The prevalence of maxillary canine impaction has been reported in 1.7%–4.7% of the population. A high incidence of maxillary canine impaction has been reported in the Turkish population at 3.29%. The lowest incidence has been reported in the Japanese population.

Mandibular canine:

Its impaction is less frequent, and the incidence has been reported to be 20 times lower than that for maxillary canines. The incidence of mandibular canine impaction is 0.31%–1.35%. In the Turkish population, the incidence was 0.44%. Migration of a tooth across the midline is even less frequent but not rare. At least 157 cases of mandibular canine transmigration have been published.

Palatally and buccally impacted canines differ in their aetiology, prevalence and risk factors.

Most maxillary canine impactions are palatal (85%) and only 15% are labial. Unilateral impaction is much more common than bilateral impaction. It has been reported that only 8% of canine impactions are bilateral ( Table 74.2 ).

• Race distribution: Maxillary canine impactions occur five times more often in Caucasians than in Asians. Most canines are impacted palatally among Caucasians and buccally among Asians.

• Sex distribution: Gender has an association with maxillary canine impactions occur twice as often in females than in males in a ratio of 2.3:1.

Although there has been considerable controversy regarding the exact aetiologic factors associated with palatally impacted canines, two leading schools of thought have emerged.

• 1.

  Environmental aetiology: Becker and coworkers supported the idea that environmental/local influences are the main aetiology of canine impaction. They believed that local factors, including a long path of canine eruption, were primarily responsible for the palatal displacement of the tooth. Becker was a believer in the ‘guidance theory of eruption’. The ‘guidance theory’ proposes that local predisposing conditions cause palatal canine displacement. Local conditions include congenitally missing lateral incisors, peg lateral supernumerary teeth, odontomas, transposition of teeth and other physical barriers that interfere with the path of eruption of the canine.

  • A high occurrence of maxillary canine impaction, 42.6%, is reported in a population having a congenital absence of lateral incisors. As maxillary canines develop high in the maxilla, they are among the last teeth to develop and travel a long path to reach the occlusal level, making them prone to environmental influences and increased risk of tooth impaction.

• 2.

  Genetic theory: Peck and colleagues have proposed a theory suggesting a significant genetic influence on palatal canine impaction. This theory is supported by evidence showing that palatally impacted upper cuspids often coexist with genetically linked dental abnormalities, such as tooth size, shape, number and morphology alterations. Up to 33% of patients with palatally impacted cuspids have congenitally missing teeth, four to nine times more frequent than the general population. Studies also show that up to 64.7% of patients with palatally impacted cuspids coexist with small, peg-shaped or missing lateral incisors.

  • In patients with congenitally absent maxillary lateral incisors, the co-occurrence of palatally impacted canines is 2.4 times that of the general population. However, whether the anomalous lateral incisor is a local causal factor for palatally displaced canines (PDCs) or an associated genetic developmental influence remains uncertain. The role of the lateral incisor root is considered critical for the normal eruption of the maxillary canine. A missing or microdontic lateral incisor fails to guide the erupting canine. The erupting canine eventually dives into the palate. Whether the anomalous lateral incisor and palatal maxillary impaction are co-variables or a primary aetiologic factor must be confirmed.

  • Palatally impacted maxillary canines are also associated with anomalies such as enamel hypoplasia, infra-occluded primary molars, and aplastic second bicuspids.

• Genetic mutations in canine impactions: Very few studies have evaluated the gene polymorphism related to canine impactions. It was seen that single nucleotide polymorphism of the AG genotype of MSX1 and CT genotype of PAX9 were seen in palatal canine impaction. PAX9 genes are essential for localisation and odontogenesis. In correlation, PAX9 with SNP3 and 4 were significantly associated with maxillary canine impaction.

  • In addition, Sella turcica bridging is commonly associated with palatal canine impaction. Sella turcica bridging is the ossification of the ligament between the posterior and anterior clinoid process. The anterior wall of Sella turcica and dental progenitor cells share common embryogenic roots from neural crest cells. Therefore, any homeobox genetic mutations disrupt the normal development of Sella turcica, midface and teeth. The Sella bridging was seen in 59.3%–50% of the maxillary palatal canine impaction. The labial impaction of maxillary canines is more common in crowded dentitions, while palatal impaction is more often associated with spaced arches.

