In vivo degradation of resin-dentin bonds in humans over 1 to 3 years

The longevity of resin restorations is currently an area of great interest in adhesive dentistry. However, no work has been conducted to investigate t he durability of resin-dentin bond structures using human substrate in vivo . The purpose of this study was to investigate the degradation of the resin -dentin bond structures aged in an oral environment for 1, 2, or 3 years. C avities were prepared in primary molars, and an adhesive resin system (Scot chbond Multi-Purpose) was applied to the cavity. After 1 to 3 years, follow ing the eruption of the succedaneous permanent teeth, the resin-restored te eth were extracted. Immediately after extraction, those teeth were sectione d perpendicular to the adhesive interface and trimmed to produce an hourgla ss-shaped specimen. Then, a micro-tensile test was performed at a crosshead speed of 1.0 mm/min. The mean bond strengths were statistically compared w ith one-way ANOVA and Fisher's PLSD test (p < 0.05). Further, all fractured surfaces were observed by SEM, and the area fraction of failure mode was c alculated by means of a digital analyzer on SEM photomicrographs. There wer e significant differences in tensile-bond strength among all 3 groups (p < 0.05), with mean values ranging from 28.3 +/- 11.3 MPa (control), to 15.2 /- 4.4 MPa (1 to 2 years), to 9.1 +/- 5.1 MPa (2 to 3 years). Moreover, und er fractographic analysis, the proportion of demineralized dentin at the fr actured surface in specimens aged in an oral environment was greater than t hat in control specimens. Furthermore, degradation of resin composite and t he depletion of collagen fibrils was observed among the specimens aged in a n oral environment. Analysis of the results of this study indicated that th e degradation of resin-dentin bond structures occurs after aging in the ora l cavity.