M. L. Siers, W. L. Willemsen & K. Gulabivala
Department of Cariology and Endodontology, Faculty of Dental Science, University of Nijmegen, Nijmegen, the Netherlands.
Department of Conservative Dentistry, Eastman Dental Institute for Oral Health Care Sciences, University of London, London, UK.

Introduction.
Autotransplantation is a valid treatment option to replace missing teeth (Ahlberg et al . 1983, Paulsen et al . 1995). Careful manipulation of the root and socket under favourable preoperative, surgical and postoperative conditions ensures survival of the cells of the periodontal ligament and promotes the reformation of a normal supporting apparatus. However root resorption can be a major complication that can be exacerbated by pulp necrosis and infection.
The occurrence of pulp necrosis is influenced by a number of factors, including most crucially the maturity of the roots at the time of transplantation. As far as the pulp is concerned, revascularization is more likely in teeth with open apices than in those with closed apices (Andreasen et al . 1970, Altonen et al . 1978, Andreasen 1986), where an 85% chance of pulp necrosis is reported (Andreasen et al . 1990). On this basis, some clinicians have adopted a clinical protocol that indicates routine root canal treatment for transplanted teeth with mature root apices (Lownie et al . 1986). On the other hand, some clinicians may adopt a more conservative policy preferring to wait and see even in cases involving transplanted teeth with mature roots. But as yet this practice remains unsupported by the published literature.
This paper describes a case of pulp revascularization after transplantation of a tooth with closed apices and aims to initiate a discussion on the value of a conservative approach for the management of transplanted teeth.

Report.
An 18-year-old female patient was referred to an endodontist by an oral surgeon for root canal treatment of tooth 38, which had been transplanted to the site of tooth 16, that had been lost as a result of trauma. Figure 1 shows the radiographic appearance immediately after transplantation. It was not until 5 months after transplantation and referral that the patient made an appearance at the endodontist; she reported no problems. The intraoral investigation showed a sound transplanted tooth with no discolouration and painless on percussion. It did not react to electric pulp testing or cold. The probing depths around the tooth were in the range of 2–3 mm, whereas on the mesial aspect of the tooth it was 4 mm, but without bleeding on probing. The bone levels were similar to that of the neighbouring teeth with no pathological radiolucencies discernible. Figure 2 shows the tooth 5 months after transplantation. No record of root maturity was available, but radiographically when seen by the endodontist they appeard (nearly) closed. In view of the period since transplantation and the absence of pathological signs, it was decided to reschedule the patient for follow-up after 6 months, before considering root canal treatment.

Figure 1. Situation immediately after transplanting the 38 to the position of the 16. Radiograph by oral surgeon.





Figure 2. Situation 5 months after autotransplantation. First visit of patient to endodontist.





Figure 3. Second visit: situation 14 months after autotransplantation. Partial obliteration of the pulp space is visible.





Figure 4. Third visit: situation 26 months after autotransplantation. Almost total obliteration of the pulp space is visible.

However, it was 9 months before the patient reported again. There were no symptoms and no clinical changes were observed; the tooth still gave no response to sensitivity tests. The radiographic appearance at this time (Fig. 3), 14 months after transplantation, showed no pathological bone changes and no evidence of root resorption. However, the pulp space of the transplanted tooth showed partial obliteration. Since this may be considered a sign of vital pulp tissue, and since there were no pathological conditions present, the patient was given another follow-up appointment 1 year later.
Twenty-six months after transplantation no pathological signs were detected clinically or radiographically. The pulp space at this time was completely obliterated, without a widening of the periodontal ligament space. The accompanying radiograph is shown in Fig. 4. Thus, 26 months after transplantation, the transplanted tooth 38 functioned without discernible problems or discomfort.

