples (TZ-3YSB-E) were treated by UV irradiation, oxygen plasma, or argon plasma for 12 minutes each and compared with the nontreated samples. Surface analysis was conducted using scanning electron microscopy, roughness analysis, and x-ray photoelectron spectroscopy. Cell proliferation, viability, and cell attachment as well as cytotoxicity were evaluated using MC3T3-E1 murine osteoblasts cultivated directly on the zirconia samples. Results: Surface structure and roughness were not affected by the surface treatments. CAP and UV irradiation significantly reduced organic material and increased the surface oxidation on the zirconia samples. Furthermore, CAP and UV treatment significantly decreased the contact angle on the zirconia samples, indicating superhydrophilicity. Cell attachment was significantly increased on oxygen plasma-treated zirconia samples compared with the nontreated samples at all times (P .001). After 24 and 48 hours, cell proliferation and viability (P .001) were significantly increased on oxygen plasma-treated samples in comparison with the nontreated, UV-treated, and argon plasma- treated samples. Neither UV nor CAP treatment led to cytotoxicity. Conclusion: In vitro, surface treatment by UV irradiation or CAP causes a significant reduction of organic material, increases the hydrophilicity of zirconia, and improves the conditions for osteoblasts. The results stipulate that treatment of zirconia surfaces with oxygen plasma may favor cell proliferation. Keywords: cold atmospheric pressure plasma, dental implant, implant surface, photofunctionalization, UV light, zirconia

Purpose: This study investigated the effect of fracture strength and fracture mode characteristics related to reduced interocclusal space on computer-aided design/computer-aided manufacturing (CAD/CAM). ZrO₂ fixed partial denture (FPD) frameworks subjected to quasi-static loads. Materials and Methods: First, two dental implants (4 × 10 mm) were positioned simulating a three-unit FPD (second premolar and second molar abutments). The implants were distributed into two groups: control group (n = 10), positioned at the same level; and the test group (n = 10), where the interocclusal space corresponding to the second molar was reduced by 3 mm in relation to the second premolar to simulate a clinical situation. After FPD wax-up (25-mm long; connector height = 5 mm; connector width = 3 mm, proximal and lingual collar reinforcement), casting was made in a Co-Cr alloy to serve as a prototype. Upon scanning, screw-retained CAD/CAM ZrO₂ FPDs were fabricated for each group. Then, FPDs were subjected to quasi-static axial loading until fracture in the mid-occlusal pontic area using a universal testing machine at the crosshead speed of 0.5 mm/min. Next, the samples were analyzed by scanning electronic microscopy (SEM) to describe the fracture characteristics. Results: The mean fracture strength values for the control group (1,747.4 ± 122.3 N) and test group (1,817.7 ± 158.9 N) showed no significant difference (Student t test, P .124). The SEM images of the fracture sites revealed two cleavage areas in the test group, providing representative sites with increased fracture energy storage in this group compared with the control group. Conclusion: Within the limitations of this study, the results showed that reduced interocclusal space and reduced length did not decrease the fracture strength of the ZrO₂ FPD frameworks. Keywords: CAD/CAM, dental implants, fracture strength, interocclusal space, zirconium oxide fixed partial dentures

Purpose: To evaluate the survival rate of mini implants used to retain mandibular overdentures. Materials and Methods: An electronic search, supplemented by hand searching of the references, was conducted with no time or language restriction in October 2016 and updated in October 2017. The results were reviewed independently by the two authors. All randomized controlled trials, clinical trials, observational studies, and case series were included. The primary outcome measure was implant survival (months). Results: The search retrieved a combined total of 391 articles. Following screening, 17 articles were included. A total of 1,715 mini implants were assessed in 475 patients. Follow-up periods ranged from 6 to 84 months (mean: 28.24 months). There were 75 failures in total. The overall survival rate was 95.63%. The majority of patients received four implants to retain their prostheses. Most studies used a flapless surgical technique, but there were vast differences in loading protocols and retention methods. Formal meta-analysis was not conducted due to the heterogeneity between studies. Conclusion: Based on the findings of this systematic review, mini dental implants exhibit excellent survival rates in the short to medium term. They appear to be a reasonable alternative treatment modality to retain mandibular complete overdentures from the available evidence. Keywords: complete dentures, failure, mini implants, survival, systematic review

