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The etiology of maxillary canine impaction: Part 1

Published: April 2013

Bulletin #21 April 2013

The etiology of maxillary canine impaction: Part 1

Introduction

Almost without fail, an article on the various aspects of the impaction of maxillary permanent canines, be it etiology, prevalence, diagnosis, treatment or prognosis, begins with a sentence describing the phenomenon as the most common form of tooth impaction, after third molars. Relatively recent studies into the frequency with which maxillary canine impaction occurs in the general population have indicated a prevalence of between 0.27% in a Japanese population1 to as much as 2.4% among Italians.2 The condition affects females 2.3 to 3 times more frequently than males. 2-5

Notwithstanding a broad peppering of the orthodontic literature with articles offering the unwavering opinion of a number of researchers in favor of a single overall cause for its occurrence, there are many and varied causes for the impaction of the maxillary canine. The causes may be divided into those that are due to local obstruction, those due to local pathology, those due to a departure from or disturbance of the normal development of adjacent teeth and those directly due to hereditary/genetic factors.

Local Obstruction

AA Fig.1_1

Fig. 1. Panoramic view of a 12 year old girl with a palatally impacted left maxillary canine. There is an enlarged dental follicle surrounding its crown and the deciduous canine has a long unresorbed root.

From the impression gleaned from a clinical and radiographic assessment of a number of impacted canine cases, Lappin6 observed that the deciduous canines were frequently over-retained, often with a long and unresorbed root present (Fig. 1). He speculated that it was the non-resorption of the deciduous canine that was the cause of the anomaly. It is important to emphasize that this was not a controlled study, but solely conclusions that he drew from what he observed. While the mechanism for root resorption of a deciduous tooth is unknown, we do know that it occurs when there is proximity of the dental follicle of an unerupted permanent tooth. This being the case, it is equally plausible to argue the converse, i.e. that resorption has not occurred due to the distance of the permanent tooth and, therefore, that the unresorbed root of the deciduous canine is not the cause of the displacement, but its result.

On the other hand, Lappin’s conclusion might be justified, since a number of studies have all shown that prophylactic extraction of the deciduous canines, in cases where there is potential maxillary permanent canine impaction, appears to encourage spontaneous eruption of a majority of quite markedly displaced permanent canines.7-9

In my assessment of this outcome and its significance is that it clearly illustrates a strong environmental influences on canine eruption.

AA_Fig.2

Fig. 2. Odontome preventing eruption of the canine.This photograph is reprinted from Becker A. Orthodontic treatment of impacted teeth. 3rd ed. Wiley Blackwell, Oxford, 2012.

From parallel work relating to impacted incisors, we know that hard tissue pathology in the immediate area may cause displacement of a developing tooth. The first entity that comes to mind is the supernumerary tooth or odontome, a diagnosis which is highly definitive and it presents an etiologic role which is easily understood. While this is a potent cause of impaction and is frequently seen in relation to impacted central incisors, supernumerary teeth and odontomes in the canine area are unusual (Fig. 2).10

But perhaps a little more surprising is the finding that in unilateral cases of central incisor impaction, whether this be because of obstruction by a supernumerary tooth or odontome, or because of dilaceration or recent trauma, there is a phenomenally high frequency of eruption disturbance of the canine on the same side. 11 This investigation revealed that there was a significant increase in prevalence and severity of displaced canines of the ipsilateral side (41.3%), of which palatal displacement occurred in 9.5%, buccal displacement in 30.2%, and canine-lateral incisor transposition in 1.6% of the patients. This compared with 4.7% in total on the contralateral side. Half of the buccally displaced canines in the ipsilateral side were pseudotransposed with the adjacent lateral incisor.

AA_Fig.3a AA_Fig.3b

Fig. 3a Intra-oral view of an 8 year old child with an unerupted left central incisor. The adjacent lateral incisor has erupted and is strongly tipped mesially, encroaching on the space for the missing tooth.

Fig. 3b Panoramic film of the patient in Fig. 3a taken prior to the extraction of the deciduous central incisor (#61). The permanent central incisor (#21) is dilacerated with its crown in the area of the anterior nasal spine. The long axis of the lateral incisor (#22) is strongly tipped, displacing the root end distally and into close relation with the canine crown (#23).


These abnormal features may be explained by the fact that the lateral incisor tips mesially to encroach on the space of the unerupted central incisor to a considerable degree (Fig. 3a). The corollary of this is that the root apex tips distally and into a position where it interferes with the eruption path of the unerupted canine.

