Blankenstein F H, Truong B, Thomas A, Boeckler A, Peroz I
Charité-Centrum 3 - Zahn-, Mund- und Kieferheilkunde, Charité - Universitätsmedizin Berlin.
Rofo. 2011 Aug;183(8):727-34. doi: 10.1055/s-0031-1273424. Epub 2011 May 30.
When using dental duo-magnet systems, a mini-magnet remains in the jaw after removal of the prosthesis. In some cases, implant-borne magnets may be removed, whereas tooth-borne magnets are irreversibly fixed on a natural tooth root. The goal of this paper is to identify the impacts of the duration and orientation of exposure on these magnets in a 1.5 or 3 Tesla MRI.
For this study, 30 SmCo and 60 NdFeB magnets were used. During the first experiment, they were exposed with free orientation for 64 minutes. During the second experiment, the magnets were fixed in position and exposed at 1.5 and 3 Tesla while aligned in a parallel or antiparallel direction.
While the duration of exposure in MRI is irrelevant, the orientation is not. The coercive field strength of these NdFeB and SmCo alloys is not sufficient to reliably withstand demagnetization in a 1.5 or 3 T MRI when aligned in an antiparallel direction. At 1.5 T neodymium magnets were reduced to approx. 34 % and samarium magnets to approx. 92 % of their initial values. At 3 T all magnets were reversed.
As a precaution, the worst-case scenario, i. e. an antiparallel orientation, should be assumed when using a duo-magnet system. If an MRI can be postponed, the general dentist should remove implant-borne magnets. If there is a vital indication, irreversible damage to the magnets is acceptable in consultation with the patient since the replacement costs are irrelevant given the underlying disease.
使用牙科双磁体系统时，去除假体后颌骨中会残留一个微型磁体。在某些情况下，种植体支持的磁体可以取出，而牙支持的磁体则不可逆地固定在天然牙根上。本文的目的是确定在1.5或3特斯拉的磁共振成像（MRI）中，暴露时间和方向对这些磁体的影响。
本研究使用了30个钐钴磁体和60个钕铁硼磁体。在第一个实验中，它们以自由方向暴露64分钟。在第二个实验中，磁体固定在适当位置，并在1.5和3特斯拉下以平行或反平行方向排列时进行暴露。
虽然在MRI中的暴露时间无关紧要，但方向并非如此。当这些钕铁硼和钐钴合金磁体以反平行方向排列时，其矫顽场强不足以可靠地承受1.5或3特斯拉MRI中的退磁。在1.5特斯拉时，钕磁体降至其初始值的约34%，钐磁体降至约92%。在3特斯拉时，所有磁体都发生了反转。
作为预防措施，使用双磁体系统时应假设最坏的情况，即反平行方向。如果可以推迟MRI检查，普通牙医应取出种植体支持的磁体。如果有重要指征，在与患者协商后，磁体的不可逆损伤是可以接受的，因为鉴于潜在疾病，更换成本无关紧要。
