Mandibular instantaneous centers of rotation in patients with and without temporomandibular dysfunction.

PATIENTS AND METHODS: The free opening movement of the mandible was examined in 30 patients with and without dysfunctions, using the CADIAX electronic axiography system. All patients in the diseased group showed dysfunctions in the left temporomandibular joint. Half of the 20 asymptomatic patients were skeletal Class II, the other half skeletal Class III. Based on the data collected for the left temporomandibular joint, the movement of the mandible during the mouth-opening movement in the sagittal and vertical planes was described as the pathway over time of the various instantaneous centers of rotation (ICR), using physico-biomechanical factors. RESULTS AND CONCLUSION: It emerged that the ICR path in the patients with dysfunctions was irregular with erratic changes of direction. A harmonious ICR path beginning near the condyle was typical of the healthy group; as the mouth opened, the path moved toward downward backward and finally shifted toward forward and forward upward. Therefore, such an ICR path pattern can be used as an indicator in detecting dysfunctions.

In vitro study on the fatigue limit of single-lap joints.

Lasting adhesion between attachment and tooth is an essential prerequisite for all adhesive techniques in dentistry. However, the maximum static fatigue load is only one material-related parameter for the quality of this adhesion. Another parameter is the dynamic loading capacity of a bonded joint, which was determined in the present study for Dual adhesive resin by means of fatigue testing. This revealed a significant correlation between the recorded static and dynamic fatigue load and the gap width, which varied between 0.01 mm, 0.15 mm and 0.5 mm in the experimental setup. At 18.8 MPa, the median gap width of 0.15 mm yielded the highest static resistance, with a dynamic resistance 15% below this figure. Both the smaller and the larger gap showed significantly lower static fracture strengths (0.01 mm: 13.6 MPa; 0.5 mm: 13.7 MPa), whereas a dynamic load on the 0.01 mm bond, in contrast to the 0.5 mm bond, led to only a 5% reduction in bonding strength.

The helical axis of the mandible during the opening and closing movement of the mouth.

BACKGROUND: The movement of a rigid body through space may be comprehensively described by constructing a "finite helical axis" (FHA). The rigid body carries out a rotation around this axis for discrete periods of time while at the same time moving along this axis. MATERIAL AND METHODS: The free opening and closing movement of the mouth was registered in eight asymptomatic test persons, using the CADIAX electronic axiography system (GAMMA-DENTAL, Klosterneuburg, Austria). Subsequently, the position of the FHA in space, the angle of rotation around this axis, and the amount of translation along the FHA were determined for each subject, using the coordinates of the measuring styluses. RESULTS: During the initial phase of the mouth-opening movement, the FHAs were near the condyle. Over the course of the opening movement, they moved toward downward backward, downward and downward forward, and finally to forward upward toward the condyle upon reaching maximum mouth opening. During the closing movement, the FHAs shifted back in the reverse direction. During both the opening and the closing movement, there was a slight translational movement along the FHAs, which provided an indication of mandibular deviation.