A new approach for evaluation of canine dento alveolar distraction using cone-beam computed tomography.

OBJECTIVE: The aim was to evaluate and plan the canine dento alveolar distractions (DADs) with the use of cone-beam computed tomography (CBCT).
MATERIALS AND METHODS: 5 patients are requiring 10 canine DADs were selected for the study. A custom-made DAD distractor was fabricated for the study. CBCT scans were taken prior to and post thedistraction. DAD parameters such as Canine retraction, canine and molar rotation, molar anchor loss and level of the osteotomy cut above the canine was evaluated.
RESULTS: Average canine retraction was 7.5 mm in 17 days, molar anchor loss was 0.5 mm, canine and molar rotations were 8° and 0.40° and thedistance of the osteotomy cut to the canine was1.93 mm.
CONCLUSION: The CBCT can be used to accurately evaluate the canine DADtechnique.

Orthodontic research has always been focused on the development of faster and more effective tooth movement. The canine tooth shares an important role in oral functions, esthetics, occlusion, arch shape, and stability. Their unique position connects the anterior and posterior segments of the dental arch and makes their Orthodontic movement of great clinical importance, especially in the first premolar extraction cases.

One of the most commonly used procedures in orthodontics is the retraction of canines into the space created by extraction of first premolars. Conventional methods of canine retraction are generally grouped into frictional and frictionless mechanics. The frictional mechanics involves sliding of a canine along a continuous arch wire while the frictionless method involves canine retraction with the arch wire using loops incorporated in the wire. The fastest rate of canine retraction achieved by these methods as reported in the literature is about 2 mm/month. Thus, it takes a minimum time period of 6 – 8 months to retract the canines completely into the first premolar extraction space by current conventional methods. To overcome this hurdle, the principles of distraction osteogenesis were employed to enhance the rate of canine retraction.

Distraction osteogenesis is a process of growing new bone by the mechanical stretching of the reparative bone tissue by a distraction device through an osteotomy or corticotomy site. The bone to be lengthened is segmented at an appropriate position by an osteotomy or corticotomy. The reparative callus formed between the divided bone segments is subjected to the incremental traction at the rate of about 1 mm/day with the help of a distraction device. New bone is generated in the osteotomy or corticotomy gap.

Dentoalveolar distraction is based on the principles of distraction osteogenesis, where transportation of a bone disc is used to move a dentoalveolar segment. The distraction is usually carried out by a tooth-borne appliance. As the teeth are moved more rapidly during treatment, the tissue changes elicited by Orthodontic forces are more marked and extensive. It has been assumed that the application of force will result in hyalinization caused partly by anatomic and partly by mechanical factors. The hyalinization period usually lasts 2 or 3 weeks, and tooth movement continues at a rate of 1–1.5 mm in 4–5 weeks.[12]

Imaging is an important diagnostic adjunct to the clinical assessment of the dental patient. The introduction of panoramic radiography in the 1960 's and its widespread adoption throughout the 1970 's and 1980 's heralded a major progress in dental radiology, providing clinicians with a single comprehensive image of the jaws and maxillofacial structures. The introduction of cone-beam computed tomography (CBCT) specifically dedicated to imaging the maxillofacial region heralds a true paradigm shift from two-dimensional toa three-dimensional approach to data acquisition and image reconstruction.

Although the use dental distraction osteogenesis for retraction of canines has been advocated and proved for a while,[34] the use of CBCT as an evaluative tool to plan and evaluate the technique needed investigation.

Materials and Methods

This study was conducted on five patients (three males and two females: Ten maxillary distractions) ranging in age from 15 years to 22 years who needed Orthodontic treatment with fixed appliances and the treatment plan included tooth extractions (first premolars). The study was approved by the appropriate Institutional Ethical Review Board.

Ten canine distractions were carried out with a custom-made, tooth-borne intra-oral distraction device. All patients were in the permanent dentition and had a class first molar relation with both the canine properly aligned over the basal bone at the beginning of the treatment.

Case selection criteria

The patients included in the study met the following criteria:

Treatment plan required the bilateral extraction of maxillary first premolars followed by individual maxillary canine retraction

The dentition did not exhibit any gross anatomic root anomalies as assessed from panoramic radiographs

Cases with deep carious lesions or endodontic lesions involving the maxillary canines and buccal segments were not selected

Cases with severely rotated or grossly malpositioned canines were not selected for the study

Patients who were medically fit to undergo dental extractions and the minor surgical procedures involving local anesthesia were selected for the study.

Predistraction records

The following predistraction records were obtained prior to treatment for each patient.

Lateral cephalogram

Panoramic radiographs

CBCT scan

Standard photographs (extra oral and intra-oral)

Orthodontic study models.

Device selection

A custom-made, rigid, tooth-borne intra-oral canine distraction device was designed for dentoalveolar distraction and rapid tooth movement. The device was made of stainless steel (SS) and had a distraction screw and guidance bars. The patient or parent turned the screw clockwise with a screwdriver, and this moved the canine distally. After the bands had been selected for the canines and first molars, an impression was obtained, the bands were transferred into the impression material, and the working cast was made. The canine distraction device was soldered to the bands in canine and first molars. The device consisted of an anterior section, a posterior section, a screw, and a screwdriver to advance the screw. The posterior section was soldered to the molar bands. 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 (canine tube) was soldered to canine band and included a retention arm (with rectangular tip) for the canine tube and two nongrooved slots for the sliding rod and screw.

