9 1 muscle activity and the coordination between the different chewing muscles.1 It determines the amount of available force to cut and crush food.10 When the maximum mouth opening is reduced, this can have an adverse effect on food intake and the maintenance of good oral health, due to a lower masticatory efficiency.11 The tongue plays an essential initial role in breaking down food into a food bolus and moving food between the molars. The number of teeth determine the size of the occlusal area where the food is grinded and broken down during each chewing cycle.1,10 Tooth loss, the presence of cavities, inadequate restorations, malocclusion or periodontal disease can therefore adversely affect chewing function.2,5 Finally, the production of sufficient saliva is indispensable for good chewing as it moistens the food and binds the particles into a coherent bolus that can be easily swallowed.1,5 Saliva consists for 99% of water and 1% of ions, enzymes and other proteins. Chemicals in the food are dissolved in saliva and are therefore more easily transported to the taste buds, enabling us to taste food. Furthermore, saliva plays a role in the digestion of starch and lipids and in the clearance of food debris after swallowing.5 After the food is chewed and processed, swallowing takes place. This is a physiological process formed by oral, pharyngeal and esophageal phases.12 Swallowing occurs due to neuromuscular actions involving sensitive cranial, motor and parasympathetic nerves.13 Its purpose is to transport food from the mouth to the stomach, promoting hydration and nutrition. To transport food, a number of rapid, coordinated and accurate events have to occur, such as soft palate elevation, vocal fold closure, pharyngeal muscle contraction, laryngeal elevation and anteriorization and epiglottis lowering.14 These mechanisms occur involuntarily after stimulation of sensory receptors, especially located in the oropharyngeal cavity.13 The initiation of oral swallowing is voluntary, and depends on a threshold for food particle size and particle lubrication.1 The pharyngeal phase is considered a reflex response, and the esophageal phase is mainly under dual control of the somatic and autonomic nervous systems.15 The primary function of the oral phase is movement of the tongue, pressing the bolus against the hard palate, and initiating the movement of the bolus to the posterior part of the tongue and towards the oropharynx. In this stage, the contraction of the lips and cheek muscles are crucial to prevent the escape of solids and liquids from the oral cavity.15 The pharyngeal phase involves not only pharyngeal and laryngeal muscles, but also muscles in the oral cavity such as the tongue and suprahyoid muscles.15 The shape of the pharynx is altered dynamically for breathing, eating and vocalization. The pharynx dilates in order to maintain airway patency for breathing, and is constricted to push the food bolus down the esophagus during swallowing.16 The passage of food is separated from the lower airway and nasal cavity. It is essential that the coordination between respiration and digestion is well coordinated so that food can be efficiently transported to the stomach and intestines,