A Cone-beam CT Investigation On Tempormandibular Joint Between Two Phase Treatment And Fixed-only Treatment

Objectives:To assess the effects of two phase treatment (Herbst and fixed appliance) andfixed-only treatment (edgewise appliance only) on tempormandibular joint of classⅡmalocclusion patients combined with mandibular retrusion by CBCT analysis, and toprovide references for the clinical treatment.Methods:According to the inclusion criteria, this study selected30patients of permanentdentition with classⅡ malocclusion combined with mandibular retrusion. The groupA consisted15patients (9male,6female, average age12.4years) with two phasetreatment. They were taken CBCT at the following stages: two weeks before Herbsttreatment (T1), at the start of treatment when Herbst appliance was placed (T2),immediately after Herbst appliance removal (T3) and immediately after the edgewiseappliance removal (T4); The group B consisted15patients (8male,7female, averageage12.8years) with extraction treatment, They were taken CBCT at the T1and T4stages. The InvivoDental software was used to calculate the relevant parameters oftemporomandibular joint from the three-dimensional CBCT images. The acquireddata were then statistical analyzed.Results:At the end of treatment of both two groups, upper and lower dentitions werealligned and levelled, canines and molars obtained neutral relationship, anterior teethestablished normal overbite and overjet and proifile improvement.1. The changes of skeletal structure of temporomandibular jointIn group A, at T3, CBCT imagines showed hyperplasia imaging similar to"crescent" at the posterior-superior border in14patients of the28condyles that theouter edge was high density and inner region was low density no similar imaging atother period. It was taken a quantitative evaluation of the relevant parameters oftemporomandibular joint. No significant differences were found in the condylarlongitudinal distances, condylar anterior-posterior diameters, condyle height, condylar head height, glenoid fossa width, glenoid fossa depth and articular tuberclegradient between T2and T1stage; From T2to T3stage, condylar anteroposteriordiameters and condylar head height increased by0.62mm,0.54mm (P <0.01), but nosignificant differences were found in other skeletal structure measurements (P>0.05)between T2and T3stage; From T3to T4stage, all the skeletal structuremeasurements had no significant changes (P>0.05); From T1to T4stage, thecondylar head height increased by0.66mm,0.53mm (P <0.01), but no significantdifferences were found in other skeletal structure measurements between T1and T4stage(P>0.05).In group B, neither T1nor T4stage showed hyperplasia imaging of condyle atthe CBCT images. all the skeletal structure measurements had no significant changes(P>0.05) between T1and T4stage.After T1-T4period of treatment, the increment of condylar head height in groupA were0.56mm more than in group B. The changes of other skeletal structuremeasurements showed no statistical difference between group Aand B.2. The changes of condylar position in the glenoid fossaIn group A, From T1to T2stage, the anterior joint space decreased by0.52mm（P＜0.05), superior joint space and posterior joint space increased by3.88mm and4.51mm（P＜0.01); From T2to T3stage, the anterior joint space increased by0.48mm （P＜0.01), superior joint space and posterior joint space decreased by3.65mm and4.10mm（P＜0.01）；From T1to T3stage, the posterior joint spaceincreased by0.40mm（P＜0.05), anterior joint space and superior joint space had nosignificant differences(P＞0.05)；From T3to T4stage, the superior joint space andposterior joint space decreased by0.30mm and0.42mm（P＜0.01), bue anterior jointspace had no significant difference between T3and T4stage (P＞0.05); Nosignificant differences(P＞0.05) were found in the anterior joint space, superior jointspace and posterior joint space between T1and T4stage.In group B, No significant differences (P＞0.05) were found in the anterior jointspace, superior joint space and posterior joints pace between T1and T4stage.After T1-T4period of treatment, the changes of the anterior joint space, superiorjoint space and posterior joint space of the two groups had no significance differences (P＞0.05).Conclusions:1. There are condylar growth changes during Herbst treatment;2. At the start of treatment when Herbst appliance was placed，the condyle wasdisplaced in an anterior and inferior direction, but drawed back nearly the originalposition after the first phase treatment, especially the end of two phase treatment;3. The skeletal morphology of temporomandibular joint and the condyle positionin the glenoid fossa did not produce significant changes during fixed-only treatment;4. Compared with fixed-only treatment, except condylar growth changes, thechanges of other skeletal morphology of the temporomandibular joint and the condyleposition within the glenoid fossa showed no statistical difference by two phasetreatment.