Ligand-mediated Thermal Stabilization of Demineralized Collagen in its Hydrated State

The infiltration of hydrophilic monomers into the interstices between the exposed collagen fibrils of demineralized dentin is important in the bonding of restorations to tooth. Any interaction of collagen with these adhesive monomers (ligands) may be associated with its thermal stability from denaturation in the presence and absence of these adhesives. Objectives: The objective of this investigation was to characterize the thermal denaturation of demineralized dentinal collagen treated with water (control) and typical dentin primers, namely aquous ethanol solutions of 2-hydroxyethyl methacrylate   (30% HEMA) and monomethacryloyloxyethyl phosphate (20% PM). Methods: Mid-coronal sound dentin sections were prepared and demineralized with EDTA (pH=7.4).  Modulated differential scanning calorimetry (TA Instruments DSC model 2910) was used for the analysis.  All thermal scans were carried out at 10^oC/min. A typical thermal scan of demineralized collagen structure revealed two endothermic peaks associated with (a) hydration network (£100^oC) and (b) collagen denaturation (>100^oC). A baseline treatment (BT) of demineralized collagen was carried out by a programmed thermal scan to 100^oC to remove the hydration peak. BT structures were rescanned between –10^oC and 220^oC under different conditions of no treatment (NT) and 1 hr exposure to water (WT), aqueous HEMA (HT) and aqueous PM (PT). Results: The solvent treated collagen denaturation peaks occurred at significantly lower temperatures than the NT peak at 108^oC. Significant differences in the integrated heat flow (J/gm) were also observed (p<0.05). The integrated endothermic heat flows of HT and PT denaturation were significantly higher than that of WT indicating enhanced thermal stability of collagen in the presence of ligands. HT and PT denaturation temperatures were also higher than that of WT. Conclusions: The thermal stabilization of BT structure by the ligand mediated aqueous solutions indicates ligand interaction with dentinal collagen enhancing its stability against denaturation in its hydrated state.