title: Nanocomposites with Ca and PO4 release: effects of reinforcement, dicalcium phosphate particle size and silanization.
abstract: OBJECTIVE
  Nanoparticles of dicalcium phosphate anhydrous (DCPA) were synthesized in our laboratory for the first time and incorporated into a dental resin. Our goal was to develop a mechanically strong dental composite that has Ca and PO(4) ion release to combat tooth caries, and to investigate the effects of whisker reinforcement, DCPA particle size and silanization.
  
  
  METHODS
  DCPA nanoparticles and two larger DCPA particles were used with nano-silica-fused whiskers as fillers in a resin matrix. Composite mechanical properties were measured via three-point flexure, and the release of Ca and PO(4) ions were measured versus time.
  
  
  RESULTS
  Using DCPA nanoparticles with a diameter of 112nm, the composite at a DCPA:whisker mass ratio of 1:1 had a flexural strength (mean+/-S.D.; n=5) of (112+/-17)MPa, not significantly different from (112+/-14)MPa of a commercial non-releasing composite; both were higher than (29+/-7)MPa for the composite at DCPA:whisker of 1:0 (p<0.05). The composite with DCPA particle size of 112nm released Ca to a concentration of 0.85mmol/L and PO(4) of 3.48mmol/L, higher than Ca of 0.67mmol/L and PO(4) of 1.11mmol/L using DCPA with 12microm particle size (p<0.05). Silanization of DCPA increased the composite strength at DCPA:whisker of 1:0 compared to that without silanization, but decreased the Ca and PO(4) release (p<0.05). Increasing the DCPA particle surface area increased the Ca and PO(4) release.
  
  
  CONCLUSIONS
  Decreasing the DCPA particle size increased the Ca and PO(4) release; whisker reinforcement increased the composite strength by two- to three-fold. The nano DCPA-whisker composites, with high strength and Ca and PO(4) release, may provide the needed, unique combination of stress-bearing and caries-inhibiting capabilities.
authors.affiliation: Paffenbarger Research Center, American Dental Association Foundation, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA. hockin.xu@nist.gov
authors.forename: Hockin H K
authors.initials: HH
authors.lastname: Xu
authors.forename: Michael D
authors.initials: MD
authors.lastname: Weir
authors.forename: Limin
authors.initials: L
authors.lastname: Sun
mesh_terms: D002118:Calcium; D002130:Calcium Phosphates / Q000737:chemistry*; D002327:Cariostatic Agents / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry*; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D016503:Drug Delivery Systems; D004548:Elasticity; D008422:Materials Testing; D053761:Nanocomposites / Q000737:chemistry*; D010316:Particle Size; D010710:Phosphates; D018583:Pliability; D012821:Silanes
chemical_list: D002130:Calcium Phosphates; D002327:Cariostatic Agents; D003188:Composite Resins; D010710:Phosphates; D012821:Silanes; C485829:calcium phosphate, dibasic, anhydrous; D002118:Calcium