Introduction to the oral cavity

Abstract

The oral cavity plays a critical role as the seeder and gatekeeper of the microbiome that populates the continuum of mucosal surfaces of the gastrointestinal tract, as well as that of the respiratory tract. The mouth has a variety of discrete niches and environmental conditions (microhabitats) that select for and discriminate against a vast array of microorganisms that ultimately determine the microbiome. The oral microbiome is an important contributor to host health and refers specifically to the microorganisms that reside on or in the human oral cavity and its contiguous mucosal surfaces to the distal esophagus. The oral microbiome is composed of approximately 700 species of bacteria, and also includes viruses, fungi, protozoa and archaea associated with the varied microhabitats that define the oral microbial ecosystem. The normal microbiota of the mouth is responsible for maintaining homeostasis of the oral cavity, but is also responsible for two of the most common diseases of bacterial etiology in humans-dental caries and periodontal diseases. Oral diseases have also been linked to systemic chronic diseases including: cardiovascular disease, stroke, abnormal pregnancy outcomes, diabetes, aspiration pneumonia, cancers and Alzheimer’s disease. This Chapter aims to highlight the unique features of the main niches that compose the oral cavity and have influence on its microbiome composition.