Bibliografia 2018-07-09T10:41:01+02:00

Impacted and transigrant mandibular canines incidence, aetiology, and treatment: a systematic review

European Journal of Orthodontics, 2017

Domenico Dalessandri, Simone Parrini, Rachele Rubiano, Diletta Gallone and Marco Migliorati


Altered tooth eruption in a clinical condition characterized by failure of the tooth to emerge in the appropiate position. This may lead to a tooth impaction, translocation or even trasmigration. Impaction is defined ad the failed eruption of a permanent tooth with a completely deloped root, while the migration of an impected tooth across the midline by more than half of ots lenght is defined as transmigration (1-2).

The canine plays important funcrional ad estetic roles in humans, and altered ereuption of these teeth is an important patient concern. A sound diagnostic and therapeutic approach, together with clear knowledge of all prognostic implications, is mandatory for timely diagnosis and appropriate treatment planning.

Maxillary canines are the second most frequentely impacted teeth after the third molars, with a prevalence ranging from 0.9 to 5 per cent. Therefore, several studies with large patient samples have investigated different treatment strategies for impacted maxillary canines, ranging from interceptive approaches to guided forced eruption or extraction and orthodontic space closure (3-6).

However, mandibular canine impaction, translocation and, in particular, transmigration are rare: therefore, few studies on these topics are available. The majority of published works are case reports involving a single patient or a limited number of patients.

Consequently, it is difficult for the clinician to find reitable data regarding the incidence, tratment outcomes, and potential complications of impacted and transmigrant mandibular canines. A combination of the results of all studies conducted to date will allow to find a sounf evidence regarding the advantages and disadvantages of every possible clinical  approach and a more precise estimation of the actual incidence (7,8).

Therefore, the aims of this systematic review were to summarize currently available data pertaining to the incidence of mandibular canine impaction and transmigration, provide and overview of the aetiology, and elevate the success rate for different treatment strategies.

Materials and methods

This systematic review was registered in the international database PROSPERO (CRD42014006175) and conducted in coordance with PRISMA and CRD (Centre for Reviews and Dissemination, University of York) statements.

A computerized systematic search of studies published up to February 2016 was conducted without language restrictions, using the strategy illustrate in Table 1, in the following electronic database: Medline (via PubMed), Cochrane Central Register of Controlled Trials (issue 1, 2015), ISI Web of Knowledge, and Scopus.

A hand serch was thoroughly performend for additional articles in the medical library of Turin University with assistance of a senior health sciences librarian. The authors’ personal libraries and the reference lists of all selected articles were also searched manually. Title and abstract (TIAB) screening was performed to select articles for full text retrieval. A limited grey literature search was conducted through the use of Google Scholar.

The inclusion and exlusion criteria for this systematic review were based on the type of study and are shown in Table 2. Literature reviews, case reports, abstracts, author debates, summary articles, and animal studies were excluded. The reference lists of these articles were perused and related references were saerched. Studies were indipendently selected for analysis by two of the authors (SP and DG). In case of degreement, a study was included by discussion and consensus between the two. From the selcted articles, the investigators indipendently extracted data that answered the clinical research questions.

A costumized data extraction from was developed, wich included the following items: first author’s name and year of publication, study design, origin of studied population, incidence of impactation and transmigration, aetiology, and treatment strategy. The Newcastel-Ottawa Scale (NOS) was applied to assess the quality of reviewed articles (9). The qaulity of the selected articles was independetly assessed by the two authors who selected the studies (SP and DG). In case of disagreement, a consensus was reached after discussion with a third author (DD). Studies were considered of low quality if they received between 0 and 3 stars, of medium quality between 4 and 6, and of high quality between 7 and 9 stars.


The article selection process is illustrated through the PRISMA flow diagram presented in the Figure 1. The electronic databases search yieleded 1342 articles. Overlapping data among the databases were identified and duplicates removed, following wich 630 articles were screened. On the basis of TIAB screening, 147 articles were selected for full-article review. Application of the inclusion and exlusion criteria identified 13 relevant publications that were included in the qualitative analysis. Two studied, one was a cohort study, two were observational studies, and four were retrospective observational study.

Four of these analysed samples comprising a collection of intraoral photographs, dental casts and different types of radiographs, such as dental panoramic tomograms (DPTs), periapical radiographs, occlusal radiographs, and lateral cephalograms, obtained from patients who presented with at least one missing permanent mandibular canine or a retained deciduos canine. One study eas based on intraoral radiographs and DPTs. Four studies evaluated only DPTs. Seven studies used a randomization method for sample selection (10-12).

