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Iatrogenic, appliance-generated, obstruction of impacted maxillary canines

Published: October 2014

Bulletin #37 – October 2014

Iatrogenic, appliance-generated, obstruction of impacted maxillary canines

In last month’s bulletin1, I discussed the case of a young child whose unerupted maxillary permanent canines were in an ectopic location which appeared certain to result in their bilateral impaction. Orthodontic correction of the orientation of the roots of the adjacent incisors was used as a preventive measure to alter the relationship between the canines and the lateral incisor apices. This alteration in the environment encouraged the canine teeth to adopt a normal path of eruption.

In the present bulletin, a case of bilateral canine impaction is presented in which the exact opposite situation occurred. Here, an orthodontic appliance was used with the intention of creating space for the canines. Instead however, the roots of the lateral incisors were unintentionally moved in the opposite direction, thereby complicating the impaction of both canines. On the one side, the canine had become obstructed by the incisor root, while on the other, the canine and the incisor had become transposed.

The female patient was 17 years of age at her only visit to my office, on July 4 2014, on the recommendation of the treating orthodontist and oral surgeon. The patient had been in orthodontic treatment with the orthodontist for the past 4 years.

Her medical/surgical history revealed a background of benign lymphatic malformation of the upper lip, which had been treated surgically in Boston several years earlier. At examination, her appearance was good, with some relatively minor asymmetric residual swelling of the upper lip. There was a related loss of height of the labial sulcus in the upper jaw, presumably associated with adhesions and scarring of the oral mucosa from the surgical procedures.


Fig. 1a-e. intraoral views of the of the dentition after space had been re-opened in the canine region to accommodate the impacted canines. The right second premolar bracket had debonded. The pigtail stainless steel ligature can be seen attached by a traction elastic tie to the premolar bracket.


Fig. 1d, e. A front view, with the teeth apart and an occlusal view, showing space opening for the canines and the widened premolar area.

The malocclusion was defined as Angle’s class 1 bimaxillary protrusion, with large teeth and a mild degree of lower incisor crowding (Fig. 1a-e). The molar relation was normal. A fixed multibracketed edgewise appliance was present in the upper jaw, which had brought about alignment of the teeth and the creation of space in both canine regions to accommodate the two unerupted maxillary permanent canines. A full thickness rectangular NiTi archwire was in place. However, there was also uncontrolled widening of the premolar area into a buccal crossbite. The maxillary canines were impacted although only the left one had been surgically exposed 2 years earlier, followed by the application of traction in the direction of the bracket on the first premolar. The patient’s complaint was that there appeared to be little or no progress in the treatment of the left side, while nothing had been done about the right canine.


Fig. 2. The 2006 panoramic radiograph of the early mixed dentition and showing the maxillary canines very high up and in close relation with the incomplete root apices of the lateral incisors. The unerupted right first premolar is tipped distally and the early development of the root has encroached mesially on the eruption path of the canine.

The patient produced a series of 4 panoramic radiographs starting from 2006 and 2 separate CBCT imaging records taken in 2010 and 2014, respectively. The panoramic view from June 2006 was taken when the patient was 9 years old and it showed that all her permanent teeth were developing with the exception of the third molars (Fig.2). Both permanent canines could be seen high in the maxilla and appeared to be following a more mesial path than normal, with the left one in the process of mesially by-passing the lateral incisor. The right canine was closely related to the wide open apex of the lateral incisor, while the adjacent and unerupted right first premolar had a mild but abnormal distal crown angulation. A degree of crowding was clearly visible on the film, in the anterior regions of both jaws.


Fig.3. The 2008 panoramic view of the late mixed dentition. The two impacted canines have acquired enlarged follicles and have reached the distal of the central incisor roots, by-passing the lateral incisors.

The December 2008 panoramic view showed both canines still very high up, with the left one showing a greater degree of vertical development than the right one but, at this point, both were in close proximity of the distal side of the roots of the central incisors and both displayed enlarged follicles (Fig. 3). Orthodontic treatment had not commenced at that time.


Fig. 4. The May 2013 film shows how the bonded appliance has tipped the roots of the lateral incisors distally, creating a partial transposition with the mesially tipped canines. An attachment is present on the unerupted left canine and a steel ligature can be seen leading from it directly towards the first premolar.

The May 2013 panoramic film showed the orthodontic appliance in place (Fig. 4). Space had been achieved at the occlusal level between the crowns of the lateral incisor and first premolar on each side. However and presumably due to misjudged bracket placement on the lateral incisors, the roots of these teeth had been distally tipped, where they were in close proximity to the roots of the first premolars. The right unerupted canine had not been exposed and its location was largely unchanged, although its relationship to the distally moved apex of the lateral incisor had now been severely worsened. The left canine had been surgically exposed and an attachment bonded. The subsequent traction, using a steel ligature to the premolar, had brought the tooth down to a minimal degree, but it could now be seen to be wedged between central and lateral incisor.


Fig. 5. The November 2013 panoramic view showing no appreciable progress.

From the panoramic film taken a half year later, in November 2013, there appeared to have been little significant change in the positions of either impacted canine, which is not surprising since the right canine was still untreated and the left was being continuously drawn to the premolar region while being trapped between lateral and central incisor (Fig. 5).

