MULTIMETHOD ANALYSIS OF APATITES IN SOUND HUMAN TOOTH ENAMEL

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, infra-red spectroscopy to evaluate the relative concentration Of CO3 and PO4 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 data were analysed using Normalized Principal Component Analysis. The chemical analyses show that FCI and FCE samples are affected by CO3 substituting for PO4, HCI and HCE samples by HPO4 substituting for PO4. 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 CO3 concentration. Packing order along c (Cs(002)) plays a discriminant role ; it is verv hi-h for FCE and verv 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.