The effect of mechanical trauma on the tooth germ of rat molars at variousdevelopmental stages: a histopathological study

Intrusive trauma was experimentally applied to the tooth germ at different developmental stages in the rat first molar. The tooth germ at the earliest (postnatal day 1, initiating stage of enamel matrix formation) and the lat est (postnatal day 10, calcifying stage of preformed enamel matrix) develop mental stages studied showed localized enamel hypoplasia as a direct sequel a of trauma. The tooth germs in which enamel matrix was rapidly thickening (postnatal days 3, 5, 7) and had not yet started to calcify showed the most intense and extensive injuries to the formation and structural organizatio n ob both enamel and dentin. As for indirect effects secondary to trauma, t ooth germ dislocation was observed chiefly in tooth germs at the same devel opmental stages, frequently resulting in ankylosis. The present experimenta l model may be helpful for clarifying the histogenesis of traumatic changes in the developing tooth germ.