It just happened again. We replaced a few 25+ year old silver fillings for one of my patients because there were cavities under them, and one of the teeth became very sensitive after treatment. So bad, in fact, that now she needs a root canal. My patient isn’t happy, and frankly, neither am I! So…why does this happen, and can it be prevented?

Reason #1: Your old filling was deep, and the cavity made it deeper!

Under old silver filling

Common appearance before and after removing an old filling in a molar

20+ years ago, dentists were taught a method of filling teeth called “Extension For Prevention.” (Fact, I was taught this in dental school 25 years ago, but have since learned differently!) This means when we treated a small cavity, we were taught to make the filling even wider to prevent other spots from being affected.  Also, we had to make the filling deep enough for strength of the materials we used then (silver fillings). When you have a new cavity, removing the old filling and cavity naturally make the “hole” larger, which can lead to problems. Now, we can treat only the area that needs treatment and we have filling materials to use that are still strong even when thin. The hope is that when this conservative filling has to be replaced down the road, not only will we have still better materials to use, but we can do it in a kinder way than is possible now. Our field is always improving!

Reason #2: Your old filling actually hurt your tooth!

cracked tooth silver filling

Cracked tooth with an old silver filling

The older silver fillings (also known as amalgam, metal, or mercury fillings) expand and contract when you eat and drink hot and cold things. This happens inside the very tight space the filling is crammed into, and it creates tiny microscopic cracks in your tooth that we can’t see with our eyes or even an x-ray. Over time, those cracks get bigger, the filling no longer fits against the tooth properly, and food and plaque get inside, travelling through those cracks and infecting your tooth. Gross…but true. In most cases we get lucky, and we can remove all of the bacteria from inside the tooth when we replace the old filling, but we can’t see it all…and it can kill the nerve of the tooth.

Reason #3: Good old-fashioned wear and tear!

Like any other part of our body, teeth wear! I always tell patients that if they make it into their 30’s or 40’s without having any cavities, the likelihood of losing their teeth (other than from an accident or lack of care) is extremely small. However, in my practice I certainly don’t see a decline in the number of cavities I treat. And any time the same tooth is treated more than once there is a risk this will be more than the nerve of the tooth can take, and it dies. We especially see this in back teeth where the chewing pressure is heaviest and further damages the nerves of your teeth.

Reason #4: You grind your teeth!

These are the teeth of a 57 year old male with bite disease

These are the teeth of a 57 year old male with bite disease

Our teeth touch each other between 2,000-3,000 times per day (depending on the research source) under normal circumstances (eating and swallowing).  However, if you grind your teeth you multiply that number…and if you clench your teeth, not only are they touching more, but are doing so with such force it’s no wonder the nerves of your teeth are dying! Many people think they only clench or grind while they sleep, but studies show that patients who clench or grind do it all day long.  This means that the “night guard” your dentist made for you to wear while you sleep doesn’t actually solve the problem.

What might be the “problem”? To explain it simply…if your teeth don’t touch evenly everywhere when you close, your muscles will work your jaw to “rub out” the spot or spots that are interfering with your bite. Typically once one area is worn away, a different area is now not touching evenly, and so you grind more…and this keeps going and going…until the teeth are quite flat and nothing is in the way. What can happen before the teeth are flat is that a lot of pressure is placed on the teeth and those with larger fillings, especially in the back teeth, become injured in such a way that the nerve of the tooth dies.

There are ways to correct a bite that is uneven, including orthodontic treatment (braces) or placing crowns on some or all of the teeth to build biting surfaces that meet each other properly and add back all of the “tooth” that was ground away in the first place.  This can be fairly extensive work to do, but it is work we do often for our patients. The goal is to strengthen teeth which have suffered from years of damage and prevent continued damage from uneven wear and tear. Believe it or not, we dentists also don’t like to tell a patient that he or she needs a root canal; we much prefer to be proactive rather than reactive when managing your oral health.

Dr. Andrea Stevens is a cosmetic and family dentist in practice in Kanata, Ontario. If you have dental questions, you can call her at 613-271-7091 or visit her at kanatacosmeticdentist.com Please also feel free to leave comments or questions below, and Dr. Stevens will be happy to answer!