Premolar autotransplantation in orthodontic treatment : a clinical and radiographic long-term study

Premolar aplasia and avulsed or malformed anterior teeth are common in young people. Using autotransplantation, it is possible to move problems in the dental arches to regions where they are more easy to solve orthodontically. In a long-term study, 370 premolars were evaluated by a standardised technique for monitoring pulp and periodontal healing, root development and root resorption subsequent to transplantation and orthodontic rotation. It was realised that the stage of root development at the time of grafting was the most important single factor determining successful healing. Transplantation of premolars with three quarters root formation or full root formation with wide-open apical foramina provides the best prognosis for long-term survival. Furthermore, evaluation of 118 premolars by radiographic assessment and evaluation of pulp canal obliteration showed evidence of pulp healing earlier than electrometric pulp testing. Orthodontic rotation resulted in slight surface root resorption and a significantly shorter root. It was suggested that the occurrence of pulp necrosis subsequent to orthodontic rotation is due to damage to eccentrically located apical blood vessels, especially in the late stages of pulp canal obliteration. It was further suggested that rotation should be postponed until after pulp and periodontal healing has taken place but before pulp canal obliteration, i.e. 3-9 months after transplantation. A new colour-coding technique was developed, making it possible to visualise changes that take place after premolar transplantation. Radiographs from the same sequence were digitised and then transformed into monochromatic images: red, blue and green. To combine the information in three monochromatic images into one polychromatic image, the colour-coding method offers the possibility of identifying radiographic changes that take place over time, such as bone healing, modelling and remodelling, and root development. The method was applied to 14 autotransplanted premolars and controls in a comparison study of tooth eruption and root development. The eruption speed of transplants and controls in relation to the first molar was found to be similar in the long term. However, the initial eruption of transplants seemed to be faster. Eruption of transplants does not seem to be related to root growth.