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Why Your Dentist Can’t Get You Numb

Dentist Getting Patient NumbDid you know that over four million dental injections are given every year in the United States?  The failure rate is estimated to be anywhere from 5 to 15%.  that means that there are anywhere from 200,000 to 600,000 dental injections that don't get the patient numb.  That means that people get poked by their dentist with a needle and don't end up getting numb about every minute.

It's no wonder that a lot of people come into my dental school and tell me something similar to, "My dentist has trouble getting me numb -  I usually need a lot of novocaine in order to get numb."  As a side note, we normally use lidocaine, not novocaine as many patients believe.

So why do so many dental anesthetic injections not work - why can't your dentist get you numb?

Seven Reasons Why Your Dentist Can't Get You Numb

An article published in the January 1991 issue of the Journal of the American Dental Association sheds some insight into this issue by giving five reasons why dental injections sometimes don't work.  I also found a couple of others and added them onto the list below.

1 - Anatomic Variations

Everyone is different.  Some people's jaw flares out wider than others, making it hard to visualize where that person's nerve is.  Some people have a longer jaw or extra muscle and/or fat around their jaw. In patients that are missing lots of teeth in the back of their mouth, it's harder to visualize where the nerve is.  Also, young patients can have different anatomy depending on their stage of growth, making it hard to get the anesthetic in the right spot.

2 - Technical Errors by the Dentist

Dentists aren't perfect!  Sometimes we can put the needle in the wrong place and give the anesthetic too low, too high, or too far to the side.  Also, we might not put the needle in deep enough, or we may accdentally deposit the anesthetic in a blood vessel, which is why your heart can beat fast when getting a dental injection.

3 - Anxious Patients

Some anxious patients may think that they aren't numb and jerk away in fear when we start to drill.  In cases like this, I usually tap around their gums on the numb side and then on the side that isn't numb to let them feel the difference and realize that they really are numb.

4 - Inflammation or Infection

When people have swelling in an area, it can be harder to get them numb.  One theory says that the acidic tissue makes it harder for the anesthetic to take effect.  Antoher theory says that since the patient has been in pain for so long, they have an increased sensitivity to pain which makes it harder for them to get numb.

5 - Defective Anesthetic Solutions

I haven't had experience with this one, since my dental school has a pretty good quality control program to ensure that the dental anesthetic stays potent.  However, sometimes a dentist may use dental anesthetic that has expired or was improperly stored or manufactured.  This made me realize that I should always go with a respected brand name of dental anesthetic and not get the cheaper stuff to save money.  There's no point in cutting corners if it will inconvenience my patients.

6 - Having Red Hair

People with red hair have more difficulty succumbing to the numbing effects of dental anesthetic.  They also have a greater fear of the dentist.

This article published in the July 2009 Journal of the American Dental Association states, "People with naturally red hair are resistant to subcutaneous local anesthetics and, therefore, may experience increased anxiety regarding dental care."

7 - Having Joint Hypermobility

Those who suffer from Ehlers-Danlos Syndrome can be insensitive to local anesthetics used in dentistry.  You can check out this article for more information on local anesthetic failure in those with joint hypermobility.


If your dentist can't get you numb, more than likely there is a specific reason.  In my experience, I've found that there are many people who have slightly different anatomy in their jaws which makes it harder to position the needle so that the anesthetic gets deposited where their nerve is located.

Do you have any questions, questions, comments, or concerns about getting numb at the dentist?  If so, feel free to go ahead and leave a comment below.  Thanks for reading!

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9 Comments |  Leave A Comment

  1. This is a very informative blog! I feel that it is very important to inform your patient of everything going on and why certain proccrdures or medications may or may not be effective. By helping them to understand it alleviates their fears because they understand what is going on.

    • Thanks for your comment, Dr. Barkhordar. I agree!

    • Today I had a tooth that needed pulling. After 5 or 6 injections of novacaine and an hour of excruciating pain the dentist gave up and sent me to an oral surgeon. Due to the nitrous i couldn't tell you how many injections he gave me, but he ended up drilling into my tooth and giving me an injection thru the root directly into the nerve... Holy cr*p, it was like an electric shock, and it still didn't get numb. Pulled it anyway. Sheesh, at least the gas helped...

      he told me as I was leaving that I was a mystry to him!

