Resin adhesion to carious dentin.

PURPOSE

To investigate the microtensile bond strength (microTBS) of a self-etching priming adhesive system to normal, caries-affected and caries-infected dentin, and to observe the ultrastructure of the resin-dentin interface by transmission electron microscopy (TEM).

MATERIALS AND METHODS

Twelve extracted human molar teeth with deep occlusal caries were stained with caries detector solution and ground flat occlusally. The red-stained soft dentin was classified as caries-infected. The surrounding discolored dentin was classified as caries-affected dentin. The surrounding normal dentin served as a control. The entire flat surface was bonded with Clearfil Liner Bond 2V (CV) and covered with resin composite to form a composite crown 5 mm high. One day later the specimens were serially sectioned vertically into multiple slabs 0.8 mm thick. Under microscopic observation, the specimens were divided into normal or caries-infected or caries-affected dentin. These regions were isolated by cutting away the remaining dentin to form hour-glass shapes with the smallest surface area at the test site. After measuring the areas, the specimens were fixed to a microtensile tester and pulled under tension to failure. Additional slabs that were not used for bond strength tests were processed for TEM. Bond strength data were analyzed by Kruskal-Wallis one-way ANOVA and Student-Newman-Keuls multiple comparisons.

RESULTS

The microTBS of CV to normal, caries-affected and caries-infected dentin were 45 +/- 10 MPa, 30 +/- 10 MPa, 10 +/- 5 MPa, respectively. TEM images showed that CV formed thin hybrid layers that were less than 1 microm thick in normal dentin, but that were between 6-8 microm thick in caries-affected dentin. Bacteria were only sparsely observed in the dentin tubules of bonded caries-affected dentin. However, in caries-infected dentin, an unusual interface was seen in which carious bacteria within disorganized non-banded collagen fibrils could be seen embedded by the adhesive. The hybrid layer in caries-infected dentin was found to be 30-60 microm thick.