ICD-9-CM 521.6 is a billable medical code that can be used to indicate a diagnosis on a reimbursement claim, however, 521.6 should only be used for claims with a date of service on or before September 30, 2015. For claims with a date of service on or after October 1, 2015, use an equivalent ICD-10-CM code (or codes).
Solid fixation of a tooth resulting from fusion of the cementum and alveolar bone, with obliteration of the periodontal ligament. It is uncommon in the deciduous dentition and very rare in permanent teeth. (jablonski's dictionary of dentistry, 1992)