September 10, 2019
by Paul J. Helpard, BSc, DDS, MS, Certificate in OrthodonticsJ. Helpard, BSc, DDS, MS, Certificate in Orthodontics
Impacted maxillary canines are a relatively rare but always memorable clinical presentation. They occur in just two per cent of the population. Eighty-five per cent of the time, the canine impaction is facial. This usually occurs as a result of excessive crowding. Fifteen per cent of the time canine impaction is palatal. The palatally impacted canine is three times more likely to occur in females than males and is two times more likely to be unilateral versus bilateral.1
Palatal canine impaction can be of environmental, genetic or pathologic origin. For practical purposes it is important to know that maxillary canines should erupt between the ages of 10 and 12, and should do so similarly on both the right and left sides. If this doesn’t happen then a clinical and radiographic evaluation should be undertaken.
The maxillary canine starts to calcify as early as the first molar but takes nearly twice as long to erupt. It has the longest period of development, the deepest area of development and a complicated path of eruption. This makes it susceptible to environmental influences.2 It is commonly believed that a small, malformed or missing adjacent lateral incisor plays a role in the ectopic eruption and possible impaction of the maxillary canine. This is known as the guidance theory, which hypothesizes that the root of the adjacent lateral incisor is an important determinant of the eruption path of the canine.3
Peck et. al.4 have postulated that palatal impaction occurs as a result of polygenic multifactorial inheritance. They base this on the following observations:
1. Occurrence with other dental anomalies,
2. Bilateral occurrence,
3. Sex differences in occurrence,
4. Familial occurrence; and
5. Population differences in occurrence.
The most common pathological origins of canine impaction are the dentigerous cyst and a supernumerary tooth.
Clinical palpation of the erupting maxillary canines should be possible by the age of 10. The clinician should be able to feel two round bulges of 5 to 10 mm in diameter distal to the erupted permanent lateral incisors and apical to the deciduous canine. If these bulges can’t be palpated or if only one side is obvious then a panoramic radiograph should be taken.
The following signs should be observed in that radiograph:
1. Stage of resorption of the deciduous canine root: if there is minimal root resorption and the crown of the permanent canine is overlapping the root of the deciduous canine then it is likely that the permanent canine is palatally displaced. Palatal displacement by definition means that the permanent canine is deflected into the palate on its path of eruption but is not impacted or unable to erupt naturally.
2. Inclination of the permanent canine relative to the occlusal plane. The steeper the inclination the more likely the canine is palatally displaced.
3. The cusp tip of the erupting canine overlapping the root of the adjacent lateral incisor root is an indication of palatal displacement and possible palatal impaction.
4. Vertical position of the cusp tip. The more superiorly the cusp tip the more likely that the canine is palatally displaced.
Extraction of deciduous canines
The position of the canine cusp tip relative to the root of the adjacent lateral incisor on a panoramic radiograph is the most important determinant in how best to manage the situation when a permanent canine cannot be palpated facially.
Ericson and Kurol5 introduced the concept of sectors to help determine if the extraction of the deciduous canine would help normalize or improve the path of eruption of a palatally ectopic canine. This author uses a modified ‘zone’ concept based on an adaptation of the Ericson and Kurol data and his clinical experience to determine if the extraction of the deciduous canine would allow for the eruption of the permanent canine (Diagram 1).
Location of the cusp tip of a palatally displaced canine determines the likelihood of permanent canine eruption with the extraction of the overlying deciduous canine. In Zone 1 there is a 90% chance of eruption, Zone 2: 65% and Zone 3: 0%.Adapted from Erickson and Kurol.5
When the cusp tip of the permanent canine is distal to the root of the adjacent lateral incisor then the canine is in Zone 1. Extraction of the deciduous canine in this instance leads to normal eruption 90 per cent of the time (Figs. 1A & 1B).
Panoramic radiograph male age 11y6m. The cusp tip of 1.3 is in Zone 1. The deciduous canines were extracted at this time.There is a 90% chance that 1.3 will erupt normally.
Panoramic radiograph of the same patient 14 months later at age 12y8m.
When the cusp tip of the permanent canine is past the distal surface but not past a line down the mid-root of the adjacent lateral incisor then the canine is in Zone 2. Extraction of the deciduous canine leads to normal eruption of the affected canine 65 per cent of the time (Figs. 2A & 2B). Thirty-five per cent of the time, the palatally displaced canine in zone 2 becomes palatally impacted (Figs. 3A & 3B).
