Plaque accumulation on abutments or implant surfaces induces an inflammatory reaction in the gingiva/alveolar mucosa just as around teeth. The longevity of oral implants can be jeopardized by either peri-implantitis and/or an occlusal overload. In the partially edentulous patient in whom pockets around teeth act as a reservoir for the colonization of the pockets around implants, the risk for inflammatory reactions of the peri-implant soft tissues seems especially more plausible than in the fully edentulous patient. This is especially true for implants with a very rough surface (e.g., plasma-sprayed), because of the positive relationship between surface roughness and supra- as well as subgingival plaque formation. Several medium-term (from 5 to 10 years) clinical studies support this hypothesis, through the observation of ongoing bone loss and subsequent decreasing success/survival percentages. Occlusal overload increases the risk for microfractures at the implant-bone interface in two-stage implants, which can result in significant marginal bone loss and even failure. There is ample evidence that occlusal factors are related to marginal angular defects around two-stage implants.