Reliability and correlation between microshear and microtensile bond strength tests of composite repairs

Abstract

The aim of this study was to evaluate the reliability of microshear (μSBS) and microtensile (μTBS) bond strength tests on composite repairs using universal adhesives with or without the application of additional silane. Cylindrical (μSBS) and block-shaped (μTBS) specimens were fabricated using nanofilled (F–Filtek One Bulk Fill) and nanohybrid (T-Tetric EvoCeram Bulk Fill) bulk-fill composites. The specimens were aged by thermocycling (5,000 cycles, 5–55 °C), sandblasted, and then divided into three groups (n = 30) as follows: non-repaired (FC and TC), repaired with universal adhesives (FA, Scotchbond Universal; and TA, Adhese Universal), and with the previous application of silane (FS and TS). After 48 h, the specimens were repaired using the same composite. The μSBS and μTBS specimens exhibited bonded areas of 1 mm2 and were subjected to shear stress and tension until failure, at a crosshead speed of 0.5 mm/min in a universal testing machine. Weibull analyses and Pearson correlation (α = 0.05) were applied to the data. At characteristic strength, FC, FA, and FS exhibited significantly higher μSBS when compared with TA and TS (p < 0.05). However when tested by μTBS at the same parameter, FA presented significantly lower bond strength when compared to FC, FS, and TA (p < 0.05). The correlation between Weibull modulus was strongly negative and not significant (p > 0.05). Both bond strength tests exhibited a material-dependent behavior. The microtensile bond strength test demonstrated more reliability than the microshear test for composite repair evaluation.