Purpose: To radiographically investigate ligature-induced peri-implant bone loss around loaded titanium (Ti-SLA) and zirconia (ZrO₂-ZLA) implants using a canine model. Materials and Methods: Forty sandblasted and acid-etched titanium and zirconia implants were alternately placed in the mandibles of five canines (20 Ti-SLA, 20 ZrO₂-ZLA). Implants were restored after 6 weeks of unloaded healing. After 4 weeks of functional loading, oral hygiene procedures were stopped and experimental peri-implant bone loss was initiated by placing cotton ligatures. After 8 weeks of active progression, ligatures were removed and plaque was allowed to accumulate for another 16 weeks of spontaneous progression (without ligatures). Standardized radiographs were taken at implant placement, at functional loading, and every 2 weeks during active and spontaneous progression of bone loss. Results: Before ligature placement, all implants were successfully osseointegrated and no clinical or radiographic signs of peri-implant infections were detectable. Two weeks after ligature removal, one titanium implant was lost; however, no zirconia implant failures were observed during the study. Radiographically, zirconia implants revealed statistically significantly less crestal peri-implant bone loss compared to titanium implants at the end of the active progression period (Ti-SLA: 3.92 mm; ZrO₂-ZLA: 2.65 mm; P .01); however, no significant differences occurred after the spontaneous progression period (P = .6). Combining the active and spontaneous progression periods together, zirconia implants demonstrated significantly reduced peri-implant bone loss compared to titanium implants (Ti-SLA: 3.76 mm; ZrO₂-ZLA: 2.42 mm; P .01). Conclusion: These results demonstrate a significantly reduced ligature-induced inflammation and bone loss for ZrO₂-ZLA implants compared to Ti-SLA implants in the canine model. Keywords: bone remodeling, dental implants, peri-implantitis, titanium, yttria stabilized tetragonal zirconia, zirconium oxide

Purpose: This study compared the three-dimensional (3D) accuracy of conventional impressions with digital impression systems (intraoral scanners and dental laboratory scanners) for two different interimplant distances in maxillary edentulous arches. Materials and Methods: Six impression systems comprising one conventional impression material(Impregum), two intraoral scanners (TRIOS and True Definition), and three dental laboratory scanners (Ceramill Map400, inEos X5, and D900) were evaluated on two completely edentulous maxillary arch master models (A and B) with six and eight implants, respectively. Centroid positions at the implant platform level were derived using either physical or virtual probe hits with a coordinate measuring machine. Comparison of centroid positions between master and test models (n = 5) defined linear distortions (d_x, d_y, d_z), global linear distortions (d_R), and 3D reference distance distortions between implants (ΔR). The two-dimensional (2D) angles between the central axis of each implant to the x- or y-axes were compared to derive absolute angular distortions (Absdθ_x, Absdθ_y). Results: Model A mean d_R ranged from 8.7 ± 8.3 μm to 731.7 ± 62.3 μm. Model B mean d_R ranged from 16.3 ± 9 μm to 620.2 ± 63.2 μm. Model A mean Absdθ_x ranged from 0.021 ± 0.205 degrees to -2.349 ± 0.166 degrees, and mean Absdθ_y ranged from -0.002 ± 0.160 degrees to -0.932 ± 0.290 degrees. Model B mean Absdθ_x ranged from -0.007 ± 0.076 degrees to -0.688 ± 0.574 degrees, and mean Absdθ_y ranged from -0.018 ± 0.048 degrees to -1.052 ± 0.297 degrees. One-way analysis of variance (ANOVA) by Impression system revealed significant differences among test groups for d_R and ΔR in both models, with True Definition exhibiting the poorest accuracy. Independent samples t tests for d_R, between homologous implant location pairs in Model A versus B, revealed the presence of two to four significant pairings (out of seven possible) for the intraoral scanner systems, in which instances d_R was larger in Model A by 110 to 150 μm. Conclusion: Reducing interimplant distance may decrease global linear distortions for intraoral scanner systems, but had no effect on Impregum and the dental laboratory scanner systems. Impregum consistently exhibited the best or second-best accuracy at all implant locations, while True Definition exhibited the poorest accuracy for all linear distortions in both models A and B. Impression systems could not be consistently ranked for absolute angular distortions. Keywords: 3D accuracy, CMM, dental laboratory scanner, digital impression, implant, intraoral scanner

