[Effect of experimentally induced trauma to the incisors in rats]

The purpose of this study was to produce developmental lesions of enamel in rats by a quick and simple method and to examine the enamel hypoplasia caused by trauma. 4-day-old and 3-week-old Wistar rats were used. Trauma was produced by needle pricking and hitting on the mandibula. After one week incisors were removed together with jaws and prepared for microradiography, X-ray diffraction, light microscope and transmission electron microscope examination. Microradiographic findings in the needle pricking group revealed hypocalcified and hypoplastic enamel. The incidence was 73.7%. In the hitting group of 4-day-old rats the incidence was lower, 70.0%. Microradiographic findings in this group were diffuse hypoplasia in the surface enamel. Hitting of 3-week-old rats produced no enamel hypoplasia. Crystallinity of hypoplastic enamel was reduced in both a-axis and c-axis direction. Histological findings in 4-day-old rats revealed disarranged and detached ameloblasts at location trauma. These results indicate that a needle pricking method involving secretory stage ameloblasts of 4-day-old rat incisors can induce a considerable amount of enamel hypoplasia.