Crystal characteristics of tooth enamel and dentin were investigated using XRD, SEM, and EPMA methods. The results show that the mineral phase in enamel is HA and in dentin is HA and minor whitlockites. The dentin HA and the enamel HA have different crystallinity, the crystallinity of enamel HA is much higher than that of dentin HA. The average particle size of the enamel HA and dentin HA are 897 ? and 309 ?, respectively. The HA in enamel is regularly arranged, and in dentin the arrangement of HA is different from the enamel HA in the same section. Both the enamel and the dentin are mainly consisted of Ca, P, O, and C, and the trace elements Mg, Sr, Al, Na, and K. The dentin contains more trace elements than the enamel. However, the incorporation of trace elements in both dentin and enamel are very limited. Other impurities such as F and Cl are less than their detection limit. The a and c values of enamel HA are 9.433 ? and 6.896 ?, and those of the dentin HA are 9.498 ? and 6.896 ?, respectively. The expansion in a value results from those the larger size of CO3 2- group substituing for the smaller OH- group in the channel, and replacement of OH- by CO3 2- dominates the change in cell parameter, taking into account of other trace elements.
