Efeito do diâmetro da ponta aplicadora de carga e do orifício central da base no desempenho biomecânico do teste de push-out: avaliação experimental e validação por análise em elementos finitos

Abstract

Even though the push-out test is widely used, its parameters aren t well established in literature. The aim of this study was to evaluate the influence of indenter and base diameters on push-out test results, by means of laboratorial and finite element analysis (FEA). Three bases with different central orifices diameters (2.5, 3.0, and 3.5 mm) and three diameters of indenters (0.5, 1.0, and 1.5 mm) were used. For the push-out test 90 bovine incisors with similar roots were selected and had its coronal part removed, leaving a root remanescent of 15 mm. These roots were prepared and restored with the fiberglass post White Post nº3 (FGM, Brazil) and RelyX Unicem (3M ESPE, USA). The roots were randomly divided into nine groups and two slices of 1 mm height were obtained from the cervical third of each one. All slices were analyzed in an optical microscope and the higher and smaller diameter of the post was determined by software of digital measurement for the bonding surface area (mm²). For the push-out test the slices were placed in the center of the base orifice, with the side of the higher diameter of the post facing downwards, allowing its extrusion during the test. A compressive load was applied with constant velocity of 0.5 mm/min, until failure of the system occurs. The bonding resistance (MPa) was calculated by the ratio between the load (N) required to cause failure of the system and the bonding area (mm²) of the post. Statistical analysis were made with ANOVA two-way and Tukey s test (p<0.05). All slices were analyzed with stereoscopic magnifying glass (40x) and classified into six failure pattern. FEA was performed using 3D models in the MARC/MENTAT software, following the same parameters of the laboratorial test. Modified von Mises stress, principal maximum stress, shear stress and tensile component were analyzed. Bond strength values significantly lower only for the smaller indenter (0,5mm). The failure pattern indicated that larger bases and small indenter lead the samples to fail more cohesively (dentin or post). FEA showed that the diameter base size had more significant influence on the stress distribution than the indenter. The indenter diameter and base size influence on stress generation and the experimental results of push-out tests. The association of failure mode and stress distribution analysis using FEA is important to better explain bonding test performance. The use of specific indenter and base diameter sizes for specimens originated by different root third should be pursued.