Half my patients over the age of 60 have significantly less saliva than they had when they were in their 20s and 30s. Part of that is medication, part of that is that our salivary glands don’t work as well when we get older.
Saliva is a huge protector of the teeth in that it neutralizes acids that can erode the teeth.
Saliva inhibits demineralization of the tooth surface and promotes remineralization.
That means that when acids try to dissolve the outer layer of your teeth (the enamel), your saliva is right there, super-saturated with extra calcium and phosphate to prevent the acid from demineralizing your teeth.
When the acid is so strong that it does demineralize the tooth, your saliva will neutralize the acid as soon as possible, and then replace the lost tooth with calcium and phosphate.
I have patients in their 80s, 90s and even 100s who have lost the protection of their saliva so they end up with more cavities and more acid erosion from their stomach acid.