A quantitative microradiographic study of mineral content of supragingival and subgingival dental calculus.

This study was undertaken to determine the distribution and concentration of mineral in supragingival and subgingival dental calculus. Extracted incisors and premolars with attached dental calculus were used. After fixation the specimens were dehydrated and embedded in methylmethacrylate and 100-micrometers-thick ground sections were made. Microradiographs were produced and the mineral content in the sections was determined photometrically, using an aluminum step-wedge as a reference system. The distribution of the mineral varied considerably within the specimens and between different specimens. Supragingival calculus appeared heterogeneous and often stratified, containing areas that seemed to be non-calcified. The average mineral content was 37% by volume. By contrast subgingival calculus appeared homogeneously calcified, with an average mineral content of 58%. No differences in mineral content between surface areas and portions close to the tooth were seen. This indicates that once the calculus is formed no changes occur in the mineral content, i.e. no maturation occurs with age. Local variations in mineral content within the calculus might be explained by periodic differences in the fluid environment of the microbial plaque.