Influence of occlusal contact area on cusp defection and stress distribution.

OBJECTIVE: The purpose of this study was to evaluate the effect of occlusal contact area for loading on the cuspal defection and stress distribution in a first premolar restored with a high elastic modulus restorative material. MATERIALS AND METHODS: The Rhinoceros 4.0 software was used for modeling the three-dimensional geometries of dental and periodontal structures and the inlay restoration. Thus, two different models, intact and restored teeth with three occlusal contact areas, 0.1, 0.5 and 0.75 mm(2), on enamel at the occlusal surface of buccal and lingual cusps. Finite element analysis (FEA) was performed with the program ANSYS (Workbench 13.0), which generated a mesh with tetrahedral elements with greater refinement in the regions of interest, and was constrained at the bases of cortical and trabecular bone in all axis and loaded with 100 N normal to each contact area. RESULTS: To analysis of maximum principal stress, the smaller occlusal contact area showed greater compressive stress in region of load application for both the intact and inlay restored tooth. However, tensile stresses at the occlusal isthmus were similar for all three tested occlusal contact areas (60 MPa). To displacement of the cusps was higher for teeth with inlay (0.46-0.48 mm). For intact teeth, the smaller contact area showed greater displacement (0.10 mm). For teeth with inlays, the displacement of the cusps were similar in all types of occlusal area. CONCLUSION: Cuspal displacement was higher in the restored tooth when compared to the intact tooth, but there were no significant variations even with changes in the occlusal contact area. RELEVANCE CLINICAL: Occlusal contacts have a great influence on the positioning of teeth being able to maintain the position and stability of the mandible. Axial loads would be able to generate more uniform stress at the root presenting a greater concentration of load application in the point and the occlusal surface. Thus, is necessary to analyze the relationship between these occlusal contacts as dental wear and subsequent occlusal interferences.

Silica-Nylon Reinforcement Effect on the Fracture Load and Stress Distribution of a Resin-Bonded Partial Dental Prosthesis.

This study investigated the influence of silica-nylon reinforcement on the stress distribution and fracture load of a resin-bonded fixed partial dental prosthesis (RBFDP). Three-unit RBFDPs (N = 60) were inserted between the first premolar and the first molar of a maxillary model. The groups were divided according to the nylon reinforcement (n = 20/group): conventional fixed prosthesis (without reinforcement), prosthesis with silica-nylon reinforcement positioned vertically, and prosthesis with silica-nylon reinforcement positioned horizontally. Half of the specimens were tested after 24 hours in a universal testing machine until fracture (1,000 kgf; 1 mm/minute) to determine the single load to fracture. The other half was submitted to mechanical aging during 106 cycles (100 N, 2 Hz), totaling 6 groups (n = 10/group). The results were analyzed by two-way analysis of variance (ANOVA) (α = 5%). The stress distribution for non-aged groups was simulated using finite element analysis. The numeric prostheses were modeled similarly to the in vitro assay. ANOVA showed no statistical difference between groups (P < .05) for load to fracture. However, the use of the reinforcement provided stability even after the failure, as the parts did not separate. The computational analysis showed similar biomechanical behavior among the groups. The use of the nylon reinforcement does not influence the fracture load or the stress distribution, but it does enable the prosthesis to remain in position after failure.

Reinforced Glass-ceramics: Parametric Inspection of Three-Dimensional Wear and Volumetric Loss after Chewing Simulation.

