Functional or Nonfunctional Cusps Preservation for Molars Restored with Indirect Composite or Glass-Ceramic Onlays: 3D FEA Study.

Evidence regarding the effect of the onlay preparation design for different CAD/CAM restorative materials considering the preservation of cusps is lacking. Molars were 3D-modeled in four preparation designs for onlay restoration: traditional design with functional cusp coverage (TFC), non-retentive design with functional cusp coverage (NFC), traditional design with non-functional cusp coverage (TNFC) and non-retentive design with non-functional cusp coverage (NNFC). The restorations were simulated with two CAD/CAM restorative materials: LD-lithium disilicate (IPS e.max CAD) and RC-resin composite (GrandioBloc). A 100 N axial load was applied to the occlusal surface, simulating the centric contact point. Von Mises (VM) and maximum principal (Pmax) stress were evaluated for restorations, cement layer and dental substrate. The non-retentive preparation design reduced the stress concentration in the tooth structure in comparison to the conventional retentive design. For LD onlays, the stress distribution on the restoration intaglio surface showed that the preparation design, as well as the prepared cusp, influenced the stress magnitude. The non-retentive preparation design provided better load distribution in both restorative materials and more advantageous for molar structure. The resin composite restoration on thenon-functional cusp is recommended when the functional cusp is preserved in order to associate conservative dentistry and low-stress magnitude.

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.

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

BACKGROUND: 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. METHODS: The abutment teeth (first molar and first premolar) were modeled using the BioCAD protocol containing 1.5 mm of axial reduction and converging axial walls. A static structural analysis was performed in the computer-aided engineering software, and the Maximum Principal Stress criterion was used to analyze the prosthesis and the cement layers of both abutment teeth. The materials were considered isotropic, linearly elastic, homogeneous and with bonded contacts. An axial load (600 N) was applied to the occlusal surface of the second premolar. RESULTS: Regardless of the restorative material, the region of the prosthetic connectors showed the highest tensile stress magnitude. The highest stress peak was observed with the use of RC (129 MPa) compared to PEEK and AR. For the cement layers, RC showed the lowest values in the occlusal region (7 MPa) and the highest values for the cervical margin (14 MPa) compared to PEEK (21 and 12 MPa) and AR (21 and 13 MPa). CONCLUSIONS: Different interim restorative materials for posterior fixed partial dentures present different biomechanical behavior. The use of resin composite can attenuate the stress magnitude on the cement layer, and the use of acrylic resin can attenuate the stress magnitude on the connector region.

Avaliação da resistência à flexão 4 pontos e tolerância a defeitos superficiais de vitrocerâmica de dissilicato de lítio / Evaluation of 4-point flexural strength and tolerance to surface defects of lithium disilicate vitroceramics

