I find a similar thing has happened with me. Not with teeth grinding, but with twitching and motor tics. I was a really twitchy child...always had at least one motor tic on the go that varied in severity, however it had all but died down by the time I was a teenager. But since taking MDMA, as well as other stimulanting drugs that make you grind and twitch, they've come back again and are basically ever present. One tic especially, when I suddenly flick my head/nod began over a year ago and still hasn't died off yet. It pisses me right off!
It seems like MDMA/similar can rediscover and reinforce old neural pathways to childhood habits such as grinding or twitching. It'd probably be a difficult job to surpress them again.