INTRODUCTION

Permanent canines are the secondmost commonly impacted teeth after third molars, and almost 1%–3% of the population has been found to have impacted maxillary canines.^1,2 In about 85% of cases with impaction, maxillary canines are palatally displaced.³ Genetic predisposition and several other factors are implicated in the etiology of palatally displaced maxillary canines (PDCs).⁴ The management of these clinical problems may require interdisciplinary approaches in addition to substantial participation by orthodontists.⁵ Complications resulting from PDCs include loss of space in the dental arch, displacement and resorption of adjacent roots, and formation of cysts in rare cases.⁶ Moreover, patients may undergo traumatic surgical exposure of PDCs, followed by prolonged and costly fixed orthodontic treatment.^7,8

The management of PDCs may require surgically exposing the canine and applying a fixed orthodontic appliance to guide it into appropriate occlusion or extracting the primary canine to provide space for its successor to eliminate or minimize developing malocclusion, an approach called “interceptive orthodontics.”⁹ Early interceptive treatment can lessen the degree of developing malocclusion and thus decrease the need for future orthodontic treatment of permanent teeth.¹⁰ It can also minimize the time and cost of treatment in addition to improving self-esteem and patient satisfaction.¹¹

Previously, Ericson and Kurol¹² reported that extraction of primary canines is the treatment of choice for impacted maxillary canines, as 78% of such cases resulted in normal occlusion. Several prospective studies^12–14 and a retrospective cohort study¹⁰ have also shown that primary canine extraction facilitated the eruption of PDCs. Other studies have reported interceptive extraction of PDCs combined with orthodontic treatment (rapid maxillary expansion) or extraction of primary molars.^15–18 However, these studies varied considerably in their design, sample-size calculation, criteria for clinical examination, and outcomes.

Parkin et al.¹⁹ conducted a systematic review in 2009 in which they were unable to provide reliable evidence to support the effectiveness of interceptive extraction of deciduous canines to manage PDCs. Later, Naoumova et al.³ (2011) included two studies in their systematic review to determine whether extraction of primary canines helps prevent the impaction of permanent maxillary canines. However, robust evidence in favor of their hypothesis was limited. In 2012, Parkin et al.²⁰ considered two studies for their systematic review to determine whether complications of PDCs can be prevented via the extraction of primary canines. Due to the lack of reliable studies, the authors of these systematic reviews stressed the need for more clinical trials with high-quality methodology.^3,19,20 As a result, two recent randomized clinical trials reported the spontaneous correction of PDCs after the extraction of primary canines.^21,22

The present systematic review summarized the relevant randomized clinical trials to provide reliable estimates of the efficacy of interceptive orthodontic intervention, specifically, to find out whether successful management of PDCs can be achieved by interceptive extraction of deciduous maxillary canines.

MATERIALS AND METHODS

The preferred reporting items for systematic reviews and meta-analysis (PRISMA) guidelines were followed for the present systematic review (www.prisma-statement.org).²³

Search Strategy

The search strategy made use of Boolean operators with different key words. The key words included “canine,” “cuspid,” “maxillary,” “palatal,” “impacted,” “unerupted,” “retained,” “ectopic,” “displaced,” “interceptive,” “orthodontics,” “primary,” “deciduous,” “treatment,” “management,” “extraction,” and “removal” (Table 1).

Table 1. Search Strategy in Different Databases

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Eligibility Criteria

The inclusion and exclusion criteria were established based on populations, interventions, comparisons, outcomes, and study designs (PICOS). Details of inclusion and exclusion criteria are given in Table 2.

Table 2. Inclusion and Exclusion Criteria

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Study Selection and Methodological Quality Criteria

Calibration for interexaminer reproducibility was carried out for two reviewers (N.N.A. and M.A.N.). Both reviewers independently reviewed the titles and abstracts of the articles for inclusion in the present systematic review. Disagreements about the inclusion of certain articles were resolved by discussion and mutual consensus. The articles that met the inclusion and exclusion criteria were read fully and evaluated for their quality based on methodological quality criteria (Table 3) adapted from the CONSORT statement,²⁴ Jadad quality assessment scale,²⁵ and previous similar studies.^3,20

Table 3. Methodological Quality Criteria^a

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Each reviewer independently scored the selected studies and discrepancies in the scoring of studies were resolved through discussion. Each study received a score out of 11 points (Table 4). The studies were classified as good (>9 points), moderate (7–9 points), or poor (<7 points) in quality based on the scoring of the methodological criteria.

Table 4. Summary of the Characteristics of Included Studies

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Table 4. Extended

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RESULTS

Study Selection

The flow diagram in Figure 1 illustrates the PRISMA process that was used to identify, screen, and select studies for inclusion in the present review. Searching through Medline, Scopus, and Web of Science retrieved about 866 articles. Duplicate articles (repetitions) were removed. Titles of the articles were read and those found unrelated to the topic of research were excluded, which led to the exclusion of 791 articles. The remaining 75 articles were selected and their abstracts were thoroughly read. This resulted in selecting 33 articles for complete reading, and the inclusion and exclusion criteria were applied to these papers. Finally, four articles met the inclusion and exclusion criteria, to which were applied the methodological quality criteria.

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Quality Assessment of Selected Studies

Table 5 presents the evaluation of the methodological quality of the four studies included in the present systematic review. The two recent studies^21,22 scored higher than did the two older studies.^26,27

Table 5. Methodological Quality of Selected Studies

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Risk of Bias

The risk of bias was assessed in the four selected studies using PRISMA guidelines.²⁸ Most studies were found to have a high risk of bias (Table 6).

