Susceptibility of Enamel and Dentin to Demineralization by Cariogenic Acid

Objectives: This project aims to quantitatively analyze the Vickers hardness of the outer enamel, inner enamel, and dentin before and after cariogenic acid treatment in vitro. The purpose of the study is to provide insights into the outer enamel’s protective ability and to provide quantitative data for future applications.
Methods: By measuring the Vickers Hardness of the dentin, inner enamel, and outer enamel; and comparing to the Vickers Hardness of the same zones after demineralization of the samples, this research provides quantitative data to support the hypothesis that outer enamel is more resistant to cariogenic acid than the inner enamel and the dentin.

Samples were prepared by, removing the roots and subsquently cutting 3rd molars (N=3) through the center, longitudinally with a Buehler IsoMet Low Speed, from the cusps to the bottom of the crowns. After polishing, microindentation was made using a Leco M-400-H1 microhardness testing unit with Confident Software to measure the Vickers Hardness in HV of each zone (dentin/ inner enamel/ outer enamel) before and after demineralization. For each sample, three zones, including dentin, inner enamel, and outer enamel, were measured. Within each zone, three areas were measured and marked. In each area, 10 measurements were taken. A total of 90 measurements per sample were made. Then the samples were treated with a demineralization solution (pH 4.6) for 19 hours to mimic the demineralization of teeth by cariogenic acid in the oral cavity. Measurements of the Vickers Hardness were retaken at each previously marked area.
Results: The statistical analysis of change in each zone is listed in Table 1. All zones show a statistically significant decrease in Vickers microhardness after demineralization. Our new findings are 1) the dentin microhardness shows a 3.59 times more percent decrease than the outer enamel, and 2) the inner enamel shows a 2.55 times percent decrease than the outer enamel.
Conclusions: Our data on the change in different tooth zones supports the hypothesis in which the outer enamel is more resistant to cariogenic acid than the inner enamel and the dentin. The results provide insight into the outer enamel’s protective ability.