Periodontal ligament distraction: A simplified approach for rapid canine retraction.

Distraction osteogenesis is a method of inducing new bone formation by applying mechanical strains on preexisting bone. The process of osteogenesis in the periodontal ligament during orthodontic tooth movement is similar to the osteogenesis in the midpalatal suture during rapid palatal expansion. A new concept of "distracting the periodontal ligament" is proposed to elicit rapid canine retraction in two weeks. At the time of first premolar extraction, the interseptal bone distal to the canine was undermined with a bone bur, grooving vertically inside the extraction socket along the buccal and lingual sides and extending obliquely toward the socket base. Then, a tooth-borne, custom-made, intraoral distraction device was placed to distract the canine distally into the extraction space. It was activated 0.5 mm/day, immediately after the extraction. Canine was distracted 6.5 mm into the extraction space within two weeks.

INTRODUCTION

Conventional orthognathic surgery and craniofacial reconstruction have experienced widespread success, but several limitations are associated with these treatment modalities. Distraction osteogenesis is the process of new bone formation at the vascularized margin of bone segments separated by incremental traction. The most common technique in distraction osteogenesis is mechanical stretching of the reparative bone tissue by a distraction device through an osteotomy or corticotomy site.[1] With this technique, new bone is generated in the gap of osteotomy or corticotomy at the approximate rate of 1 mm per day.

This procedure was used as early as 1905 by Codivilla[2] and later popularized by the clinical and research studies of Ilizarov[3-5] and Ilizarov et al.[6] In 1992, distraction osteogenesis was first applied to the human mandible by McCarthy et al.,[7] and since then, it has been applied to all the bones of the craniofacial skeleton, including the mid face and maxilla.

Orthodontic tooth movement is a process in which a mechanical force is applied to induce alveolar bone resorption on the pressure side, and alveolar bone deposition on the tension side.[8] On the tension side, the periodontal ligament is stretched (distracted) and followed by alveolar bone deposition (osteogenesis). The periodontal ligament is a “suture” between alveolar bone and tooth. The process of osteogenesis in the periodontal ligament during orthodontic tooth movement is similar to that in the midpalatal suture during rapid palatal expansion or to that in the midface sutures in the growing animal during mid face distraction. The major difference is the rate of osteogenesis. The regular rate of osteogenesis in orthodontic tooth movement during canine retraction is about 1 mm per month, which is much slower than that in distraction osteogenesis. Periodontal ligament can be distracted just like the midpalatal suture in rapid palatal expansion. Liou and Huang[910] first applied this concept to orthodontic tooth movement and performed rapid canine retraction through distraction, since that there is scarcity of literature about it. In this case report, a technique of rapid canine distraction through the periodontal ligament is presented.

CASE REPORT

A 16-year-old post pubertal female with Angle's class I malocclusion with bimaxillary protrusion presented to our department for orthodontic treatment. According to the protocol of our department, all the essential orthodontic diagnostic records including facial photographs [Figure 1] were taken and analyzed. Treatment plan for this patient was fixed orthodontic mechanotherapy with extraction of all four premolars and retraction of anterior teeth. As with conventional orthodontic mechanotherapy retraction of canine takes around five to seven months. To reduce the treatment time, we have decided to retract the canine by distraction device. Patient was informed about the treatment procedure, and a written informed consent was obtained.

Figure 1

Photographs of patient (a-d) before orthodontic treatment

Distraction device

The individual canine distractor was a tooth-borne, semi-rigid device. After the bands were fabricated for the canine and first molar, an impression was obtained, the bands were transferred into the impression material, and the study cast was made. The device consisted of an anterior section, a posterior section, a screw, and a hex wrench to advance the screw [Figure 2]. A 360° activation of the screw produced 0.5 mm of distal movement in the canine tooth.

Figure 2

Distraction device and lab procedure (a-c)

Surgical procedure

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 [Figures 3 and 4]. The distractor was cemented in place after the surgery. Slight swelling was observed on the patient's face after the surgery, and it was resolved after three to five days, postoperatively.

Figure 3

Vertical and oblique osteotomies (dotted line) for undermining bone distal to canine

Figure 4

Clinical intraoral photograph (a-c) of extracted tooth and surgical technique

Distraction protocol

The distraction was initiated just after the surgery. An advancement of 0.5 mm was performed per day, until each canine tooth was distracted into the desired position in two weeks. The patients were closely monitored during the distraction period, and at the time of the activation of the device to retract the canine, patient often felt pain, but pain was subsided after 5 to 10 minutes of the device activation. Intraoral photographs of a patient, before and after rapid canine distalization, are shown on right side [Figures 5 and 6] and on left side [Figure 7], in the mandibular arch. Initially, we have planned the distraction of maxillary and mandibular canines simultaneously, but our canine distractor was bulky, as we have used custom made distractor which was inexpensive. So, we planned to distract the maxillary and mandibular canine separately.

Figure 5

Intra-oral photograph of patient before distraction on right side in mandibular arch

Figure 6

Intra-oral photograph of patient at end of distraction on right side in mandibular arch

Figure 7

Complete canine distraction procedure with retention device on left side in mandibular arch

DISCUSSION

Reducing the orthodontic treatment time and controlling the anchorage loss are common aims of research in modern orthodontic practice. Rapid canine distalization is a cornerstone for these goals, and was first introduced by Liou and Huang in 1998. Since then, however, studies of rapid canine distalization through distraction of the periodontal ligament are limited because individual canine retractors are not available on the market and the long-term effects are unknown. We have observed that degree of the patient problem in terms of pain and discomfort vis a vis regular canine retraction and enmasse retraction using microimplants was more with this procedure, especially during the osteotomy, to reduce the bony resistance, and during the activation of the device, to distract the canine. After the seven days of the surgery, patient was completely comfortable with no report of pain and discomfort. Clinically, after the completion of distraction procedure, periodontium was sound with considerable amount of keratinized gingival and radiographically newly formed bone, which was indistinguisible after three to four months of distraction. We closely monitored the canine root during distraction period as the canine distraction was completed within two weeks, while the root resorption is initiated two to three weeks, after the orthodontic force is applied, and may continue for the duration of force application. The best way to minimize the root resorption induced by orthodontic tooth movement is to complete the tooth movement in short duration or even before the initiation of root resorption. 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. With this technique, the average orthodontic treatment time can be reduced three to four months.

CONCLUSION

By using this concept, canines can be distracted distally in premolar extraction space in three weeks without significant complication. However, the clinical techniques and procedures in canine distraction still need to be refined. This new concept and technique is best used on those cases whose anterior teeth are severely crowded or protruded. The canines can be distracted rapidly, and almost all of the extraction space can be used for anterior dental alignment or retraction. After distraction, the anterior tooth retraction can be rapid as well, while the new bone tissues distal to the lateral incisors are still fibrous. In addition to orthodontic tooth movement, we might possibly use this new concept and technique to generate new bone and keratinized gingival tissue for treating periodontal disease.

Currently, the canine distractors are bulky, unidirectional, and unavailable in 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 clinical and histological research is needed.