**3. Host susceptibility**

The tooth has a unique situation in the mammalian biology and presents a special challenge to the immune system [8]. The marginal gingiva includes the epithelial and connective tissue attachment apparatus that provides a biological seal between the tooth and the gingival soft tissues.

The oral cavity is a unique microenvironment where millions of bacteria live in harmony with our host defense mechanisms, with the bacterial host balance maintained by the amount of bacterial load through our regular oral hygiene practices. It is therefore important to understand the cellular and molecular elements involved in the pathways from health to disease and from disease to repair and regeneration.