The aim of this study was to investigate the three-dimensional wear, volumetric loss and surface roughness after chewing simulation of two glass ceramics. Lithium disilicate (LD, Emax CAD, Ivoclar) and Zirconia reinforced lithium silicate (ZLS, Vita Suprinity, Vita Zhanfabrick) discs (n=20/g) were scanned to obtain stereolithography (STL) files for each sample. All discs were submitted to chewing simulation with sliding configuration (30 N, 300,000 cycles, 6 mm and 1.7 Hz) with steatite as antagonist. The samples were then scanned again and the volume loss and the deepest defect depth was measured using the superimposed file from the baseline using three-dimensional digital parametric inspection software (GOM Inspect, Braunschweig, Germany). Surface roughness (Ra and Rz) was analyzed with a contact profilometer. Data were analyzed by one-way ANOVA and Tukey test (α=0.5%). ANOVA showed significant differences among the groups. Considering the ceramic volume loss, wear depth defect length and Rz roughness, LD (-22.09±5.57%; 0.80±0.06 µm; 3.08±1.02 µm) showed higher mean values than ZLS (-15.67±4.51%; 0.56±0.09 µm; 1.51±0.90 µm). Ra mean values were similar for both materials (p=0.064). All discs exhibited slight surface scratches along with the sliding direction with pitted wear patterns, while large cracks were observed on wear traces. These same areas can be identified in blue, overlapping the STL files before and after chewing simulation in inspection software. The linear reduction generated by sliding contact shows a graph with a similar wear pattern shape. ZLS was more resistant to wear than LD, with less volume loss and shallower surface defects.

Reinforced glass-ceramics: parametric inspection of three-dimensional wear and volumetric loss after chewing simulation

Abstract The aim of this study was to investigate the three-dimensional wear, volumetric loss and surface roughness after chewing simulation of two glass ceramics. Lithium disilicate (LD, Emax CAD, Ivoclar) and Zirconia reinforced lithium silicate (ZLS, Vita Suprinity, Vita Zhanfabrick) discs (n=20/g) were scanned to obtain stereolithography (STL) files for each sample. All discs were submitted to chewing simulation with sliding configuration (30 N, 300,000 cycles, 6 mm and 1.7 Hz) with steatite as antagonist. The samples were then scanned again and the volume loss and the deepest defect depth was measured using the superimposed file from the baseline using three-dimensional digital parametric inspection software (GOM Inspect, Braunschweig, Germany). Surface roughness (Ra and Rz) was analyzed with a contact profilometer. Data were analyzed by one-way ANOVA and Tukey test (α=0.5%). ANOVA showed significant differences among the groups. Considering the ceramic volume loss, wear depth defect length and Rz roughness, LD (-22.09±5.57%; 0.80±0.06 µm; 3.08±1.02 µm) showed higher mean values than ZLS (-15.67±4.51%; 0.56±0.09 µm; 1.51±0.90 µm). Ra mean values were similar for both materials (p=0.064). All discs exhibited slight surface scratches along with the sliding direction with pitted wear patterns, while large cracks were observed on wear traces. These same areas can be identified in blue, overlapping the STL files before and after chewing simulation in inspection software. The linear reduction generated by sliding contact shows a graph with a similar wear pattern shape. ZLS was more resistant to wear than LD, with less volume loss and shallower surface defects.

Resumo O objetivo deste estudo foi investigar o desgaste tridimensional, perda volumétrica e rugosidade após a simulação de mastigação de dois materiais vitro-cerâmicos. Discos de dissilicato de lítio (LD, Emax CAD, Ivoclar) e silicato de lítio reforçado com zircônia (ZLS, Vita Suprinity, Vita Zhanfabrick) (n=20/g) foram confeccionados e digitalizados para obtenção de arquivos de estereolitografia (STL) de cada amostra. Todos os discos foram submetidos à simulação de mastigação com configuração deslizante (30 N, 300.000 ciclos, 6 mm e 1,7 Hz) com esteatita como antagonista. As amostras foram escaneadas novamente e a perda de volume e o defeito mais profundo foram medidos usando o arquivo sobreposto da linha de base através de um software de inspeção paramétrica digital e tridimensional (GOM Inspect, Braunschweig, Alemanha). A rugosidade superficial (Ra e Rz) foi avaliada através de rugosímetro de contato. Os resultados foram analisados por ANOVA 1-fator e teste Tukey (α=0,5%). ANOVA mostrou diferenças significantes entre os grupos. Considerando a perda de volume cerâmico, comprimento do defeito e rugosidade Rz, LD (-22,09±5,57%; 0,80±0,06 µm; 3,08±1.02 µm) apresentou valores médios superiores a ZLS (-15,67±4,51%; 0,56±0,09 µm; 1.51±0.90 µm). Todos os discos exibiram pequenos arranhões na superfície conforme a direção de deslizamento com padrões de desgaste, enquanto grandes ranhuras foram observadas nos traços de desgaste. Essas mesmas áreas podem ser identificadas em azul, sobrepondo os arquivos STL antes e depois da simulação de mastigação no software de inspeção. A redução linear gerada pelo contato deslizante mostra um gráfico com uma forma de padrão de desgaste semelhante. ZLS foi mais resistente ao desgaste do que LD, com menor perda de volume e menores defeitos superficiais.

