Is it true that brushing right after cola or coffee dissolves the teeth? When should I brush?

It is true. Right after an acidic drink such as cola or juice, the tooth surface (enamel) is temporarily softened, so brushing immediately can wear the teeth down. It is safer to rinse with water and brush about 30 minutes later, once saliva has neutralized the acid. If you often drink acidic beverages, using a straw to reduce contact with the teeth also helps. However, this rule applies to acidic drinks; after an ordinary meal you can brush as usual.