Calcium and phosphate ion releasing composite: Effect of pH on release and mechanical properties

Abstract: Objectives: Secondary caries and restoration fracture are the two main challenges facing tooth cavity restorations. The objective of this study was to develop a composite using tetracalcium phosphate (TTCP) fillers and whiskers to be stress-bearing, and to be “smart” to increase the calcium (Ca) and phosphate (PO4) ion release at cariogenic pH. Methods: TTCP was ball-milled to obtain four different particle sizes: 16.2, 2.4, 1.3, and 0.97μm. Whiskers fused with nano-sized silica were combined with TTCP as fillers in a resin. Filler level mass fractions varied from 0 to 75%. Ca and PO4 ion releases were measured vs. time at pH of 7.4, 6, and 4. Composite mechanical properties were measured via three-point flexure before and after immersion in solutions at the three pH. Results: TTCP composite without whiskers had flexural strength similar to a resin-modified glass ionomer (Vitremer) and previous Ca–PO4 composites. With whiskers, the TTCP composite had a flexural strength (mean±S.D.; n =5) of (116±9)MPa, similar to (112±14)MPa of a stress-bearing, non-releasing hybrid composite (TPH) (p >0.1). The Ca release was (1.22±0.16)mmol/L at pH of 4, higher than (0.54±0.09) at pH of 6, and (0.22±0.06) at pH of 7.4 (p <0.05). PO4 release was also dramatically increased at acidic pH. After immersion, the TTCP–whisker composite matched the strength of TPH at all three pH (p >0.1); both TTCP–whisker composite and TPH had strengths about threefold that of a releasing control. Significance: The new TTCP–whisker composite was “smart” and increased the Ca and PO4 release dramatically when the pH was reduced from neutral to a cariogenic pH of 4, when these ions are most needed to inhibit caries. Its strength was two- to threefold higher than previously known Ca–PO4 composites and resin-modified glass ionomer. This composite may have the potential to provide the necessary combination of load-bearing and caries-inhibiting capabilities. [Copyright &y& Elsevier]