INTRODUCTION

Conventional orthognathic surgery and craniofacial reconstruction have experienced widespread success, but several limitations are associated with these treatment modalities.1–3 Distraction osteogenesis or callus distraction, which is a process of bone formation between the surfaces of bone segments gradually separated by incremental traction can be an alternative treatment approach for other treatment modalities.4–7 In 1927, Rosenthal first performed this technique in the maxillofacial region, and he was followed by Kazanjian and Crawford;8 however, distraction osteogenesis did not gain immediate acceptance. The introduction of distraction protocols for limb lengthening by Ilizarov et al9 stimulated interest in distraction osteogenesis, and it has been successfully performed on endochondral bones for over 45 years. The report of Snyder et al10 demonstrated the application of Ilizarov's principles to the facial skeleton. McCarthy et al11 showed ramus lengthening in humans using an extraoral distractor, and Polley and Figueroa12 also used a rigid extraoral device to lengthen the maxilla in the treatment of severe maxillary deficiency and cleft problems. In recent years, because of the increasing popularity of callus distraction, a variety of devices have been introduced to lengthen the maxilla and mandible.13–22

Rapid palatal expansion (RPE) is another modality of distraction osteogenesis, and conventional devices used for RPE are tooth-borne.2324 Tooth-borne devices, however, may cause undesired effects on the abutment teeth and periodontal tissues during expansion and retention even if they are accompanied by corticotomies.25–28 Mommaerts28 reported that bone-borne distractors had a considerable advantage over tooth-borne devices in RPE.

Because distraction osteogenesis techniques create edentulous spaces in the maxillary and mandibular dental arches, the treatment of transverse and sagittal discrepancies between the jawbones to relieve dental crowding without extraction became possible with this approach.151829–32

The process of osteogenesis in the periodontal ligament during orthodontic tooth movement is similar to the process in the midpalatal suture during RPE or to that in the midface sutures in the growing animal during midface distraction.33 Liou et al34 created edentulous spaces using an intraoral distraction device in the mandible of mature Beagle dogs between the third and fourth premolars and tried to move the fourth premolars into the edentulous space. They observed that the best time to initiate orthodontic tooth movement was when the edentulous space was fibrous and bone formation was just beginning. They reported that rapid orthodontic tooth movement was a form of distraction osteogenesis of the periodontal ligament.

In 1998, Liou and Huang33 demonstrated the rapid distalization of 26 canine teeth in humans using distraction of the periodontal ligament. They achieved an average of 6.5 mm distraction of the canines and called this technique “dental distraction.” However, comprehensive studies about rapid canine distalization with this technique cannot be found in the literature except from the studies of Liou and Huang.3235 The aim of this research was the rapid distalization of canine teeth with semirigid, unidirectional, individual tooth-borne distractors and the statistical evaluation of the effects of rapid canine distalization on dentoalveolar structures.

MATERIALS AND METHODS

Our research was carried out on 18 (seven male and 11 female) patients who required first premolar extractions because anterior crowding or dentoalveolar protrusion. Patients with the canines in palatoversion or excessive labioversion were not included in the study. The average age of the treatment group was 16.7 years. The sample consisted of 43 (32 upper and 11 lower) canine teeth. Criteria regarding malocclusion, sex, and age were not considered in patient selection. Orthodontic models, cephalometric and panoramic radiographs, and standard photographs of all the patients were obtained before treatment and after the consolidation period. Periapical radiographs of the canines and first molars were taken before distalization and repeated every week during the distraction period to observe the root resorption and the changes in the periodontal ligament and alveolar bone. The study was carried out according to the guidelines for patient treatment of the Gulhane Military Medical Academy Ethic Committee.

Distractor construction

The individual canine distractor was a tooth-borne, semirigid device which was designed by one of us (Dr Bengi). After the bands were selected for the canines and first molars, an impression was obtained, the bands were transferred into the impression material, and the study cast was made. Conventional palatal tubes (2 × 0.9 mm) were soldered on the buccal surface of the molar and canine bands, perpendicular to each other. The device consisted of an anterior section, a posterior section, a screw, and a hex wrench to advance the screw (Figure 1A). The sections of the distractor were obtained from a conventional Hyrax screw, and the tips of the sections were formed rectangularly to fit tightly in the tubes.

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The posterior section included a round sliding rod (1.5 mm), a retention arm (with a rectangular tip) for the first molar tube, and a grooved screw socket. The anterior section included a retention arm (with rectangular tip) for the canine tube and two nongrooved slots for the sliding rod and screw. The screw (2.5 mm) and the hex wrench were produced in a military establishment and fabricated from stainless steel. The top of the screw was designed thicker than the grooved part and was of a rectangular shape to facilitate patient activation of the screw with the hex wrench. Because the distractor was unilateral, a 360° activation of the screw produced 0.5 mm of distal movement in the canine tooth. The length of the screw was arranged according to the distance between the distal point of the canine and the mesial point of the first molar (Figure 1B).

Surgical method

After the first premolar extraction, vertical osteotomies were carried out at the buccal and lingual sites of the interseptal bone adjacent to the canine tooth. The vertical osteotomies were connected with an oblique osteotomy extending toward the base of the interseptal bone to weaken the resistance (Figure 2). The distractors were cemented in place after the surgery.

