Introduction
Mandibular condyle as well as glenoid fossa are important structures of temporomandibular joint (TMJ) that helps to sustain good occlusion and balanced stomatognathic system. Several factors like facial growth pattern, pathologic/functional alterations, decreased or increased muscular action, occlusal force and dental occlusion changes could affect TMJ morphology and pattern. As a result of these changes there is remodelling of articulating surfaces of condyle and glenoid fossa as an adaptation response. Many studies showed condyle and glenoid fossa are different in shape among patients with different malocclusions. Position of condyle in glenoid fossa influences sagittal, transverse and vertical relationships of jaws which eventually contribute to development of various malocclusions.1 Considering this, it can be stated that assessment of condyle position is important before starting treatment, concentric position of condyle is suggestive of normal subjects without TMJ disorders. Harold Gelb, in 1953, first described an Orthopaedic technique that correlates with the normal physiologic position of the mandibular condyle in the glenoid fossa.2 Now a days there are so many imaging modalities available to visualize TMJ, and lateral cephalogram is one of them and it’s taken routinely for orthodontic treatment. Hence the aim of this study was to asses condylar position using Gelb’s grid in subjects with different malocclusion.
Materials and Methods
The study was carried out on pre-treatment Lateral Cephalogram of 45 patients (aged above 18yrs) who had come for treatment to our department for fixed Orthodontics treatment. The sample was equally divided into three groups, Group I (Class I skeletal malocclusion), Group II (Class II skeletal malocclusion) and Group III (Class III skeletal malocclusion) based on values of ANB, Yen angle and Wits appraisal.
Methodology
All the lateral cephalogram were hand traced by single operator. Following parameters were taken to confirm anteroposterior dysplasia (Figure 1).
ANB angle: Angle between point A to Nasion (N) and Nasion to point B 3 (Figure 1a).
WITS Appraisal: Distance between perpendiculars drown from point A and point B to functional occlusal plane 4 (Figure 1b).
YEN angle: Angle between Sella to point M, and point M to point G 5 (Figure 1c).
After dividing groups the condylar position was determined according to Gelb grid [Gelb H, Arnold G, 1959],2 in maximum intercuspation.
To form the Gelb’s grid draw a tangent to the roof of the fossa (line-1) and to eminentia (line-2), and drawing a third line half-way between these two lines. (Figure 2)
And draw two vertical lines, one vertical line drawn from the highest point of the roof of the articular fossa and another one from the point where the third line (the middle horizontal line) intersects the descending slope of eminence (Figure 3).
In this way divides the fossa into eight areas. The normal position of the condyle is Gelb’s positions 4 and 7 (Figure 4).
The following condylar positions were considered in this study (Figure 5):
Observation and Result
Shows normal and mean values of ANB, YEN angle and Wits as obtained from sample for dividing the sample into Class I, Class II and Class III malocclusion.
Shows condylar position in respect toglenoid fossa in group I,II and III.
Shows intergroup comparison of condyle position in different malocclusion group.
Table 1
Normal and mean values as obtained in study of ANB, YEN angle and Witsapprsal.
Table 2
Condylar position in respect toglenoid fossa in Group I, Group II and III.
Discussion
Position of condyle in glenoid fossa influences sagittal, transverse and vertical relationships of jaws which eventually contribute to development of various malocclusions.1 Diagnostic imaging could provide useful information on the TMJ structures. There are various imaging methods 2 dimentional (x-ray) and 3dimentional (CBCT) which are use to see the glenoid fossa and condylar relation, 3D imaging has its own benefits over 2D imaging (lateral cephalogram). However 3D imaging is not routinely taken for orthodontic treatment because it is expansive and high amount of radiation exposure. Lateral cephalogram is routinely taken for orthodontic diagnosis hence no additional radiation exposure is needed, were taken for the present study. The limitations of a two-dimensional projection for therapeutic positioning of the condyle in relation to the fossa must be considered but this technique was chosen because of its easy availability. In present study we found that for Group I condyle was positioned normally (4,7) in 86.66% of subjects and was displaced posteriorly (5,8) 13.33% of subjects. For Group II condyle was displaced posteriorly (5,8) in 86.66% of subjects and in normal position (4,7) for remaining subjects. For Group III subjects condyle was again found in posteriorly displaced 66.66% of subjects and normally positioned in rest. On overall comparison we found statistically significant P vale (0.0001). On inter group comparison, it was found that condylar position of Group I differed significantly with Group II (P= 0.0001) and Group III(0.0001), however Group II and Group III did not differed significantly for condylar position.
The study was based on Gelb’s description about condylar position in relation to glenoid fossa. In this study it was observed that 5, 8 position of Gleb’s grid was more comman in Class II and Class III while 4,7 (Anterior position) position was more comman in Class I. Thus, we consider that the normal position of condyles should be in areas 4 and 7 (Figure 4). There are many studies in which position of condyle to glenoid fossa has been evaluated by various methods.
Amongst studies done on lateral cephalogram, Kikuchi et al found that the condyle in adolescent subjects showed a symmetrical anterior position relative to the glenoid fossa. 6 Serra et al found condylar position was centric in maximum number of subjects in normal occlusion group using Gelb’s grid on transcranial radiograph whereas displacement increased in subjects with open bite, over bite, posterior crossbite etc.7 Hedge et al did not show variation in condylar position in different malocclusion groups when assessed based on angular parameter. They did not find condylar position with respect to glenoid fossa.8 Wigal et al did his study on subjects with Class II malocclusion treated with herbst appliance found significant positioning of condyle and glenoid fossa in compare to control group.9
Vankadara et al did his study on CBCT and states that centric position is most common position of condyle and 4,7 position is the most common according to Gelb’s 4,7 grid. 4,7 position is found only 11.45% in angle’s Class I cases.2
Kaur et al visualized and compared the position of condyle in the glenoid fossa for different occlusions using CBCT and found that 80% of the subjects exhibited superior-anterior position of the condyle.1
Stasiuk et al found symmetric position of the condyle in 20% of subjects, out of which symmetric position is 17.65% subjects had on both sides and for class II malocclusion the most common position was ¼ followed by 1/5 and for Group III 1/5 was most common and didn’t observe 4/7 in any subject.10 According to authors the age dynamics of the aggravation of wrong position of TMJ head is clearly seen. Regardless of malocclusion, the number of patients with the correct position of the articular heads in 4/7 segment decreases from 20% to 5%. Symmetric position of condyle is most common in subjects with normal occlusion similar study was for other group with skeletal Class I malocclusion where no skeletal discrepancy existed. It can be suggested that condylar position showed variability in malocclusion groups. Further studies should be done on larger sample size and to compare condylar position between pre and post treatment radiographs after premolar extraction.
