Introduction: In orthodontic therapy ,different materials are used and their presence in oral cavity may modify their properties. The purpose of this study was to evaluate the direct and indirect biocompatibility of three orthodontic composite resins on culture of human oral fibroblasts. Methods: This was an interventional experimental study. The biocompatibility of three orthodontic composite resins including two kinds of self cure composite resins(Unite,3M and Fantastic,Zar Dent)and one kind of light cure composite resin (Transbond,3M) were studied. After a releasing period of each material in the culture medium for 20 days, the viability of oral cultivated fibroblasts was compared to negative control(Teflon) and together with MTT assay(3-(4,5dimethylthiazolyl-2) -2,5-diphenyltetrazolium bromide).In order to evaluate the direct biocompatibility, after direct contacting of composite resins with cell culture ,the viability of oral cells was evaluated with invert phase contrast microscope. Results: The results of MTT assay showed the biocompatibility of light cure composite (P.V=0.114) In comparison to control group. There were significant differences between biocompatibility of self cure composite resins and control group(P.V=0.029). On the other hand, significant statistical difference was not seen between biocompatibility of three composites.The results of direct method showed grade 0 for light cure composite, grade1 for fantastic and grade 2 for unite( 3M) . Conclusion: This study suggested that under these experimental conditions, chemically cured(no-mix) composite resins were more cytotoxic than light cured ones in both direct and indirect methods. Further investigations into the influence of the modes of polymerization and biologic effects of primers on cytotoxic effect and animal studies are warranted to verify its clinical implication.

Keywords: Biocompatibility, Human oral fibroblasts, Orthodontic composite resin, MTT assay

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