Introduction: Orstavik's periapical index is widely used for radiographic assessment of periapical status. This study analyses the reliability and reproducibility of a modified guide for the interpretation of the periapical index (PAI) scores recorded by undergraduate students.
Materials and method: Two groups of 4th-year students were asked to assess the PAI scores of 100 X-rays two or three times depending on the group. The reliability of their judgment was evaluated by comparing the students' assessments to those of a standard, based on the evaluations made by three teachers. Short-term stability was evaluated for two lengths of interval separating the Test and Retest phases, respectively, 1 week for Group 1 and 2 weeks for Group 2. Long-term stability was evaluated by having Group 1 repeat the Retest phase after 15 months.
Results: Overall mean success rates ranged from 61% to 65% according to the student group and the study phase. Intergroup comparisons showed no statistical difference. The reliability of the PAI score evaluation by students was excellent in both groups. Short-term and long-term stability were also excellent regardless of the duration of the interval between the study's phases.
Discussion: The image misinterpretations are discussed according to the study phases and the PAI score values.
Conclusion: Undergraduate students can be trained to use the modified guide for scoring PAI for self-evaluation of the outcomes of the root canal treatments and re-treatments they are asked to perform during their clinical sessions.
Keywords: evaluation; periapical index score; reliability; stability; students.
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