There are three major salivary glands that generate and empty saliva into the mouth: the submandibular gland, sublingual salivary glands and the parotid glands. Surgery of the parotid gland, also known as parotidectomy, is the operation to remove tumours that grow in the gland. It is estimated that over 70% of these tumours are benign (noncancerous) but all instances should be investigated. The type of operation performed depends on the type of tumour , its size and its location. The most common are superficial parotidectomy or total parotidectomy, with conservation of the facial nerve, which also involves a lymph node dissection. The salivary glands may also develop other diseases. The most common are sialolithiasis, which is blockage and inflammation of the salivary glands by calcium stones that do not allow the output of saliva; and sialadenitis which can be an effect of sialolithiasis, or be caused by a virus or bacteria.