lips and teeth
Literal meaning referring to the body parts. Often used in set phrases or classical contexts.
Cold air leaked from between his lips and teeth.
mutually dependent relationship
Figurative use based on the idea that lips and teeth are interdependent; often appears in the idiom 唇歯輔車 (しんしほしゃ) or similar classical expressions.
The two countries are said to have a mutually dependent relationship like lips and teeth.
labiodental consonant
mutual dependence; interdependence
mutual dependence
Compound of 唇 (しん, 'lips') and 歯 (し, 'teeth'). The figurative sense derives from the classical Chinese metaphor that lips and teeth rely on each other.