Alveolar bone homeostasis in health and disease

Periodontal diseases constitute a variety of inflammatory conditions affecting the health of the periodontium, with the primary etiological factor being microbial dental plaque biofilms. This chapter addresses alveolar bone metabolism and homeostasis considering osteoimmunomodulatory implications of the normal commensal oral flora in periodontal health and effects of pathogenic shifts in the oral microbiota during periodontitis disease states. Pattern-recognition receptors (PRRs) are expressed in the periodontium in health, and notably have been reported to be upregulated in periodontal tissues afflicted by periodontitis. Periodontitis is the presence of gingival inflammation with irreversible detachment of periodontal ligament collagen fibers from cementum, which can progress to alveolar bone loss. Germ-free versus specific-pathogen-free animal investigations are actively delineating how the commensal flora impacts normal host immune response mechanisms, knowledge which is critical in understanding how pathogenic flora shifts disrupt periodontal tissue health and homeostasis.