Mastication is the process of chewing and grinding food between teeth so as to break it down into smaller fragments to prepare it for swallowing. It is the first step of digestion, and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned by the cheek and tongue between the teeth for grinding. Whilst many muscles are actually involved in mastication, the primary four muscle of mastication are masseter, temporalis, lateral pterygoid and medial pterygoid.
The movements of the mandible brought about by the muscles of mastication occur at the temporomandibular joints (TMJs). These movements involve elevation, depression, protrusion and retraction of the mandibular condyles.
Initially the incisors are used bite food off, which means the contraction of masseter, medial pterygoid and temporalis. Chewing, grinding or side-to-side movements are brought about by alternate contraction of the left and right pairs of pterygoid muscles. Masseter further contributes during chewing to maintain occlusion of the teeth. Temporalis is able to retract the mandible if food is sticky. Digastric, mylohyoid and geniohyoid may also help to separate the teeth if a food bolus is sticky. The tongue, orbicularis oris and both buccinators all contribute to keeping the bolus in the centre of the mouth. Once a suitable consistency has been achieved, the bolus is collected and swallowed.