Orthodontics

Kate Counihan EA Al-Awadhi and Jonathan Butler

Guidelines for the Assessment of the Impacted Maxillary Canine

Abstract: Canine impactions are frequently encountered, occurring in 1.7% of the population. The aim of this paper is to provide guidance on the assessment and management of cases which present in general dental practice. Canine position is considered in four categories; canine overlap with adjacent incisor, vertical canine height, angulation to midline and position of canine root apex. Good, average and poor prognostic outcomes are considered for each category and a brief outline of their management is included. Clinical Relevance: Canine impactions frequently present during routine examination. Appropriate recognition, investigation and referral, if necessary, are paramount to successful treatment. Dent Update 2013; 40: 770–777

Treatment of impacted maxillary canines 8% are bilateral.5 The canine has a long arch. Occasionally, canines can be found is a common challenge faced by dental root and good bony support, which is lying horizontally above the apices of the professionals in daily practice. According advantageous in lateral excursions, and maxillary incisors, or displaced near to Mead, an impacted tooth is one that it serves as an excellent abutment for the nose. is prevented from erupting into position fixed and removable prostheses. For because of malposition, lack of space or these reasons, the canine is often referred other impediments.1 After lower third to as the ‘corner stone of the maxillary Aetiology molars, maxillary canines are the most arch’. An absent canine poses aesthetic Buccally and palatally impacted frequently impacted teeth.2 The incidence and functional problems and should be canines have different aetiologies. Jacoby’s of ectopic canine eruption has been shown avoided at all costs. study found that 85% of palatally displaced by Ericson and Kurol to be 1.7%.3 According canines had sufficient space to erupt, to the literature, 85% of canine impactions whereas 83% of buccally impacted canines 4 Development occur palatally and 15% buccally. Impacted had insufficient space to erupt. Therefore maxillary canines have been shown to Canine development crowding was determined as the main occur twice as commonly in females as commences at 4−5 months of age, high aetiological factor in buccal impactions.9 5 males. Dachi and Howell also showed that in the maxilla, lateral to the piriform fossa, Two theories have been proposed to explain the majority of impactions of maxillary and has the longest path of eruption at 22 the aetiology of palatally impacted canines. canines are unilateral at 92%, and only mm.6 Crown calcification starts at 1 year, The guidance theory described by Becker between the roots of the deciduous first et al,10 in 1981, suggests that the distal molar, and is complete at 5−6 years of age. aspect of the lateral incisor is the guide for It then migrates forward and downwards canine eruption. In his study, Becker found Kate Counihan, BDS, MFDS RCS(Ed), to lie buccal and mesial to the apex of that palatally impacted canines were very Specialist Registrar in Orthodontics, the deciduous canine, then continues to closely associated with spaced dentitions EA Al-Awadhi, BDentSc, BA, MSc, PhD, move down the distal aspect of the root and lateral incisors that are peg-shaped, MFD(RCSI), MOrth RCS(Eng), FFD(RCSI), of the upper lateral incisor. As the canine of small mesiodistal width, or congenitally Consultant Orthodontist, Director of erupts into position, the physiological absent. Approximately half of the cases of Teaching and Learning (Postgraduate) median diastema may close.7 Maxillary palatal impactions that were examined were and Jonathan Butler, BDentSc, canines erupt on average at 11−12 years associated with anomalous lateral incisors. MFD(RCSI), MSc, MOrth RCS(Ed), Specialist of age, erupting earlier in females than in The genetic theory described by Peck et Orthodontist, Dublin Dental School and males.8 Canine displacement is classified al,11 in 1994, considers the dental anomaly Hospital, Trinity College, Dublin 2, Ireland. as buccal, palatal, or in the line of the of impacted canines to be a product of 770 DentalUpdate November 2013 Orthodontics

