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Dentistry/2nd opinion - Root canal and lack of ability to get local anaesthesia



Dear Doctor,

Please pardon my interruption of your day, I was hoping for a very quick favor, even though you do not know me...

I had a temporary filling on a crown (tooth #18) for several months (with no pain or sensitivity), and I did a crown impression about one month ago. Last week, I went to my dentist, and they were supposed to set the permanent crown.

The problem was that the permanent crown did not fit properly, and they said they had to do another impression. So, they had to renumb me in order to do the impression. For some reason, they were unable to get me numb. Everything around my face was still numb, but I still had too much pain and sensitivity from blowing air, that they could not do the impression.

Thus, the dentist concluded that I would likely need a root canal. This was news to me, because I had no pain whatsoever prior to the first crown impression. I was wondering if you could give your opinion on two things:

1) Is the root canal truly necessary? (I have attached two X-rays)
2) Why was local anaesthesia unable to be achieved? (This scares me greatly).

Like I said, I am very worried and would be immensely grateful for a moment of your expertise. I would also be glad to come in person if that would be better. My appointment with the dentist is currently scheduled next week on Apr 15.



I am so sorry for the late reply! I was out of town and forgot to update my settings.

In regards to your question;

If you don't have pain with the temporary, and there was no pain to hot/cold/eating on the tooth, then you most likely do not need a root canal. If there is constant pain, or when using the tooth for eating/drinking, then you do need a root canal. I am not saying your dentist is incorrect, but based on the information you provided it does not sound like a root canal is necessary. (Of course, I can't see what exactly is inside your mouth and the xray is limited, so I can't guarantee that.)
Also, even if there was no pain on the temporary, there is a chance that once the permanent crown is seated that the tooth would be painful and then need the root canal.

In regards to the anesthetic;
Lower second molars are the most difficult teeth to get numb in the mouth. Couple that with the tooth having a temporary restoration can make the nerve inside the tooth more difficult to numb. In these situations where you are numb, but not fully numb, you may need additional anesthetic in other areas of the mouth. Unfortunately, this is common enough.. :(
Sometimes, they just need to go back another day and try again!

I wish you the best!
Let me know if you need anything further!


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Benjamin Schwartz, DDS FAGD


I can answer a range of questions in dentistry, ranging from cosmetic dentistry, fillings, root canals, and comprehensive treatment. Specifically, my fields of interest are in CEREC technology, Invisalign (Invisable braces), and Endodontics (root canals).


Full time practicing dentist in New York City, treating all phases of adult dental needs. Specific focus on Invisalign cases, Endodontic (root canal) treatment, and CEREC single visit restorations.

Schwartz Benjamin, Boczko Fae, McKeon S. Oral Care For The Elderly. Perspectives in Gerontology December 2006

New York University College of Dentistry - D.D.S.
Woodhull Medical Center, 1 year post-graduate residency program - GPR

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