Purpose: This study evaluated the influence of labial implant inclination on the retention and stability of different resilient stud attachments for mandibular implant overdentures. Materials and Methods: Four identical mandibular edentulous acrylic resin models were fabricated. For each model, two implants were inserted at the canine areas with different degrees of labial inclination: 0, 10, 20, and 30 degrees. Four experimental overdentures were fabricated over the models and fitted to the implants using resilient stud attachments. Regular retentive inserts (extra-light, light, and medium retention) were used for all implant inclinations, and extended-range inserts (extra-light and medium retention) were used for 30-degree inclination only. Vertical (retention) and oblique (stability) dislodging forces (lateral, anterior, and posterior) were evaluated initially (initial retention) and after overdenture insertion and removal (final retention). Results: After repeated insertions and removals, 30-degree inclination recorded the highest retention and lateral stability, and 0 degrees recorded the highest posterior stability; 20 degrees showed the lowest retention, and 30 degrees recorded the lowest posterior stability. The highest stability and retention values were recorded with light and medium regular inserts, and the lowest values were noted with extra-light regular inserts. Conclusion: Within the limits of this study, moderate labial implant inclination (10 degrees and 20 degrees) was shown to negatively affect retention and anterior/lateral stability, and excessive implant inclination (30 degrees) to negatively affect posterior stability. When implants are inclined labially, it is recommended to use light and medium regular stud attachments to obtain high levels of retention and stability for two-implant-retained overdentures. Keywords: attachment, implant, inclination, Locator, overdenture, retention, stud

Purpose: The aim of this study was to evaluate the responses of human gingival fibroblast (HGF-1) in contact with provisional materials with various chemical compositions and fabricated using different methods. Materials and Methods: A total of 210 specimens in eight experimental groups were used. Groups were divided by chemical compositions (poly[ethyl methacrylate], poly[methyl methacrylate], bis-acryl, and hybrid ceramic) and fabricating methods (direct, indirect, and computer-aided design/computer-aided manufacturing [CAD/CAM]). To evaluate the surface characteristics of each group, roughness, water contact angle, and degree of conversion were measured. The responses of HGF-1 to provisional materials were evaluated with cytotoxicity and cell attachment assay. The roughness, surface energy, degree of conversion, level of cytotoxicity, and cell attachment were compared between groups using one-way analysis of variance (ANOVA) and Tukey's multiple comparison (α = .05). Results: The poly(ethyl methacrylate)-direct/indirect and poly(methyl methacrylate)-direct/indirect groups showed higher roughness than the bis-acryl-direct/ indirect, poly(methyl methacrylate)-CAD/CAM, and hybrid ceramic-CAD/CAM groups with statistical significance (P .05). The poly(ethyl methacrylate)-direct group showed the significantly highest water contact angle, and the hybrid ceramic-CAD/CAM group showed the lowest water contact angle (P .05). The groups that used indirect fabrication methods showed a higher degree of conversion than those that used direct fabrication methods, regardless of chemical composition (P .05). The poly(ethyl methacrylate) groups showed significantly lower cell viability than the other groups regardless of fabricating methods (P .05). The poly(ethyl methacrylate)-direct method group showed the lowest cell attachment, and the hybrid ceramic-CAD/CAM method group showed the highest cell attachment (P .05). Conclusion: Poly(methyl methacrylate) and bis-acryl have lower cytotoxicity to HGF-1 than poly(ethyl methacrylate). Indirect fabrication and CAD/CAM are recommended to prevent residual monomer and achieve high cell attachment. To use direct fabrication methods, the auto-mix system is beneficial for the favorable cell response, as it derives a smooth surface. Keywords: dental abutment, dental implants, fibroblast, provisional resin, surface properties

Regulation of cellular function is key to bone formation at endosseous implant surfaces. Osseointegration was "discovered" prior to the discovery of genetic regulation of osteoinduction or characterization of mesenchymal stem cells. Understanding osseointegration in cellular and molecular terms has benefited from genome-wide characterization of this healing process at endosseous implants in vivo. These in vivo studies also demonstrate a role for osteoprogenitor cells and cells involved in immune regulation and osteoclastogenesis. The identification of noncoding RNAs, including microRNAs, as key factors controlling cell function has highlighted the role of microRNAs in cell differentiation control. This review summarizes emerging in vitro and in vivo investigations emphasizing the role of microRNAs in the osseointegration process. Many microRNAs influence key osteoinductive pathways controlling Osterix, runt-related transcription factor 2 (RUNX2), and bone morphogenetic protein (BMP)/SMAD function. Others influence the monocyte/ macrophage lineage. While significant progress has been made in elucidating the mechanisms associated with the regulation of surface modulation of osteoblast differentiation by microRNAs, knowledge gaps are evident in the identification and characterization of microRNAs linked to osseointegration. Given existing knowledge regarding the varied expression of microRNAs and their role in inflammation, it is important to understand how microRNA expression may influence the process of bone accrual at implant surfaces during osseointegration. Keywords: bone remodeling, dental implants, implant surfaces, microRNAs, osseointegration

