A Study of the Eruption Rate of the Rat Mandibular Incisor †‡

Several different theories have been advanced to explain the mechanism of tooth eruption. This has been defined by Massler and Schour' as the process whereby a developing tooth migrates from an intraosseous location in the jaw to its functional position within the oral cavity. They also evaluated each of these theories with regard to clinical and experimental observations. Substantial factual evidence for the support of any one of them is lacking, since this aspect of tooth development has been little investigated. However, much support has been given to a concept linking the vascularity of the pulpal and periodontal tissues with tooth eruption and theoretically suggesting that the local eruptive force results from osmotic pressure or tissue tension. Constant8 was the first to suggest a relationship between vascularity and eruption. He considered the blood pressure exerted in the vascular tissues at the base of a forming tooth as the active mechanical factor in eruption. Tomesn agreed that the blood pressure, by keeping up a state of general tension in the area, could drive a tooth in any direction. The rich vascular bed of the rat incisor was believed by Boyle' to be comparable in effect to a hydraulic chamber. Schour and Massler' concluded that the eruptive force was probably related to vascularity and tissue tension at the basal end of the tooth. Several investigators (Leist, Breitner and Leist,' King, ' and Edwards and Kitchin') by performing unilateral cervical sympathectomies in guinea pigs and rabbits induced temporary accelerations in eruption rates ;¶ and,