CYTOTOXICITY AND DENTIN PERMEABILITY OF CARBAMIDE PEROXIDE AND HYDROGEN-PEROXIDE VITAL BLEACHING MATERIALS, INVITRO

There has been recent concern about the inadvertent exposure of dentin with patent tubules as well as gingiva to bleaching systems containin g 10-15% carbamide peroxide or 2-10% hydrogen peroxide for more than a few minutes. The aims of the present study were: (1) to determine the cytotoxicity of dilutions of hydrogen peroxide in cell culture; (2) t o measure hydrogen peroxide diffusion from bleaching agents through de ntin in vitro; and (3) to determine the risk of hydrogen peroxide-indu ced cytotoxicity from exposure of dentin to these vital bleaching agen ts. The 50% inhibitory dose (ID50) of hydrogen peroxide to succinyl de hydrogenase activity in cultured cells was found to be 0.58 mmol/L aft er 1 h, All bleaching materials demonstrated diffusion of hydrogen per oxide through dentin in an ''in vitro pulp chamber'' device. The one- and six-hour diffusates of all bleaching agents through 0.5-mm dentin exceeded the ID50 in monolayer cultures. Inhibition of succinyl dehydr ogenase activity corresponded to the amount of hydrogen peroxide that can rapidly diffuse through dentin in vitro and reach concentrations w hich are toxic to cultured cells in less than 1 h.