Bjorn U. Zachrisson, DDS, MSD, PhD, on Current Trends in Adult Treatment, Part 2

This offers a unique possibility to use teeth with a poor or hopeless long-term prognosis for regenerative purposes (Figs. 14, 16, and 17). Salama and Salama suggested the term "orthodontic extraction", since the purpose is to extrude the tooth, with all the augmentative benefits inherent to the process.²² They used four to six weeks for the eruptive phase, followed by six weeks of stabilization before the tooth was removed and the implant was placed. It should be noted that the orthodontic extrusion does not create a new attachment, but merely relocates the existing attachment in a coronal direction. The relationship between the CEJ and the bone crest is maintained--in other words, the bone follows the tooth. The marginal periodontium migrates with the extruding tooth, while the location of the mucogingival junction remains stable.^23,24 The labial gingival margin follows the extruded tooth about 80% of the distance (Figs. 14 and 15). Thus, the clinical crown length of an extruded tooth may increase by some 20%,²⁴ and the width of the attached gingiva will also increase.

In the horizontal plane, tooth movement may be an exciting alternative to bone grafting or other surgical augmentation procedures (Figs. 18 and 19). The principle is that a tooth (generally a premolar) is moved orthodontically into an edentulous space, and the implant is placed in the position previously occupied by the tooth that has been moved. The bone deposited on the tension side behind the orthodontically moved tooth recreates a surprisingly wide bony ridge that will be optimal for placement of the implant (Figs. 18B,C and 19B-D).

DR. KEIM How fast can teeth be erupted to prepare a site vertically?

DR. ZACHRISSON Slow orthodontic extrusion of teeth (and roots) appears to have a unique potential for significant vertical alveolar and labiolingual ridge augmentation without surgery. However, we do not know at present how slowly it is necessary to extrude the teeth for the bone to follow optimally and to obtain the most successful orthodontic ridge augmentation. To my knowledge, there exist no scientific studies of what kind of force systems (continuous vs. interrupted forces, segmented vs. continuous archwires, etc.) and what force levels and treatment times should be recommended to obtain the most efficient, complete, and predictable regeneration of bone. As I mentioned, Salama and Salama used only four to six weeks for the extrusive phase,²² whereas a more recent study by Zuccati and Bocchieri of nine teeth in seven patients used three to four months for the extrusion, and the implants were inserted two to four months later, when the soft-tissue healing was complete.²¹ Based on empirical considerations, we prefer to use interrupted continuous forces that allow rest periods between the activations, and our treatment times may be as long as 10 months or more (Figs. 14, 15, 16, and 17).

DR. KEIM How fast can teeth be moved horizontally to develop a hypoplastic implant site? Is there any danger to the teeth or alveolar bone from moving the teeth too rapidly?

DR. ZACHRISSON By slow, bodily movement of teeth into edentulous areas of reduced bone height, the periosteum on the labial and lingual surfaces of the alveolus will normally form bone.²⁵ On the tension side of the teeth, the full height of the bone will be maintained (Figs. 18 and 19). If the teeth are moved too rapidly, there is a risk for development of a dehiscence.^25,26 Since the principle involved in horizontal implant site development as a rule is to move a selected premolar one tooth width mesially or distally, and the rate of tooth movement is optimally around 1mm per month when a continuous force is used, the treatment periods for horizontal implant site development may approach one year.

However, the problem of how fast the teeth can be moved without compromising the integrity of the moved teeth and without losing any bone largely depends on the degree of vertical and horizontal atrophy of the edentulous segment. Clinical studies have shown that reconstruction of an atrophied alveolar ridge after previous extractions may occur during tooth movement.^27-29 Periosteal bone apposition takes place in the pressure direction in front of the tooth and in a labiolingual direction. However, when the alveolar ridge is quite narrow, as with long-standing extraction spaces (approaching a knife-edge appearance), with buccal and lingual layers of dense cortical bone and little trabecular bone in between, we have experienced iatrogenic damage. Thus, extensive lateral root resorptions may occur in the alveolar ridge areas when teeth are moved with continuous force from superelastic coil springs (Fig. 20). We don't know yet if we can avoid such resorptions by using discontinuous forces, preorthodontic alveolar ridge augmentation by means of guided tissue regeneration, ³⁰ surgical alveolar ridge augmentation,²⁹ corticotomy, or cortical perforation.³¹ Further studies are needed to elucidate this problem.

DR. KEIM In what instances would you use orthodontic tooth movement to develop bone in both planes of space?

