Measurement of the force needed to restrain eruptive movement of the rat mandibular incisor

This study describes the precise determination of the extrusive force in the rat mandibular incisor measured for a relatively longer period of time under artificial respiration with halothane anaesthesia. Following restraint of the eruptive movement of the incisor for a period of 20 h, the pushing force increased gradually and was maintained as an extremely gentle slope toward the end of the experimental period. The maximum pushing forces were estimated to be 9.1 ± 2.5 (SD) mN in impeded incisors and 9.8 ± 2.3 mN in unimpeded incisors. When force was converted to pressure, values were 30 ± 8 (SD) mmHg and 32 ± 8 mmHg, respectively; the difference was not significant. The maximum pushing force decreased rapidly—almost in parallel—with the fall of systemic arterial blood pressure after death of the animals; the amounts of reduction were 7.2 ± 1.8 mN (24±6 mmHg) in impeded incisors and 7.0 ± 2.0 mN (23 ± 7 mmHg) in unimpeded incisors. Residual pushing forces were 1.7 ± 1.0 mN (5.6 ± 3.3 mmHg) in impeded incisors and 2.5 ± 0.6 mN (8.2 ± 2.0 mmHg) in unimpeded incisors; the difference was significant (p < 0.05). These results suggest that, under these experimental conditions, the pushing force of the rat incisor originates primarily from localized blood pressure within the incisor socket and, in part, from tissue growth.