In fact, it is! As long as a few guidelines are followed. There have been quite a few studies done on the topic, and some do show that chewing gum can have an indirect positive effect on your teeth. Gum stimulates production of saliva which is a natural buffering agent that washes the teeth and neutralizes some of the acid produced by bacteria which is what erodes enamel and eventually causes cavities.
And if you’re one of those people who doesn’t produce enough saliva in general, gum can help here too! Chew gum for 10 minutes every hour for two weeks and you can actually increase your salivary flow to a functional level which will lead to an increased buffering capacity.
However, as I said, it’s important to remember a few guidelines. Since gum typically contains some type of sweetener, be sure to avoid the ones containing sugar. Artificial sweeteners like Xylitol are a much better choice and some can actually prevent cavities. Sugar can be harmful to your teeth if you chew gum with sugar too often or, interestingly, if you remove the gum from your mouth too soon. So if you must chew gum with sugar, chew it for at least 15 to 20 minutes. After this time, the sugar is gone, but the saliva is sufficiently stimulated to rinse away some of the sugar residue.
But the better choice: sugar-free gums.