I've just returned from a seminar where one of the leading experts on CEREC, which is dental technology that allows a dentist to do crowns in a single appointment, was touting the advantages of what is referred to as "quadrant dentistry."
What this refers to is having your teeth repaired in sections rather than one at a time. A quadrant is one quarter of your teeth--think upper left, upper right, lower left, etc.--and working on all the teeth together provides a much more stable and longlasting restoration of your teeth.
Think of it this way. Your back molar has a huge metal filling in it that was put in when you were 17. The tooth in front of it has had a couple of cavities, and though the dentist used composite fillings, they are really only good for 5-8 years on average, and then they can start to decay on the sides and underneath. And now the tooth in front of that one has a new cavity.
Ideally, what your dentist should do is remove the fillings in the other two teeth at the same time as he or she is treating the cavity in the third tooth. This is better for two reasons: first, the older the fillings are, the more likely there is decay underneath, which can lead to infection and possibly needing a root canal; second, when you fix all the teeth in a row at the same time, they will all fit together better, and they will align better with the teeth above (or below) them.
When I was 35, I had a dentist go quadrant by quadrant through my mouth, removing old fillings and replacing them with new porcelain inlays and crowns (I had a lot of decay when I was younger). Because I did this, I have never had a root canal, and I don't expect I ever will. (I'm very regular in my checkups!) Were I to do it now, it would get done a lot faster if the dentist had a CEREC machine.
Many dentists are reluctant to suggest quadrant dentistry because their patients might think they are just out to make more money by doing unnecessary work. But the ones that believe in it and tell you about it are helping you to keep your teeth for a long, long time. Consider it.