The relation of lipids to the mineral components in salivary calculi.

Using lipid histochemical and microradiographic methods, the distribution of lipids and the inorganic component in different areas of salivary calculi was investigated. Two main groups of lipids were found, i.e. hydrophilic phospholipids and hydrophobic lipids. The hydrophilic phospholipids were shown to be composed mainly of phosphosphingosides and of the hydrophobic lipids cholesterol was demonstrated. Phosphosphingosides were localized in more or less lamellar zones as also in large homogeneous areas. In some cases the calculi were surrounded by a structureless non-mineralized zone exhibiting a strongly positive reaction for phosphosphingosides. Cholesterol was found in isolated band-formed areas. Phosphosphingosides and cholesterol were especially prevalent in areas showing a low or slight degree of mineralization. In areas showing a high degree of mineralization the corresponding lipids gave a weak or absent histochemical reaction. After EDTA-decalcification, however, an increase in the concentration of lipid was noticed in high mineralized areas, indicating a masking process. The influence of various factors on the presence and distribution of different lipids was discussed.