Influence of Conditioning Time of Universal Adhesives on Adhesive Properties and Enamel-Etching Pattern

SUMMARY Objectives: To evaluate the effect of application protocol in resin–enamel microshear bond strength (μSBS), in situ degree of conversion, and etching pattern of three universal adhesive systems. Methods and Materials: Sixty-three extracted third molars were sectioned in four parts (buccal, lingual, and proximals) and divided into nine groups, according to the combination of the main factors—Adhesive (Clearfil Universal, Kuraray Noritake Dental Inc, Tokyo, Japan; Futurabond U, VOCO, Cuxhaven, Germany; and Scotchbond Universal Adhesive, 3M ESPE, St Paul, MN, USA)—and enamel treatment/application time (etch-and-rinse mode [ER], self-etch [SE] application for 20 seconds [SE20], and SE application for 40 seconds [SE40]). Specimens were stored in water (37°C/24 h) and tested at 1.0 mm/min (μSBS). The degree of conversion of the adhesives at the resin–enamel interfaces was evaluated using micro-Raman spectroscopy. The enamel-etching pattern was evaluated under a scanning electron microscope. Data were analyzed with two-way analysis of variance and Tukey test (α=0.05). Results: In general, the application of the universal adhesives in the SE40 produced μSBS and degree of conversion that were higher than in the SE20 (p<0.01) and similar to the ER mode. The deepest enamel-etching pattern was obtained in the ER mode, followed by the SE40. Conclusions: The active and prolonged application of universal adhesives in the SE mode may be a viable alternative to increase the degree of conversion, etching pattern, and resin–enamel bond strength.