[Studies on the standardization of parameters for jaw movement analysis--6 degree-of-freedom jaw movements analysis].

Purpose: To establish standardized evaluating methods for jaw movements analysis. In this paper, we investigated evaluating parameters for 6 degree-of-freedom jaw movements data.

Methods: Recorded data of jaw border movements from 20 male adults were employed as basic samples. The main parameters were as follows: 1. The displacement of an intercondylar midpoint: the length of a straight line between 2 positions of this point, the intercuspal position and other jaw position. 2. The angle of intercondylar axes: the angle between 2 position of the intercondylar axis, the intercuspal position and other jaw position. 3. The angle of incisal-condylar planes: the angle between 2 position of the plane, the intercuspal position and other jaw position (this plane was defined with the incisal point and condylar points of both sides 4. The mandibular motion range index: quantitative values calculated with 2 of 3 parameters described above.

Results: The mandibular motion range index showed a close correlation with respective projected areas of the incisal paths, with the projected area of sagittal border movements on the sagittal plane r = 0.82 (p < 0.001), with the projected area of lateral border movements on the frontal plane: left lateral border movements r = 0.92 (p < 0.001), right lateral border movements r = 0.84 (p < 0.001), Spearman rank correlation.

Conclusion: New parameters were based on 6-degree-of-freedom jaw movements data and relative relationship between the intercuspal position and other jaw position. They were independent of reference coordinate systems and could measure jaw movement quantitatively.