Fine structure and composition of coronal cementum in guinea-pig molars

Abstract

Guinea-pig molars consist, in part, of a cartilage-like form of coronal cementum located within the buccal and lingual developmental grooves, and a more conventional coronal cementum occurring as small “pearls” on the peripheral surface of the enamel. The ultrastructure of demineralized cementum “pearls” was characterized by a relatively dense network of typically banded collagen fibrils within a finely granular organic matrix. The cartilage-like cementum matrix consisted primarily of finely granular, spherical aggregates, approximately 1–3 μm dia, closely packed together, which contained occasional, poorly defined collagen fibrils. Mineralization of this matrix was closely associated with matrix vesicles in a pattern similar to that reported for other mineralized tissues. Numerous lacunae within the calcified matrix contained the cellular remains of trapped cementoblasts. Chemical analysis indicated that cartilage-like cementum is approximately 62 per cent mineralized and is, therefore, more mineralized than cartilage. The collagen content of this form of cementum was approximately 5.5 per cent of total dry weight or 14 per cent by weight of demineralized matrix, a value considerably below that for dentine, conventional cementum, bone or cartilage. The hexosamine content was considerably below that reported in cartilage, but in the same range as that reported for bone. The organic matrix appeared to include elevated levels of acidic proteins which normally account for a small fraction only of the matrix of other calcified tissues. The Ca Pi and Ca + Mg Pi ratios were similar to those reported for apatite in other mineralized tissues.