Assessment of clinical validity of KPG index for 3D classification of impacted maxillary canines by cone beam computed tomography in patients

Objectives

The primary objective of this study was to assess the validity of the KPG index in predicting the difficulty of treatment involving impacted maxillary canines. The secondary objective was to assess the reliability and reproducibility of the index.

Materials and Methods

A retrospective study was conducted on 96 maxillary impacted canines (MIC) in 60 patients aged 13–35 years. Cone-beam computed tomography (CBCT) scans were used to predict the treatment difficulty of MIC using the KPG index. Patient case files were assessed for the actual difficulty encountered in treating MIC. Cohen's kappa correlation coefficient was used for intra-observer reliability and Kendell's W test was used for inter-observer reliability. Spearman's correlation coefficient test was used to assess the correlation between predicted and actual treatment.

Results

Easy and moderately difficult cases exhibited a moderate correlation between actual and predicted treatment outcomes, whereas difficult cases displayed a weak correlation. The perfect correlation was observed exclusively in extremely difficult cases. The intra-observer reliability for assessing CBCT scans using the KPG guide was found to be 0.88, and the inter-rater reliability was 0.94.

Conclusion

The KPG index displayed 87%, 71%, 50% and 100% validity in easy, moderately difficult, difficult, and extremely difficult cases, respectively. This index showed good reliability and reproducibility. However, it is imperative to consider a multitude of other factors, including the patient's age, presence of associated root resorption in adjacent teeth, and duration of treatment, to make an informed decision between surgical exposure and extraction.