In this study, we examined the variation of the temporomandibular joint (TMJ) horizontal and vertical condylar angles in 1,143 patients who were referred for tomographic evaluation of the TMJ. Both angles showed a wide range of variation with the mean right and left horizontal con­dylar angles being 24.2 and 25.3 degrees, respectively. The mean right and left vertical condy­lar angles were found to be 3.3 and 4.5 degrees, respectively. The horizontal and vertical con­dylar angles were measured on a dry skull with a prominent morphologic landmark (os­teophyte). Corrected lateral cephalometric hypocycloidal tomograms were produced by com­pensation for the true horizontal and vertical condylar angles, and by varying each angle +2, -2, or +4, -4 degrees from the true measured angles. It was found that a slight variation of +2 or -2 degrees in either the horizontal or vertical condylar angles would affect the shape, size and anatomic relationships of the bony components of the TMJ. These results demonstrate the need for individual compensation of the horizontal and vertical condylar angles to obtain high quality diagnostic tomographic images of the TMJ.
 

Radiography is an important tool in achieving a proper diagnosis and planning a successful treat- ment and follow-up of the TMJ dysfunction. The desire to obtain high quality diagnostic image of the TMJ led to the development of various radiog- raphic techniques. Among these techniques are the transcranial, transorbital and transpharyngeal imaging.¹¹² All attempts were made in these forementioned techniques to eliminate the superimposition of the base of the skull on the joint image. However, these techniques fell short of achieving this vital objective as variable degrees of superimposition were still present on the produced images.¹³

The variability in the morphology of condylar head, as well as in the orientation of its long axis due to the variability of the condylar horizontal and vertical angulations, makes it difficult and nearly impossible to obtain an ideal TMJ image using the transcranial, transorbital or transpharyngeal techniques.¹²¹³ Tomography, or sectional radiog- raphy, produces images of the joint at different places and different sections for thorough evalua- tion of the joint. While some investigators recom- mended positioning of the patient's head with a standard 20 degrees horizontal angle,¹⁴ others recommended individual compensation of the horizontal angle of each condyle¹⁵¹⁶ while a third group of researchers considered the vertical angu- lation of the condylar axis.¹²'¹³¹⁵¹⁷

To fulfill the objective of producing reproducible images of the TMJ, tomography was modified to compensate for the specific morphology of the condyle and its axis. Corrected lateral cephalometry was developed as early as 1961 by Yale and Rosenberg¹⁵ at the University of Illinois in Chicago. This technique was based on the com- pensation for the individual right and left horizontal and vertical condylar angulation for each patient. It was further modified in 1986 by Rosenberg and Graczyk¹⁷ by the introduction of corrected antero- posterior cephalometric tomography of the TMJ. This modified technique was based on positioning the patient's head in a specially-designed cephalostat according to the previously measured horizontal and vertical angle of each condyle. This technique produced maximum diagnostic and reproducible radiographs of the joint.¹⁷

The present study was designed with two objec- tives. First, to study the variation of both horizontal and vertical condylar angulation in a large group of patients who presented for corrected lateral tomographic examination of the TMJ. Second, to evaluate the importance of individual correction of the horizontal and vertical condylar angles and its effect on the diagnostic quality of the produced tomographic images.

The records of corrected lateral cephalometric hypocycloidal tomographic images of the TMJ of 1,143 patients examined at the Department of Oral Radiology, College of Dentistry, University of Illinois in Chicago between 1982 to 1992 were reviewed. In all of these patients, the individual right and left condylar horizontal and vertical ang- les were measured prior to the tomographic exami- nation according to the technique described by Rosenberg and Graczyk in 1986.¹⁷ A submental vertex (SMV) radiograph was produced by posi- tioning the patient's Frankfort plane parallel to the film and perpendicular to the X-ray central beam. On the SMV view, three lines were constructed [Fig. 1 ]. The first line {line A-A) connected the metal markers within the earposts "intermeatal line". The second line {line B-B) represents an arc determined by the radius of the intermeatal line and the third line {line C-Q was drawn from the visible condylar long axis to intersect with the intermeatal line. The angle formed between the condylar axis and the intermeatal line represents the horizontal condylar angle. An AP tomogram was produced by position- ing the patient's Frankfort plane in the frontal plane and perpendicular to the X-ray film. On the AP tomogram, the intermeatal line, an arc represent- ing the radius of the intermeatal line and a third line representing the long axis of the condyle were drawn. The angle formed by the intersection of the long axis of the condyle with the intermeatal line represents the condylar vertical angle [Fig. 2]. For each patient, age, sex and right and left horizontal and vertical condylar angles were recorded. Data were analyzed using statistical analysis system (SAS) and a main frame computer [IBM 3083 of KingSaud University] to calculate the range, mean, standard error, and 95% confidence interval for the right horizontal, the right vertical, the left horizon- tal and left vertical angles separately.

