Ultrastructural changes in human dentine exposed to a weak acid

Abstract

The demineralization pattern in dentine exposed in vitro to an acid buffer was studied by electron microscopy. When ground dentine surfaces were exposed to 1 M acetate buffer at pH 5.8 for 20 hr a partially demineralized lesion was consistently produced which was distinctly demarcated against the underlying normal tissue. Decalcification of the peritubular dentine preceded that of the intertubular regions, not only in areas where the tubules opened on the experimental surface but also in areas where they were orientated parallel to this surface, indicating that the peritubular zone represents the most easily demineralized part of dentine. The peritubular zone became completely demineralized throughout most of the lesion. Varying amounts of mineral persisted in the intertubular regions. The remaining crystals were primarily those that were intimately associated with the collagen fibrils whereas interfibrillar crystals had been preferentially dissolved. Reprecipitation of material from dissolved apatite occurred in the dentinal tubules of some specimens. The precipitate contained large needle-like crystals, as well as rhombohedral or irregular, plate-like crystals. Electron diffraction patterns indicated the presence of whitlockite in these deposits. The results indicate that the mineral component of dentine is composed of several fractions which differ in their rate of solubility in weak acids.