The objectives of this study were to determine the cytotoxic concentrations of 11 components of resin composites on monolayers of cultured Balb/c 3T3 fibroblasts, to study the inhibitory effects of these components on DNA synthesis, total protein content, and protein synthesis, and to determine whether effects were reversible when the components were withdrawn from the medium. These data were reported as concentrations which inhibited 10% (ID10) and 50% (ID50) of a particular metabolic process as well as the range of concentrations over which cell metabolism was irreversibly inhibited. For any individual component, the ID50 values for all three metabolic parameters were of the same magnitude. The same was true for the ranges of irreversibility. Ethoxylated Bis-phenol A dimethacrylate (E-BPA) was the most toxic molecule of the group (ID50 being between 1 and 10 mumol/L). The ID50 concentrations for three of the components, including Bis-GMA, UDMA, TEGDMA, and Bis-phenol A, ranged between 10 and 100 mumol/L, while the ID50 values of three components (N,N dihydroxyethyl-p-toluidine, camphoroquinone, and N,N dimethylaminoethyl methacrylate) were above 100 mumol/L. The concentrations to which the cells and tissues are exposed in vivo are not known. This study should help to identify the concentrations of organic composite components which pose clinical cytotoxic hazards.

Abstract. Previous studies have shown a wide range of pulpal reactions to dentin bonding systems and a poor correlation between in vitro and in vivo toxicity of dentin bonding agents. Because dentin bonding agents are composed of multiple components which may diffuse through dentin, we hypothesized that these components may cause cytotoxicity through interactive (synergistic) effects. We investigated the cytotoxicities of four dentin bonding components-HEMA, Bis-GMA, TEGDMA, and UDMA-and interactive effects for three binary combinations of the dentin bonding components-HEMA and Bis-GMA, Bis-GMA and TEGDMA, and TEGDMA and UDMA. Cytotoxicities to Balb/c 3T3 mouse fibroblasts were measured by the MTT assay. Concentrations which caused 50% toxicity compared with controls (TC50 values) were compared, and the interactive effects were determined by evaluation of the differences between observed and expected MTT activities of the cells. The ranks of toxicity of the dentin bonding components in terms of TC50 values were as follows: Bis-GMA > UDMA > TEGDMA >>> HEMA (least toxic) after 24-and 72-hour exposures. As binary combinations, the three combinations of dentin bonding components interacted in three ways-synergism, additivism, and antagonism-which were influenced by the concentrations of both components. The longer period of exposure resulted in a significant increase in the cytotoxicity of the dentin bonding components and combinations. The findings indicate that both exposure time and the interactions between the dentin bonding components may be important parameters in determining the cytotoxicity of dentin bonding agents in vivo.

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There has been recent concern about the inadvertent exposure of dentin with patent tubules as well as gingiva to bleaching systems containing 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) to measure hydrogen peroxide diffusion from bleaching agents through dentin in vitro; and (3) to determine the risk of hydrogen peroxide-induced cytotoxicity from exposure of dentin to these vital bleaching agents. The 50% inhibitory dose (ID50) of hydrogen peroxide to succinyl dehydrogenase activity in cultured cells was found to be 0.58 mmol/L after 1 h. All bleaching materials demonstrated diffusion of hydrogen peroxide 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 dehydrogenase activity corresponded to the amount of hydrogen peroxide that can rapidly diffuse through dentin in vitro and reach concentrations which are toxic to cultured cells in less than 1 h.

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