The KPG index--a novel 3D classification system for maxillary canine impactions.

Introduction: Advancements in Cone Beam Computed Tomography (CBCT) have improved localization of impacted canines. The KPG index is the first 3-D classification system for classifying the position of canines based on their distance from the norm (1). The aim of this study was to determine if this index provides an estimate of the time necessary to treat an impacted canine using closed eruption.

Materials And Methods: CBCT scans of 28 impacted canines at The University of Texas School of Dentistry at Houston Department of Orthodontics were classified using the KPG index. The scores and categories were compared to the time from surgical exposure to proper positioning.

Results: Four canines were classified as "Easy," 11 as "Moderate," 9 as "Difficult," and 4 as "Extremely Difficult." Average treatment times associated in months were: "Easy"--11.23, "Moderate"--11.36, "Difficult"--12.76, and "Extremely Difficult"--13.23.

Conclusions: The KPG index currently cannot be confirmed as an accurate means of estimating treatment time for an impacted canine. Further verification studies should include larger sample sizes and compare differing mechanics. However, there are limitations to 2-D imaging; therefore, the 3-D CBCT images and the KPG index, with further validation, will become increasingly valuable to orthodontists.