[Effect of Aging on the Mechanical Properties of CAD/CAM-Milled and 3D-Printed Acrylic Resins for Denture Bases].

PURPOSE: The purpose of this study was to investigate the mechanical properties of acrylic resins at different aging times for denture bases manufactured using the conventional method, microwave processing, milling, and 3D printing. MATERIALS AND METHODS: A total of 160 rectangular samples (64 Å~ 10 Å~ 3.3 ± 0.03 mm) were prepared, divided among the four main resin groups, and subdivided into four analysis times (T0, T1, T2, and T3), resulting in 10 samples per subgroup. The samples were stored in distilled water at 37° ± 2°C for 24 hours (T0), then subjected to thermocycling at temperatures of 5° ± 1°C and 55° ± 1°C in different numbers of cycles: 5,000 (T1); 10,000 (T2); and 20,000 (T3). The mechanical properties evaluated were surface microhardness, flexural strength, and modulus of elasticity. Statistical differences between resin groups and aging time were evaluated using two-way analysis of variance (P < .05). RESULTS: The 3D-printed resin showed the significantly lowest values of microhardness, flexural strength, and modulus of elasticity compared to other resins (P < .001). CONCLUSIONS: The CAD/CAM-milled denture resin showed mechanical properties similar to those of traditional resins (conventional and microwave-processed). The 3D-printing resin did not show adequate mechanical properties for long-term clinical use. Despite this, new studies are developing better properties of this resin for long-term use.

Prevalence of proximal contact loss between implant-supported prostheses and adjacent natural teeth: A systematic review and meta-analysis.

STATEMENT OF PROBLEM: Proximal contact loss between implant-supported prostheses and adjacent natural teeth is a complication that has been reported in clinical practice. However, the prevalence of the condition is unclear. PURPOSE: The purpose of this systematic review and meta-analysis was to assess the proportion of reported proximal contact loss between implant-supported prostheses and adjacent natural teeth. MATERIAL AND METHODS: This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology criteria and was registered on the international prospective register of systematic reviews (PROSPERO) platform (CRD42021225138). The electronic search was conducted by using the PubMed/MEDLINE, Embase, and Cochrane Library databases to September 2020. The formulated population, intervention, comparison, outcome (PICO) question was "Is there a correlation of the proximal contact loss between implant-supported prostheses and the adjacent natural tooth?" A single-arm meta-analysis of proportion was performed to evaluate the cumulative prevalence of survival and complication rates. RESULTS: This review included 10 studies, half of which presented proximal contact loss rates higher than 50%. In the general analysis, the open proximal contact showed a cumulative proportion of 41% (confidence interval: 30% to 53%; heterogeneity: I2=98%; t2=0.578; P<.01). From the subanalysis, the mesial contact (47%; confidence interval: 32% to 62%; heterogeneity: I2= 96%; t2=0.657; P<.01) and the mandibular arch (41%; confidence interval: 30% to 52%; heterogeneity: I2=92%; t2=0.302; P<.01) were found to have higher prevalence. CONCLUSIONS: The prevalence of proximal contact loss was high, occurring more frequently with the mesial contact and in the mandibular arch. Significant differences were not found in relation to sex or between the posterior and anterior regions.

Effect of Splinting of Tilted External Hexagon Implants on 3-Unit Implant-Supported Prostheses in the Posterior Maxilla: A 3D Finite Element Analysis.

PURPOSE: To assess the effects of tilted external hexagon implants and splinted restorations in terms of stress distribution on the bone tissue, implants, and prosthetic screws, using three-dimensional finite element analysis. MATERIALS AND METHODS: Six models were used to simulate a posterior maxilla bone block (type IV) from the first premolar to the first molar. Each model included three 4.1-mm-diameter external hexagon implants with varying inclinations (0°, 17°, and 30°) and crown designs (splinted and nonsplinted restorations). The forces applied were as follows: 400 N axially (50 N for each slope of the cusp) and 200 N obliquely (45° only on the buccal slope of the cusp). Stress distribution on the implants and prosthetic screw was evaluated using Von Mises stress, while the maximum principal stress was used to evaluate the stress distribution in the bone tissue. RESULTS: The oblique load increased the stress on all the structures in all the models. Increased inclination of the implants resulted in higher stress concentration in the bone tissue, implants, and prosthetic screws. However, splinted restorations contributed to reduction of the stress for the oblique loading, mainly in the bone tissue and prosthetic screw of the first molar, as the stress was shared between the first and second premolar restorations. CONCLUSIONS: Tilted implants increased proportionally the stress on bone tissue and prosthetic screws of models. Additionally, splinting restorations reduced the stress concentration area in the simulated bone tissue, implants, and prosthetic screws in the first molar, as the stress was shared with the adjacent implants.