Failure rates and associated risk factors of orthodontic – surgical treatment of impacted canines

Abstract

Introduction: An impacted tooth is a tooth having more than three-quarters of its root developed, which has not erupted and is not expected to erupt in the near future. Canine impaction constitutes a clinical entity that may affect both functional occlusion and smile aesthetics, and may even lead to the development of certain pathological conditions, including cystic lesions and root resorption of adjacent permanent teeth. The frequency of maxillary canine impaction has been reported to be between 0.9-5% in the Caucasian population depending on the population under investigation, while the mandibular canine impaction demonstrates a much lower frequency, estimated to range between 0.3% to 1.35%. Numerous etiological factors have been proposed and investigated as responsible for the impaction of a developing canine and various treatment methods are available, some of which aim at the prevention of impaction, while others’ purpose is its resolution. The most widely used treatment approach, if the prevention (early interceptive treatment) is not undertaken or it is unsuccessful, is the orthodontic alignment upon surgical exposure, otherwise known as orthodontic–surgical treatment. The surgical part of the treatment can be performed with two approaches, the closed and the open exposure. The investigation of numerous factors that could potentially have an impact on numerous stages of this procedure, influencing the final outcome, the canine treatment duration and/or the need for repeat intervention, is considered imperative, should we aim at providing adequate information to both clinicians and patients to assist their making evidence-based decisions regarding the treatment. Aim: The main purpose of the present study was to determine the overall failure rate of orthodontic–surgical treatment of impacted canines of Greek adolescent and adult patients who underwent treatment. The secondary outcomes included the identification of possible risk factors associated with treatment failure, potential predictors of increased canine treatment duration and risk factors associated with the need of repeating the surgical procedure. Material and methods: The present study was designed as a retrospective observational study retrieving and analyzing panoramic radiographs and clinical records of 2594 patients who consecutively visited the Postgraduate Clinic of the Department of Orthodontics of the School of Dentistry of the Aristotle University of Thessaloniki, Thessaloniki, Greece. The main investigator (IPZ) examined all of the patient records, analyzed the panoramic radiographs and collected the necessary data, determining both patient-related and treatment-related factors. Treatment was defined as successful if it was completed to full alignment of the impacted canine in the dental arch, and as failed if the canine could not be fully aligned. The treatment duration was measured in months and determined as the time period from the date of the surgical exposure to the date the canine reached the dental arch and was fully ligated into a nickel-titanium main archwire. The need for reintervention during the course of the orthodontic treatment was defined as the need to perform an additional surgical procedure and the number of surgical interventions needed until the completion of treatment was calculated. Results: The frequency of the presence of at least one impacted canine was 4.2%, significantly higher in females (6.97 %) than in males (2.32 %). The frequency of maxillary impacted canines was 3.97%, while mandibular canine impaction was scarce, with a frequency of 0.46%. Transmigrant canines were detected solely in the mandibular arch, with a frequency of 0.11%. In total, 106 impacted canines were included in the study, with the majority of them being maxillary (90.6%, n = 96), as opposed to mandibular (9.4%, n = 10). Overall, 12 canines failed to erupt; therefore, a failure rate of 11.3% was reported (or otherwise a 88.7% success rate). In terms of patient-related factors, based on the multivariate logistic regression, the only significant factor associated with treatment failure was the patient’s age (aOR:1.2; 95% CI:1.1-1.3; P <.001), while the multivariable linear regression indicated that increased angulation of the impacted canine (B:0.22; 95% CI:0.03-0.42; P = 0.02) and its proximity to midline (B:7.4; 95% CI: 0.41-14.4; P = 0.03) were statistically significant predictors of increased duration of its alignment. Regarding treatment-related factors, the closed surgical approach was highlighted as a significant predictor of prolonged time for canine alignment, when compared to the open surgical approach (B: -6.01; 95% CI:-11.7-(-0.31); P = 0.04). In terms of reintervention, a need was documented in 23 canines (21.7%) [20 maxillary (87%) and 3 mandibular (13%)], with a median of 2 times of reoperation being reported. Among the reoperated canines, 16 (69.6%) were successfully aligned at the end of treatment, while 7 (30.4%) failed to erupt. The most common cause was suspected ankylosis (n=9, 39.1%). According to the multivariable logistic regression, the increased age (aOR:1.08; 95% CI:1.01-1.51; P < 0.05) and the choice of closed over open surgical technique (aOR:0.2; 95% CI:0.05-0.77; P < 0.05), were underscored as significant predictors of need for reoperation. Concerning the comparison of two frequently implemented biomechanical systems for the treatment of palatally impacted canines, the ballista springs were found not to be significantly superior over the cantilever configurations, in terms of both canine treatment success (P > 0.99) and duration (P = 0.56). Further, the use of brackets over eyelets as bonded attachments, though not significantly affecting the treatment outcome (P = 0.52), may lead to prolonged duration of canine alignment (P = 0.009).Conclusion: In the present study a 11.3% failure rate of the orthodontic–surgical treatment of impacted canines was documented (88.7% success rate). Regarding the patient-related potential risk factors, the only statistically significant predictor of treatment failure was the increased patient’s age, while the increased angulation and the proximity of the impacted canine to midline were statistically significant risk factors for increased duration of the canine alignment. Pertaining to the treatment-related risk factors, the closed versus the open exposure technique was the only statistically significant risk factor related with increased duration of canine alignment. The increased patient’s age and the choice of closed over open surgical exposure technique were found to be statistically significant risk factors for the need of reintervention to surgically expose the impacted canines. Taking into consideration the abovementioned associated risk factors during the conduction of careful treatment planning, which should be followed by an interdisciplinary treatment approach, is considered highly essential for a successful outcome.

Σκοπός: Ο προσδιορισμός του ποσοστού αποτυχίας της ορθοδοντικής-χειρουργικής θεραπείας εγκλείστων κυνοδόντων και ο εντοπισμός προγνωστικών παραγόντων σχετιζόμενων με την αποτυχία, την αυξημένη διάρκεια θεραπείας και την ανάγκη επανεπέμβασης.Μέθοδος: Πανοραμικές ακτινογραφίες και κλινικά αρχεία 2594 ασθενών της Μεταπτυχιακής Κλινικής του Ορθοδοντικού Εργαστηρίου του ΑΠΘ ανακτήθηκαν και αναλύθηκαν αναδρομικά. Αποτελέσματα: Συμπεριελήφθησαν 106 έγκλειστοι κυνόδοντες, εκ των οποίων, 12 δεν ανέτειλαν επιτυχώς (ποσοστό αποτυχίας 11.3%). Ο μοναδικός παράγοντας αποτυχίας ήταν η αυξημένη ηλικία, ενώ η αυξημένη γωνίωση, η εγγύτητα στη μέση γραμμή και η επιλογή κλειστής αντί ανοιχτής χειρουργικής τεχνικής, ήταν παράγοντες κινδύνου αυξημένης διάρκειας κυνοδοντικής ευθυγράμμισης. Η ηλικία και η επιλογή της χειρουργικής προσέγγισης σχετίζονταν με την ανάγκη επανεπέμβασης.Συμπεράσματα: Καταγράφηκε ποσοστό αποτυχίας 11.3%. Ο μοναδικός προβλεπτικός παράγοντας αποτυχίας ήταν η ηλικία, ενώ η γωνίωση, η εγγύτητα στη μέση γραμμή και η χειρουργική τεχνική ήταν παράγοντες κινδύνου αυξημένης διάρκειας. Υπήρξε συσχέτιση μεταξύ της ηλικίας και της χειρουργικής προσέγγισης με ανάγκη επανεπέμβασης.