Maxillary canines are important both esthetically and functionally and are the second most commonly impacted teeth after the third molars.^1–6 The frequency of unerupted maxillary canines is approximately 0.8% to 2% in the general population, with ethnic variations.⁴ The incidence of canine impaction is twice as common in females as in males and the teeth are palatally impacted in 85% of these patients and buccally impacted in 15%.⁶ Patients with impacted maxillary canines are perceived to be more difficult and time consuming to treat than those with a routine malocclusion.

Position of the impacted canines and treatment mechanics are the two major factors affecting total treatment time and the final position of the canines in the oral cavity.^7,8 With new technologies such as cone beam computed tomography (CBCT), the impacted canine can be precisely located in three dimensions.⁷ An optimal force system is then needed for the treatment and this system is defined as that which results in a greater biological response with minimal tissue damage, resulting in rapid tooth movement with few or no deleterious effects.⁹

Traditional force systems are attenuated as a result of deactivation during tooth movement or because of the physical properties of the force delivery system.¹⁰ Appliance design has been focused on improving force delivery. Although an ideal spring that can deliver a continuous force day after day is only a theoretical possibility, various inter-arch and intra-arch mechanics have been devised for the successful management of impacted canines. Oppenhuizen¹¹ and Jacoby¹² devised an extrusion spring for palatally impacted canines using prefabricated 0.018-inch stainless steel archwires. Bowman and Carano¹³ devised new directional force springs called Kilroy I and Kilroy II, used for palatally and buccally impacted canines, respectively. Haydar et al.¹⁴ used microscrews with either an elastic traction or a ligature wire for management of the impacted tooth. Vardimon et al. recommended the use of magnets to treat impacted canines on the basis of a less invasive surgical procedure, effective forces at short distances, and controlled spatial guidance.^14a

However, none of these authors have discussed the mechanics involved with the use of their appliances. The use of improper mechanics (direction and magnitude of force applied, direction and magnitude of reactionary force) when treating impacted and ectopically erupted canines increases the chance of root resorption of the adjacent teeth. A knowledge of mechanics is essential for effective treatment and an important step toward evidence-based treatment.^10,15