Abstract
Gingival debris were collected from two groups of children, one group having black extrinsic tooth stain, and the other being a control group with no apparent coloured staining of the teeth. The material from the former group had a significantly higher content of calcium and phosphate than the latter but no significant difference in either carbohydrate or protein could be shown. The calcium and phosphate content of the debris from the black-staining group was significantly lower than that of samples of dental calculus. The increased calcium and phosphate content of the gingival debris from individuals with extrinsic black tooth stain is thought to largely account for the reduced incidence of caries.