‘牙齿’ (yá chǐ) is the standard, neutral term for ‘tooth’ in modern Mandarin — used collectively to refer to teeth as a body part or individually in general contexts. The character 牙 (yá) originally meant ‘fang’ or ‘tusk’ and now commonly refers to front teeth or teeth in everyday speech; 齿 (chǐ) means ‘tooth’ more formally, often appearing in compound words like 年齿 (age) or 齿轮 (gear). Together, 牙齿 emphasizes the full set of teeth in the mouth and is preferred over either character alone when speaking medically, hygienically, or descriptively about oral health.

This word appears frequently in health-related discussions — dentists use it in diagnoses (e.g., 牙齿疼痛), parents teach children about brushing, and textbooks describe dental anatomy. It’s not used for animal teeth in zoological contexts (where 牙 or 齿 may appear separately), nor for metaphorical uses like ‘sharp teeth’ meaning aggression — those require other constructions. As a compound noun, it’s always plural in reference but can be quantified with measure words like 颗 (kē) for individual teeth.