Primary Study Of Magnetic Resonance Imaging Of Temporomandibular Joint: Comparision In Asymptomatic Volunteers And Patients

Objectives:To analyse the shape and position of the temporomandibular joint disc from MRI of symptomatic temporomandibular disorders(TMDs) patients and asymptomatic volunteers.To determine the normal range of meniscus's position and the ease with which the meniscus was located.To compare the signal intensity of the disc in asymptomatic volunteers and TMDs patients.Methods:Forty temporomandibular joints(TMJs)in 20 asymptomatic volunteers and thirty TMJs in 15 TMDs patients were imaged with a 1.5-T magnetic resonance(MR) imaging system.A 3-inch (7.5-cm)surface coil was used and the slice thickness was 3mm,slice space was 0.5mm(24-cm field of view with a 256×256 matrix).The positions of the mouth include closed-,partially open-,and open-mouth.The partially open-mouth images were obtained with a 10-mm bite-block placed between the incisors.Fully open-mouth images were obtained with maximal,comfortable mouth opening with a notched bite-block placed between the incisors,which ranges from 3 to 4cm.Each joint was studied in parasagittal plane in the openand closed mouth ,and in the paracoronal plane in closed mouth only.The sagittal slices were orientated perpendicular to the long axis of the condyle and the coronal slices parallel.The closed mouth position were obtained with T1-weighted(500/16ms),T2-weighted and PD-weighted (2000/84,14ms) sequences.The partially-open and fully open-images were obtained with a T1-weighted sequence(500/16ms) only.The confidence of visualization of meniscus was rated as poor ,fair or good for all three mouth positions based on the ease with which the disc was identified.The position of the meniscus relative to the condyle was measured as follows: A line at the 12 o'clock position relative to the condyle was defined by the vertical axis of the head.The posterior margin of the posterior band of the meniscus was identified and a line drawn through this landmark to a point estimated to be the center of curvature of the top surface of the condyle.Result:The confidence of visualization of the meniscus was subjectively rated as either good or fair in 93% of cases(52 of 56).We found the shape of normal disk was like a bow tie.All the asymptomatic volunteers but 3 had high or intermidiate signal intensity identified in the posterior band of the disk. When the jaw closed,the thin intermediate zone was between the closely apposed bony cortices of the articular eminence and condyle.At the partially-open and open-mouth position the intermediate zone was between thecondyle and the posterior or inferior surface of the articular eminence. 3 disc displacement in patient was considered to feature reduction when opening,the normal relationship between the disc and the condyle was restored,whereas no reduction in present in the other 9 disc displacement when the disc was still displaced on opening. The position of the disc in asymptomatic volunteers was -7°to 19°in closed mouth view.There was no statistic difference between the signal intensity of the posterior part of the disc in asymptomatic volunteers and TMD patients.Conclusion:Magnetic resonance(MR) imaging with high field strength and small surface coils allows excellent visualization of the normal and abnormal temporomandibular joint(TMJ).This noninvasive method of depicting the soft-tissue structure of the TMJ in various jaw positions surpassed previously available diagnostic imaging modalities.The partially open view is useful in detection of more advanced displacement.In analysing the disc of patients,we should pay more attention to the shape and position of the meniscus,rather than the disc signal intensity.All in all,mangentic resonace imaging of the TMJ will become the gold standard for the basic diagnosis of TMJ and the evaluation of the operative or conservative therapeutic effect.