You had that molar filled back in high school, and now your dentist is telling you that you need to get it replaced. You, like most of us, probably thought the filling would last the rest of your life. Same with any crowns you might have. If that's not the case, what is the lifespan of a filling or a crown? Why do I have to get a new filling?

First, let’s look at that filling you got back in high school. Your dentist decided you needed a filling because tooth decay had eaten a hole through the enamel of your tooth. If the decay was not removed and filled, it would have would have worsened, causing pain and putting the tooth at risk. The two most common materials for fillings are amalgams and composite resins

An amalgam is a mixture of mercury, silver, tin and other metals. It is the easiest material for your dentist to use and is the least expensive type of filling. Composite resins are tooth colored materials and often used in more visible areas of the mouth.

So, how long should you expect your fillings to last? Amalgams should last at least ten to fifteen years. Composite resins should last at least five years.

Next, what's a crown and how long do crowns last?  Crowns are made of gold alloys, stainless steel and porcelain on metal and ceramic. 

Your dentist will recommend a crown for a tooth if the tooth is no longer structurally sound, but the roots are attached to bone. This may be because of large fillings or traumatic fracture of a tooth. These can last from five to thirty years, depending on the material.