Influence of Hydroxyapatite Microspheres on Mecanichal Properties of Light-Cured Composites

OBJECTIVES: The purpose of the present study was to prepare a series of experimental resin composites with hydroxyapatite (HAP) microsspheres as filler and to investigate the influence of the composition upon the mechanical properties of the light-cured materials. MATERIALS AND METHODS: HAP microsspheres having size <50 ìm were prepared by thermal debinding and sinteing at 1100oC, 3 h, of HAP/ EVA(ethylene vinyl acetate co-poymer)70/30 w/w.As stabilizer for HAP granules resulting in spherical shape was used polyvinyl alcohol (PVA) with 0,1 wt% concentration. The stirring speed was 1500 rpm. The porous microsphere shape permit to incorporate more filler in the monomers mix, and a better anchorage of the filler in the organic matrix.Silanisation of the filler was made by using ã-metacriloyloxypropyl-trymethoxysilane. The Organic phase consists of a mixture of dimethacrylate monomers: Bis-GMAo or Bis-GMA0-2 oligomers mixtures consisting of 83% mol Bis-GMA0 monomer -2,2-bis[4-(2-hydroxy-3-methacryloyloxy-propoxy) phenyl]-propane, 16% Bis-GMA1 dimer and 1% Bis-GMA2 trimer/ TEGDMA in 65/35 ratio,using camphorquinone/amine as initiator/activator system. The composites were prepared as mono- paste, by dispersing of the silanizated bioactive inorganic fillers in the organic phase. The inorganic filler consisted of HAP microsphere and silanized colloidal silica. The powder/liquid ratio was 3/1 in dental resin composites. For the obtaining of specimens, the resin composites were light-cured by exposing to a visible radiation in the wavelength range of 400-500 nm (Optilux stomatological lamp). RESULTS: The strength properties increased with the increasing of superior Bis-GMA oligomers amount in the monomer mixture and with the amount of HAP microspheres as filler. The addition of hydroxyapatite microspheres increased the compressive strength of the resultant composites. CONCLUSIONS: These new dental composites have increased mecanical properties then composites filled with precuipitated HAP and may be biocompatible since hydroxyapatite is a natural mineral present in the dental structure.