polygenetic multifactorial inheritance. They for supervising the eruption of maxillary based their theory on the fact that palatally canines.13 It was found that positive displaced canines are concomitant with palpation indicated a good prognosis for other dental anomalies, such as lateral- eruption and in 92% of cases palpation premolar hypodontia and peg laterals, that was positive. they occur bilaterally and that there is a gender, familial and population difference in occurrence. Other factors documented Radiographic assessment in the multifactorial aetiology for impacted Radiographic examination is canines include: warranted where there is asymmetry on Figure 1. Buccally impacted canine.  Presence of supernumeraries; palpation or a pronounced difference  Odontomes; in the eruption of canines between left  Pathological lesions, eg cysts; and right side is noted. A radiograph may  Delayed exfoliation of the deciduous also be wise when the canines cannot canine (although this is thought to be palpated in the normal position and be an indicator rather than a cause of the occlusal development is advanced, or displacement); when the lateral incisor is late erupting or  Early trauma to the maxilla; shows a pronounced buccal displacement  Cleft lip and palate; or proclination. Radiographic examination  Ankylosis; of canine position was only indicated in Figure 2. Palatally impacted canine.  Displacement of crypt; 7% of the children in Ericson and Kurol’s  Long path of eruption; and group over 10 years of age, according to the  Syndromes, eg cleidocranial dysplasia. clinical diagnostic criteria used.13 The canine region should be palpated from the age of 8 years, however, lack of positive palpation is Investigations only considered abnormal at the age of 10 Investigations for unerupted years plus. canines should be carried out clinically and Radiographs are required to radiographically. Clinical assessment will view impacted canines in three dimensions involve visual inspection and palpation. (vertical, mesio-distal and buccopalatal), Radiographic assessment will involve the to view the relationship to the midline Figure 3. Distally inclined lateral in palatal use of parallax or Cone Beam Computerized and adjacent teeth and to evaluate any impaction. Key: yellow and black stripes – palatal Technology (CBCT). resorption.14 The views commonly used position. for assessing ectopic canines include panoramic, periapical, cephalometric, lateral Clinical assessment skull and maxillary occlusal. When localizing Clinical investigation involves impacted canines, two radiographic the following: views are needed to locate the tooth in  Visual inspection of the canine bulge, the buccolingual plane.15 The right angle whether it is buccal (Figure 1) or palatal technique uses two radiographs taken (Figure 2), which should be seen between at right angles to each other. This has the lateral incisor and first premolar roots, been done with a lateral cephalometric and inspection of the angulation of the radiograph and a posterior anterior Figure 4. Mesially inclined lateral in buccal lateral incisor, eg a distally inclined lateral radiograph but is not commonly used. impaction. Key: yellow and black boxes – buccal incisor may infer palatal impaction (Figure The most common means of radiographic position. 3) and a mesially inclined lateral incisor localization currently in use are parallax may indicate buccal impaction (Figure 4). and CBCT. In addition, the colour and mobility of the The preferred means of deciduous canine should be inspected as localization is parallax, which is the this might indicate resorption of the root. apparent displacement of an image  Palpation of the buccal surface of relative to the image of a reference object the alveolar process distal to the lateral and is caused by an actual change in incisor from 8 years of age may reveal the the angulation of the X-ray beam.16 The position of the maxillary canine and has reference object is normally the root of an been recommended as a diagnostic tool adjacent tooth. The image of the tooth that by Kettle.12 A longitudinal study of 505 is farther away from the X-ray tube moves Figure 5. Resorption area on radiograph and clinically on extracted tooth. school children evaluated clinical methods in the same direction as the tube, whereas November 2013 DentalUpdate 771 Orthodontics