To correlate the relationship between the true horizontal and vertical condylar angles and the quality and image clarity of the condyle and other bony components of the TMJ (fossa and emi- nence), a dry skull with a prominent bony osteophyte on the anterior aspect of the right con- dyle was used in this study. To prevent the move- ment of the mandible during the investigation, the right and left condyles were kept in the center of their respective fossae. The upper and lower teeth were kept in maximum occlusion and were fixed in such position using sticky wax. The horizontal and vertical angles for the right and left condyles were measured separately according to the corrected lateral cephalometric technique mentioned above. Corrected lateral tomograms were made for each joint, using the true measured horizontal angle and varying the vertical angle by +2, -2, +4 and -4 degrees from the actual vertical angle. Another set of tomograms was also made for each joint by cor- recting for the true measured vertical angle and var- ying the horizontal angle by +2, -2, +4 and -4 degrees, respectively. The produced tomograms were examined and evaluated for any changes in the relationship between the bony components of the TMJ and image clarity.

The age and sex distribution of the 1,143 patients included in the present study are summarized in Table 1. Over 80% of these cases were female patients and the rest were males. Age-range was 3 to 81 for male patients with a mean age of 31.5 years while the range for female patients was 7 to 80 years with a mean age of 30.7 years. The major- ity of the patients were in the age-range of 11 to 45 years. Variation of the right horizontal angle is shown in Figure 3 and ranges from -15 to 52 degrees. Majority of the patients showed a right horizontal angle in the range of 11 to 40 degrees with a mean right horizontal angle of 24.2 degrees. The right vertical angle [Fig. 4] ranged from -19 to 23 degrees with the majority of patients showing a range from -A to 10 degrees and with a mean of 3.3 degrees. The left horizontal angle [Fig. 5] ranged from -7 to over 53 degrees with most of the patients falling in the range of 11 to 40 degrees with a mean of 25.3 degrees. The distribution of the left vertical angle [Fig. 6] showed a range from -14 to 43 degrees with the majority of patient having a range from -4 to 10 degrees with a mean of 4.5 degrees.

Table 2 summarizes the statistical analysis of the variation of horizontal and vertical angles in this study.

As for the dry skull studies, Figure 7 shows a photograph of the skull from the frontal and lateral views. The anterior, medial and lateral aspects of the right condyle are shown in Figure 8, which clearly demonstrates the bony osteophyte on the anterior aspect of the right condyle. The right con- dylar angles of this dried skull measured 15 degrees horizontally and 5 degrees vertically. The cor- rected tomographic image of the right condyle made by varying the horizontal angle is shown in Figure 9, while that made by varying the vertical angle is shown in Figure 10. The corrected tomog- raphic image with the actual horizontal and vertical angles clearly reveals the osteophyte in its position. The position, size and angulation of this bony struc- ture were altered by changing either the horizontal or vertical angle by +2 or -2 degrees. Changing either the horizontal or vertical angles by +4 ox-A degrees resulted in a higher degree of superimpos- ition, and image distortion making it difficult to separate different structures. The photographic appearance of the left condyle of the dried skull is shown in Figure 11. The horizontal and vertical angles of the left condyle of the dried skull mea- sured 17 and 7 degrees, respectively. The tomog- raphic images of the left condyle made by varying the horizontal angle and vertical angle are shown in Figures 12 and 13, respectively. Both figures illus- trate the changes in the shape, size and density of the condyle by varying either the horizontal or ver- tical angle. They also show the obvious change in the density, size and shape of the fossa and emi- nence. The horizontal condylar angles for the dried skull were measured on the SMV image and the vertical angles were measured on antero-posterior tomographic views that were made for the patients.

Variation of the horizontal and vertical condylar angles was studied on 1,560 skulls of the Terry Col- lection by Yale and associates in 1966. These authors reported that the horizontal angle in most of the skulls studied (99% ranged between 0 to 33 degrees. The vertical condylar angle in their study ranged between -45 to +35 degrees with a mean vertical condylar angle of +5 degrees. They also reported that in 48.1% of the mandibles studied, there was symmetry in the horizontal angle, while in 51.8% there was symmetry in the vertical angle. The symmetry in both horizontal and vertical con- dylar angles occurred in only 26% of the case.¹⁸

Our results, which showed a wide range in the horizontal and vertical condylar angles, are consis- tent with Yale and associates findings.¹⁸ These results support the need to measure the horizontal and vertical angles individually for each joint prior to the tomographic examination of the TMJ. This measurement becomes of great importance in pro- ducing tomographic images which are free of dis- tortion of the condylar image. The concept of a standard 20 degrees horizontal rotation of the head before tomographic examination of the TMJ was proposed and adapted by some investigators.⁴¹⁹ However, others, like Lundberg and Walander,²⁰ Eckerdal,¹⁶ Eckerdal and Lunberg,²¹ reported that a small difference of 5° in the horizontal condylar angle correction between two radiographs of the same joint can lead to marked changes in the image of the anatomic structures and might lead to a risk of erroneous interpretation of the joint relation- ships. On the other hand, Danforth and co-work- ers in 1991 reported that there was no difference between the standard 20° positioning and the actual condylar horizontal angle as measured on the patient's SMV radiograph.²² Our results derived from the tomographic images of the dried skull clearly showed that a slight variation of +2 or -2 degrees in either the horizontal or vertical con- dylar angles resulted in alteration in the anatomic relationships as well as distortion of the image clarity.

Based on the findings in the present investigation, we can conclude that compensation for individually measured horizontal and vertical condylar angles is essential for the production of high quality diagnostic tomographic images of the TMJ.

The authors wish to express their grateful thanks to Ms. Cora L. Alano for typing the manuscript and to Ms. Jane M. Sembrano for the computer graphics.