Effect of polymerization methods in the cytotoxicity of two resins used in removable prosthodontics – an in vitro study

Abstract

Introduction: Polymethylmethacrylate resins are essential materials in the Oral Rehabilitation field. However, their use is being called into question once they can cause adverse reactions in the adjacent tissues [1]. Previous work has shown that ProBase® Cold releases a higher amount of monomers MMA and HEMA when compared to the heat-polymerized ProBase® Hot [2]. Having that in consideration, it is important to know if polymerization methods have influence in cytotoxicity of these materials. In this in vitro study, our aim is to evaluate the cytotoxicity level of ProBase® Hot and ProBase® Cold in fibroblastic cell line through cell viability assay and our hypothesis is that ProBase® Cold is more cytotoxic than ProBase® Hot.

Materials and methods: Specimens of each resin were prepared according to manufacturer’s instructions for clinical use. Then, 4 disks (5mm in diameter x 2mm in height) were immersed in 7mL of culture medium and incubated for 4 different times (30 minutes, 24 hours, 7 days and 14 days). Serial dilutions of the previously incubated resin extracts were placed in contact with 4×10³ of 3T3 mouse fibroblasts that have been plated in a 96 well plate the day before. After 24 hours of exposition, cell viability was evaluated through the Crystal Violet assay. Absorvance was measured at 595nm in a microplate reader (Biorad 680). The results were evaluated by Student’s t-test (SPSS, Chicago, IL) and the level of significance was chosen as p-value <0.05.

Results: Undiluted extracts of both resins produce significant differences in mouse fibroblasts viability when they were incubated for 14 days (Figure 1). Even though, with all dilutions and incubation times of the extracts tested, cell viability was never below 70%, which is the threshold stated in ISO 10993-5:2009 to be considered cytotoxic [3].

Figure 1. Cell viability of 3T3 fibroblasts when exposed to ProBase® resins. The values are present as mean ± SD in relation to non-exposed cells (defined as 100% cell viability). *p < 0.05 when compared to non-exposed cells.

Discussion and conclusions: Our results show that ProBase® Hot and ProBase® Cold are not cytotoxic in our cell model. In this case, our hypothesis was not verified. The polymerization method of both resins does not influence their cytotoxicity.

Acknowledgements

The authors acknowledge financial and material support by Cooperativa de Ensino Superior Egas Moniz, CRL for the accomplishment of this study.