A Magnetic Resonance Imaging Comparative Study On Changes In The Structure Of Temporomandibular Joint During Mandibular Advancement Between Angle’s Class Ⅱ And Class Ⅱ Adult Male

Objective:The aim of this experiment was to investigate the changes in the structure of temporomandibular joint and compare the different change patterns during mandibular advancement between Angle’s Class Ⅰ and Class Ⅱ adult male.Methods:Forty non-apnea adult male were divided into two groups according to the Angle’s Classification, including Angle’s Class Ⅰ and Class Ⅱ groups. There were twenty volunteers in each group. Each volunteer was scanned by Magnetic Resonance Imaging in three positions respectively, including central occlusion (Fo),75% of the maximum mandible advancement(F75) and maximum of the mandible advancement(F100). The indexes correlate with disk-condyle angle、the articular spaces、morphology of articular disk、horizontal migration angle and rotational angle of disk in different positions during mandibular advancement,the size of condyle of these two groups were measured and calculated statistically by Magnetic Resonance Imaging.Result:The disk-condyle angles were decreased as mandibular advanced in these two groups(P<0.01). The length of disk got shorten as mandibular advanced in both groups from Fo to F75(P<0.01), but they did not keep getting shorten from F75 to F100. In F0,the ratio of disk anterior displacement in Class Ⅱ was higher than Class Ⅰ’s(P<0.01), both of anterior spaces and posterior spaces in Angle’s class Ⅱ were wider than class Ⅰ’s. Posterior spaces of class Ⅱ were wider than class Ⅰ’s in F100,the statistically was significant difference(P< 0.05),while there was no difference in F75 in these two groups. The posterior spaces were increased as mandibular advanced of these two groups,the statistically was significant difference(P<0.01). The ratio of condylar displacement in Class Ⅱ was higher than Class Ⅰ’s in Fo(P<0.01). The size of condyle between these two groups was difference, the internal and external diameters of Class Ⅰ was larger than Class Ⅱ’s(P<0.05). The rotational angles were increased as mandibular advanced, the angles from Fo to F100 were different from Fo to F75, the difference were statistically significant(P< 0.05),but there were no differences between these two groups.Conclusion:1、There are some differences in the the structure of temporomandibular joint between Angle’s class Ⅰ and Ⅱ adult male.2、There are some differences in the the changes of temporomandibular joint structure as mandibular advanced between Angle’s class Ⅰ and Ⅱ adult male, it mainly displays in disk and condylar displacement.3、The posterior band of disk steps backward as mandibular advanced, it will not bring about the disk anterior displacement, mandibular advancement moderately may play an positive role in patients with disk anterior displacement, but long-term excessive mandibular advancement may not be favorable for temporomandibular joint.