How Is Excess Salivation Related To Dementia?

Hello! My mom is the old lady with dementia , with a lot of problems in her stomach (such as 3 ulcers). She drinks a little bit of insure and tea... everything is getting worse. I understand... but why she has a lot of saliva. when it coming, my mom is so scared and she like choking. Is it a lot, because of her stomach problems? poor mom...she keeps it in her mouth and so scared. sometimes she listen to me and open her mouth. what kind of medication would help her ? Thank you.