Purpose: This study aimed to evaluate the safety and efficacy of newly designed, laser-perforated pure titanium membranes for guided bone regeneration and to compare them with an existing product, the FRIOS BoneShield (FBS). Materials and Methods: Acute-type lateral ridge defects were bilaterally created in the mandibles of 13 dogs (two defects per animal). The defects were randomly divided into three groups and were reconstructed with particulate autologous bone (PAB) in combination with three different titanium membranes: (1) F001M0 (prototype without a frame), (2) F001M1 (prototype with a frame), and (3) FBS as a standard membrane. All animals were observed periodically and sacrificed 26 or 27 weeks postoperatively. At 26 weeks, approximately half of the dogs in each group underwent membrane removal to examine the postoperative condition of the titanium membranes. The samples were dissected and processed for radiographic, histologic, and histomorphometric analyses. Results: Membrane exposure was not found in the F001M0 or F001M1 groups, and their membranes were removed easily without adhesion to the surrounding tissue. Regenerated bone tissue volume was largest in the F001M1 group, followed by the F001M0 and FBS groups. A significant difference was observed only between the F001M1 and FBS groups (P = .047). In contrast, bone mineral density was similar among the three groups. Histologically, a layer of fibrous tissue was present underneath the titanium membrane, overlying the regenerated cortical bone in all the groups. Notably, the tissue was highly vascular in the F001M1 and F001M0 groups compared with the FBS group. In addition, there was little difference in the semiquantitative soft tissue evaluation and histologic findings of bone regeneration among the three groups. The histomorphometric analysis revealed that the regenerated bone area was larger in the F001M1 and F001M0 groups than in the FBS group, and a significant difference was observed only between the F001M1 and FBS groups (P = .045). Calcific osseous area was similar among the three groups. Conclusion: The safety and efficacy of both F001M0 and F001M1 were equivalent to or greater than those of FBS, thereby indicating their potential for future clinical applications. Keywords: animal model, barrier membrane, guided bone regeneration, mandible, titanium membrane, ultrafine microperforation

Purpose: This study aimed to perform a systematic review and meta-analysis of the literature on mandibular incisive canal (MIC) studies using cone beam computed tomography (CBCT). Materials and Methods: A PROSPERO-registered systematic review (#42017056619) was conducted following the PRISMA statements to summarize current knowledge on the CBCT aspects of the MIC. A search was performed in PubMed's Medline and Scopus databases, without date or language restrictions, using the algorithm {[(Interforaminal region) OR (mandibular incisive channel) OR (mandibular incisive nerve) OR (mental mandible) OR (anterior mandible) (cone beam computed tomography)]}. Also, the references were crosschecked. The Meta-Analysis of Statistics Assessment and Review Instrument and meta-analysis was used to evaluate the selected studies. Results: A total of 410 articles were found, and 25 studies were selected after a two-step selection process. The CBCT systems differed regarding field of view (FOV) (large, n = 3; medium, n = 2; small, n = 4; not informed, n = 16) and voxel size (0.15 to 0.4 mm). Geographically, the studies were distributed across four continents (South America, North America, Asia, and Europe), and there was a statistical significance of studies from the American and Asian continents (P .0001). From 3,421 CBCT exams, the number of female patients was slightly higher than male, and the mean age ranged from 29.8 to 59.1 years. The overall mean prevalence of MIC was 89.6% ± 15.08%, and bilateral occurrence was statistically significant (P .0001). The studies using a voxel size lower than 0.3 mm showed the highest mean prevalence (93.88%) in comparison with voxel size described as ≥ 0.3 mm (89.33%). Diameter (0.45 to 4.12 mm) and length (6.6 to 40.3 mm) showed great variability among the included studies. Conclusion: The results of this systematic review evidenced a high worldwide prevalence of MIC. There was no prevalence of MIC in relation to sex, and its presence was mainly related to adults between the fourth and sixth decades of life. In addition, great heterogeneity of methodologies was observed. Keywords: cone beam computed tomography, epidemiologic studies, mandibular incisive canal, systematic review

Purpose: The aim of this study was to investigate the in vivo performance, including bone regeneration and biomaterial degradation, of three hydroxyapatite-based bone substitutes at surgically created defects in the cranium of rabbits. Materials and Methods: A bovine-derived hydroxyapatite (BHA), a synthetic hydroxyapatite (SHA), and a nano-hydroxyapatite with collagen I (nHAC) composite were characterized and then placed in calvarial defects in rabbits. After surgery at 6 weeks and 12 weeks, the animals were sacrificed for further microcomputed tomography, histologic, and histomorphometric analyses. The amounts of newly formed bone, residual grafting materials, connective tissues, and tartrate-resistant acid phosphatase staining positive multinucleate cells were evaluated. Results: The three hydroxyapatite-based bone substitutes displayed different surface topography. BHA had the highest amount of newly formed bone at both 6 weeks and 12 weeks, yet no significant difference was found between the three groups at 6 weeks. The amount of residual materials was significantly higher in the SHA group than the other groups at both time points. The amount of connective tissue was highest in BHA. More multinucleated cells were observed in the nHAC group. Conclusion: The three tested bone substitutes are suitable for grafting defects related to early bone healing. BHA had a better impact on bone formation with the prolongation of time. An integration of collagen type I and nano-hydroxyapatite may not improve bone regeneration of pure synthetic hydroxyapatite but helps to modify the degradation rate of pure hydroxyapatite. Keywords: animal experiments, bone regeneration, bone substitute, degradation, hydroxyapatite