Tables 3, 4, and 5 summarize the key data pertaining to the incidence, aetiology, and teatment from these 13 articles. The incidence of impacted and transmigrant mandibular canines was higher among men than among women in five studies. In most cases, the data belonged to orthodontic patients; therefore, these values can be higher than those for the general population. This is because patients with one or more missing canines are more likely to look for an orthodontic or dental consultation compared with patients with normal dentition.

Fig. 1 – PRISMA flow diagram.

With regards to the aetiology, in one study, 3 per cent of the impacted mandibular canines were associated with lateral incisor anomalies in two studies.

The most frequent tratment strategy in three studies waas surgical removal. In two studies, the missing canine was correctly positioned in the dental arch through orthodontic treatment and foced eruption. In one study, two different approaches were selected with the same frequency: orthodontic treatment and radiographic monitoring (wait-and-watch approach). In three studies, the approach was the first choice. As a consequence of the heterogeneity of the selected studies, a meta-analysis of the combined study results was not conduced.

Table 6 summarizes the quality assestment of these 13 articles, performed using the NOS: 12 articles were rated as medium quality, 1 article was rated as low quality.


The present systematic review was performed to summarize data pertaining to the incidence and aetiology of impacted and transmigrant mandibular canines and the success rates of various treatment strategies.

Our comprehensive search resulted in the selection of 13 articles: two cross-sectional studies, four retrospective cohort studies, one cohort study, two observational studies, and four retrospective observational studies. As a result of their methodological heterogeneity, these studies were assessed according to a format that enabled a structured summary of data pertaining to incidence, aetiology, and treatment. Such a template format was not perfectly fitting to all the included studies because of the different study designs, particularly with regards to patient and control selection methods. Nevertheless, it was the best possible approach to a systematic assessment of the relevant literature. All the pertinent details of the included studies were summarized in tables. On the basis of the data for each individual study, the tables also summarized the reviewers’ responses to the clinical research questions. All studies were separately assessed by the investigators, and in case of divergent assessments with regards to strengths and weaknesses, a consensus was reached by discussion.

Two studies were conducted in different departments of the same dental school (15,17), with a possible 2 years overlap of patients records included in the analysed databases: considering that any meta-analysis was performed combining different study data, both manuscripts were included in our report. Furthermore, it was not possible to establish if there was another overlap between Yavuz (15) and Aras (13) studies, apparently performed in two different Turkish universities during a collaboration between these two researchers.

The first aim of this review was to assess the incidence of mandibular canine impaction and transmigration. Several studies analysed the incidence of transmigrant mandibular canines, and our result of an incidence ranging between 0.1 and 0.31 per cent confirmed values already reported in previous narrative reviews. However, this finding was not observed for the incidence of mandibular canine impaction; we derived an incidence ranging from 0.92 to 1.35 per cent, which was higher than that (0.05–0.4 per cent) reported in previous narrative reviews. This was possibly because different studies focused on different populations ranging from orthodontic patients to the general population, different ethnic groups, and different sample sizes.

In all 13 articles, the aetiology was considered and, when possible, investigated. The suggested causes of impaction included abnormal displacement of the dental lamina during the embryonic life, hereditary factors, cancers, endocrine glands malfunction, vestibular inclination of the mandibular incisors, traumatic fracture of the mandible near the site of mandibular canine eruption, and other local factors such as odontomes, cysts, shape anomalies of adjacent teeth, and retained root stumps. These results are in accordance with those of previous reviews.

With regard to the treatment of impacted and transmigrant mandibular canines, the following different strategies were evaluated: orthodontic traction, autotransplantation, and surgical removal of impacted canines; and orthodontic traction, autotransplantation, surgical removal and radiographic monitoring of transmigrant canines. The most commonly employed treatment strategy for impacted mandibular canines was surgical removal, because it was considered easier and faster than bringing the canine to its actual position: it must be considered that canine impaction is generally diagnosed when its root is already well developed to more than two-third of its final length; this can complicate orthodontic traction and repositioning. When the root development stage is more favorable, orthodontic traction is planned in order to obtain ideal function and aesthetics through correct positioning of the impacted canine. Orthodontic traction is probably more difficult and complicated, although it is the most efficient strategy to restore physiological occlusion. The use of temporary anchorage devices such as mini-implant and mini-screws could help to reduce negative effects of anchorage loss, if used to reinforce anchorage of teeth where the canine traction force is applied or if used as direct point of application of this force. Autotransplantation was rarely used.

