Odontogenic cyst induction by periapical infection in rats

The purpose of this study was to test the hypothesis that odontogenic cysts can be induced by periapical infection. Pulp extirpation and reaming beyond the root apices were performed in 53 lower first molars in 27 Sprague-Dawley rats. The cavities were left open to allow continuous contamination by oral bacteria. Animals were killed at 6 and more than 8 months after operation. Odontogenic cysts were found in association with 8/53 teeth in 6 animals. Histologically, cysts were observed around the lower incisors below the first molars. The cyst wall consisted of fibrous connective tissue with inflammation and was lined with keratinized squamous epithelium. The cyst cavity contained a mass of keratin and necrotic debris. These results support the hypothesis that inflammatory stimulation from the apices can cause cystic changes in the enamel epithelium of underlying teeth.