Purpose: Only limited information on the effect of implant surface hydrophilicity in conjunction with simultaneous bone augmentation is available. In this study, new bone growth around implants with a superhydrophilic modSLA (SLActive) and hydrophobic SLA (SLA) surface were compared in circumferential defects when grafted in conjunction with mineralized cancellous bone allograft (MCBA, maxgraft) or sintered bovine bone mineral (SBBM, cerabone). Materials and Methods: The osseointegration and bone formation in circumferential defects in minipig mandibles around Straumann Roxolid, Ø 3.3 mm, length 8 mm, either SLA or SLActive, were evaluated. Following implant placement, the 2-mm circumferential defects around the implants were filled with MCBA or SBBM. The distance from the implant shoulder to first bone-to-implant contact (f-BIC), percentage of bone-to-implant contact (BIC), and bone aggregate percentage (amount of new bone and remaining graft) within the defect area were evaluated after 8 weeks of healing. Results: In the SBBM group, lingual f-BIC and buccal BIC were significantly lower for SLA (mean -0.404 ± 0.579 mm for modSLA vs -1.191 ± 0.814 mm for SLA, P = .021, and mean 62.61% ± 9.49% for modSLA vs 34.67% ± 24.41% for SLA, P = .047, respectively). Bone aggregate percentage was significantly higher for modSLA vs SLA implants in SBBM (77.84% ± 6.93% vs 64.49% ± 13.12%, P = .045). The differences between implant surfaces in MCBA showed a similar trend but were less pronounced than in the SBBM group and did not reach a statistically significant level. Conclusion: The results suggest that implants with a superhydrophilic modSLA surface are more conducive to faster osseointegration even in conjunction with simultaneous bone grafting procedures. Keywords: bone graft, guided bone regeneration, histology, hydrophilicity, surface

Purpose: The goal of this study was to compute the estimated cumulative survival and success rates of alumina-toughened zirconia (ATZ) abutments used for external connection-type implant-supported fixed dental prostheses (FDPs) after a mean follow-up of 6.9 years (82.3 months). Materials and Methods: From May 1998 to July 2016, patients who provided informed consent and received implant-supported restorations with ATZ abutments were recruited. Clinical performance of zirconia abutments was evaluated using survival analysis. Failure was defined as the removal of the restoration due to zirconia abutment fracture, and complications included both failure and abutment screw problems. Survival and success were the counterparts of failure and complications, respectively. The effects of restoration-related factors (restored area, type of prosthesis, and implant system) on the survival and success of the abutments were estimated. Results: A total of 231 patients were included in this study. One hundred twenty-six implantsupported single-unit and 204 multiple-unit FDPs were evaluated. All the placed implants had the external hex connection. The estimated cumulative 5-year, 7-year, and 10-year survival rates (95% confidence interval [CI]) of zirconia abutment-supported FDPs were 97.3% (95.5% to 99.1%), 96.8% (94.8% to 98.8%), and 94.1% (90.4% to 97.8%), respectively. The estimated cumulative 5-year, 7-year, and 10-year success rates (95% CI) were 94.1% (91.4% to 96.8%), 90.8% (87.3% to 94.3%), and 80.1% (73.6% to 86.6%), respectively. The type of prosthesis (P = .001) and implant system (P .001) were the significant factors in the success of zirconia abutment-supported FDPs. Conclusion: Prefabricated ATZ abutments have a high predictability of survival at 10 years when used in implant-supported FDPs that replace both anterior and posterior teeth. However, the success of zirconia abutments was significantly influenced by the type of prosthesis and implant system. Keywords: alumina-toughened zirconia abutment, implant-supported fixed restoration, implant system, prosthesis type, survival analysis