A 360° activation of the distraction screw produced 0.4 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. The device was designed and fabricated in the Department of Orthodontics, SBDC and H [Figure 1].

Figure 1

Custom-made distractor device

Surgical procedure

Surgery was performed on an outpatient basis, at the Department of Oral and Maxillofacial Surgery, SBDC and H with the patient under local anesthesia, at times supplemented with sedation. The surgical procedure involved extractions of the maxillary first premolars as well as preparation of the alveolar bone to facilitate alveolar distraction (transport bone disc). A crevicular incision was made along the gingival margin of the incisor to the molar region and entire gingival flap was raised. Later cortical holes were made in the alveolar bone with a thin, tapered, fissure carbide bur (701-bur) from the canine to the second premolar, curving apically to pass 3 –5 mm from the apex. The same bur was then used to connect the holes around the root. Fine osteotomes were advanced in the coronal direction till the entire thickness of buccal cortical bone and including the spongious bone. The first premolar was extracted, and the buccal bone removed between the outlined bone cut at the distal canine region anteriorly and the second premolar posteriorly. The palatal shelf was preserved, leaving the sinus membrane intact to avoid interferences during the active distraction process.

Later the incision was closed with absorbable sutures, and an antibiotic and a nonsteroidal antiinflammatory drug were prescribed for 5 days. The distraction device was fitted to the canine and first molar with glass ionomer cement at the end of the surgical procedure.

The CBCT panoramic (pan)-like image, which projects the canine tooth in mesio-distal angulation accurately (DANA VAN AJO2010, 137) was taken for pre- and post-distraction The CBCT panoramic (pan)-like image was obtained by curved slicing at slice thickness of 10.2 mm. The pan image was obtained by marking the upper arch on the curved slice reconstructed image.

The following anatomic landmarks were marked from the CBCT reconstructed orthogonal slice (axial slice), for evaluating the canine retraction prior to and post dento alveolar distraction (DAD).

Incisive foramen

Perpendicular to incisive foramen

True vertical line passing through mid-palatal suture

Long axis passing through maxillary canines

Long axis passing through maxillary first molar on both the sides

Tip of the canine tooth on both upper quadrants

Mesio-buccal cusp tip of both maxillary first molars.

The following tooth movements were measured by calculating the difference between the preretraction and postretraction tooth position on the CBCT.

Anchor loss, that is, amount of forward movement of the maxillary first molars

The angulation of canine prior to surgery and after complete retraction of canine by dentoalveolar distraction technique.

Rotation of the maxillary canines

Rotation of the maxillary first molars

Total amount of space closure achieved

To determine the location for the osteotomy cut that was placed above canine and the maxillary sinus during the surgical procedure.

Cone-beam computed tomography measurements

Canine tipping (orthogonal slicing AT 58.60 mm)

The long axis of the canine was marked, and an angle was formed with the true horizontal plane. The internal angle was measured in pre- and post-distraction cases [Figure 2a and b].

Figure 2

(a and b) Surgical technique (c) Placement of distractor

Amount of anchorage loss of molar

In orthogonal slice (axial slice) incisive foramen was marked, and a perpendicular to incisive foramen was constructed in the transverse axis. The mesiobuccal cusp tip was marked and a line constructed from the same to the true sagittal plane.

Distance between the two transverse line was measured in the pre- and post-distraction CBCT images and amount of molar anchor loss was estimated [Figure 3a and b].

Figure 3

(a) Pretreatment canine inclination (b) Posttreatment canine inclination

Degree of rotation of canine

A true vertical line was marked along the mid-palatal suture, the long axis of the canine was marked and later the angle between the two lines were measured in both pre- and post-distraction CBCT (orthogonal slice) [Figure 4a and b].

Figure 4

(a) Pretreatment anchor position (b) Posttreatment anchor position

Degree of rotation of molar

The mesiobuccal cusp tip of maxillary first molar was marked, and a line constructed passing through the long axis of the molar to the true sagittal plane. The angle formed between the two lines was measured in the pre- and post-distraction CBCT and the amount of molar rotation was estimated [Figure 5a and b].

Figure 5

(a) Rotation of canine pretreatment (b) Rotation of canine posttreatment

The amount of canine retraction

The amount of canine retraction was measured both intra-orally by a digital caliper and by a CBCT scan. All measurements were carried out twice and the mean was taken as the amount of retraction.

Cone-beam computed tomography panoramic (pan)-like image in curved slice

The amount of canine retraction was measured in CBCT panoramic (pan)-like image from the distal point of the lateral incisor to the mesial point of the canine that was distracted [Figure 6].

