Periapical Index
Also written as: PAI — Periapical Index
A five-point ordinal scale used to grade periapical tissue status on radiographs, from normal to severe apical periodontitis, in endodontic research.
Full Definition
The Periapical Index (PAI) was developed by Ørstavik et al. (1986) as a standardized radiographic scoring system for assessing periapical pathology. Scores range from 1 (normal periapical structures) to 5 (severe periodontitis with exacerbating features). It is widely used as the primary outcome measure in endodontic clinical studies to categorise treatment success or failure. Editors should verify that radiographic calibration procedures and inter-examiner reliability statistics (such as kappa coefficients) are reported whenever the PAI is used. The scale is ordinal, not interval, and statistical analyses should reflect this; editors should flag inappropriate use of means and standard deviations applied to PAI scores.
Usage
Usage note: PAI scores are ordinal; use median and interquartile range rather than mean and standard deviation. Flag any manuscript that applies parametric statistics directly to raw PAI values.
In Context
- "Pre-operative and one-year follow-up radiographs were scored using the Periapical Index by two calibrated examiners blinded to treatment allocation." — Endodontic RCT methods
- "The use of a mean PAI score in Table 3 was queried by the editor, as the ordinal nature of the scale does not support parametric averaging." — Statistical review note