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Distraction protocol

The distraction was initiated just after the surgery. An advancement of 0.25 mm was performed three times a day until each canine tooth was distracted into the desired position. The patients were closely monitored during the distraction period, and a Class I canine relationship was attained after an average of three weeks. After a two-week consolidation period, the distractors were removed and the edgewise mechanics were begun. Intraoral photographs of a patient before and after rapid canine distalization are shown in Figures 3–5.

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Intraoral measurements

The distances from the lateral incisor to the first molar (6M2D), from the canine to the second premolar (3D5M), and from the canine to the first molar (6M3D) were measured before distraction and every week thereafter (Figures 6 and 7) with a sliding caliper (Dentaurum). The movement characteristics of the teeth during the distraction period are shown in Figure 8. A periapical radiograph was also obtained at the same appointments.

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Cephalometric analysis

Cephalometric radiographs were obtained on all patients before and after canine distalization. All cephalometric radiographs were exposed with standardized settings and the Frankfort Horizontal plane parallel to the floor. Every parameter was measured by three different clinicians, and the mean values were used in the statistical analysis. The cephalometric parameters used in the study and the radiographs of the patient before distraction and after the consolidation period are presented in Figures 9–12.

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Model analysis

The distances between the lateral incisor and the first molar (6M2D), between the canine and the second premolar (5M3D), and between the canine and the first molar (6M3D) were measured on the study models (Figures 13 and 14).

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RESULTS

Some patients mentioned a feeling of discomfort associated with the size of the distractor, but this vanished in one week. The patients did not report severe pain, but all of them reported the feeling of strain and slight pain after activation of the distractor. According to their anamnesis, this feeling lasted for 15–20 minutes, and there was no need for the use of analgesics.

Cephalometric findings

Maxillary dentoalveolar findings

In the cephalometric evaluation, U6M-y increased significantly by 0.56 mm (P = .011). The U6M-x distance increased by 0.64 mm (P = .004), the U6A-x distance increased by 0.53 mm (P = .004), and the differences were statistically significant. The U6M-y-U6A-y distance increased significantly by 0.71 mm (P = .023). A significant decrease of 5.76 mm (P = .000) was observed in U3D-y. The U3D-y-U3A-y distance decreased by 4.64 mm (P = .000), and the U3/FH angle decreased by 11.47° (P = .000). The decrease in U1/FH by 1.44° (P = .050) was also statistically significant (Table 1).

TABLE 1. Cephalometric Evaluation of Maxillary Dentoalveolar Measurements Before and After Rapid Canine Distalization

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Mandibular dentoalveolar findings

The L3D-y distance decreased by 3.5 mm (P = .026), the L3D-x distance decreased by 0.91 mm (P = .039), and these were statistically significant. The L3D-y-L3A-y distance decreased by 2.25 mm (P = .043). Finally, the L3/FH angle showed a significant increase by 7.16° (P = .043) (Table 2).

TABLE 2. Cephalometric Evaluation of Mandibular Dentoalveolar Measurements Before and After Rapid Canine Distalization

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Study model findings

Maxillary findings

In the study model evaluation the decreases in 6M2D, 5M3D, and 6M3D were 0.52 mm (P = .008), 6.29 mm (P = .000) and 6.03 mm (P = .000), respectively. All the changes were statistically significant (Table 3).

TABLE 3. Statistical Evaluation of the Maxillary Study Model Find ings Before and After Rapid Canine Distalization

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Mandibular findings

All the parameters decreased significantly as in upper study models. The decreases were 0.59 mm (P = .003) in 6M2D, 5.16 mm (P = .003) in 5M3D, and 4.96 mm (P = .003) in 6M3D (Table 4).

TABLE 4. Statistical Evaluation of the Mandibular Study Model Findings Before and After Rapid Canine Distalization

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DISCUSSION

Minimizing the orthodontic treatment time and controlling the anchorage loss are common aims of research. Rapid canine distalization is a cornerstone for these goals and was first introduced by Liou and Huang33 in 1998. Since then, however, studies35 of rapid canine distalization through distraction of the periodontal ligament are limited because the technique is primarily indicated in adults who require maximum anchorage control. In addition, individual canine retractors are not available on the market and the long-term effects are unknown.

The lag period concept is used for controlling the anchorage of posterior teeth in this technique, and the philosophy of canine distraction can be summarized as rapid distalization of the canines through the extraction socket while the posterior teeth are still in a lag period and before the orthodontic force causes undesired root resorption.33

Liou and Huang33 used fixed orthodontic appliances before first premolar extractions for leveling. We chose to not use fixed appliances before canine distraction in this study because it was thought that leveling would trigger the lag period. The movements of the canines and first molars were determined according to Sella Verticale and Frankfort Horizontal planes. Our surgical concept was similar to the one that Liou and Huang33 described in 1998. However, the authors altered the surgical technique in their next study35 and reduced the overall thickness of the interseptal bone distal to the canine with a cylindrical carbide bur. Besides, they also decreased the rate of distraction from 1 to 0.70 mm/d, diminished the intraoral canine retractors, and used them with the archwires. The distraction rate in this study was 0.75 mm/d (0.25 mm × 3). Mucosal irritations and pathological findings of the attached gingiva were not observed during canine distraction. However, the attached gingiva distal to the canine teeth showed invagination in some patients. Significant root resorption was not observed in the canine teeth as previously demonstrated by others33 because the distraction was nearly finished by the time external root resorption was just being initiated.

