This refers to a localized infection of small extent concentrated in a focus. It is a potential source of disease of the whole organism, most often in the case of its weakening (surgery, chemotherapy ...). Active detection and elimination of focal infection are necessary before starting oncological treatment (radiotherapy, chemotherapy), before major surgical procedures (cardiac surgery, orthopaedics...), etc. The most common focal infections include odontogenic focal infections - the source can be periapical granulomas, cysts, any teeth without vital pulp, pulpitis, remaining roots, ...

Dental focal infections are various diseases of distant organs that are triggered from infectious foci in the oral cavity. The breakdown of tissues produces microorganisms, toxins and other substances that spread via the haematogenous route.