Drago Skrtic

Quantitative Assessment of the Efficacy of Amorphous Calcium Phosphate/Methacrylate Composites in Remineralizing Caries-like Lesions Artificially Produced in Bovine Enamel

Recent studies show that methacrylate-based composites with amorphous calcium phosphate (ACP) as a filler can release supersaturating levels of calcium and phosphate ions in proportions favorable for apatite formation. These findings suggest that such composites could be effectively used as coatings for remineralizing teeth damaged by tooth decay. To examine this hypothesis, we tested composites in vitro for their efficacy to remineralize artificially formed caries-like lesions in extracted bovine incisors. Single 120-μm-thick sagittal tooth sections were placed in holders that exposed only the carious enamel surface. The exposed surfaces were coated with a 1-mm- to 1.5-mm-thick layer of the composite containing, by mass, 40% apatite, silica, or P2O7 4--stabilized ACP and 60% photoactivated resin comprised of Bis-GMA, TEGDMA, HEMA, and ZrM. The photocured composite-coated sections were immersed either in a remineralizing solution for 4 weeks at 37°C (static model) or cyclically immersed in demineralizing (0.5 h) and remineralizing solutions (11.5 h) for 2 weeks (dynamic model). Quantitative digital image analysis of matched 102 μm x 220 um areas from contact microradiographs taken of the sections before and after immersion showed that lesions coated with ACP-filled composites fractionally recovered 71% ± 33% of their lost mineral compared with 14% ± 13% for apatite controls in the static model and 38% ± 16% compared with -6% ± 24% in the dynamic model. The results suggest that sealants based on ACP-filled methacrylate composites have the potential to remineralize carious enamel lesions.

Improved properties of amorphous calcium phosphate fillers in remineralizing resin composites

OBJECTIVESnThe rationale for this study was based on the hypothesis that the mechanical strength of methacrylate composites containing the bioactive filler, amorphous calcium phosphate, can be enhanced by synthesizing this filler in the presence of glass-forming agents. Specifically, this study was conducted to prepare composites with zirconia- and silica-modified amorphous calcium phosphate fillers, and to determine whether the remineralization potential from the release of calcium and phosphate ions and the mechanical properties of the corresponding methacrylate composites were enhanced.nnnMETHODSnThe modified amorphous calcium phosphates were synthesized at pH 10.5 by mixing 800 mmol/L Ca(NO3)2 solutions and either 250 mmol/L zirconylchloride (ZrOCl2) or 4.4 mol/L tetraethoxysilane (TEOS) solutions with solutions containing 525 mmol/L Na2HPO4 and 11 mmol/L Na4P2O7. After washing and drying, the amorphous calcium phosphates were mixed with visible light-activated resins and photopolymerized to form composite disks that were then examined for their ability to release Ca2+ and total ionic phosphate (PO4(3-) + HPO4(2-) + H2PO4-, hereafter indicated as PO4) by immersion in HEPES-buffered (pH 7.4) saline at 37 degrees C. Solution ion concentrations were compared at regular intervals up to 265 h. Biaxial flexural strengths of the composites before and after immersion were compared, and significant differences were established by Students test (p < 0.05).nnnRESULTSnBoth ZrOCl2- and TEOS-modified amorphous calcium phosphate composite disks released Ca2+ and PO4 ions at sustained levels requisite for remineralization to occur. The transformation of amorphous calcium phosphate into hydroxyapatite within the composites was also retarded, particularly in the case of amorphous calcium phosphate modified with ZrOCl2. Biaxial flexure strength values of composite disks showed that TEOS- and ZrOCl2-amorphous calcium phosphate-filled composites increased in strength by 33% and 21% before immersion and by 25% and 27% after immersion, respectively, compared to unmodified amorphous calcium phosphate composites (controls). All strength increases except TEOS after immersion were significant (p < 0.05).nnnSIGNIFICANCEnProperly modified amorphous calcium phosphate fillers can be used to prepare bioactive composites with enhanced mechanical properties for more demanding dental applications without compromising their remineralizing potential.