Effect of magnetic resonance imaging on microleakage of amalgam restorations: an in vitro study

The technique of MRI, using powerful magnets, plays an important role in the diagnosis of diseases of the head and neck without any ionizing radiation. Because of the potential hazard imposed by the presence of ferromagnetic metals, patients with implanted metallic objects are excluded from MRI. However, amalgam restorations seem to be safe. The purpose of this study was to evaluate microleakage of amalgam restorations following MRI.

63 human freshly extracted premolars were divided into 3 groups based on 3 high-copper amalgams used to restore standard class V preparations on both buccal and lingual surfaces. Three different amalgam materials were used: Cinalux, GS-80 and Vivacap. The teeth were transferred into saline solution for 2 months at room temperature and then sectioned mesiodistally. MRI was randomly applied to one half of each section, and the other half was kept as a control. Following MRI, all specimens were immersed in a dye solution, sectioned and scored for any microleakage using a stereomicroscope.

Differences in microleakage within each group following MRI were significant in the GS-80 and Vivacap groups but not in the Cinalux group. However, there was no significant difference between the three groups regarding the microleakage score.

The results of this study suggest that MRI is not a completely safe technique in patients with amalgam restorations. It was shown that the main effect of fields led to the appearance of thermoelectromagnetic convection, which is responsible for the enhancement of the diffusion process, grain boundary migration and vacancy formation resulting in microleakage.