Comparing different methods to assess erosive lesion depths and progression in vitro

The aim of this study was to compare the precision and accuracy of 5 different methods applied to assess surface substance loss or changes in surface microhardness (SMH) on the same enamel surfaces after repeated acid exposures. Ground specimens from human molars were exposed to 0.01 M HCl (pH 2.2) for 6 min × 2 and measurements performed 3 times to estimate precision. The accuracies (systematic errors) were calculated against the manufacturer's calibration standard. Lesion depth progression was from 94 to 110%, related to repeated acid exposure. The precisions/accuracies were: WLI (white light interferometry), 0.5/0.4%; SP (stylus profilometry), 4.7/0.7%; OP (optical profilometry), 1.4/12%; AAS (atomic absorption spectroscopy), 0.4/17% (measured calcium loss was converted to lesion depth). The correlation between WLI and SP was R² = 0.98, and between WLI and OP it was R² = 0.85. SMH gave information on qualitative changes of the surface (precision: 5.5%, accuracy: 4.0%). WLI performed best in precision and accuracy, but SP, OP and AAS are all relevant methods for analysing lesion depths and progression, SMH seems suitable for analysing minor changes in surface enamel only.