The Discrepancy Between Mid-sagittal Planes For Evaluation Of Asymmetry In Skeletal Class Ⅲ Adults Using Cone Beam CT

Objective: The aim of this study is to compare the capacity of the analysis onfacial symmetry by three different types ofMid-sagittal planes(MSP) inskeletalclass Ⅲmalocclusion using cone beam computed tomography (CBCT), and to analyze theindicators for the deviation of maxilla and mandible. The research will provide areference for the evaluation on facial symmetry adultsfor orthodontists.Material and methods: We select50patients with skeletal class Ⅲ malocclusionas the objects for this study from the department of orthodontics of DalianStomatological Hospital during September,2012to September2013. They are dividedinto two groups according to the different types of facial asymmetry: the experimentalgroup including15females and15males(20.3±2.1years old)that have remarkablefacial asymmetry; the control group including15females and15males(21.8±3.2yearsold)that do not have facial asymmetry. We collects all the CBCT images for each patientbefore the orthodontic therapy, and do the three-dimensional reconstruction withInvivoDental5.1. To investigate the three-dimensional images, we use three differentways to establish three types of coordinate systems, which are Frankfort Plane R(FHR);Frontozygomatic sutures (Fzs)on both sides and Endocanthions (En) points on bothsides. After that, we obtain three sagittal planes from those different coordinate systemsand measure the deviation from anterior nasal spine (ANS) and menton (Me) to thethree types of sagittal planes, respectively. ANOVA is used to do the statistical analysisfor the volume of deviation, in order to compare the difference among the threemid-sagittal planes on the evaluation for skeletal class Ⅲ facial asymmetry. On the other hand, we measure the deviation for the control group so that it will be theindicator as the acceptability for skeletal class Ⅲ facial asymmetry.Results: In experimental group, there are statistical difference for the analysis onmaxillary deviation when using En points and other twoplanes to define the MSP.What’s more, all of the three ways among each other have statistical difference whenevaluating the mandibular deviation. In the control group, all three ways among eachother have no statistical difference when investigating maxillary deviation. But there arestatistical difference between the way using FHR and the way using Fzs and En point,separately when analyzing mandibular deviation. At last, the indicators for the deviationof the maxilla and mandible from symmetry skeletal class Ⅲ subjects are±1.14mm、±1.96mm, respectively.Conclusions:The way that how to establish coordinate system will affect thejudgment on facial asymmetryin skeletal class Ⅲ malocclusionadults and thedefinition for MSP when using CBCT, which will lead to different diagnosis for thefacial deviation. Especially for those severe patient, different MSP will have theopposite outcomes when analyzing maxillary deviation. Therefore, the orthodontistsshould choose the right method to make the coordinate system when usingthree-dimensional system to evaluate the facial asymmetry in skeletal class Ⅲ adults.