[A method of measuring eruptive movement of the rat incisor using a non-contacting displacement detector]

The axial movements of rat incisors were recorded continuously for over 20 hr. The rats were anesthetized with halothane delivered by intratracheal intubation using an artificial respirator. A hemostatic clamp was used to immobilize the jaw. The displacement detector that detects changes in the electric eddy current exhibited high resolution, good linearity and low drift. The average eruption rates of the rat incisor were estimated to be 406 and 516 microns/ 24 hr at 34 and 37 degrees C of the rectal temperature, respectively. The values were within the normal range. We also measured the force needed to restrain eruptive movement of the rat incisor using the same apparatus combined with a load cell. The maximum pushing force was estimated to be 9 mN or 29 mmHg (converted value) on average. Then the effects of adrenaline on axial movement of the incisor and arterial blood pressure were examined. Adrenaline caused a rapid extrusive tooth movement with a nearly simultaneous increase in the blood pressure, followed by a marked intrusive tooth movement and a decrease in blood pressure. These results support the view that the systemic arterial blood pressure and vasculature in the tooth socket play important roles to determine the position of teeth. We assume that our method would be useful to clarify the precise relationship between tooth displacement and vascular change in the tooth socket.