*2.3. Study Design and Participants*

This is a retrospective case-control study conducted between January 2019 and February 2020 at the College of Dentistry, King Saud University, Riyadh, Saudi Arabia. The participants were classified into three groups on the basis of peri-implant status and selfreported habits of cigarette smoking: (1) cigarette smokers with peri-implantitis (Group-1); (2) never smokers with peri-implantitis (Group-2); and (3) never smokers without periimplantitis (control-group).
