thanks for your query, i have gone through your question, the pain and swelling could be secondary to a tooth infection
since you are telling decay and bone loss...and you are telling dry mouth
and a parotid mass it can be a salivary gland tumor
....or it could be superimposed with both the conditions...consult a oral physician and ENT surgeon for complete examination and proper diagnosis before treatment.. i hope my answer will help you....
Dr. Mahesh kumar T.S