Effect of Clinically Relevant Smear Layers and pH of Universal Adhesives on Dentin Bond Strength and Durability

Abstract

Purpose: To evaluate the effects of different smear layers on the microtensile bond strength (µTBS) of a reference two-step self-etch adhesive and two universal adhesives.

Materials and methods: Mid-coronal dentin of 90 teeth was exposed and divided into three bur groups (coarse diamond, fine diamond, or tungsten carbide). Each bur-prepared group was further divided into three adhesive groups: Clearfil SE Bond (SE, Kuraray Noritake), Single Bond Universal (SB; 3M Oral Care), and G-Premio Bond (GP, GC). After adhesive application, 4-mm-thick resin composites were built up. Half of the teeth in each bur-adhesive group were used in immediate µTBS testing, and the others were tested after thermal aging (n = 5). Rectangular sticks were prepared using a low-speed diamond saw. For each tooth, 6 central sticks were used in the µTBS test. Statistical analysis was performed using three-way ANOVA and Bonferroni tests (α = 0.05).

Results: SE presented higher µTBS than universal adhesives and SB presented higher µTBS than GP regardless of dentin surface preparation and thermal aging (p ˂ 0.05). For SE and SB, the tungsten carbide bur demonstrated higher immediate and aged µTBS than did the extra-fine diamond bur (p ˂ 0.05). The immediate µTBS was similar for GP with all bur types (p ˃ 0.05); the tungsten carbide and extra-fine diamond burs presented higher µTBS than did the coarse-diamond bur after thermal aging (p ˂ 0.05).

Conclusion: Dentin surface preparation and adhesive type had significant effects on µTBS. The smear layer created with an extra-fine diamond or tungsten carbide bur is favorable when mild and ultra-mild self-etch adhesives are used.

Keywords: bond strength; microtensile bond strength; self-etch adhesives; smear layer; universal adhesive.

Fig 1

Representative FE-SEM images of failure mode in groups at 2000X (inserts: 150X) original magnification. SE bonded to coarse diamond-prepared dentin (a); SE bonded to fine diamond-prepared dentin (b); SE bonded to coarse 8-fluted tungsten carbide-prepared dentin (c); SU bonded to coarse diamond-prepared dentin (d); SU bonded to fine diamond-prepared dentin (e); SU bonded to coarse 8-fluted tungsten carbide-prepared dentin (f); GP bonded to coarse diamond-prepared dentin (g); GP bonded to fine diamond-prepared dentin (h); GP bonded to coarse 8-fluted tungsten carbide prepared dentin (i).

Fig 2

Representative FE-SEM images of dentin smear layers. A longitudinal section of the dentin surface prepared by a coarse diamond bur at original magnifications of (a) 3000X and (b) 10,000X, fine diamond bur at magnifications of (c) 3000X and (d) 10,000X, and 8-fluted tungsten carbide bur at magnifications of (e) 3000X and (f) 10,000X. Dentin surface prepared by a coarse diamond bur at original magnifications of (g) 500X and (h) 2000X, fine diamond bur at magnifications of (i) 500X and (j) 2000X, and an 8-fluted tungsten-carbide bur at original magnifications of (k) 500X and (l) 2000X.

Fig 3

Representative FE-SEM images of adhesive-dentin interfaces of the tested adhesives, according to the bur type dentin surface preparation at an original magnification of 5000X (inserts 2500X). SE bonded to coarse diamond-prepared dentin (a); SE bonded to fine diamond-prepared dentin (c); SE bonded to coarse 8-fluted tungsten carbide-prepared dentin (e); SU bonded to coarse diamond-prepared dentin (g); SU bonded to fine diamond-prepared dentin (i); SU bonded to coarse 8-fluted tungsten carbide-prepared dentin (k); GP bonded to coarse diamond-prepared dentin (m); GP bonded to fine diamond-prepared dentin (o); GP bonded to coarse 8-fluted tungsten carbide-prepared dentin (r). RC: resin composite; A: adhesive layer; D: dentin; white arrows indicate voids; * cracks between adhesive and resin composite.