Evaluation of Condyle Position in Skeletal Class I & Class III Growing Subjects

Introduction: Evaluation of temporo-mandibular joint (TMJ) anatomy and function is an essential part of orthodontic diagnosis and treatment planning. It has been hypothesized that dental and skeletal malocclusions alter the functional loading of TMJ which can affect joint morphology. Objective: Three dimensional (3D) evaluation of condylar position using CBCT in skeletal Class I and Class III growing subjects. Materials & Method: CBCT images of ten growing skeletal Class I & ten Class III patients in the age range of 7-14 years were analyzed. 3D condylar position were evaluated representing antero-posterior, vertical, laterolateral position of condyle, axial condylar angle and coronal condylar angles which were measured in axial, coronal and sagittal sections using Dolphin Imaging software. Antero-posterior and vertical difference of right and left condyle were measured in axial and coronal sections respectively. Result: Paired t-Test revealed no significant difference between right and left sides of condyle in skeletal Class I as well as Class III subjects. Independent t-test and Mann-Whitney U test showed no significant difference between position of condyle in Class I and Class III subjects. Conclusion: 3D CBCT analysis shows no significant difference in condylar position of skeletal Class I and Class III subjects.


INTRODUCTION
For majority of patients undergoing orthodontic therapy, esthetics is the primary concern however the long term success of orthodontic therapy can only be ascertained by ensuring optimal functional efficiency of the masticatory apparatus.The relationship between malocclusion pattern and temporo-mandibular joint (TMJ) problems are not clear and so is the relationship between orthodontic treatment and TMJ disorders. 1ost of the previous studies [2][3][4] suggest that the incidence of TMJ disorders between subjects who have received orthodontic therapy and those who have not were similar but orthodontist should always be aware of the fact that nearly all orthodontic therapy alters patients' existing occlusion and may predispose the patient to TMJ disorders.Hence knowledge of normal anatomy and its variations are essential for orthodontist.The effect of function on form is well documented in orthodontic literature.The form of temporo-mandibular joint can be affected by various anatomical and pathological factors.Facial anatomical factors like growth pattern, dental and skeletal malocclusion can affect the morphology of TMJ by altering the loading pattern of the joint. 5,6][9] Some studies have reported no significant difference between the condylar position in Class I and Class III subjects, 7,8 while others have reported the difference. 5,9hese discrepancies might be due to differences in measuring technique and parameters used to assess the condylar position.Various two dimensional radiographic views like panoramic radiograph, TMJ radiograph, cephalograms have been used to asses condylar position but the overlapping of surrounding structures over the TMJ limit the accuracy of these methods. 53D imaging procedures like conventional CT had also been used, 10,11 but the risk of high radiation exposure has limited the use of this method.CBCT has emerged as a useful imaging technique owing to significantly low radiation exposure as compared to conventional CT and high quality of 3D images; 12 however very few studies, till date have used CBCT data to evaluate condylar position

MATERIALS AND METHOD
The study was conducted at a university orthodontic department.Cone beam computed tomography (CBCT) image were retrieved from department archives of the patients in the age range of 7-14 years.The DICOM (Digital Imaging and Communications in Medicine) images were evaluated with Dolphin imaging software Version 11.7 (Dolphin Imaging & Management Solutions, Chatsworth, California).These images were rendered into volumetric images and reconstructed sagittal, axial, coronal slices and the 3D models were obtained.The 3D images were oriented such that the mid-sagittal plane passed through the skeletal midline, the axial plane showed the FH plane (right porion to right orbitale), and the coronal plane passed through the furcation of the right maxillary first molar (Figure 1).After orienting the images, lateral cephalograms were obtained from the CBCT images using ray-sum feature of the software.Subjects were classified on the basis of ANB angle.Ten Class I subjects (seven male, three female) and ten Class III subjects (five The landmarks used were as follows (Figure 2): 1. Centre of condyle (CC): Intersection of lines representing largest anteroposterior and mediolateral widths of condyle, identified in axial slice.

External acoustic meatus (EAM): The most external
point in the posterior wall of external acoustic meatus, identified in axial slice.

Laterosuperior condylar landmarks (LSC):
The point at the intersection of tangent to the most superior and lateral part of condyle, identified in coronal slice.
After landmark identification, digitization was done on the software to measure following parameters:  13 and modifications suggested by Balachandran et al. 14 All measurements were done by principal investigator.

DISCUSSION
In the present study, ANB angle was used to classify subjects in two skeletal groups.Despite its shortcomings ANB angle is most commonly used to differentiate sagittal skeletal patterns. 15The accuracy and reliability of Dolphin software for linear and angular measurements has been established by previous studies. 169] In some studies, lateral cephalograms were used to evaluate the position of condyle which cannot be considered reliable because of the superimposition of surrounding structures like petrous temporal bone, mastoid process and articular eminence; making visualization of condyle difficult. 5,8n this study we have modified the methodology of Melgaco et al 13 in two ways.First, the head orientation was not reestablished after land mark orientation.Second, a large slice thickness was used when two landmarks were not visible in single slice.This was true mainly for measurement of coronal condylar angle.As suggested by Balachandran et al, 14 this could increase the chances of error but we could not find any suitable alternate method.
Marrieta et al 5 reported some spatial difference in condylar position between Class I, Class II and Class III groups.They found that condyle in Class III was more superiorly and anteriorly placed as compared to Class I and the difference was statistically significant.Previous studies showed variation in condyle position in subjects with hyperdivergent and hypodivergent subjects. 21In our study all subjects had average growth pattern, hence the findings could not be directly compared.
Alhammadi et al 9 reported significant difference between vertical position and antero-posterior inclination in Class I and Class III subjects.In their study anteroposterior inclination of condyle was higher in Class III subjects while centre of condyle was more anteriorly placed in Class I subjects.These findings are similar to our study.The intercondylar distance was higher in Class I subjects as compared to Class III subjects which is in contrast to our findings.This disparity may be due to the difference in growth status of study sample and difference in landmark measurement parameters between the studies.
The authors could find only three similar previous studies and all those studies have differences in landmark identification and measurement methodology.No previous studies have used methodology similar to ours, thus direct comparison of these studies are not possible.
In the present study, the subjects were in growing stage, hence the position of condyle may also change with aging.The power of the study is inadequate because of small sample size.All the CBCT images were retrieved from archives and no image was obtained for purpose of this study.

CONCLUSION
Three dimensional CBCT analyses revealed no difference in condylar position between skeletal Class I and Class III growing subjects. OJN