This clinical trial seeks to investigate a promising new approach to enhance the effectiveness and duration of Botulinum Toxin A (BTX-A) for the treatment of hyperactive masseter muscles. By investigating the role of oral zinc supplementation, this study could provide a cost-effective, sustainable solution for patients suffering from both aesthetic concerns and functional limitations associated with MMH and bruxism. The findings of this study will expand the clinical applications of BTX-A, offering longer-lasting relief and reducing the need for frequent injections, which could revolutionize the management of MMH in clinical practice.

This study aims to explore the potential for oral zinc supplementation to enhance the efficacy and duration of Botulinum Toxin A (BTX-A) in treating hyperactive masseter muscles (MMH). MMH leads to cosmetic deformities like a "square jaw," and is sometimes associated with bruxism and functional issues. While BTX-A is effective for reducing muscle activity, its effects typically last 2-3 months, requiring frequent re-injections. The study hypothesizes that zinc supplementation, which plays a crucial role in synaptic transmission, may prolong and enhance the effects of BTX-A. The trial will be a randomized, double-blind, two-period design at Lattakia University Hospital, recruiting 20 participants aged 18-60 years, who will be randomly assigned to two treatment sequences.

The intervention protocol includes participants with a clinical diagnosis of MMH (with or without bruxism). They will undergo two separate treatment periods: one with zinc gluconate (50 mg/day for 4 days) followed by BTX-A injection, and the other with an identical placebo followed by the same BTX-A protocol. The two treatment periods will be separated by a 5-6 month washout period to eliminate carryover effects, ensuring that the results of the first treatment phase do not influence the second phase.

The primary outcome will be the percentage change in masseter electromyographic (EMG) amplitude at 12 weeks post-injection, compared with baseline (normalized to maximal voluntary clench [MVC]). This will provide data on the magnitude and duration of BTX-A's effect when combined with zinc supplementation. Secondary outcomes will include pain reduction (measured by the Visual Analog Scale [VAS]), patient satisfaction (assessed by a 5-point Likert scale), and time to recovery (time taken for EMG to return to 80% of baseline levels). Additionally, adverse events such as muscle weakness, asymmetry, and bruising will be monitored.

The results of this research could provide a cost-effective and sustainable solution for MMH patients, improving the duration and efficacy of BTX-A treatment.

Inclusion Criteria:

Participants will be adults aged 18-60 years presenting with clinically confirmed masseteric hypertrophy or hyperactivity, as approved by EMG.

Exclusion Criteria:

• Pregnancy or lactation;
• Patients have aminoglycosides or vit B12.
• Prior BTX-A treatment to the masseter within the previous 12 months;
• Neuromuscular disorders or hypersensitivity to BTX-A or zinc compounds;
• Systemic illness affecting zinc metabolism (e.g., hepatic, renal, or metabolic disorders);
• Active infection, inflammation, or cutaneous lesions at the injection site.

The investigational pharmacy will prepare identical opaque capsules (zinc or placebo) labeled solely by subject ID and treatment period.