Volume-Stable Collagen Matrix vs. Connective Tissue Graft for Peri-Implant Soft Tissue Defects

Peri-implant buccal soft-tissue thickness will be measured non-invasively using high-resolution intraoral ultrasonography (LOGIQ P10 XDClear R4.5, GE Healthcare) with an L8-18i-RS high-frequency linear "hockey-stick" probe (8 MHz). Measurements will be repeated preoperatively (baseline) and postoperatively at 1 week, 1 month, 3 months, and 6 months. On static B-mode images, linear soft-tissue thickness will be assessed at three levels 1.5, 3, and 5 mm apical to the alveolar crest margin and recorded in millimeters by a single calibrated examiner blinded to group allocation. The primary outcome is the change in linear soft-tissue thickness from baseline to 6 months, compared between the VCMX and CTG groups.

Peri-implant soft-tissue perfusion will be evaluated using Power Doppler ultrasonography (PDUS) with the same unit and probe, preoperatively (baseline) and postoperatively at 1 week, 1 month, 3 months, and 6 months. Quantitative analysis will use the device's integrated Color Quantification (CQ) module: a circular region of interest (ROI) 6 mm in diameter (area 28.274 mm²), originating from the alveolar crest margin, will be defined. Within this ROI, the proportion of colored (Power Doppler) pixels representing blood flow relative to the total number of pixels will be calculated to obtain a semi-quantitative Power Doppler pixel density . The outcome is the change in pixel density from baseline to 6 months, compared between the VCMX and CTG groups.

Tissue echogenicity will be evaluated preoperatively (baseline) and postoperatively at 1 week, 1 month, 3 months, and 6 months from static B-mode images obtained with the probe positioned longitudinally over the mid-buccal region of the edentulous site. Echo intensity will be measured in decibels (dB) using the unit's grayscale (echo-intensity) function. The ROI will extend 7 mm apically from the soft-tissue margin. As the device references echo intensity to the system's saturation level, soft-tissue reflections yield negative dB values; less negative values indicate higher echogenicity (denser, more organized tissue), and more negative values indicate hypoechoic/less dense tissue. Measurements will be performed by a single calibrated, blinded examiner, with intra-examiner reliability assessed beforehand. The outcome is the change in echo intensity from baseline to 6 months, compared between the VCMX and CTG groups.

Patient-rated pain intensity at 1 week, recorded on a Visual Analog Scale (VAS) anchored at 0 (no pain) and 10 (most severe pain). Compared between the VCMX and CTG groups.

Patient-rated swelling at 1 week on a Visual Analog Scale (VAS) from 0 (no swelling) to 10 (most severe). Compared between the VCMX and CTG groups.

Patient-rated fatigue at 1 week on a Visual Analog Scale (VAS) from 0 (no fatigue) to 10 (most severe). Compared between the VCMX and CTG groups

Total number of analgesic tablets taken during the first postoperative week, recorded by patient self-report. Compared between the VCMX and CTG groups.

Early wound healing at 1 week scored with the Wound Healing Index (Huang et al., 2005) based on edema, erythema, discomfort, flap dehiscence, and suppuration, from 1 (uneventful healing) to 3 (poor healing). Compared between the VCMX and CTG groups.

Soft-tissue appearance at 6 months graded with the Aichelmann-Reidy et al. (2001) tissue-appearance system across five parameters (tissue consistency, contour, color match, scar formation, and integration with adjacent tissue), each scored against predefined criteria and summed into a total appearance score. Compared between the VCMX and CTG groups.

Number of participants rating the appearance of the treated site as "satisfactory" versus "not satisfactory" at 6 months. Compared between the VCMX and CTG groups.

Number of participants rating their treatment experience as "satisfactory" versus "not satisfactory" at 6 months. Compared between the VCMX and CTG groups.

Descriptive light-microscopic evaluation (hematoxylin-eosin and Masson's trichrome) of tissue architecture, integrity and cellular organization, extracellular matrix organization, and the presence of necrosis, edema, hemorrhage, inflammation, foreign-body reaction, and fibrosis.

Number of vessels counted in the superficial connective tissue at x400 magnification (single field = 0.237 mm²) across three consecutive fields, averaged per specimen. Compared between the VCMX and CTG groups.

Number of CD163-positive cells counted at x400 magnification (single field = 0.237 mm²) across three hot-spot fields, averaged per specimen. Compared between the VCMX and CTG groups.

Number of CD11c-positive cells counted at x400 magnification (single field = 0.237 mm²) across three hot-spot fields, averaged per specimen. Compared between the VCMX and CTG groups.

Number of TIMP-1 positive cells counted at x400 magnification (single field = 0.237 mm²) across three hot-spot fields, averaged per specimen. Compared between the VCMX and CTG groups.

Number of MMP-1 positive cells counted at x400 magnification (single field = 0.237 mm²) across three hot-spot fields, averaged per specimen. Compared between the VCMX and CTG groups.

Immunohistochemical Collagen I staining, quantified as the percentage of positively stained area relative to the total microscopic field area. Compared between the VCMX and CTG groups.

Immunohistochemical Collagen III staining, quantified as the percentage of positively stained area relative to the total microscopic field area. Compared between the VCMX and CTG groups.