To clench one's teeth; to grit one's teeth to endure pain or hardship, or figuratively to suppress emotions and persevere.
痛みに耐えきれず、彼は歯を食いしばって医者を呼んだ。
Unable to bear the pain, he clenched his teeth and called a doctor.
試験中、最後まで諦めずに歯を食いしばって問題を解いた。
During the exam, she gritted her teeth and worked through the problems until the end without giving up.
その知らせを聞いて彼女は歯を食いしばり、涙をこらえた。
Upon hearing the news she gritted her teeth and held back her tears.