noun · the age of domestic animals such as cattle or horses, typically judged by their teeth

看这匹马的口齿，正当壮年。

expression · the clarity of articulation and quality of speech or diction

这位播音员口齿伶俐，吐字清晰。

noun · the physical parts of the mouth, specifically the teeth

他平时很注意保护口齿卫生。