Changes Of Skeletal Muscles Of Teeth Before And After Mandibular Retrusion Treatment

OBECITIEV: To investigate the effects of joint,muscle and occlusal changes and coordination on the stability of mandibular shape,position and long-term effect of functional treatment by measuring the changes of temporomandibular joint related indexes,masseter muscle direction,posterior occlusal plane inclination,occlusal plane inclination and lower incisor inclination before and after functional treatment.METHODS: Fifteen patients（male or female）with type ⅱ mandibular retrusion who had completed functional correction at the peak of growth and development were selected.The changes of joint,muscle and occlusal related indexes in CBCT images before and after treatment were measured and analyzed by invivo software.The data paired t-test was performed by SPSS25.0 software.RESULT: After treatment,the length and short axis neck of condyle increased,the supracondylar space and posterior space increased,the glenoid fossa distance increased,the glenoid fossa width increased,the angle between the anterior boundary of masseter muscle and the horizontal plane increased by an average of 3 °,and the angle with the direction of maximum occlusal force increased by an average of 2.5 °;the occlusal plane rotated clockwise,and the inclination of lower incisors increased.The above data had statistical significance（P < 0.05）.The angle between the long axis of the first molar tooth and the horizontal plane decreased but was not significant.CONCLUSION:（1）Adaptive remodeling of glenoid fossa and condyle occurs after mandibular advancement in patients with mandibular retrusion,condyle grows itself,and anteroinferior displacement occurs in the position of glenoid fossa.（2）After treatment,the direction of masseter muscle was not coordinated with the direction of maximum occlusal force,which adversely affected the long-term stability of the efficacy.（3）The inclination of posterior occlusal plane and occlusal plane became larger,which adversely affected the forward growth of mandible and chin;（4）The increase of labial inclination of lower anterior teeth affected the forward growth of mandible,which was one of the causes of orthodontic recurrence.Changes in joints,muscles,and occlusion after functional correction may have an impact on the sagittal growth of the mandible and the long-term stability of the efficacy.