J Dent. 2026 Aug 29:107005. doi: 10.1016/j.jdent.2026.107005. Online ahead of print.
ABSTRACT
BACKGROUND: The association between sustained anterior head flexion during portable electronic device use and neuromuscular function remain poorly understood. This study aimed to investigate the relationship between TMD status, the HT operational classification, and the surface electromyographic activity of the masticatory muscles.
METHODS: This cross-sectional study included 100 adults (63 F, 37 M; mean age 32.4 ± 11.3 years), equally distributed into four groups according to TMD status and HT classification. HT operational classification was defined by portable electronic device-use duration and an illustrated postural scale. Surface electromyography was recorded during clenching in the neutral head position and during 40°-60° anterior head flexion. POC TA, POC MM, Asymmetry Index, Activity Index, Torque Index, and Impact were analyzed. Main effects and interactions were assessed using Scheirer-Ray-Hare tests, and within-group changes using paired Wilcoxon tests. Statistical significance was set at p < 0.05. Multiple related comparisons were adjusted using the Benjamini-Hochberg false discovery rate procedure (FDR).
RESULTS: TMD status was significantly associated with POC TA, POC MM, Asymmetry Index, and Torque Index in both positions (all pFDR ≤ 0.027). HT operational classification was significantly associated with Activity Index in both conditions (both pFDR < 0.001). Activity Index decreased during flexion in all groups (all pFDR ≤ 0.041), but the magnitude of change did not differ by TMD status, HT operational classification, or their interaction (all p ≥ 0.205).
CONCLUSIONS: TMD status and HT operational classification showed distinct associations with the investigated sEMG parameters. Participants with TMD exhibited lower muscular symmetry and greater imbalance, whereas HT operational classification was associated primarily with differences in temporalis-masseter recruitment. Activity Index emerged as a potentially posture-sensitive parameter. However, TMD-related findings should be interpreted cautiously because the analyses were not adjusted for demographic differences.
CLINICAL RELEVANCE: Activity Index may represent a potentially posture-sensitive sEMG parameter reflecting posture-associated differences in neuromuscular function; however, its clinical, diagnostic, and prognostic relevance remains to be established.
PMID:42668105 | DOI:10.1016/j.jdent.2026.107005