      Any ideas?


  2. I need a lot of work done because I had mercury fillings which cracked because they are very old and I grind my teeth at night. I went to a dentist in Atlanta.Cleveland Ave. She gave me lidacaine instead of novocaine anyway I was in pain the entire time she removed my tooth and the chips. then she gave me water to rinse my mouth.the water was brown. I asked what is in the water. she said that is the way it comes out of the pipe. I saw her child in the other room and her husband at the desk up front. I asked if this is the water you give your family. she said she has some bottled water and asked if I wanted one. I paid that dentist 200.00 cash to treat me on that dreadful Saturday. I had to ask for a prescription for pain medication and I had to ask if I needed an antibiotic for any infection. she did not want to but finally gave me a pain medication prescription. I asked her how long she had been in business and she told me she had been in business a long time and has awards for her work. I do not see how that could be true. I would never send anyone, not even someone I did not get along with to that woman.

  3. does getting an injection in your mouth hurt?

  4. I've been seeing my current dentist for several years and he has done two crowns and a filling or two with no problem. Recently he's twice been unable to get one of my lower tooths numb. We waited 3 weeks after the first attemp, and second attempt went the same. My tongue would go numb, but my lip and tooth would not. In fact, the tooth actually seemed hypersensitive after the two shots. Touching the tooth with a dental pick made me alost jump out of the chair. The dentist sent mme home and about two hours later my lip finally went numb (like it norally does in the dentist's office after the shot). The numbness lasted maybe 30-40 minutes...then went back to normal.

    Is there anything I can tell my dentist that might help me get me numb next time? He's a great dentist and I know "it's me" not "him". This work, btw, is to replace an existing, old, filling....which tells me that at least at some point, some dentist years ago was able to get that tooth numb.

  5. how can i make my dentist understand that my lower right back tooth WILL NOT geet numb my last dentist who was wonderful by the way tried three times but no luck i've had other extractions and there was no problem ....... my last dentist tried amoxicillian and ciproflaxin but no luck, then i stoped going to her because i moved and my new dentist didnt listen to my complications in the past with these two teeth when i told her she was like that was probaly becase you had an infection dont worry u dont have onr now there shouldnt be any problem .......but ther was and when i complained about the exscruiating pain she snaped at me that it wasnt pain just pressure .. um i know the difference between pain and presure i hae had several extractions before so the pain went on and i was only able to get out one tooth that day and on my way out she says"WELL AT LEAST YOU KNOW WHAT TO EXSPECT NEXT TIME" what should i do i dont have insurance and this is the only program that is literally free her in sanantonio im happy to get the free treatment but the pain was just horriable .

  6. You think you've got problems with your dentists; at least you can communicate with them.
    I live in mainland China and dental treatment here is awful, really awful. Today after a few days of intense toothache I gave in and decided to go to a local dentist. One of the big problems in China is that many people are against western medicine because (they say) it damages the body. The upshot of this is that (I believe) their lidocaine sits around for a long time in high temperatures and maybe past it's sell-by-date. Then an unsuspecting foreigners turn up for treatment and asks for an injection of bad lidocaine.
    I myself have always had a problem with my nerves not getting numb prior to drilling and this occasion was no different. Even after four shots I could still feel pretty bad pain. Now if you add to this the fact that dental practices here are very bizarre in as much that they drill your tooth, then insert cotton wool with some kind of Chinese medicine on it and tell you to go away until tomorrow. What this means is that you have a big hole in your tooth with exposed nerves and a big lump of cotton wool. Imagine the problems this creates in trying to drink or eat, and this can go on for several days. I am sure my little story has put your problems into context!
    Incidentally I am a UK man who teaches English here.

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Tom, Creator of Oral AnswersHi, I'm Tom. I recently graduated from dental school and am now a dentist in Bridgewater, Virginia. I started this blog to help people take better care of their teeth. You can learn more about me or ask me a question.

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