Liou and Huang33 found that maxillary canines distalized 6.5 mm and the mandibular canines distalized 6.6 mm in three weeks. Although these findings were not statistically evaluated, they reported the distal tipping movement was insignificant.33 In their second study,35 they reported the mean distalization of maxillary canines as 6.00 and 6.50 mm in adults and adolescents, respectively. However, despite the efforts to attain parallel canine movement, they stated that 17° of distal tipping had occurred in the adult patients. In our study, cephalometric evaluation showed a mean maxillary canine distalization of 5.76 mm, whereas the mandibular canine teeth were distalized 3.5 mm, on average. The mean distal tipping of the maxillary and mandibular canines was 11.47° and 7.16°, respectively. The distances between the distal points and apexes of the canine teeth were increased, supporting the angular measurements. This parameter decreased by 4.64 mm for maxillary canines and 2.25 mm for mandibular canines. In the study model evaluation, the average distalization of maxillary canines was 6.03 mm, whereas it was 4.96 mm for mandibular canines. However, the study model findings were not found reliable when mesial movement of the maxillary molars was considered. The mean distalization values were decreased when compared with the previous studies,3335 perhaps because of the required canine distalization of the sample.

In the cephalometric analysis, the mean mesial movement of the maxillary molars was 0.56 mm, and the mesial movement of the mandibular molars was not statistically significant. The average decrease in the distance between first molars and laterals was 0.52 mm in the upper study model and 0.59 mm in the lower study model. Study model findings were not considered reliable because the distal movement of the laterals accompanied the distal movement of the canines. Liou and Huang33 reported that 73% of the first molars did not move mesially and the average anchorage loss was 0.10 mm in the remaining 27%. The increase in the mesial movement of maxillary molars in our study was perhaps related to the different measurement method of the previous study.33

The extrusion of maxillary canines and mandibular molars was not significant in cephalometric evaluation. However, the mandibular canines and the maxillary molars were extruded 0.91 and 0.64 mm, respectively. The average extrusion of the apex of the maxillary molars was 0.53 mm, indicating mesial tipping of these teeth. The distance between the mesial point and the apex of the maxillary first molars increased by 0.71 mm, and this supports the concept of tipping. The maxillary central incisors showed 1.44° of palatal tipping, and diastemata were present between the maxillary incisors after the distraction period. The edentulous space in the maxillary dental arch was closed up to 93% at the end of the canine distalization, but same measure was 80% in the lower arch.

Fractures were observed in the interseptal bone adjacent to the apex of the canine in some of the periapical radiographs, indicating a considerable resistance to the applied force. It was considered that this might increase the potential tipping movement and the extrusive effect of the mechanism by causing the canine center of resistance to move closer to the apex. We concluded that reducing the entire thickness of the interseptal bone between the canine and first premolar would be more useful in minimizing the undesired tipping and extrusion movements of the canine teeth.

The major advantages of rapid distalization were shortening the treatment time, eliminating the need for additional anchorage, and rapid retraction of incisors using the new bone tissue distal to the lateral incisors. The average treatment time was reduced three to four months. However, varying degrees of anchorage loss were determined in some of the patients during incisor retraction, requiring additional anchorage such as a headgear or a Nance button. This indicated that the two-week consolidation period in our study was short and needed to be extended.

Considering the lag period of posterior teeth and the reorganization of the new bone mesial to the canine tooth, the need for additional anchorage during incisor retraction will reduce with an extension of the consolidation period. However, this will prolong the treatment time. We believe that the consolidation period has to be evaluated extensively in further studies and a concept needs to be determined to retract the incisor teeth without additional anchorage. In our opinion, incisor teeth can be retracted simultaneously during canine distraction using bone-supported implants. This treatment approach would not only eliminate the risk of anchorage loss but also decrease the orthodontic treatment time even further.

CONCLUSIONS

• Rapid canine distalization with the distraction of the periodontal ligament reduces the treatment time, and both the upper and lower canines can be distalized successfully in three weeks with controlled distal tipping. Incisor retraction can also be facilitated with this technique because the bone distal to the lateral incisors is still fibrous.

• Canine distraction is primarily indicated in adults presenting bimaxillary protrusion, a Class II division 1 malocclusion with maxillary dentoalveolar excess, or anterior crowding. When maximum anchorage is required, it can also be used in the treatment of adolescent patients with anterior crowding.

• The relevant teeth must be closely monitored during the distraction period.

• Currently, the canine distractors are bulky, unidirectional, and unavailable on the market. They need to be refined, developed, and oriented with fixed appliances in the future. Moreover, the long-term effects of this method are unknown and histological research is needed.