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



Hockin D. Xu, Michael Weir, Limin Sun


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 m, 2.4 m, 1.3 m, and 0.97 m. Whiskers fused with nano-silica were combined with TTCP as fillers in a resin. Filler level mass fractions varied from 0% to 75%. Ca and PO4 ion release 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 ± sd; 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 3-fold that of a releasing control. Significance. The new TTCP-whisker composite was “smart” and increased the Ca and PO4 release by 6-fold 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 2-3 fold higher than previous Ca-PO4 composites and resin-modified glass ionomer. This composite may have the potential to provide the needed combination of load-bearing and caries-inhibiting capabilities.
Dental Materials


dental composite, tetracalcium phosphate, particle size, mechanical properties, tooth caries inhibition, Ca and PO4 ion release


Xu, H. , Weir, M. and Sun, L. (2008), Calcium and phosphate ion releasing composite: Effect of pH on release and mechanical properties, Dental Materials, [online], (Accessed April 15, 2024)
Created October 27, 2008, Updated February 19, 2017