Comparison and Inter-System Agreement of Three Digital Jaw-Tracking Systems: A Comparative Within-Subject Study

Background: Digital mandibular kinematic analysis complements clinical examination by quantifying movement amplitude, symmetry, coordination, and trajectories. However, device-specific acquisition and processing characteristics may influence the measurements obtained with different jaw-tracking systems. Therefore, this study aimed to assess systematic differences in mandibular kinematic measurements and inter-system agreement among three commercially available digital jaw-tracking systems. Methods: Twenty healthy adults (12 M, 8 F; mean age, 27 ± 5 years) underwent assessment with Zebris JMA-Optic (Amann Girrbach AG, Koblach, Austria), Modjaw (Modjaw SAS, Villeurbanne, France), and Itaka (Itaka Way Med Srl, Marcon, Italy). Maximum mouth opening, protrusion, and bilateral lateral excursions were recorded in at least three valid trials, with the maximum excursion used for analysis. Differences among systems were evaluated using repeated-measures ANOVA with Bonferroni-adjusted post hoc comparisons. Overall inter-system agreement was assessed using the absolute-agreement intraclass correlation coefficient (ICC), while pairwise agreement was further characterized using Bland–Altman analysis. Proportional bias was assessed by linear regression of pairwise differences against their corresponding means. Results: Maximum mouth opening differed significantly among systems (p = 0.047; partial η2 = 0.148). Modjaw recorded higher values than Itaka (mean difference, 2.49 mm; adjusted p = 0.038; Cohen’s dz = 0.62). No significant differences were found for right lateral excursion (p = 0.161), left lateral excursion (p = 0.293), or protrusion (p = 0.873). Agreement was moderate for maximum mouth opening (ICC = 0.601), right lateral excursion (ICC = 0.747), and protrusion (ICC = 0.718), but poor for left lateral excursion (ICC = 0.443). Bland–Altman analyses showed movement- and system-pair-specific variability in measurement differences, with no evidence of proportional bias. Conclusions: The three digital jaw-tracking systems showed movement-dependent differences in mandibular kinematic measurements and varying levels of inter-system agreement. These findings indicate that measurements obtained with different systems should be interpreted in the context of the specific movement assessed and the characteristics of the corresponding acquisition and processing workflows. Further studies are needed to determine the clinical relevance of the observed inter-system variability.