General information will be gathered from the patients' charts. Patients' age, self-reported smoking habits and the number of cigarettes per day, medical history, medication intake, reason for tooth loss and the date of prosthesis insertion will be recorded in "patient's summary forms". Type and distribution of implants will be retrieved from patients' charts. Cases with a chart documentation of an incidence of biological or mechanical complications during the follow-up period will be closely reviewed and recorded as following: