Assessments Of Morphological Change Of Mandible And Temporomandibular Joint For Mandibular Asymmetries Of Patients With Class Ⅱ Subdivision Malocclusions By Three-Dimensional Reconstruction

Objective:To build up a set of 3-D reconstruct positioning standards for the hard tissue of teporomandibular joint(TMJ) and mandible of mandibular asymmetries of patients with class Ⅱ subdivision malocclusions by CBCT. Analyze the morphological character of mandible and temporomandibular joint for mandibular asymmetries of patients with class Ⅱ subdivision malocclusions and the change of before and after the orthodontic treatment with the three dimensional positioning standards.Methods: For 60 cases of mandibular asymmetries of patients with class Ⅱ subdivision malocclusions, we reconstructed the CT images into 3D models by Mimics 15.0, and analyzed the positioning accuracy of two orthodontic doctors on the selecting 17 hard tissue landmarks in mandibe and TMJ by linear correlation and linear regression analysis. Select 60 patients of mandibular asymmetries of patients with class Ⅱ subdivision, according to the cervical spine bone age its were divided into two groups, the first group included 39 patients for pubertal with the mean age of 13.45±1.55 years old(10 males, 29 females), the second group included 21 patients after pubertal stage with the mean age of 1.35±6.25 years old(4 males, 17 females), we reconstructed the CT images into 3D models by Mimics 15.0 and set up 3D coordinate system. Anatomical landmarks of mandible, condyle and glenoid fossa were located and established reference planes. Eleven sets of measurements from anatomical landmarks of mandible, condyle and glenoid fossa were used for statistical analysis.Results:(1) the left and right Entoglenoid process(ENPL,ENPR) points showed incosistencies in the X axis(rENPL=0.9375/bENPL=0.9643;rENPR=0.9424/bENPR=0.9824), while in the Y and Z axis showed good consistency; the left and right Gnathion points(Gnl,Gn R), the right Postglenoid process point(Po PR), and the left Porion point showed inconsistent in the Z axis(rGn L=0.9658/bGn L=1.0544;rGn R=0.9869/bGn R=1.0514;rPo PR=0.9498/bPo PR=1.0328;rPo L=0.9637/bPo L=1.0548), However, the MPL、MPR、LPL、LPR、Co AL、Co AR、Co PL、Co PR、ATL、ATR、POPL、FRL、FRR、Co TL、Co TR、Ag L、Ag R、Ra L、Ra R、Rp L、Rp R、Go L、Go R、MNL、MNR、Gn L、Gn R、Fo L、Fo R、Po R points expressed good consistent.(2) The morphology of class Ⅰ side and class Ⅱ side of the mandible, condyle and glenoid fossa for mandibular asymmetries of patients with class Ⅱ subdivision malocclusions at pubertal stage has no difference before and after orthodontic treatment(P>0.05).(3) Female patients after puberty, the length of mandibular rumus, condylar height and anterior fossa width at class Ⅰ side was obvious longer than that of class Ⅱ side before orthodontic treatment(P<0.05); But after treatment, only the anterior fossa width at class Ⅰ side was longer than that of class Ⅱ side(P=0.023), While the male patients only in the length of glenoid fossa in class Ⅱ side was greater than class I side( P=0.048), and the rest of the measurements indexes had no statistical significance( P>0.05).(4) The morphology changes of class I side and class Ⅱ side of mandible, condyle and glenoid fossa for mandibular asymmetries of patients with class Ⅱ subdivision malocclusions at pubertal stage and at after pubertal stage had no difference before and after orthodontic treatment(P>0.05).(5) The changes of mandibular rumus length and condylar height of class I and class Ⅱ side had high positively correlated before and after orthodontic treatment of mandibular asymmetries of female patients with class Ⅱ subdivision malocclusions after the pubertal stage.Conclusions:(1) We choose the anatomical landmarks in the 3-D coordinates showed good consistency and repeatability, it can provide basis and reference for us, when we research the morphological characteristic of mandible and TMJ for mandibular asymmetries of patients with class Ⅱ subdivision malocclusions.(2) Mandible and TMJ morphology had no obvious asymmetry for mandibular asymmetries of patients with class Ⅱ subdivision malocclusions at pubertal stage before and after orthodontic treatment, most likely for functional and teeth deformity, Patients after puberty, mandible and TMJ showed osseous asymmetry for mandibular asymmetries of patients with class Ⅱ subdivision malocclusions at pubertal stage before and after orthodontic treatment. The patients during puberty stage without osseous before and after orthodontic treatment, while patients after puberty with osseous, this showed orthodontic treatment may not improve osseous asymmetry deformity, and Mandibular asymmetries of patients with class Ⅱ subdivision malocclusions is developed from functional mandibular deviation to skeletal deviation, and it is beneficial to reduce the deformity of late stage to treat it at the pubertal stage.(3) The changes of mandibular rumus length may be associated with the change of condylar length for the mandibular asymmetries of female patients with class Ⅱsubdivision malocclusions before and after orthodontic treatment, because the occlusal relationships may be changing by orthondtic treatment, according to reconstruct occlusal balance, the condylar may be renovated, thus improve the mandibular asymmetries of patients with class Ⅱsubdivision malocclusions.