  • The ongoing research on the cause of palatally displaced canine suggests that a combination of environmental factors and genetic predisposition may be responsible for its occurrence.

While palatally impacted canines are related to genetic predisposition or the lack of guidance to the erupting tooth, labial canine impaction is often seen in crowded dentitions. It has been reported that up to 83% of arches with a labial displacement of maxillary canines are associated with arch length deficiency. Thilander and Jakobsson found that dental crowding typically resulted in labial displacement of the canine rather than impaction. Premature loss of primary molars and the mesial shift of permanent molars leads to arch length deficiency, resulting in a lack of space for the canine, the last tooth to erupt in the upper arch (excluding third molars).

A visual examination should include careful observation of the dental eruption status of a child vis-à-vis chronological age. It is imperative to recognise that to classify a tooth as impacted, and one must establish a correlation between the developmental status of the concerned tooth and the dental age of the child, irrespective of chronological age. The maxillary canines can be clinically palpable in the buccal vestibule 1–1.5 years before they emerge, and the absence of the canine bulge after the age of 10 indicates that the tooth is displaced from its normal position. Ectopic eruption or impaction of the concerned tooth may be expected. However, in younger patients, asymmetries and differences in bilateral palpation could be due to differences in the eruption rate, and such cases should be kept under observation. In general, in patients above 10 years or so, showing asymmetry of the bulge among the right and left sides should raise suspicion of a possible impaction.

Evaluating dental root formation is a reliable method for determining dental age. A tooth is considered impacted when its root formation has exceeded the expected level, for the age but the tooth has not yet erupted. The dentition should be charted, and all the missing tooth/teeth should be recorded with a measure of crowding or spacing and loss of arch length. The area of the missing tooth should be inspected for any noticeable soft tissue bulge or discolouration of oral mucosa. In addition, the adjacent teeth need special attention for any abnormal inclination, which may suggest impingement on their roots by the impacted tooth.

An absence of canine bulge in the buccal sulcus by the age of 10 years, over-retained primary cuspids, delayed eruption of their permanent successor and asymmetry in the exfoliation and the eruption of the right and left canines are indicative of possible impacted maxillary canines. The palate and labial vestibule should be carefully examined for any bulge associated with an impaction.

Retained primary cuspids beyond the age of 13 years and not showing significant mobility strongly indicate displacement and impaction of permanent canines. The maxillary canine is considered late in its eruption sequence if it has yet to emerge by 12.3 years in females and 13.1 years in males. However, the correlation between chronological age and dental eruption is not strong. Overall, dental development and teeth eruption in the arches must be considered when investigating delayed canine eruptions.

A detailed clinical examination of the permanent lateral incisors is essential when looking for canine impaction signs. The lateral incisor should be examined for its abnormal position, angulation and/or rotation. The maxillary lateral incisor may be tipped distally, inclined labially and/or rotated. A disto-palatally tipped crown of the lateral incisor could result from a mesially displaced palatal canine, indicating palatal canine impaction. A mesio-labially inclined lateral incisor could result from a displaced canine lying on the labial aspect of the lateral incisor root.

Root resorption caused by a displaced canine can result in excess mobility of the maxillary lateral incisor. Andresen et al. reported an incidence of 12.5% of incisor root resorption in plain radiographs associated with ectopically erupting maxillary canines. However, CT and CBCT examinations have shown a higher incidence of root resorption, 48% and 66% respectively. Therefore, 2D radiographs are insufficient for detecting canine-induced root resorption in all situations.

Palpation of the buccal and lingual mucosa using the index fingers is an excellent way to locate the bulge and, hence, the site of the impacted tooth. The index finger should be used with its pulp facing the vestibular mucosa. A gentle palpation of the buccal alveolus, deep into the vestibule extending from the midline of the maxilla to the premolar molar region, helps to locate the unerupted tooth. On the palatal side, palpation is extended in the pre-maxillary palatal region towards the root apices of maxillary incisors and back in the premolar region. Some clinicians like to palpate the palatal and buccal sides simultaneously using the index fingers of both hands. In the case of bilateral impaction, a variation in the position of the impacted tooth on either side is not unusual.

