Surface properties of eroded human primary and permanent enamel and the possible remineralization influence of CPP-ACP

Abstract

It has been widely accepted that the microstructure and composition of human primary enamel differ from those of human permanent enamel. However, the difference of their erosion behaviour has not been fully understood. To extend the understanding of dental erosion, the surface properties of eroded human primary enamel and the possible remineralization influence of CPP-ACP were investigated in vitro by comparing them with those of human permanent enamel in this study. Enamel specimens were prepared from human primary and permanent molar teeth. The enamel specimens were firstly immersed in citric acid solution (pH=3.20) for 0.5, 1, 3, 5, and 10min, respectively, to obtain eroded specimens. After 10min of erosion, remineralization treatment was conducted in vitro by immersing the eroded specimens in 2% w/v casein phosphopeptide-stabilized amorphous calcium phosphate solution (CPP-ACP) for 12h. The surface morphologies of enamel were analyzed by means of various microscope examinations, and its nanomechanical and microtribological properties were examined using nano-indentation/scratch technique. Results showed that the erosion resistance of primary enamel was inferior to that of permanent enamel. An obvious honeycomb-like structure caused by acid attack appeared on the surface of primary enamel only after 3min erosion but appeared on the surface of permanent enamel after 5min erosion. Both the nanomechanical and microtribological properties of the two enamel decreased significantly after erosion treatment. Compared with permanent enamel, the influence of erosion on the nanomechanical properties and microtribological behaviour of primary enamel was more significant. The loss of hardness and Young's modulus and the decrease of wear-resistance of enamel surface by acid erosion were recovered obviously after remineralization treatment. But the recovery of primary enamel was weaker than that of permanent enamel. These results indicated that the primary enamel should be more susceptible to acid-erosion and the remineralization treatment with CPP-ACP could contribute to the repair of its erosion lesions less effectively as compared to permanent enamel.