利用環口放射線影像評估顳顎關節內部紊亂症

Abstract

根據America academy of pediatric dentistry and the American academy of orofacial pain 建議 當臨床診斷發現關節病變時，可以利用環口放射線攝影作為最初篩選的工具。其在顳顎關節疾病之中的價值在於診查出骨頭形變以及下顎斷裂。然而病人為了顳顎關節疼痛問題而前來求診大多是為了顳顎關節內部紊亂症。因環口放射線影像的呈像方式容易造成顳顎關節產生形變進而導致影像判讀困難，所以使用環口放射線影像來觀察髁頭形變以判別顳顎關節內部紊亂症的診斷價值仍是令人存疑(2.3)。而此次的實驗目的為藉由定義出明確的環口放射線影像中正常的髁頭形態並以髁頭形變以及外極皮質骨層變化做為評估標準試圖提高環口放射線影像的診斷價值。 實驗材料與方法 本實驗分析之影像是選自國立台灣大學附設醫院牙科部顳顎關節障礙特別門診之磁振影像資料庫以及口腔顎面放射線室之影像資料庫，選取標準為18至30歲之間同時接受過顳顎關節磁振攝影與環口放射線攝影檢查之117位年輕女性的影像資料。實驗方法為一位顳顎關節門診主治醫師與另一位資深牙科放射師共同參與環口放射線影像之判讀。判讀者先根據環口放射線影像上之髁頭形態作為診斷標準,之後再加上髁頭皮質骨之狀態來加以評估。此外也同時將環口放射線影像中髁頭寬度與磁振影像中的髁頭長軸長度以及水平角度做測量。另一方面，在本實驗中有87位受試者之骨質密度資料亦參與髁頭形變的分析。 結果 具正常髁盤關係的顳顎關節沒有觀察到明顯的髁頭形變；而具可復位性移位關節盤者約3.5%呈現髁頭形變；具不可復位性移位關節盤者約占63.8 %出現髁頭呈現明顯形變。利用環口放射線影像中髁頭形變為診斷標準來評估是否罹患顳顎關節內部紊亂症，在整體的樣本中，診斷正確率為48%，敏感性為30。而特異性為95%。若加上皮質骨層作為環口放射線攝影診斷顳顎關節紊亂症的第二項評定標準。由實驗數據顯示敏感性提升為35%，而特異性降為84%且診斷正確性不變。利用核振影像中的髁頭形變作為黃金準則，評估環口放射線影像中髁頭形變的診斷正確率為78%，敏感性為50%，而特異性為92%。以髁盤關係與關節水平角度之相關，不可復位性移位關節盤比起其他髁盤關係之髁頭水平角度明顯較大。若將環口放射線影像之髁頭寬度作為與髁頭長軸長度相關性較大，而與髁頭水平角度相關性較小(Linear Regression，p<0.05 )。 結論 本實驗數據顯示只有嚴重的顳顎關節內部紊亂症才會出現明顯的骨性破壞。而環口放射線影像能夠顯示大部分的髁頭形變，因此環口放射線影像僅能用來篩選嚴重程度的顳顎關節內部紊亂症。此外，顳顎關節的皮質骨變化似乎與髁頭型變有相當大的關聯。因此皮質骨變化並未能增加診斷效力。而在環口放射線影像中，髁頭長軸長度所造成髁頭影像形變比髁頭水平角度影響大。另一方面，不可復位移位關節盤類別比起可復位移位關節盤以及正常髁盤關係類別，其髁頭的水平角度較小，但其臨床意義仍須進一步實驗證實。

Introduction: Clinically images prescribed for diagnosis of TMJ problems are mostly related to the internal derangement (ID) and its consequences. It is of no doubt that MRI is the image modality of choice for such purpose. However, a cheap and easily available image option, such as the orthopantomogram (OPT), is still valuable especially used for screening, if its diagnostic power can be promoted. The value of OPT assisting in diagnosis of TMJ ID has been criticized. Its limitations might be attributed to projection distortion, lack of clearly defined criteria, and the fact that TMJ ID is not necessary to be associated with obvious bony changes. It has been proposed that sequential structural changes, namely from erosion to re-cortication, might occur along with natural course of TMJ ID. Interestingly, such bony changes are frequently occurred near lateral condylar pole, which is often clearly depicted on the OPT. The aim of this study was thus to explore a possible gain of diagnostic value of TMJ ID by assessing the cortex on the orthopantomogram. Materials & Methods: Both sagittal serial TMJ MR images and OPT of 117 female subjects (18 years to 28 years , mean age 22.19, SD 2.85) were used for this analysis. The existence of TMJ ID of every single joint was diagnosed based on TMJ MRI by an experienced dentist. The reading of OPT was done by a TMD specialist and a radiological technician. The 2 readers read the OPT with discussion to achieve an agreement on diagnosis, but blind to MRI gold standard. Since there’s no general consensus on norms of TMJ condyle shown on OPT, we defined normal condyle should be convexly round in shape and covered with thin and even-thickened cortex . If the condylar morphology was deviated from the norms, it was then diagnosed to have internal derangement . If the cortical bone near the lateral condylar pole was missing or became thickened, it would also be diagnosed to have internal derangement. The sensitivity and specificity of using OPT with different diagnostic criteria diagnosis to diagnose the existence of TMJ ID were then calculated Results: 39 TMJs were excluded from the analysis because severe overlapping of condyle to its surrounding bony structures. For the 198 TMJ, 57 were with normal disc/condyle relationship, 50 were with disk displacement with reduction (DDwR) and 88 were with disk displacement without reduction (DDw/oNR). By using condylar shape alone, only 48% were corrected diagnosed. The sensitivity and specificity were 30% and 95%, respectively. By considering the additional information of cortical bone, the correct diagnosis was still remained as 48%, the sensitivity slightly raised to 35%, but the specificity fell down to 84%. MRI indicated that 2 of the 50 DDwR TMJ and 67 of the 88 DDw/oR TMJ, their condyles were with obvious bony deformation. For those 69 TMJ with bony deformation, 78% can be revealed by using condylar shape alone (sensitivity and specificity were 50% and 92%). If the cortical bone was taken into consideration, 75% can be correctly diagnosed, the sensitivity became 56% and specificity was 84%.

Conclusion: With the limitation of this study, the following conclusions might be drawn: 1. Only severe TMJ ID would be often associated with obvious bony changes. 2. Most of the condylar deformation can be revealed by the OPT. Therefore, OPT seems to be suitable only for screening severe TMJ ID. 3. TMJ showing cortical bone seems to be also have morphological changes. Therefore, the information of cortical changes don’t promote too much on diagnostic power.