Role of circulatory system in the process of the rat incisor eruption

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1. A method was established with which the force generated by the erupting rat mandibular incisor could be measured when the tooth is placed in isometric condition under artificial respiration with halothane anaesthesia. This method also enables us to measure the displacement of the tooth under isotonic forces.2. The maximum pushing forces measured by the erupting incisor were 9.1(]SY.+-。[)2.5 mN in impeded teeth and 9.8(]SY.+-。[)2.3 mN in unimpede teeth when the teeth were placed in isometric condition for 20 hours.3. The forces generated by the incisor after death of the animals were measured under isometric condition. The retractive forces were 3.7(]SY.+-。[)1.3 mN in impeded teeth and 3.0(]SY.+-。[)1.2 mN in unimpeded teeth. These results suggest that the main eruptive force of the rat incisor was produced by the pressure of the vasculature in the pulp and/or periodontal tissues which will be antagonized by the retractive forces generated by the colloid osmotic pressure of the serum and recoil of the ligament.4. The incisor showed biphasic displacements following the application of isotonic intrusive or extrusive forces, i.e.the tooth shhowed an initial rapid displacement followed by a continuous slow movement by the force of either direction.5. Significant correlations were found between the magnitudes of the forces applied to the inicisor and the rates of the tooth displacement.6. Eruptive forces of the incisor were estimated as the forces needed to stop the eruptive movement from the formulae of the regression lines. They were 5.6(]SY.+-。[)1.1 mN in impeded teeth and 3.0(]SY.+-。[)0.6 mN in unimpeded teeth when intrusive forces were applied, and 7.5(]SY.+-。[)4.4 mN in impeded teeth and 4.2(]SY.+-。[)1.7 mN in unimpered teeth when extrusive forces were applied. These results suggest that eruptive force of the rat mandibular incisor ranges from 3 to 8 mN.