Calcium and phosphate ion releasing composite: effect of pH on release and mechanical properties.
OBJECTIVE
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 (PO(4)) ion release at cariogenic pH.


METHODS
TTCP was ball-milled to obtain four different particle sizes: 16.2, 2.4, 1.3, and 0.97 microm. 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 PO(4) 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-PO(4) 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). PO(4) 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.


CONCLUSIONS
The new TTCP-whisker composite was "smart" and increased the Ca and PO(4) 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-PO(4) composites and resin-modified glass ionomer. This composite may have the potential to provide the necessary combination of load-bearing and caries-inhibiting capabilities.
Xu
Hockin H K
HH
Department of Endodontics, Prosthodontics and Operative Dentistry, University of Maryland Dental School, 650 West Baltimore Street, Baltimore, MD 21201, USA. hxu@umaryland.edu
Weir
Michael D
MD
Sun
Limin
L
D002118:Calcium / Q000032:analysis; D002130:Calcium Phosphates; D002327:Cariostatic Agents / Q000138:chemical synthesis / Q000737:chemistry* / Q000627:therapeutic use*; D003188:Composite Resins / Q000138:chemical synthesis / Q000737:chemistry* / Q000627:therapeutic use*; D003731:Dental Caries / Q000517:prevention & control*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D006863:Hydrogen-Ion Concentration; D007101:Immersion; D008422:Materials Testing; D053758:Nanoparticles; D010710:Phosphates / Q000032:analysis; D018583:Pliability; D017655:Silicon Compounds
D002130:Calcium Phosphates; D002327:Cariostatic Agents; D003188:Composite Resins; D010710:Phosphates; D017655:Silicon Compounds; C485830:tetracalcium phosphate; C032734:silicon nitride; D002118:Calcium