What? Why on Earth would your dentist leave some of the caries when you go in for a filling? Actually, this makes perfect sense and is common in dentistry.
Part of good dentistry is communication. So much in dentistry is diagnosed and treatment-planned based on symptoms that are reported by the patient to the dentist that communication is key for appropriate diagnostics.
In dentistry, we treat cavities all the time. It is mostly what we do, whether we are treating caries (cavities) with a filling, fluoride treatment for remineralization, a crown, a root canal, or an extraction. Generally we want to rid the mouth and the tooth of any decay. However, sometimes when doing a filling or a restoration we may elect to leave a very small amount of caries on a tooth, and I’ll explain why.
A patient comes in with a big cavity, which looks like it is wrapping around the nerve of the tooth. When tested to cold, it gives a positive response and they have a lingering response for more than a couple of quick seconds. This cavity has compromised the nerve, and all of the caries needs to be removed and the nerve treated as well.
A different patient comes in with a big cavity, one that looks like it is wrapping around the nerve, but this tooth has absence of symptoms. When the tooth is tested to hots and colds it responds normally. The patient feels the cold, but doesn’t feel it for seconds and minutes after the cold stimulus is gone. This tooth can have the cavity treated and the nerve left alone, most likely.
During the filling process for this cavity, the dentist will attempt to remove the decay. Now, as the tooth is being cleaned out and all the walls become decay-free, we leave the portion adjacent to the nerve for last. We can continue to remove the caries there. As we get closer to the nerve tissue, we need to take our time to not expose the center tissue of the tooth. If we get real close to the nerve and there is still some decay, and I mean a very small amount of decay, it can be left there. This saves the nerve from being treated and saves the patient some money, too! Now care has to be taken to treat the rest of the tooth correctly at this point. The area right over the nerve should be disinfected, the filling process started, and a liner or base applied over the nerve that contains medicaments to help soothe the nerve and remineralize the area. Then with a well-sealed filling placed over the top of the liner, the few bacteria that remain are trapped and have no oxygen to grow.
Fillings done like this can last for years. It is hard to make the decision whether the tooth can be treated this way or a root canal needs to be started and the tooth treated with a more protective type of restoration, but being minimally invasive pays off to conserve as much tooth structure as possible when and where we can.