Changes in Canine Angulation after Dentoalvelaor Distraction with a Rigid Maxillary Intraoral Distractor: A Radiographic Study

Distraction osteogenesis (DO) is a process of growing new bone by mechanical stretching of the preexisting bone tissue.1 It has gained its widespread recognition in orthopedic surgery as an effective means of bone lengthening, deformity correction and filling large diaphyseal defects. Recently distraction osteogenesis has been extensively applied to the craniofacial complex and is increasingly becoming a viable treatment option in the correction of craniofacial deformities.


INTRODUCTION
Most orthodontic patients present with tooth crowding.
Although non-extraction treatment has become very popular during the last decade many patients do need extractions. 2 The first phase of treatment in premolar extraction case is the distal movement of the canine with conventional techniques. Extraoral or Intraoral anchorage is required during canine distalization particularly when maximum anchorage is required.
Biologic tooth movement with canine retraction phase usually lasts for 6 to 8 months. The duration of treatment is one of the problems that orthodontic patients complain mostly by adults. To address this problem dentoalveolar distraction osteogenesis (DAD) technique has been developed.
In the present technique of rapid orthodontic canine retraction through distraction osteogenesis as described by Reha-kisnisci and Halukiseri; 2 the dentoalveolus is itself is designed as a bone transport segment for posterior movement. Vertical osteotomies are performed around the root of the canine followed by splitting of spongy bone around it. Therefore the design of surgical technique itself does not rely on the periodontal stretching which obviates overloading and stress accumulation in this tissue, which was the drawback of the previous attempts of canine distraction through periodontal ligament as described by Eric Liou, Shing Huang. 3 This procedure does not require any extraoral force and has significant clinical application. 4,5 A tooth can be moved into the fibrous new bone created by the distraction process at a rapid rate. 6 Thus using distraction osteogenesis technique rapid tooth movement can be achieved. The purpose of the study was to evaluate the changes in canine angulation after dentoalvelaor distraction with a rigid intraoral distractor in the maxilla.  The osteotomy was continued and curved apically passing 3 to 5 mm from the apex. A vertical osteotomy was made in a similar manner along the posterior aspect of the canine tooth. A thin tapered fissure bur was used to connect the holes around the canine root. The root of the canine was then outlined anteriorly and posteriorly with a cone shape at the apical region. Fine osteotomies were then introduced and advanced in the coronal direction. The bone apical to the extraction socket and the possible bony interferences at the buccal aspect that may be encountered during the distraction process were eliminated and smoothened between canine and second premolar with the preservation of the palatal cortex. Osteotomies were then used along the anterior aspect of the dentoalveolar segment that includes the canine tooth to split the surrounding bone around its root off from the palatal cortex and neighbouring teeth. The osteotomy cut was performed between the palatal cortex and the palatal aspect of the canine root, taking care of the canine root, without involving the lamina propria using a thin curved spatula osteotome keeping it close to the palatal cortex. The transport dentoalveolar segment includes the buccal cortex and the underlying spongy bone that envelopes the canine root, leaving an intact apical, palatal cortical plate ( Figure 2).

Sliding rod is soldered to
The wound was irrigated with saline and closed in a single mucosal layer with 3-0 catgut suture. The distraction device was fitted and cemented to the first molar and canine teeth at the end of the surgical procedure. The patient was prescribed antibiotics and anti-inflammatory drugs for 5 days. Dentoalveolar distraction was started on the day of surgery and continued at a rate of 0.5 mm twice a day. There was no latency period. It was discontinued when the canine tooth moved posteriorly into the desired position.
The distracted dentoalveolar segment after distraction was kept for 3 months of consolidation period till the radiographic evidence of bony regenerate was confirmed. Later orthodontic therapy was carried out with fixed appliance. During and after the completion of activation phase, as well as during early and late consolidation periods, the following records were obtained for each patient;

Determination of canine tipping
To analyze inclination of canine, lateral cephalometric radiographs were taken before and after canine distraction ( Figure 5). Orientation markers were fabricated using custom made acrylic zigs with brackets on canines to be distracted with Stainless steel wire soldered vertically to the canine band. The canine brackets with vertically oriented markers were temporarily ligated in patient's mouth, which invariably coincided with crown and root angulation of canine. Cephalometric radiographs were taken with the orientation markers in place before the placement of distraction device pre-operatively. These markers were removed after initial cephalogram and were stored with the name of the patient and the side of the canine specified. At the end of the canine distraction (consolidation phase), after the removal of the distraction appliance, postoperative cephalogram was taken again with the same markers which was temporarily ligated to the canine brackets. Figure 5: Cephalometric radiographs; before & after procedure The composite tracing was done on the pre-distraction and post-distraction lateral cephalograms. The amount of canine tipping was measured with reference to palatal plane (ANS-PNS) using ANS as the reference point. The amount of canine tipping was calculated by difference of tip between the markers in pre-distraction and postdistraction cephalometric radiographs. Thus the angulation of the canine to the palatal plane was measured. Each measurement was made twice and the values were recorded. (Table 1)

RESULTS
The results were evaluated based upon clinical and radiographic findings (Figures 6,7). Clinically and radiologically, although some canines tipped slightly after distraction most of the canines moved bodily with minimal amount of tipping of about 3.4 o on an average. In our study, maximum amount of tipping occurred was 10 o and minimal amount of tipping occurred was 2 o . Canine roots were parallel to the long axis of second premolar after the distraction.
Immediate post operative complications were slight discomfort, pain and swelling over the surgical site, tenderness over premolar-molar regions, injury in the cheek due to impingement of distal end of the distractor screw. These problems were subsequently resolved within one week post-operatively. Impingement of distractor screw was managed by cutting the appropriate length of the screw end. Orientation of the distraction device was parallel to the maxillary occlusal plane and distraction vector orientation was horizontal. It is said that tipped canine can then be uprighted during retraction of the anterior teeth and finishing procedure later. Also considerations should be given that the canine on the recent extraction site move faster than that on the healed side, but with more amount of tipping, as the centre of resistance of tooth may be located further apically and bone distal to canine being denser near the apex than the marginal area.