I'm planning to see a neuromuscular dentist for treatment of TMJD. Usually after Phase I, which is wearing the splint, Phase II is either orthodontics, teeth reconstruction or permanent splint. I'd asked what the permanent splints are made of, thinking that acrylic might not last very long. Permanent splints can also be made of metal. I haven't heard specifically of metal nightguards, but if it can be done for permanent splints, I don't see why it couldn't be for nightguards. Good luck.