Alternative technique for preliminary impression in edentulous patients / Técnica alternativa para moldagem preliminar de pacientes desdentados totais

Objective: The aim of this study was to analyze the reproducibility of the anatomic models of edentulous maxillary and mandibular arches. Material and Methods: Alginate molds of the edentulous arches of standard model were performed and the tray was placed to the special device. These models received three metal spheres on surface with two positioned on the crest of the alveolar ridge (spheres 1 and 2) and other one perpendicular to the intersection of the midpalatal suture (sphere 3) and impression was performed using alginate. The proportion powder/ liquid was measured according manufacturer for both arches. To double molding technique with alginate was necessary to uniformly relieve using an acetate film. After that, were performed the first impression and the second layer of alginate with conventional water-powder-proportion and also the second layer of alginate with altered waterpowder-proportion. The distances of each spheres wereobtained using a three-dimensional measuringmachine, and the data were analyzed byDunnet, ANOVA and Tukey tests with a significant level of 5%. Results: A comparison of the water-powderproportion showed significant differences in the maxillary archer with sphere distance between 3-2 (p< 0.0001) and 1-3(p< 0.0001). The mandibular archer showed significant differences when relief between distance 1-2 (p< 0.041). The Dunnet test showed different in 1-2 mandibular groups (p< 0.0450). Conclusion: The reline alginate techniques showed differences in results in comparison to the conventional technique, however, the proportion water/powder technique modified, decreasing the viscosity, showed satisfactory results, the relief variable showed no difference statistically significantly and the techniques proposed could be employed in clinical practice (AU)

Objetivo: O propósito deste estudo foi analisar o grau de reproducibilidade de modelos anatômicos de arcos maxilares e mandibulares. Material e Métodos: Moldes de alginato de modelos padrão desdentados foram realizados a partir do uso de uma moldeira adaptada em um dispositivo metálico. Os modelos receberam três esferas em sua superfície onde duas eram posicionadas na crista do rebordo alveolar (esferas 1 e 2) e uma outra perpendicular à interseção da rafe mediana (esfera 3) e a moldagem foi realizada com o emprego do alginato. A proporção pó e liquido foi mensurada de acordo com o fabricante do alginato para ambos os arcos. Para a técnica de moldagem dupla com alginato foi necessário fazer um alívio com filme de acetato. Após isto foi realizada a primeira moldagem e depois uma segunda camada onde empregou-se a proporção pó líquido convencional e ainda, uma outra situação onde esta proporção foi alterada. A distância entre as esferas foi medida no modelo por uso de equipamento de mensuração tridimensional e os dados foram analisados por Dunnet, Anova e teste Tukey com nível de significância em 5%. Resultados: A comparação da proporção água e pó mostrou diferença estatística significante para os arcos maxilares entre as esferas 3-2 (p< 0.0001). O arco mandibular mostrou diferenças significantes quando avaliada a distância 1-2 (p<0.041). O teste Dunnet mostrou diferenças para o grupo mandibular entre esferas 1-2 (p< 0.0450). Conclusão: A técnica de rembasamento de alginato mostrou resultados diferentes à técnica convencional, contudo a técnica de modificação da proporção água pó diminuiu a viscosidade do alginato, mostrou resultados satisfatórios, outrossim a variável alívio não mostrou diferenças estatísticas. A variação técnica proposta mostrou-se ser viável do ponto de vista clínico.(AU)