Root length and alveolar bone level of impacted canines and adjacent teeth after orthodontic traction: a long-term evaluation

Abstract Objective The aim of this retrospective study was to evaluate the long-term effects of orthodontic traction on root length and alveolar bone level in impacted canines and adjacent teeth. Material and Methods Sample consisted of 16 patients (nine males and seven females), mean initial age 11 years and 8 months presenting with unilaterally maxillary impacted canines, palatally displaced, treated with the same surgical and orthodontic approach. Teeth from the impacted-canine side were assigned as Group I (GI), and contralateral teeth as control, Group II (GII). The mean age of patients at the end of orthodontic treatment was 14 years and 2 months and the mean post-treatment time was 5 years and 11 months. Both contralateral erupted maxillary canines and adjacent teeth served as control. Root length and alveolar bone level (buccal and palatal) were evaluated on cone-beam computed tomography (CBCT) images. The comparison of root length and alveolar bone level changes between groups were assessed by applying paired t-test, at a significance level of 5% (p<0.05). Results There were no statistically significant differences in root length and buccal and palatal bone levels of canines and adjacent teeth among groups. Conclusions Impacted canine treatment by closed-eruption technique associated with canine crown perforation, has a minimal effect on root length and buccal and palatal alveolar bone level in both canine and adjacent teeth, demonstrating that this treatment protocol has a good long-term prognosis.


Introduction
Dental abnormalities are often found during the diagnosis of orthodontic patients, especially the ectopic eruptions 30 . Several studies have associated the canine impaction with other anomalies 1,18,27,29 , such as agenesis, microdontia and dental transpositions, pointing to the hypothesis that these events have the same genetic origin 1 . Disregarding the third molars, maxillary canines present the greatest prevalence of ectopic eruption, ranging from 1% to 3% depending on the studied population group [5][6][7]13 the palatal displacement is more frequent than the buccal one 2 .
It is important to highlight that failure in early diagnosing and treating the impacted tooth can result in serious damages, such as external resorption of adjacent teeth esthetic problems, reduced dental arches, and increased follicular cyst formation, that may eventually cause tooth loss and periodontal involvement 9,12 .
The main side effect of orthodontic traction when managing ectopic canines is root resorption, which can affect not only canines but also adjacent teeth 20,25 .
In a study using periapical radiographs to evaluate patients presenting palatally displaced canines treated by means of open surgical exposure and leveling approach, the roots of impacted canines and lateral incisors were smaller than those of contralateral teeth used as control 28 .
Factors, such as the initial positioning of the teeth, the size of the follicle and the proximity of impacted responsible for root resorption of the involved teeth. Ericson and Kurol 14 (1988) concluded that the size of the follicle or the positioning of the lateral incisor showed no correlation with root resorption. However, it resorption in the adjacent teeth especially because of the physical proximity (<1 mm) between them 32 .
Another important sequelae related to orthodontic traction of impacted canines is the alveolar bone loss around the canine and the adjacent teeth as well as the 11,18,31 . The diagnosis of these complications and specially its extension can be critical in deciding the treatment plan to be adopted and the prognosis of the tooth impaction. In this regard, the advent of cone-beam computed tomography (CBCT) was extremely important, because it enabled minor changes to be detected with greater accuracy 24 . Thus, root resorption and alveolar bone loss of support tissues surrounding each tooth can now be more accurate and precisely diagnosed 24 . Ericson and Kurol 15 (2000) demonstrated that the use of CBCT increased the detection of root resorption in approximately 50% compared with conventional x-ray exams.
Therefore, the aim of this study was to evaluate the long-term effects of orthodontic traction on root length and alveolar bone insertion in impacted canines and adjacent teeth.  (Figures 1 and 2).   in the two groups was 0.03 mm found in the premolars (Table 2) and regarding the palatal alveolar bone level (PABL) was 0.39 mm, found in lateral incisors (Table   3). When comparing GI and GII, 56% of GI showed a decrease in BABL measurement and 58.3% in the PABL measurement. In three premolars, one in GI (impacted) and two in GII (control group), the absence of buccal alveolar bone was noted.

Discussion
The   Also, the traction protocol and the initial position the role of adequate oral hygiene during appliance 6,16,18 . More reliable results should be achieved in performing measurements in CBCT scans, but in two different periods, before and after treatment. The limitations of this study are its retrospective design. But exposing patients to unnecessary radiation should also be avoided, even considering only the maxillary area. Other limitation of our study is that the sample size seemed small (16 subjects), but the sample size calculation showed that 10 subjects were necessary to achieve reliable results.
It is important to emphasize that an early diagnosis is always better to prevent irreversible damages to the involved and adjacent teeth 9,12 . Even after an early diagnosis, in some cases it is necessary to perform tooth traction. Besides that, according to this research we can state that the traction protocol associated with the orthodontic corrective treatment did not negatively affect the periodontal status and the root length of the impacted canines and adjacent teeth.

Conclusion
The treatment of impacted canines had minimal effect on root length and buccal and palatal alveolar bone levels, not only in orthodontic canines that suffered traction, but also in adjacent teeth (lateral term prognosis of this treatment protocol. Root length and alveolar bone level of impacted canines and adjacent teeth after orthodontic traction: a long-term evaluation