Purpose: To evaluate in vitro secondary caries formation and inhibition by using a confocal laser scanning microscope (CLSM), and further map the calcium distribution with an X-ray analytical microscope (XAM).
Materials and methods: 36 box-shaped cavities were prepared on bovine root dentin and restored with Fuji II, Fuji II LC (improved), or Clearfil Liner Bond 2V system with a non-fluoride releasing resin-based composite; Clearfil AP-X was used as a negative control. After immersion in a buffered demineralizing solution of 50 mmol/L of acetic acid adjusted to pH 4.5 for 3.5 days, longitudinal half sections were cut through each restoration and polished for analysis under CLSM. In order to confirm the CLSM results, the same samples were subsequently examined by means of the X-ray analytical microscope (XAM). The values of the outer lesions and the inhibition zones obtained by the two different CLSM and XAM measurements were then analyzed by one-way ANOVA, Fisher's PLSD Test at the 95% level of confidence and correlation coefficient.
Results: Inhibition zones and outer lesions were clearly detected under CLSM around the glass-ionomer and resin-modified glass-ionomer restorations. As expected, an inhibition zone was not detected adjacent to the resin-based composite restoration. Additionally, using the transmission x-ray images of XAM, the inhibition zones were observed as high density areas, and the outer lesions as low density areas. The width of the inhibition zones and the depth of the outer lesions measured under the CLSM were similar to those obtained from the XAM.