TNFSF13B and Peri-Implantitis: The aim of this study was to analyze and compare the expression of APRIL and BAFF in the peri-implant soft and bone tissue in patients with peri-implantitis; to analyze the expression of osteonectin (ON) and ∝-smooth muscle actin (∝-SMA), to quantify the osteocytes and blood vessels in the peri-implant bone tissue in patients with peri-implantitis, and to quantify the number of mast cells in peri-implant soft tissue in patients with peri-implantitis.