How does any doctor know when someone has got an overactive salivary gland?

Hypertrophy?: Sialry gland tumours called sialadenomas cause enlargement and swelling. There are 3 pairs of major salivary glands called parotid, submandibular below the lower jaw and submental beneathtt he chin .We have to differentiate the adenomas -benign tumours from hypertrophy and stones causing blocking of salivary ducts , and the gland enlargements. By obvious swelling, and increase in size with eating.