VALIDATING KPG INDEX – 3D CLASSIFICATION SYSTEM FOR CANINE IMPACTIONS

Objectives: The KPG index was formulated in 2009 as a means of classifying the difficulty of impacted canines based on their position in three dimensions using a CBCT image.  The aim of this study was to determine if this index would be able to provide an adequate estimate of the treatment time necessary to successfully bring an impacted canine into the arch using a closed eruption technique.  

Methods: CBCT scans of twenty-eight impacted canines treated at a private practice and the graduate clinic of The University of Texas School of Dentistry at Houston Department of Orthodontics were scored using the KPG index.  Each canine was given a numerical score based on the three-dimensional position of the cusp and root tips.  Depending on the cumulative score, categories of “Easy”, “Moderate”, “Difficult”, and “Extremely Difficult” were assigned.  Treatment information was kept electronically using Axium Electronic Patient Record software.  Subsequently, the scores and categories were compared to the actual clinical time from exposure and bonding of a gold chain to proper positioning in the arch.

Results: Based on the KPG index, four canines were classified in the “Easy” category, eleven in the “Moderate”, nine in the “Difficult”, and four in the “Extremely Difficult” category.  The treatment times associated with the impaction categories were as follows: “Easy” took an average of 11.23 months, “Moderate” took an average of 11.36 months, “Difficult” took an average of 12.76 months, and “Extremely Difficult” took an average of 13.23 months.

Conclusions: Based on the results of this study, the KPG index cannot be confirmed or rejected as an accurate means of estimating treatment time needed for an impacted canine.  Further verification studies of the KPG index are needed to include larger sample sizes while also comparing the differences between closed and open eruption mechanics.