Computer Aided Design Modelling and Finite Element Analysis of Premolar Proximal Cavities Restored with Resin Composites

This study evaluated the stress distribution in five different class II cavities of premolar models restored with conventional or bulk-fill flowable composite by means of finite element analysis (FEA) under shrinkage and occlusal loading. An upper validated premolar model was imported in the software, and five class II cavities with different occlusal extensions and dimensions were prepared: horizontal cavity on the mesial surface (horizontal slot), mesio-occlusal cavity, mesial cavity (vertical slot), tunnel type cavity and direct access cavity. The models were restored with conventional or bulk-fill flowable resin composite. The tested materials were considered as homogeneous, linear, and isotropic. The Maximum Principal Stress criteria was chosen to evaluate the tensile stress results. The lowest shrinkage stress value was observed in the direct access cavity restored with bulk-fill flowable resin composite (36.12 MPa). The same cavity, restored with conventional composite showed a score of 36.14 MPa. The horizontal slot cavity with bulk-fill flowable showed a score of 46.71 MPa. The mesio-occlusal cavity with bulk-fill flowable had a score of 53.10 MPa, while with conventional composite this was 55.35 MPa. Higher shrinkage stress was found in the vertical slot cavity with conventional resin 56.14 MPa, followed by the same cavity with bulk-fill flowable 56.08 MPa. Results indicated that the use of bulk-fill flowable composite resin more significantly decreased the polymerization shrinkage stress magnitude. The larger the cavity and the volume of material necessary to restore the tooth, the greater the residual stress on enamel and dentin tissue

Influence of Polymeric Restorative Materials on the Stress Distribution in Posterior Fixed Partial Dentures: 3D Finite Element Analysis

This study evaluated the effect of interim restorative materials (acrylic resin (AR), resin composite (RC) or polyetheretherketone (PEEK) for dental computer-aided design/computer-aided manufacturing (CAD/CAM)) on the stress distribution of a posterior three-unit fixed partial denture

Influence of the dental implant number and load direction on stress distribution in a 3-unit implant-supported fixed dental prosthesis

Background. The choice between 2 or 3 implants to support a 3-unit implant-supported fixed dental prosthesis (FDP) still generates doubt in clinical practice. Objectives. The aim of this study was to evaluate stress distribution in 3-unit implant-supported FDPs according to the implant number and load direction. Material and methods. A numerical simulation was performed to analyze stress and strain according to the implant number (2 or 3) and load direction (axial or oblique). A model of a jaw was created by means of the modeling software Rhinoceros, v. 5.0 SR8. External hexagon implants, micro-conical abutments and screws were also modeled. The final geometries were exported to the computer-aided engineering (CAE) software Ansys, v. 17.2, and all materials were considered homogeneous, isotropic and elastic. Different load directions were applied for each model (300 N) at the center of the prosthesis. Results. The von Mises stress and strain values were obtained for the titanium structures and the bone, respectively. The implant number influenced the prosthesis biomechanics, with higher stress and strain concentrations when 2 implants were simulated. The oblique load also affected the mechanical response, showing higher stress and strain in comparison with the axial load, regardless of the implant number. Conclusions. It was concluded that for a 3-unit implant-supported FDP, a greater number of implants associated with axial loads can result in a better mechanical response during chewing

Bond Strength between Different Zirconia-Based Ceramics and Resin Cement before and after Aging

The objective of this study was to evaluate the bond strength of different stabilized zirconias with resin cement and evaluate the susceptibility to thermal aging of the adhesive interface. Zirconia discs (Vita Zahnfabrik, Bad Säckingen, Germany) were obtained: 3Y-TZP first generation (translucent), 3Y-TZP third generation (high-translucent), 4Y-PSZ (super-translucent), and 5Y-PSZ (extra-translucent). Each disc had its surface polished with a standardized protocol. The specimens were cleaned and sintered according to the manufacturer’s recommendation (conventionally: ~12 h). However, 3Y-TZP groups were subdivided into subgroups and sintered following the speed sintering process (~80 min). After their sintering shrinkage, the dimensions of the final discs were 12 mm × 2 mm. The specimens were blasted with 50 μm aluminum oxide (1 cm distance, 2 bar pressure, and 2 s/cm²), cleaned, and silanized with an MDP primer. After the surface treatment, a resin cement cylinder was built on the ceramic surface (Ø = 1 mm; h = 2 mm). Half of the specimens of each group were subjected to a microshear bond strength test in a universal testing machine after 24 h of cementation, while the other half were subjected to thermocycling prior to the bond strength test (6000 cycles; 5 °C–55 °C, 30 s for each bath). Bond strength data were submitted to two-way ANOVA and Tukey’s test (95%), as well as Weibull analysis, to determine adhesive reliability. Bond strength was statistically different among the materials, and only 3Y-TZP third generation and 4Y-PSZ were not affected by thermal aging. The speed sintering method was statistically similar to the conventional process for 3Y-TZP first generation. However, 3Y-TZP third generation showed higher immediate bond strength when speed sintered. The Weibull modulus was superior for conventional 3Y-TZP third generation and 4Y-PSZ. In this study, thermal aging caused a degradation of the adhesive interfaces of 3Y-TZP first generation and 5Y-PSZ with the resin cement; however, it did not affect the interfaces of 3Y-TZP third generation and 4Y-PSZ. The speed sintering method did not affect the long-term bond strength with the resin cement. Adhesive reliability was superior for 3Y-TZP third generation and 4Y-PSZ