The effect of magnetic resonance imaging on mercury release from dental amalgam at 3T and 7T

Objectives: To measure mercury release from standardised hydroxyapatite/amalgam constructs during MRI scanning and investigate the impact of static field strength and radiofrequency (RF) power on mercury release.Methods: Amalgam was placed into 140 hydroxyapatite disks and matured for 14-days in artificial saliva. The solution was replaced, and samples split into five groups of 28 immediately prior to MRI. One group had no exposure, and the remainder were exposed to either a 3T or 7T MRI scanner, each at high and low RF power. Mercury concentration was measured by inductively coupled plasma mass spectrometry. Groups were compared using one-way ANOVA, and two-way ANOVA for main effects/ interaction of field strength/ RF power.Results: Mercury concentration was increased in the 7T groups (high/ low: 15.43/ 11.33 ng mL-1) and 3T high group (3.59) compared to control (2.44). MRI field strength significantly increased mercury release (p < .001) as did RF power (p = .030). At 3T, mercury release was 20.3 times lower than during maturation of dental amalgam, and for the average person an estimated 1.50 ng kg- 1 of mercury might be released during one 3T investigation; this is substantially lower than the tolerable weekly intake of 4,000 ng kg- 1.Conclusion: Mercury release from amalgam shows a measurable increase following MRI, and the magnitude changes with magnetic field strength and RF power. The amount of mercury released is small compared to release during amalgam maturation. Amalgam mercury release during MRI is unlikely to be clinically meaningful and highly likely to remain below safe levels.

Automated summary

This study investigates the release of mercury from amalgam during MRI scanning. The results show that the magnetic field strength and RF power have an impact on the release of mercury, but the amount released is small compared to the release during amalgam maturation. Therefore, the release of amalgam mercury during MRI is unlikely to have a clinically meaningful impact and is highly likely to remain below safe levels.