title: Measuring mandibular asymmetry in Class I normal subjects using 3D novel coordinate system.
abstract: BACKGROUND
  Orthodontic treatment plays a major role in cosmetic dentistry. A harmonious facial balance is normally the end point in comprehensive orthodontic outcomes. In order to achieve this goal, correct diagnosis of asymmetry should be done starting from the outer facial morphology forms and progressively moving to the dental occlusion. The prime importance of measuring mandibular asymmetry is its tremendous effect on the occlusion.
  
  
  OBJECTIVE
  The aim of this study was to measure mandibular asymmetry in a cohort Class I molar relationship comparing right and left sides using new three-dimensions (3D) imaging technique with the aid of 3D software (in vivo 5.2.3 [San Jose, CA]).
  
  
  METHODS
  35 DICOM files were initially collected retrospectively and seven were excluded due to (1) condylar resorption, (2) history of trauma and (3) unclear DICOM file. A new coordinate system was set for the mid-sagittal plane (MSP), Frankfort horizontal plane and frontal plane (FP). Each cone beam computed tomography (CBCT) was appraised using 16 evaluation criteria bilaterally. Five mandibular landmarks were selected: Condylion_R, Gonion_R, Menton, Gonion_L and Condylion_L. Using these points, the mandible was further divided into four parts: (1) Ramus length right side, body of the mandible right side, body of the Ramus left side and Ramus length left side. The angles between each line and the three different planes were acquired in order to compare each line from a 3D aspect. Mean and standard deviation were calculated for the 28 CBCTs.
  
  
  RESULTS
  Significant bilateral differences were reported in the angle between the ramus length and MSP and the ramus length and the FP (P < 0.05). Significant lateroanterior shift of the mandibular ramus on the left side in comparison with the right side.
  
  
  CONCLUSIONS
  Viewing an object using three different angles between the four parts of the mandible and each plane is a valid method to replicate the actual object.
authors.affiliation: Department of Orthodontics, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Nadia Abou
authors.initials: NA
authors.lastname: Kheir
authors.affiliation: Department of Orthodontics, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Chung How
authors.initials: CH
authors.lastname: Kau
keywords: Three-dimensions imaging; cone beam computed tomography; mandibular asymmetry