A pre-treatment cone beam CT had been taken in June 2010 and comprised only a single printed page of transaxial cuts, with no labeled grid guide to show where these cuts were made and to which side of the patient they referred. No other print-outs from this CBCT scan were available and the radiology institute no longer had these records in its archive – a serious display of disregard for the standard of care, on the part of the institute.


Fig. 6a. The graded section of the CBCT version of the panoramic view of the untreated right side. Parts b, c & d are transaxial “slices” through the ridge at cuts 29, 17 and 8 respectively on the grid of the panoramic view and reoriented to comply with it. Parts e, f & g are axial cuts to show how the apex-crown orientation of the canine straddles the alveolar ridge from lingual to labial, between the roots of the lateral and central incisors.

A second CBCT was taken in February 2014 and it illustrated the impacted right canine with no apparent pathology and with a good root. The tooth was oriented labio-lingually across the dental arch, at the level of the apical third of the roots of the other teeth, with a strong mesial tip and its root apex palatal and crown labial to the lateral incisor. The mesial aspect was located in the lateral aspect of the root apex of the central incisor, while the extreme tip of the crown was on the labial side of the alveolar ridge, unerupted and high in the sulcus. Its relationship to the lateral incisor had been reversed and a transposition had been created by the iatrogenic, appliance-generated, distal displacement of the root of the lateral incisor (Fig. 6).


Fig 7a. The graded section of the CBCT version of the panoramic view of the treated side. Parts c, e and f show the contact of the crown of the canine with the root of the lateral incisor. The root of this lateral incisor is being labially torqued by the rectangular archwire and directly iimpinging against the canine. This is overwhelming the canine from responding to the distal traction applied to it. The axial cut in part d shows the right canine root to be located in the medial bony partition between maxillary sinus and nasal cavity.

As we have already noted, the root apices of both lateral incisors had been distally displaced by the orthodontic appliance. However, their roots were also lingually displaced to a marked degree, no doubt due to the influence of the labial locations of the unerupted canines. With a full thickness rectangular NiTi archwire ligated into the teeth of the maxillary dentition, there was a strong labial torqueing moment on both lateral incisors. This had obviously brought about a clash between the root end of the left lateral incisor and the canine, which was the most likely cause of lack of progress in moving the unerupted left canine distally (Fig. 7). The same torqueing moment acting on the right lateral incisor was similarly a contributory cause preventing the right canine from autonomously migrating in a downward direction.

To complicate matters still further, the axial (horizontal) cuts of the CBCT show the root apex of the right canine to lie on the medial aspect of the maxillary sinus, on the partition wall between the sinus and the nasal cavity. This effectively means that the tooth will require much labial roots torque, following its relocation in the dental arch and, drawing the tooth to the lateral incisor location and accepting the transposition, would appear to be an acceptable remedy for the problem.

Attempting to move the right canine distally around the lateral incisor to its place in the arch is an option, but treatment would be considerably longer and the prognosis of each of the teeth consequently poorer.

One further factor which often goes unnoticed in these situations is the orientation of the premolar teeth.2, 3 On both sides of the jaw in this case, the premolar roots were tipped mesially and in close proximity to the roots of the canines, which can unquestionably contribute to the resistance to movement of the teeth.

Recommendations for treatment:

1. Relocate the brackets on the premolars to over-upright the roots of these teeth distally and rotate the tooth in a mesio-lingual rotation, thereby to distance the palatal root from contact with the root of the mesially angulated canines. 2, 3

2. Surgical exposure of the right canine, from high on the labial side to avoid the resorbing area of the central incisor and traction using an auxiliary labially-directed ballista-type spring, initially.

3. Redirect the twisted steel ligature on the left canine to permit labial traction

4. Relocate the bracket on the left lateral incisor for mesial uprighting on a round cross-section archwire. The use of a rectangular archwire is strongly contraindicated.

5. Use a labially-directed auxiliary ballista-type springs, piggy-back style, to move the left canine crown labially around the root of the incisor, before re-applying distal traction once the tooth is clear.

On the right side, as noted above, one may feel justified in accepting the iatrogenically created transposition and align the canine and lateral incisor in their reversed order, particularly since the patient has already experienced 4 years of orthodontic treatment. For this option, it will be necessary to move the right lateral incisor distally into the canine location, expose the right canine and draw it labially, erupting it inferiorly in the line of the arch in the place of the lateral incisor.

Nevertheless, a careful study of the inter-relations between the teeth on the right side should lead the reader to conclude that the lateral incisor root is both inferior to and lingual to the canine. This would indicate that a mesial re-uprighting of the incisor root and a distal and inferior movement of the crown of the canine are possible without their roots colliding, provided no labial incisor root torque is performed until the transposition has been fully resolved. This means that a round base archwire, rather than a rectangular base archwire, should be used with light wire springs and auxiliaries to effect individual movements. Thus, alignment of these teeth in their correct order is possible. It will take much additional time but, since the esthetic zone is the area affected, it may be the preferred line of treatment.


1. Bulletin #36 – October 2014 Interceptive uprighting of incisor roots to eliminate maxillary canine impaction.

2. Bulletin #6 – December 2011. Salvaging a failing case.

3. Bulletin #7 – January 2012. Opening space for the canine – it’s not as simple as it seems!