Panoramic radiograph of male age 13y1m. The cusp tip of 2.3 is in Zone 2. The deciduous canine was extracted at this time.There is a 65% chance that 2.3 will erupt normally.
Panoramic radiograph of the same patient 14 months later at age 14y3m.
Panoramic radiograph of female age 10y4m. The cusp tip of 2.3 is in Zone 2. The deciduous canine was extracted that this time.There is a 35% change that 2.3 will not erupt normally.
Panoramic radiograph of the same patient 8 months later at age 11. 2.3 is palatally impacted. The extraction of the deciduous canine did not allow for normal eruption.
When the cusp tip of the permanent canine is past a line down the mid-root of the adjacent lateral incisor then the canine is in Zone 3. In this case the canine can be identified as being palatally impacted and the extraction of the deciduous canine will not lead to the normal eruption of the affected canine (Figs. 4A & 4B).
Panoramic radiograph from referring dentist of female age 11y3m. The cusp tip of 1.3 is in Zone 2 and the cusp tip of 2.3 is in Zone 3. There is a 65% chance that 1.3 would have erupted with the extraction of 5.3 and a 0% chance of 2.3 erupting with the extraction of 6.3.
Panoramic radiograph of the same patient taken 17 months later at age 12y10m upon referral to the author. Both 1.3 and 2.3 are palatally impacted. Ideally both canines should have been surgically exposed at age 11y3m to allow for autonomous eruption. The deciduous canines should have been left in place.
The advent of composite bonding to enamel in the 1960’s led to the development of the closed eruption technique of impacted canine treatment. Closed eruption means that the impacted canine is surgically exposed with a palatal flap, some or all of the bone covering the crown of the canine is removed and an eyelet with an attached chain is bonded to the crown. A hole is made in the flap through which the chain exits and the flap is sutured back into place against the palate. The orthodontist then applies traction to the chain to effect movement of the impacted canine facilitating its eruption through the palatal tissue.
Prior to the 1960’s canines were open exposed.2 This involved a similar exposure of the impacted canine with the elevation of a full thickness palatal flap. All bone covering the canine crown is removed to the level of the CEJ being careful not to injure the CEJ. This could lead to external root resorption. A hole the size of the canine crown is made in the palatal flap before the flap is sutured in place. Periodontal pack is placed in the hole of the flap. One week later the pack is removed by the orthodontist (Fig. 5). The patient should be seen one month later to ensure proper healing and no overgrowth of the crown. If there is evidence that the hole is diminishing in diameter an attachment can be bonded to the canine crown. If the hole does close for some reason then it should be re-opened by the surgeon. This is a simple procedure, which could be done with laser or scalpel.
Open exposure of 1.3. Note that 5.3 is still in place and has a bracket on it.
An open exposure should be performed when a canine is determined to be palatally impacted. The root of the permanent canine should be one half to two thirds formed so that it is in a state of active eruption. This can be done as early as nine years of age.
The deciduous canine should be left in place at the time of the exposure for several reasons:
1. It provides esthetics during the period of time the permanent canine is erupting or being orthodontically moved towards the alveolus.
2. A bracket can be placed on it during active orthodontic treatment to provide arch form and anchorage.
3. It preserves the facial alveolar bone prior to moving the permanent canine into place.
4. Extraction of the deciduous canine just prior to moving the permanent canine into the alveolus gives two advantages:
a. It leaves a bony socket, which creates a regional acceleratory phenomenon6 particularly if the root of the deciduous canine is minimally resorbed.
b. It leaves a defect in the alveolar soft tissue, which lessens tissue bunching as the permanent canine is moved into the alveolus. This results in better periodontal outcomes and more ideal gingival margins at the completion of orthodontic treatment.
Advantages of open exposure
The open exposure can be done prior to a patient being ready for orthodontic treatment. The tooth is able to erupt into the palate and away from the adjacent incisors thereby lessening the risk of the canines resorbing them. The canine generally erupts to the level of the occlusal plane but remains palatally positioned. In essence the problem is reduced from an impaction to a crossbite.
Generally following the open exposure the periodontal ligament becomes functional. In an adult the PDL of an impacted tooth can experience atrophy of disuse, which makes spontaneous eruption less likely, and extrusive orthodontic forces may have to be applied.7 In the case of the closed exposure the primary stimulation of the PDL comes with active force application.
