Tooth autotransplantation part 3: surgical planning and technique

Crown assessment

Donor tooth assessment is usually considered in terms of assessment of the crown and roots. A donor tooth crown should be assessed for dental caries, crown anomalies and crown dimension. One of the main considerations, when assessing the recipient site, is whether adequate space exists for the donor tooth. It is therefore essential that the donor tooth size is measured accurately at maximum bulbosity including the maximum bulbosity and cervical dimension of the crown. The mesio-distal widths of upper and lower premolars are usually only 1.5 mm smaller than that of upper central incisors (7 mm compared to 8.5 mm at maximum bulbosity), although the cervical areas are usually considerably smaller. To manage this discrepancy it has been suggested that rotating the donor premolar tooth approximately 90 degrees improves the emergence profile when transplanted into the upper central incisor region (Figure 1).

Root assessment

Donor tooth roots are assessed with regards to number of roots, stage of formation, morphology and dimensions in order to inform recipient site preparation. Single-rooted donor teeth with a single root canal system, such as mandibular second premolars, canines and incisors, are commonly the preferred choice due to their single root morphology and high frequency of single canal (85%) and single foramen (97.5%). The mandibular first premolars similarly have a single root morphology but the frequency of a single canal is lower (73%) and the likelihood of a single canal dividing into two apical foramens is higher (25%) than the mandibular second premolar. Maxillary second premolars are less commonly used as only 40% of cases demonstrate a single root with single root morphology canal system.¹

Immature teeth are associated with better long-term success than mature teeth and present fewer restrictions in terms of bone height and tooth positioning. The ideal time for transplantation is when root formation is approximately 75% with an apical opening of at least 1 mm to encourage revascularization of the root canal bundle.² In these teeth, the risk of transplant failure and subsequent extraction was reported to be 70% less than those teeth with closed apices.³

For teeth with complete root formation, careful selection is required as the root length can introduce height restrictions for positioning the donor tooth within the recipient bone. The average root length of premolars and canines is 13–16 mm. Such average root lengths provide an indication of the bone height required at the recipient site.

Radiographic assessment

Two-dimensional radiographs, such as long-cone periapicals and orthopantograms (OPTs), are usually sufficient for assessing donor tooth morphology and stage of root development (Figure 2). The use of cone-beam computed tomography (CBCT) is gaining popularity for pre-surgical assessment and can aid planning for potential donor teeth with unclear root morphology.

Clinical assessment

The recipient site should be carefully examined to assess bone volume, soft tissue morphology and the proximity of adjacent structures. Bone volume is assessed clinically by palpation of the alveolar ridge in order to identify bony deficits and soft tissue morphology, supplemented with appropriate radiographs (Figure 3). In a growing child, the alveolar bone is vulnerable to atrophy following tooth loss. To avoid alveolar bone loss in the recipient site, attempts should be made to maintain teeth in the recipient site, even if the prognosis of the tooth is poor. Teeth remaining in the recipient site should be monitored regularly for infraocclusion, which may cause a localized obstruction to vertical bone growth in the region leading to severe bony defects.

Coronal space is required between the teeth adjacent to the recipient site to enable placement of the donor tooth. Space requirements can be estimated by measuring the crown of the donor tooth. The space available in the recipient site should be measured at the gingival and incisal level. If the donor tooth is to be restored prior to definitive orthodontic treatment, sufficient space is also required for the restorative camouflage. In cases with single tooth transplantation, this can be estimated by measuring the contralateral tooth. In cases where a contralateral tooth is not available, the ideal coronal dimensions can be estimated from adjacent teeth using average relative proportions.⁴

The occlusion should be checked in static and dynamic function prior to or during surgery. This ensures that there is sufficient occlusal clearance to allow the transplant to be placed with minimal occlusal interferences. The transplant can be protected by the use of a removable appliance with posterior buccal capping if it is not possible to remove occlusal interferences prior to or during surgery.

Radiographic assessment

Radiographic assessment is crucial for assessing bone volume, the health of the teeth at the recipient site and proximity of adjacent structures. This assessment usually involves conventional radiographs (Figures 2 and 3) supplemented with 3-dimensional imaging, where further details are required. Radicular infection, infection-related resorption and any other pathology at the recipient site must be diagnosed and appropriately managed in order to optimize bone quality. The proximity of adjacent structures, such as adjacent tooth roots, the maxillary sinus and mental nerve, will impact on treatment planning.

