Oral phase preparation and propulsion: Anatomy, physiology, rheology, mastication, and transport

The oral cavity is a chamber surrounded by and containing hard and soft tissues, notably the lips, cheeks, tongue, palate, and teeth. The oral cavity is the entrance to the digestive, vocal, and (at times) the respiratory tract. Thus, the structures of the oral cavity serve multiple functions in speaking, breathing, mastication and swallowing. Mastication, the initial phase of digestion, is the primary process of the oral preparatory phase of swallowing. Mastication is primarily controlled by motor pattern generators in the central nervous system and modified by internal factors such as dentition and saliva production and external factors such as food consistency. Coordinated motions of the jaws, tongue, soft palate, and hyoid bone reduce and moisten ingested food to render it suitable for swallowing, and transport food to the pharynx for bolus aggregation prior to swallowing. Saliva supports mastication by lubricating food during chewing, helping to forma bolus optimized for swallowing. Saliva also has protective functions fororal health. Food properties such as hardness, water content, flavor, and temperature modify masticatory performance and influence the initiation of swallowing.