Dimeric link chain and instantaneous centers of rotation of the mandible.

Summary The primary aim of the study was to reveal whether the free opening movement of the mandible can be determined by only 2 rotational axes as suggested in recent literature. For this purpose, the free opening movement of the mandible was registered in 20 asymptomatic patients using an ultrasonic measuring system. Subsequently, the locations of the instantaneous centers of rotation (ICR) were determined directly from the raw data. In a second approach, the same data were used to construct a mandibular and maxillar rotational axis according to the dimeric link chain (DLC) concept. On the basis of the angular velocities around these 2 axes, the positions of the ICR were calculated in the sagittal–vertical plane. Calculating the ICR by the DLC method provides similar results to that of the conventional approaches. It can be concluded that the DLC method is a valid approach and that considering the planar mandibular movement as a movement with 2 degrees of freedom is justified.