Annex 1. Patient Information and Informed Consent for the Study Study Title: Effectiveness of a sodium hyaluronate 0.01% and Sh-Oligopeptide-85 SP mouthwash for the treatment of symptomatic oral lichen planus: a randomized clinical trial.

Principal Investigator: Dr. Rosa Mª López-Pintor Muñoz, Associate Professor, Department of Clinical Dental Specialties, Faculty of Dentistry, Complutense University of Madrid.

Dear Sir/Madam, Participants are invited to take part in a study evaluating the effectiveness of a mouthwash designed to reduce oral lichen planus-related lesions and pain.

Study Objective The primary aim of this study is to evaluate and compare the effect of Tectum mouthwash (containing sodium hyaluronate and Sh-Oligopeptide-85) versus a corticosteroid mouthwash (provided at no cost to participants) in reducing pain and lesion size.

Eligible participants with oral lichen planus and associated discomfort will receive either Tectum mouthwash or a corticosteroid mouthwash to use after toothbrushing for the first two weeks three times daily, twice daily in the third week, and once daily in the fourth week of treatment.

Participants will be randomly assigned to receive either Tectum mouthwash or the corticosteroid mouthwash through a process comparable to a coin toss. Treatment allocation will be blinded. Neither participants nor the attending clinician will know which treatment is being administered. Participants must use the assigned mouthwash for 4 weeks according to the clinician's instructions and attend visits at the Faculty of Dentistry at 1, 2, 3, and 4 weeks to assess improvement.

At the first visit, a series of data will be recorded, and oral lichen planus lesions and pain will be assessed. The same variables will be evaluated at 1, 2, 3, and 4 weeks to determine treatment effectiveness. Participants will also complete two questionnaires assessing pain intensity and the impact of symptoms on quality of life. During the 4-week treatment period, the use of any other mouthwashes will not be permitted, and antibiotics or anti-inflammatory medications may not be used.

The investigational mouthwash is already marketed and has been used to treat conditions such as oral mucositis and xerostomia with favorable results; therefore, potential benefit in oral lichen planus is anticipated.

If pain occurs, 400 mg ibuprofen may be taken every 8 hours as needed. If ibuprofen is taken, each dose should be recorded and reported to the attending healthcare professional.

Voluntary Participation Participation is entirely voluntary, and non-participation is permitted. Participants may withdraw at any time without providing an explanation and without any disadvantage to clinical care. Refusal to participate or withdrawal will not affect the relationship between participants and the institution.

Study Procedures The dentist providing care in the Diploma of Specialization in Oral Medicine will invite eligible individuals to participate and will provide detailed instructions. The attending dentist will request completion of a questionnaire containing study-required information. If participation is accepted, lesions will be assessed, and questionnaires will be completed.

The attending dentist will instruct participants on product use: three times daily during weeks 1 and 2, twice daily during week 3, and once daily during week 4. Follow-up appointments at 1, 2, 3, and 4 weeks will be scheduled to evaluate the same variables and to repeat the questionnaires.

Risks This study does not present additional risks beyond routine care. Improvement may not occur with use of the mouthwash. Response to corticosteroids and to the investigational treatment may vary.

Confidentiality Confidentiality will be maintained. All information collected during this research will be treated as privileged and documented in coded format. Participants have the right to access and rectify personal data at any time, as established by Organic Law 3/2018 of December 5 on the Protection of Personal Data and Guarantee of Digital Rights. In accordance with data protection regulations, consent may be revoked and rights of access, modification, opposition, and deletion of data may be exercised. Rights to limit the processing of inaccurate data, request a copy of the data, or request transfer of data to a third party (portability), as applicable, may also be exercised.

To exercise these rights, contact may be made with the principal investigator (Dr. Rosa Mª López-Pintor Muñoz, Department of Clinical Dental Specialties, Faculty of Dentistry, Complutense University of Madrid). Participants may also contact the Spanish Data Protection Agency if concerns are not resolved satisfactorily.

Participant identity and any information that could identify a participant will not be disclosed.

Patients must meet the following inclusion criteria:

1. Patients aged ≥18 years.
2. Patients with a clinical and histological diagnosis of OLP according to the criteria of the American Academy of Oral and Maxillofacial Pathology (Cheng et al., 2016).
3. Symptomatic patients, i.e., those presenting atrophic-erosive or ulcerative OLP lesions.
4. Patients with a VAS score ≤ 6.

Exclusion criteria will be:

1. Pregnant or breastfeeding women.
2. Allergy to the components of the Tectum-11® mouthwash.
3. Patients receiving corticosteroids, immunosuppressants, hydroxychloroquine, or retinoids at the time of recruitment.
4. Patients with lichenoid lesions: drug-induced lichenoid reactions, contact lichenoid lesions, or graft-versus-host disease.
5. Use of topical corticosteroids within the previous 4 weeks or systemic treatment within the previous 8 weeks.
6. Use of other mouthrinses for plaque control.
7. Patients unwilling to sign the informed consent form.
8. Patients with a VAS score > 6.

The presence of any of the following criteria will lead to withdrawal of the participant from the study:

1. Failure to attend follow-up visits.
2. Occurrence of adverse events deemed clinically relevant by the investigator.
3. The patient reports that they no longer wish to participate in the study.
4. Development of oral or systemic lesions that meet any of the exclusion criteria.
5. Non-adherence to the treatment regimen, defined as failure to follow the protocol for more than two consecutive weeks.