The commonly used X-rays include an OPG of the maxilla and mandible, occlusal view and intraoral periapical (IOPA) films. A lateral cephalogram also provides valuable information with respect to distance of impacted tooth away from the occlusal level and labiolingual inclination of the tooth ( Fig. 74.4 ).

Radiological investigations for an impacted tooth.

IOPA films provide useful information on the location of the impacted tooth and its relationship with neighbouring teeth. Note supernumerary teeth causing impaction of maxillary canine. (A) In a young child, the canine root is not yet fully formed. (B) Shows horizontal canine impaction in an adult. (C) The occlusal view was suggestive of canine palatal impaction, which has caused rotation of the lateral incisor. (D) OPG provides an overview of dentition and impacted teeth. ‘X’ denotes impacted canine. A retained deciduous canine can be seen.

If initial X-rays or OPG indicate the need for a 3D evaluation of the impacted tooth for its location and its relationship with other dental structures, a CBCT may be advised. In clinical situations of suspicion of complicated or multiple impactions, a CBCT may be indicated. In these situations, dental X-rays/OPG are avoided. However, the indication and case selection for CBCT should follow As Low As Reasonably Achievable (ALARA) guidelines.

Intra oral periapical X-rays are usually the first to be requested and are the simplest and the most informative films. They are most useful for assessing the impacted tooth’s vertical and anteroposterior position in the alveolus. The IOPA reveals significant information like the extent of root completion, the presence and the size of the dental follicle, any crown or root resorption, the root pattern and integrity, the presence of any hard tissue obstruction and its description and the presence of cysts/pathologies in the affected region. They also offer superior image clarity and excellent detail ( Fig. 74.4 A and B).

For greater radiographic detail of the maxillary arch and mandibular anterior segment in an IOPA film, the beam should be angulated 20–55 degrees to the occlusal plane. When examining the X-ray of an impacted tooth, it is important to avoid measuring the length of the tooth directly from the film. The angulation of the X-ray beam is specifically designed to capture maximum details about the impacted tooth, which can lead to distortion in the displayed length of the tooth. The beam should be kept perpendicular to the occlusal plane for the mandibular posterior region.

To locate the buccolingual position of an impacted tooth, two consecutive IOPA X-rays using Clarks’ ‘tube shift method’ or ‘parallax method’ using a long cone tube are recommended. A conventional IOPA X-ray of the canine region of the impacted tooth is made. Subsequently, the second X-ray is made with the tube shifted to the distal position. With the availability of digital images, instant diagnosis can be made based on the principle of SLOB, which is ‘same lingual opposite buccal’. If the image of the tooth moves on the side of the tube shift, the tooth is likely to be lingual since it is likely to be closer to the film ( Fig. 74.5 ). It was found that 92% of palatal canine impaction can be located using two IOPA X-rays.

Clark’s method of buccolingual location of an impacted object.

Two IOPA X-rays are made while keeping the film in the same location, but the X-ray tube is moved either mesially or distally. An object closer to the palatal X-ray film will appear to move in the same direction as the X-ray beam, while the opposite is true for a buccal object. (A) Palatal impacted canine moved distally with distal movement of X-ray. (B) Buccal impacted canine moved mesially with distal movement of X-ray.

OPG X-ray provides an overview of dentition status, eruption pattern, stages of root formation, dental anomalies and jaws. The modern digital OPG X-rays offer good contrast and brightness with minimal magnification in the central trough. The digital images can be manipulated on screen, and careful observations can be made on zoomed images to see the relationship of the impacted tooth/teeth with roots of neighbouring teeth and the eruption path ( Fig. 74.4 D). Some OPG software can create a pseudo-3D image using an advanced function, which can assist in a somewhat better location of the impaction in relation to its neighbouring dental and skeletal structures.

Localisation of maxillary canine impaction on OPG can be predicted using the inclination angle of the canine with a horizontal line passing through the mesiobuccal cusp of the maxillary molars. It was found that canine impaction with an inclination of more than 65 degrees was 26.6 times located buccally.

