Is a mouth guard for bruxism effective?

It will help: It does help soften the force applied to the teeth. There are also other ways that may, or may not, be more effective for you, such as an occlusal adjustment. See you dentist for an evaluation.

Can be: There are many types of mouthguards for grinding and clenching. Over the counter ones actually may be too thick and throw the muscles into more spasms. Dentists can make custom made, well fitting mouthguards, either upper or lower (i like the lower ones.) the guards can be made of soft plastic or hard acrylic...Depends on severity of grinding. For daytime clenching, other types are indicated.

Sometimes: Try it, You'll be able to tell if it works. You may need a custom mouthguard from your dentist.

Depends: Yes, a custom made dental mouth guard, an Occlusal Orthotic, will prevent wear and fractures. The best thing to do for British is diagnose and treat the cause. OTC mouth guards are a poor substitute for custom made appliances, and can even do damage. They also don't work as well as a custom athletic mouth guard to prevent sports injuries. See your Dentist.