Improvement of Bonding to Caries-affected Dentin

Abstract

After caries removal and cavity preparation for an adhesive restoration, large areas of the cavity floor are composed of caries-affected dentin, however previous studies have reported that the bond strength to caries-affected dentin was lower than that to normal dentin. The physical and chemical characteristics of caries-affected dentin are very different from those of normal dentin, due to a loss of mineral content during the carious process. Also, the characteristics of smear layers of normal and caries-affected dentin differ because the composition of a smear layer is generally similar to the originating tissue; thus, it is assumed that the smear layer in caries-affected dentin is enriched with organic phase, resulting from the loss of minerals. Sodium hypochlorite (NaOCl) is a nonspecific proteolytic agent that effectively removes organic compounds at room temperature. Therefore, pre-treatment of the smear layer with NaOCl could eliminate the collagen phase. The aim of this study was to evaluate the effect of pre-treatment of NaOCl with or without a reducing agent on the microtensile bond strength to normal and caries-affected dentin. Twenty extracted human molars with occlusal caries were used. The occlusal dentin surface was ground flat to expose normal and caries-affected dentin using #600 SiC paper under running water. The dentin surface including caries-affected dentin was treated with 6% NaOCl solution for 30s followed by application with or without aromatic sulfinate solution (Accel®, SunMedical) for 10 and 30s, or none (control). After rinsing off, the treated dentin surface was applied with Clearfil Mega Bond FA® (Kuraray Medical) according to the manufacturer's instructions and the crown was built up with resin composite. After storage in water for 24 hours, the bonded specimens were serially sectioned into 0.7 mm-thick slabs and trimmed to an hour-glass shape with 1mm² cross-section isolated by normal or caries-affected dentin, and then subjected to a micro-tensile bond test. Data were analyzed by one and two-way ANOVA, and post hoc test(Dunnett T3 and T-test, p<0.05). For the control group, caries-affected dentin showed a significantly lower bond strength of the self-etch system than normal dentin. However, NaOCl treatment of the dentin surface followed by application of a reducing agent before the bonding procedure improved the bond strength to caries-affected dentin, in which there was no significant difference between bond strength of normal and caries-affected dentin. The effect of the reducing agent on bonding to caries-affected dentin treated with NaOCl depended upon the application time.