- 期刊
覆蓋式義齒的磁性固位裝置於核磁共振下之消磁現象
Demagnetization of Magnet Attachment for Overdenture in MRI
摘要
磁鐵的利用與植入鈦金屬植體，在提升顎顏面贋復物(maxillofacial prostheses)或覆蓋式義齒(overdenture)的臨床表現上有卓越的貢獻，可以大幅增加其固位性。核磁共振掃瞄(MRI)在頭頸部軟組織病變的診斷上也有特殊的臨床價值。但當病患配戴裝有磁鐵的義齒或贋復物暴露於核磁共振之強大磁場下時，內部的磁鐵可被永久消磁而發生義齒或贋復物鬆脫的現象。本體外研究乃模擬植體支持式覆蓋式義齒的磁固位裝置（選用Dyn(上標 ®)WRS5(上標 TM)荷蘭製之抗磨耗磁鐵），於主磁場強度B0=l.5T的核磁共振儀下，啟動頭頸部口腔掃瞄後所發生的磁鐵消磁現象。結果發現若僅暴露於主靜磁場B0=1.5T（模擬病人於掃瞄開始前進入磁力場之靜候期），磁鐵磁力無明顯改變沒有消磁現象發生；但排程掃瞄一旦啟動後，在10、20、30、40、60、240秒累進時間點做測試後發現，掃瞄開始10秒內固位力即快速衰減，且核磁共振掃瞄僅10秒即造成磁性固位力衰減至約原始平均值之25%，幾乎喪失其臨床上足夠對抗鬆脫之的固位能力。結論：安排患者接受MRI前需仔細檢查，應預先取下含有磁性固位體的活動式義齒或顎顏面贋復物，以避免事後發生不必要的醫療糾紛或發生贋復物於強磁場中脫落移位的危險。制訂使用磁性固位體來增強固位的口腔或顎顏面贋復計畫時，宜選用可取下之單磁系統（僅活動贋復體內有磁鐵），以避免未來病患接受核磁共振時，磁鐵被消磁破壞，且導致MRI成像受干擾影響影像判讀。
並列摘要
Magnetic material can be demagnetized in a strong magnetic field. The aim of this study in vitro was to investigate the demagnetization phenomenon of magnetic attachments of overdenture exposed in the strong magnetic field of MRI scanning process. Measurement of the retention force (breakaway force) of the magnetic attachment (DYNA Corp. WR5S, the Netherlands) was performed after the exposure to a static magnetic field of MRI (MAGNETOM System, Siemens Corp., Germany) with the magnitude of 1.5 Tesla initially, then combined with pulsed and gradient electromagnetic field created by the scanning process. The measurement was done at cumulative time intervals. Demagnetization of the magnet part of magnetic attachments occurred during the MRI scanning process. No relevant of retention force alternation was measured when the magnet just in the static main magnetic field only, but when the scanning process was started, the retention force of the magnet attachment lost rapidly just in 10 seconds. With the limit findings and limitation of this investigation, we suggest that patients should not bring the overdenture or maxillofacial prosthesis with magnetic attachments into the room of MRI. If magnetic attachment for rehabilitation is indicated, the mono magnet system (single magnet in removal part, not cemented in root or fixed with dental implant) may be suitable to prevent demagnetization in MRI examination.