The Temporomandibular Joint Characteristics And Alteration After Orthodontic Treatment Of The Patients With Skeletal Class Ⅲ Malocclusion In Mixed Dentition:a Cone Beam Computed Tomography Study

[Objective] The purpose of this investigation was to study the temporomandibular joint characteristics of the patients with skeletal class Ⅲ malocclusion in mixed dentition; and the joint alteration after maxillary protraction therapy; to explore the reconstructed mechanism of temporomandibular joint and the clinical safety of class Ⅲ orthopedic therapy; and to provide theoretical guidance for the clinical treatment.[Methods] Choose twenty patients with skeletal class Ⅰ malocclusion in mixed dentition, average age is about 10.6. Twenty patients with skeletal class Ⅲ malocclusion in mixed dentition, average age is about 10.The patients with skeletal class Ⅲ malocclusion were treated with maxillary protraction.All patients underwent cone beam computed tomography scanning from NewTom company and then reconstructed the 3D image with NNT viewer 5.3 image process software. The research content included two aspects of measuring of angle line and descriptive research.Paired t test was applied to evaluate the differences. Descriptive research was evaluated with x2 test.[Results] 1.Compare the research results of skeletal class Ⅲ malocclusion group (group T1) with skeletal class Ⅰ malocclusion group (group TO):(1)both sides of TMJ in group T1 were found the decrease in superior joint space and the increase in posterior joint space; (2) The up joint space were found decreased both in the sagittal plane and the coronal plane;(3) Decrease in the glenoid fossa depth and angulation of posterior wall of articular tubercle;(4)In sagittal plane the angle of condylar was decreased;(5) In coronal plane inside and outside joint space in group T1 are smaller than group T0.2.When orthopedic therapy finished:(1)the superior joint space increased and the posterior joint space decreased, and in the sagittal direction there is backward and upward growth trend on condylar;(2) In sagittal plane the angle of condylar was increased,and mandibular clockwisely rotated to backwards and down direction following the condylar; (3)The size of the condylar and glenoid fossa is essentially unchanged;(4)In coronal plane inside and outside joint space become more wider, but the results have no statistically significant differences.3. In the results of descriptive research, the changes following orthopedic treatment were found with the size and shape of the condylar and glenoid fossa, and the bone integrity on the surface of them were found no obvious differences.[Conclusion] The characteristics of temporomandibular joint of the patients with skeletal class Ⅲ malocclusion in mixed dentition:1.condylar is usually in front of glenoid fossa and near to its top, indicating that skeletal class Ⅲ malocclusion is a large factor causing functional mandibular protrution in mixed dentition age.2.Shallow glenoid fossa and flat trajectory, smaller inside and outside joint space in the coronal plane, these morphology of the temporomandibular joint may be related to functional status in class Ⅲ patients.3. After the orthopedic therapy finished, the relationship between maxillary and mandibular have been improved, the reason for this phenomenon may be related to stimulate the development of jaw, eliminate of functional mandibular advancement, and mandibular rotation.4. After treatment of one year, the size and shape of the condylar and glenoid fossa have no obvious differences.5.After treatment of one year, there are no obvious pathological changes when checked with CBCT.