This study aims to evaluate the effects of different treatment techniques on masseter muscle thickness, pain levels and maximum mouth opening in patients with bruxism. The null hypothesis of the study is that there is no difference between the use of an occlusal splint and botulinum toxin on masseter muscle thickness in patients with bruxism.

The study was carried out on 48 patients between 21 and 52 years, who attended the clinic with the complaints of bruxism. The first group was referred to as the Control group (C) and given protective advice such as supporting the jaw when yawning, not chewing gum, not opening the mouth for too long and not opening it too wide, and chewing on both sides when eating. The second group was treated with an occlusal splint (O), the third group with an injection of botulinum toxin (B), and the fourth group with both an occlusal splint and an injection of botulinum toxin (OB). At the beginning of the treatment and after 1, 3 and 6 months, the thickness of the masseter muscles of all patients was measured bilaterally by ultrasound in relaxed and contracted positions. Maximum mouth opening values was recorded by measuring the distance between the incisal edges of the maxillary and mandibular first incisors (teeth 11 and 41) using calipers. Pain levels were assessed using the Visual Analogue Scale (VAS), where patients marked their pain severity on a 10 cm unmarked straight line, with scores ranging from 0 to 10.

Ultrasound measurements Masseter muscle thickness measurements were performed by the same radiologist, using a MyLabTMTwice ultrasound device equipped with a linear probe with a frequency range of 4-13 megahertz. To ensure reproducibility, the probe was positioned perpendicular to the ramus, aligned with the imaginary line between the corner of the lip and the inferior border of the tragus. Measurements were taken at the thickest part of the masseter muscle, with bilateral assessments in both the relaxed and contracted states.

Application of the occlusal splint The occlusal splint was fabricated from a 2 mm hard splinting resin material on the plaster model obtained by taking impressions of the patient's upper jaw. Centric and eccentric occlusal relationships were assessed to ensure equal contact between all teeth. Patients were instructed to wear the splint overnight for at least 8 hours. Patients were also educated on the care and maintenance of the splint and compliance was checked at follow-up visits.

Botulinum toxin injection All injections were administered by the same specialist maxillofacial surgeon. For each dose of 1.0 U/0.1 mL, 100 U of lyophilized botulinum toxin was diluted with 2 cc of saline. The skin area was cleansed with povidone iodine and dried. The anterior, posterior, superior and inferior borders of the masseter muscle were marked to ensure safe injection. Before injection, patients were instructed to clench their teeth to make the injection sites more visible. Intramuscular injections were performed with the needle perpendicular to the skin. A total of 50 U of botulinum toxin was injected , 25 U in each muscle, using 30-gauge injectors.

Inclusion Criteria:

• Who volunteered to participate in the study,
• Eighteen years of age or older,
• Has not received any treatment for bruxism before,
• Systemically healthy,
• Visible tooth wear,
• History of clenching or grinding with masticatory pain,
• Morning temporomandibular joint (TMJ) stiffness,
• Masseter hypertrophy

Exclusion Criteria:

• Systemic disease,
• Under the age of eighteen,
• Having received any pharmacological, dental, etc. treatment for bruxism before,
• With any known drug allergy,
• During pregnancy or breastfeeding,
• Bleeding irregularities,
• With mental retardation,
• Active orthodontic treatment