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Influence of HClO4 strength and etching time on rate of etching and surface roughness of human enamel.

The aim of this study was to compare the rate of etching and the surface roughness of HClO4 etched enamel surfaces. The average thickness of the enamel layer removed is a linear function of the total etching period (except for very short periods). The rate of etching (β) in μm s––1 with HCIO4 is strongly influenced by acid strength and stirring rate during etching; it is ∼ 0.02, 0.06, 0.18 and 0.74 μm s––1 for 0.02, 0.1, 0.5 and 2.0 M HCIO4, respectively, β is a linear function of the acid strength. Scanning electron microscopy (SEM) pictures of the specimens show that acid strength, etching time and chemical composition of the enamel are most likely important factors determining surface morphology of etched enamel. A lower acid concentration gives a sharper etch; increasing acid strength causes increasing surface roughness.