The goal of this clinical randomized trial is to examine the effectiveness of hyaluronic acid in treatment of multiple adjacent gingival recessions in 2 groups. Control group will be presented by using a coronally advanced flap only (CAF) and experimental group will be presented with addition of hyaluronic acid to a coronally advanced flap (CAF+HA). The main question it aims to answer is: is there any difference in the reduction of multiple gingival recessions between the control (CAF) and the test group (CAF + HA)? The research would be conducted on subjects referred for specialist treatment at the Department of Periodontology (Faculty of dental medicine, University of Zagreb). A record would be kept of all patients who underwent a detailed clinical examination, those who did not meet the criteria for inclusion in the study and those who refused to participate in it. Participants who meet the inclusion criteria will undergo a detailed clinical examination and if they agree to participate in the research, they will sign the informed form. During the pre-treatment, patients will receive instructions and a demonstration on proper maintenance of oral hygiene as well as a teeth cleaning. In addition to the informed form, they will fill out the OHIP-14 questionnaire, and the researcher will measure the periodontal indices at the very beginning before the operation, as well as the Schiff index. Patients will be photographed at the baseline as well as at follow-up examinations. The total number of subjects would be 42, or 21 patients in the 2 observed groups. The control group refers to surgical intervention using a coronally advanced flap to cover multiple gingival recessions without the addition of hyaluronic acid (CAF) and the experimental group indicates the surgical intervention using a coronally advanced flap to cover multiple adjacent gingival recessions with the addition of hyaluronic acid intraoperatively (CAF + HA).

Gingival recession is defined as a shift of the gingival margin towards the apical side in relation to the cemento-enamel junction, and teeth with a thinner periodontal phenotype are considered more prone to the same occurrence (Jepsen et al., 2018). The coronally advanced flap surgical technique is used to cover root recessions of one or more teeth, if sufficient tissue is present to be mobilized. In 2000., Zucchelli and de Sanctis described the coronally advanced flap technique for covering multiple adjacent gingival recessions in one procedure, and it is applicable and used in clinical practice.

Hyaluronic acid (HA) is a biocompatible and non-immunogenic linear polysaccharide of high molecular mass present in periodontal tissue that has anti-inflammatory and bacteriostatic effects and promotes healing of the surrounding tissue. The potential benefit of adding hyaluronic acid (HA) to the coronally advanced flap (CAF) operative technique to cover multiple adjacent recessions has not been sufficiently investigated. Improving esthetics is one of the primary goals of root recession coverage surgery procedures, and little is known about the same in multiple adjacent gingival recession coverage therapy. In patients with a sufficient amount (≥2 mm) of keratinized tissue, the coronally advanced flap (CAF) has been shown to be very effective in the treatment of multiple recessions, especially in terms of aesthetic results (Chambrone et al., 2018; Pini-Prato et al., 2014.) . The authors concluded by searching databases (Epistemonikos, Cochrane, Medline) that there is no evidence supporting the use of HA + CAF to achieve greater root coverage in the treatment of multiple adjacent gingival recessions.

The aim of this study is to examine the clinical efficacy of HA in combination with CAF for the treatment of multiple gingival recessions in root coverage, width and thickness of keratinized gingiva, and patient-reported clinical outcomes compared to CAF alone as monotherapy.

Implications: It is important for clinicians to choose an adequate therapy in order to achieve the best possible aesthetic and functional result when covering multiple adjacent gingival recessions, reduce postoperative pain, but also ensure an adequate cost-benefit ratio for the patient.

Inclusion Criteria:

• age ≥ 18 years
• people without systemic diseases and chronic regular therapy
• non-smokers
• percentage of areas affected by plaque (FMPS) and percentage of bleeding sites on probing (FMBS) ≤25%
• the presence of a non-carious cervical lesion (NCCL) associated with recession
• gingival recessions on at least two adjacent teeth with a minimum depth of 2 mm and a clearly visible enamel-cement junction
• selection of patients capable of understanding and maintaining oral hygiene instructions with regular follow-up appointments
• selection of patients who fully understand the nature of the proposed surgical procedure and agree to informed consent

Exclusion Criteria:

• untreated periodontitis
• the presence of fixed prosthetic work (crown or bridge) on the examined adjacent teeth
• smokers
• pregnant and lactating women
• patients with uncontrolled type I and II diabetes
• patients with medical contraindications for surgical therapy
• medical history related to malignancies, radiotherapy, chemotherapy for the last 5 years
• taking chronic therapy that affects soft tissue healing such as: steroids, high doses of anti-inflammatory drugs, anticoagulants
• patients with active systemic infection
• allergies to hyaluronic acid
• allergies to local anesthesia
• alcohol or drug use
• participation in another clinical research in the past 6 months

Randomization would first be generated using a computer-selected program, and then the protocol itself would be placed in opaque sealed envelopes and handed to the operator immediately before the procedure with a decision as to whether or not hyaluronic acid (HA) would be applied. In treated areas where HA will not be applied, the operative site will be treated only with saline. The patient as well as the researcher and the outcomes assesssor will not be informed which patient belongs to which group. Randomization and allocation of envelopes as well as allocation of patients to groups will be determined by a fourth party.