Dynamic analysis of behavior of bisphenol A in dental resin and leachable compounds

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The amount of bisphenol A can be dynamically changed by the reaction with radicals and by the hydrolysis of leachable compounds. The purposes of this study is to provide a clear instruction of possible leaching of bisphenol A from dental resins by an analysis of leaching phenomena of bisphenol A, taking into consideration of the dynamic change in the amount.1. Radical polymerization in the presence of bisphenol AIn order to clarify the effect of bisphenol A on radical polymerization, bisphenol A was added to polymerization mixture of methyl methacrylate(MMA) and the reaction was precisely examined. It was concluded that bisphenol A is unable to exist in the polymerization mixture after the polymerization of resin, since bisphenol A acted typically as an inhibitor and a minor amount of the compound in dental resins would be used up during polymerization.2. Clarification of radical-scavenging mechanism by comparing bisphenol A with its related compoundsTo elucidate the radical-scavenging mechanism of bisphenol A, its radical-scavenging phenomenon in the polymerization of MMA was compared with those of its related compounds, and the result was examined. The stoichiometric factor (n) of bisphenol A was revealed to be 1.8. It was indicated that bisphenol A with a high inhibitive activity is oxidized as a result of the radical interaction.3. Dynamic leaching phenomenon of bisphenol A and production of bisphenol A from leachable compoundsIt was demonstrated that benzoyl peroxide(BPO) is unreactive to bisphenol A coexisting in dental resins, since no reaction product of bisphenol A was newly found even after 549 hr of reaction with BPO. On the other hand, several tens ppm of bisphenol A in visible light-curing resin was consumed during the cure of resins. Therefore, it was concluded that leaching of bisphenol A out of cured resins or production of bisphenol A as a result of hydrolysis does not practically occur, when its amount in dental resins is 10 ppm or less.