Tooth discoloration may have various causes. It can appear on the tooth surface having its causes from the outside. Whitening tooth pastes and mouth rinses can possibly remove some of the extrinsic tooth discolourations. However, for the removal of discolourations that develop from the inside, in the micro-fissures of the tooth enamel, deep in the dentine, the only choice can be the professional bleaching agents allowed to be used only in the dental surgery. Should a discolouration occur as a consequence of illness, injury or medical treatment (eg. after a root canal treatment), then special strategies and medical products are needed in order to whiten the affected teeth.