Tooth autotransplantation part 4: Alternative treatment options

Decoronation

Decoronation is a popular method for preventing bone defects associated with infraocclusion that occurs secondary to ankylosis in growing patients. It is most commonly used for growing children who have undergone severe dental trauma in the anterior maxilla region. Decoronation involves a coronectomy to remove the crown of the ankylosed tooth. This needs to be extended below the level of the cemento-enamel junction and 1 mm under the crestal bone margin. Previous endodontic materials are removed through instrumentation of the pulp canal and saline is used for thorough irrigation. The aim is to induce bleeding and clot formation in the canal, providing cells for replacement resorption.⁵ The root of the ankylosed tooth is left in the bone with primary closure of the mucosa to encourage soft tissue healing and bone apposition.⁶ Replacement resorption of the root is expected to continue but with simultaneous bone deposition, resulting in minimal loss of alveolar bone. Reorganization of the transeptal fibres encourages bone growth in line with vertical alveolar development of adjacent teeth. Placing an interim removable or fixed tooth replacement into the coronal space following mucosal healing helps to maintain the space in the arch and restore aesthetics. Observational studies demonstrate that decoronation successfully maintains the alveolar bone and can even lead to a small gain in ridge height, although success depends on timing the procedure correctly.⁷ Decoronation is used as an interim treatment to maintain bone in growing patients whilst awaiting the necessary dental development for definitive treatment. Figure 1 illustrates the decoronation procedure, which was undertaken to manage progressive ankylosis of an incisor following trauma in a young patient. The bone was maintained in the site until the patient was ready for tooth autotransplantation.

Dento-osseous osteotomy

An alternative method for managing ankylosed, infraoccluded teeth involves repositioning a tooth or blocks of teeth within the surrounding bone using a dento-osseous osteotomy. This technique is most commonly used for a single tooth and subsequently is referred to as a single tooth osteotomy. The tooth is separated within a segment of bone, usually using a piezoelectric instrument to minimize damage to adjacent tooth roots. The fragment can then be repositioned in one of two ways. In cases where the movement is small, the segment can be placed immediately into the correct position and secured using fixed ligation.⁸ Alternatively, in cases where this is not feasible due to the extent of movement required, an orthodontic appliance can be used to move the segment into the correct position gradually using a distraction osteogenesis type technique with the ankylosed tooth as the point of force application.⁹ Bone healing is completed within four to six weeks and orthodontic post-surgical mobilization of the segment should therefore be completed within two to four weeks.¹⁰Figure 2 illustrates the use of single-tooth osteotomy to reposition an ankylosed incisor in a non-growing patient following dental trauma.

Dento-osseous osteotomies are not without risks and the main concerns are loss of tooth vitality, avascular necrosis in the bone segment, gingival recession, loss of crestal bone and pocket formation, and a delay in movement of the segment due to bone interferences.¹⁰ Single tooth osteotomies are only suitable for patients where minimal further growth is expected, as the underlying ankylosis is not addressed, so the tooth will remain static following the cessation of orthodontic treatment. In addition, the process of replacement resorption will progress more rapidly in growing patients, leading to earlier loss of the ankylosed tooth and therefore less treatment benefit. Single tooth osteotomy technique provides a method for moving an ankylosed tooth within an orthodontic treatment plan. It allows other aspects of malocclusion to be resolved but it is not a definitive treatment. The eventual loss of the ankylosed tooth should be considered and the long-term plan is likely to involve tooth replacement.

Alveolar ridge preservation

Another suggested approach to bone management is alveolar ridge preservation, also called socket preservation or alveolar ridge grafting. This is an umbrella term for techniques that aim to maintain favourable alveolar ridge architecture for future tooth replacement. Alveolar ridge preservation techniques involve placement of a graft material alone, or in combination with a barrier membrane, at the time of tooth extraction, theoretically to encourage osteoconduction and osteoinduction. Alveolar ridge preservation has been widely reported in conjunction with implant-supported tooth replacement, but it is less likely to have a role in tooth transplantation as the donor tooth is usually transplanted at the same time as the failing tooth is extracted, eliminating the risk of alveolar resorption. A Cochrane review of eight RCTs evaluating alveolar ridge preservation techniques in adults found limited evidence to demonstrate their effectiveness in minimizing ridge changes,² and no evidence could be found for growing patients.

Orthodontic tooth movement to develop bone

The alveolus is functional bone and therefore bone only develops and persists in the presence of teeth. Underdevelopment causing atrophic alveolar ridges or local bony deficits is most often reported in people with hypodontia¹¹ and management through orthodontic movement of adjacent teeth through agenesis sites has been advocated as a method to increase bone volume prior to tooth replacement.¹² This technique can theoretically be applied to any site with inadequate bone. However, the results from this are variable and bone resorption can occur if bone-maintaining methods of tooth replacement are not considered prior to orthodontic movement.^13,14,15

Orthodontic space closure

All methods of tooth replacement, including tooth transplantation, carry a risk of failure that obligates patients to future dental treatment. For some people with existing or potential tooth loss, this commitment to long-term dental treatment may be insurmountable and, instead, they may wish to consider treatment planning options that obviate the need for tooth replacement. Most commonly this involves orthodontic space closure, where fixed appliances are used to move the adjacent teeth either to eliminate the need for tooth replacement completely or to relocate the edentulous space into a site that is more amenable to tooth replacement. The suitability of orthodontic space closure depends on the site of the missing tooth, the morphology of adjacent teeth and other aspects of malocclusion (Table 2). Elimination of maxillary lateral incisor, mandibular incisor and second premolar agenesis sites are the most common application for orthodontic space closure. Camouflage of maxillary lateral incisors in the central incisor position is challenging due to the discrepancy in crown and root widths and the subsequent difficulties in achieving a satisfactory functional and aesthetic restoration. Modifications in tooth positioning aid restoration and reduce the occlusal forces on the substitute tooth.¹⁶Figure 3 shows a patient who lost both central incisors through dental trauma. The treatment plan involved orthodontic space closure with the lateral incisors camouflaged as central incisors and the canines replacing the lateral incisors.