DR. ZACHRISSON Whenever it is needed. Figures 15 and 20 and Figures 21 and 22 show two such cases. In the first case, early extractions of both mandibular first molars in a female 55-year-old patient had left an alveolar process that was thin buccolingually, so that implant placement was contraindicated on both sides without some form of ridge augmentation (Fig. 20A). At the same time, this patient had marked labial gingival recessions on the maxillary right lateral and central incisors (Fig. 15A). As an alternative to surgical correction of both problems, a biological, nonsurgical approach was chosen.

The complicated case in Figures 21 and 22 required orthodontic extrusion of the right lateral and left central incisors to develop alveolar bone for three implants, as well as mesial movement of the right central incisor toward the midline. The extrusion of the incisors required 11 months of treatment, and the implants were inserted at 15 months (Fig. 22D).

DR. KEIM How long after bone development by tooth movement can implants be placed?

DR. ZACHRISSON Significant resorption and narrowing of the alveolar ridge after the orthodontic treatment could jeopardize placement of the implant. Fortunately, an edentulous ridge created by orthodontic extrusion or separation of teeth appears to be less prone to resorption over time compared to what occurs following conventional tooth extractions. For example, research has shown that after extractions, the ridge will narrow by approximately 30% over just the first three months.³² If bone grafting is performed after the extraction, the shrinkage may be reduced to 10% at six months. However, the amount of bone loss when the bone is regenerated by horizontal tooth movement is much less. This problem is illustrated by the events following distal movement of a maxillary canine to provide space for a lateral incisor implant. Using tomograms through the edentulous ridge at four-year recall appointments, and sectioning dental casts across the ridge, Spear and colleagues revealed that the amount of bone loss in a sample of 20 such patients was less than 1% over four years.³³ This demonstrates that considerably less resorptive changes are likely to occur over time after orthodontic tooth movement compared to what occurs following tooth extractions.

DR. KEIM What techniques other than tooth movement are available to implantologists for bone and gingival development?

DR. ZACHRISSON Augmentation of the resorbed alveolar crest can be achieved with different surgical techniques, including onlay bone grafts, membrane techniques, bone distraction, and bone splitting.^33,34 Maxillary sinus floor elevation and bone grafting may increase the height of bone in the maxillary posterior areas. Bone grafting and guided bone regeneration (GBR) can increase the width and, to some extent, the height of the alveolar bone. Lateral widening without vertical augmentation is possible with a crestal-split technique. All these methods for osseous reconstruction are technique-sensitive.

The gold standard at present is autogenous bone grafts taken from the maxillary tuberosity, the ramus, the symphysis, or the mandibular retromolar area. The most commonly recommended technique to build up soft-tissue thickness and height is to use connective tissue grafts from the palate, frequently in combination with coronally repositioned flap procedures.

It's interesting to note that a recent review of the current literature concerning augmentation of a narrow alveolar crest after dental and alveolar trauma, prior to implant placement, covered a multitude of methods to increase bone quantity and quality, including augmentation with bone grafts; augmentation with allogenic grafts; GBR; osteoinduction, osteopromotion, and osteoconduction; osteocondensation; distraction of low and narrow alveolar crests; and widening of alveolar crests with chisels.³⁴ Orthodontic tooth movement was hardly mentioned as an alternative in this review, and was just briefly commented upon as an application of the principles of distraction. It is apparent that the use of orthodontic tooth movement for implant site development is little known among our colleagues in other areas of dentistry.

DR. KEIM Is there a difference in the prognosis for implants placed in sites developed by tooth movement vs. sites that did not need any development or sites that were developed by one of the other techniques?

DR. ZACHRISSON So far, publications in this area comprise case reports of only one or a few cases. We don't have any evidence-based scientific or clinical data to reliably answer your question. Reports of Spear and colleagues³³ and Thilander and colleagues²⁶ have shown successful long-term follow-ups when a premolar was moved orthodontically into an edentulous space, with an implant then placed in the position previously occupied by the premolar and provided with an implant-supported crown.

Zuccati and Bocchieri reported that after the extrusion of nine teeth with poor prognosis in seven patients, enhancement of the implant site and successful osseointegration were achieved in every case that had a healthy apical residual attachment.²¹ They also showed that orthodontic movement can be used to enhance the thickness of the bony ridge by combining the extrusion with labial root torque. However, no bone growth was detected around one tooth where repeated abscesses occurred during treatment. Our experiences are in agreement with these findings.

DR. KEIM Is the quality of bone different between implant sites developed by tooth movement and sites developed by other techniques?

