Bunjamon saidI'm not sure where you're getting that sucrose is the main ingredient, since medicine ingredients are listed first by active/inactive, then by amount. If you look on the official Tums website, sucrose is listed a second-to-last inactive ingredient, right before talc, for both Tums flavors.
Drinking orange juice, soda, eating acidic fruits, etc. also all decay enamel and can eventually cause mineral loss. I think the antacid benefit of Tums (since acid reflux can result in esophageal damage that can be life-changing) could outweigh the risk of having it on your teeth at night. Besides, who wants that chalky taste in their mouth before bed? Best take it and then brush your teeth.
You're wrong about the ant-acid side of things. An ant-acid usually contains a compound similar to calcium carbonate, which, when reacted with hydrochloric acid (HCl, stomach acid), produces a neutral salt and a pH buffer, to limit how high or low the pH can go; when you're experiencing acid reflux, the acid from your stomach isn't bathing your teeth, it stops in your esophagus.
The reason demineralisation of enamel occurs, is due to microbes living on your teeth and gums. One of the metabolic by-products microbes produce is acid - it's this acid that actually leads to the demineralisation of tooth enamel; not stomach acid.
All the sugars you digest can be metabolized by the microbes in your mouth - which produces acid. In addition, amylase, the enzyme in your saliva responsible for catalyzing the breakdown of carbohydrates, converts carbohydrates into their monomers- sugar. This sugar from the carbohydrates also is metabolized by the microbes in your mouth, and more acid is produced.