Oral Health Group

Treatment of a Patient in the Late Mixed Dentition with Severe Crowding in the Maxillary Arch, Ectopic Eruption of the Maxillary Canines, and Unilateral Transposition

September 7, 2017
by Morris H. Wechsler, DDS, FRCD(C); Jean Rizkallah, DMD, MSc, FRCD(C); Laurent Richard, DMD, MSc, FRCD(C)

The purpose of this article is to describe the treatment of a 14-year-old boy in the late mixed dentition with over-retention of several primary maxillary teeth. This situation has caused a palatal eruption of the permanent incisors and a transposition of the upper right maxillary canine between the lateral and central incisors. The case was treated non-extraction by a combination of palatal expansion, protraction facemask, and fixed appliances. All teeth were aligned with highly satisfactory results.

Prolonged retention of deciduous teeth in the mixed dentition may result in the impaction of one or more permanent teeth, or in their ectopic eruption. Rigorous follow-up and extraction of these primary teeth at an appropriate time is essential in order to prevent the development of a severe malocclusion in the permanent dentition. In some cases, there may be dental transposition, (i.e., a positional interchange of two permanent teeth). This is a rare anomaly that has a prevalence of less than 1%.1-6

There is a distinction to be made between partial and complete transpositions. Partial transpositions involve either the crowns or the root apices, whereas complete transpositions involve both the roots and the crowns.

The maxillary canine is the tooth most often reported in transposition2, usually with the first premolar2,7,8 and less often with the lateral incisor.8 The most important etiologic factor in maxillary canine-lateral incisor transposition is dental trauma in the deciduous dentition.

Maia5 described the orthodontic correction of the complete transposition of a maxillary canine and lateral incisor by moving the canine distally and palatally, and the lateral mesially and labially. Upper and lower first premolars were first extracted in that case.

Shapira and Kuftinec9, showed a case of a 10-year-old girl with complete canine-lateral transposition, which was corrected by canine retraction followed by movement of the lateral incisor labially to its normal position in the arch.

Peck and Peck8, with a sample of 201 cases, have classified five types of maxillary tooth transposition, and concluded that canine-lateral incisor cases were the second most common transposition types.

Chong and Font11 studied the skeletal and dental changes in the sagittal, vertical, and transverse dimensions following rapid palatal expansion, and noted that the greatest increase in the transverse direction was in the interpremolar width. Adkins et al.10 reviewed arch perimeter changes and the relationship between perimeter and arch width changes resulting from rapid palatal expansion. They found that rapid palatal expansion with the Hyrax appliance produced increases in the maxillary arch perimeter at the rate of approximately 0.7 times the changes in the first premolar width.

It would seem, therefore, that treatment planning of canine-lateral incisor transposition cases requires the consideration of the precise location and position of the involved teeth, the position of the ectopic teeth, and the decision of whether – and which – extractions should be carried out.

Diagnosis and Etiology
A 14-year-old boy presented with a chief complaint of over-retained primary teeth and malaligned permanent teeth. The patient was healthy, with no contraindications regarding orthodontic treatment.

Extraoral examination showed that the patient had a symmetrical dolichofacial front view with a convex retrognathic profile. The front smiling view indicated that he had a short upper lip, with excessive gingival display (Fig. 1). The intraoral examination revealed that the patient had both primary maxillary central incisors, primary right maxillary lateral incisor, and both maxillary canines still in the mouth (over-retained). The four permanent maxillary incisors had erupted ectopically in the palate, in cross-bite (Fig. 1). The upper left permanent canine was completely blocked out of the arch, and had erupted labial to the central incisor, and in between the left permanent central incisor and the primary canine. In the upper occlusal view, it can be seen that both right and left permanent lateral incisors had erupted palatally and mesially to the first premolars. The upper central incisors were palatal to the primary teeth, and in crossbite to the lower teeth. The lower occlusal view showed milder crowding in the lower arch and the presence of the lower right second deciduous molar. With the teeth in occlusion on the right side, there was a Class 1 molar and canine relationship. On the left side, the molars and premolars were in Class 2 relationship (Figs. 1 & 2).

Figure 1

Pre-treatment extra-oral and intra-oral photographs.


Figure 2

Pre-treatment models.


