title: Effects of incorporating nanosized calcium phosphate particles on properties of whisker-reinforced dental composites.
abstract: Clinical data indicate that secondary caries and restoration fracture are the most common problems facing tooth restorations. Our ultimate goal was to develop mechanically-strong and caries-inhibiting dental composites. The specific goal of this pilot study was to understand the relationships between composite properties and the ratio of reinforcement filler/releasing filler. Nanoparticles of monocalcium phosphate monohydrate (MCPM) were synthesized and incorporated into a dental resin for the first time. Silicon carbide whiskers were fused with silica nanoparticles and mixed with the MCPM particles at MCPM/whisker mass ratios of 1:0, 2:1, 1:1, 1:2, and 0:1. The composites were immersed for 1-56 days to measure Ca and PO4 release. When the MCPM/whisker ratio was changed from 0:1 to 1:2, the composite flexural strength (mean +/- SD; n = 5) decreased from 174 +/- 26 MPa to 138 +/- 9 MPa (p < 0.05). A commercial nonreleasing composite had a strength of 112 +/- 14 MPa. When the MCPM/whisker ratio was changed from 1:2 to 1:1, the Ca concentration at 56 days increased from 0.77 +/- 0.04 mmol/L to 1.74 +/- 0.06 mmol/L (p < 0.05). The corresponding PO4 concentration increased from 3.88 +/- 0.21 mmol/L to 9.95 +/- 0.69 mmol/L (p < 0.05). Relationships were established between the amount of release and the MCPM volume fraction v(MCPM) in the resin: [Ca]= 42.9 v(MCPM) (2.7), and [PO4] = 48.7 v(MCPM) (1.4). In summary, the method of combining nanosized releasing fillers with reinforcing fillers yielded Ca- and PO4-releasing composites with mechanical properties matching or exceeding a commercial stress-bearing, nonreleasing composite. This method may be applicable to the use of other Ca-PO4 fillers in developing composites with high stress-bearing and caries-preventing capabilities, a combination not yet available in any dental materials.
authors.affiliation: Paffenbarger Research Center, American Dental Association Foundation, Gaithersburg, Maryland 20899, USA. hockin.xu@nist.gov
authors.forename: Hockin H K
authors.initials: HH
authors.lastname: Xu
authors.forename: Limin
authors.initials: L
authors.lastname: Sun
authors.forename: Mike D
authors.initials: MD
authors.lastname: Weir
authors.forename: Shozo
authors.initials: S
authors.lastname: Takagi
authors.forename: Laurence C
authors.initials: LC
authors.lastname: Chow
authors.forename: Bernard
authors.initials: B
authors.lastname: Hockey
mesh_terms: D002130:Calcium Phosphates / Q000737:chemistry*; D017554:Carbon Compounds, Inorganic / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D003731:Dental Caries / Q000517:prevention & control; D003764:Dental Materials / Q000737:chemistry*; D004548:Elasticity; D008422:Materials Testing; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D017655:Silicon Compounds / Q000737:chemistry; D013718:Tensile Strength
chemical_list: D002130:Calcium Phosphates; D017554:Carbon Compounds, Inorganic; D003188:Composite Resins; D003764:Dental Materials; D017655:Silicon Compounds; C485838:calcium phosphate, monobasic, anhydrous; C022088:silicon carbide