Abstract
The removal or modification of smear layers that cover the dentin is critical to allow the penetration of adhesive molecules and to ensure a strong bond between resin and dentin. Aiming to establish a model for clinically-relevant dentin-bond testing, we evaluated the effects of smear layers created by abrasives having similar coarseness (180-grit SiC paper; fine-grit diamond bur) and application modes (single application; double application) on the microtensile bond strengths (µTBS) of two currently available universal adhesives (G-Premio Bond; Scotchbond Universal Adhesive) and a two-step self-etch adhesive (Clearfil Megabond 2). Sixty extracted human third molars were used for the μTBS test. Data were analyzed by three-way ANOVA and Tukey’s test (α = 0.05). Fracture modes were determined using stereomicroscopy. An additional 24 third molars were prepared for observation of the resin–dentin interface by TEM and adhesive-smear layer interaction by SEM. μTBS was significantly affected by the adhesives and their application modes (p < 0.001), implying that the double application of universal adhesives should be recommended to improve their performance. The effect of smear layers was not significant (p > 0.05), indicating that 180-grit SiC papers could be used to prepare dentin as a substitute for fine-grit diamond burs for dentin-bond testing in laboratory settings.
Highlights
The composite nature and inherent wetness of dentin make it a difficult substrate to use for bonding [1]
In our previous study [30], we demonstrated that the hardness of the adhesive layers of Scotchbond Universal Adhesive (SB) and Megabond 2 (MB) was significantly higher than that of G-Premio Bond (GP), in both single and double application modes
The teeth were randomly allocated to 12 groups (n = 5) according to the adhesive systems: G-Premio Bond (GP; GC Corporation, Tokyo, Japan), Scotchbond Universal Adhesive (SB; 3M ESPE, Neuss, Germany) and Clearfil Megabond 2 (MB; Kuraray Noritake Dental Inc, Nigata, Japan); dentin smear layers: created either with 180-grit silicon carbide papers (SiC) papers (P; Sankyo-Rikagaku Co., Saitama, Japan) or fine-grit diamond burs (B; Diamond Point FG, F102R, ISO 223 090 016, Shofu Inc., Kyoto, Japan); and the adhesives application modes: single application according to manufacturers’ instructions (S) or double applications with light curing only after the application of the second coat (D)
Summary
The composite nature and inherent wetness of dentin make it a difficult substrate to use for bonding [1]. Self-etch adhesive systems can ensure the optimal wetness of dentin required for efficient bonding [6]. These systems are less technique-sensitive, require shorter application times [7], and induce little or no post-operative sensitivity [8]. The latest and most versatile version of one-step systems, i.e., universal adhesive systems, have been gaining more attention from clinicians [10] These systems are more convenient because they can be applied both in self-etch and etch-and-rinse modes, as well as for direct and indirect restorations [11]. Universal adhesive systems have been left with the shortcomings of their predecessors, i.e., one-step systems [14], and their bonding performance with dentin needs to be evaluated using different variables which are known to modify the bond strength results in vitro [15]
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