Again, this illustrates the existence of powerful environmental influences on canine eruption (Fig. 3b).

AA_Fig.4 AA_Fig.5

Fig. 4. A cone beam CT 3D screen shot of an impacted right maxillary canine to show how the orientation of the palatal root of a first premolar can cause canine impaction (yellow arrow). Note the resorption of the lateral incisor root (green arrow). The successful treatment of this case was described in the January 2012 Bulletin #7 which may be accessed from the Newsletters Archive on the right side of this page.

Fig. 5. This periapical view of another patient was taken to check why there was no progress in the attempted resolution of the canine impaction. Both roots of the first premolar can be seen to turn mesially in their apical third (arrows) and lie in the direct path of the impacted canine. The successful treatment of this case was described in the December 2011 Bulletin #6.


In the immediate neighborhood of the canine, the sequence of eruption of teeth dictates that the maxillary lateral incisor and the first premolar precede the canine by 3 years and 1 year, respectively. For as long as the canine is in its normal eruptive position, i.e. slightly buccal to the line of the dental arch, its path of eruption will permit it to erupt unhindered. However, if it is high up in the alveolus and if the premolar has erupted with a mesio-buccal rotation (a clockwise rotation when viewed from the occlusal) then the palatal root of the premolar will be rotated mesially and forward, directly in the path of the canine (Fig. 4). Bulletins # 6 and 7 from December 2011 and January 2012 on this website present an approach to the successful treatment of such cases. In certain very unusual situations, the root or roots of the premolar may exhibit a mesial turn in their apical third, which too will provide a formidable obstacle in the path of the canine (Fig. 5). Thus, a rotated orientation or abnormal root anatomy of the adjacent first premolar may provide the impediment that becomes the cause for the impaction of the maxillary permanent canine.

Local Pathology

AA_fig.6

Fig. 6. Periapical view of a palatal canine. The deciduous canine has a distal restoration, is no-vital and can be seen to exhibit periapical pathology (arrow).

Dentally related soft tissue lesions very frequently occur and often go unnoticed or are ignored. However, they may constitute significant etiologic factors. Over-retained deciduous canines are commonly non-vital by the age of 12 years, due to caries, trauma or extreme attrition. The resulting chronic periapical granuloma, by itself, is a soft tissue inflammatory lesion that will have a potent effect on arresting eruption or on deflecting the eruption path of an adjacent developing tooth (Fig. 6).

Extraction of a diseased deciduous canine usually eliminates the granuloma and, with it, the displacing factor for the permanent tooth. Investigations into the efficacy of prophylactic extraction of the deciduous canines have been referred to above. Whether or not cases with non-vital deciduous canines were included in the study samples was not mentioned in the Methods and Materials sections of those articles. One may be permitted to wonder just how many of the deciduous canines in these study samples were non-vital. A high percentage of the permanent canines had later erupted spontaneously in what was claimed to be the apparent sequel to the extraction of the deciduous predecessor. It may be argued that their successful eruption was attributable to the concurrent elimination of the periapical lesion.

In rare instances, a granuloma develops into a radicular cyst by stimulating the rests of Malassez in the area and this expanding, space-occupying, turgid and epithelium-lined balloon, filled with liquid, will displace adjacent unerupted teeth. It is more likely, however, that a long-standing granuloma at the apex of a deciduous canine, may induce cystic change in the follicular sac of the adjacent unerupted permanent canine which begins as benign enlargement of the follicular sac surrounding the permanent canine and increases to become a dentigerous cyst. The hydrostatic pressure within the cyst overcomes the innate force of eruption of the tooth, arresting the downward progress of the tooth and even causing the tooth to “back up” in more advanced cases. The cyst may continue to enlarge laterally by initiating pressure resorption of the adjacent bone, until the cyst lining comes into contact with the roots of adjacent teeth, which will displace them into an adjacent area of potentially resorbable bone.

AA_Fig.7a AA_Fig.7b

Fig. 7a. September 2008. A large cyst occupies much of the left side of the maxilla (approximately demarcated by the yellow ring). The lateral incisor root has been tipped mesially into contact with the central incisor root. The first premolar lies horizontally in the floor of the cyst and the canine has been pushed upwards and tipped almost horizontally. This appears to be a radicular cyst resulting from the non-vital deciduous first molar. These case photographs are reprinted from Becker A. Orthodontic treatment of impacted teeth. 3rd ed. Wiley Blackwell, Oxford, 2012.

