Tabriz University of Medical Sciences Journal of Dental Research, Dental Clinics, Dental Prospects 2008-210X 14 1 2020 03 15 Effect of preheating on the cytotoxicity of bulk-fill composite resins 19 25 10.34172/joddd.2020.003 EN Mohammad Esmaeel Ebrahimi Chaharom https://orcid.org/0000-0002-8163-8510 Mahmoud Bahari Leila Safyari https://orcid.org/0000-0002-5302-2399 Hossein Safarvand https://orcid.org/0000-0002-1444-7386 Hajar Shafaei Elmira Jafari Navimipour Parnian Alizadeh Oskoee Amir Ahmad Ajami Mahdi Abed Kahnamouei Journal Article 10.34172/joddd.2020.003 2019 05 30 2019 12 29 Background. Due to the effect of pre-heating on the degree of conversion of composite resins and the possible effect on cytotoxicity, the effect of pre-heating of bulk-fill composite resins was investigated on cytotoxicity in this study. Methods. In this study, three different types of composite resin were used, including Tetric N-Ceram Bulk-Fil, Xtrafil, and Xtrabase. From each composite resin, 10 cylindrical samples (5 mm in diameter and 4 mm in height) were prepared, with five samples preheated to 68°C, and the other five samples polymerized at room temperature (25°C). Twenty-four hours after polymerization, cytotoxicity was assessed by MTT assay on human fibroblasts. Statistical analysis of data was carried out with two-way ANOVA and Sidak Post-Hoc. The significance level of the test was determined at 0.05. Results. There was no statistically significant difference between the mean percentage of cytotoxicity in terms of pre-heating (P>0.05), but the cytotoxicity of the studied composite resins was significantly different (P<0.001). The cytotoxicity of Tetric N-Ceram Bulk-fil composite resin was higher than that of the two other composite resins. Conclusion. Pre-heating of bulk-fill composite resin did not affect their cytotoxicity. In addition, the cytotoxicity of different bulk-fill composite resins was not the same.