Rapidly progressing extracanal invasive resorption.

Frank and Bakland coined the term "Extracanal invasive resorption" (EIR) to identify a resorptive entity that has been variously classified. This external resorption originates in the cementum adjacent to the periodontal ligament. The lesion is believed to be a response to injury and irritation of the periodontal ligament, or to pressure from ectopic eruption, orthodontic pressure, intracoronal bleaching, periodontal treatment, or an unknown idiopathic cause.