Cause-Effect Relationship of Varying Bonding Thicknesses in Dentin Adhesion of Universal Adhesives

Abstract

Purpose: To evaluate whether varying thicknesses of universal adhesives utilizing the additional coating strategy would affect their microtensile bond strength (μTBS) to dentin, hardness, and elastic modulus (mechanical properties). Materials and Methods Ninety-nine human maxillary premolars were cut to expose coronal dentin, ground with regu lar-grit diamond burs, and randomly distributed into nine groups based on 1. adhesive: Scotchbond Universal Adhe sive (SB; universal), G Premio Bond (GP; universal) and Clearfil Megabond 2 (MB; two-step self-etch; control); and 2. application strategy (one, two or three coats; each coat light cured). After adhesive application and resin composite buildup, the bonded teeth were stored in distilled water (37°C; 24 h). Resin-dentin sticks from eight premolars per group (each premolar yielded three sticks; n 24 sticks altogether) were prepared for the μTBS test, followed by mea surement of the adhesive thicknesses at their fractured ends using SEM. The mechanical properties of the adhesive layers produced by different coats were evaluated on separate resin-dentin slices (n = 3 teeth per group). Results Two coats significantly increased the μTBS (p 0.001) of all the adhesives. The correlation between adhe sive thickness and bond strength was positive for GP but negative for SB. MB did not show any correlation. Additional coating significantly increased the mechanical properties of GP (p 0.05) but did not affect SB and MB (p 0.05). Conclusion An additional adhesive coating over the manufacturers’ recommendations improved the bond strength of all the adhesives tested. However, the increased mechanical properties of the adhesives with additional curing was material dependent