The methodological quality of clinical trials included in our review was mainly medium, with only one study judged of low quality: therefore, the results of these studies should be interpreted with a moderate caution. An evaluation of the methodological quality provides an indication of the strength of evidence provided by a study, because flaws in its design or conduct can result in biased results. The NOS was used because it was found to be reliable and ease of use for assessing the quality of nonrandomized studies, as the studies considered in the present systematic review.

The possible limitations of this systematic review include a selection bias, which variably affects all systematic reviews, the fact that we attempted to extend our search to the grey literature, and the inability to plan a meta-analysis because of the nonhomogeneous study designs and the low incidence of impacted mandibular canines, which resulted in small sample sizes in the analysed studies. Furthermore, available data mainly derive from specific populations (mainly Turkish and Chinese) that could not be fully representative of a general Caucasian population: this gap could be only filled if new studies are performed on more representative population groups.

Nevertheless, based on the finding of the present review, some diagnostic measures are suggested and a decision tree is proposed in order to guide practitioners through the diagnostic process and the treatment plan elaboration (Figure 2).

A radiological screening with a DPT is appropriate in late mixed dentition in presence of teeth morphology anomalies, family history of teeth impaction or transmigration, presence of aggressive caries destruction or poorly restored deciduous teeth with possible presence of inflammatory cysts.

From a therapeutic point of view, the time of diagnosis plays a crucial role in treatment options and prognosis. During the mixed dentition phase the extraction of the deciduous canine and, if present, of the adjacent first deciduous molar could stimulate the impacted canine to spontaneously erupt; likewise, surgical removal of mechanical obstacles such as odontomes and cysts could allow a complete eruption, if space is available, or at least the emergence of the impacted canine in a more favourable position for the following forced orthodontic eruption. During this period if an impacted canines is migrating towards the midline a comprehensive orthodontic evaluation must be performed in order to decide the best treatment plan case by case. In the permanent dentition, when the development of the root of the impacted canine is complete, the possibility of a spontaneous eruption after obstacles removal decreases dramatically with the increase of patient age: in these patients both orthodontic and periodontal prognoses of impacted and transmigrant mandibular canines after the orthodontic guided eruption should be carefully considered, because of the inverse relation with the complexity and the duration of the orthodontic traction.

The overall occlusal pattern and the position of the permanent canine with regard with adjacent teeth and anatomically sensible structures certainly influences treatment plan formulation.

Finally, several conditions should be generally taken into account: the reabsorption of the root of an adjacent tooth, signs of ankylosis or coronal/cervical reabsorption of the impacted canine, patient preferences and treatment compliance, regarding oral hygiene maintenance and orthodontic auxiliaries use.

Undoubtedly, the key to the restoration of a perfect occlusion using orthodontic traction is the timing, that is knowledge of the optimal stage of intervention to achieve acceptable functional and aesthetic success. Unfortunately, this timing remains unclear, and radiological and clinical predictability indexes for mandibular canine impaction or transmigration are lacking. On the other hand, the same data are available in abundance for maxillary canines since a long time, including conventional and three-dimensional (3D) radiological findings. Cone beam computed tomography (CBCT) technology, which is currently evolving with the aim of developing scanning protocols that can provide 3D images of an acceptable quality and an X-ray dose that is truly equivalent to the sum of that used for conventional digital DPT and lateral cephalogram examinations, is currently the most reliable and informative diagnostic tool for impacted teeth. It can be used for the precise evaluation of treatment difficulties and clinical strategies, and, in future, it can be proposed as a screening tool when 3D indicators of impaction and transmigration risks are established. Furthermore, multicenter clinical trials investigating the effects of different timings of intervention are required to determine the correct stage of eruption at which orthodontic treatment should be initiated, considering that an orthodontic treatment could be defined interceptive if performed at an early stage or corrective if the eruption is already altered (23–41).


  1. The incidence of mandibular canines impaction ranges between 0.92 and 5.1 per cent, while that of transmigration ranges from 0.1 to 0.31 per cent.
  2. Although the precise aetiology remains unknown, odontomes, cysts, and lateral incisor anomalies are more likely to play a role.
  3. The most common treatment strategies are surgical extraction and orthodontic traction for impacted mandibular canines, surgical extraction, and radiographic monitoring for transmigrant mandibular canines: based on the finding of the present review, a decision tree was proposed in order to guide practitioners through the treatment plan elaboration.


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