DENTAL CARE

Q:

Can’t You See Everything on An X-ray?

A:

The short answer is “no”. The longer answer requires some discussion. To understand this question, we need to analyze the basis of it. Maybe it all started years ago with Superman. After all he had super powers and he had x-ray vision. We use x-ray scanners at airports to visually rifle through our baggage. And yet, in medicine, in general, and dentistry specifically, we can’t see everything. We need to comprehend how x-rays work. X-rays, which were originally called X-Radiation, is a form of energy. When this energy is passed through certain materials, it will either penetrate totally, not at all or somewhere in between. This is why we can see the outline of a bone or a tooth that has been looked at through the use of x-rays.

We call tissue or objects that stops the radiation as “radio-opaque”. Those substances that allow the radiation to pass through are known as “radiolucent”. These different degrees of density form an outline on a film or on a digital sensor that allows us to look at the object. In our case it is a tooth or the jaw. When a patient has hole or a cavity in their tooth, the x-rays go right through it as there is nothing to slow it down. This shows up as a black or dark area. Where the tooth is healthy, it allows some x-rays to go through and others not to go through. The image of this portion of the tooth is gray. We must compare the gray areas to the darker areas and make a diagnosis. If a tooth has a silver filling or a metal crown, then the area on the film is totally white. This is because the metal totally halted the penetration of the x-rays and nothing went through the tooth. The tooth is “opaque” to the x-rays. All these degrees of gray must be analyzed and interpreted to get an idea of what is going on in the object that is under investigation.

Okay, that’s how basic x-rays work, but it doesn’t answer our original question. We can see the cavity... that is correct. What can’t we see? The answer to that is sometimes position or actual location of the decay. Is it in the center or the tooth or is on the outside of the tooth. Decay in the center is more severe than that on the outside. This inability to see the position is not really the fault of the x-ray. It is a function of very basic physics. We are trying to look at a three dimensional (3D) object on a two dimensional (2D) film or computer screen. This point was driven home today. Let me take a moment to explain the situation.

I had the privilege of meeting a new patient who had done a wonderful job of maintaining her mouth over the years. She had replaced missing teeth with implants and broken down teeth were sustained with crowns. As I have mentioned in other columns, crowns can last for decades. The reason to remove and replace a crown is usually due to a failure of the tooth underneath it. Such was the case with this patient, she had extensive decay that showed up on the x-rays on the root surface below the crowns and below the gum line. I told her that she may be losing another tooth, but if we were lucky, I could perform a root canal treatment. She was expecting the worst for this tooth and needless to say, was not excited about either prospect. When I actually removed the crown and began locating and removing all of the decay, the concept that I spoke about above came to light. Her decay wrapped around the tooth and due to the two dimensional (2D) limitation of the x-ray, made the decay appear much worse than it was. Yes it was all over and below the gum, but it did not encroach upon the nerve. It was not in the center of the tooth. I used a special instrument to move the gum away, removed and fixed the areas of decay. No root canal... no extraction! All that was needed was a new crown. You can imagine as to how happy my patient and I were. The three dimensional (3D) reality of the tooth made the two dimensional (2D) xray appear worse than it really was.

Yes, x-rays are great and they are an indispensable tool in reaching a diagnosis. However, they need to be interpreted and investigated by an experienced clinician so conclusions are not jumped to and needless work performed. If you have received an opinion from someone and would like to have another pair of eyes weigh in on the matter, I would be delighted to be that second pair of eyes. Feel free to call me at 440.951.7856 I look forward to hearing from you.