The panoramic radiograph (Fig. 3), shows that the upper right canine seemed to be impacted between the right central and lateral incisors. It is also evident that the left mandibular first molar had been treated endodontically. The periapical radiographs (Fig. 4), indicate that the maxillary left canine root is positioned distal to the lateral incisor root.

Figure 3

Pre-treatment panoramic radiograph.

Figure 4

Pre-treatment periapical radiographs.

Figure 5

Pre-expansion occlusal radiograph.

Figure 6

Periapical radiograph showing maxillary canine erupting between upper right lateral incisor and central incisor.

Figure 7

Pretreatment lateral cephalometric radiograph.

Figure 8

Pre-treatment lateral cephalometric tracing.


The cephalometric assessment (Figs. 7 & 8) indicates that both maxillary and mandibular apical bases are retrognathic relative to the cranial base (SNA = 78°; SNB = 71°); the difference between them (ANB = 6°) pointed to a Class 2 skeletal pattern, as well as a vertical growth pattern (FMA = 36°), and a long lower anterior face height (79.4 mm) (Table 1).

Table 1

Treatment Objectives
Both parents and patient were primarily concerned about the significant crowding of the upper anterior teeth, and the resulting unattractive smile. In planning treatment, the following objectives were considered:

1. To align the upper and lower anterior teeth.

2. To correct the anterior crossbite.

3. To make room for the eruption of the impacted canines.

4. To achieve a Class 1 molar and canine relationship.

5. To obtain a functional occlusion.

6. To obtain a pleasing smile.

Treatment Alternatives
There are two main approaches to treating this type of malocclusion (i.e., complete transposition of teeth). One option is to try to cross over the roots of the teeth, by orthodontically reversing the transposition.5,9 This is usually a challenging procedure because of the risks of resorption of the roots of the teeth involved, as well as the possibility of loss of bone. This reversal may be more readily done in cases of partial or incomplete transposition. The other approach is to proceed with the correction of the malocclusion while maintaining the positions of the canine-lateral incisors in the arch.

The significant crowding and the numerous anterior teeth in crossbite in this case, presented a challenge in treatment. Because of the severe crowding, extraction of the four first premolar teeth was considered. However, this would have produced an even more retrognathic profile than before. Consideration was given to the extraction of only the maxillary first premolar teeth; this would have resulted in a loss of tooth material in the maxilla only, possibly resulting in a concave profile, and making it more difficult to correct the anterior crossbite. There were several other possibilities: one, was to extract the lateral incisor, move the canine to its proper position, thereby opening space for a lateral incisor to be replaced by a prosthetic tooth, or by an implant. Another option was to extract the canine, and to replace it with an implant, while maintaining the lateral incisor in its normal position. Neither of these propositions appealed to the parents, because both of the above suggestions involved extraction of teeth and further expense for their prosthetic replacement.

Another treatment alternative would have involved surgery for the impaction and advancement of the maxilla, as well as the extraction of the two upper first premolars. The surgical approach would have had the advantage of correcting the vertical growth tendency and facilitating the correction of the anterior crossbite. This procedure would also have reduced the patient’s excessive gingival display. However, this option would have involved major risks associated with surgery and general anesthesia. It would have required possibly postponing treatment and waiting until growth was completed before proceeding with the surgery. This option was also rejected by the parents.

Yet another option was to try to obtain more space in the maxillary arch by increasing the size of the upper arch with a rapid maxillary expansion appliance. Attaining a positive anterior overjet could be achieved by proclining the upper incisors and using a protraction facemask at the same time as the rapid palatal expansion appliance. This non-extraction alternative would result in an increase in lip protrusion and width of the smile, improving the patient’s esthetics while avoiding the risks of major surgery. However, this option has the main disadvantage of increasing the vertical dimension in a patient with a vertical growth pattern.

Treatment Progress
Taking into consideration the age of the patient, his profile and the esthetics of his smile, as well as the parents’ rejection of surgery, it was decided to proceed with a non-surgical option.

