Enamel surface alterations after repeated conditioning with HCl

BACKGROUND The aim of this study was to investigate the influence of etching time with 15% hydrochloric acid (HCl) on the enamel surface destruction by studying the resulting roughness and erosion depth. METHODS The vestibular surfaces of 12 extracted, caries free human incisors were divided into four quadrants, and each quadrant was etched with 15% HCl for different numbers of etching cycles (1×2, 2×2, 3×2 and 4×2 min). Surface roughness and erosion depth were measured quantitatively with optical profilometry, and the surface morphology was imaged with scanning electron microscopy (SEM). RESULTS After two minutes of 15% HCl application a median enamel substance loss of 34.02 μm was observed. Lengthening of etching time (2×2, 3×2 and 4×2 min) resulted in significantly increase in erosion depth to each additionally, between 13.28 -15.16 μm (p < 0.05) ending up in a total median enamel surface loss of 77 μm. Regarding surface roughness no significant (p > 0.05) difference was found between unetched enamel and the etched enamel surfaces. CONCLUSION Repeated 15% HCl conditioning of the enamel surface increases the depth of the etched surface erosion. However, the total erosion depth is rather shallow and therefore negligible.