Table 6. Assessment of Bias Risk

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The measures of effect size of published studies such as odds ratio, relative risk, and standardized mean differences are calculated in meta-analysis to report the strength of the relationship between intervention and control groups (two variables) and thus the effect of intervention.²⁹ Hence, due to the nature and inconsistencies of the data reported in the selected studies, it was not possible to perform a meta-analysis.

DISCUSSION

It was encouraging to find two recent studies^21,22 with better methodological rigor than previous studies^26,27 that were also included in similar systematic reviews.^3,20 Although a large body of high quality research is still lacking in the literature, it was reasonable to conclude, based on the available evidence, that the interceptive extraction of primary maxillary canines can be employed as an acceptable approach to facilitate the eruption of PDCs.

All studies included in the present systematic review compared the percentage of success or improvement between the intervention and control groups. Naoumova et al.²¹ found that 69% of cases in the extraction group had spontaneous eruption of the permanent maxillary canines compared with 39% of the control group. Bazargani et al.¹⁸ reported a success rate of 67% at the extraction sites and 42% at the control sites. Similarly, Baccetti et al.²⁶ found a significantly higher success rate of 65.2% in the treatment group, compared with 36% in untreated controls. Leonardi et al.²⁷ demonstrated that the 50% success rate in the extraction group was not significantly different from that in the control group.

Three studies^21,22,26 received ethical approval from the respective institutional review boards/committees, and these studies also specified that verbal or written consent was obtained from the subjects or their parents/guardians. Leonardi et al.²⁷ did not obtain ethical approval from an institutional review board; however, the authors received informed consent from the study participants or parents.

Sample size calculations were performed appropriately in two of the four studies.^21,22 The clinical diagnostic procedures used in the selected studies involved clinical and radiographic examinations at baseline and during and after the follow-up period. Bazargani et al.²² also took impressions for study casts and included a single examiner who assessed the reproducibility of measurements performed every 3 months during the observation period. Similarly, Baccetti et al.²⁶ and Leonardi et al.²⁷ reported a high rate of reproducibility of measurements in their studies. Two calibrated examiners independently performed all the measurements in the study performed by Naoumova et al.²¹

The inclusion of a control group was adequately reported in three studies.^21,26,27 Bazargani et al.²² recruited a sample of 24 consecutive patients with bilateral PDCs; one side of the maxilla served as the extraction site (treatment group), while the contralateral side as the nonextraction site (control group). Details of the randomization process were discussed in all four selected studies. Naoumova et al.²¹ employed a block randomization method and concealment of allocation. Bazargani et al.¹¹ generated a computerized randomization list and briefly described the process of randomization. On the other hand, in the two older studies,^16,17 the methods of randomization were not adequately discussed and an unequal number of cases were allocated to the intervention and control groups.

Discrepancies in the reporting of information were found in the study by Leonardi et al.²⁷ The authors mentioned that there were 50 participants at the start of study and that 7 of them dropped out. However, they also stated that 46 participants were divided into three groups. Similarly, Baccetti et al.²⁶ reported that 75 participants were enrolled and 70 individuals completed the trial, as 5 subjects left the study. Later, they described the allocation of 69 participants into three groups. No such data inaccuracies were found in the two recent trials.^21,22

The follow-up period varied among the four studies. Naoumova et al.²¹ reported a follow-up period of 12 months, after which surgical exposure of the canine and orthodontic treatment were performed on those subjects who did not exhibit spontaneous canine eruption; thus, the total observation period was 24 months. The remaining three studies had an average follow-up period of 18 months, but the total observation period in the study by Leonardi et al.²⁷ was 48 months. Regarding dropouts, Baccetti et al.²⁶ and Leonardi et al.²⁷ mentioned five and seven dropouts, respectively, in their studies. However, neither the reasons for dropout nor their effects on the overall results were discussed. Naoumova et al. (2015)²¹ investigated the effect on the resorption of adjacent teeth, but found no differences in control or intervention groups. Similarly, Bazargani et al., (2014)²² observed no midline shift after unilateral extraction of the primary maxillary canine. Two previous studies did not report any side effects of intervention.^26,27

All the studies in the present systematic review had more than single outcomes. Naoumova et al. (2015) investigated whether extraction of the primary canine facilitated the eruption of the palatally displaced canine and also evaluated the root resorption of teeth adjacent to PDCs.²¹ Two outcomes were evaluated in two studies conducted by Baccetti et al. (2008) and Leonardi et al. (2004).^26,27 Authors of both these studies observed two interceptive methods for managing PDCs, that is, extraction of the deciduous canine alone and extraction of the deciduous canine along with using cervical pull headgear. Bazargani et al., (2014) analyzed three main outcomes in their randomized clinical trial.²² They evaluated the (1) effect of extraction of the primary canine on the successful eruption of PDCs, (2) age of patients appropriate for interceptive treatment, and (3) impact of unilateral extraction of the primary canine on midline shift. In addition, included studies did not report confounding factors that could affect the results.

Some studies were not included in the present systematic review because they did not fulfil the inclusion and exclusion criteria. However, those studies reported that most cases of PDCs achieved a normal eruptive position after extraction of deciduous maxillary canines.^12,13,30,31 It is hoped that the present systematic review will help clinicians and orthodontists make informed decisions about the management of PDCs by interceptively extracting primary canines, preferably in children aged 10–11 years, as reported by Bazargani et al.²²

CONCLUSIONS

• Based on the currently available body of research, it is reasonable to conclude that the eruption of PDCs can be facilitated by the extraction of primary canines.

• Although evidence about the efficacy of extracting deciduous canines for the successful management of PDCs is mounting, there is still a need to conduct further high-quality, randomized, clinical trials recruiting different population groups.

• It is also important to evaluate the side effects and a cost analysis of this procedure.