Effect of finishing protocols on dentin surface characteristics and bond strength after tooth preparation for indirect restorations.

Statement of problem: The impact of different finishing protocols following preparation for indirect restorations on surface roughness, smear layer, and bond strength remains unclear, with potential implications for clinical longevity.

Purpose: The purpose of this in vitro study was to evaluate the effect of different dentin finishing protocols on surface (roughness and morphology), smear layer thickness, and bond strength to a resin-matrix glass-ceramic.

Material and methods: Unused preparation instruments were characterized under scanning electron microscopy (SEM), and 144 human third molars were prepared and divided into groups: control (medium grit diamond rotary instruments, no finishing [CT]), fine/superfine diamond rotary instruments [FB], fine/superfine tungsten carbide burs [CB], fine/superfine ultrasonic diamond tips [UT], SiC/Al₂O₃ mounted stones [MS], fine/superfine sintered diamond rotary instruments [SB], Al₂O₃ airborne-particle abrasion [AO], and resin coating [RC]. Surface roughness and morphology were analyzed using laser scanning confocal microscopy and SEM. Smear layer thickness was assessed using SEM combined with the ImageJ software program, and bond strength was evaluated using microtensile testing. One-way analysis of variance (ANOVA) and post hoc tests were used for statistical analysis, followed by Pearson correlation. Failure modes were analyzed using the chi-squared test (α=.05).

Results: Significant differences in surface roughness, smear layer thickness, and bond strength were observed across the groups (P<.001). All finishing protocols resulted in lower surface roughness and higher bond strength compared with the control. RC achieved the highest bond strength, followed by MS. A very weak correlation was found between surface roughness, smear layer thickness, and bond strength.

Conclusions: Finishing protocols affect dentin roughness, smear layer, and bond strength after tooth preparation. Resin coating and fine and superfine mounted SiC and Al₂O₃ stones improved adhesion and may enhance outcomes for indirect restorations.