Purpose: The management of patients with a severely atrophic or resected maxilla with zygomatic implants can be surgically challenging, but postoperative complications are relatively uncommon. This retrospective cohort study evaluated the percentage survival rates of zygomatic implants placed over an 18-year period. Materials and Methods: This study evaluated patients receiving zygomatic implants in primary-care (specialist referral dental practice) and secondary-care (hospital) settings over an 18-year period. Results: In total, 88 zygomatic implants were placed in 45 patients aged between 42 and 88 years. Of the 88 implants, 54 were immediately loaded. The implant survival rate was 94.32%, with five implants failing during the study period (implant-level cumulative failure rate: 5.68%; mean follow-up: 7.5 years; maximum: 18 years). The failures were not significantly associated with sex, surface finish, implant length, zygomatic anatomy-guided approach (ZAGA) classification, or implant position (all P values > .05). All failed implants were fitted with fixed prostheses. Failures occurred between 6 months and 15 years after placement. Conclusion: This study of zygomatic implants placed in patients with a severely atrophic and resected maxilla confirms that this approach is a predictable method for supporting fixed or removable prostheses up to 18 years, demonstrating high survival rates. Given the low number of failures, no potential risk factors for failure could be identified. Keywords: implant-supported denture, maxilla, survival, zygomatic implant

Purpose: The aim of this clinical study was to evaluate the long-term outcome of the split bone block (SBB) technique for vertical bone augmentation in the posterior maxilla in combination with sinus floor elevation using a tunneling approach. Materials and Methods: Patients were treated for extensive vertical and horizontal alveolar bone defects without simultaneous implant placement and followed up for at least 10 years postoperatively. Autogenous bone blocks were harvested from the mandibular retromolar area following the MicroSaw protocol. The harvested bone blocks were split longitudinally according to the SBB technique. Implants were inserted and exposed after every 3 months, and prosthetic restoration was performed. Results: One hundred forty-two consecutively treated patients, 154 grafted sites, and 356 inserted implants were documented. Minimal graft exposure (1 to 3 mm) 4 to 8 weeks postoperatively was documented in two sites; infection of the grafted area occurred in one other case. The mean preoperative clinical vertical defect was 7.8 ± 3.9 mm, and the mean horizontal width was 3.1 ± 2.2 mm. Postoperatively, the mean vertical gained dimension was 7.6 ± 3.4 mm (maximum: 13 mm), and the mean width was 8.3 ± 1.8 mm. Implants could be inserted in all sites, with additional local small augmentation in 21 cases. The amount of maximum vertical bone resorption was 0.21 ± 0.18 mm after 1 year, 0.26 ± 0.21 mm after 3 years, 0.32 ± 0.19 mm after 5 years, and 0.63 ± 0.32 mm after 10 years. As part of a total patient dropout of 16.9%, four implants were lost within 10 years. The mean vertically gained bone was stable at 6.82 ± 0.28 mm (maximum: 12 mm). The resorption rate after 10 years was 8.3%. Conclusion: The described tunneling flap approach allows a hermetic soft tissue closure, characterized by a reduction of dehiscence and a secure bone graft healing. The combination of thin autogenous bone blocks and bone particles according to the SBB technique allows an acceleration of transplant revascularization, and thus, of graft regeneration, allowing a shortening of the patient treatment time as well as long-term three-dimensional volumetric bone stability. Keywords: 3D bone augmentation, MicroSaw protocol, posterior maxilla, sinus floor elevation, split bone block technique, tunnel technique, vertical alveolar ridge augmentation

Purpose: This cohort study evaluated patient satisfaction for maxillary implant-retained overdentures (IODs) on two implants up to 4 years and assessed the treatment effect over time. Materials and Methods: Patients encountering problems with their conventional dentures were included and received maxillary IODs on two titanium-zirconium implants and ball anchors in the canine area. Patient satisfaction was assessed using the oral health impact profile (OHIP-20E) questionnaires both for dentures and IODs. Two months after insertion of IODs (baseline), the patients chose the preferred overdenture design with full or reduced palatal coverage. OHIP-20E questionnaires were followed according to the individual choice at 1 and 4 years, and outcomes were compared with baseline. Results: Sixteen out of 21 patients were evaluated at a mean follow-up of 4 years (range: 2.4 to 4.8 years). There was no significant difference in the OHIP domains for IODs at 1 year (OHIP__total__1y: 9.5, SD: 13.0) and 4 years (OHIP__total__4y: 14.2, SD: 19.1) compared with baseline (OHIP__total__BL: 12.4, SD: 14.7). Patients were most satisfied with social disability both for IODs (OHIP__BL: 6.0, SD: 7.6; OHIP__1y: 3.4, SD: 5.4; OHIP__4y: 5.7, SD: 9.5) and dentures (OHIP__CD__old: 28, SD: 29.7; OHIP__CD__new: 25.4, SD: 28.67). Patients were least satisfied with functional limitation both for IODs (OHIP__BL: 6.0, SD: 7.6; OHIP__1y: 3.4, SD: 5.4; OHIP__4y: 5.7, SD: 9.5) and dentures (OHIP__CD__old: 28, SD: 29.7; OHIP__CD__new: 25.4, SD: 28.67). Conclusion: Patient satisfaction with maxillary IODs on two implants did not change from baseline to 4 years and was high at 4 years of function. Keywords: dental implants, dental prosthesis, edentulous, implant-supported, jaw, maxilla, overdenture, patient-reported outcomes, patient satisfaction, quality of life

