Active_comparator: Subepithelial connective tissue group (SCTG)

A SCTG will be harvested from the patient's palate with a dimension dependent on the size of the peri-implant osseous defect. The technique of harvesting a soft tissue grafting is well described and established in the literature. Following the administration of local anesthesia, the SCTG will be harvested using a single incision technique. The periosteum will be left intact. The thickness of the SCTG will be at least 1.5mm. A cross suture will be used to close the palatal incision.~The SCTG will be placed on the buccal exposed implant threads (above the DBBM-C) exceeding 1mm in a coronal and apical direction, 3mm in a mesial and distal direction and then immobilized using a horizontal mattress connecting it to the lingual or palatal flap. The flaps are then closed primarily and tension-free following a horizontal periosteal releasing incision.

Active_comparator: Volume stable Collagen Matrix group (VCMX)

A VMCX (FibroGide®) will be hydrated in sterile saline, trimmed and adjusted to a dimension dependent on the size of the osseous peri-implant defect. The VCMX will then be placed as described above and then immobilized using a horizontal mattress connecting it to the lingual or palatal flap. The flaps are then closed primarily and tension-free following a horizontal periosteal releasing incision.

Sham_comparator: No soft tissue augmentation (GBR)

No barrier membranes will be placed. After filling the defect with the bone substitute, the flaps are closed primarily and tension-free following a horizontal periosteal releasing incision.