Objectives <p>This study aimed to explore the immediate effects of transcutaneous electrical nerve stimulation (TENS) on localized masticatory muscle mechanical hyperalgesia, jaw-muscle activation, and mandibular movement measures in individuals with probable bruxism but without DC/TMD-defined painful TMD, compared with sham TENS.</p> Materials and methods <p>Forty participants (7 men, mean age: 25.6 years; 33 women, mean age: 23.6 years) classified as having probable bruxism and presenting with localized masticatory muscle mechanical hyperalgesia were randomly assigned to TENS/sham TENS (sTENS) treatment groups, using a randomized and double-blind design with 20 participants in each group. TENS or sham TENS was applied once. TENS was delivered using rectangular pulse current waveforms, with the output current set above the sensory threshold, for 30&#xa0;min. The primary pain-sensitivity outcomes were the immediate changes in pressure pain threshold (PPT) at the masseter and temporalis sites from baseline to post-treatment. Thenar PPT was assessed as a remote reference site and was not considered a primary outcome. Secondary exploratory outcomes included mandibular movement measures and electromyography (EMG) activity of the masseter and temporalis muscles during MRP and MCE tasks. Because the study was exploratory, the secondary outcomes should be interpreted cautiously.</p> Results <p>Baseline data revealed no significant differences between the two groups before treatment. Within-group comparisons showed that, after intervention the TENS group showed increased PPT values (masseter, <i>p</i> = 0.003; temporalis, <i>p</i> = 0.002), decreased EMG activity during mandibular rest position (MRP) (masseter, <i>p</i> = 0.003; temporalis, <i>p</i> = 0.004), increased EMG activity during maximum clenching effort (MCE) on 10-mm cotton rolls (<i>p</i> = 0.003). In contrast, the sTENS group showed no significant pre-to-post changes in these outcomes (PPT: masseter, <i>p</i> = 0.422; temporalis, <i>p</i> = 0.266) (EMG at MRP: masseter, <i>p</i> = 0.553; temporalis, <i>p</i> = 0.539). Two-way mixed-design ANOVA revealed significant time × treatment interactions for masseter PPT (<i>p</i> = 0.007), masseter EMG activity during MRP (<i>p</i> = 0.011), and maximum opening distance (<i>p</i> = 0.004). Temporalis PPT showed a significant main effect of time but no significant time × treatment interaction. Post-hoc comparisons indicated greater increases in masseter PPT and greater reductions in masseter EMG activity during MRP in the TENS group than in the sham TENS group. Maximum opening distance was interpreted cautiously as a secondary exploratory finding.</p> Conclusion <p>In this proof-of-concept study, a single session of TENS was associated with immediate increases in masseter PPT and changes in selected EMG and mandibular movement measures in individuals with probable bruxism and localized masticatory muscle mechanical hyperalgesia but without DC/TMD-defined painful TMD.</p> Clinical relevance <p>These results support further investigation of repeated TENS sessions and longitudinal follow-up in this specific subclinical phenotype. The present study does not establish whether TENS modifies bruxism activity or prevents the development of painful temporomandibular disorders.</p> Trial registration <p>Chinese Clinical Trial Registry ChiCTR2400086817, registered on July 11, 2024. Retrospectively registered.</p>