that of the tooth closer to the X-ray tube superimposition of the incisor roots and the with physical contact between the root of moves in the opposite direction to the crown of the impacted canine obscuring the incisor and prominences on the canine tube (SLOB Rule − Same Lingual Opposite morphology. CBCT overcomes this problem, crown (Figure 5).30 However, the response Buccal). An orthopantomogram (OPG) and increasing detection of resorption by 50%.25 of incisors with resorbed roots following anterior occlusal radiograph are commonly CBCT eliminates potential problems with treatment of impacted canines was used, giving a 60° tube shift approximately. magnification and superimposition which assessed by Becker and Chaushu31 and they This is vertical parallax, as the angulation make interpretation and localization with suggested that, once the impacted canine of the X-ray beam changes in the vertical conventional radiography challenging. had been moved away, there is no risk for plane from 8°, for an OPG, to 60° for an An important consideration for clinicians further resorption. Falahat et al,32 in their anterior occlusal.17 Horizontal parallax prescribing CBCT outlined by IR(ME)R follow-up of root resorption, also showed is caused by change in the angulation 2000 and British Orthodontic Society that root resorption associated with ectopic of the X-ray beam, or tube shift in the Guidelines for use of radiographs in clinical canines, in most cases, did not threaten the horizontal plane, and two periapicals orthodontics26 is the need to interpret and long-term viability of the affected incisor, or a periapical and an anterior occlusal report all the image data, including those even when resorption was severe. Results radiograph are the radiographs of choice areas outside the jaws, since any occult from their study showed good clinical and for this technique. Armstrong et al18 showed pathology or abnormalities found in the radiographic evidence of healing in all cases, that the diagnostic sensitivity for palatally scans must be reported on and, if necessary, except for one ankylosed tooth and one placed canines was significantly greater referred for further management. with pulpal obliteration. for horizontal parallax (88%) than for vertical parallax (69%) and concluded that horizontal parallax is superior to vertical Sequelae Management parallax in diagnostic accuracy. In cases of Possible sequelae of impacted The management of impacted two unerupted canines, a single OPG can canines include cyst formation, internal canines usually involves five treatment be used to assess position, with the palatal resorption of the impacted tooth, external options: canine appearing bigger on radiograph, resorption of impacted or neighbouring  No active treatment, ie leave in situ and however, this method is difficult for even teeth, ankylosis, infection and migration monitor radiographically for cyst formation; experienced clinicians to use.19 of neighbouring teeth with loss of arch  Interceptive treatment; Computerized tomography (CT) length.27 Resorption and pathology are  Surgical exposure and orthodontic was developed by Sir Godfrey Hounsfield more likely in females, in age groups alignment; in 1967 and, since the first prototype, greater than 14 years, and in cases where  Surgical repositioning; there has been a gradual evolution to the angulation of the canine to the  Extraction. five generations of such systems.20 Cone midline is more than 25°.28 Ericson and The general dental practitioner beam computerized tomography (CBCT) Kurol showed, in a study of 107 children, is well placed for early detection of was designed to overcome some of the that resorption on the roots of incisors ectopic canines. When canine impaction limitations of conventional CT devices (eg adjacent to ectopically positioned canines is identified, extraction of the maxillary high radiation dose to produce the multiple occurred in 38% of lateral and 9% of central deciduous canine may, in some cases, allow images which are stacked to produce a incisors.25 Walker et al showed that 66.7% the impacted canine to erupt in the correct complete image). CBCT was developed in of lateral and 11.1% of central incisors were position. In Class I non-crowded cases, the 1990s and is the most precise method resorbed following ectopic eruption of where the permanent maxillary canine is of radiographic localization, maximizing adjacent canine.29 The reported incidence impacted or erupting buccally or palatally, diagnostic yield and reducing exposure,21 of resorption depends upon the imaging the preventive treatment of choice has been the total radiation being approximately technique used. Superimposition of the shown to be extraction of the deciduous 20% of conventional CTs and equivalent incisor roots and the crown of the impacted canine from the ages of 10−13 years.33 It 22 to full mouth periapicals. It uses a cone canine on intra-oral radiographs obscures is important that no crowding is present. 29 34 shaped X-ray beam to acquire a volumetric root morphology in 45% of cases. Power and Short showed that interceptive dataset of the region of interest with a Computed tomography overcomes this extraction of the deciduous canine single rotation of the patient.23 Computed problem. Ericson and Kurol25 concluded that completely resolved permanent canine image reconstruction produces 3D images resorption on maxillary incisors after ectopic impaction in 62% of cases, and a further at high resolution. Mah et al24 used CBCT to eruption of canines was more common than 17% showed some improvement in terms locate impacted canines precisely and to previously thought. CT scanning increased of more favourable canine positioning. 35 design treatment strategies that allowed for detection of root resorption by 50%. The Ericson and Kurol analysed the effect of minimally invasive surgery to be performed. sensitivity of intra-oral films was low when extraction of the deciduous canine on 46 A common problem in orthodontics is diagnosing resorption, and was reported palatally erupting ectopic maxillary canines underestimating the degree of resorption in 0.71% of children in earlier studies.13 in 35 individuals aged 10−13. They found associated with unerupted teeth, especially The most likely cause of root resorption that, in 78% of palatally erupting ectopic maxillary canines. Resorption is not always is inherent pressure due to migration of canines, the eruption paths normalized detected on plain radiographs owing to the displaced erupting canine, combined within 12 months after extraction of the 772 DentalUpdate November 2013 Orthodontics

deciduous canine. In 64% of these cases, be sought before embarking upon any improved positions were noted after only 6 interceptive treatment. Not all canines months, and in 36% the position improved normalize, and an orthodontist would after 12 months. Inclusion criteria specified be equipped to manage those that fail that normal space conditions were present to show improvement. Furthermore, and no incisor root resorptions were greater success for re-alignment was found. Baccetti et al looked at interceptive shown by Baccetti et al37 with the use of treatment of palatally impacted canines space creation by cervical pull headgear by extracting the deciduous canine alone and rapid maxillary expansion, where a or in association with the use of cervical specialist opinion again would be ideal. pull headgear.36 They showed that removal of the deciduous canine alone showed Figure 6. Canine crown horizontal overlap. Key: correction of palatal displacement in Assessment for interceptive 1. No horizontal overlap; 2. Up to half root width; 65.2% of cases, compared with 87.5% management 3. Complete overlap. where cervical pull headgear was used and Four aspects of canine position 36% in the untreated control group. In a should be assessed, as well as the age later study, Baccetti et al37 showed that the of the patient carefully being taken into use of a rapid maxillary expander as an account. The prognostic factors have been early interceptive approach is effective for investigated by McSherry39 and Pitt et al,40 increasing the rate of eruption of impacted who suggested the use of these factors in canines. In the treatment group, 65.7% an index to estimate treatment difficulty. erupted successfully compared to only These factors are discussed below:

