Evaluation of pH and erosion time on demineralisation.

In the current study the effect of various pH values of citric acid and erosion time on erosion depth and subsurface demineralisation of human enamel was studied. In a laboratory investigation, six groups of 10 samples were eroded in 0.3% citric acid for 2 h at pH 2.54, for 2 h or 4 h at pH 3.2 and for 2 h, 4 h or 8 h at pH 4.5. The erosion depth was measured using a profilometer. The demineralised layer was then removed by ultrasonicating the samples with profilometric measurements taken at 5, 30, 120, 240 and 480 s ultrasonication time. The six test groups were classified by analysis of variance into four homogeneous groups according to their erosion depth and into three homogeneous groups according to their subsurface demineralisation. Erosion depth clearly depended on the pH value of the acid and the contact time. Depth of subsurface demineralisation and surface morphology did not depend on erosion depth. Similar subsurface demineralisation depths can be produced by appropriate combinations of pH and contact time.