You may have seen over the weekend that a few of the papers ran a story claiming that dental fillings can cause decay. 

But what is the truth of the matter?

The story links to a recent paper that shows where a filling is placed, the adjacent tooth surface runs a 60% chance of developing decay. This much is true, and has been known for a long time, but to say that fillings cause the problem is misguided. It’s a lot more complex than that, and there are several factors that lead to this issue.

1. Plaque stagnation

It is known that dental decay frequently starts between the teeth, at the point where plaque is present and unable to be cleaned. The plaque produce an acid when exposed to sugar, and given enough time and enough exposures, decay sets in. This is between the teeth – so it is common to see BOTH teeth affected. Even with one filling placed, it is possible that the decay still continues to affect the adjacent tooth because of plaque stagnation. So the best thing to do is limit sugar exposure and make sure that the plaque is removed between the teeth.

2. Scuffs during the procedure

It is known that scuffs to adjacent teeth happen frequently during preparation for fillings. This has been known for a long time, and studies show that this can happen in up to 85% of preparations. Enamel damage can predispose the tooth to decay, but the acid from bacteria is still needed.

Fortunately, we have been using a simple device known as a WaveGuard for years to prevent this. This is a simple wedge that has a metal guard to prevent damage to the next tooth.

WaveguardUsing strong magnification helps also, and the use of a microscope really helps to improve accuracy during preparation.

3. Poor contact points in the filling

When a filling is placed where the contact point is either too open or of a poor form, plaque stagnation can increase in this area and lead to more decay. That is why we use what are known as sectional matrices, and where the contact is very wide, it is recommended that you have an inlay placed rather than a filling. This is a lab made restoration that allows us to control the contact point much more delicately and ensures that food and plaque trapping is kept to a minimum.


So while the reports raise an interesting and valid point, it would be foolish to think that fillings cause decay. These problems have been known about for a long time, and we have already taken steps to reduce the chances of decay in adjacent teeth following fillings. Of course, the best thing is prevention, and it would be far better to not get decay in the first place. This can best be achieved by controlling sugar intake to no more than 4 times a day (and watch for hidden sugars!), and using a fluoride toothpaste twice a day.