Correlation Of Bilateral Anterior Disc Displacement Of Temporomandibular Joint And Mandibular Retrusion In Juvenile

PURPOSE: To explain the cause-effect relationship of juvenile bilateralanterior disc displacement (ADD) of temporomandibular joint (TMJ) and mandibularretrusion (MR), and to study the correlation between progress of ADD and change ofMR during its natural course.METHODS: Subjects were comprised of174juvenile (under20years old,including20years) with bilateral ADD diagnosed by magnetic resonance image(MRI). Metric MRI measurement and lateral cephalometric analysis were used toevaluate the severity of ADD and the sagittal skeletal patterns of ADD patients.Pearson correlation test was used to calculate the correlation coefficient and test itsstatistical significance. Thirty-eight patients with no treatment were followed up formore than6months with MRI and lateral cephalometric radiographs, and paired-t testwas used to study the changes of severity of ADD and MR.RESULTS: Of all the174cases, the average SNB angle was76.04°±3.61°, andeighty-nine cases(51.1%) were diagnosed as MR. As ADD progressed, MR displayeda tendency to increase(p<0.05). After a mean13.0months’ follow up, the distance ofdisc displacement was increased by0.92mm (p<0.05), the disc length was decreasedby0.58mm (p<0.05) and the condylar height was decreased by0.64mm (p<0.05). TheSNB angle showed no significant difference (p>0.05), but the MP-FH and Y anglewas increased (p<0.05).CONCLUSION: There was a significant correlation between juvenile bilateralADD and MR. A high occurrence of MR was found in ADD patients. Natural courseof ADD led to a tendency of mandibular clockwise rotation. Juvenile bilateral ADDmight be one of the cause of MR.