Autogenous Dental Transplants

The movement of one or more teeth from one part of a person's mouth to another location in that individual's mouth is referred to as an autogenic dental transplant. It is thought that Ambrose Pare, in 1562, was the first author to describe "replantation of teeth". He detailed the replacement of a tooth for a woman of nobility, which was provided from the mouth of one her "ladies in waiting." This would have been an allogenic transplant; these have not been shown to be very successful.

Conversely, autogenic transplants have been well documented and gained acceptance, especially in Europe and Japan, but have not risen to popularity in North America, in spite of documented success. Examples of author's findings are as follows: Slagsvold, in 1978, reported on 34 consecutively transplanted premolars with 100% success (38); Alberg's article in 1983 discussed the transplantation of 33 maxillary canines with 88% success (1); in 1987 Pogrel's article discussing 416 transplants provided a 72% success rate under less than ideal circumstances (35); and Andreasen's 1990 four article series discussing 370 premolar transplants revealed success rates of 95% for transplants with incomplete roots and 98% for completed roots (3-6). Our own survey generated a success rate of 80.2% among members of the Angle society who responded as having been involved in transplants and 73.9% among chairmen of oral surgery departments who had provided transplants.

The indications for autogenic transplants have historically constituted the need for a tooth in one region in the mouth while having an abundance of teeth in another part of that same mouth. A comparison of the esthetic results that have been produced by transplantation in the maxillary incisor area with those found following osseointegrated implants might lead one to strongly consider transplants for anterior replacement. Further, the property of developing increased alveolar bone while the transplanted root develops in areas of diminished alveolus provides a powerful incentive for transplantation in such edentulous areas. With the advances in stem cell research and the progress being made in "growing" dentin, it is quite probable that tooth-like structures with the potential for implantation will begin replacing edentulous areas in the not too distant future (17,18,25,26,28).

Multiple authors (1,3,21,29,31,35,36,39) have reported on the significance of the care taken during the procedure involved; it is, in fact, the most critical aspect in the determination of success. Consequently, the practitioner that delivers the transplant should be carefully selected and well prepared. It is generally suggested that the donor be carefully measured so that the recipient site can be precisely developed. It is often instructive to have a mock tooth constructed by matching long-cone x-rays of the donor; this can be used for trial insertion prior to extracting the donor tooth. This is especially helpful in minimizing the amount of time that the transplant remains outside of the extraction socket. It is best to have a direct delivery - remove the transplant and place it directly into the recipient site. This requires preparing the recipient site before the donor is harvested. Minimal desiccation of the periodontal membrane or dental follicle can occur in this way. Furthermore, damage and contamination of the peripheral cells can occur if the transplant is put down. If it cannot be placed immediately into the recipient site, it can be returned from the donor site; or, another compromise might be to place it into a culture medium. There are commercially available receptacles for this predicament (Sav-a-tooth or ToothSaver).

The extraction should be carried out in a very delicate manner, carefully dissecting the surrounding bone so that no damage is done to the root sheath or its components. Sometimes, a more aggressive removal of surrounding bone must be enacted so as to allow a coronal delivery with an intact follicle. An excellent discussion of the surgical technique is provided in Part I of Andreasen's four part article, "A long-term study of 370 autotransplanted premolars. Part I. Surgical procedures and standardized techniques for monitoring healing."( 3) With more periodontists performing implants, they have become much more adept in providing such a service. It is not a bad idea to consider having a periodontist provide this procedure. They often are more accustomed to the kind of attention to soft tissue and care that are necessary. They are also more likely to have a recall system that is conducive to the monitoring of transplant cases.

Case 1 is useful in demonstrating a number of the relevant issues discussed here. She is missing two premolars in the upper left quadrant and can spare one from the lower left. At initial observation, the root length of the donor tooth was about one-third complete, so we waited for almost a year to allow for increased development. The follow-up photos demonstrate continued root elongation and a successful replacement which has provided 26 years of service to date.

