In an X-ray, cavities are seen as dark areas in a tooth. Cavities start at the outside layer covering the tooth, called the Enamel, which has the lightest color in an X-ray. Cavities will then advance to the layer under enamel, called the Dentin, which is softer and has a darker color than enamel in an X-ray. Cavities should not be confused with the nerve in the center of the tooth that has the darkest color because it is consists completely of soft tissue. When X-rays are magnified on a screen and are looked at for more than just a couple of seconds, these dark areas in the enamel and dentin become more obvious. The change in the tone or the shades of gray in an x-ray corresponds to a change in the density of tooth structure, which we know is caused by tooth decay (cavities):
The cavities in this X-ray are outlined in yellow:
Cavities between teeth are rarely seen without X-rays unless they are very large or when teeth break. The following pictures are the same teeth in the X-rays above:
Once cavities are exposed, it is not surprising that they are always larger than they look in X-rays. This is because X-rays are a 2 dimensional representation of a 3 dimensional object; thus healthy tooth structure can superimpose over cavities. The brown areas are decay (cavity) in the dentin; dentin has a light yellow color when healthy:
After cavities are cleaned and all decay is removed, they are filled and sealed with tooth colored fillings:
The X-ray confirms well sealed and contoured fillings (fillings have the lightest color in an X-ray):
Our recommendation is that if dark areas in X-rays are in enamel only, they can be reversed and re-mineralized by brushing, flossing and using fluoride. Then a “watch and wait” approach is recommended. Whenever these dark areas extend beyond the enamel into dentin, they are considered irreversible and treatment is advised. If irreversible cavities are not treated promptly, cavities progress towards the nerve, infects the nerve causing pain, at which time these teeth end up needing root canal treatments and crowns, which are much more costly and time consuming.
This x-ray shows multiple cavities with different depth and proximity to the nerve. Cavities are the dark areas in teeth other than the dark nerve at the center of teeth. The furthest left tooth was already causing pain because the cavity has already reached the nerve. In the second copy of the same X-ray, the yellow lines outline the cavities, and the red lines outline the nerve:
All cavities were treated with fillings; but unfortunately, the tooth furthest to the left still needed a root canal treatment and crown:
Delaying the treatment of cavities when they are not reversible will lead to more tooth damage and pain requiring more invasive and costly treatment. Our goal is to provide our patients adequate information so they can make informed decisions about the care they prefer to receive.
We thank the patients who gave us the permission to utilize these images in this informational column.
Fellow of the Academy of General Dentistry