This clinical trial aims to investigate whether treatment of temporomandibular joint disorder with a stabilizing occlusal splint is justified to alleviate somatosensory tinnitus. The main questions we aim to answer are:

• Determine if treatment of temporomandibular disorder with a stabilizing occlusal splint improves somatosensory tinnitus.
• Identify which patient-related, tinnitus-related, and temporomandibular disorder-related factors contribute to the therapeutic effect.

The clinical variables of somatosensory tinnitus (ZS) will be assessed by a researcher blinded to the treatment type, using the Tinnitus Handicap Inventory (THI) and Visual Analogue Scale (VAS) at time points T1, T2, T3, T4, and T5, with 30 days interval. The THI, validated and adapted to Portuguese, is the most frequently used questionnaire in clinical trials for tinnitus patients, quantifying the subjective impact of tinnitus on quality of life across three main domains: functional, emotional, and catastrophic. THI classifies tinnitus into five grades: (a) I - negligible (0-16); (b) II - mild (18-36); (c) III - moderate (38-56); (d) IV - severe (58-76); (e) V - catastrophic (78-100). Audiometry and psychoacoustic measures of tinnitus (pitch, loudness, minimum masking level) will be performed at T1 and T5 by an audiologist blind to the treatment group.

The clinical variables of temporomandibular dysfunction (TMD) will also be assessed by a researcher blinded to the treatment type, using the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) and VAS at the same time points. The DC/TMD is a validated tool, adapted to Portuguese, used in clinical trials that provides a systematic assessment, including a standardized clinical examination and questionnaires. This classification system, based on the biopsychosocial model of pain, includes a physical assessment through Axis I, using reliable and well-operationalized diagnostic criteria, and an assessment of the psychosocial status and pain-related disability through Axis II.

Both assessments will be conducted at T1, T2, T3, T4, and T5.

Inclusion Criteria:

• Patients over 18 years old;
• Sufferers of somatosensory tinnitus and TMD for more than 6 months;
• Dentition in good health, with at least minimal occlusion up to the second premolars on both sides;
• Availability for at least 4 months of follow-up;
• Able to speak and read the Portuguese language.

Exclusion Criteria:

Pregnant patients; Treatment for TMD in the last 3 months; Treatment for tinnitus in the last 3 months; Use of total or partial removable prostheses Presence of orofacial pain disorders not related to TMD; Medical contraindication to treatment; Reluctance to accept any designated treatment; Unable or unwilling to give informed consent; Language barrier or delay in neuropsychomotor development.