Cosmetic Dentistry Blog Cosmetic and General Dentistry Questions Answered

September 11, 2013

How to tell from the x-ray if a tooth needs a root canal treatment

Kathryn from New Jersey asked me if she could wait to have a root canal treatment. She had a tooth that was recently filled, then went to a new dentist who said that there was something on the x-ray that looked like decay under the filling, therefore she needed a root canal treatment. See the earlier post: “There are a lot of things that can look like decay on an x-ray.”

Here is the x-ray she sent, with the tooth in question marked:

does this tooth need a root canal treatment?
And here are my comments:

Maybe there needs to be more training in dental school on radiographic diagnosis. This is by no means a case calling for plunging in and doing a root canal treatment.

Yes, I see the dark area under the filling, but I see three characteristics of this dark area that they are not telling you about:
1) While tooth decay will show up as a dark area, not all dark areas are decay. This could be a radiolucent base material under the filling, a gap in the filling, or decay – three different possibilities.
2) The dark area is on the surface of the tooth. If it is decay, the dentist should be able to poke that area with an explorer and it will be soft. You gave me no indication that they did this because you said, “There is what looks like some decay under the filling on x-rays.”
3) The dark area does not go anywhere near the pulp. Now there is an optical illusion that creates the impression that the dark area is directly under the filling and between the filling and the pulp. The way to deal with that is to cover up the filling, which is white, with your finger. Now look at the remaining tooth structure. When you do that, you can see the clearly defined margins of the dark area (decay would have fuzzy edges) and that they stop well short of the pulp. There are a good 2 to 3 millimeters of solid tooth structure between this radiolucent area and the pulp.

Now I can’t give a definitive diagnosis here without actually seeing your tooth and finding out more about what went on, but I can tell you that if they are just relying on the x-ray, there is no justification for doing a root canal treatment. There is no indication of inflammation near the root tip, which is the first indication of an infected tooth. And you are saying that the tooth feels fine.

Finally, there is some clear evidence on the x-ray that the root of the tooth is healthy.

If you look at a clearly healthy tooth – for example, the canine tooth next to this one. There is a thin white line that goes all the way around the root of the tooth. This is called the lamina dura. When a tooth gets infected, one of two things happens to this white line. It either becomes broken in the area around the root tip, or it pulls away from the tooth. When I look at the lamina dura of your lateral incisor, I can follow it all the way around the root tip. Because of the angle, the lamina dura appears more fuzzy than it does on the canine, but it is nonetheless there and intact. THAT is the key to the diagnosis of this tooth. The root is healthy.

Dr. Hall

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About David A. Hall

Dr. David Hall was one of the first 40 accredited cosmetic dentists in the world. He practiced cosmetic dentistry in Iowa, and in 1990 earned his accreditation with the American Academy of Cosmetic Dentistry. He is now president of Infinity Dental Web, a company in Mesa, Arizona that does complete Internet marketing for dentists.


  1. My husband is scheduled for total hip replacement surgery in 2 weeks. He recently had tooth pain and went to dentist for xray. He was told he possibly needs two root canals in tooth #5 & 15 & put on antibiotics. He would like to postpone the root canal until after the surgery for a few reasons. What are your thoughts? Will the pain return once he stops the antibiotics?

    – Comment by Dr. Hall:
    Yes, if the pain is from a toothache, antibiotics will not cure it. It will come back once he stops the antibiotics. I question the expertise of this dentist who didn’t explain this to you. What I would have done in your situation is give you two options – do the root canal treatment right away, or take antibiotics clear through the hip surgery and do the root canal treatment at the point near when you are done with the antibiotics. I’m also suspicious of this diagnosis of “possibly” needing root canals. Now I don’t know the whole situation, but in most cases the dentist should be able to determine this without throwing a “possibly” in there. If you have any vibes about this dentist that make you uneasy at all, I would go for a second opinion, maybe this time from a root canal specialist (endodontist).

    Comment by JoAnn Stormo — November 13, 2018 @ 12:26 pm

  2. I recently got an extracted wisdom tooth, a crown and 4 cavities filled. Every since then my entire right side of my mouth has been hurting for a couple weeks now.. it makes my whole head hurt and I can’t even function and since I have a newborn baby this is just horrible..I have went back to the dentist 3 times and he says he cannot see anything from the xray. I can’t tell exactly which tooth is causing the pain and we have already taken a guess and done 1 root canal already and still the pain is there.. could u possibly take a look at my xray? they have almost maxed out my insurance for the year and it just started. 🙁 I don’t know what to do…
    – Jennifer

    Jennifer – contact me through the Ask the Dentist a Question link and I’ll arrange for you to send me the x-ray.

    Comment by Jennifer — January 23, 2019 @ 9:55 pm

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