The Bond Between Resin Composite Restorations and Dentin may Degrade in the Mouth Over Time

The subjects were outpatients who attended the Department of Pediatric Dentistry of Hokkaido University for treatment of caries. The laboratory study of the dentin-restoration interface of the pulpal wall of Class II composite resin restorations in extracted deciduousmolars were collected from 2 different sources. The first source was restored teeth from a prospective cohort with up to 3 years of observations (n = 22), and the second source was intact teeth from a cross-sectional convenience sample that were subsequently prepared using the same restorative materials and procedure as in vivo and restored extraorally (n = 13) as control specimens. Ethical approval was obtained by the appropriate institutional review board.The primary study factor was the length of time spent by the resin-dentin bond in the oral cavity: (1) control (24 hours in distilled water only); (2) 1 to 2 years; or (3) 2 to 3 years.The primary outcome measure was the integrity of the resin-dentin bond, measured within 2 weeks of tooth extraction represented by microtensile bond strength and by micromorphometric measurements of the fracture surfaces in a scanning electron microscope.There were significant differences inmicrotensile bond strengths among all 3 groups-control group, 28.3 +/- 11.3 MPa; 1 to 2 years, 15.2 +/- 4.4 MPa; 2 to 3 years, 9.1 +/- 5.1 MPa (P < .05)-to suggest that the structural integrity of resin-dentin bonds decreased over time. The investigators related the characteristics of the microstructure of the fractured specimens to the observed reductions in microtensile bond strength and attributed this association to in vivo degradation of adhesive and composite resin and of exposed collagen located in the demineralized dentin beneath the resin-impregnated hybrid layer.The authors concluded that degradation of resin-dentin bond structures occurs after aging in the oral cavity.