Cross striation in human permanent and deciduous enamel measured with confocal Raman microscopy

Dental enamel is the most mineralized tissue in the human body and has a very complex organization. The aim of the present study was to evaluate chemical composition and orientation of crystals in human enamel cross striation using confocal Raman microscope. Slices of teeth were prepared and scanned using a confocal Raman microscope. Cross striation spacing was calculated according to the variation of PO43- peak intensity. The measurements showed a characteristic length between two cross striations of 2.70 (SD 0.43) mu m for permanent teeth and 1.75 (SD 0.37) for deciduous teeth. Ratios between OH and PO43- peaks, for 0 and 90 degrees angulation, are, respectively, 9.18 (SD 0.80) and 44.74 (SD 3.12) for decidual teeth, and 11.72 (SD 1.46) and 22.12 (SD 3.15) for adult teeth. This confirmed that the hydroxyapatite crystal is well oriented along the enamel prism, as reported in the literature, but with a significant increase in deciduous teeth. K-mean cluster binary images were calculated to compare the ratio of the centroid peaks of the cross striation zone and inter cross striation material. The regions corresponding to inner prism, included cross striations, are more mineralized than the outer part of enamel prism. In the prism, the Pearson correlation test was performed based on the intensity of hydroxyapatite characteristic peaks (nu(1) PO43-, nu(1) CO3,2- and OH). The variations were well correlated: These results indicated that cross striations corresponded to the variation of hydroxyapatite concentration and not to a variation of crystals orientation.