An occlusal X-ray of the maxilla provides an excellent view for evaluating the relationship of the impacted tooth with the midline of the jaw and the roots of the lateral incisors ( Fig. 74.4 C). A slight modification in obtaining the occlusal X-ray technique is required for the impacted tooth.

• Maxillary arch : For the occlusal view in the maxillary arch, the anterior teeth are recorded on the film with a tube angulation of 60 degrees, while for the posterior region, a true occlusal view is desired. The horizontal parallax method can be obtained using one standard occlusal radiograph and IOPA. Herein, the beam is angulated 110 degrees to the occlusal plane, and the film is exposed from just behind the vertex of the skull. Although the clarity of this view is not so good, and there is a risk of increased radiation exposure, the advantage is that one can establish the exact labiolingual position of the impacted tooth in the palate ( Fig. 74.6 A).

  

  Position of head and X-ray tube for the occlusal views

  (A) Maxilla (B) Mandible.

• Mandibular arch: For the mandibular arch, a true occlusal view is usually required. An accurate occlusal view displays upright teeth with crowns superimposed on roots. To capture the anterior region, the patient is asked to tilt their head back while positioning the X-ray tube at 110 degrees to the horizontal plane. On the other hand, for the posterior region, the tube should be angled at 90 degrees to the horizontal plane with a 15-degree mesial shift to account for the natural mesial tipping of the teeth ( Fig. 74.6 B).

The lateral cephalogram depicts the distance of the crown tip of the impacted canine tooth from the occlusal plane and the angulation of the canine in reference to a vertical plane. This information is of prognostic significance. Similarly, a horizontally impacted incisor will be accurately seen on a lateral cephalogram for its relationship with the palate and vertical distance from the occlusal plane.

The PA view of the skull or a PA cephalogram provides valuable information on the long axis and the inclination of the tooth in relation to the midsagittal reference (MSR) plane. The crown of a normally erupting canine should lie slightly mesially inclined and below the level of the root apex of the lateral incisor and the lateral border of the nasal cavity. The cuspid root lies buccal to the lateral border of the nasal cavity.

Multi-detector Computed Tomography (MDCT) has been used in the past to locate the position of the impacted tooth in bone precisely and its relations with the adjacent structures. MDCT scan offers accurate position, inclination and orientation of the impacted tooth and its relationship with the adjacent structures in three dimensions of space. However, due to the high cost and exceptionally high radiation doses, routine use of MDCT to diagnose an impacted tooth could not be justified.

The CBCT has resolved the issue of high radiation dose compared to MDCT up to some extent. CBCT, with its advanced software functions on 3D reconstruction, provides a virtual reality view of the impacted tooth/teeth and their spatial relationship with adjacent teeth and bone. CBCT is a valuable investigation in orthodontic diagnosis in cases of impacted teeth ( Fig. 74.7 ). The 3D CBCT images of impacted teeth help determine the buccolingual position and angulation, the proximity of impacted teeth to the roots of the adjacent teeth and the degree of resorption, if any.

Impacted right mandibular canine.

This young girl who reported with protrusion of upper front teeth was discovered to have a retained right mandibular deciduous canine. (A) OPG showing impacted right canine in the mandible. (B) A lateral cephalogram is helpful in locating the distance of the tooth from the occlusal plane and labiolingual position. (C) 3D CT is showing slice locations from left to right. (D) From buccal to lingual CT. (E) Shows the labiolingual position of the impacted canine. (F) In the panoramic view, slice number 6 shows the relationship of the impacted canine with incisor roots. (G) CBCT helps reconstruct virtual reality models of structures, which are of great diagnostic help. (H and I) Special software’s function can render bone burn-out and provide virtual reality insight to visualise the impacted tooth with neighbouring structures.

Advanced capabilities of 3D software assist better visualisation through volume-rendered mode or multi-planar view, which provides a real life view of the impacted tooth position and the status of the adjacent tooth structures ( Fig. 74.8 ). These features assist in planning the surgery and direction of orthodontic traction to avoid the root resorption of the adjacent teeth roots.

