Effect of Novel Calcium Phosphate Nanocomposites on Remineralization of Dentin

The use of composite dental restorations is limited by the formation of secondary caries over time.  Objectives: To investigate the remineralization of an artificially created lesion in human dentin in vitro after restoration with a nanocomposite containing nanoparticles of amorphous calcium phosphate (NACP) or a nanocomposite containing NACP and micron-sized tetracalcium phosphate (TTCP).  Methods: NACP was synthesized by a spray-drying technique and incorporated into an adhesive dental resin consisting of a 50:50 mixture (by mass) of ethoxylated bisphenol A dimethacrylate (EBPADMA) and the acidic pyromellitic glycerol dimethacrylate (PMGDM). After restoring the dentin lesions with the two nanocomposites as well as the non-releasing commercial hybrid composite TPH control, the specimens were treated with a cyclic demineralization/remineralization regimen for 4 and 8 weeks.  Calcium and phosphate ion release was measured over 56 days. Dentin remineralization was measured at 4 and 8 weeks by transverse microradiography (TMR).  Results: Lowering the pH substantially increased the amount of ion release in the NACP-TTCP nanocomposite. At 56 d, the released calcium ion concentration (mean±sd; n=3) was (13.39±0.72) mmol/L at pH 4, much higher than (1.19±0.06) mmol/L at pH 7 (p<0.05).  At 56 d, the released phosphate ion concentration (mean±sd; n=3) was (5.59±0.28) mmol/L at pH 4, much higher than (0.26±0.01) mmol/L at pH 7 (p<0.05).   Quantitative microradiography showed typical subsurface dentin lesion formation prior to the cyclic demineralization/remineralization treatment, and significant remineralization in dentin via NACP and NACP-TTCP nanocomposite after 4 and 8 weeks of treatment.  The NACP nanocomposite had dentin remineralization (mean±sd; n=15) of (48.2±11.0)% at 8 weeks, significantly higher than the (5.0±7.2)% for commercial non-releasing composite control (p<0.05). Conclusions: Novel NACP-based nanocomposites were effective in remineralizing dentin lesions in vitro. The new NACP and NACP-TTCP nanocomposites have promise for use in restorations to inhibit secondary caries.