Surface Modified Hydroxyapatite Whisker Filler Reinforced Dental Composite Resin

Hydroxyapatite (HAP), which is the main component of teeth, has excellent biological characteristics. It has been reported that adding the precursor of hydroxyapatite as a filler in composite resin leads to release Ca and PO4 ion in buffer imitating of oral cavity environment which will promote the remineralization of teeth. However, the mechanical properties decreased, when compared with the resin matrix, failing to meet requirements of clinical application. Whiskers, as a new type of composite reinforcement material possess extremely high strength, adding in resin the composite strength, foughness efc. could be enhaned.So the HAP whiskers was used to be filling, Tetraethoxysilane(TEOS) was employed to modify the surface of hydroxyapatite (HAP) whiskers. The whisker/ resin composite materials were prepared via blend. Orthogonal experiment was be designed to study the impact of HAP:TEOS rate, sintering temperature and inorganic filler content to strength and Ca2+ release of the composites. The following points will be considered:1.Hydroxyapatite whiskers were synthesized by template-mediated/ homogeneous-precipitation, with diammonium hydrogen phosphate, calcium nitrate, sorbitol as raw materials. The whiskers were 5～30μm in length, with an average length of 18μm; 0.2～2μm in diameter, with average diameter of 0.8μm; 6.25～37.5 in aspect ratio with average of 22. The main phase of whiskers is hydroxyapatite, composited with small amount of calcium-deficiency phase. The whisker was shown to be a single crystal wit the electron diffraction pattern.2. Tetraethoxysilane(TEOS) was hydrolysied, added to whiskers surface and then fused to modify the surface of hydroxyapatite (HAP) whiskers. A layer of Si-O network were formed on the surface of the whiskers. Combination between the coupling agent and the whisker were enhanced, and whisker retention were significanly increased. SEM observation showed that the effect of surface modified was good and the dispersion of whiskers has been greatly improved.3. Composite materials were prepared using the modified whiskers and carbamate dimethyl acrylate (UDMA), triethylene glycol dimethyl acrylate (TEGDMA). Orthogonal experiment were designed to study the impact of HAP:TEOS rate, sintering temperature and inorganic filler content to strength and Ca2+ release of the composites. It was showed that the fexural strength was increased with the whisker/Si ratio at 1:1～3:1, while a downward trend at 3:1～4:1; and the strength of the material was not increased obviously then whiskers/TEOS was not fused,, when fused at 800℃system strength has been greatly improved, but after 1200℃fused, fexural strength showed a downward trend again. Mass fraction of inorganic filler at 50%～70% increased fexural strength. The material could release Ca and PO4 ion in buffer imitation of oral cavity environment, the level with the whisker/Si ratio and the mass fraction of filler increased, with the fused temperature decreases. And the rate was rapidness before 21 days, at 21-35 days basicly turn into the platform period.4. The composites, with high strength and Ca2+ release, may provide the needed, unique combination of stress-bearing and caries-inhibiting capabilities.