A Review of Impacted Permanent Maxillary Cuspids — Diagnosis and Prevention

Prevalence and Etiology

Eighty-five per cent of impacted maxillary permanent cuspids are palatal impactions, and 15% are labial impactions.^1-3 Inadequate arch space and a vertical developmental position are often associated with buccal canine impactions.² If buccally impacted cuspids erupt they do so vertically, buccally and higher in the alveolus.² Due to denser palatal bone and thicker palatal mucosa, as well as a more horizontal position, palatally displaced cuspids rarely erupt without requiring complex orthodontic treatment.⁷ Palatally erupting or impacted maxillary canines occur twice as often in females than males, have a high family association and are 5 times more common in Caucasians than Asians.^7,8 It is not unusual for maxillary canine impaction to occur bilaterally, although unilateral ectopic eruptions are more frequent.⁹

The exact etiology of palatally impacted maxillary cuspids is unknown; however, 2 common theories may explain the phenomenon: the guidance theory and the genetic theory. The “guidance theory of palatal canine displacement” proposes that this anomaly is a result of local predisposing causes including congenitally missing lateral incisors, supernumerary teeth, odontomas, transposition of teeth and other mechanical determinants that all interfere with the path of eruption of the canine.^1,4,10,11 Maxillary canines develop high in the maxilla, are among the last teeth to develop and travel a long path before they erupt into the dental arch.¹² These factors increase the potential for mechanical disturbances resulting in displacement and, thus, impaction.

The second theory focuses on a genetic cause for impacted cuspids.^10,13,14 Palatally impacted maxillary cuspids often present with other dental abnormalities, including tooth size, shape, number and structure, which Baccetti¹⁰ reported to be linked genetically. Several abnormalities are believed to have a common hereditary link, manifested as a developmental disturbance during embryonic growth.⁶ Research demonstrates that up to 33% of patients with palatally impacted cuspids also have congenitally missing teeth, a frequency that is 4-9 times that of the general population.⁸ Studies also show that up to 47.7% of patients with palatally impacted cuspids have small, peg-shaped or missing lateral incisors.¹¹ In patients with congenitally absent maxillary lateral incisors, the co-occurrence of palatally impacted canines is 2.4 times that of the general population.⁷ Palatally impacted maxillary canines are also associated with such anomalies as hypoplastic enamel, infra-occluded primary molars and aplastic second bicuspids.¹⁰ However, it remains uncertain whether the anomalous lateral incisor is a local causal factor for palatally displaced canines or an associated genetic developmental influence.⁸

Diagnosis

Early detection of impacted maxillary canines may reduce treatment time, complexity, complications and cost. Ideally, patients should be examined by the age of 8 or 9 years to determine whether the canine is displaced from a normal position in the alveolus and assess the potential for impaction.⁹ The clinician can investigate the presence and position of the cuspid using 3 simple methods: visual inspection, palpation and radiography.

Visual Inspection

Clinical signs that may indicate ectopic or impacted succedaneous cuspids include lack of a canine bulge in the buccal sulcus by the age of 10 years, overretained primary cuspids, delayed eruption of their permanent successor and asymmetry in the exfoliation and eruption of the right and left canines⁹ (Fig. 1). Primary cuspids that are retained beyond the age of 13 years and have no significant mobility strongly indicate displacement and impaction of permanent canines.^9,15 Although Power and Short¹⁵ assert that the maxillary canine is late in its eruption sequence if it has not emerged by the age of 12.3 years in females and 13.1 years in males, correlation between chronological and dental ages is poor and overall dental development must be considered when investigating delayed canine eruption.

