Evaluation of bacteria-induced enamel demineralization using optical profilometry

Objectives: Streptococcus mutans is considered a major causative of tooth decay due to its ability to rapidly metabolize carbohydrates such as sucrose. One prominent excreted end product of sucrose metabolism is lactic acid. Lactic acid causes a decrease in the pH of the oral environment with subsequent demineralization of the tooth enamel. Biologically relevant bacteria-induced enamel demineralization was studied. Methods: Optical profiling was used to measure tooth enamel decay with vertical resolution under one nanometer and lateral features with optical resolution as a result of S. mutans biofilm exposure. Comparison measurements were made using AFM. Results: After 72 h of biofilm exposure the enamel displayed an 8-fold increase in the observed roughness average (R_a), as calculated over the entire measured array. Similarly, the average root mean square (RMS) roughness, R_RMS, of the enamel before and after biofilm exposure for 3 days displayed a 7-fold increase. Further, the direct effect of chemically induced enamel demineralization using biologically relevant organic acids was shown. Optical profiles of the enamel surface after addition of a 30% lactic acid solution showed a significant alteration in the surface topography with a corresponding increase in respective surface roughness statistics. Similar measurements with 10% citric acid over seconds and minutes give insight into the demineralization process by providing quantitative measures for erosion rates: comparing surface height and roughness as metrics. Significance: The strengths of optical profilometry as an analytical tool for understanding and analyzing biologically relevant processes such as biofilm induced tooth enamel demineralization were demonstrated.