The objective of this study was to compare the clinical effectiveness of personalized thermoformed occlusal splints together with behavioral and self-care therapy in the management of myalgia of the masticatory muscles. A controlled clinical trial was carried out with a total of 46 subjects diagnosed with myalgia according to the diagnostic criteria for temporomandibular disorders (DC / TMD). All subjects were treated with behavioral and self-care therapy (BST) at the beginning of the study, and were then randomized into 4 groups: behavioral and self-care control group; rigid occlusal splint group; soft occlusal splint group and non-occlusive splint group. Follow-ups were carried out at 2, 6 and 10 weeks, where it was evaluated: pain in the masticatory muscles, mandibular range of motion, mandibular functional limitation and occlusal discomfort.

Materials and method This randomized controlled clinical trial was conducted between October 2017 and January 2018 at the Dental Clinic of the Andrés Bello University (Viña del Mar, Chile). The study subjects were recruited from the universe of patients seeking treatment for jaw pain at the School of Dentistry. All subjects were informed about the study by their operator and gave their written consent before starting the study. The protocol, design and implementation were approved by the Scientific Ethics Committee of the Faculty of Dentistry of the Andrés Bello University, Viña del Mar, Chile (Folio No. 033, October 2017). Which was in accordance with the latest version of the Declaration of Helsinki of the World Medical Association (World Medical Association Declaration of Helsinki, 2013).

Sample Size Calculation It was calculated according to a confidence level of 95% and a statistical power of 80%. Based on a previous study by Niemelä et al. (Niemelä et al., 2012) it was determined that the variance of the main variable (masticatory muscle pain) of the reference group is 2.6. In turn, the pain variable was measured on the visual analog scale (VAS), where a minimum clinically relevant difference was considered if a 3.5 point decrease was achieved on the VAS scale with respect to treatment, a reference that was also considered in this study.

Randomization and interventions. After meeting the inclusion and exclusion criteria, the subjects were randomly assigned to four groups through a computationally generated sequence "list randomizer" developed by random.org.

Evaluation methods The initial evaluation, to determine the degree of involvement of axis I, was carried out following the symptom questionnaire and clinical examination guidelines according to the DC / TMD protocol. Additionally, the questionnaire for the chronic pain degree scale (GCPS v2.0) and the functional limitation scale (JFLS-20) of axis II of the DC / TMD protocol were applied. In turn, an intraoral clinical examination was performed to exclude pain of dental origin. No subject was excluded for odontogenic pain.

Statistic analysis The demographic characteristics of the sample were reported descriptively. The data studied were tested to determine normality by using the Shapiro-Wilk and Doornik-Hansen tests, data that were parametric, so they were analyzed with a mixed ANOVA test, a factorial part and a repeated means part for the variables degree of chronic pain, masticatory muscle pain, mandibular range of motion, functional limitation and occlusal discomfort. The level of significance used was established at p 0.05. All statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) version 17 software (IBM, Chicago, USA).

Inclusion Criteria:

• Age between 18 and 40 years
• Presence of myalgia of the masticatory muscles with or without limitation of the mouth opening according to DC / TMD diagnostic criteria

Exclusion Criteria:

• Painful joint TMD
• History of treatment for TMD
• Recent history of facial or cervical trauma
• Current orthodontic treatment
• Tooth mobility secondary to periodontal disease
• Subjects with loss of more than two teeth other than third molars and / or premolars due to orthodontic indication
• Subjects with systemic musculoskeletal diseases or who are under analgesic treatment
• Subjects with a diagnosed intellectual disability who cannot express their will to participate in scientific research as established by law 20.584 of Chile

All the collected individual participant data (IPD), study protocol, statistical analysis plan, informed consent form and a clinical study report will be shared, including results, discussion and bibliography studied.

One-year database availability period, starting on October 19, 2020

Database will be shared in Open Security Foundation (OSF), a non-profit public organization founded as a support organization for open source security projects.

In the first session, operator A explained to the study subjects the alternatives, benefits and possible complications of the treatments, but it was indicated that at the time of delivery of the treatment it would not be explained to them in which group they were assigned in order to protect blinding of treatments. Operator B was in charge of delivering the treatments randomly among the subjects selected by operator A. Finally, the controls were carried out by operator A in order to protect the blinding by not knowing the treatments of the patients at the time controls.