FMMI: An Innovative, Comparative, and Integrated Protocol to Unravel Integral

Objective: This protocol article outlines the theoretical development and prospective clinical validation plan for the Functional Mandibular Movement Index (FMMI), a composite and objective metric designed to overcome the limitations of subjective and single-parameter assessments in the evaluation of Temporomandibular Disorders (TMD). Methods: The FMMI quantitatively integrates functional maximal mouth opening (MMO_F), protrusive and lateral excursions, and an innovative Multiplicative Symmetry Factor (Φ). The proposed validation protocol involves a two-phase prospective cohort study: 1) a cross-sectional analysis comparing TMD patients (DC/TMD criteria) to asymptomatic controls to establish diagnostic cut-off points via ROC analysis and to correlate the FMMI with biopsychosocial measures (pain intensity, Jaw Functional Limitation Scale, PHQ-9); and 2) a longitudinal arm, following a subset of patients over six months to assess the FMMI's sensitivity to therapeutic changes, comparing it with the standard maximum mouth opening (MMO) measure using mixed linear models. Computational simulations were performed to illustrate the expected behavior of the index and to underpin sample size calculations. Anticipated Results: Based on simulations, the FMMI is projected to demonstrate high diagnostic accuracy (area under the ROC curve >0.90) for discriminating TMD patients from controls and for differentiating TMD subtypes (e.g., arthrogenic vs. myogenous). It is also expected to exhibit strong negative correlations with pain and functional limitation scores, alongside greater sensitivity as a therapeutic outcome measure when compared to MMO alone. Conclusion: This protocol aims to establish the theoretical and methodological foundation for the validation of the FMMI, a proposed integrative indicator designed to bridge biomechanical assessment with the biopsychosocial model of TMD. The prospective validation study seeks to determine its clinical utility for differential diagnosis, treatment planning, and longitudinal monitoring in TMD-related research and clinical practice.