Why Can Some Chelators Inhibit While Others Promote Remineralization Dentin?

Objectives: Mineral inhibitors are crucial components of all body fluids. Hence, their inhibitory potential needs to be overcome to induce mineral formation in bone and teeth. Recent studies suggest that acid and/or phosphorylated matrix proteins act as transporters of calcium and phosphate ions to supramolecular protein scaffolds like such as collagen fibrils. Here, we evaluated a series of organic molecules for their ability to bind calcium, stabilize calcium phosphate solutions, and remineralize dentin collagen.
Methods: Stability of saturated calcium phosphate solutions was determined by measuring nucleation lag-time (starting pH 7.4) over 24-hours with addition of 0.01-0.5 mg/ml of one of these organic molecules: polyAspartic acid (pAsp, MW: 27, 14, and 6.8kD), polyGlutamic acid (pGlu, MW: 30kD), Osteopontin (OPN10, Arla Foods) and matrix-gla protein derived peptides MGla (4 variations) with and without gamma-carboxylated glutamic acid (gE) and phosphorylated serine (pS). Particle diameter and Zeta-potential were analyzed by dynamic light scattering. Demineralized dentin lesions were created in undersaturated buffers, subsequently exposed to remineralizing solutions with different chelators for 14 days and examined by SEM/EDX.
Results: Additions of pAsp, OPN10, and MGla with pS stabilized solutions for over 24 hours, while pGlu and 2 variants of MGla without pS did not. SEM and elemental mapping demonstrated that demineralized dentin can be remineralized in PILP-solutions comprised of 27 and 14kD pAsp and OPN10, whereas all other molecules did not facilitate dentin collagen mineralization. Particle size analysis showed that only the chelating agents that formed particles of less than 30nm in diameter (27, 14kD pAsp, OPN10) remineralized dentin. All other molecules formed larger particles and did not remineralize dentin.
Conclusions: An association of particle size of charged molecules suspended in saturated calcium phosphate solutions with the ability to mineralize dentin collagen was identified. This size-dependency can be explained on the basis of the structural model of collagen fibrils.