Fig. 7b. December 2010. Following marsupialization of the cyst, the canine has progressed rapidly with excellent fill-in of alveolar bone behind it to eliminate the former cyst cavity (orange arrows). The premolar has uprighted. Note the large eruptive cyst encompassing the crown of the right maxillary canine (yellow arrows). A palatal arch space maintainer was placed immediately after the surgery. No other treatment was provided.


One of the methods of treatment of a dentigerous cyst involves opening the cyst to the exterior – marsupialization – allowing for drainage and effectively defusing the displacing factor. The area previously occupied by the cyst remains lined with follicular epithelium. Lacking the increased hydrostatic pressure, bone begins again to fill in behind this epithelial lining, which undergoes metaplasia as it becomes continuous with the oral epithelium. The residual cyst cavity slowly shrinks and teeth that had previously been located in the cyst wall, begin to migrate with the returning bone towards more accessible positions. Again, therefore, prophylactic extraction of a deciduous canine to resolve potential palatal canine impaction may be successful in producing spontaneous eruption, due to the simultaneous and inadvertent rupture and evacuation of an associated and enlarged follicular sac/early dentigerous cyst (Fig.7). This has also been beautifully illustrated in several published case reports.10, 12, 13

AA_Fig.7c

Fig. 7c. February 2013. Following extraction of the deciduous canine of the right side, the eruptive cyst has dispersed and there is good bony fill-in following the autonomous eruption of both canines.

Trauma to the face may cause laceration of the soft tissues of the lips and cheek and we have already referred to trauma to the incisor region secondarily causing disturbance in eruption of the canine. Trauma may also be transmitted to the upper jaw and cause displacement of the unerupted canine tooth or a dilaceration of its developing root, particularly in the younger child.14 Pursuant to incidents of this kind, the tooth may become impacted.

References

1. Takahama Y, Aiyama Y. Maxillary canine impaction as a possible microform of cleft lip and palate. Eur J Orthod 1982; 4: 275–277

2. Sacerdoti R, Baccetti T. Dentoskeletal features associated with unilateral or bilateral palatal displacement of maxillary canines. Angle Orthodontist 2004;74:725-732.

3. Oliver RG, Mannion JE, Robinson JM. Morphology of the maxillary lateral incisor in cases of unilateral impaction of the maxillary canine. Br J Orthod 1989; 16: 9–16.

4. Becker A, Smith P, Behar R. The incidence of anomalous lateral incisors in relation to palatally-displaced cuspids. Angle Orthod 1981; 51: 24–29.

5. Johnston WD. Treatment of palatally impacted canine teeth. Am J Orthod 1969; 56: 589–596.

6. Lappin MM. Practical management of the impacted maxillary canine. Am J Orthod 1951; 37: 769–778.

7. Ericson S, Kurol J. Early treatment of palatally erupting maxillary canines by extraction of the primary canines. Eur J Orthod 1988; 10:283–295.

8. Lindauer SJ, Rubinstein LK, Hang WM et al. Canine impaction identified early with panoramic radiographs. J Am Dent Assoc 1992; 123:91–97.

9. Power SM, Short MBE. An investigation into the response of palatally displaced canines to the removal of deciduous canines and an assessment of factors contributing to favourable eruption. Br J Orthod 1993; 20: 215–223.

10. Becker A. Orthodontic treatment of impacted teeth. 3rd ed. Wiley Blackwell, Oxford, 2012.

11. Chaushu S, Zilberman Y, Becker A. Maxillary incisor impaction and its relation to canine displacement. American Journal of Orthodontics and Dentofacial Orthopedics 2003; 124:144-150.

12. Fearne J, Lee RT. Favourable spontaneous eruption of severely displaced maxillary canines with associated follicular disturbance. Br J Orthod 1988; 15: 93–98.

13. Sain DR, Hollis WA, Togrye AR. Correction of a superiorly displaced impacted canine due to a large dentigerous cyst. Am J Orthod Dentofacial Orthop 1992; 102: 270–276.

14. Brin I, Solomon Y, Zilberman Y. Trauma as a possible etiologic factor in maxillary canine impaction. Am J Orthod Dentofacial Orthop. 1993;104:132-7.

In the next bulletin #22 for May 2013 on this website, we shall discuss those causes that relate to a departure from or disturbance of the normal development of adjacent teeth and those whose origin is directly due to hereditary genetic factors.