Figure 6

(a)Rotation of molar pretreatment (b)Rotation of molar posttreatment

Evaluation of the distance of the osteotomy cut placed on the alveolus above the canine and the floor of maxillary sinus

The distance of the osteotomy cut placed on the alveolus above the canine and the floor of maxillary sinus was evaluated in oblique slice. First the floor of the maxillary sinus was marked, later the proposed osteotomy cut was marked and the least linear distance was recorded [Figure 7a and b].

Figure 7

Amount of canine retraction

Amount and rate of space closure

The distance between the contact point of the canine and lateral incisor (amount of distraction) was recorded to 0.1 mm with a digital caliper preoperatively, and at the end of the retraction. Each measurement was done twice and the mean of the two values was recorded. The number of days taken to complete each canine retraction was recorded.

Results

Space closure and time taken

The canine retraction was recorded in time intervals, that is, 0.4 mm/day that is, till the canine retracted and contacted the second premolars. Rate of canine distraction was calculated as the amount of canine distraction in mm (millimeters) divided by each time interval.

Type of canine tooth movement

Clinically and radiographically, the canines showed varying amounts of tipping, with the crowns moving more than the roots. Slight extrusion of the canines was also seen during the distraction procedure.

Anchorage loss

On an average the amount of anchorage loss in first molar is found to be 0.40 mm on right side and 0.60 mm on left side respectively. Thus, the total amount of anchorage loss was evaluated as 0.50 mm.

The distance of the osteotomy cut placed on the alveolus above the canine and the floor of maxillary sinus

The linear distance of the osteotomy cut placed on the alveolus above the canine and in proximity to the floor of maxillary sinus found to be of average 1.93 mm [Figure 8].

Figure 8

(a and b) Distance of the osteotomy cut placed on the alveolus above the canine and the floor of maxillary sinus

Discussion

The amount of canine retraction

Rapid canine retraction

The maxillary canine was distracted 7.5 mm in a period of 17 days. Clinical examination was suggestive of bodily distraction. However the radiographs revealed a mild tipping component.[Figure 9]

Figure 9

Postdistraction intra-oral

Our study compared well with those of Liou and Huang et al.[5] who in their study of rapid canine distraction achieved 6.5-6.6 mm of canine retraction.

Rate of retraction

In this study, the rate of canine retraction was 0.8 mm/day and canine distalization was achieved with in 14 – 16 days. Liou and Huang et al.[5] in their study reported a mean rate of 0.5 – mm/day and achieved canine distalization in 3 weeks. Huffman and Way et al.[6] reported a mean rate of canine retraction of 1.37 mm/month on 0.16-inch SS wire and 1.20 mm/month on 0.20-inch SS wire.

Canine tipping (orthogonal slicing AT 58.60 mm)

In this study tipping of canine was on an average of 8°. This is due to the force geometry and relates to the point of application of the force.

Liou and Huang et al.[5] reported 17° of canine tipping during rapid canine distraction. They attributed that to the tipping, the position of the distraction device and the overall length of the tooth. Ideally the distraction device should be located as close to the canine's center of resistance as possible in order to reduce tipping of the canine. As, it is clinically impossible to achieve the desired device orientation due to a shallow buccal vestibule; thedevice must be placed at a compromised position to prevent impingement of the muscosal soft tissues. They also suggested that the tipped canine could be uprighted during a retraction of the anterior teeth and finishing procedures.

Amount of anchorage loss of molar

In this study anchorage loss of molar was 0.5 mm. Liou and Huang et al.[5] stated that any technique that takes longer than 3 weeks to retract a canine would result in loss of anchorage. Not only the canine, but also the anchor unit would start to move at the end of the lag period. The average time of a canine retraction with conventional methods takes 4 ߝ 6 months. However, by this time the anchor unit also moves forward. The best way to avoid losing anchorage is to move the canine before the anchor unit moves.

Sayin et al.[7] in their study showed about 0.52 mm of anchorage loss during rapid canine retraction. In this study, the canine distraction was completed while the first molar was still in its lag period or just initiating its mesial movement. Hence, the anchorage loss of molar was about 0.5 mm.

Degree of rotation of canine and molar

The mean rotation of canine was 8° and molar rotation was 0.40°, which was negligible. The probable cause of the lower rotation could be attributed to the rigidity of the appliance. In spite of the rigidity, there was some rotation that could be due to the dentoalveolar segment, which is a free segment, and the buccal force of distraction appliance could have probable caused minimal rotation of canine.

Evaluation of the distance of the osteotomy cut placed on the alveolus above the canine and the floor of maxillary sinus

In our study, the average distance was 1.93 mm for the osteotomy cut placed on the alveolus above the canine and the floor of maxillary sinus. As the canine is placed very close to the maxillary sinus, an accurate evaluation of the distance of the canine tip to the sinus floor would assist the maxillofacial surgeon to plan the osteotomy cut for the DAD thereby reducing the chance morbidity of this procedure.

Summary

Dentoalveolar distraction of the canine is an established protocol, with minimal side effects and with the added benefit ofreduced treatment time and anchor loss

CBCT has found varied uses in dentistry in general and orthodontics in particular, this study highlights yet another innovative use of this revolutionary technology in orthodontics.