Abstract
The signs and symptoms of canine impaction can vary, with patients only noticing symptoms when they are suffering from unsightly esthetics, faulty occlusion, or poor cranio-facial development. While various surgical interventions have been proposed to expose and help erupt impacted canines, these treatment modalities have a high degree of difficulty compared to other types of dental cosmetic surgeries. This paper focuses on multi-disciplinary strategies for treating and managing canine impaction, reviews patient and clinical selection criteria, and discusses the evidence underlying existing interventions to reduce complications and improve patient-centered outcomes following treatment.
Introduction
An impacted tooth is defined as a tooth that fails to erupt after the normal development pattern is complete. Maxillary canines are the most common impacted tooth, following the third molar teeth. Tooth impaction is often diagnosed during routine dental examination by pediatric dentists, orthodontists, or general dentists. The early detection, timely management, and appropriate surgical and orthodontic intervention can lead to esthetically and functionally acceptable outcomes. An interdisciplinary patient care approach with specialists from different disciplines- orthodontists, pediatric dentists, periodontists, oral surgeons and general dentists- cooperating and collaborating together is necessary to manage this condition successfully. Proper positioning and alignment of canines plays an extremely important role in establishing an acceptable facial contour, esthetic smile line, and occlusion especially for canine guidance or group function occlusion. If this condition is not treated properly, the outcome of orthodontic treatment might be less desirable and the treatment duration might be extended. Additionally, under certain circumstances, the presence of an impacted canine may play a role in root resorption of adjacent teeth. Thus, the aims of this paper are to review the prevalence and the etiology of canine impaction, methods for the radiographic assessment of canine impaction, and treatment intervention based on the labio-lingual position of impacted canines. A patient case accompanies this article to highlight several key steps in treating and managing impacted canines.
Prevalence and etiology of canine impaction
The maxillary canine is the second most commonly impacted tooth following the maxillary third molar. Yet, the prevalence of the impacted maxillary canine is actually quite low, with the prevalence ranging from 0.92% to 2.2% of the population, and a predilection to affect females more often than males, at a ratio of 2:1. Furthermore, the unerupted impacted maxillary canine tends to be positioned more palatally than labially, at a ratio of 2:1 or 3:1. In comparison, the prevalence of the mandibular canine impaction is lower (0.35%) than that of the impacted maxillary canine.
While the exact etiology of the unerupted impacted maxillary canine remains somewhat elusive, there is strong evidence to suggest that multiple broad and complex mechanisms- namely, genetic, systemic (like endocrine disorders, febrile conditions, and/or irradiation), and local factors- are involved. Several local factors- such as 1) tooth size–arch length discrepancies; 2) failure of the primary canine root to resorb; 3) prolonged retention or early loss of the primary canine; 4) ankylosis of the permanent canine; 5) cyst or neoplasm; 6) dilaceration of the root; 7) absence of the maxillary lateral incisor; 8) variation in root size of the lateral incisor (peg-shaped lateral incisor); and 9) variation in timing of lateral incisor root formation, are believed to play critical roles in canine impaction.
Of all the local factors listed above, arch length deficiency is believed to be the most common cause of labially impacted canines. Jacoby observed that while approximately 85% of palatally impacted canines had sufficient space for eruption, only 17% of labially impacted canines had sufficient space to erupt in the arch. Therefore, it was proposed that the primary etiology of the labially impacted canines is insufficient arch length which limits the amount of space available for the unerupted canine to erupt normally. On the other hand, for palatally impacted canines, the absence of the maxillary lateral incisor is believed to be the most common cause for eruption failure. In order for a canine to erupt normally into the arch, the prevailing theory is that the root of the adjacent lateral incisor serves as a “guide” for the canine to erupt along it. However, when the adjacent lateral incisor is either missing or malformed, there is no “guide” for the canine to travel along; as a result, the canine will fail to erupt. This is known as the “guidance theory.” To further substantiate this important relationship between the erupting canine and the maxillary lateral incisor, Becker reported an increase of 2.4 times in the incidence of palatally impacted canines adjacent to missing lateral incisors compared to palatally impacted canines in the general population.