Evaluation of a palatally impacted canine (13) in relation to its neighbouring teeth and roots after segmentation of CBCT data.

Case courtesy: Dr Daljit Kaur, Banga. Segmentation done by Dr Mayank Khandelwal, Bengaluru.

A systematic review by Eslami et al. assessed the comparisons between CBCT and conventional radiography in localising maxillary-impacted canines. The CBCT scans are more accurate than the traditional methods. A CBCT study by Keener et al. assessed the 3D position of impacted canine and root damage to the adjacent teeth. The treatment decision after 3D reports changed 22% of the time, and CBCT was essential to assess root damage to adjacent incisors, overlap and overall severity. However, the evidence showed that the CBCT image is not the first line of imaging modality for impacted maxillary canine evaluation.

The CBCT should be performed, the first and only radiological investigation, if clinical examination suggests an unusual location or unexpected complications associated with impacted tooth/teeth ( Fig. 74.9 ). In other situations, the CBCT is the last investigation to be performed should an initial X-ray suggest that additional conventional radiography is not likely to provide the requisite information.

Clinical and 3D radiological visualisation of an impacted left maxillary canine.

A 19-year-old female reported with a complaint of upper irregular front teeth. (A) The intraoral pictures reveal a retained upper left deciduous canine with a palatal bulge. The rotation of the left permanent lateral incisor is caused by impaction. (B) The CBCT multiplanar reconstruction images depict the palatal canine impaction. (C) 3D volume rendering images provide virtual 3D visualisation of the impacted canine.

It includes a watchful observation of developing dentition and all those incidents and factors that have the potential to prevent a normal eruption of a tooth:

• •

  In the canine area, loss of arch length due to premature loss of deciduous molars and mesial migration of first permanent molars and other such factors need therapeutic attention.

• •

  Presence of physical barriers such as supernumerary tooth, odontome, missing lateral incisors or microdontic maxillary laterals.

• •

  Lack of a bulge or a bulge away from the usual site of eruption, such as distal to premolars and incisors or a bulge in the palate, should make the clinician suspicious of the abnormal path of tooth eruption.

• •

  It is also essential to check for pathological cyst formation, lateral incisor root resorption and transmigration using X-rays.

When to suspect a maxillary canine impaction ( Table 74.3 ):

• •

  Radiographic examination of erupting canines is helpful for the prediction of canine impaction only for children between 10 and 15 years of age because it has been shown that radiographic examination before the age of 10 does not provide a reliable basis for prognosis of a future unfavourable eruption path of the maxillary canines.

• •

  A spontaneous correction of palatally placed canines up to the age of 10 years is highly probable.

The prediction of future canine impaction and its spontaneous correction by early intervention can be estimated on OPG using sector classification proposed by Ericson and Kurol and, which were later modified by Lindauer ( Table 74.4 ).

Ericson and Kurol found that the more mesially located the crown, the lesser the likelihood of eruption after deciduous extraction. Lindauer’s method used the location of the cusp tip of the canine in question and its relationship to the adjacent lateral incisor. He determined the probability for impaction based on the canine cusp tip location in one of the four sectors. Lindauer et al. reported that this method identifies up to 78% of the canines that are destined to become impacted, all of which have cusp tips located in sectors II–IV ( Fig. 74.10 ). Similar findings were found in Warford et al. that 82% of impacted canines were found in sector II–IV.

Sector classification of canine impaction.

The four sectors are based on the relationship of the developing canine tip and its relationship with the neighbouring lateral incisor.

The sector classification system was developed to predict the likelihood of spontaneous eruption or repositioning of canines after deciduous canines have been removed. This system does not directly indicate the prognosis of surgical procedures or orthodontic interventions aimed at facilitating the eruption of canines.

Another method of predicting the chances of canine impaction is based on calculating the angulation of the canine on an OPG or a lateral cephalogram. ^, Power and Short also looked at angulation as a predictor and found that if the tooth is angled more than 31 degrees to the midline, its chances of eruption after deciduous extraction decrease. Its prognostic value over sector classification has not yet been ascertained ( Fig. 74.11 ).

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