13.6% in the control group. The success  The amount the canine crown of interceptive treatment depends on the horizontally overlaps the adjacent incisor degree of impaction, age at diagnosis (Figure 6). The closer the canine lies to and canine position. Generally speaking, the midline, the poorer the prognosis when the degree of overlap between for alignment. No horizontal overlap of Figure 7. Vertical height of canine crown and the impacted canine and adjacent lateral the adjacent incisor would indicate good key opposite. Key: 1. CEJ to halfway up the root; incisor exceeds half the width of the incisor prognosis, overlap up to half the root 2. > halfway < full root length ; 3. > full root root, the possibility of total recovery using width suggests average prognosis and length. interceptive treatment alone decreases.34 complete overlap of root would indicate Ericson and Kurol35 showed that, if the poor prognosis. canine overlapped the lateral incisor by  Vertical height of the canine crown more than half of the lateral root, only 64% (Figure 7). The more apical the position of normalized, compared to 91% when the the crown, the poorer the prognosis for overlap was less than half the lateral root. alignment. From the level of the cemento- The chance of successful eruption following enamel junction to less than halfway extraction of the deciduous canine also up the root of the lateral incisor would decreases as the angle from the vertical indicate a good prognosis; more than increases.35 The degree of horizontal overlap halfway up the root but less than the full with the lateral incisor has been found length root length would indicate average to have more impact on prognosis than prognosis; and above the full length of Figure 8. Canine angulation to midline. angulation.34 A Cochrane review published root would have poor prognosis. in 2009 concluded that ‘there is currently no  Canine angulation to the midline evidence to support the extraction of the (Figure 8). As canine angulation to deciduous maxillary canine to facilitate the the midline increases, the prognosis eruption of the palatally ectopic maxillary decreases. Angulation of 0−15° would permanent canine’.38 This review stated that point towards a good prognosis, randomized controlled trials were identified angulation of 16−30° an average but, owing to deficiencies in reporting, they prognosis, and angulation of 31° or more, could not be included in the review. The a poor prognosis. authors recommended that further clinical  The position of the canine root apex trials should be conducted, and greater in the horizontal plane (Figure 9). If the attention to the design and reporting of canine apex is located above the normal Figure 9. Position of canine root apex studies should be given to improve the canine position, prognosis for alignment horizontally and key opposite. Key: 1. Above quality of clinical trials. For these reasons, is good, if the apex is above the first canine position; 2. Above 1st premolar; 3. Above an orthodontic opinion should always premolar region, prognosis is average, and 2nd premolar. November 2013 DentalUpdate 775 Orthodontics

Category Good Prognosis Average Poor

Overlap of incisor No horizontal overlap Up to half root width Complete overlap

Vertical height CEJ – halfway up root >half full root length

Angulation 0–15° 16–30° >30°

Position of apex Above canine position Above 1st premolar Above 2nd premolar

Table 1. Prognosis for re-alignment depending on assessment in various categories. Key – Green: good prognosis; Yellow: average prognosis; Pink: poor prognosis

if it is above the second premolar, prognosis canine. Many clinicians choose to remove the eventual loss of the deciduous canine is poor. the deciduous canine interceptively and and the need for permanent restoration. The evidence basis for these monitor the situation. If the canine fails to If one or more of the criteria prognostic indicators has been documented erupt or improve within 12 months, the suggest a poor prognosis, or there is by McSherry,39 Stivaros and Mandall14 orthodontic treatment will most likely be evidence of pathology, then orthodontic and Pitt et al.40 It is recommended in the exposure and alignment.35 treatment is essential and the deciduous RCS Eng Guidelines on The Management In cases where prognosis is canine should not be removed (Table 1). of the Palatally Ectopic Maxillary Canine average, ie two categories suggest a good In these cases, all factors must be carefully that less experienced practitioners seek prognosis and two suggest an average considered before a decision on definitive the opinion of an orthodontic specialist prognosis (Table 1), definitive treatment treatment can be made. prior to initiating treatment.41 The above could be the extraction of the canine, criteria may aid decision-making regarding depending on the overall malocclusion and management of cases. According to the the associated factors, such as patient age, Conclusion criteria, if canine prognosis is good in all crowding and condition of the dentition. Incidence of maxillary four categories, then a decision may be Therefore maintaining the canine could be canine impaction is 1.7%, therefore a made by the orthodontist to extract the important for the bone level or to avoid the common encounter for general dental deciduous canine (Table 1). This may allow need for restoration in an adolescent. The professionals. Practitioners should be aware spontaneous eruption of the impacted patient should of course be made aware of of normal canine development, relevant 776 DentalUpdate November 2013 Orthodontics

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