Cysts
Salivary cysts are characterized by an accumulation of thick, sticky saliva because of a blocked-up duct (canal) through which the saliva travels to the mouth). The duct can become obstructed by food particles, or even by the thickening of saliva at the onset of the problem. If the saliva can’t flow, it backs up and collects as a fluid-filled cyst in the gland itself. Usually, the actual cause cannot be immediately determined. We see only the effect. 
Nevertheless, we do know that salivary cysts can be caused by traumatic or an inflammatory occlusion or rupture of the duct of the salivary glands (situated below the tongue, in the area of the jaw or the parotid gland). Because the channel of the mandibular (lower jaw) salivary gland and the major duct of the sublingual (below the tongue) salivary gland frequently empty through a common opening, these glands often are involved in the ailment simultaneously.
We have encountered quite a few salivary cysts over the years, usually in the salivary gland under the tongue (sublingual), on the floor of the oral cavity.