The oral cavity offers a range of different niches where periodontopathogens can adhere and survive (e.g. the mucosa, the tongue, the tonsils, the saliva and all intra-oral hard surfaces such as teeth, dentures, oral implants). Transmission of bacteria from one niche to another is likely to occur. Recent studies, for example, illustrated that initially sterile abutments of oral implants were rapidly colonized by bacteria from the subgingival environment around teeth. This transmission of bacteria can occur spontaneously via the saliva, or by means of oral hygiene aids and/or dental instruments. Such an intra-oral transmission, if it occurs at a high speed, could jeopardize the outcome of periodontal therapy. To overcome a bacterial transmission, a 'one-stage full-mouth disinfection' was recently introduced for the treatment of periodontal infections. This new treatment strategy resulted in significant clinical and microbiological improvements when compared with the standard sequential treatment.