Comparative evaluation of 3 microbond strength tests using 4 adhesive systems: Mechanical, finite element, and failure analysis

Abstract Statement of problem Bond strength (BS) values from in vitro studies are useful when dentists are selecting an adhesive system, but there is no ideal measuring method. Purpose The purpose of this in vitro study was to investigate the influence of the evaluation method in the BS between dentin and composite resin. Material and methods Molars with exposed superficial dentin (N=240) were divided into 3 groups according to the test: microtensile (μTBS), microshear (μSBS), and micropush-out (μPBS). Each one was subdivided into 4 groups according to the adhesive system: total etch, 3- and 2-step; and self-etch, 2- and 1-step). For the μPBS test, a conical cavity was prepared and restored with composite resin. An occlusal slice (1.5 mm in thickness) was obtained from each tooth. For the μSBS test, a composite resin cylinder (1 mm in diameter) was built on the dentin surface of each tooth. For the μTBS test, a 2-increment composite resin cylinder was built on the dentin surface, and beams with a sectional area of 0.5 mm2 were obtained. Each subgroup was divided into 2 (n=10) as the specimens were tested after 7 days and 1 year of water storage. The specimens were submitted to load, and the failure recorded in units of megapascals. Original BS values from the μTBS and μSBS tests were normalized for the area from μPBS specimens. Original and normalized results were submitted to a 3-way ANOVA (α=.05). The correlation among mechanical results, stress distribution, and failure pattern was investigated. Results Significant differences ( P .05). Within the 7 days of storage, the original BS values from μTBS were significantly higher ( P