1. Extraction of the donor tooth

Extraction of the donor teeth using only coronal force application is performed to ensure minimal trauma to the root, and prevent damage to the periodontal ligament and cementum. Traumatic extraction with significant damage to the periodontal ligament is less likely to recover and will result in the transplanted tooth becoming ankylosed. In cases where there is more than one tooth available for transplantation, donor tooth selection is made based on root morphology, stage of development and anticipated ease of extraction. Direct visual assessment can be used to determine the root shape following extraction. The preferred donor tooth is then repositioned back into its original socket to prevent damage to periodontal ligament cells while the socket is prepared in the recipient site.

2. Socket preparation

The steps required for socket preparation depend on the presence or absence of a tooth in the recipient site. Preparation of existing sockets is easier than creation of new ones in an edentulous alveolar ridge. Socket preparation for a recipient site with a poor prognosis tooth is shown in Figure 4.

3. Socket assessment

The socket is assessed during preparation to ensure that it is able to accommodate the donor tooth. Traditionally, this was achieved by transplantation of the donor tooth into the prepared socket. Several attempts are usually made before a suitable socket is created, which risks further damage to the periodontal ligament cells and increases the risk of future ankyloses.⁵ Consequently, different techniques have been proposed to aid assessment of socket height and width (Figure 5). These include pre-surgical radiographic measurements,² acrylic stents constructed using radiographic measurements,⁶ surgical metal stents constructed using average measurements of premolar teeth⁷ and construction of 3D tooth replicas using Cone-Beam Computerized Tomography (CBCT).⁸ Pre-fabricated surgical templates assist the surgical component of premolar transplantation by establishing and replicating the root dimensions of the donor premolar tooth. The correct template is used to assess the width and depth of the socket preparation prior to placement of the transplant in the recipient site.

4. Placement of the transplant

The transplanted tooth should ideally be seated a few millimetres from the occlusal plane to prevent occlusal trauma and damage to the periodontal ligaments. This has the additional advantage of allowing the tooth to erupt into a functional position with corresponding bone deposition. Transplants with complete root formation require root canal treatment, therefore coronal reduction could be performed at time of transplantation, if required. On the contrary, particular care should be taken with immature teeth, as revascularization is desirable and may be compromised by enamel reduction. If ideal positioning is not possible, occlusal reduction of immature teeth could be undertaken gradually to optimize pulp recovery. Positioning immature teeth in relation to the occlusal plane is less critical as these teeth have the potential to erupt, encouraging bone growth and improved gingival contour.

5. Transplant splinting

The transplanted tooth is splinted using a physiologic splint such as a titanium trauma splint (TTS) with the transplanted tooth splinted to at least one tooth on either side (Figure 4g). Sutures are reported for splinting teeth, particularly where no adjacent teeth are available for bonding a splint, but care must be taken to ensure that the sutures provide adequate stabilization of the transplanted tooth. The splint should be passive to prevent damage to periodontal cells and attached to the teeth with composite.

Post-operative instructions

Post-surgical instructions for autotransplant patients are given as follows:

Pulp and PDL management

Patients are reviewed, following the autotransplantation, after 7–10 days to assess recovery and healing. Clinical examination focuses on:

Interim restorative camouflage

At the review appointment, an interim temporary restoration can be provided to improve the appearance of the transplant if required. This has the advantage of improving aesthetics and normalizing the coronal morphology for positioning adjacent teeth; however, it may also obscure the transplant morphology during orthodontic tooth positioning and increase plaque stagnation. Firm transplants with healthy gingiva can be camouflaged using direct composite veneers.

Monitoring healing

Transplanted teeth are then followed up clinically and radiographically following the same guidelines for avulsed and replanted teeth. The initial follow-up appointment is after 7–10 days where splint removal and the interim composite camouflage restoration is placed. For transplants with closed apices, where revascularization is not expected, pulp extirpation is performed at this appointment. This is followed by an appointment 4 weeks post-transplantation for completion of endodontic treatment with definitive obturation. The transplant is then reviewed clinically and radiographically at 3 months, 6 months and 12 months.

Transplants are assessed in relation to:

Definitive restoration

Following completion of orthodontic treatment, a definitive restoration can be provided if required. Composite veneers are preferable to porcelain veneers as modification to address continued growth and gingival maturation is easier. Adjunctive treatments, such as gingival re-contouring and tooth bleaching, can be used to improve the aesthetic outcome (Figure 7).