He clenched his teeth.

他咬紧牙关。

youdao

He lay there, his teeth set, his hand clenched, his eyes looking straight up.

他躺在那儿，牙紧咬，双手握拳，两眼直勾勾看着上面。

youdao

She came close to him, and he quickly clenched her ear with his teeth and bit it off.

母亲走到他身边，他猛地用牙齿咬住母亲的耳朵，并把它咬下来。

youdao

He opened his mouth, clenched his teeth over the handle, and pulled it up for about eight seconds.

WSJ: At These Olympics, It Helps

It's Hong Kong film star and Hollywood hopeful Chow Yun Fat striking what appears to be a kung fu pose, a matchstick clenched between his teeth, presumably for extra threat value.

CNN: Raw, Original and Truthful

"He turned towards me, he had both fists clenched... grinding down on his teeth, " PC Milby said.

BBC: Dale Burns inquest: Officer fired Taser 'out of fear'