Measuring Mandibular Asymmetry Using 3D Novel Coordinate System

Macroesthetic analysis is the diagnostic key to achieve a harmonious facial balance at the end of orthodontic treatment. Disharmony between Macroesthetic, Miniesthetic and Microesthetic will jeopardize the harmony in the facial complex. The prime importance of measuring mandibular asymmetry is its effect on the occlusion, which can alter the treatment outcomes. Objectives: The aim of this study was to measure mandibular asymmetry bilaterally in a cohort Class 1 molar relationship using a new 3D imaging technique with the aid of 3D software [Invivo 5.2.3(San Jose, CA)]. Methods: Thirty five 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 Co-ordinate System was set for the Mid-Sagittal, Frankfort Horizontal and Frontal Plane. Each CBCT was appraised using 16 evaluation criteria bilaterally. Five mandibular landmarks were plotted: Condylion_R, Gonion_R, Menton, Gonion_L, and Condylion_L to divide the mandible 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 3 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 mid-sagittal plane, and the ramus length and the frontal plane (p<0.05). Significant lateroanterior shift of the mandibular ramus on the left side in comparison with the right side. Conclusion: Viewing an object using 3 different angles between the four parts of the mandible and each plane is a valid method to replicate the actual object. 3D CBCTs are a better way to diagnose asymmetry present in the third dimension which is absent in Orthopantomographic or cephalometric radiographs.