Force effect of MRI scanner on dental appliances and instruments

This study aimed to measure magnetically induced displacement forces on metallic dental appliances and instruments in a 3 T MRI scanner and to examine its relationship with magnetic flux density.

Magnetic flux density was measured along the gantry centreline, and both the spatial field gradient and the product of magnetic flux density and spatial field gradient were calculated. Displacement force measurements were conducted according to ASTM F2052-21. Tests were performed on a representative material along the gantry centreline and on 29 metallic dental materials-including fixed and removable dental appliances, and dental and medical instruments-at two positions outside the gantry entrance.

Displacement force increased rapidly near the scanner entrance, reflecting trends in spatial field gradient and the product of magnetic flux density and gradient, with a maximum observed between 0 and 5 cm inside the gantry entrance. At 25 cm outside the gantry, all tested single fixed and removable dental appliances exhibited displacement forces below 0.03 N. In contrast, nearly all stainless steel dental and medical instruments demonstrated deflection angles exceeding 90° at the same position.

In the MRI environment, dental appliances composed of stainless steel or iron that are not securely fixed in the patient's oral cavity are subject to magnetically induced displacement forces. Therefore, assessing intraoral fixation is essential before and after MRI. Additionally, most stainless steel dental and medical instruments, if inadvertently brought into the MRI environment, pose significant safety risks and must be strictly excluded.