In Situ Study of Tooth Wear and Dentifrice RDA

Objectives: The objective of our study is to (1) determine the relationship between dentifrice RDA and tooth wear using an in situ model and (2) assess the clinical relevance of the degree of tooth wear found. Methods: The in situ study used a double blind, randomized, cross-over design in which standardized enamel blocks mounted in removable oral appliances were brushed with three silica based dentifrices (RDA=108, 150, and 210) for a six week period. Twelve male and female subjects were recruited for the study and instructed to brush the enamel blocks with the assigned dentifrice for 60 seconds twice daily. Tooth wear in the enamel blocks was measured by the change in length of three Knoop indents before and after the six week test period according to the method of Joiner et al. The amount of enamel abrasion was calculated by the average change in indent depth between baseline and six weeks based on change in indent length using the equation: Δd = 0.5 Δl / Tan(86.25) = 0.032772 Δl. Results: Statistical analysis (ANOVA) performed on the six week data showed no statistical difference between groups (p>0.05). RDAs of 108, 150, and 210 showed wear of 0.099, 0.100, and 0.131 μm respectively. The nearly identical values for RDA of 108 and 150 combined with only 30% increase in wear with a 2x RDA increase reflect lack of a clear linear relation. Conclusions: This study shows there is no significant difference in the amount of tooth wear from commercial dentifrices with RDA values of ~100 to 210. Poor linearity between RDA and enamel wear demonstrate RDA is not a predictive measure of enamel loss in vivo. Finally, the degree of enamel wear seen in this study was clinically insignificant when extrapolated over a lifetime of brushing.