The masticatory cycle is a coordinated sequence of mandibular movements closely associated with masticatory muscle activity. However, the chewing pattern may be altered in temporomandibular disorders (TMDs). The aim of this study was to evaluate the masticatory cycle in patients with TMD through an integrated electromyographic and kinematic analysis, comparing the results with the correlations previously reported in the literature for healthy subjects. In this cross-sectional study, twenty-four adults diagnosed with TMD (mean age: 26 ± 6.7 years; 16 females and 8 males) were recruited at the Department of Dentistry at San Raffaele Hospital, Milan. The jaw tracking system Modjaw^® (version 3.6.4; MODJAW SAS, Villeurbanne, France) made it possible to record three-dimensional mandibular movements, including opening and closing, protrusion, lateral movements and the masticatory cycle. As for surface electromyography, the Myowise^® device (software version 1.4; Cometa S.r.l., Bareggio, Italy) was used to assess the electrical activity of the masticatory muscles during chewing. Subsequently, descriptive statistics were performed, and possible correlations between selected kinematic and electromyographic parameters were investigated. No statistically significant correlations were identified, except for a moderate negative correlation between right masticatory cycle height and right masseter muscle impact. Mandibular kinematics showed limited associations with electromyographic parameters in patients with temporomandibular disorders, differing from the correlations previously reported in healthy subjects.

Background: The widespread use of portable electronic devices may involve prolonged exposure to altered cranio-cervical postures. This study investigated whether participants classified as HT+ and HT− according to a predefined operational classification differed in masticatory muscles recruitment. Methods: This cross-sectional study included 50 healthy adults (30 F, 20 M; mean age, 27 ± 5 years) classified into two operational groups. The HT+ group (n = 25) was defined by the simultaneous presence of portable electronic device use >8 h/day and habitual marked anterior head flexion, whereas the HT− operational group (n = 25) included participants who did not simultaneously meet both criteria. Participants underwent surface electromyography of the masseter and anterior temporalis muscles during maximum voluntary clenching (MVC) in the neutral head posture and during anterior head flexion (approximately target range 40–60°) using the MyoWise device (MyoWise, Via Gran Sasso 18, 20008 Bareggio, Milan, Italy). Percentage Overlapping Coefficients, Asymmetry Index, Activity Index, Torque Index, and Impact were assessed. Between-group comparisons, within-group posture-related changes, and between-group comparisons of change scores (Δ) were performed using parametric or non-parametric tests according to data distribution. The between-group comparison of the Activity Index in the reference posture was predefined as the primary analysis, whereas secondary analyses were adjusted for multiple comparisons using the Benjamini–Hochberg false discovery rate (FDR) procedure. Statistical significance was set at p < 0.05 for the primary analysis and at FDR-adjusted q < 0.05 for secondary analyses. Results: The Activity Index was significantly more negative in HT+ than in HT− participants in both the reference posture (p < 0.001) and during anterior head flexion (p = 0.003; q = 0.032). The Activity Index decreased significantly from the neutral head posture to anterior head flexion in both groups (HT+: q = 0.025; HT−: q = 0.002), whereas the magnitude of this change did not differ significantly between groups (p = 0.101; q = 0.607). No other sEMG outcome remained significant after FDR correction. Conclusions: The HT+ operational group was associated with a distinct temporalis–masseter recruitment pattern in asymptomatic adults. The Activity Index emerged as the sEMG parameter most strongly associated with operational HT classification, indicating that the observed between-group differences primarily involved the relative recruitment balance between the jaw-elevator muscles.