This study determined the influence of thermocycling (TC) and flowable composite on microtensile bond strength (MTBS), crack formation and mechanical properties of the bonding interface using swept-source optical coherence tomography (SS-OCT) and nanoindentation. MTBS test beams prepared from human dentin bonded with self-etch adhesive and hybrid composite with or without flowable lining were aged for either 0 or 10,000 thermocycles, resulting in 4 groups of specimens according to the placement technique and TC (n=10). 2D images were obtained before and after MTBS test to detect crack at interface using SS-OCT. Hardness across resin-dentin bonding area were measured using nanoindentation. Two-way ANOVA showed that flowable lining significantly increased MTBS (p<0.05). TC significantly increased crack percentage in composite while there was no significant difference in dentin crack. Moreover, TC significantly affected the hardness of dentin and resin composites (p<0.05). SS-OCT is effective in detecting internal fracture in substrate.
Keywords: Internal fracture; Micro-tensile bond strength test; Nanoindentation; OCT; Resin composite.