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Background. This systematic review and meta-analysis investigated the prevalence of proximal contact loss and its associated factors. Methods. A bibliographic search was conducted in June 2021 with no limitation in the article date or language and updated in January 2022 by hand searching. There was no time limit on the search to retrieve all studies. The search included randomized controlled trials or quasi-experiments, and cross-sectional or cohort studies were included in the absence of these studies. Two authors screened the title and abstract. After evaluating the full texts of selected articles, irrelevant studies and or non-English papers that were impossible to translate were excluded. Disagreements between the re­viewers’ selection process were resolved by debate on the eligibility of studies. Standardized critical appraisal instruments from the Joanna Briggs Institute for different types of studies were used to assess the studies’ quality. Comprehensive Meta-Analysis (CMA) software (Version 2.2; Biostat, Englewood, NJ) was used for data analysis. Results. The proximal contact loss (PCL) frequency was %29. According to the results, the frequencies of PCL for the distal and mesial aspects were %7 and %21, respectively. The meta-analysis results showed that the contact loss events on the mesial aspect were statistically higher than on the distal aspect (P%50, the proximal contact loss was higher (OR: %95[ 2.43 CI: 4.03‒1.47], P=0.0006). The PCL in the anterior area was lower than in the posterior area (P=0.004). Although the frequency of contact loss in females was higher than in males, this rate was not statistically significant. Conclusion. The PCL on the mesial aspect and the posterior area was high. In individuals with bone loss >%50, the proximal contact loss was higher than in others.

Background. The most common problem associated with dental implants is the abutment screw loosening. This research aimed to investigate the effect of the type of connection on screw loosening, using a finite element method (FEM). Methods. Periosave system and different types of the implant–abutment connection were used for modeling. After being measured, CAD files were modeled using CATIA software and imported to the ANSYS analysis software, and the model was loaded. Results. A force of 100 N was applied at 0.1 second, and no force was applied at 0.42 second. The screw head deformation at 0.1 and 0.42 seconds was 8 and 3.8 μm, and 7.6 and 2.8 μm at morse taper and octagon dental implant connections, respectively. The displacement rate of the internal surface of the abutment at 0.1 and 0.42 seconds was 10.7 and 8.4 μm, and 5.7 and 5.6 µm in the octagon and morse taper dental implant connections, respectively. The displacement of the implant suprastructure–abutment interface from the screw head at 0.1 and 0.42 seconds was 9 and 7 μm, and 7 and 6 μm in the morse taper and octagon dental implant connections, respectively. At intervals of 0 to 0.1 seconds and 0.6 to 0.8 seconds, the octagon connection was separated at the maximum screw head displacement and the internal part of the abutment, but the morse taper connection did not exhibit any separation. In the above time intervals, the results were similar to the maximum state in case of the minimum displacement of the screw head and the internal part of the abutment. Conclusion. Screw loosening is less likely to occur in the morse hex connection compared to the octagon connection due to the lack of separation of the screw from the internal surface of the abutment.

Background. Monolithic zirconia is an emerging material for crowns and bridges. The possibility of full digital design has made it an attractive alternative material for implant-supported prostheses. A proper design is vital in the success of such a prosthesis like any other. This study, in the shortage of scientific evidence, has tried to assess the stress distribution of occlusal forces inside the implant-prosthesis system of a 3-unit bridge made of monolithic zirconia. Methods. A 3-unit monolithic zirconia bridge supported by two implant fixtures placed on the teeth #13 and #15 was digitalized. It was converted to a mesh of 59000 nodes and 34000 elements. Five types of occlusal forces (one as vertical centric, two at 15º and 30º simulating canine pattern of lateral movement, and two at 15º and 30º simulating group function pattern) were applied. The stress distribution among all the components of the implant-bridge system was assessed using Ansys Workbench 14 software and finite element analysis. Results. The maximum stress was between 286 and 546 MPa, which were found in either the fixture‒abutment screw area or in the upper part of the pontic connector between the canine and first premolar. The maximum pressure increased with an increase in the angle of occlusal force. Significantly higher stress was recorded in the group function occlusal pattern. Conclusion. Monolithic zirconia can be promising in designing bridges in the canine‒premolar area. However, proper design is necessary with more attention to the connectors and types of occlusal forces.

Background and aims. Various materials and methods have been introduced for obturating cleaned and shaped root canal systems. This in vitro study aimed to evaluate the sealing ability of single-cone obturation technique with mineral trioxide aggregate and calcium-enriched mixture based on bacterial leakage approach. Materials and methods. Sixty-four single-canal teeth were prepared and randomly divided into 5 groups, consisting of three experimental groups (n = 16) and two control groups (n = 8). In group 1, root canal obturation was performed using gutta-percha with 0.02 taper and AH26 sealer by lateral compaction technique. In groups 2 and 3, single Protaper guttapercha cone was used for obturation with MTA and CEM cement, respectively. A bacterial leakage apparatus was utilized for leakage assessment for 60 days. Leakage comparison between the experimental groups was performed by one-way ANOVA using SPSS 16 statistical software. Results. The mean bacterial leakage intervals in groups 1, 2 and 3 were 33.68 ± 9.39, 40.68 ± 11.03 and 39.56 ± 9.03 days, respectively. One-way ANOVA indicated no significant differences in bacterial leakage between the three experimental groups (P = 0.109). Conclusion. Single-cone obturation with well-fitted gutta-percha and MTA and CEM cement is an appropriate alternative for traditional lateral compaction technique.