BabyGirlBlue- I knew a sub with TMJ as well. She found the simple bite gags worked for her and didn't hurt allowing her to keep it for much longer periods of time.

Also, she had a gag that was thin leather, but had a piece that went into the mouth and held the tongue down. This she could keep in for hours as it didn't keep her mouth open that much at all, it just kept her from using her tongue.

Hope this helps.