The patient was referred for the extraction of all deciduous teeth still present in the mouth. Then, a rapid palatal expansion appliance (Haas type) with bands on the upper first molars and occlusal rests on the first premolars was placed in order to increase the maxillary width and the perimeter of the arch.10,11 It was initially (erroneously) thought that the upper right canine would erupt into its normal position, and that the transposition was incomplete (Fig. 3); therefore, space was opened between the upper right lateral incisor and the first premolar (Fig. 9). However, an occlusal radiograph (Fig. 5), and a periapical radiograph (Fig. 6) indicated that the transposition was complete. Therefore, the space between the right lateral and central incisors was opened in order to allow for the eruption of the canine (Fig. 10). An elastic ligature tied to this tooth was used to accelerate its eruption (Fig. 11). With the palatal expansion having opened the maxillary and circummaxillary sutures, a protraction facemask was worn by the patient for several months, in order to help maintain a positive anterior overjet, and a Class 1 relationship of the buccal segments.

Figure 9

Progress intra-oral photographs (before space opening for right maxillary canine).

Figure 10

Progress intra-oral photographs (after space opening between maxillary central and lateral incisors).

Figure 11

Progress intra-oral photographs (during eruption of right maxillary canine).


The lower arch was treated by conventional means with bonded fixed appliances. In the finishing stages, the use of anterior vertical elastics was necessary to achieve an adequate vertical overbite and coinciding upper and lower midlines.

At the end of treatment, the patient was referred to his dentist for reconstruction of his upper right lateral incisor, to give it the appearance of a canine, and of the upper right canine to resemble an upper right lateral incisor (Fig. 12). During the retention phase, two bonded lingual retainers were placed – one on the maxillary arch between the upper right canine and the upper left lateral incisor, and one on the lower from canine to canine. In addition, the patient was given a removable upper Hawley retainer, to minimize transverse relapse.

Figure 12

Post-treatment extra-oral and intra-oral photographs.

Figure 13

Post-treatment models.


Treatment Results
The treatment objectives were achieved: the upper anterior teeth were aligned, the crossbites were corrected, the posterior occlusal interdigitation was improved, and Class 1 canine and molar relationships on both sides were obtained. The palatal expansion was sufficient to correct the lack of width of the maxilla, as well as to create enough space to align all the teeth without the need for extraction of permanent teeth. The use of the protraction facemask permitted the correction of the anterior crossbite (Fig. 10). The orthodontic treatment allowed the eruption of the maxillary right canine into the space created between the central and lateral incisors. The upper left canine, which was initially completely blocked out of the arch, was retracted and distalized to its proper position in the arch. The crown of the right lateral incisor was restored with light-cured composite, and the crown of the canine was reshaped to look like a lateral incisor (Fig. 12). The upper and lower midlines were aligned, and interarch symmetry was established.

Measurements of the initial space available and the space required in the maxillary arch, indicated a deficiency of 9.5 mm (Table 2). Usually, in such cases, it is recommended that extractions be done.

Table 2

What is also noteworthy in this case is that the maxillary left lateral incisor moved from its original position mesial and lingual to the upper first premolar (a total of 10 mm) to final position.

The final radiographs (Figs. 14 & 15) demonstrate satisfactory root paralleling, with no apical root resorption of the teeth involved. The lower third molars show mesial-angular impaction due to lack of room (Fig. 14).

Figure 14

Post-treatment panoramic radiograph.

Figure 15

Post-treatment periodical radiographs.

The post-treatment cephalometric radiograph (Fig. 16), the cephalometric analysis (Fig. 17), and Table 1, indicate that the maxillary apical base has been reduced (from SNA = 77.6° to 74°), while the mandibular base has increased slightly (from SNB = 71.4° to 72.8°). The superposition of the pre- and post-treatment tracings (Fig. 18) shows that there has been a clockwise rotation of the mandible (FMA = 36° to 40°), as well as an increase in lower anterior face height (79.4 mm to 86.4 mm). The maxillary incisors were proclined from 18.9° to 26.5° relative to NA, and the mandibular incisors have been retroclined from 87.6° to 86.4° (Table 1).

A comparison of pretreatment (age 14) and posttreatment (age 17) profile photographs (Figs. 1 & 12) shows that the profile is still convex, although this is not detrimental to the patient’s appearance. An examination of before and after smile photographs shows a marked improvement in the esthetics of the smile.

Photographs (Fig. 21) taken at age 24, after some restorative and periodontal work had been done in the maxillary arch show that the occlusion has remained stable, and that the frontal, profile, and smiling views have improved considerably.

