Abstract
The effect of experimental injuries to the lower incisors and their investing tissues was studied in 22 rats of 21-450 days of age and over a period of from 31 to 158 days. The experimental animals were selected at random from the normal rats of 4 different colonies and over a period of more than 2 years in order to avoid the possibility of using a susceptible strain. Litter-mate controls of 17 experimental animals were studied in addition to 63 normal animals obtained from similar sources.
The rate of eruption was measured and weekly records of the gross appearance of the teeth and jaws were kept throughout the duration of the experiments. A radiographic, anatomic and histologic study was made of the teeth after death. The experimental injuries were in the nature of fracturing of one or 2 lower incisors and their investing tissues. In some cases, one lower incisor and its investing tissues were fractured while the enamel epithelium of the other lower incisor was injured with a fine needle. In no case were the upper incisors injured.
The control animals showed a normal rate of eruption and a normal radiographic and histologic picture of the dental tissues. Those of the experimental animals that were studied preceding the injuries showed a normal rate of eruption and a normal appearance of the teeth.
In 85% of the experimental animals, the result of the injuries were: (a) Considerable retardation in eruption and (b) more or less severe histo-pathologic changes in the dental tissues, particularly the enamel and the enamel epithelium, in the injured teeth and in varying degrees in the uninjured teeth as well.
The changes were progressive and more or less permanent. In some cases they appeared within a week following the operations.
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