This case study describes the diagnosis and treatment of a deciduous left maxillary canine tooth root that had been displaced into the pulp of the developing permanent left maxillary canine tooth in a 23-month-old female neutered Cavalier King Charles Spaniel. The patient was initially presented for bilateral persistent deciduous maxillary canine teeth extraction. Seventeen months later the permanent left maxillary canine tooth was found to be non-vital and tooth development had ceased prior to apical closure. Radiographs revealed a radio-opaque dentine-like structure and straight line centrally within the pulp of the permanent tooth. The displacement of the deciduous tooth into the developing permanent tooth was confirmed. This unusual potential complication should be considered when performing deciduous teeth extraction.