Cytotoxicity of Deflected Stainless Steel Orthodontic Wires

Backgrounds: The stainless steel orthodontic wire remains favored due to its affordable price and excellent formability. However, the biocompatibility of this alloy is still questionable. Despite its corrosion resistant feature attributed to the chrome oxide film on its surface, stainless steel alloy may be tarnished and corroded, causing mechanical and chemical perturbances. Objectives: To evaluate the potential of cytotoxic reaction due to the deflection of stainless steel orthodontic wire in oral environment with certain pH and salivary flow rate. Methods: The sample in this study are pieces of .016×.022 inches stainless steel designated into two groups, deflected and nondeflected. The wire extract is generated by acid cycling immersion method in artificial saliva solutions with pH 4 and 7. The extract is collected after 24, 48, 72, and 168 hours of immersion. Subsequently, the cytotoxicity of wire extract is tested using the MTT method with Chinese Hamster Ovary cell. Results: The statistical analysis using three-way ANOVA among cytotoxicity and deflection, pH, and salivary flow cycle duration shows that citotoxicity is attributed to pH (F=7,29;p<.05), salivary flow cycle duration (F=144,14;p<.05), and interaction between pH and deflection (F=15,04; p<.05). The multiple comparison between groups shows significant difference (p<.05) between pH 4 and 7 groups, among all salivary flow cycle groups, between deflected stainless steel wire in pH 4 and 7, between deflected and nondeflected stainless steel wire in pH 4, and between deflected and nondeflected stainless steel wire in pH 7. Conclusion: Stainless steel wire cytotoxicity is not attributed to the deflection.