Purpose: Cone beam computed tomography (CBCT) is an important imaging technique in maxillofacial evaluations. However, application-specific image analysis methods aimed at extracting quantitative information from these images need to be further developed. The aim of this study was to provide a robust and objective method that could assess radiologic changes around dental implants after sinus elevation surgery with simultaneous implant placement. Materials and Methods: The study was performed retrospectively on patients fulfilling the inclusion criteria. The included patients had been CBCT scanned preoperatively, at baseline (early after surgery), and 6 months postoperatively. In order to quantify the radiologic changes, an image analysis workflow was developed based on the postoperative baseline and 6-month scans. The workflow included metal artifact reduction, registration, and a standardized protocol for semiautomatic segmentation. Validation of different steps of the method was conducted by comparing scans from all time points. Comparison of constant volumes (eg, screws and bony parts not subjected to change) was used. Additionally, the Dice similarity coefficient (DSC) was used to measure the overlap of the segmentations. Results: The study included nine maxillary sinuses from six patients. The bone formation was quantified and visualized in 3D. In the validation, no significant differences were found for the constant volumes at the different scanning time points. The DSC showed accurate results with values > 0.92. Conclusion: The method presented in this study provides an objective and robust evaluation of bone formation around dental implants. The same methodologies can be applied in other studies of dental CBCT images, eg, for comparison of grafting materials or surgical strategies. Keywords: 3D, bone volume, cone beam computed tomography, radiology, sinus elevation

Purpose: The peri-implant bone and mucosa architecture contribute to the health and esthetics of singletooth dental implants. The implant-tooth distance (ITD) has been regarded as a key determinant of their outcomes. This study was conducted to determine the relationship between ITD and peri-implant bone, mucosa, and pink esthetic scores (PES) for anterior single-tooth implants. Materials and Methods: For 44 dental implants with a microthread conical abutment interface design placed in 38 participants, periapical radiographs and photographs were evaluated at 1 and 4 years to assess interproximal bone levels and PES. Results: Mean mesial and distal marginal bone level change over 4 years was 0.20 ± 1.00 mm and 0.20 ± 0.74 mm, respectively. In this cohort, there was no relationship between ITD and interproximal bone changes or papilla fill at 4 years; however, marginal bone changes influenced PES score-the smaller the ITD, the lower the PES (P .001). Alone, ITD did not influence marginal bone levels or papilla in this cohort. Conclusion: These results imply a complex relationship between ITD, marginal bone levels, and PES scores for single-tooth implants. Keywords: implant-tooth distance, marginal bone loss, pink esthetic score, single tooth dental implant

Purpose: To evaluate the current scientific evidence on estimating cumulative risk for biologic complications relating to dental implants and to develop a patient-centered risk assessment tool for establishing aggregate risk. Materials and Methods: A review of the scientific literature on risk indicators relating to dental implants was completed with the goal of identifying and weighting individual risk indicators so aggregate biologic risk could be estimated. Three authors completed independent reviews of the literature, identifying 31 systematic reviews on risk indicators for biologic complications with dental implants, from which 24 potential risk indicators were considered. Due to inconclusive scientific data on risk indicators, a Delphi process was used to gather structured expert opinion to supplement findings from the literature. Eleven Delphi participants with expertise in prosthodontics or periodontics participated in two email exchanges and one face-to-face meeting to comment and debate on the initial identification and weighting of risk indicators, propose the addition or removal of risk indicators, and provide recommended clinical management for each risk indicator. Results: After literature review, three rounds of debate, and additions and removals of various risk indicators, consensus (defined as 95% or more in agreement) was achieved on 20 risk indicators. The Delphi group concluded that the risk indicators of smoking, diabetes, periodontal disease, plaque levels, antiresorptive agents, and cemented restorations should include subcategories to more accurately identify and represent patient-specific risk. Clinical recommendations based on individual and aggregate risk were established by consensus. Conclusion: The literature on risk indicators for biologic complications was conflicting and inconclusive. The Delphi method was used to identify and establish the weighting of individual risk indicators, resulting in a risk assessment tool for estimating aggregate risk. Keywords: antiresorptive agents, diabetes, peri-implantitis, periodontal disease, risk assessment, smoking