Although distal crown tip on the maxillary lateral incisors is common in the mixed dentition stage before eruption of the maxillary canines, an exaggerated distally tipped incisor should increase suspicion of a mesially deflected and palatally impacted canine.⁹ In these cases, the lateral incisor crown may be tipped distally because the impacted cuspid is exerting force on the distal aspect of the lateral incisor root. Such palatal impactions can cause the lateral incisor to rotate as well.⁹ Retroclined lateral incisors can also occur when buccally directed forces cause the root to tip labially and the crown to tip palatally.¹⁶ In severe cases, the central incisor may also be affected, and its crown may become malpositioned.¹⁶

Palpation

Palpation of the buccal and lingual mucosa, using the index fingers of both hands simultaneously, is recommended to assess the position of the erupting maxillary canines.⁹ Eruption time of a maxillary canine varies from 9.3 to 13.1 years.¹² Because canines are palpable from 1 to 1.5 years before they emerge, the absence of the canine bulge after the age of 10 years is a good indication that the tooth is displaced from its normal position, and ectopic eruption or impaction of the maxillary cuspids is possible.^12,17 Asymmetries in the alveolar process are not considered significant in children younger than 10 years, and differences in bilateral palpation could be due to vertical differences in eruption rates at young ages.^12,17 However, in patients older than 10 years, an obvious palpable bilateral asymmetry could indicate that one of the permanent cuspids is impacted or erupting ectopically.¹⁷

Radiographs

Radiographs are indicated when canine bulges are not present; right and left canine development and eruption is asymmetrical (Fig. 2); occlusal development is advanced and there are no palpable bulges indicating the presence of the cuspids in the alveolar process; and the lateral incisor is delayed in eruption, malpositioned, or has a pronounced labial or palatal inclination in relation to the adjacent central incisor.^17-19 Accurate radiographs are critical for determining the position of impacted canines and their relation to adjacent teeth, assessing the health of the neighbouring roots and determining the prognosis and best mode of treatment.²⁰ A panoramic radiograph taken in conjunction with 2 periapical views obtained using Clarke’s Rule (Buccal Object Rule) or a 60% maxillary occlusal film (Fig. 3) allows the impacted teeth to be located either palatally or buccally relative to adjacent teeth.²⁰ Ericson and Kurol¹⁹ found that periapical radiographs allowed accurate location of the teeth in 92% of the cases they evaluated. Although periapical films are diagnostic for transverse position, occlusal radiographs are more accurate for determining the positions of the canines relative to the midline.^16,21 Lateral cephalometric radiographs are also helpful in assessing the anterior–posterior position of the displaced tooth, as well as its inclination and vertical location in the alveolus.²⁰

Although conventional dental radiographs provide satisfactory diagnostic images, they lack the accuracy necessary for assessing palatal or buccal root resorption of the lateral incisor especially with mild or early resorption.^21,22 Computed tomography (CT) is more accurate in terms of locating the impacted cuspid in 3 dimensions and for diagnosing associated lesions such as root resorption of adjacent teeth.²¹ However, although CT is an asset in cases where root resorption is suspected, cost, time and increased radiation exposure restrict its routine use.¹⁷

The association of palatally impacted maxillary cuspids with other dental anomalies — regardless of whether there is a true genetic relation — is clinically significant for the general practitioner. When an associated abnormality is suspected or diagnosed, further clinical and radiographic examinations are indicated to investigate the possibility of maxillary canine displacement.²³ If palatally displaced canines are identified early during mixed dentition, interceptive treatment may prevent future complications and more extensive orthodontic treatment.

Interceptive Treatment

In Class I noncrowded situations where the permanent maxillary canine is impacted or erupting buccally or palatally, the preventive treatment of choice is extraction of the primary cuspids when the patient is 10-13 years old.^16,21 However, if any root resorption is visible before this age and there is suspicion of impaction, the primary cuspids should be extracted and appropriate treatment implemented, i.e., monitoring the eruption path or orthodontic alignment. When canines are impacted buccally, overretained primary cuspids should be extracted to create a path and space for the permanent cuspids to erupt into the arch. This is especially important if both the permanent and primary cuspids are visible in the arch at the same time.

