Validation of In Vitro Initial Erosion Protocol Using Different Methods

Objectives: The aim of this in vitro study was to establish and validate a protocol for the formation of initial erosion lesion with extrinsic and intrinsic acid. In addition, different measurement methods were compared regarding their ability to detect the beginning of enamel loss.
Methods: Twenty-four bovine enamel blocks were selected by surface microhardness and randomly divided into two groups (n=12): intrinsic- hydrochloric acid (0.01 M, pH 2.3) and extrinsic- cola drink (Coca-Cola™, pH 2.4). Each block was immersed in 17.5 ml of cola drink or hydrochloric acid for 240 seconds (under stirring, 24^oC). After 15s, 30s, 60s, 120s and 240s enamel alterations were determined by surface Knoop hardness, roughness measurement (Ra), profilometry, and depth of hardness impression (based on length indentation) before and after each erosive attack. Data were analyzed by repeated measures ANOVA and Tukey test (p <0.05).
Results: Independent of the groups, surface hardness decreased progressively with increasing erosive effects. The depth of hardness impression decreased only after 30s of erosive challenge for both groups. The indentation length could not be measured on the enamel samples eroded for >60s. The profilometry showed enamel loss for all evaluated periods of erosion, however there was no difference among 15s, 30s and 60s and between groups. Roughness increased significantly only after 240s of erosion for both studied acids.
Conclusions: According to the results, intrinsic and extrinsic acids were able to promote in vitro initial erosion by the immersion of bovine enamel in 17.5 ml under stirring for 30 seconds (24^oC) of hydrochloric acid and Cola drink, respectively. After 30 seconds acids promoted enamel loss. All the methods used on the study gave complementary data for the understanding of the process of dental erosion.