Biodegradation of a dental composite by esterases: dependence on enzyme concentration and specificity

Studies have shown that inflammatory (cholesterol esterase, CE) and salivary (pseudo-cholinesterase, PCE) enzymes can cause the breakdown of bisphenol-A diglycidyl dimethacrylate (bisGMA) and triethylene glycol dimethacrylate (TEGDMA) components from composite resins. Based on the above consideration, it was desired to show how CE- and PCE-catalyzed hydrolysis of resin components was dependent on the enzymes' concentration and to determine their distinct specificities (if any) towards resin components. Photopolymerized model composite resin samples (60% weight fraction silanated barium glass filler) based on bisGMA and TEGDMA monomers (55/45 weight ratio of the matrix, respectively) were incubated with PBS and either 0.01, 0.05, 0.1 or 1 unit/ml of CE or PCE for 16 days (pH 7.0, 37 degrees C). Incubation solutions were analyzed by high-performance liquid chromatography (HPLC), UV spectroscopy and mass spectrometry. The composite samples were characterized by scanning electron microscopy (SEM). Degradation rates of bisGMA and TEGDMA monomers were assessed. The results showed that CE had a greater specificity towards cleaving bisGMA while PCE showed a greater specificity towards TEGDMA. A strong enzyme concentration dependence was observed which suggests that the level of degradation products generated for a material will depend on the esterase make-up of an individual's saliva in combination with the specific formulation of monomer components used.