Development and Clinical Validation of a Self‐Administered Wax Bite Test for the Assessment of Posterior Functional Units: Agreement, Reliability and Feasibility

OBJECTIVES: To clinically validate a self-administered Wax Bite Test (WBT) for counting posterior functional units (PFU) by assessing its agreement with the articulating-paper reference method, reliability, feasibility and acceptability. METHODS: In this cross-sectional study, 44 adults were enrolled. PFU were assessed using the reference method (PFU-reference) and the self-administered WBT (PFU-WBT) with pre-sized modelling wax. Two calibrated evaluators independently interpreted each wax record twice. Agreement with the reference method was assessed using Bland-Altman analysis and method-comparison regression using orthogonal distance regression (ODR). Equivalence was evaluated using TOST with a predefined margin of ±1 PFU. Intra- and inter-rater reliability were quantified using intraclass correlation coefficients (ICC). Feasibility was assessed by the frequency and determinants of unreadable records. Acceptability was evaluated using visual analogue scales. RESULTS: Participants completed two successive rounds of the WBT, generating 176 wax bites records, read twice by two investigators (704 assessments). Overall, 22.2% of records were unreadable, but this limitation was concentrated mainly among fully edentulous participants (p < 0.001) due to insufficient bite force. Bland-Altman analysis showed a bias of 0.20 PFU (95% CI: -0.11 to 0.51) with limits of agreement from -1.66 to 2.06 PFU. ODR indicated a slope near unity and TOST confirmed equivalence within the predefined ±1 PFU margin. Reliability was good to excellent in fully dentate and partially dentate participants (ICC > 0.826). Acceptability was high for all participants. For severe impairment (PFU ≤ 4), the WBT showed high specificity (97%) and good sensitivity (80%) compared with the reference method. CONCLUSIONS: In nutritional research, simple and reliable tools to assess oral functional capacity are essential for understanding dietary choices and nutritional risk. The WBT appears to be a practical, self-administered tool for monitoring PFU in clinical and community settings. However, adaptations are required for fully edentulous individuals wearing complete dentures, in whom unreadable records were frequent because of reduced bite force. TRIAL REGISTRATION: IRB00013412, December 19th, 2024 CLINICAL SIGNIFICANCE: WBT provides a low-cost, participant-friendly way to monitor PFU in clinical and community settings.