Power and Short¹⁵ showed that interceptive extraction of the primary canine completely resolves permanent canine impaction in 62% of cases; another 17% show some improvement in terms of more favourable canine positioning. Ericson and Kurol²⁴ found that, in 78% of palatally erupting cuspids, the eruption paths normalize within 12 months. However, extraction of the primary cuspid does not guarantee correction or elimination of the problem. If there is no radiographic evidence of improvement one year after treatment, more aggressive treatment, such as surgical exposure and orthodontic eruption, is indicated.¹⁵

The success of early interceptive treatment for impacted maxillary cuspids is influenced by the degree of impaction and age at diagnosis.¹⁶ As a general rule, when the degree of overlap between the permanent maxillary cuspid and the neighbouring lateral incisor exceeds half the width of the incisor root, the chances for complete recovery are poor¹⁵ (Fig. 4). Clinical studies purport resolution of palatal impaction in 91% of cases in which the crown of the canine is distal to the midline of the lateral incisor when treatment is initiated.²¹ The success rate drops to 64% if the cuspid crown is positioned mesial to the midline of the lateral incisor before interceptive treatment.²¹

Other factors influencing prognosis include canine angulation and crowding. The chance of successful eruption of an impacted canine following extraction of the primary canine is less than favourable as the angle from the vertical increases.^15,25 Power and Short¹⁵ found that an angle exceeding 31% from the vertical significantly reduces the chance of normal eruption following an extraction. However, the degree of horizontal overlap with the adjacent lateral incisor has been found to have more influence on prognosis than angulation.¹⁵ Ericson and Kurol²⁵ found that more mesially positioned canine cusp tips are associated with greater resorption of lateral incisor roots. Arch crowding can also have a significant influence; moderate to severe crowding indicates the need for complex orthodontic treatment to resolve the impaction and the malocclusion.¹⁵

Sequelae from Maxillary Canine Impactions

The permanent canines are the foundation of an esthetic smile and functional occlusion,⁷ and any factors that interfere with their development and eruption can have serious consequences. Although extraction of primary cuspids can be beneficial in specific cases, inappropriate extraction of primary maxillary cuspids must be avoided, due to the increased potential for arch collapse and arch crowding, which could lead to a buccal impaction. Abnormal eruption paths within the dentoalveolar process may result in impactions and serious clinical ramifications. Unerupted or partly erupted cuspids may increase the risk of infection and cystic follicular lesions and compromise the lifespan of neighbouring lateral incisors due to root resorption^2,15,20 (Fig. 5). Clinical studies have determined that 12% of lateral incisors that are adjacent to ectopically erupted canines have some degree of external root resorption, while the prevalence of lateral incisor root resorption in 10-13 year olds is 0.7%.^15,26 Brin and others¹¹ found that there was an increased chance of lateral root resorption adjacent to an impacted cuspid when the lateral incisor was of normal size. A mesial-horizontal eruption path has also been shown to be more devastating to the adjacent lateral incisor, as is advanced root formation of the palatally displaced maxillary canine.²⁶ The lateral incisor often produces low-grade pain and has negligible mobility, although up to two-thirds of the root may be destroyed in affected teeth²⁶ (Fig. 5). This pathologic condition is often realized late (mean, 12.5 years of age) and after a significant degree of damage has occurred to adjacent teeth.²⁶

Conclusion

The prevalence of maxillary canine impaction is significant and the frequency increases with other genetically associated dental anomalies. The astute practitioner should be aware of dental anomalies that occur with palatally impacted maxillary canines so that early recognition and interceptive treatment is possible. More important, if signs of ectopic eruption are detected early, every effort should be made to prevent impaction and its consequences. Current protocol involves judicial extraction of the primary cuspid and radiographic follow-up for 12 months to monitor eruption. The need for complex orthodontic therapy and surgical intervention may be avoided if the deciduous canines are extracted appropriately. Early intervention can spare the patient time, expense, more complex treatment and injury to otherwise healthy teeth.

M^me Richardson est étudiante de quatrième année en médecine dentaire à l’Université Dalhousie de Halifax.

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