Prevalence and etiology of canine impaction
The maxillary canine is the second most commonly impacted tooth following the maxillary third molar. Yet, the prevalence of the impacted maxillary canine is actually quite low, with the prevalence ranging from 0.92% to 2.2% of the population, and a predilection to affect females more often than males, at a ratio of 2:1. Furthermore, the unerupted impacted maxillary canine tends to be positioned more palatally than labially, at a ratio of 2:1 or 3:1. In comparison, the prevalence of the mandibular canine impaction is lower (0.35%) than that of the impacted maxillary canine.
While the exact etiology of the unerupted impacted maxillary canine remains somewhat elusive, there is strong evidence to suggest that multiple broad and complex mechanisms- namely, genetic, systemic (like endocrine disorders, febrile conditions, and/or irradiation), and local factors- are involved. Several local factors- such as 1) tooth size–arch length discrepancies; 2) failure of the primary canine root to resorb; 3) prolonged retention or early loss of the primary canine; 4) ankylosis of the permanent canine; 5) cyst or neoplasm; 6) dilaceration of the root; 7) absence of the maxillary lateral incisor; 8) variation in root size of the lateral incisor (peg-shaped lateral incisor); and 9) variation in timing of lateral incisor root formation, are believed to play critical roles in canine impaction.
Of all the local factors listed above, arch length deficiency is believed to be the most common cause of labially impacted canines. Jacoby observed that while approximately 85% of palatally impacted canines had sufficient space for eruption, only 17% of labially impacted canines had sufficient space to erupt in the arch. Therefore, it was proposed that the primary etiology of the labially impacted canines is insufficient arch length which limits the amount of space available for the unerupted canine to erupt normally. On the other hand, for palatally impacted canines, the absence of the maxillary lateral incisor is believed to be the most common cause for eruption failure. In order for a canine to erupt normally into the arch, the prevailing theory is that the root of the adjacent lateral incisor serves as a “guide” for the canine to erupt along it. However, when the adjacent lateral incisor is either missing or malformed, there is no “guide” for the canine to travel along; as a result, the canine will fail to erupt. This is known as the “guidance theory.” To further substantiate this important relationship between the erupting canine and the maxillary lateral incisor, Becker reported an increase of 2.4 times in the incidence of palatally impacted canines adjacent to missing lateral incisors compared to palatally impacted canines in the general population.
Clinical and radiographic assessments
Clinical examination usually involves a comprehensive periodontal examination. Clinical signs of canine impaction include the retention of primary canines and an absence of buccal and palatal bulges when compared to the contralateral side of the affected area after a patient reaches 12–15 years of age. Careful palpation of the alveolar housing would be useful for clinicians to identify the presence or absence of bulges. Other possible clinical signs include tipping or irregular positioning of adjacent teeth.
Although palpation of the alveolar ridge is one way of the most common clinical methods to identify the location of the impacted canines, sometimes impacted canines are not clinically palpable. Ericson showed that approximately 3–5% of impacted teeth are not clinically palpable based only on the clinical examinations. Consequently, due to the limitations of clinical examinations, many radiographic assessment methods,such as panoramic, periapical, occlusal, and lateral cephalometric radiographs have been utilized to evaluate the presence and position of impacted canines. If the tooth is not palpable, 2 or more periapical radiographs taken at different angles can confirm the position of the impacted tooth by utilizing the principle of the SLOB or Clark’s rule. The SLOB rule means “Same Lingual, Opposite Buccal”. If the beam angle moves mesially, then the image of the impacted canine moves mesially too. This means the impacted tooth might be located on the lingual or palatal side. On the other hand, if the beam angle moves distally and the image of the impacted canine moves mesially, the tooth is likely located on the buccal side. This principle has been useful to locate the position of the tooth. Approximately 90% of the time, clinicians can identify the position of an impacted tooth on the labial or palatal sides. However, there are many limitations including measuring the exact distance from the impacted tooth to the adjacent teeth and identifying the presence or absence of root resorption on adjacent teeth. Orthodontists and surgeons need to be aware of the precise position of the tooth in order to generate appropriate treatment plans. Three dimensional analysis with cone beam computed tomography (CBCT) has significantly improved our ability to localize the position of the tooth accurately. After obtaining a CBCT scan, a panoramic radiograph can also be recorded. The customized arch is made on the panoramic view, and the customized slice view can be used for accurate detection of tooth position. ( Figs. 1 and 2 ) In addition to those sliced views, a 3D reconstructed view can be useful in identifying the exact location of an impacted canine ( Fig. 3 ).
