The lamina limitans of human dentinal tubules.

Fractured coronal surfaces of both fixed and unfixed human teeth were examined by scanning electron microscopy following HCl demineralization and collagenase digestion. This treatment removed a considerable amount of matrix from the surface of dentin. Tubular structures, termed lamina limitans, were not affected by this treatment and remained on the surface of the tissue. The lamina limitans extended from the pre-dentin-dentin junction to the dentin-enamel junction. Further enzymatic digestion of unfixed specimens with hyaluronidase resulted in the complete removal of the lamina limitans. The susceptibility of the lamina limitans to hyaluronidase digestion indicates a high content of glycosaminoglycan, suggesting that they are extracellular in nature. These data provide further evidence that lamina limitans are not odontoblast processes.