Resistência à tração; Cimento de fosfato de zinco; Cimentos dentários. Tensile strength; Zinc phosphate cement; Dental cements. Influence of Tooth Preparation Surface and Zinc Phosphate Cement on the Tensile Bond Strength of Metallic Copings Objective: To assess the tensile bond strength of silver-tin copings cemented in human dentin varying the zinc phosphate cement and tooth preparation surface. The null hypothesis was that the preparation surface and the type of zinc phosphate cement have no influence on the tensile bond strength of the metallic copings. Method: Standard full crown preparations were made on a power lathe in 60 human third molars extracted for periodontal reasons. Thirty preparations (G1) were made with diamond burs (Komet, USA) and the other 30 (G2) were made with carbide burs (Komet, USA). For each preparation, metallic copings were fabricated and cemented (axial load: 5 kg; time: 7 minutes) on the respective tooth preparation with three different zinc phosphate cements (n=10): G1a/G2a: S.S.White; G1b/G2b; DFL; and G1c/G2c: LS (Vigodent). After 48 hours of storage at 37ºC, the specimens were subjected to the tensile bond strength test (1 mm/min; 50 kgf) in a universal testing machine (EMIC). The data were subjected to statistical analysis by two-way ANOVA and Tukey's test at 5% significance level. Results: The values (kgf) obtained under the experimental conditions were the following: G1a (20.43±2.4), G1b (23.5±5.6), G1c (33.2±6.3), G2a (25.1±9.5), G2b (27.8±3.6) and G2c (32.5±8.3). The results demonstrated that tooth preparation surface did not have a significant effect (p=0.1), but the analysis of the type of cement showed that G1c and G2c were better than the other groups (p=0.001). The null hypothesis was rejected. Conclusion: The LS cement provided higher tensile bond strength values, regardless of the type of bur used for tooth preparation.

To evaluate the stresses generated in upper premolars rehabilitated with ceramic fragments (table-top) of lithium disilicate on the occlusal surface. An upper premolar was modeled following its anatomical references using computer aided design software (Rhinoceros version 5.0 SR8, USA). The dental tissues were individually designed containing enamel, dentin and periodontal ligament. The main anatomical points were used as parameters for model creation. Ceramic fragments were modeled varying their maximum thicknesses as: 0.5 mm, 1.0 mm and 1.5 mm. Solid geometries were exported to the analysis software (ANSYS 17.2, USA) in STEP format. The materials were considered isotropic, homogeneous and linear, and the values of the elastic modulus of the materials and structures were used to perform a static structural mechanical analysis. The set was submitted to 200 N load. The system fixation was defined on the basis of the threedimensional model, and the results were obtained in MPa according to the failure criteria of the analyzed materials (tensile stress). Occlusal restoration was not detrimental to mechanical behavior. Stress distribution in the internal region of the restoration was similar between the groups. Thicker fragments presented a lower concentration of tensile stress, therefore suggesting better prognosis in attenuating tensile stresses in the tooth region. More conservative occlusal ceramic fragments presented worse prognosis. However, all evaluated thickness for table-tops support the occlusal rehabilitation of upper premolars when submitted to 200 N loading.