The host defences are like a two-edged sword, since although they are meant to be protective, bystander damage to the periodontal tissues may also occur. A delicate balance exists between the host defences, microbial challenge and ecological environment within the periodontal tissues, such that any upset can tip the balance and lead to periodontal destruction (Fig. 7.1).
Microbial plaque is the primary aetiological agent in the development of periodontal diseases, however patient susceptibility is strongly influenced by the patient’s host defences (Fig. 7.2), as well as genetic factors. Plaque in the gingival crevice initiates an inflammatory response. Innate immunity is inbuilt and requires no prior experience or exposure. Adaptive immunity is stimulus specific, and uses recognition, memory and binding to help in the elimination of the infecting agents, either by the humoral immune response or the cell-mediated response. Mediators link inflammation and immunity.