Autogenous vs. Xenogeneic Peri-implant Soft Tissue Grafts Placed in Full vs. Split Thickness Flaps

Randomized, outcome assessor and data analyst blinded, single center trial with four parallel arms and a 1:1:1:1 allocation ratio, with the aim of comparing which combination of bilaminar technique (split vs. full thickness flap) and graft type (autogenous or xenogeneic) provides better clinical, aesthetic, morphological, vascular and patients related outcomes, when augmenting the buccal peri-implant mucosa at the reopening of submerged implant fixtures

This randomized four parallel arms controlled clinical trial with blinded outcome assessment and data analysis aims to establish which combination of bilaminar technique (split vs. full thickness flap) and graft type (autogenous subepithelial connective tissue graft vs. volume stable collagen matrix) provides better clinical, aesthetic, morphological, vascular and patients related outcomes, when augmenting the buccal peri-implant mucosa at the reopening of submerged implant fixtures. The primary outcome is the gain in soft tissue thickness (standardised measurement at baseline, after surgery, at 1m and 6m). Secondary outcomes include changes in tissue volume (intraoral scans at baseline, post-op, 14d, 1m, 6m), RAL and KTW (clinical measurements at baseline, 1m, 6m), tissue color integration (∆E at 1m and 6m), and PROMS (7d, 14d, 30d). Exploratory outcomes include tissue morphology (histology at 1m,2m,4m,6m), microcirculation (Doppler flowmetry at pre-op, 7d, 14d, 1m) and revascularization (IHC at 1m,2m,4m,6m). A figure of 10 subjects per group was obtained for a 0,3mm difference in tissue thickness increase (SD 0,23mm), using 80% power, alpha 0.05, and a 10% drop-out rate. Patients will be randomly allocated to four groups: test (STF+VCM), control 1 (FTF+VCM), control 2 (SFT+CTG), control 3 (FTF+CTG). Patients will be the unit of analysis and ANOVA (normality) or Kruskall-Wallis (no normality) tests will be performed setting the significance level at p \< 0.05.

Eligibility Criteria:
Inclusion Criteria:

Any male or female adult (≥ 18 year old) patient from the University Complutense of Madrid, being able to sign an informed consent form, presenting a submerged dental implant scheduled to undergo a second stage surgery, which is bounded mesially or distally by a remaining natural tooth, and exhibits a lack of buccal soft tissue volume, will be potentially eligible for this trial.

The case definition for a lack of buccal soft tissue volume will be the presence of a thin buccal mucosa (\< 2mm) or a minor volumetric contraction of the alveolar process (flat or concave buccal mucosal profile at the edentulous area).

Exclusion Criteria:

Patients fitting to all the above inclusion criteria will be not included in the study if unable to attend to the study-related procedures (including the follow-up visits) or if one or more of the following systemic or local exclusion criteria will be found during enrolment or through the study:

Systemic primary exclusion criteria:

* Compromised general health status contraindicating the study procedures (≥ASA IV);
* Drug abuse, alcohol abuse, or smoking \> 10 cigarettes a day;
* Chronic use of corticosteroids, NSAIDs, or immune-modulators (any type, any dose);
* Assumption of bisphosphonates (any type, any dose, past or present);
* Pregnant or nursing women;
* Hypersensitivity to paracetamol;

Local primary exclusion criteria

* History of previous mucogingival surgeries in the area of interest;
* Lack of adequate vestibule depth to perform a bilaminar procedure;
* Lack of osseointegration at the time of implant reopening;
* Need for additional bone grafting at the time of implant reopening;
* Intraoperative evidence of a flap thickness \< 0,5mm or \> 2mm.

Secondary exclusion criteria:

- Non compliant patients: poor oral hygiene at 2 consecutive visits.