Orthodontic space redistribution

Space redistribution can be used to move sound teeth with good root length and morphology into sites which provide a good occlusal, restorative, aesthetic and functional result. For example, in a case where canines and second premolars are missing, the first premolar can potentially be mesialized into the canine position. Restoration of the canine region is highly unpredictable with limited availability of successful options, compared to the premolar sites, which have lower aesthetic and occlusal demands and more treatment options from adjacent strategic teeth.

1. Removable prostheses

Removable prostheses are usually considered in the interim, rather than as a definitive method of tooth replacement in young people where only one or two teeth are missing. The prostheses rely on the soft tissues or the dentition for support and retention. However, in certain cases, removable prostheses may be the definitive treatment option if other methods of tooth replacement are contra-indicated; for example, in those with complicated risk factors or medical health issues, long edentulous spans and poorly strategic adjacent teeth. The prosthesis of choice is most commonly an acrylic denture, although cobalt chrome dentures and orthodontic retainer type designs may also be considered. Removable prostheses have a number of advantages: replacement of hard and soft tissue defects,¹¹ appliance removal to facilitate effective oral hygiene, relatively cheap and easy to manufacture, capacity for adjustments and incorporation of additional features. Removable prostheses can take some time to adjust to and compliance in young children is variable.

2. Tooth-supported fixed prostheses

The two main types of tooth-supported fixed prostheses commonly considered for replacing one or two missing tooth units are resin-bonded bridges and conventional bridges.¹⁷ Resin-bonded bridges (RBB) with either a single wing cantilever design or a double wing fixed-fixed design are the most popular type of tooth-supported fixed prostheses. Single wing cantilever designs are preferred by many restorative dentists as there is concern that bond failure of one wing in a fixed-fixed design may result in undetected caries under the debonded wing. In the RBB design, a ceramic pontic is attached to adjacent teeth via a non-precious wing or wings, using enamel bonding adhesives. The main advantage of RBBs is that no or minimal preparation is required to facilitate placement. Estimated 10-year survival rates are 80.4% (95% confidence interval 77.6–83.2%).¹⁸ Clinical variables influencing survival revealed that design of the restoration, consideration of the occlusion, cementation technique and experience of the operator were significant factors. Minimal tooth preparation was shown to be superior for longevity compared with other types of preparation. Patient satisfaction has been shown to be high for this type of treatment. This makes treatment simple and predictable to deliver, with or without anaesthetic, and with no biological cost to the patient. For young patients, RBBs can be attached with provisional cement, allowing removal at a later date, if necessary, making them a suitable temporary measure for tooth replacement. The pontic is able to deliver excellent aesthetics, and improvements in opaque luting cements have reduced the problems caused by grey discoloration as a result of shine-through from the metal wing.¹⁷Figures 4 and 5 show patients who underwent tooth replacement with a RBB, as autotransplantation was contra-indicated due to the lack of a suitable donor tooth.

Conventional bridges are less commonly used due to the need for extensive tooth preparation of the abutment teeth to provide sufficient coronal reduction for placement of a full-coverage abutment. Conventional bridges are indicated for patients who have existing coronal coverage restorations in suitable abutment teeth, where further preparation would not be deemed to be destructive and a full coverage restoration would be beneficial.

3. Implant-supported tooth replacement

Implant-supported tooth replacement has gained widespread popularity over the last 40 years. The survival rate of implants in adults has been shown to be as high as 96.5% over 10 years,¹⁹ although success is more difficult to estimate due to wide variation in the criteria used to evaluate success²⁰ and heterogeneity in treatment protocols. Patient-reported outcomes from implants, such as satisfaction with appearance and function, have been demonstrated to be high in well planned cases with good bone quantity and favourable clinical factors.²¹ Implant success is dependent on osseointegration to gain stability and this fusion to the bone prevents the implant-supported structure adapting and erupting with the surrounding teeth. As such, implants are not advocated for use in growing patients.²² Evidence of infraocclusion of up to 1.6 mm over 3 years has been demonstrated in anterior implants placed in adolescents.²³ In those where growth is complete, additional factors associated with the recipient site need to be assessed to determine the feasibility of implant treatment. Implants require adequate bone volume for placement to allow for a functional and aesthetic result. Ideally, a distance of 1.5–2.0 mm of interseptal bone is required between the implant and adjacent roots to encourage papilla regeneration.²⁴ Augmentation procedures may be possible to manage horizontal and some vertical and bucco-lingual deficits; however, inadequate mesio-distal space between the adjacent tooth crown and roots may prevent their use. Sufficient coronal space is required to allow a restoration that mimics the natural contours and is in harmony with the surrounding teeth.²⁵ The distance between the contact point and alveolar crest has been shown to be highly important to papilla presence.²⁶ Lack of mesio-distal space and bone quality are the most common contra-indications to implant use in maxillary lateral incisor and mandibular incisor sites. Figure 6 shows implant-supported tooth replacement in an adult who did not wish to undergo tooth autotransplantation.