The best age for transplantation is determined by stage of development. Because it is desirable that the tooth experiences revascularization, the best results are obtained well before the apex of the root closes. In 1970, Andreasen first set the ideal time as three-quarter root completion. (2) Slagsvold later discussed the other aspects of development that need to be taken into consideration when determining best stage: the number of roots (depending on which tooth is being transplanted) and the depth of the recipient site. (36) Stressing that the root responds best when it about 4-7mm in length, he pointed out that the proximity of the maxillary sinus or the mandibular nerve might dictate moving up the timetable for providing the transplantation.

It is worth noting that, as the apices of transplantable teeth are approaching apexification (typically about 18 years of age for third molars), and the opportunity for vital revascularization is waning, the appropriate age for using an implant is just arriving - when facial and alveolar growth is coming to a halt. Of course, teeth can be transplanted later, but these will require endodontic treatment after the periodontium has healed.

Monsour performed experiments with Beagle pups, transplanting teeth at various stages of development and placing them at different depths: half had just completed crown formation and others had differing amounts of root completion; some were placed completely submerged, some partially erupted, and some in partial occlusion. (29,30 )The transplants that responded the best were those that had partially completed roots and were placed in a submerged state; any that were placed in occlusion simply did not survive. There was a gradient of success between these two extremes.

If the transplant survives the procedure well, there is an excellent chance that the root will continue to grow in length; this is obviously desirable in terms of functional support for the tooth. Slagsvold reported in 1974 that radiographs demonstrated a 1.3mm (6%) reduction in root length.(35 ) Andreasen reported in 1990 (in his four part article detailing the transplantation of 370 premolars) that 14% of transplants would experience a total arrest of root development at the time of transplantation, 65% would have a partial arrest, and 21% of the transplants would continue on to full root development.(6)

Case 2 demonstrates the ability of transplanted teeth to continue to grow and even to provide a viable canal that will allow endodontic treatment. It is regrettable that the perceived urgency of the impaction did not allow a bit more formation of the root. Teeth transplanted at a developmental stage too near crown completion can have greater difficulty forming than those with perhaps as much as one-half completion. Another complicating factor in this case was the questionable quality of dental care prior to receiving the bridge and lapses in oral hygiene shortly thereafter. Nevertheless, the patient continues to do well with a highly functional prosthesis.

As suggested above, this becomes important because of the trade off in systems. On one hand, the practitioner can be more assured of an increased root length by delaying the timing of transplantation; however, prolonged delay can reduce the chances for a vital pulp. Once the tooth is transplanted, the vital components within the pulp chamber have the potential of being totally replaced through a process of revascularization. Initially the neurovascular components necrotize, but an infiltration of new capillaries marks a revitalization of the pulp chamber during the first four weeks; this progresses to a proliferation of mesenchymal cells and the laying down of new cell layers along the dentinal wall. As new dentin is formed a regenerating of new, functioning nerve fibers can be seen. The apex can close off, forming a normal root ending. Endodontics is typically not required for these teeth.

Once a root approaches apical closure (stage 5, or about four-fifths root completion), the potential for complete revascularization becomes compromised. Irreparable necrosis places the tooth at risk for infection and rejection. It is advisable to initiate a coronal opening for a conventional endodontic treatment about 7-10 days after the transplant. This will allow critical healing of the periodontal apparatus. Once the pulp has been extirpated, the canal should be treated with calcium hydroxide to encourage continued healing and eventual apical closure. The tooth can be monitored at progressively increasing intervals and a conventional root canal can be performed. Andreasen stresses the need for complete sealing of the root canal all along the root surface. He distinguishes this from the needs of teeth infected by decay and subsequent periapical lesions, where the important seal must be obtained primarily at the apex.( 16) This treatment results in a completed root transplant, a procedure that yields a 98% success rate in his studies.

