Strip Graft w/ Xenogeneic Matrix vs Free Gingival Graft for the Augmentation of Peri-implant Keratinized Mucosa

The primary objective of this study is to compare changes in peri-implant keratinized mucosa (PIKM) following the application of apically repositioned flap (ARF) using a combination of a Strip graft and a Xenogeneic matrix, or with a free gingival graft (FGG), in implants in the second stage with \<2 mm of PIKM.

Additionally, as a secondary objective, the investigators compare postoperative blood supply in both recipient and donor sites based on the type of graft obtained. Meanwhile, the investigators evaluate differences between the two groups concerning microcirculation values (perfusion units, PU), soft tissue thickness (STT), volume change, vestibular depth, as well as clinical, aesthetic, and patient-reported outcome measures (PROMS).

1. BACKGROUND The importance of keratinized tissue around teeth and dental implants is a frequently investigated topic in the literature. The need for an adequate amount of peri-implant keratinized mucosa (PIKM), which is defined as a minimum width of 2 mm is demonstrated according to a recently published systematic review and consensus report.

   The standard of care in the PIKM augmentation is the apically repositioned flap (ARF) combined with a free gingival graft (FGG), as it represents a predictable and documented strategy to gain KT width. However, such technique implies the harvest of abundant autogenous grafts, and is frequently associated to sub-optimal aesthetic results due to the poor color mimicry of the grafted tissue.

   In light of such limitations, some alternatives based on the use of soft tissue substitutes have been proposed, with the aim of reducing surgical invasiveness through the avoidance of large autogenous grafts and improving aesthetic outcomes.

   Among those, the sole use of as xenogeneic collagen matrices (XCM) has been associated with promising clinical outcomes albeit with lesser KT width gains as compared to autogenous FGGs.

   Recently, a novel approach called the Strip Technique (ST) has been introduced, where the exposed periosteal bed of a ARF is covered with the combination of a xenogeneic collagen matrix and a 2-3 mm wide strip of autogenous free gingival graft, sutured at the apical border of the matrix. The rationale for this "combined grafting technique" stands on reducing surgical invasiveness and improving color mimicry through the use of a XCM, while providing a source of autogenous keratinizing cells in the apical border of the grafted area to promote better PIKM gains. Albeit this new approach seems promising, there is limited evidence regarding its clinical efficacy and there is a lack of knowledge regarding how the adoption of such combined approach affects the re-perfusion of the grafted tissue and the overall microvascular healing of the surgical site.

   Furthermore, the pattern of the revascularization of both the autologous grafts and the XCM requires further understanding. Most of our recent knowledge comes from classical animal studies that evaluated the microvascularization of FGG when placed over periosteum with microscopy. The postoperative blood supply of these free grafts is of key importance to their survival.

   Recently a new non-invasive technique has been introduced in the field of medicine and dentistry the Laser Speckle Contrast Imaging (LSCI) system, that provides further understanding on the dynamics of postoperative blood supply of the applied grafts and elucidate regarding the healing pattern of the strip combination technique.
2. JUSTIFICATION There is a lack of knowledge regarding the clinical performance, the healing pattern and the dynamics of revascularization when performing apically repositioned flaps combined with either the autogenous strip-XCM technique or autogenous FGGs.

Results from this study could assess whether the strip-XCM technique represents a reliable, less invasive, and simplified alternative to autogenous FGGs for the increase of PIKM.

Moreover, it could provide additional knowledge regarding the healing and revascularization pattern of both strip-XCM and FGGs around dental implants, assessed through an innovative technology as Laser Speckle Perfusion.

Eligibility Criteria:
Inclusion Criteria:

* Patients older than 18 years
* Short-span dental implants in the mandible at second stage with inadequate PIKM (\<2 mm) with at least one adjacent tooth mesially
* Periodontally healthy patients with a pristine or reduced periodontium
* Plaque index (FMPS) less than 20%.

Exclusion Criteria:

* Compromised general health status that contraindicates study procedures (≥ASA III);
* Drug or alcohol abuse;
* Smoking of \> 10 cigarettes per day;
* Chronic use of corticosteroids, NSAIDs or immunomodulators (any type or dose);
* Pregnant or lactating women;
* History of previous mucogingival surgeries in the area of interest