## 1 Introduction
It is a central sensitization syndrome, characterized by chronic musculoskeletal pain, affecting approximately 5% of the global population [13]. Several studies have highlighted the common presence of a painful condition associated with TMDs and fibromyalgia [13]. This syndrome involves a combination of factors that predispose individuals to, and trigger, TMDs, which may account for the high prevalence of TMDs signs and symptoms in these patients [14]. Bruxism can occur during sleep as an activity of the masticatory muscles, particularly during the N1 sleep stage, including brief daytime naps, and may be rhythmic (phasic) or non-rhythmic (tonic) [15]. It is associated with morning headaches, and some studies have highlighted its effect on insomnia [16]. On the other hand, daytime bruxism is described as masticatory muscle activity during wakefulness, characterized by repeated or prolonged contact of opposing teeth and/or jaw clenching or thrusting. It is not considered a motor disorder in otherwise healthy populations [17]. Sleep disturbances are recognized as a risk predictor for developing painful TMD [18]. There is a proportional and bidirectional relationship between sleep quality and TMD pain, as pain can disrupt sleep, and poor sleep, in turn, exacerbates pain [18]. TMDs affect up to 15% of adults, with as many as 90% of TMDs patients reporting poor sleep quality [19]. Insomnia and sleep apnea are the two most common forms of sleep disturbances observed in individuals with TMDs [19]. To prevent the negative effects of sleep bruxism, stabilizing and occlusal splints can be used [20]. These splints eliminate occlusal interferences, relax the masticatory and neck muscles through passive stretching, improve occlusal and neuromuscular stabilization, and reposition the mandibular codyles and articular discs [20]. In addition to occlusal splint, treatment for bruxism may involve various therapeutic options, such as patient education about harmful habits, biofeedback, muscle relaxation exercises, short-term medications, botulinum toxin injections, psychotherapy (including stress reduction, lifestyle changes, hypnosis), electrical methods, and correction of speech pattern disturbances [21; 22]. However, few studies have explored the combination of these variables and pathologies in patients with fibromyalgia and bruxism. Both bruxism and fibromyalgia are conditions that may lead to increased pain sensitivity and muscular hyperactivity, which can contribute to the onset and exacerbation of TMD symptoms. The combination of fibromyalgia and bruxism is especially important to study because both conditions may share underlying mechanisms like central sensitization and disrupted pain regulation. They belong to a group of disorders known as central sensitization syndromes--which also includes conditions such as irritable bowel syndrome, chronic fatigue syndrome, and migraine. These syndromes often overlap in the same patients and can make symptoms worse when they occur together. Looking at this comorbidity helps us better understand why some people experience more severe or complex TMD symptoms [18]. Additionally, the presence of bruxism in individuals with fibromyalgiagia has been linked to increased muscle tension, which may further aggravate TMD symptoms [11]. Given these physiological connections, investigating the impact of occlusal splints in these specific groups is crucial to understanding potential therapeutic approaches. It would be valuable to investigate whether the use of an unloading splint could offer an effective solution for these patients. Therefore, the aim of this study was to evaluate the impact of splint therapy on TMDs symptoms and overall well-being in patients with fibromyalgia and bruxism.