parotid duct obstruction symptomsblocked salivary duct symptomsblocked salivary duct under tongueparotid gland duct obstructionblocked salivary gland ductblocked salivary duct cheekblocked salivary duct roof of mouthparotid duct blockagepancreatic duct blockageblocked submandibular ductblocked saliva ductparotid obstruction