We read with interest the article by Kandasamy et al in the October issue investigating the condylar position by magnetic resonance imaging after various bite position registrations, in an effort to evaluate the reliability and validity of 3 bite registrations (centric occlusion, centric relation, and Roth power centric relation) in relation to condylar position in the glenoid fossae. The findings question the accuracy and predictability of the bite registrations. Although we congratulate the authors for their effort, we have some objections about the selection of subject population.
All 19 subjects (ages 20-39 years) examined in the study had no TMD signs or symptoms, and no significant incidental pathology was found by MRI check. Thirty-three condyles (87%) were reported to be concentric in an anteroposterior plane, and all condyles were concentric in the transverse anatomic plane in centric occlusion. Since many investigators believe that there is a range for centric relation, it stands to reason that there were only small differences between the condylar positions of centric occlusion and centric relation in these healthy subjects. Accordingly, the change of condylar position caused by bite registrations (centric occlusion and Roth power centric relation) could be little. As showed in the Table, the means of the differences were 0.03 to 0.36 mm. Moreover, there are individual variations and normal ranges of asymmetry in the mandible and the glenoid fossa, and these should not be neglected because the differences are so small. Therefore, we think that authors should be very careful to try to detect any statistical significance in such a small range, especially when the sample size is not large.
More importantly, the practice of positioning condyles is clinically conducted in patients with abnormal condylar positions to alleviate or prevent TMD. Thus, it would have more clinical significance to use MRI to assess whether the condyles of these patients can be repositioned to centric relation by bite registration.