您说的是一种情形，

A dentist will often recommend crowns for teeth that they see are at risk for fracture, such as teeth that have very large fillings, or teeth that show fracture lines (especially if the patient has a history of grinding or clenching).

所有跟帖： 

• 看来你也没搞懂，你光看definition有什么用？ -goingplace- ♀ (0 bytes) () 06/21/2019 postreply 17:21:47

• 用处是因为我自己有过不需要root canal， 只加crown的经历 -Angel06- ♀ (0 bytes) () 06/21/2019 postreply 17:32:46

• 当牙齿碰到冷热都会疼痛时，说明牙齿蛀到牙髓了，这时医生做root canal弄干净神经，之后的牙齿虽然仍然好用， -goingplace- ♀ (210 bytes) () 06/21/2019 postreply 17:41:16