Untreated tooth decay can lead to dark spots on your teeth, which are cavities. Once a dentist has filled those cavities (using a tooth-coloured composite dental resin), your teeth have been restored. So why, potentially years later, are you developing yellow spots on your teeth?

Enamel and Fillings

The outer layer of human teeth is made of dental enamel, which is highly mineralised and incredibly strong. However, when this enamel decays, your dentist will fill any cavities with composite resin, which is designed to match the colour of your dental enamel. The final stage for a filling is for a dentist to polish its surface, which allows it to match the texture of natural dental enamel. A completed filling should look just like enamel and will blend into the surface of the tooth, but it has a different composition.

Staining and Colour Mismatches

Just as teeth can become stained, the composite dental resin can similarly become discoloured. It may not happen at the same rate as the rest of your teeth, since composite resin absorbs extrinsic staining elements in a different way than dental enamel. It's not going to happen overnight either, but the same things that can stain your teeth (certain foods and drinks, and unfortunate habits such as smoking), can stain the fillings in your teeth. This will eventually lead to a mismatch between the colour of the filling and the natural tooth structure that surrounds it, and these are the yellow spots you've been noticing.

Attempting to Whiten Your Teeth

Your default reaction may be just to whiten your teeth. This might seem sensible, but you're not going to like the results. The composite resin of your fillings will not lighten when exposed to hydrogen peroxide, which is the active ingredient in most teeth whitening kits. Your dental enamel will respond to the treatment, becoming whiter when your fillings stay the same colour. This will make those yellow spots stand out even more. You'll need to see your dentist.

Replacement and Prevention

Unfortunately, there's not much that can be done to whiten a dental restoration like a filling. And considering how easy they are to replace, doing so much work on a simple restoration can be counterproductive. It's likely that your dentist will suggest replacing the fillings, and will recommend an improved oral hygiene plan for the future to prevent the problem from affecting you again.

Please don't try to whiten tooth-coloured fillings that have become stained. They're tooth-coloured, but they're not part of the tooth's natural structure so only a dentist can help. 

For more info, contact a local dentist