noun
permanent tooth
Refers to the second set of teeth that replace deciduous (baby) teeth in humans and other mammals. Common in dental and everyday contexts.
6歳ごろから永久歯が生え始めます。
Permanent teeth start to come in around age six.
永久歯を大切にしましょう。
Take good care of your permanent teeth.
乳歯 means baby tooth or deciduous tooth, which is replaced by 永久歯.
Compound of 永久 (eternal, permanent) and 歯 (tooth). The term directly describes teeth that are meant to last a lifetime.