The aim of this research is to perform a comparative clinical and histomorphometric analysis of soft tissues in the area of soft tissue graft and collagen matrix transplantation. Thirty patients diagnosed with partial absence of teeth will be examined on the basis of the Department of Surgical Dentistry of the E.V. Borovsky Institute of Dentistry of I.M. Sechenov First Moscow State Medical University. Patients have a soft tissue thickness deficiency from the vestibular surface in the area of the planned dental implant placement in the esthetic zone of the maxilla, which is an indication for its increase. All patients will be randomly divided into two groups depending on method of soft tissue augmentation used. In 1 group (n=15) transplantation of a free connective tissue graft (CTG) from tuberosity area of the maxilla or palate is performed. In 2 group (n=15) collagen matrix "Fibro-Gide" will be used. According to gender and age characteristics, both groups will be comparable. Randomization of patients will be carried out at the stage of surgical intervention as follows: after a dental implant placement and preparation of recipient's bed, an envelope with a randomly assigned treatment method (using a connective tissue graft or a collagen matrix) will be opened.

During the operation, incision will be made along the top of the alveolar ridge within the defect; a full-thickness muco-periosteal flap will be elevated. Traditional 2-stage dental implantation is performed according to surgical protocols of dental implant systems Astra Tech (Dentsply Implants Manufacturing GmbH, Germany; registration in Russia 27.12.2019 No FSZ 2015/3214). A free connective tissue graft will be harvested in patients of the first group. Graft will be fixed with a horizontal U-shaped suture to the buccal muco-periosteal flap. In second patients group a fragment of the collagen matrix "Fibro-Gide" will be fixed to the buccal muco-periosteal flap (Geistlich Pharma AG, Bahnhofstrasse 40, 6110 Wolhusen, Switzerland; registration in Russia 19.08.2020 No FSZ - 20207/11765). For patients of all groups mobilization of the muco-periosteal flap conducts followed by suturing the wound tightly without tension with simple interrupted sutures.

Postoperative recommendations will include rinsing with 0.2% chlorhexidine gluconate mouthwash solution (Corsodyl, GlaxoSmithKline 77.99.11.915.Д.005285.07.03) twice a day for a week and receiving antibiotic (Amoxicillin + Clavulanic Acid, 1 g Amoxiclav, LEK, d.d., Slovenia, 22.07.2011, П N012124/01) twice a day for 5 days. To relieve pain, 100 mg of Nimesulide (Nise; Dr. Reddy's Laboratories Ltd., India, 26.05.2009, П N012824/03) will be prescribed. The stage of the implant uncovering with hilling abutments installation is carried out 3 months after the intervention. At this stage, a soft tissue fragment will be taken using a mucotome in the area of the previously performed mucous membrane thickness increasing for subsequent histomorphometric analysis. In the study we will use both conventional light microscopy (microscopy in the light field) and polarizing microscopy - to estimate the content of collagen fibers in preparations stained with picrosirius red. During a morphometric study we will carry out a quantitative assessment of the characteristics of the epithelial layer, the basement membrane relative length (the ratio of the absolute length of the basement membrane to the length of the epithelial layer), the characteristics of the underlying connective tissue.