Influência do método experimental na resistência flexural de materiais restauradores: ensaio mecânico, análise por elementos finitos e fractografia

Abstract

Besides the differences in chemical composition, which has a direct influence on the mechanical properties of restorative materials, the various methods of evaluation have generated different results that make it difficult any comparison among their properties. The aim of this study was to determine and compare the flexural strength (FS) of four restorative materials and the influence of the measurement method in such property. Twelve groups (n=15) were obtained and each tested material (Filtek Z350, Epricord, Super Porcelain EX-3 and IPS Empress 2) was submitted to three mechanical tests to assess their FS. For three and four-point bending tests rectangular beams (25x2x2 mm) was used and disc-shaped (12x1,2 mm) was used in the biaxial test. Specimens were submitted to load at the 1 mm/min speed in an EMIC machine, the analysis of stress distribution was performed by 3D finite element analysis and fracture site was visually evaluated. Mean values of FS were obtained from the fracture load of the samples and subjected to statistical analysis. Two-way ANOVA and Tukey's test indicated significant differences between the materials with higher values for IPS Empress 2 (a), followed by Filtek Z350 (b) in all methods, followed by Super Porcelain EX-3 (c) and Epricord (d) in two of three tests. Three-point bending and biaxial tests showed significantly higher values (A), while the four-point bending test was inferior (B). Fracture modes observed correlated with the finite element analysis. Results indicated reliability of all methods, supported by reasonably low coefficients of variation and the highest values of the materials further strengthened in its composition. However, due to lower sensitivity, lower reproducibility (higher coefficient of variation) and greater difficulty of implementation, the four-point bending test seems to be less suitable.