IMPROVED PROPERTIES OF AMORPHOUS CALCIUM-PHOSPHATE FILLERS IN REMINERALIZING RESIN COMPOSITES

Objectives. The rationale for this study was based on the hypothesis t hat the mechanical strength of methacrylate composites containing the bioactive filler, amorphous calcium phosphate, can be enhanced by synt hesizing this filler in the presence of glass-forming agents. Specific ally 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 an d phosphate ions and the mechanical properties of the corresponding me thacrylate composites were enhanced. Methods. The modified amorphous c alcium phosphates were synthesized at pH 10.5 by mixing 800 mmol/L Ca( NO3)(2) solutions and either 250 mmol/L zirconyl chloride (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, t he amorphous calcium phosphates were mixed with visible light-activate d resins and photopolymerized to form composite disks that were then e xamined for their ability to release Ca2+ and total ionic phosphate (P O43- + HPO42- + H2PO4, hereafter indicated as PO4) by immersion in HEP ES-buffered (pH 7.4) saline at 37 degrees C. Solution ion concentratio ns were compared at regular intervals up to 265 h. Biaxial flexural st rengths of the composites before and after immersion were compared, an d significant differences were established by Student's t test (p < 0. 05). Results. Both ZrOCl2- and TEOS-modified amorphous calcium phospha te composite disks released Ca2+ and PO4 ions at sustained levels requ isite for remineralization to occur. The transformation of amorphous c alcium phosphate into hydroxyapatite within the composites was also re tarded, particularly in the case of amorphous calcium phosphate modifi ed with ZrOCl2. Biaxial flexure strength values of composite disks sho wed that TEOS- and ZrOCl2-amorphous calcium phosphate-filled composite s increased in strength by 33% and 21% before immersion and by 25% and 27% after immersion, respectively, compared to unmodified amorphous c alcium phosphate composites (controls). All strength increases except TEOS after immersion were significant (p<0.05). Significance. Properly modified amorphous calcium phosphate fillers can be used to prepare b ioactive composites with enhanced mechanical properties for more deman ding dental applications without compromising their remineralizing pot ential.