Influences Of Nucleation Lag Time On Remineralization Of Demineralized Dentin

Objectives: Remineralization of dentin lesions with calcium phosphate solutions is a slow process and requires several days of treatment. The current experiment examined the effectiveness of a constant composition titration system to remineralize demineralized dentin.  Methods: Extracted human molars were cut with a low-speed Buehler saw and a diamond blade, polished with a strip grinder, adhesive polishing discs, and diamond polishing slurries to 1um and ultrasonicated between each process. These dentin discs were later cut into 3 by 6 mm² dentin slabs and covered with nail varnish leaving only a 3 by 3 mm² window on the occlusal surface. Artificial caries lesions were made using 0.05M acetic acid buffers with calcium and phosphate at pH 5.0 for 66 hours to create a lesion depth of 100µm. Lesions were completely dehydrated and stored prior to use. Next, specimens were immersed into a pH 7.4 metastable remineralization solution of 8mM CaCl₂ and 5mM KH₂PO₄ with the constant composition system titrating two separate pH 7.4 solutions of 8mM CaCl₂ and 5mM KH₂PO₄ at a constant rate into the reaction vessel containing the dentin samples.  This was either done for 7 days or 14 days. Samples were later embedded into epoxy, sectioned perpendicular to the exposed surface,  air dried, polished down to 0.25µm, ground down to a thickness of 100µm and analyzed by polarized light microscopy (PLM).  Nanoindentation was used to test the mechanical properties of the remineralized lesions.  Results: Lesion depth: Control averages are 109.5±10.3µm, 7 days averages are 77.0±5.8µm, 14 days averages are 82.4±8.2µm. Conclusions: The constant composition titration system increases the nucleation lag time thereby allowing demineralized dentin more time to nucleate and potentially more time to nucleate within the intrafibrillar (within collagen fibrils) dentin so that more mechanical properties are regained.