Abstract Background While discrepancies in periodontal diagnosis and classification among dental providers with various educational backgrounds have been reported when the 2017 Classification of Periodontal Conditions was applied, the cognitive reasoning processes underlying these discrepancies remain underexplored. This observational study investigated the underlying reasoning for errors in periodontal assessment and diagnosis by analyzing dental students’ responses to open‐ended questions (OEQs) using a mixed‐methods approach. Methods A total of 138 dental students responded to three OEQs addressing periodontal diagnosis, risk factor identification, and periodontitis staging. Quantitative analysis using descriptive statistics assessed overall performance. Qualitative content analysis—independently conducted by two investigators—identified key periodontal diagnostic terms and reasoning trends. Alluvial plots visualized cognitive reasoning pathways. Results Only 39 respondents (28%) correctly diagnosed a gingivitis case by integrating clinical and radiographic assessments. Fifty‐three respondents (38%) answered smoking as the appropriate risk factor for periodontal disease; the remaining included systemic diseases, etiologic and local contributing factors, and/or clinical signs along with smoking. One hundred respondents (72%) correctly assigned Stage III for a periodontitis case, which demonstrated the highest accuracy among the three tasks; the remaining showed an overestimation tendency, often skipping consideration of tooth loss and overemphasizing case complexity. Conclusion The study findings revealed that diagnosing gingivitis was more challenging than determining periodontitis stage, with an overestimation tendency by relying on a single parameter, such as pocket depth. Difficulty in integrating clinical and radiographic data and interpreting case complexity contributed to misdiagnosis and incorrect periodontitis staging. Plain language summary This study explored how dental students think through periodontal cases by analyzing their written responses to three OEQs on real‐world case scenarios involving periodontal diagnosis, risk factor identification, and periodontitis staging. Among 138 respondents, 28% correctly diagnosed the gingivitis case; 38% identified smoking as the risk factor; 72% correctly assigned Stage III. Common errors included overreliance on probing depth, limited use or misinterpretation of bone loss on radiographs. For staging, respondents frequently overlooked the number of teeth lost due to periodontitis and overweighted isolated periodontal complexity features, leading to overrating. These findings indicate a need for structured, case‐based training emphasizing integration of clinical and radiographic data to improve diagnostic accuracy.
Heo et al. (2026) studied this question.