When enacting a transplant it would be best to try to deliver the graft at the same level from which it was harvested.(16 ) As mentioned above, the length of the graft or the surrounding anatomy can prevent this. In that case, the transplant should be placed as deep as allowable, certainly sufficiently deep that the surrounding gingival tissue can be placed coronal to the cementoenamel junction. An optimal tissue closure is to have the gingiva from the facial/buccal abut with that on the lingual; such a depth will generally provide an excellent result. A depth that will only allow closure of the soft tissue around the crown will also work, but it is preferable to have this no deeper than the cervix of the tooth.

When it comes to securing the transplant, rigid fixation must be avoided. Not only will hygiene be a problem, but the graft must have a dynamic interface with the newly created socket in order for periodontal ligament cells to proliferate and form a healthy suspension. A likely alternative would be ankylosis.(5) If the graft is placed deep enough to allow soft tissue closure, sutures are an excellent method of fixation. Triple O black silk sutures have excellent closing properties and are easy to retrieve. These sutures can also be used to close the gingiva on the crown and create a hammock to hold the tooth into its socket. As more of the crown is left exposed following the transplant, orthodontic attachments can be improvised to secure the graft. If wires are used to fixate the transplant, they should be very light and flexible. The figures enclosed provide examples of appropriate fixation. (Figure 1)

The prognosis for a transplant is considerably improved if areas of infection are avoided during the placement of transplants or if efforts are taken to heal the region prior to transplantation.(35) Even so, it is recommended that the patient be placed on a full regimen of antibiotics, beginning about two days prior to the procedure.(16) Andreasen suggests the possibility of arrested revascularization if the graft becomes infected and lists as possible sources of contamination as extra-oral handling or exposure to bacteria from the saliva or the coagulum. Again, it bears repeating that the care exercised during the transplant is among the most important considerations in the success of the procedure.

Once a transplant has healed and sufficient time has been allowed for revascularization to take place (about 3-4 months), there is a brief period (approximately 6-9 months) during which the transplant will tolerate orthodontic tooth movement.(33) Heavy and prolonged forces should be avoided as should eccentric tooth movements. The skills that have been developed for implants should be implemented in planning cases that involve transplants. Effort should be taken to place the transplant near its ultimately prescribed position so that minimal movement will be required to fine tune the placement of the tooth.

Another area where the science of implants bears similar insight into that of transplantation is the concept of space: having enough room to be able to accommodate a transplant. As with the creation of a socket for the delivery of an implant, care must be taken to avoid the adjacent root structures by at least 1-2mm when preparing the recipient site for a transplant. It is also helpful to have about 0.5-1mm of bone both labial and lingual to the transplant graft. In the text by Andreasen, cases demonstrate the removal and replantation of the labial plate of bone to accommodate the placement of the graft into a compromised alveolus.(16) Between the osteogenic potential of the transplanted root surface and the remarkable healing potential of autogenous bone, these grafts work with incredible success. Such transplant cases, as presented by Scandinavian surgeons, profoundly challenge the esthetic potential of today's finest implants. To this extent, proficiency with the procedure could well force a new paradigm in the realm of esthetic replacement of anterior teeth. The fact is that the esthetics of a restored biological root -that which is left when a premolar is used to replace an incisor - has far more esthetic potential than most implants. And we only know what the implants look like 15-20 years out! What will an incisor implant look like when the patient is aging and losing alveolar support?

One of the more recently perceived benefits of autogenic transplants is the aforementioned osteogenic potential. As the root develops its full potential length, alveolar bone has been shown to develop in the vicinity; if the tooth is erupting, the alveolus is brought along. If the root is growing away from the plane of occlusion - for example, growing into the maxillary sinus, the depth of the alveolar bone is increased. Considering this new potential, transplants might well be considered the treatment of choice in cases where grafting is a likelihood, especially when the encroachment of the maxillary sinus yields a limited alveolar dimension. Even if the transplant fails, it might be considered useful in the development of the site of an eventual implant. Especially considering the propriety of age in planning either an implant or a transplant, a transplant might buy time for the eventual placement of a transplant - once alveolar growth has been determined to be finished.

