Abstract
Four commercial bisphenol-glycidilmethacrylate based composites used mainly for dental applications have been investigated. Differential thermal analysis performed on samples aged in water for different times indicated a small residual monomer reactivity which disappeared after ageing. A further crosslinking reaction facilitated by water plasticization and a monomer loss could be the main reasons for such 8 phenomenon. The embrittlement of these materials with ageing time has been detected from flexural mechanical properties. Water sorption/desorption experiments have been performed on G!! the materials studied at different temperatures. The decrease of diffusion coefficients with increasing water content together with the microscopic analysis of the fracture surfaces demonstrated good filler/matrix adhesion for all the four composites. The decrease of water diffusion coefficients with time for Miradapt, Silar and Adaptic has been explained on the base of the presence in the polymeric networks of different density regions due to inhomogeneous polymerization. This hypothesis is also in line with the Miradapt, Silar and Adaptic hysteresis phenomena observed in the sorption/desorption cycles.
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