In vitro mechanics of the periodontal ligament in impeded and unimpeded rat mandibular incisors.

Load-deformation curves and/or the stress-strain curves were obtained by the mechanical testing of transverse sections of impeded and unimpeded rat incisors in vitro to evaluate more precisely the mechanical properties of the periodontal ligament. Perimeters of the lingual dentine and socket wall and the sectional area of the periodontal ligament were measured radiographically. An extension rate of 5 mm/min in an extrusive direction was used. The average maximum shear load, the elastic stiffness (tan beta) and the failure energy in shear in the impeded group were respectively 6.4, 6.0 and 5.7 times those in the unimpeded group. The average maximum deformation was similar. The average maximum shear stress, the elastic stiffness (tan alpha) and the failure strain energy density in the impeded group were respectively 7.2, 8.1 and 6.5 times those in the unimpeded group. The average maximum strain in the unimpeded group was significantly greater (1.4 times) than that in the impeded group. Mechanical responses of the periodontal ligament seem to be very sensitive to internal and external disturbance of the tooth: changes in such properties may be detectable even when other techniques fail to reveal differences. Our method provides a useful tool for such mechanical analysis.