25 February 2020

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Duration of forced eruption of impacted canines

Davide Elsido

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In the latest issue (December 2019) of the American Journal of Orthodontics and Dentofacial Orthopedics an article was published to identify factors that affect the duration of forced eruption for impacted maxillary canines.

The maxillary canine is the second most commonly impacted tooth, after the third molar, with an incidence ranging from 0.8% to 2.8%, depending on the population examined. An impacted canine requires complex therapeutic management, which can be considered successful only if forced eruption and the subsequent alignment lead the tooth to the correct position in the dental arch.
Forced eruption for impacted maxillary canines typically necessitates surgical and orthodontic intervention to bring the canine into the dental arch successfully. Variations in buccopalatal, vertical, and anteroposterior locations of impaction define treatment complexity and duration. Reliable pretreatment estimates of orthodontic treatment duration would be helpful in the decision-making process for patients with impacted canines and in providing accurate information to the patient.

Several variables have been proposed to predict the duration of forced eruption: age, number of impacted canines, pretreatment radiographic variables in panoramic radiographs, indices calculated from cone beam computed tomography (CBCT). 

Materials and methods
 The records of 27 patients treated surgically and orthodontically to align 29 impacted maxillary canines (25 unilateral, 2 bilateral) from 2009 to 2016 were reviewed. The patients were aged 9-22 years (mean age, 12.5 6 2.9 years). The inclusion criteria were
(1) impacted and labially displaced maxillary canines unilaterally or bilaterally treated using forced eruption with fixed orthodontic appliances;
(2) presence of pretreatment panoramic radiographs and both pre- and posttreatment CBCT;
(3) all treatment completed;
(4) complete treatment records.
All patients underwent a closed-flap surgical procedure followed by orthodontic traction. After local anesthesia, a vestibular and vertical incision was performed at the level of the impacted maxillary canine. The mucoperiosteum was then dissected off the bone. The bony covering was removed with a round bur, and the dental follicular tissue was removed from the surface of the enamel. Further soft tissue and/or bone removal was performed to enhance the forced eruption of the canine. An orthodontic bracket was bonded, and orthodontic traction force was applied after 7 days.

Results
A total of 29 treated canines moved into the arch over a period of 13.0 +- 8.3 months (range, 5-33 months). Simple regression analysis showed that the only significant factor, with duration of traction as the dependent factor, was pretreatment inclination of the canines toward the midsagittal plane; stepwise regression analysis indicated a strong direct correlation between the duration of traction and this factor.
The other variables were not significantly associated with the duration of traction. The most desirable approach for managing impacted maxillary canines would be early detection and timely interception of potential impaction.
An age range of 9-22 years might not be wide enough to show the age correlation with treatment time: this is a limitation of this study.

Conclusions
Impacted canines with a higher angle toward the midsagittal plane have a closer crown and farther apex relative to the midsagittal plane.
Active traction cannot be directed to a place in the dental arch because it may result in resorption of the roots of the incisors located in the direction of the traction.
Therefore, they require therapeutic uprighting with orthodontic traction on the opposite side of the lateral incisor root. When located closer to the occlusal plane, root torsion must be added to obtain the correct position, resulting in extension of the treatment duration.

For additional informations:  Factors affecting forced eruption duration of impacted and labially displaced canines.