Comparison of 'normal' TMJ-function in Class I, II, and III individuals

Fifty-seven non-orthodontically treated young adults, judged as either clinically healthy or with only mild symptoms of TMJ-dysfunction, were divided into groups according to their sagittal molar relationship (Class I-, Class II-, and Class III-group). All underwent a standardized clinical and axiographic examination with an axiographic recording device (SAS-SYSTEM). The comparison of the lengths of the axiographical protrusive curves showed significantly higher values in the Class II group than in the Class I (P less than 0.01) and in the Class I group than in the Class III group (P less than 0.001). Analogous differences could be found in clinical protrusive measurements at the incisal point and in lateral excursions. It was concluded that the protrusive condylar movement capacity coincides with the dental sagittal relationship. In opening, significant differences were seen axiographically (Class I v. Class III: P less than 0.001; Class II v. Class III: P less than 0.01), but not clinically. Since axiographic measurements show only condyle translation, but not rotation in contrast to measurements at the incisal point, it can be concluded that the differences in opening are also translatory and not rotational. Measurements of the average change of curvature of axiographic tracings showed significantly less curved protrusive tracings in Class III than in Class I (P less than 0.001) and Class II individuals (P less than 0.01), supporting the concept that in the Class III group condyle movement is restricted to the straight posterior slope of the tubercle.(ABSTRACT TRUNCATED AT 250 WORDS)