|Year : 2013 | Volume
| Issue : 1 | Page : 6-11
Evaluation of correlation between cephalometric variables and internal derangement of temporomandibular joint in asymptomatic class II division I high angle patients using Helical computed tomography
Diravidamani Kamatchi1, Vasanthan Palanivel2, Sathesh Kumar Sivalingam3
1 Department of Orthodontics, CSI College of Dental Sciences and Research, Madurai, Tamil Nadu, India
2 Department of Orthodontics, Vinayaka Mission's Sankarachariyar Dental College, Ariyanoor, Salem, Tamil Nadu, India
3 Department of Dental Sciences, JKK Nataraja Dental College, Komarapalayam, Tamil Nadu, India
|Date of Web Publication||22-Aug-2013|
135c, Madurai Road, Manaparai - 621 306, Trichy, Tamil Nadu
Introduction: The aim of this study was to identify the presence of articular disk displacement using helical computed tomography (CT) in asymptomatic Class II Division I patients and to find a correlation between internal derangement of temporomandibular joint (TMJ) and certain lateral cephalometric variables. Materials and Methods: After screening 578 patients in the age group 18-25 years, 30 patients who met the case selection criteria and willing to cooperate were included in the study. Frontal and profile photographs and lateral cephalograms were taken. Helical CT of TMJ were taken and the disk tissue of the joint was analyzed. Composite cephalometric analysis was performed to evaluate cranial base, vertical skeletal relationships, maxillary and mandibular skeletal relationships, and dental relationships. Results: Mean and standard deviation were estimated from the sample in each group. Mean values were compared using Student's independent t-test. Patients with disk displacement have shorter anterior and posterior cranial base, small posterior facial height (PFH), backward rotation of mandible, decreased mandibular body length, and an increase in proclination of lower incisors. Conclusion: Certain cephalometric variables correlate well with helical CT findings of patients with internal dernagement of TMJ (TMJ ID), and thus could assist in identifying patients with potential TMJ disorders.
Keywords: Helical computed tomography of temporomandibular joint, internal derangement of temporomandibular joint, lateral cephalometric variables
|How to cite this article:|
Kamatchi D, Palanivel V, Sivalingam SK. Evaluation of correlation between cephalometric variables and internal derangement of temporomandibular joint in asymptomatic class II division I high angle patients using Helical computed tomography. SRM J Res Dent Sci 2013;4:6-11
|How to cite this URL:|
Kamatchi D, Palanivel V, Sivalingam SK. Evaluation of correlation between cephalometric variables and internal derangement of temporomandibular joint in asymptomatic class II division I high angle patients using Helical computed tomography. SRM J Res Dent Sci [serial online] 2013 [cited 2021 Jul 27];4:6-11. Available from: https://www.srmjrds.in/text.asp?2013/4/1/6/116823
| Introduction|| |
It becomes a task of prime importance to assess the temporomandibular joint (TMJ) prior, during, and after comprehensive orthodontic treatment to ensure a functionally and physiologically successful orthodontic result. In most cases, TMJ disk displacement remains asymptomatic depending on the patient's tolerance level and adaptive capacity. ,,,, Such patients when subjected to orthodontic tooth movement produce overt symptoms of TMD. Various imaging procedures are available for the joint including Arthrography, helical computed tomography (CT), magnetic resonance imaging (MRI), cone beam computed tomography (CBCT), etc., However, these investigations require complicated setup and are too expensive for the patient to be recommended routinely.
Lateral cephalogram has long been a well-recognized orthodontic diagnostic aid. Certain lateral cephalometric variables can be identified to be of diagnostic value and can point to potential patients with internal derangement. ,,,,, This study aims in finding such a correlation between internal derangement of the joint and certain lateral cephalometric variables. A positive correlation of these variables can guide the orthodontist in further investigations, diagnosis, and treatment procedures as well as in patient education.
| Materials and Methods|| |
A total sample of 578 patients in the age group of 18-25 years was screened, out of which 123 patients with increased facial convexity and high clinical frankfort mandibular plane angle (FMA) were shortlisted. The following case selection criteria were applied: (1) No history of juvenile rheumatoid arthritis, (2) no prior TMJ complaints, (3) no prior orthodontic treatment, (4) posterior divergence, (5) increase lower facial height, (6) class II division I malocclusion, (7) no posterior tooth loss, and (8) no posterior tooth replacement. Thirty patients who met the case selection criteria and were willing to cooperate and undergo the investigations were selected. The participants were informed about the study in detail including radiation exposure for diagnostic purpose and their willingness to participate in the study was confirmed with written consent. The following investigations were performed: (1) Helical CT of the TMJ and (2) lateral cephalogram.
