What mechanical and chemical digestion occurs in the oral cavity

Oral cavity is the first part of the digestive system where the food is introduce to start the process of digestion. It contains several structures that aid in chemical and mechanical digestion. These structures include teeth, tongue, hard and soft palates. It is a cavity where the salivary glands secrete the saliva to enhance digestion.
Salivary glands. There are three types of salivary glands in the digestive system and they include parotid which is located underneath the cheeks, the sublingual found under the tongue and submandibullar located on the floor f the mouth. These gland synthesize and secrete saliva into the mouth through various ducts into the oral cavity. saliva contains various components that enhance the process of digestion and to keep the mouth moist.
Tongue plays an important role in the process of
digestion. one of the functions of the tongue is mixing the food with
saliva to lubricate it as well as expose it to the digestive enzymes.
The other role of the tongue is to help in the process of swallowing by
making bolus and raising them leading into the throat.  
bolus. a bolus is a ball of food that moves from the mouth to the stomach by the process of peristalsis. when the food is introduced in the mouth, the teeth break down food mechanically by the process referred to as mastication. after this process the tongue rolls the food into balls referred to as boluses to enhance the process of swallowing.
In the mouth, both the mechanical and chemical digestions occur. mechanical digestion is physical breakdown of food into smaller pieces to increase the surface area for chemical digestion. In the mouth mechanical digestion is enhanced by the teeth and tongue in the process referred to as mastication. On the other hand, chemical digestion in the mouth is carried out my the enzyme ptyalin, which is on of the components of saliva. this enzyme acts on amylose in case of ingestion of carbohydrates.
A number of mechanisms prevent food from entering the trachea. When swallowing the food the flip-like tissue called epiglottis covers the larynx thus preventing the food from entering the airway. After swallowing, the epiglottis returns back to its normal position allowing the breathing to continue. The other mechanism is referred to as gag reflex which prevents items from entering into trachea.