龄
JLPT HSK 4

líng
Left: Zahn 齿/齒 (Below the nose 止 an open mouth 凵 with teeth 人), right: order 令 (A lid on the bent person卩, was ordered)
(From the teeth of horses you can read the age:) The teeth got the order to show the: age.

	齿
JLPT HSK 5

chǐ
Top: to stop 止 (here: nose), bottom: open mouth 凵 with teeth 人
Below the nose is an open mouth with teeth.

	龋
JLPT no HSK

qǔ
Left: Zahn 齿/齒 (Below the nose 止 an open mouth 凵 with teeth 人), right: Yu the Great 禹 (special insect 虫)
In the teeth, the special insect causes caries.

	龈
JLPT no HSK

kěn, yín
Left: tooth 齿/齒 (Below the nose 止 an open mouth 凵 with teeth 人), right: 'not good' 艮 ('good' would be 良, but here the accent 丶 is missing, thus 'not good')
(They destroy something:) The teeth are not good when they: bite.