With open exposure there is less risk of undermining resporption of the overlying palatal bone, which results in leaving better bone support on the tension side of the root of the tooth. With the closed exposure approach there is a greater risk of undermining resorption during the application of traction particularly if sufficient bone covering the crown was not removed at the time of exposure.8
There are three phases of movement of the palatally impacted canine into its final position.
1. Movement in the palate. The canine may require extrusion, lateral movement towards the alveolus and rotation. The final position of the canine in this phase is directly lingual to the deciduous canine, known as the docking position. These movements can be accomplished with auxillary appliances and attachments as necessary (Fig. 6).
1.3 in the docking position following movement in the palate. At this point the patient is sent to have 5.3 extracted.
2. Movement into the alveolus. Once the canine is docked it is time to have the deciduous canine extracted. At docking the canine must be properly vertically positioned such that the cusp tip is at the plane of occlusion. There must be sufficient arch length at the site of the canine. An overlay round small diameter nitinol arch wire is very effective in moving the canine quickly into the alveolus. It is very important that there is a full size rectangular base arch wire in place with a v-bend stop mesial to first molar brackets with a cinch on the distal. This ensures that there are no reactionary forces to the movement of the canine. The overlay wire should extend to the distal of the premolars through auxillary slots on the premolar brackets as found on Damon Q or Speed brackets. This allows the overlay wire to slide without friction as the canine moves into the alveolus (Fig. 7).
An overlay wire in place moving 1.3 into the alveolus. Note that the base wire has a v-bend stop mesial to the first molar brackets and a cinch on the distal.
3. Final positioning of the crown and root of the canines. Once the canine is positioned in the alveolus, it is important to take a progress panoramic radiograph to evaluate root tip. The root torque can be evaluated with CBCT imaging or simply by palpating the root of the canine in the alveolus. It is important to provide adequate buccal torque of the canine roots to limit future relapse potential. This is most easily accomplished if the crown of the canine is in a Class I relationship with the opposing arch.
In an ideal finish the ginvigal margin of the impacted canine is ideally positioned relative to the CEJ with a normal biological width. The open exposure technique is known to result in a better alveolar bone and periodontal response.9 The biomechanical process of tooth movement described here limits tissue bunching as the canine is moved into position. Excellent oral hygiene is critical to a healthy periodontal outcome.
If the gingival margin(s) are not ideal then the following factors should be considered and managed as necessary:
1. Inflammation: improved oral hygiene.
2. Excess tissue: gingival recontouring to establish a normal biological width.
3. Short anatomical crowns: this can only be managed with crown lengthening and restorative care.
4. If the root is too lingually inclined the gingival tissue will rest lower on the crown of the tooth. This would require the application of further orthodontic tooth movement to torque the root buccally.
Palatally impacted canines are highly prone to relapse even when ideally positioned. They tend to intrude, move lingually and rotate. A bonded lingual wire from canine to canine is necessary to prevent intrusion and rotation (Fig. 8). A removable retainer worn at bed time will help prevent lingual movement of the canine. If possible, a clear full coverage retainer extended to the gingival margin of the canine also helps prevent intrusion. Also helpful is a circumferential supracrestal fiberotomy. This can be performed in conjunction with gingival recontouring if necessary.
Bonded lingual retainer from canine to canine. This patient had palatal impaction of 1.3 and 2.3.
In summary, the most important takeaways for the predictable management of palatally impacted canines are the following:
1. Open exposure as soon as palatal impaction is detected provided there is one half to two thirds formed. This will allows for autonomous eruption.
2. Leave the ‘c’ in place until the ‘3’ is docked.
3. Ensure adequate canine root torque and finish in a Class I relationship.
4. Retain with a bonded lingual 3 to 3 wire and removable retainer. In addition, perform a circumferential supracrestal fiberotomy.
About the Author
Dr. Helpard is in the private practice of orthodontics on Vancouver Island, British Columbia. He is a consultant orthodontist on the Cleft Palate and Craniofacial Anomalies Team at BC Children’s Hospital. He is also a Clinical Assistant Professor in the Graduate Orthodontics Program at the University of British Columbia. Dr. Helpard is a Fellow of the Royal College of Dentists of Canada and has also served as an examiner. He is a Diplomate of the American Board of Orthodontics and is a Member of the Northwest Component of the E.H. Angle Society.
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