The effect of altering jaw position on the transmission of vibration between the skull and teeth in humans

The forces that develop in the human temporomandibular joint during functio n have never been directly measured, yet many patients exhibit excessive lo calized wear and tear of the joint, suggesting that at times these forces e xceed tissue tolerance. The purpose here was to gain insight into vibration transmission between the cranium and mandible in healthy humans during var iations of jaw position. In 13 normal healthy adult men (age 25-40 years) w ith normal dentitions, vibration (around 400 Hz. sine wave) was applied to the skull vertex and changes in the intensity of the vibration signal were measured using several small linear accelerometers cemented to the buccal s urfaces of mandibular first molars and the labial surfaces of maxillary cen tral incisors. The jaw was opened. protruded and moved laterally by the ind ividual participant and vibration signal intensities were tested (lower fir st molar signal/upper incisor signal) for change at each mandibular positio n by ANOVA. The results showed the vibration signal changed significantly w ith opening and less so on protrusion and laterotrusion. The vibration sign al during opening could be categorized into three types: (1) signal increas ed continuously with increased opening; (2) signal increased, then reached a plateau during last third of opening; (3) signal increased, then decrease d when the individual moved from 40 mm to maximum opening. These findings s how that as the jaw moves laterally. and especially as it opens, the magnit ude of the vibration signal increases substantially compared with the near- closed position. (C) 2001 Published by Elsevier Science Ltd.