ABSTRACT
Rater's reliability is an important issue in index calculation. The purpose of this study was to evaluate the intra-examiner agreement in identification of orthodontic treatment needs using modified IOTN. In this analytical cross-section study, six senior dental students identified IOTN on 42 dental casts by means of a standard DHC ruler with a two-week time lag. The kappa and association models were used to analyze the data. The kappa statistics showed intra-rater agreements between 0.54 and 0.77 [ +/- 0.65], which can be considered as [good]. About 33% of the students had problems in distinguishing the first and second levels of the index, while there were fewer problems in distinguishing between the second and third levels. The category identification with most problems was the distinction between the first and second levels [0.48], and the one with the least problem was that of the second and third levels [0.99]. The distinction of the first and second levels in modified IOTN is hard for the examiners. Therefore, this issue should be considered in calibration training programs when using this index in screening, survey or epidemiological evaluations