Relationship between condylar and incisor point displacement during habitual maximum open-close movements

The relationship between condylar movements and incisor point movements during habitual maximum open-close movements were studied in 10 healthy male and 10 healthy female subjects. Jaw movements were recorded by means of an opto-electronic jaw movement recording system, OKAS-3D, capable of recording the six degrees of freedom at a sample frequency of 300 Hz. The lower jaw position of the lateral pole of the condyles was found by means of palpation. In order to analyse the movements, the opening and closing path of the incisor point were divided into ten equal intervals and the corresponding condylar displacement in each interval was calculated. A displacement index was obtained by normalizing the condylar displacement with respect to the maximum condylar displacement. Due to the normalization, the displacement index is not sensitive to possible errors in the location of the lateral condylar point. A clear condylar displacement was already recorded in the first movement interval, right at the start of opening (average displacement index in the first opening interval was significantly greater than zero, P < 0.0005). The condylar displacements in the start and the end interval of opening and closing were smaller than in the intermediate movement intervals (P < 0.00005).