Electromyographic Assessment of Masticatory Muscle Function After Short-Term Vertical Dimension Increase in Class II Division 2 Malocclusion: A Pilot Clinical Study

Background: Alterations of the vertical dimension of occlusion may affect masticatory muscle function, which is critical in pre-prosthetic planning, especially in Class II division 2 malocclusions. This study aimed to evaluate the impact of increasing VDO on the myoelectric activity of masticatory muscles using surface electromyography (EMG). The null hypothesis was that a 2–4 mm increase in VDO does not significantly influence muscle activity. Methods: Nine patients with Class II division 2 malocclusion were evaluated. EMG recordings of the masseter and anterior digastric muscles were obtained using the BioEMG II system (BioResearch Asoc., Milwaukee, WI, USA) and Biopak™ software (AcqKnowledge 4.x). VDO was increased using the Dupas universal jig. EMG was recorded for 30 s under six conditions: resting posture, intercuspal position (IM), swallowing, resting posture after VDO increase, IM with increased VDO (IM2), and swallowing with increased VDO (swallowing 2). Results: Most EMG variables showed no statistically significant differences after short-term VDO increase. Significant differences were observed only in the resting activity of both masseter muscles and in the right masseter during maximum intercuspation. No significant changes were identified during swallowing. Conclusions: Within the limitations of this pilot study, a 2–4 mm increase in VDO appears to produce minimal short-term changes in masticatory muscle activity in Class II division 2 patients. These findings should be interpreted with caution due to the small sample size and short observation period, and further studies are required to evaluate long-term neuromuscular adaptation.