Multimethod analysis of apatites in sound human tooth enamel

Abstract

A multimethod analysis of mineral apatite of sound human tooth enamel was used to study the chemical variation and crystallinity of 20 samples originating from high-caries-activity mouths (HC), with impacted (HCI) or erupted teeth (HCE), and from mouths free of caries activity (FC), with impacted (FCI) or erupted (FCE) teeth. The different methods used are electron microprobe analysis to determine the concentration of Ca, P and Mg, infrared spectroscopy to evaluate the relative concentration of CO 3 and PO 4 in the different samples. X-ray diffraction was used to calculate the lattice parameters and the coherent scattering thickness (Cs) deduced from (300), (002) and (004) reflections. All the datat were analysed using Normalized Principal Component Analysis. The chemical analyses show that FCI and FCE samples are affected by CO 3 substituting for PO 4 , HCI and HCE samples by HPO 4 substituting for PO 4 . The apparent coherent scattering thickness (Cs) along c is lower for FCI and HCE than for FCE and HCI. There are more crystal defects along c for the former two samples. Data analysis shows that a, c and packing order along c are, in part, inversely correlated with CO 3 concentration. Packing order along c (Cs(002)) plays a discriminant role; it is very high for FCE and very poor for HCE, moderate for FCI and HCI. Chemical substitutions and size of lattice parameters are not really discriminant either for the position (I or E) or for the origin (FC or HC) of the samples. The caries susceptibility can be related to an increase of Cs(002) in erupted teeth and a decrease of Cs(002) in impacted teeth and also to an apparent excess of cationic charge. These observations seem to be indicative of the existence of a predisposition to caries correlated to chemical and structural (crystallographic) parameters of enamel