Structure and Composition of the Peritubular Dentine Matrix

Peritubular dentine is a hypermineralised structure that surrounds dentine tubules. Recent studies have suggested that non-collagenous proteins, such as proteoglycans (PG) and glycosaminoglycans (GAG), might serve as scaffold for deposition of the peritubular mineral. Furthermore, it has been proposed that these non-collagenous components form an organic membrane that underlies the peritubular dentine, called “lamina limitans”. Objectives: Our experiments aimed to investigate these hypotheses by evaluating the dentine nanostructure after subjecting the tissue to partial demineralisation and specific proteolysis. Methods: Dentine cubes, obtained from non-carious teeth, had half their surfaces covered with masking tape and were partially demineralised with 10vol% citric acid for 2min. Subsequently, all specimens were treated with 1mg/mL TPCK-treated Trypsin containing 0.2M NH4HCO3(pH=9.5) for 48h at 37°C to unselectively remove PG and GAG from the dentin matrix. The specimens were then dehydrated using a graded series of acetone-H20 mixtures, coated with platinum and imaged using an FE-SEM. Results: Results suggested that after demineralisation the peritubular dentine was removed, thus widening the tubules' lumen and also revealing a thin membrane suggested to be the “lamina limitans”. More careful evaluation of the inner structure of the tubules also revealed the presence of collagen underneath this thin membrane. In addition, images of the partially demineralised tissue revealed nanostructured fibril-like strings running across the tubules' lumen. Following trypsin digestion, both the membrane-like structures and the nanostructured fibril-like strings, completely vanished, and a much more exposed collagenous network was revealed. Conclusion: Therefore, our results suggest that the “lamina limitans” may be primarily composed of noncollagenous proteins, such as PG and GAG, and may also contain collagen fibrils. Additionally, our images provide novel evidence that the peritubular dentin may be supported by PG and GAG. These results may provide insights into dentinal caries development as well as improved dental adhesive techniques and/or pre-treatments.