Case 3 presents the condition of oligodontia, microdontia and severely inadequate depth of alveolus. While the case presented and treatment was started in 1977 (before osseointegration was an accepted phenomenon in North America), it would have presented a challenge even today. Numerous grafts would have been required, lifting the maxillary sinus and attempting a vertical augmentation of the alveolus, especially on the left side where ankylosis was causing an intrusion of the premolar region. The final result is one that would allow easy restoration, but the significance of this case lies in the vertical increase in alveolar bone in the region of the developing transplant.

Case 4 also presents an example of alveolar development in a case of multiple congenitally missing teeth. In this case she is also handicapped by a profound Class II, division 1 malocclusion. Serial extraction was incorporated concurrent to phase I treatment by a Function Regulator (Frankel). During that time the overjet was reduced from 9mm of overjet to 3 and the depth of bite was reduced anteriorly. Lower second molars were placed into the upper premolar region. Serial periapical x-rays demonstrate a nice increase in the alveolar height as the roots grew into the maxillary sinus. When it was determined that growth was complete, implants were placed in the maxillary canine sites as well as in two among the lower posteriors. She finishes with a very adequate occlusal table.

Cases presented by Andreasen and Zachrisson, as well as cases presented by Hans Paulsen in his chapter of this monograph, where transplanted premolars have been used to replace missing maxillary incisors, demonstrate a development of interproximal gingival papillae and gingival contours that are not currently predictably possible when using implants.(16,21,23-4) The cases shown reveal tissues that were judged to be normal or slightly hyperplastic, making them a superior treatment alternative to implants when replacing maxillary anteriors. When it is considered that we are not far from being able to culture stem cells that will allow the creation of dentin specific to an individual patient and that we will be able to develop that tissue into a scaffolding that will take on the form of the root that we wish to replace, it becomes even more regrettable that we in North America are not actively developing the techniques and experience to predictably deliver transplants.

One of the more disconcerting aspects of transplants is case selection limitation due to inadequate donor teeth. The inadvertent use of a premolar might cause a drain on anchorage in terms of providing a full facial profile. When one considers the esthetic benefits of premolars used to replace maxillary incisors - especially in the aftermath of a traumatic episode and resultant compromised alveolar width - we gain a new appreciation for the concept of intentional loss of anchorage (protraction) to support facial profile.

Case 5 provides an excellent example the beneficial use of transplants to turn this potential loss into a real positive. The patient is missing four second premolars. His significant Class II, division 2 malocclusion, with deep bite, 6mm overjet, and the roll and entrapment of his lower lip provide a situation that would render a disastrous collapse in facial fullness if we were to simply remove the four premolars and close the spaces through conventional orthodontics.

Instead, a functional appliance was used to facilitate the eruption of the lower posterior teeth while encouraging a shift in his dentition that resulted in an excellent overbite and overjet relationship. Use of this appliance simultaneously protects the transplant from heavy occlusion and improves space closure potential. An excellent improvement in facial profile is attained in a case that was highly prone to labial inversion.

The Surveys

All members of the Edward H. Angle Society of Orthodontics were surveyed, as were each of the departmental chairpersons of all of the American departments of oral surgery. The response rate among Angle orthodontists was 65.5%; it was 46.6% for surgical chairs. Of the respondents 20.9% of the orthodontists had been involved in a transplant case, while 47.9% of the oral surgeons had transplanted a tooth. As the Figure 2 shows, those orthodontists who had been involved in more than four transplant cases experienced about a 90% success rate, while those who had been involved in fewer revealed a generally lower success rate. Figure 3 demonstrates that the incidence of success did not appear to be correlated to experience among oral surgeons. Nine of the responding 48 departments nation-wide teach autogenic transplantation of teeth, with about forty-five being done by oral surgery residents annually (15-20 of those are all being done in one department - the University of California San Francisco).

