Cross-sectional microhardness of enamel subjected to erosive and/or cariogenic challenges

Methods: During 2 experimental 14-day crossover phases, 8 volunteers wore intraoral appliances containing four human enamel blocks randomly assigned. In the first phase, the appliances were immersed in a cola drink 3-times daily. Two enamel blocks were free of plaque (erosion only - EO) and two were covered with plaque (erosion and plaque - EP). In the second phase, four new blocks were all covered with plaque and subjected to a 20% sucrose solution eight times daily. Among the four new blocks two were also subjected the cola drink 3-times daily (erosion and caries - EC) while two were not (caries only - CO). Thus, in EO, the specimens were fixed at the intraoral appliance level. In EP, EC and CO they were fixed 1.0 mm under the appliance level and covered by plastic meshes for dental plaque accumulation. Enamel alterations were measured using longitudinal microhardness (10, 30, 50, 70, 90, 110, 220 and 330 µm depth, Kp/mm2). Data were tested using Linear Mixed Model and Bonferroni's test (p<0.05).

Results: On groups EO (163.7) and EP (301.0) the demineralization was restricted to 10µm depth, and the difference between them was significant. Group EC (10µm-36.2; 30µm-35.8; 50µm-125.8; 70µm-217.2; 90µm-275.9; 110µm-349.3) and CO (10µm-20.9; 30µm-12.7; 50µm-31.0; 70µm-90.4; 90µm-151.6; 110µm-202.2) presented significant demineralization until the 110µm depth. However, CO showed significantly higher demineralization at 50, 70, 90 and 110µm depth.

Conclusions: The data suggest that the presence of dental plaque can decrease the acid attack of an erosive drink and the association of erosive and cariogenic challenges showed less subsurface demineralization when compared to cariogenic challenge only.