The Orthodontics Professors
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The Effect of Primary Canine Extraction on Palatally Displaced Permanent Canines: Useful Findings from a Study in 3D
BY WILLIAM R. PROFFIT & TATE H. JACKSON
In a follow-up to Kurol’s classic studies, a prospective clinical trial was carried out in Gothenburg in which 67 patients age 10-13 with unilateral or bilateral palatally displaced permanent maxillary canines were randomly assigned to extraction or retention of maxillary primary canines. Clinical examination and CBCTs were obtained initially and at 6 and 12 months later; total observation time was 24 months.
Significantly more spontaneous eruption of the permanent canines was seen in the extraction than control group (69% vs 39%), and faster eruption was noted in the extraction group. The relationship of the canine cusp tip to the midline was the best predictive measure of the outcome. If this distance was 11 mm or more, spontaneous eruption of the canine was achieved; if it was 6 mm or less, some positional improvement often occurred but surgical exposure was needed despite interceptive extraction of the primary canine.
WHAT THE PROFESSOR THINKS
It is important to note that the image analyses in this study were done using multi-planar views from 3D CBCT volumes. One advantage of using 3D images is that the distortion in observed canine position inherent to 2D images is avoided. For most clinicians who use 2D panoramic images everyday to assess canine position, the absolute numbers reported in this study must be used with some caution.
Nonetheless, this study was well done and carries useful contemporary clinical guidelines. Specifically, early extraction of the primary canines is particularly indicated for patients with cusp tip to midline distances of 7-10 mm. When the distance from the cusp tip to the midline is less than 7mm, primary canine extraction can still be helpful in facilitating later surgical exposure.
Article Reviewed: Naoumova J, Kurol J, Kjellberg H. Extraction of the deciduous canine as an interceptive treatment in children with palatally displaced canines--part I: Shall we extract the deciduous canine or not?; Part II: Possible predictors of success and cut-off points for a spontaneous eruption. Eur J Orthod 37: 209-218 and 219-229, 2015