**3. Healthy periodontium and the pathogenesis of periodontitis**

The periodontium consists of the tooth's surrounding anatomical structures, which include, from superficial to deep, the gingiva, gingival ligament, root cementum, and alveolar bone (**Figure 3**).

In a healthy periodontium, the supportive anatomical structures adhere to the tooth by way of connective and epithelial tissue types [35]. The epithelia exist as different subtypes around the erupted tooth and have been described as the first line of defence, protecting the underlying tissues of the periodontium from microbial infiltration from the oral cavity (**Figure 4**) [35]. The pathogenesis of PD first involves

**Figure 3.** *An illustration of a healthy tooth and its surrounding structures (i.e., periodontium).*

#### **Figure 4.**

*An overview of the pathogenesis of PD starting with gingivitis progressing to severe PD.*

#### **Figure 5.**

*Measuring of the depth of periodontal pockets with a probe is part of the diagnostic criteria predicting the severity of periodontal disease.*

a shift in the oral milieu which optimizes the formation of a dysbiotic microbial biofilm, resulting gingival inflammation, which then progresses to the subgingival region (**Figure 4**) [36].

Clinically, people suffering from PD present with bleeding gingiva upon probing and varying degrees of detachment (i.e., clinical attachment loss [CAL]) of the gingiva from the tooth as measured with a periodontal probe (ada.org) (**Figure 5**).
