I havent took lexapro, but I have experienced the same thing with prozac, and IT SUCKED!
The only thing that stopped me from clenching them was my klonopin.
and, yes it was worse at night, I woke up hearing popping sounds cause I was clenching them so hard.
But I have noticed that it has pretty much stopped, on occasion I'll grit them, but not nearly as bad.
It was to a point where I couldnt hardly talk, because my jaws hurt so bad, I thought I was getting TMJ, lol
Moltrin 800 seemed to work pretty good for the pain, and all of that, talk to your doc, maybe you can get something temp to counter the negative side effects, I do believe its supposed to pass though, like almost all the other Side effects, "besided the Libido one"
but, If it doesnt go away within like 4 weeks or so, Id talk to your Doc about that too.
What's your dosage on Lexapro? I took Lexapro for a long time, and never experienced that.
However, I do clench my teeth at night in bed... and I've done that for the longest I can remember.
It's not enough for me to have TMJ, but it does leave my jaw soar sometimes.
My Dr. said it's just my anxiety causing me to tense up like that.
Good luck figuring it out.