I would like to know if ground-coffee stains the enamel of our teeth. If so, how long and how frequent would its exposure to coffee be in order to acquire a taint or colouring? It is possible too that only additives to the coffee result in an affect to the enamel of our teeth.
Yes...tea and wine too. Hydrogen peroxide and baking soda can remove coffee stains from enamel. Organic bits of the plants stain enamel over time.
Yes, a few cups a day of black coffee will stain your teeth noticeably over a month or two (personal experience). It's easy to fix with a whitening toothpaste. You don't need one containing bleach; the one I use contains titanium dioxide. It got rid of the staining in a few days.