Discussion.
Revascularization is a process in which ingrowth of highly vascularized connective tissue occurs into the pulp space; or in which blood vessels already present in the pulp of the transplanted tooth anastomose with blood vessels from the periodontium (Skoglund et al . 1978, Skoglund & Tronstad 1981). Relationships have been shown between the occurrence of pulp revascularization and the level of tooth development, the surgical procedure, the extra-alveolar time period, the type of tooth and the level of oral hygiene (Andreasen 1986, Andreasen et al . 1990). Teeth that still have open apices have a high chance of revascularization and the possibility for further root development (Andreasen & Pedersen 1985). In the presented case, hard tissue was deposited in the original pulpal cavity. This tissue could histologically turn out to be tissue resembling bone or cementum in combination with a necrotic pulp. However, as an alternative, the original pulp tissue could have survived the operation (Skoglund & Tronstad 1981), and the pulp space obliterated with dentine. This process can be accelerated by trauma, such as transplantation (Andreasen et al . 1987). Though not fully understood, the accelerated deposition of hard tissue in the pulp space is explained as an uncontrolled cellular response to a trauma through which the blood supply to the pulpal tissues has been diminished (Biesterfeld et al . 1979). One explanation for the obliteration of the pulp space in an apparently mature, transplanted tooth could be that the radiographic appearance of mature root apices was in fact false. Since only the mesiodistal width of the root canal can be judged radiographically apices may seem closed, when they are open bucco-palatally facilitating the occurrence of pulp revascularization (Duell 1973). Secondly, the atraumatily and sterile surgical procedure, during which the extra-alveolar time was reduced to a minimum, may have helped to limit the chance for infection of the transplant and the surrounding tissues (Andreasen et al . 1970, Altonen et al . 1978, Kahnberg 1987). Furthermore, if the apices were actually closed, pulp revascularization might have been the result of so-called ‘transient apical breakdown’ (Andreasen 1986).
Elective root canal treatment has been proposed for transplanted teeth with closed apices (Lownie et al . 1986). Justification for this treatment is the low proportion of pulps that actually revascularize, and the high incidence of inflammatory resorption of the root. It is also justified when the pulp space is obliterated, which would make root canal treatment difficult or impossible in the event of pulp necrosis. However, it has been shown that teeth with obliterated pulp space do not become necrotic more often than those without pulp obliterations (Robertson et al . 1996). Further, if such a pulp did eventually become necrotic, root canal treatment may still be possible since the root canal has to be accessible in order to become infected with bacteria (Cvek et al . 1982).
An alternative to elective root canal treatment immediately after transplantation of teeth, even for apparently closed apices, may be to strictly monitor the patient for signs of pulpal revascularization or periradicular disease. This regime involves inspection for discolouration, sensitivity tests, tenderness on percussion, signs of inflammation, periradicular pathology and root resorption. The appointments for these assessments should be scheduled 1 week, 3 weeks, 6 weeks, 3 months, 6 months and 1 year after transplantation (Andreasen et al . 1987). This schedule is also proposed for the follow-up of avulsed teeth, which are similarly at risk for developing pulpal pathology and consequent periradicular disease (Andreasen et al . 1990). If during one of these follow-up inspections pathological signs are present, root canal treatment should commence. It is important to note that the lack of reaction to sensitivity tests alone does not mean that pulpal necrosis has occurred (Andreasen 1989). Lack of reaction to sensitivity tests at a certain inspection can be followed by a reaction the next. The possibility also exists that sensitivity does not recur after a trauma, but vitality does, as can be deduced from radiographs on which the root develops as normal without any pathological signs.
The decision not to start root canal treatment in this case was a relatively easy one, since at presentation, 5 months had already passed following the transplantation. At that time, no signs of pathology were present and the transplanted tooth has functioned without any problems or signs for 26 months. This represents a good prognosis for retaining the tooth, since most cases of pulp necrosis develop within 2 years (Andreasen & Pedersen 1985).

References.

Ahlberg K, Bystedt H, Eliasson S, Odenrick L (1983) Long-term evaluation of autotransplanted maxillary canines with completed root formation. Acta Odontologica Scandinavia 41 , 23-31.
Andreasen FM, Pedersen BV (1985) Prognosis of luxated permanent teeth - the development of pulp necrosis. Endodontics and Dental Traumatology 1 , 207-20.
Andreasen FM (1986) Transient apical breakdown and its relation to color and sensibility changes after luxation injuries to teeth. Endodontics and Dental Traumatology 2 , 9-19.
Andreasen FM (1989) Pulpal healing after luxation injuries and root fracture in the permanent dentition. Endodontics and Dental Traumatology 5 , 111-31.
Andreasen FM, Zhijie Y, Thomsen BL, Andersen PK (1987) Occurrence of pulp canal obliteration after luxation injuries to teeth. Endodontics and Dental Traumatology 3 , 103-15.
Andreasen JO, Hj?rting-Hansen E, Jolst O (1970) A clinical and radiographic study of 76 autotransplanted third molars. Scandinavian Journal of Dental Research 78 , 512-23.
Andreasen JO, Paulsen HU, Yu Z, Bayer T, Schwartz O (1990) A long-term study of 370 autotransplanted premolars. Part II. Tooth survival and pulp healing subsequent to transplantation. European Journal of Orthodontics 12 , 14-24.
Altonen M, Haavikko K, Malmstrom M (1978) Evaluation of autotransplantations of completely developed maxillary canines. International Journal of Oral Surgery . 7 , 434-41.
Biesterfeld RC, Taintor JF, Marsh CL (1979) The significance of alterations of pulpal respiration. Journal of Oral Pathology 8 , 29-39.
Cvek M, Granath L, Lundberg M (1982) Failures and healing in endodontically treated non-vital anterior teeth with posttraumatically reduced pulpal lumen. Acta Odontologica Scandinavia 40 , 223-8.
Duell RC (1973) Conservative endodontic treatment of the open apex in three dimensions. Dental Clinics of North America 17 , 125-34.
Lownie JF, Cleaton-Jones PE, Fatti P, Lownie MA (1986) Autotransplantation of maxillary canine teeth. International Journal of Oral and Maxillofacial Surgery 15 , 282-7.
Kahnberg KE (1987) Autotransplantation of teeth. (I) Indications for transplantation with a follow-up of 51 cases. International Journal of Oral and Maxillofacial Surgery 16 , 577-85.
Paulsen HU, Andreasen JO, Schwartz O (1995) Pulp and periodontal healing, root development and root resorption subsequent to transplantation and orthodontic rotation: a long term study of autotransplanted premolars. American Journal of Orthodontics and Dentofacial Orthopedy 108 , 630-40.
Robertson A, Andreasen FM, Bergenholtz G, Andreasen JO, Noren JG (1996) Incidence of pulp necrosis subsequent to pulp canal obliteration from trauma of permanent incisors. Journal of Endodontics 22 , 557-60.
Skoglund A, Tronstad L, Wallenius K (1978) A microangiographic study of vascular changes in replanted and autotransplanted teeth. Oral Surgery, Oral Medicine and Oral Pathology 45 , 17-28.
Skoglund A, Tronstad L (1981) Pulpal changes in replanted and autotransplanted immature teeth of dogs. Journal of Endodontics 7 , 309-16.