Helical CT of the TMJ were taken with SOMATOM Smile (Siemens; Serial No. 20170). Serial axial sections were taken parallel to the ala-tragus line, starting a few millimeters above the base line over a distance of 5 cm. The patients were placed in supine closed mouth position and followed by unassisted maximal vertical open mouth position [Figure 1]. The configuration of CT machine to obtain the sections of the joint is summarized in [Table 1]. Scanning data were reformatted into 1 mm interval axial images. The axial images were converted into sagittal images by using multiplanar reconstruction (MPR) technique [Figure 2]. All the images were evaluated with soft tissue display to visualize the disk tissue (window width: 230-250, window level: 30-50).
|Figure 1: Patient positioning in SOMATOM smile (a) Somatom smile (b) Patient in position|
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|Figure 2: Multiplanar reconstruction technique for reconstruction (a) Axial slice (b) Multiplanar reconstruction|
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To assess disk displacement in helical CT, the angle between the condylar head and glenoid fossa is closely examined in each scan [Figure 3]a-c. The TMJ disk tissue composed of high density fibrous tissue appears as a white structure interposed between the condyle and glenoid fossa. Increased soft tissue density anterior to the condyle in closed mouth view is interpreted as anterior displacement of the disk. When the mouth is open, if the disk is recaptured on the condyle, it is indicative of disk displacement with reduction (DDR). If the disk remains anterior in open mouth position acting as a barrier to condylar translation, it is termed as disk displacement without reduction (DDNR).
Lateral cephalograms were taken with CEI OPX/105 (Villa India Medical Systems, Italy). Patients' facial height (FH) was placed parallel to the floor, patients aligned within ear rods of the cephalostat exerting moderate pressure on the EAM. Nineteen landmarks were located on each radiograph and twenty-five variables were calculated. A composite cephalometric analysis was performed to evaluate four areas: (1) Cranial base, (2) vertical skeletal relationships, (3) maxillary and mandibular skeletal relationships, (4) dental relationships. The angular and linear measurements were taken from the analysis previously described by Downs,  Jarabak  and McNamara.  The position of the landmarks is shown in [Figure 4] and their measurements in [Figure 5], [Figure 6] and [Figure 7].
|Figure 5: Angular measurements 1. Saddle angle (N-S-Ar), 2. Articular angle (S-Ar-Go), 3. Gonial angle (Ar-Go-Me), 4. Mandibular plane angle (SN-MP), 5. Maxillomandibular plane angle (PP-MP), 6. Interincisal angle (U1-L1), 7. U1-SN. 8. U1-PP|
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|Figure 6: Angular measurements contd 1. SNA angle, 2. SNB angle, 3. Facial convexity (ANB), 4. Frankfort mandibular plane angle (FMA), 5. Mandibular incisor to FH plane (FMIA)|
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|Figure 7: Linear measurements 1. Anterior cranial base length (S-N), 2. Posterior cranial base length (S-Ar), 3. Anterior facial height (N-Me), 4. Posterior facial height (S-Go), 5. Lower anterior face height (ANS-Me), 6. N perpendicular to Point A, 7. N perpendicular to pogonion, 8. Mandibular body length (Go-Me), 9. Ramal length (Ar-Go), 10. Effective mandibular length (Co-Gn), 11. Lower incisor to A-Pog|
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| Results|| |
This study evaluated 30 Class II Division I high angle cases using helical CT of the TMJ, lateral cephalogram, and study models. The results obtained are discussed under the following headings:
- CT assessment
- Correlation with lateral cephalometric findings
- Cranial base
- Vertical skeletal relationships
- Maxillary and mandibular relationships
- Dental relationships.
In the helical CT, angle between the condylar head and glenoid fossa is closely examined. Based on the above findings for interpreting disk position; out of 30 individuals, 13 revealed normal disk positions, 16 had DDR, while only one patient had DDNR. These patients were grouped as Group I, Group II, and Group III, respectively. Mean and standard deviation (SD) were estimated. Mean values were compared between group I and II using Student's independent t-test. One sample t-test was used to compare the mean values in group I/II with group III. P ≤ 0.05 was considered as level of significance.
Correlation with lateral cephalometric findings
Various cephalometric variables were then evaluated for their correlation between patients with normal disk position (group I), disk displacement with reduction (group II), and disk displacement without reduction (group III). Student's t-test and one sample t-test were used to calculate P value. The results are tabulated [Table 1], [Table 2], [Table 3] and [Table 4].
|Table 2: Mean, standard deviation, and test of significance of mean values between group I and group II|
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|Table 3: Mean, standard deviation, and test of significance of mean values between group I and group III|
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|Table 4: Mean, standard deviation, and test of significance of mean values between group II and group III|
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No statistically significant difference is found in anterior and posterior cranial base lengths between groups I and II. However, group III showed significant decrease in cranial base lengths.
Vertical skeletal relationships
When groups I and II were compared, there is an increase in the articular angle, basal plane angle, and mandibular plane angle in group II patients. There was also an associated decrease in Jarabak ratio and posterior facial heights in group II patients. All the analyzed parameters (articular angle, gonial angle, basal plane angle, mandibular plane angle, posterior facial height, and Jarabak ratio) show a significant difference in group III when compared to the other two groups.
