Surface properties of tricalcium phosphate and hydroxyapatite resin composites

Objectives: The objectives of the present study were to formulate tricalcium phosphate and hydroxyapatite UDMA-based resin composites and characterise their surface properties: hardness, gloss and roughness. Methods: β-Tricalcium phosphate (β-TCP) and 3 HAP were used as reinforcing phases. The morphology and size of the particles were studied by scanning Electron Microscopy and laser diffraction. Five UDMA-based resin composites with increasing amount of particles (20-60 wt%) were formulated for each reinforcing phase with a photo-initiator system of CQ and DMAEM. Cylindrical specimens (2/6 mm x 2 mm) were light cured and the post-irradiance hardness immediate and 24 h after cured (VHN0 and VHN24) was measured (n=5). Specimens were subjected to simulated toothbrush abrasion study and the surface gloss and microroughness (Ra) were evaluated before and after the abrasion study. Difference between the results was analysed by one way (ANOVA) (P<0.05) followed by Tukey`s post hoc test. Results: Each reinforcing phases showed different morphology and particles size: β-TCP nanosized rod shape, HAP1 and HAP2 3-5 µm clusters with nano HAP crystals, HAP4 10 -100 µm spherical particles. All resin composites demonstrated an increase in VHN with increasing reinforcing phases and a significant increase (over 80%) was noticed for VHN24 compared with VHN0. Gloss decreased from around 60% to 30% and Ra increased with increasing reinforcing phase. A further decrease in gloss and an increase in Ra were observed for resin composites after been subjected to polishing and toothbrush; however different trends were noticed for different reinforcing phases. Conclusion: β-Tricalcium phosphate and HAP demonstrated potentials as reinforcing phases for esthetic dental resin composites. Correlations existed between the amounts of reinforcing phases and various surface properties (a positive correlation for hardness and roughness and inverse correlation for gloss).