O objetivo principal deste estudo foi avaliar a influência de diferentes formatos de defeitos superficiais controlados na resistência à flexão em 4 pontos da vitrocerâmica de dissilicato de lítio. Para isso, o estudo foi dividido em dois experimentos, in silico e in vitro. Uma barra para ensaio de flexão 4 pontos foi modelada em CAD e exportada para software CEA para simulação de Análise Estática Estrutural Mecânica por meio do método de elementos finitos. Já para o experimento in vitro, foram confeccionados espécimes em formato de barra a partir de blocos de vitrocerâmica de dissilicato de lítio, que foram divididos em 3 grupos experimentais (n=5) de acordo com o formato do defeito: GC ­ Nenhum; GE ­ Defeito esférico em superfície; GP ­ Defeito pontiagudo em superfície. Para avaliar a morfologia, dimensão dos defeitos introduzidos e rugosidade da superfície do dissilicato de lítio, foram realizadas microscopias eletrônicas de varredura (MEV) e análise por perfilometria óptica 3D. Foi realizado ensaio de resistência à flexão 4 pontos para determinar a resistência à flexão dos espécimes de cada grupo experimental. O grupo controle (GC) apresentou resistência à flexão em 4 pontos média de 217,1 ± 38,2 MPa já os grupos defeito pontiagudo (GP) e defeito esférico (GE) apresentaram resistência à flexão em 4 pontos média de 61,6 ± 2,8 MPa e 186,7 ± 29,4 MPa. A análise qualitativa realizada por microscopia eletrônica de varredura nos espécimes do grupo GP1 possibilitou a visualização de defeitos que apresentam diversas quinas e vértices, além de quatro trincas extensas na superfície do material, localizadas nos vértices da base quadrangular da pirâmide. A partir da análise por perfilometria óptica 3D, observou-se que o grupo controle (GC) apresentou rugosidade média de 0,0614 ± 0,0127 µm, enquanto o grupo defeito pontiagudo (GP) apresentou rugosidade média de 0,0730 ± 0,0313 µm. A partir da análise pelo método de elementos finitos simulando o teste de flexão em 4 pontos, observou-se que o valor de tensão máxima principal atingido pelo grupo controle (GC) foi 108,0 MPa, enquanto o grupo defeito pontiagudo (GP) e o grupo defeito esférico (GE) atingiram valores de tensão máxima principal de 292,0 MPa e 205,5 MPa respectivamente. Para a análise do comportamento mecânico de uma restauração indireta do tipo table-top em dissilicato de lítio e a influência do formato do defeito pelo mesmo método, observou-se que o defeito pontiagudo (GP) apresentou o maior valor de tensão máxima principal, de 284,6 MPa contra 266,15 para a restauração com defeitos esféricos. A restauração sem defeitos presentes obteve valor de 254 MPa. Concluiu-se que os defeitos superficiais promovem a diminuição da resistência à flexão da vitrocerâmica de dissilicato de lítio, sendo o defeito pontiagudo mais prejudicial que o defeito esférico.

The main objective of this study was to evaluate the influence of different shapes of controlled surface defects on the 4-point flexural strength of lithium disilicate glass ceramic. For this, the study was divided into two experiments, in silico and in vitro. A 4-point bending test bar was modeled in CAD and exported to CEA software for simulation of Mechanical Structural Static Analysis using the finite element method. For the in vitro experiment, bar-shaped specimens were made from lithium disilicate glass-ceramic blocks, which were divided into 3 experimental groups (n=5) according to the shape of the defect: GC ­ None; GE ­ Spherical surface defect; GP ­ Sharp surface defect. To assess the morphology, dimension of introduced defects and surface roughness of lithium disilicate, scanning electron microscopy (SEM) and analysis by 3D optical profilometry were performed. A 4-point flexural strength test was performed to determine the flexural strength of the specimens from each experimental group. The control group (CG) had a mean 4-point flexion strength of 217.1 ± 38.2 MPa, whereas the pointed defect (GP) and spherical defect (SG) groups had a mean 4-point flexion strength of 61.6 ± 2.8 MPa and 186.7 ± 29.4 MPa. Qualitative analysis performed by scanning electron microscopy in specimens from the GP1 group allowed the visualization of defects that present several corners and vertices, in addition to four extensive cracks on the surface of the material, located in the vertices of the quadrangular base of the pyramid. From the analysis by 3D optical profilometry, it was observed that the control group (CG) had a mean roughness of 0.0614 ± 0.0127 µm, while the sharp defect group (GP) had a mean roughness of 0.0730 ± 0.0313 µm. From the analysis by the finite element method simulating the 4-point bending test, it was observed that the maximum principal stress value reached by the control group (CG) was 108.0 MPa, while the sharp defect group (GP) and the spherical defect (GE) group reached maximum principal stress values of 292.0 MPa and 205.5 MPa respectively. For the analysis of the mechanical behavior of an indirect restoration of the table-top type in lithium disilicate and the influence of the defect shape by the same method, it was observed that the pointed defect (GP) had the highest maximum principal stress value, of 284.6MPa against 266.15 for the restoration with spherical defects. The restoration with no defects present obtained a value of 254MPa. It was concluded that superficial defects promote a decrease in the flexural strength of lithium disilicate glass-ceramic, with the sharp defect being more harmful than the spherical defect.