Hello, You are correct that this could be calcified material in the salivary gland or duct. It may inhibit flow of saliva and back up causing pain and swelling. You are at risk of developing an infection. Removal is the recommended treatment. Someone with a dry mouth and thickened saliva might be at greater risk. Recommendations to avoid risk includes a nutritious diet with no vitamin deficiencies and keeping well hydrated. Some medications such as antihistamines and high blood pressure may contribute to these stones forming. Other considerations may be a tori which is hard bone that would not move and only is painful if the tissue is damaged. The location is more often to the side of the front teeth rather than perfectly behind the midline. Tori are not of concern unless interferes with dental appliances planned, gets tissue damaged often or changes are noticed. Consider any recent trauma to the area that may have caused a reaction. Some other type of growth,cyst or tumor is possible as well. An abscess can appear as a hard lump and should be ruled out. I recommend an evaluation by your dentist. Small stones may pass themselves or can be gently massaged out of the duct by your dentist. Other more involved procedures may need to be considered if it does not pass. Thank you for your inquiry. I hope the information provided is helpful to you.