Effect of crown stiffness and prosthetic screw absence on the stress distribution in implant-supported restoration: A 3D finite element analysis.

This in-silico investigation evaluated the mechanical impact of Morse tape implant-abutment interface and retention system (with and without screw) and restorative materials (composite block and monolithic zirconia) by means of a three-dimensional finite element analysis (3D-FEA). Four 3D models were designed for the lower first molar. A dental implant (4.5 × 10 mm B&B Dental Implant Company) was digitized (micro CT) and exported to computer-aided design (CAD) software. Non-uniform rational B-spline surfaces were reconstructed, generating a 3D volumetric model. Four different models were generated with the same Morse-type connection, but with a different locking system (with and without active screw) and a different crown material made of composite block and zirconia. The D2 bone type, which contains cortical and trabecular tissues, was designed using data from the database. The implants were juxtaposed inside the model after Boolean subtraction. Implant placement depth was simulated for the implant model precisely at crestal bone level. Each acquired model was then imported into the finite element analysis (FEA) software as STEP files. The Von Mises equivalent strains were calculated for the peri-implant bone and the Von Mises stress for the prosthetic structures. The highest strain values in bone tissue occurred in the peri-implant bone interface and were comparable in the four implant models (8.2918e-004-8.6622e-004 mm/mm). The stress peak in the zirconia crown (64.4 MPa) was higher than in the composite crown (52.2 MPa) regardless of the presence of the prosthetic screw. The abutment showed the lowest stress peaks (99.71-92.28 MPa) when the screw was present (126.63-114.25 MPa). Based on this linear analysis, it is suggested that the absence of prosthetic screw increases the stress inside the abutment and implant, without effect on the crown and around the bone tissue. Stiffer crowns concentrate more stress on its structure, reducing the amount of stress on the abutment.

The Use of Bulk Fill Resin-Based Composite in the Sealing of Cavity with Margins in Radicular Cementum.

The aim of this systematic review was to evaluate if the newly introduced bulk fill resin-based composite provides a better marginal sealing in cavity preparations with margins in dental cementum. The population investigation comparison outcome (PICO) framework was: in cavity preparation with margins in dental cementum of human extracted teeth, do bulk fill resin base composites provide a better marginal sealing than non-bulk fill resin-based composites? We performed our research on April 21, 2020. Two authors independently evaluated the abstract and titles for eligibility criteria. Two authors independently extracted the data and assessed the risk of bias in single studies. After the initial screening of 400 abstract and titles, the full text of the articles, that could meet the eligibility criteria, were obtained via the university library. A total of 36 full-text articles were evaluated; 11 articles were finally eligible for the review. Eight studies showed statistically differences, but not significant, in the marginal sealing between bulk fill and nonbulk fill resin-based composite (p > 0.05). One study showed statistically significant differences: SonicFill and Grandio showed better marginal sealing than GrandioSo and SDR(r) (Sirona Dentsply, New York, United States) and the latter two showed better marginal sealing than Filtek Supreme (p < 0.05). One study showed statistically significant less marginal gap of SDR than Filtek Bulk Fill (p = 0.0015) and Filtek Supreme (p < 0.0001). One study showed SDR to have a significantly higher microleakage than the other materials tested (p < 0.05). Based on our current literature review, there are not enough data to establish if bulk fill resin base composite provides a better or a worse marginal sealing at cementum margins.

Mechanical Behavior of Different Restorative Materials and Onlay Preparation Designs in Endodontically Treated Molars.

This study evaluated the effect of the combination of three different onlay preparation designs and two restorative materials on the stress distribution, using 3D-finite element analysis. Six models of first lower molars were created according to three preparation designs: non-retentive (nRET), traditional with occlusal isthmus reduction (IST), and traditional without occlusal isthmus reduction (wIST); and according to two restorative materials: lithium-disilicate (LD) and nanoceramic resin (NR). A 600 N axial load was applied at the central fossa. All solids were considered isotropic, homogeneous, and linearly elastic. A static linear analysis was performed, and the Maximum Principal Stress (MPS) criteria were used to evaluate the results and compare the stress in MPa on the restoration, cement layer, and tooth structure (enamel and dentin). A novel statistical approach was used for quantitative analysis of the finite element analysis results. On restoration and cement layer, nRET showed a more homogeneous stress distribution, while the highest stress peaks were calculated for LD onlays (restoration: 69-110; cement layer: 10.2-13.3). On the tooth structure, the material had more influence, with better results for LD (27-38). It can be concluded that nRET design showed the best mechanical behavior compared to IST and wIST, with LD being more advantageous for tooth structure and NR for the restoration and cement layer.

Influence of different restorative material and cement on the stress distribution of ceramic veneer in upper central incisor.

AIMS: Considering new ceramic systems, doubts about the appropriate combination of ceramics and cement are common. SETTINGS AND DESIGN: To evaluate the influence of the elastic modulus (E) of cement agents associated with different indirect veneers on the stress distribution using finite element analysis. METHODS AND MATERIALS: The finite element analysis was applied to evaluate the stress distribution on the structures. For that, a computer-aided design software was used for a three-dimensional (3D) modeling of an upper central incisor with preparation for an indirect veneer. The model was imported into the analysis software in STEP (Standard for Exchange of Product data) format. Tetrahedral elements formed the mesh. Solids were considered isotropic, linearly elastic, homogeneous, and with ideal contacts. Load application (100N, 45°) occurred on the lingual face. Cement agents have their E classified as low, intermediate, and high. The ceramic materials used were a hybrid ceramic, a zirconia reinforced lithium silicate and a lithium disilicate. RESULTS: It was observed that none of the factors significantly influenced the stress concentration in dentine. Groups with high E cementing agent showed the highest stress peaks. The E of restorative material was significant for the stress generated in the veneer, and groups with hybrid ceramic presented more homogeneous stress results. CONCLUSIONS: The higher E of the cement agent and the ceramic, the higher the stress concentration, suggesting that hybrid ceramic associated with low elastic modulus resinous cement has superior biomechanical behavior.

Torque Maintenance Capacity, Vertical Misfit, Load to Failure, and Stress Concentration of Zirconia Restorations Cemented or Notched to Titanium Bases.

PURPOSE: Different titanium bases for implant-supported prostheses can present different mechanical behavior. The goal of this study was to evaluate the torque before and after fatigue, the load to failure, and stress concentration of zirconia restorations cemented or notched to a titanium base. MATERIALS AND METHODS: Forty implants were included in polyurethane cylinders and divided into two groups: zirconia restoration cemented on a titanium base and zirconia restoration notched on a titanium base. The specimens had their torque loosening and vertical misfit evaluated before and after cyclic fatigue (200 N/2 Hz/2 × 106 cycles/37°C). Load to failure was evaluated in a universal testing machine (1 mm/min, 1,000 kgf). Failures were evaluated by scanning electron microscopy. Three-dimensional models were created, and the stress concentration was calculated using the finite element method. Data from the in vitro tests were submitted to two-way analysis of variance and Tukey test (α = .5). RESULTS: The cemented restorations presented less torque loosening (19.79 to 15.95 Ncm), lower vertical misfit (3.7 to 10.5 µm), lower stress concentration in the restoration (88.2 to 99.8 MPa), and higher fracture load (451.3 to 390.8 N) than notched restorations. CONCLUSION: The presence of a cement layer between the restoration and titanium base reduced the susceptibility to abutment screw loosening, improved the resistance to compressive load, and reduced the stress concentration in the restoration.