This study is designed to assess the impact of injecting sodium hyaluronic acid versus a chitosan-hyaluronate hybrid gel into the upper compartment of the temporomandibular joint (TMJ) as a treatment for anterior disc displacement without reduction. The study will include patients diagnosed with Stage III or IV TMJ internal derangement (anterior disc displacement without reduction), as classified by Wilkes, with diagnoses confirmed through clinical symptoms and MRI evaluations. Participants will be randomly divided into two groups, both undergoing TMJ arthroscopy. In the first group, 2 ml of chitosan-hyaluronic acid hybrid gel will be injected into the affected joints, whereas in the second group, 2 ml of hyaluronic acid (HA) will be administered. The study will compare and analyze outcomes in both groups, focusing on pain during TMJ function, clicking sounds, the extent of maximum mouth opening, and maximum lateral jaw movement.

This study will be a prospective randomized controlled clinical study on a convenience sample of patients who will be selected from the Department of Oral and Maxillofacial Surgery, Faculty of Dental Medicine, Suez University. Patients selected are whom will be diagnosed with TMJ internal derangement (anterior disk displacement without reduction Stage III, Stage IV Wilkes classification) based on clinical symptoms and MRI evaluations. Inclusion criteria will be adults aged between 25 - 50 years old, sufficient clinical and magnetic resonance imaging (MRI) data that could be obtained before and after the treatment. The exclusion criteria will be hematological or neurological diseases, inflammation or connective tissue diseases, head and neck malignancies, history of treatment of TMJ disease or history of craniofacial surgery not related to internal derangement treatment, insufficient clinical and MRI data.

Participants will be selected based on established criteria. A total sample size of 20 (10 in each group) was calculated to detect an effect size of about 1.33-1.34, with a power (1-β error) of 0.8 (80%) using a two-sided hypothesis test, with a significance level (α error) 0.05 for data [13]. All patients will undergo a preoperative clinical evaluation including Pain level on forced mouth opening using visual analogue scale (VAS), assessment of mean lateral jaw movements, assessment of TMJ clicking, assessment of maximum mouth opening (MMO), deviation of mandibular midline during mouth opening and closure. All patients will do a Magnetic resonance imaging (MRI) to evaluate the disc displacement.All patients will undergo conservative treatment as the first line of treatment in all TMJID cases. All patients will be under general anesthesia.

For both groups, the operation will be under GA and The skin surface of the pre-auricular region will be disinfected with povidone iodine solution. For both groups, TMJ arthroscopy will performed by the same TMJ arthroscopy surgeon. Lysis and lavage will be performed in the upper joint space in all cases based on the triangulation technique with an inferolateral approach. The arthroscopic procedure will include lysis of adhesions, lavage, manipulation, and debridement of the upper joint space. A 1.9-mm arthroscope with a video monitoring and recording system and a 2.2-mm protective cannula sheath will be used for TMJ arthroscopy. Ringer's lactate will be used as irrigation fluid. Both groups will receive the same arthroscopic treatments. In the first group, the injection of 2 ml of chitosan-hyaluronic acid hybrid gel into affected joints, while 2 ml of HA will be injected in to affected joints in the second group. Needles will be removed after the injection sites and covered its sites with gauze dressing. Postoperative care and instructions:

1. Medications:

   Brufen* as a nonsteroidal anti-inflammatory drug (NSAIDs) relieving muscle pain and swelling. Myofen* as a muscle relaxant especially for people who grind or clench their teeth help to relax tight jaw muscles.

2. Application hot & cold packs:

   All patients will be instructed to apply an ice pack to the side of his face and temple area for about 10 minutes. Also, simple stretching exercises for his or her jaw should be done. Application a warm towel or pack to the side of his face for about 5 minutes five times daily for 4 days.

3. Soft diet:

Soft food such as yogurt, mashed potatoes, cheese, soup, fish, cooked fruits and vegetables, beans, and grains should be eaten. In addition, food should be cut into small pieces. Avoid hard and crunchy foods like hard rolls, raw carrots, thick and large foods that need your mouth to open wide to fit the foods. Also, chewy sticky foods (like caramels and taffy) avoided too for next 10 days.

Inclusion Criteria:

1. Patients were diagnosed with TMJ internal derangement (anterior disk displacement without reduction Stage III, Stage IV Wilkes classification) based on clinical symptoms and MRI evaluations.
2. Age 25 - 50 years old.

Exclusion Criteria:

1. Hematological or neurological diseases.
2. Inflammation or connective tissue diseases.
3. Head and neck malignancies.
4. History of treatment of TMJ disease or history of craniofacial surgery not related to ID treatment.
5. Insufficient clinical and MRI data.