Crowns are caps that cover the teeth that are used to support a bridge. The teeth that bookend the gap are used to support the bridge. Bridges supported by crowns last longer, and take less time to install. But in order to place them properly, some of your original tooth structure will need to be removed.
I agree with Anonymous. Properly made and fitted crowns shouldn’t come off that frequently. It suggests either your teeth weren’t prepared correctly, or the crowns may not fit well, or both. I’d definitely get a second opinion. You need properly fitting crowns to prevent the teeth underneath from becoming decayed and infected.