3-T MRI safety assessments of magnetic dental attachments and castable magnetic alloys

Objectives: To assess the safety of different magnetic dental attachments during 3-T MRI according to the American Society for Testing and Materials F2182-09 and F2052-06e1 standard testing methods and to develop a method to determine MRI compatibility by measuring magnetically induced torque. Methods: The temperature elevations, magnetically induced forces and torques of a ferromagnetic stainless steel keeper, a coping comprising a keeper and a cast magnetic alloy coping were measured on MRI systems. Results: The coping comprising a keeper demonstrated the maximum temperature increase (1.42 °C) for the whole-body-averaged specific absorption rate and was calculated as 2.1 W kg^-1 with the saline phantom. All deflection angles exceeded 45°. The cast magnetic alloy coping had the greatest deflection force (0.33 N) during 3-T MRI and torque (1.015 mN m) during 0.3-T MRI. Conclusions: The tested devices showed minimal radiofrequency (RF)-induced heating in a 3-T MR environment, but the cast magnetic alloy coping showed a magnetically induced deflection force and torque approximately eight times that of the keepers. For safety, magnetic dental attachments should be inspected before and after MRI and large prostheses containing cast magnetic alloy should be removed. Although magnetic dental attachments may pose no great risk of RF-induced heating or magnetically induced torque during 3-T MRI, their magnetically induced deflection forces tended to exceed acceptable limits. Therefore, the inspection of such devices before and after MRI is important for patient safety.