Figure 16

Post-treatment lateral cephalometric radiograph.

Figure 17

Post-treatment lateral cephalometric tracing.

Figure 18

Superimposition of pre- and post-treatment cephalometric tracings at S and along SN.

Figure 19

Comparison of occlusal views before and after treatment showing the amount of transverse expansion achieved.

Figure 20

Panoramic radiograph at age 24, showing that the third molars had been extracted.

Figure 21

Extraoral and Intraoral photographs at age 24 (six-years after completion of treatment).


This case presented several significant challenges; the first of these was to bring the upper right canine into position in the maxillary arch, without resorbing the root of the lateral incisor, or that of the canine itself. The second challenge was to decide whether or not to extract permanent teeth in order to facilitate the movement of canines into the arch. Although it might have been easier to extract upper first premolars and guide the canines to their positions, this would have caused the maxillary incisors to be located further lingually and possibly more into crossbite.

It has been reported8 that dental traumas in the primary dentition can change the orientation of a tooth bud – a maxillary lateral incisor, in this case. There is a high probability that the transposition observed in this patient was caused by dental trauma – the presence of grey primary incisors (Fig. 1) might be indicative of previous trauma to the anterior teeth.

In a case such as this one, where there is significant crowding in the upper arch, a rapid maxillary expansion appliance may increase the arch perimeter sufficiently, so as to avoid the need for extraction of permanent teeth. The movement of the anterior teeth forward also helped to increase the arch perimeter. Rapid maxillary expansion has an effect on all three planes of space – sagittal, vertical, as well as, transverse.11 In this case, as shown in Table 3 and Fig. 19, measurements of the transverse dimension of the intermolar, interpremolar, and intercanine distances before and after treatment, indicate that the distances were increased by 2 mm, 5.4 mm, and 6 mm, respectively. As noted previously, according to Adkins10, the increase in arch perimeter is 0.7 mm for each mm of arch expansion. In this case, it appears that we have gained about 4 mm through expansion, and 5.5 mm because of the forward movement of the upper anterior teeth. In addition, it has been reported12 that the width of the mandibular arch also increases following rapid maxillary expansion, in response to muscle forces and the new occlusion. (This can be seen in Table 4, which shows that there has been an increase in interpremolar width of 3.3 mm). However, this expansion has the negative side effect of causing clockwise rotation of the mandible and an increase in lower anterior face heigh.t10 This rotation can help promote the production of a positive overjet in cases with anterior crossbite.

Table 3

Table 4

1. By expanding the maxillary arch both laterally and antero-posteriorly, it was possible to gain sufficient space to align the teeth.

2. It is noteworthy, considering that the maxillary lateral incisors were originally lingual and mesial to the first premolars, that they were moved into their proper positions (a distance of about 10 mm), without the removal of teeth.

3. It is significant that in a case where almost 10 mm of space were missing in the maxillary arch (as seen in Fig. 19), it was possible to achieve a significantly improved occlusal, functional, and esthetically pleasing result, which has remained stable more than six years after completion of treatment. OH

Oral Health welcomes this original article.

The authors wish to express their thanks to Dr. Howard Cytryniak for his excellent restorative and periodontal work; to Dr. Jack Turkewicz for his careful editing of the manuscript and for his numerous and most helpful suggestions; to Dr. Harvey L. Levitt and Dr. Jean-Marc Retrouvey for their review of the manuscript and their insightful input. We also want to thank Dr. Ann Wechsler for her help in the preparation of the manuscript. We are also grateful to Mr. Mourad Benmiloud, for his invaluable technical assistance in the preparation and submission of this article.


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Morris H. Wechsler, D.D.S., FRCD(C),Professor of Orthodontics, and former Chairman of the Orthodontic Section of the Department of Sante Buccale, Faculte de Medicine Dentaire, University de Montreal, Montreal QC., Associate Professor of Orthodontics, Faculty of Dentistry, McGill University, Montreal, QC, Canada.




Jean Rizkallah, DMD, MSc, FRCD(C), Private Practice of Orthodontics, Montreal, QC, Canada.




Laurent Richard, DMD, MSc, FRCD(C), Private Practice of Orthodontics, Quebec City, QC, Canada.

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