Simulated body fluid and water absorption effects on poly(methyl methacrylate)/hydroxyapatite denture base composites

Poly(methyl methacrylate) (PMMA)/hydroxyapatite (HA) composite has potential application in denture base materials. The denture base materials should exhibit good mechanical properties and dimensional stability in moist environment. Silane coupling agent [3-methacryloxypropyltrimethoxy silane (γ-MPS)] was used to treat the HA fillers in order to enhance the interfacial interaction between the PMMA and HA. In this research, the kinetics and effects of Simulated Body Fluid (SBF) and water absorption on the flexural properties of PMMA/HA composites were studied for an immersion duration of 2 months. The mathematical treatment used in analyzing the data was the single free phase model of diffusion, which assumed Fickian diffusion and utilized Fick’s second law of diffusion. The kinetics of water absorption of the PMMA/HA composites conformed to Fickian law behavior, whereby the initial moisture absorption follows a linear relationship between the percentage gain at any time t and t1/2, followed by saturation. It was found that the equilibrium moisture content and the diffusion coefficient are depending on the concentration of γ-MPS in PMMA/5HA composites. The reduction of equilibrium moisture content of PMMA/5HA is due to the hydrophobic behavior of γ-MPS and compatibility of PMMA with HA. The retention ability in flexural modulus and strength of PMMA/HA composites upon subjected to water absorption are considerably good. The reduction of flexural strength of the PMMA/HA composites after water absorption and SBF absorption could be attributed to the plasticizing effect of water molecules.