Incorporation of (35S)sulfate and (3H)glucosamine into glycoaminoglycans in rat incisor predentine and dentine: comparison by autoradiography of fixation by rapid-freezing, freeze-substitution, and aldehyde fixation.

At 4 and 24 hours after injection of (35S)sulfate, there were 22-67% fewer silver grains on conventionally fixed sections than on sections fixed by cryotechniques. Differences were smaller when (3H) glucosamine was chosen as precursor. The number of silver grains increased between 4 and 24 hours in predentine and in a 30-micron band of dentine that had already undergone mineralization. Only a few grains were observed, however, in the 5-micron dentine band located at the mineralization front. This suggests that glycoaminoglycans, which in predentine have a space-filling role, facilitate transport and diffusion and inhibit mineralization, may limit crystal growth in dentine once a certain degree of apatite formation has been reached. All these properties are correlated with the structural and functional properties of the tissues.