DR. ZACHRISSON Although we now know that it is possible to regenerate bone by extrusion of teeth with healthy residual periodontia, provided the periodontal infection is controlled, and by horizontal bodily movement of premolars and canines, there are still many questions remaining to be answered with regard to an optimal implant osseointegration. In particular, we need more information on the quality and density of the regenerated bone. In implantology, there exists a close correlation between bone density and success of osseointegration. The poorest prognosis is seen in low-density trabecular bone. It is not unlikely that both prolonged orthodontic treatment time and prolonged healing time would enhance the maturation of orthodontically regenerated alveolar bone. Until more information is gained, the surgeon should treat orthodontically regenerated bone the same as bone obtained by guided bone regeneration or particulated autografts.

In comparison, it may be mentioned that in distraction osteogenesis, a fixation period of one year or more may be required before the structure of the newly formed bony tissue is comparable to that of the preexisting bone. However, even if the volume of the new and old bone is the same, it is conceivable that the mineral content, radiodensity, and tensile strength could be lower in the new bone.

Another possibility for faster and more complete osseointegration of single implants in orthodontically regenerated bone is to use more recent, bioactive implants rather than the traditional machined Brånemark implants. Research is needed in this area.

DR. KEIM What is the potential for tooth movement into the maxillary sinus to improve implant sites in this area?

DR. ZACHRISSON Teeth can be moved "with the bone" or "through the bone". To elicit a "with the bone" type of tooth movement, a direct resorption of bone in the direction of movement must take place, with a balance between resorption and apposition. If hyalinization occurs, indirect resorption results, and the tooth will move through the bone without any apposition. Especially in adult patients, the force level should be kept low to avoid formation of hyalinization areas and promote proliferation of periodontal cells; the clinician should apply the light force with a high moment-to-force ratio.^28,35

Some recent case reports indicate that with properly controlled movement, a premolar can be moved through the maxillary sinus area while maintaining pulp vitality and bone support, and exhibit normal width of the periodontal ligament both on the pressure and tension sides.^35,36 Implant placement in the previous alveolus is then possible. The relatively complicated sinus-lift surgical augmentation procedure that would otherwise be necessary can thus be avoided. However, the real spatial relationship between the root of the displaced premolar, the subperiosteal layer, and the sinus recesses is not known, since it would require a histologic evaluation.

Figure 23 shows a case with apparently successful premolar movement into the sinus, in which I used a non-osseointegrated miniscrew (Spider Screw^**) as the source for posterior anchorage. In other instances, however, my attempts to move a premolar into the maxillary sinus region have failed, with the tooth apparently hitting against the sinus wall for a long time, while developing lateral root resorptions.

DR. KEIM Are there any other techniques particularly applicable to older patients that might be of interest to our readers?

DR. ZACHRISSON Of the techniques that I use routinely, the custom-made transpalatal arch (TPA), having one large anterior loop and two smaller posterior loops (Fig. 24), should be useful for other orthodontists in many adult and older patients.^37,38 The main differences between my design and the traditional Goshgarian-type TPA are in the amount and shape of the wire in the palatal loop. Increasing the length of the wire increases its springiness and range, reduces the load-deflection rate, and makes the forces more constant and precise.³⁸ Thus, lower and more constant moments of derotation are produced, and the engagement into the lingual attachments is easier, with less activation loss. It takes less time to derotate molars with our design than with traditional Goshgarian arches.³⁸

The improved design has several clinically relevant advantages. It appears to be an optimal appliance for supporting posterior anchorage, improving vertical control, maintaining arch widths and archforms during treatment, quickly and completely derotating mesiolingually rotated maxillary first and second molars, adding buccal root torque to the molars, expanding the maxillary arch, and correcting mesiodistal asymmetries. When soldered extension spurs are added, the TPA can act as an ideal tool for tooth movements that are difficult, if not impossible, to achieve with conventional labial archwires, including torque control, palatal intrusion, and lingual movement of maxillary second molars.³⁸

DR. KEIM What has been your experience with micro- or miniscrews?

DR. ZACHRISSON I believe that the recently developed miniscrews, or so-called temporary anchorage devices (TADs), in coming years will become a more significant aid than at present to support posterior and/or anterior anchorage in both the maxilla and the mandible for many older patients, who may have incomplete or diseased dentitions. My experience with different TADs designed for pull forces via superelastic coil springs or elastomers and, particularly, those with bracket-like heads that allow ligation of orthodontic wires (Spider Screw, Aarhus Anchorage System,^*** TOMAS^†, etc.) is positive, and the indications for using such devices are basically limited only by one's imagination. By the same token, the new, temporarily osseointegrated midpalatal or paramedian palatal implants may be increasingly used in the future to support or replace toothborne anchorage.³⁹