Odontomas are hamartomatous lesions or malformations composed of mature enamel, dentin, and pulp. They may be compound or complex, depending on the extent of morphodifferentiation or their resemblance to normal teeth. The etiology of odontoma is unknown, although several theories have been proposed. This article describes a case of a large infected complex odontoma in the residual mandibular ridge, resulting in considerable mandibular expansion.