Purpose: The aim of this cone beam computed tomography (CBCT) study was to assess bone volume changes in molar sites after modified immediate implant placement with xenografts. Materials and Methods: This prospective study was performed between June 2015 and September 2016. Surgical procedures included modified implant site preparation, atraumatic tooth extraction, implant placement, and bone grafting with deproteinized bovine bone mineral. CBCT scans were taken at the day of surgery and 6 months after surgery. Horizontal and vertical bone dimensional changes were evaluated through these two CBCTs, including variations of horizontal bone thickness (HBT), vertical bone height (VBH), and the distance from the implant platform to the tip of the intradental bone peak (DIP). Results: Fifteen patients with 17 hopeless molars were included, and no implant was lost during the observation period. With measurements at five different parallel levels (0, 1, 2, 4, and 6 mm apical to the implant platform), the mean HBT in millimeters and percentage between these two time points ranged from -0.88 (33%) to -0.03 (0.7%) buccally and -0.45 (12%) to -0.02 (0.4%) lingually. The change of VBH was greater buccally (0.74 ± 0.32 mm, P .01) than lingually (0.40 ± 0.17 mm). DIP was reduced 0.46 ± 0.27 mm mesially and 0.39 ± 0.21 mm distally. Conclusion: In molar sites, flapless modified immediate implant placement with deproteinized bovine bone is a predictable treatment. However, the dimensional change of the ridge should still be expected, and buccal bone resorption is more evident than lingual. Keywords: bone dimensions, cone beam computed tomography, immediate implant placement, molar site

Purpose: The purpose of this study was to evaluate whether fully digitally guided implant surgery may be performed with sufficient accuracy based on printing virtually designed templates after matching a surface scan with the magnetic resonance imaging (MRI) dataset mimicking edentulous cases based on cadaver maxillae of pigs. Materials and Methods: The palatal mucosa of five young pig cadavers was scanned with an intraoral scanner. High-resolution MRI of the jaws was performed, and the images were exported as DICOM files and uploaded into software for implant planning. Six implant osteotomies were virtually planned in each jaw. The intraoral surface scans were fused with the volumetric MRI data based on the palatal soft tissue, and virtual templates for guided implant surgery were created and exported as STL files. These were printed and the templates were used to perform flapless guided osteotomy, with the templates fitting on the soft tissue of the jaws alone. Cone beam computed tomography (CBCT) of the jaws was performed after osteotomy. These data were fused with the virtually planned osteotomies, and the 3D crestal, apical, and axial deviations between the virtually planned and physically performed osteotomies were determined. Results: Matching the surface scans with the mucosa was possible in three cases automatically; additional manual corrections were necessary in two cases. Thirty osteotomies were performed by applying the printed mucosa-supported templates. The mean angular deviation between the planned and realized cavities was 3.29 degrees (0.3 to 11.1 degrees; SD = 2.5 degrees), the mean 3D apical deviation was 1.3 mm (0.22 to 3.98 mm; SD = 0.94 mm), and the mean crestal deviation was 1.76 mm (0.39 to 3.79 mm; SD = 0.88 mm). Conclusion: MRI in combination with the presented workflow may be used in edentulous cases for guided implant surgery. Further studies are needed to prove the promising accuracy of this alternative approach in clinical trials. Keywords: cone beam computed tomography (CBCT), guided implant surgery, magnetic resonance imaging (MRI), ultra-short echo time (UTE), zero echo time (ZTE)

When surveyed, edentulous patients commonly state that they would prefer an implant-supported restoration to conventional removable dentures. However, acceptance of implant-supported restorations remains low, primarily due to the high cost of available solutions. To reduce cost and treatment time for patients with an edentulous mandible or failing mandibular dentition, an innovative treatment concept consisting of a standardized framework and time-efficient surgical and restorative protocols was developed. The prefabricated titanium framework is supported on three implants using an adaptive fixation mechanism that compensates for surgical misalignment of the implants to achieve passive fit. The definitive fixed, full-arch mandibular prosthesis can be delivered within 24 hours of implant placement. This patient presentation demonstrates the treatment of a man 82 years of age with complete edentulism. The entire treatment time from surgery to definitive placement was 3 hours over a single business day. After 2 years of function with immediate loading, the patient displayed favorable hard and soft tissue outcomes. Initial results indicate that treatment with this premanufactured device could potentially provide patients with a fixed fullarch implant-supported mandibular restoration with reduced clinical treatment time compared with other implant-supported treatments. Keywords: cost- and time-efficient, dental implants, edentulous, failing, mandible, terminal dentition, Trefoil

Subgingival presence of remaining excess cement may lead to implant complications and failures. This is a technical report and advice on how to cement implant-supported restorations using a simple and universal method applying liquid petroleum jelly to the peri-implant sulcus after cementation. This simple and userfriendly method eliminates excess cement and should be used in the daily practice. Keywords: cement-retained implant prostheses, cementation, complications