To clench one's teeth (to endure pain, suppress emotion, or brace oneself); often used in the phrase '歯を食いしばる'.
痛みに耐えて彼は歯を食いしばった。
He clenched his teeth to endure the pain.
最後の一周、選手たちは歯を食いしばって走った。
In the final lap, the runners gritted their teeth and kept running.
彼女は悔しさをぐっとこらえ、歯を食いしばって黙っていた。
She swallowed her frustration and kept silent, clenching her teeth.