Difficult to clarify without pics, but I'll try. The plastic one consists of teeth on edge of plastic mould which fits the roof of my mouth. The metal one had the centre part of the roof missing (so I guess could be described/seen as a ring), and also a couple of hooks which went round two existing teeth. This left the roof of my mouth free from obstruction which is more comfortable. Mind you, I only had one tooth on the metal plate, I now have 6 so I'm uncertain as to what difference that would make. I do think the metal one was marginally more secure, not sure why. It also seemed lighter - probably because the plate was thinner which of course adds to the comfort.