Measuring Depth of Erosion Using Polarized Light Microscopy Method

Objectives: Several methods are used to evaluate surface changes including profilometry and scanning electron microscopy. The purpose of this study was to evaluate the depth of erosion in enamel and dentin on exposure to different tooth bleaching materials using polarized light microscopy.
Methods: Extracted human teeth (n=72) were used with IRB approval for preparing enamel and dentin blocks. The buccal surface was flattened and protected with nail varnish leaving a 1.0mm unprotected stripe down the center of the surface. The specimens were randomly assigned to one of the following groups (n=6) for enamel and dentin: 1.0% citric acid (PC1), 0.25% citric acid (PC2), 20% Hydrogen-peroxide (Zoom QuickPro, QPRO), 10% carbamide-peroxide (Opalescence PF, OPAL), Natural White (NW) and treated according to manufacturer’s directions. The negative control (NC) was exposed to Grade 3 water. Specimens were then sectioned perpendicular to the exposed stripe to yield 3- 4 cross-sections from each specimen. Cross-sections were examined under a polarized light microscope and erosion depth for each section was based on the average of triplicate measurements. Group differences were evaluated using the Kruskal-Wallis test, with pairwise comparisons made by exact Wilcoxon rank sum tests using Bonferroni adjustment in conjunction with an overall 0.05 level of significance.
Results: There was a significant difference in the distribution of enamel and dentin erosion depth among the six groups (p<0.0001). After adjustment for multiple comparisons, there was no evidence of a significant difference in enamel erosion depth between QPRO and NC groups (p=0.0368). In dentin, there was a significant difference comparing the NC group with the other groups. Dentin erosion depth in the NW group tended to be greater than the OPAL and QPRO groups respectively.
Conclusions: The use of polarized light microscopy is a simple yet adequate method in evaluating depth of erosion in enamel and dentin.