There's decay under a large filling. The decay is into the pulp of the tooth.

在你牙齿原来大块填补物下边也有龋坏了。龋坏已经到了牙髓。

youdao

First, I'll make a small opening in the top (crown) of the tooth to expose the infected pulp..

首先，我要在牙齿的顶端(牙冠)开一个口，使受感染的牙髓暴露出来。

youdao

Teeth may also be sensitive because of irritation to the tooth pulp from habits of clenching (clamping) or grinding.

牙齿过敏也是可能因为有药咬牙或磨牙的习惯而是的牙齿根管的受到刺激。

youdao

In the most serious cases the enamel is worn away to such an extent that the dentine (the substance that comprises the bulk of the tooth) or even the pulp (the root) of the tooth are exposed.

BBC: NEWS | Health | Bad teeth blamed on fizzy drinks