The purpose of this study was to evaluate the influence of phosphoric acid etching on the enamel and dentin bond strength of single-step and two-step self-etch adhesive systems. The adhesive systems employed were Scotchbond Universal Adhesive, Peak Universal Bond and Clearfil Mega Bond. Bovine teeth were used as substitute human teeth. The adhesive was applied with and without prior phosphoric acid etching and resin pastes were inserted into the mold on the tooth surface. After storage in 37ºC distilled water for 24 h, shear bond strengths were measured at a crosshead speed of 1.0 mm/min. The bonding interface was observed by scanning electron microscopy (SEM). Though the enamel bond strength was affected by prior phosphoric acid etching, significantly higher enamel bond strengths were obtained with phosphoric acid etching. On the other hand, dentin bond strength decreased with prior phosphoric acid etching. In the SEM observations, tight adaptations were exhibited in both enamel and dentin specimens. From the results of this in vitro study, additional etching with phosphoric acid to improve bonding effectiveness should be limited to enamel. The effect of using prior phosphoric acid etching with the self-etch adhesive system should be carefully considered in clinical situations.

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The polished surfaces of CAD/CAM resin blocks covered by health insurance—Cerasmart (GC), Shofu Block HC (Shofu), LAVA Ultimate (3M ESPE), VITA Enamic (VITA Zahnfabrik), KZR-CAD HR (Yamakin) and Katana Avencia (Kuraray Noritake Dental)—were observed under SEM to examine the filled structures. The SEM images revealed various surface appearances from the filler components. In particular, VITA Enamic had a cermics-like structure, and Katana Avencia was highly filled with nano-sized fine particles. The finding implies that the blocks have different mechanical properties, and that various clinical performances can be predicted by the block used.

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