Protect Weak Teeth

If you have large fillings, your dentist may recommend for these to be crowned or have an onlay(smaller cap) made. This is to reduce the fracture potential of the tooth. 
Clinical studies have shown that root filled teeth(specifically) at the back of the mouth are more prone to fracture without this type of protection. 

The animations below illustrate some possible fracture consequences(sensitivity, broken tooth or split tooth) caused by biting hard on a weakened tooth and some preventive options.