Maxillary and mandibular skeletal relationships
Among various factors that represent the maxillary and mandibular relationships, N┴Pog and ramus height were statistically significant among the three groups with a progressive decrease in the values from group I to group III. Also the values; sella, Nasion, A point (SNA); sella, Nasion B point (SNB); A point, Nasion, B point (ANB), and nasion and pogonion (N┴Pog) increased in severity in group III patients. However, N┴PtA and ramal height decrease significantly in group II and III as compared to group I. Thus, it can be inferred that in patients with normal disk, the Class II skeletal base is mainly due to maxillary prognathism while with the presence and increase severity of ID, maxilla becomes more orthognathic, while mandible becomes more retruded in the disk displacement cases. The mandibular length is significantly decreased in group III indicating that the patients with DDNR also have shorter length of mandibular body.
Only FMIA shows a statistically significant difference among the three groups. However, lower incisor to point A on maxilla to pogonion (A-Pog) and incisor-mandibular plane angle (IMPA) also shows a significant increase in lower incisor proclination with increase in the severity of internal derangement.
| Discussion|| |
In this study, 30 asymptomatic individuals were selected to evaluate the TMJ ID. Disease prevalence in asymptomatic subjects in relation to TMJ has been cited as 10-33%. , These patients may show exaggerated symptoms on the initiation of orthodontic treatment. Various recent studies suggest that TMJ ID is associated with altered facial morphology such as compensatory clockwise rotation and retruded mandibular position. ,,,,,, Therefore, rather than selecting a random group of asymptomatic individuals, we restricted our sample to asymptomatic Class II high angle cases. Hayashi et al.,  compared the sensitivity, specificity, and accuracy of helical CT versus MRI in the evaluation of articular disk position and have reported an accuracy of 97-99% in open and closed mouth position. Hence, helical CT was employed to evaluate TMJ status in this study.
As lateral cephalogram is a routine diagnostic aid in orthodontics, it was decided to correlate certain cephalometric variables ,,,, with the CT findings, so as to enable use of cephalometrics as a guide for diagnosing potential TMJ disorders.
In this study 43% of the individuals revealed normal disk position, 53% of the sample had disk displaced in front of the condyle in closed mouth position, assuming a normal position on mouth opening. Only in 3% of the sample, the disk was displaced anteriorly in both open and closed mouth position. Similar prevalence was reported in literature. 
When comparing the lateral cephalometric variables, greater caution was exerted in interpreting group III values as the group comprised of a single sample. In this study, statistically significant differences were found in patients with disk displacement. There was also posterior rotation of mandible as evidenced by a decrease in the Jarabak ratio in the disk displacement group which was in turn due to a significant decrease in posterior facial heights. The decrease in ramus heights (43.6 ± 2.2 vs 49.6 ± 2.2 mm) actually aggravates the vertical facial pattern.  A shorter ramus height in children and adolescents with degenerative joint disease has been reported.  Hyperdivergent facial pattern in patients with TMJ ID has also been pointed out by Hwang et al.
The Class II patients with normal disk position revealed more prognathic maxilla with mild mandibular retrognathism (N┴Pt A 3.2 ± 0.7 mm and N┴Pog 6.5 ± 0.8 mm). However, patients with DD showed a higher tendency towards mandibular retrognathism (N┴Pog 7.5 ± 1.0 mm and N┴Pt. A 2.1 ± 1.7 mm). This high degree of association of TMJ ID with mandibular deficiency suggests that more severe the Class II skeletal pattern, a higher likelihood of internal derangement coexists. It has been proved that the degree of joint degeneration directly parallels the degree of mandibular retrognathism and that the TMJ ID is more common in cases with mandibular retrusion, leading to the typical facial morphology in high percentage of cases. 
The relative protrusion of mandibular incisors as demonstrated by a decrease in FMIA (48.6 ± 2.5 degrees as compared to 56.2 ± 2.5 degrees) with internal derangement is probably related to increased overjet, arising from the posterior positioning of the mandible and its clockwise rotation associated with decreased height of the mandibular ramus found in patients with TMD. 
| Conclusion|| |
This study evaluated 30 asymptomatic Class II Division I high angle cases for the presence of TMJ ID using helical CT and correlated the presence of disk displacement with various lateral cephalometric variables. The results could be summarized as follows:
Clinical implication of this study is that asymptomatic Class II Division I high angle cases require further investigations of the TMJ as they are more vulnerable to TMJ ID. CT evaluation of the joint in these patients could point to the presence of disk derangement, but is expensive for routine checkups in all cases. In the presence of above lateral cephalometric findings, the orthodontist can screen out the high angle patients with potential TMJ ID and order further investigations.
- The presence of internal derangement as evidenced by anteriorly displaced disk in helical CT was found to be 56% in asymptomatic preorthodontic adult Class II high angle cases
- ID of the joint correlates positively to the lateral cephalometric variables such as high articular angle, increased mandibular plane angle, increased basal plane angle, decreased posterior facial height, posterior rotation, and severe retrusion of the mandible and shorter ramus height.
This study can be further refined by using MRI as a dose-effective or cone beam CT as a dose-effective and a cost-effective alternative to helical CT for the diagnostic evaluation of TMJ pathologies. Future studies should also ideally consider the different subgroups of patients with articular disk displacement (according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD))  in the cephalometric evaluation of structural characteristics since, according to Bosio et al.,  the position of the articular disk can influence the condylar position and thus the jaw position and their cephalometric measurements.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3], [Table 4]