Prediction of maxillary lateral-incisor root resorption using sector analysis of potentially impacted canines.

nine is the most frequently impacted tooth in the dental arch. Although the incidence of canine impaction is about 1 in 100 in the general popula­ tion,1 the ratio tends to be much higher in an ortho­ dontic practice—perhaps as high as 23.5%, ac ­ cording to one researcher.2 Palatal impactions are more prevalent (85%) than labial impactions (15%).3­5 early detection of impactions is critical to the success of orthodontic treatment. ericson and kurol found that the more mesially located the crown of an impacted canine, the lower the likelihood of its eruption after deciduous extraction.6 Power and Short found that if a canine is angled more than 31° to the midline, its chance of eruption after deciduous extraction is reduced.7 Lindauer and colleagues, drawing on the work of ericson and kurol,6 developed a method for predicting eruption after deciduous extraction, based on the location of the impacted canine cusp tip and its relationship to the adjacent lateral incisor.8 Dividing impacted canines into four groups—sectors I through IV, with sector IV representing the most severe impac­ tion—they determined that as many as 78% of the canines with cusp tips in sectors II through IV were destined to become impacted (Fig. 1). War ­ ford and colleagues reported that 82% of all im ­ pacted canines were classified in sectors II through IV, and that angulation was not as useful as sector analysis in predicting impaction.1 Root resorption is not only the most common sequela of canine impaction but the most difficult to treat. Although the maxillary lateral­incisor root is the most commonly affected by ectopic eruption of the canine,9­11 there is also evidence that impact­ ed canines can cause root resorption of the central incisors. In a study by Bjerklin and ericson of cases with impacted canines, 38% of the lateral incisors showed root resorption, compared to 9% of the central incisors, but every case of central­incisor root resorption also showed root resorption of the adjacent lateral incisor.12 In a similar study, Walker and colleagues found that 66% of the lateral inci­ sors and 11% of the central incisors showed root resorption, and that 50% of the cases with root resorption of a central incisor also demonstrated root resorption of the adjacent lateral incisor.13 In this retrospective study, we used cone­