You can use magnesium supplementation instead.
Just before bed. It helps with the grinding plus other muscles that might get contracted during night. It's good for the body. You'll sleep better no matter with or without mouthguard. AND you won't absorb any plastic. Plus you won't scare your partner at bed. Plus the effect is cumulative as you replenish your magnesium stores.
Ray Peat has some comments about magnesium:
Before knowing Ray's opinion on magnesium, I also found that carbonate and chloride were very good forms, whereas citrate and oxide are BAD. (personal opinion)
Two teaspoons of Mg Carb. in water before bed with a bit of something acid to avoid gas.
And remember to never use mag carb with food, as the carbonate counteracts tomach acid.
Btw, at a psychological level, I think bruxism has to do with repressed anger.