Faulty Crowns
It is important to see your dentist on a regular basis for several reasons, if you have large fillings or teeth with root canal therapy completed. A very common occurrence that happens with such restorations is fracture due to bite stress and tooth dryness.
There are several types of fractures of which the vertical kind is most dangerous.  See Fig. 1.  
Fig. 1.
As one can see, this large molar has suffered a vertical fracture due to a large older filling. Notice the thin white line spanning distal to mesial. 
Unfortunately, in this case there is a high probability of tooth failure resulting in extraction regardless of whatever procedure is choses to save the tooth.  In this particular case, the tooth had endodontic root canal therapy completed after this was scene, as the fracture spanned all the way into the pulp chamber, causing extreme pain upon biting.  This was followed by a core build up (withOUT any post to prevent further possible fracture), which was later covered with a crown to hold the entire tooth together to prevent further splitting. 
One cannot be sure however, whether all micro fracture has been eliminated even with the use of microscopical dental intervention.  Unfortunately, the patient must understand before any treatment that there is a chance for an undetected micro-fracture that might continue inward.  This would result in the extraction of the tooth after-all, as pain would once again be detected.  It is impossible to predict whether this will happen or not, however we can take such measures as presented above, to try to prevent it from happening.
To prevent such fractures, it is necessary to contact your dentist, so he/she can detect any possible start fractures, as well as warn you how to prevent such from happening to you.