S. KOHNO*, Y. ARAI (Niigata University, School of Dentistry, Dept. of Removable Prosthodontics, Japan.)
Mandibular movements are guided mainly by three determinant factors, namely the temporomandibular joints (TMJ), the contact of the teeth, and the masticatory muscles. The path of the condylar movement in the TMJ is called posterior guidance of the mandibular movement, while the path of the contact translation of the teeth is called anterior guidance. Reconstruction of the natural dentition should make compatible a patient's anterior and posterior guidances so as to ensure harmonious function. For the anterior guidance we should consider two factors; the inclination of the path of anterior guidance (kinesiological Factor) and the tooth position of anterior guidance (positional factor). The objective of this article is to discuss the relationship between condylar and incisal angles in an effort to develop criteria of guidance in clinical practice.
* Method: With a computer-based system, jaw movements tracked by incisal and condylar reference points were registered simultaneous with EMG activity during protrusive and laterotrusive movements and parafunctional tasks (mandibular grinding movements and various tooth clenching efforts) and analyzed quantitatively.
*Kinesiological Factor. From the results of this kinesiologic analysis of the jaw movements, the inclination of the incisal path - which is transferred to the incisal table of an articulator as anterior guidance - should be equal to the inclination of each patient's condylar path. It is of course possible to make the incisal path steeper than the condylar path up to 25 degrees, but the incisal path should not be much flatter than the condylar path.
*Positional Factor. The results indicate that by shifting posteriorly the location of anterior guidance teeth, the range of working condyle movements considerably expanded infra-laterally during lateral grinding tasks. It can be a risk factor of TMJ disorders.