The responses as to characterization of success were vastly divergent between oral surgery departments and orthodontists. The orthodontists were generally satisfied if the tooth took on a healthy periodontal membrane, did not ankylose and was still present five to ten years down the line (hopefully for a lifetime); only UCSF had a system for following patients long term, and that was for two years. Oral surgeons are seldom called upon to have extended follow-up, making implementation of a recall program awkward. As periodontists become more proficient in the surgical techniques implicit in delivering implants, it becomes more reasonable to consider their increased utilization in the realm of transplants.

Perhaps it is the paucity of articles in their journals, but our survey yielded little knowledge or acceptance for this procedure among oral surgeons - even though it is practiced in Scandinavia and Japan with exceptional success. One director suggested that we might be better advised contacting the endodontic department. This should not be confused with intentional reimplantation. Other statements provided little evidence that oral surgeons were interested in taking autogenic transplants seriously: "In most instances, implants have eliminated the need for this procedure. At present there is not sufficient documentation and research to support teaching this technique." "Implants have obviated the need for transplants." "Last year, we transplanted 4 third molars; we did 1625 implants. We do autogenic transplants on patients who can't afford implants."

Conversely, orthodontists that responded provided the following information:

When considering treatment options in the replacement of missing teeth, we must consider space closure, replacement by a fixed or removable prosthesis, transplantation or implants. If there are sufficient teeth available, space closure is an excellent option. Generally speaking, prostheses place a drain on the integrity of surrounding teeth. As a result, transplants (especially in Scandinavia) and implants (more recently in North America) have gained favor during the last two decades. A fair comparison of these two options must take into consideration the following considerations: transplants generally are a fraction the cost of implant; transplants are a biological solution whereas implants are artificial; transplants (for the time) being rely upon the availability of donor teeth while implants can be easily purchased; transplants can grow alveolar bone and even inter-dental papillae during eruption while implants do not erupt and, therefore, cannot; the age for effecting a vital transplant is dissipating at the same time that one can, for the first time, provide an implant; transplants can be moved while implants cannot and make excellent anchor units; transplants often do not require a prosthetic completion while implants do; transplants are susceptible to caries, but implants have been shown to be prone to new-tech hygiene problems; both have excellent prognoses, but there some cases (especially those involving the replacement of maxillary anterior teeth) where the potential for soft tissue improvement profoundly tip the advantage scale toward transplants. When the time arrives when we can generate root-like structures through bioengineering, transplants will gain dominance - especially for the replacement of teeth with visible gingival margins. In the meantime, it is regrettable that the oral surgical community is not better preparing themselves for proficiency in this technique sensitive dental procedure. It is our hope that this will change.

If your appetite has not been whetted for the concept of transplantation, consider the dilemma presented by Case 6. The lower left second molar is impacted - probably ankylosed. Are you going to allow your oral surgeon to remove all four third molars at the time that the second molar is exposed and an attachment is places? Don't let it happen to you that your potential donor teeth are absent when it is decided that the tooth is not going to erupt.

Examples

Figure A: Male patient of orthodontic age whose third molar was transplanted into the site of an impacted second molar in August, 1964.
Figure B: September, 1964, one month postoperatively. Figure C: February, 1965. Figure D : July, 1965. After what appeared to be a period of arrested growth, some apical displacement of bone is now taking place. Figure E: January, 1966. Figure F: October, 1966. Figure G: October, 1968, 2-year postorthodontic follow-up. Figure H: September, 1975, following extraction of first permanent molar, apparently because of the gradual breakdown of his restorations, the patient presented to the McGill University undergraduate dental clinic.

Figure I. April 1976, three months following bridge cementation.

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