Objective: The purpose of this study was to determine the rate of change in indentation hardness and indentation modulus of enamel in permanent teeth exposed to Coca-Cola® (Coca-Cola Co. Atlanta, GA, USA). Methods: 14 specimens were randomly chosen to be treated with either Coca-Cola® (experimental group n=10) or water (control group n=4). The enamel hardness was tested after applying the fluids for 1, 2, 3 hours and overnight using a micro-indentation system (+CSM® Instruments. A diamond Vickers indenter (tip radius 50nm) indented into the enamel specimen (with a maximum applied load of 0.5 N at an applied loading/unloading rate of 1N/min). The load and depth of the indentation on the enamel surface was monitored continuously on-screen. Results: There was a ~7.4% reduction in indentation hardness after 1 hour exposure to acidulated beverage, but little further change after 2 hours. After 3 hours there was a mean 14.26% reduction in indentation hardness and with overnight exposure there was a mean 19.71% reduction. Using a multivariate model, there was a significant difference in sample hardness for duration of Coca-Cola® exposure (F=5.054, p=0.022). Conclusion: We conclude that acidulated beverage reduced the indentation hardness of enamel in permanent teeth over several hours at a highly variable rate, while indentation modulus was unaffected. There was no obvious correlation between the original hardness values at baseline and the resultant loss of hardness following Coca-Cola® application. The factors determining the rate of loss of hardness of enamel by acidulated beverages are at present unknown and require further investigation.

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