Non-surgical periodontal treatment has traditionally been based on the notion that bacterial plaque (dental biofilm) penetrates and infects dental cementum. Removal of this infected cementum via scaling and root planing (SRP) was considered essential for re-establishing periodontal health. In the 1980s the concept of SRP was questioned because several in vitro studies showed that the biofilm was superficially located on the root surface and its disruption and removal could be relatively easily achieved by ultrasonic instrumentation of the root surface (known as root surface debridement (RSD). Subsequent in vivo studies corroborated the in vitro findings. There is now sufficient clinical evidence to substantiate the concept that the deliberate removal of cementum by SRP is no longer warranted or justified, and that the more gentle and conservative approach of RSD should be implemented in daily periodontal practice.