**3.2 Immune responses in the pathogenesis of periodontal disease**

In normal health conditions, periodontal tissues are capable of coping with the presence of bacteria through several mechanisms of the host immune system (e.g., **Figure 3**) [14]. However, when the balance between the infection control mechanisms and the subgingival biofilm is lost [15], which includes *Porphyromonas* 

### **Figure 2.**

*Histopathological lesions of periodontal pathogenesis. Initial, early, established, and advanced lesions of the development of gingivitis and periodontitis.*

*gingivalis*, *Aggregatibacter actinomycetemcomitans*, *Tannerella forsythia*, and *Treponema denticola* [16], innate, inflammatory, and adaptive reactions are triggered. These processes result in the destruction of the tissues that surround and support the teeth, and eventually in the loss of tissues, bones and finally, of the teeth [17].
