Why It Can Hurt to Open Your Mouth After a Filling

Every now and then, we get a phone call from a patient who we saw a couple of days earlier. It goes something like this:

I had a filling done on my last tooth on the lower left three days ago. The filling and tooth feel fine, but it hurts to open my mouth, especially if I try to open wide.

We then go on to explain to our patient WHY this is the case and how it is normal.

So why is there pain with opening? There are two major factors.

Dental Injections for Lower Molars

In many cases, the pain while opening is from the injection. For lower molars, most dentists will do a nerve block, which involves a very long needle. See the photo below.

Dental shot for a lower tooth can cause pain while opening

A dental injection used to anesthetize a lower right molar. The needle in this photo is 1 and 1/4 inches long.

As can be seen in the above photo, a needle is inserted into the muscle in the back of the mouth. In most cases, for this injection, the needle goes in nearly to the hub, which would mean approximately 1 and 1/4 inches.

Here’s an analogy: feel your biceps and press it hard enough so you can feel the bone underneath. Then, imagine taking a needle, and inserting it through the biceps, approximately 1 inch, until the needle hits bone. Then, imagine doing that a second time. Don’t you think that moving the arm and using that muscle over the next several days would hurt?

The biceps analogy is very effective. Everyone understands that their arm would be sore. So, if you get an injection back there, or in some cases two, using that muscle in opening and closing can frequently elicit pain for several days afterwards.

Your TMJ (Temporomandibular Joint)

The second source of pain while opening after a filling can be from the actual jaw joint, known as the TMJ (temporomandibular joint). This is the area at which your lower jaw bone connects to the base of the skull.

Your jaw joint was made for all of your daily activities – talking, smiling, eating normal foods, etc. The joint was not designed for “abnormal” tasks such as gum chewing, chewing on ice, or holding your mouth open for your dentist or hygienist to work.

photo of TMJ in a skull which can have pain after opening

The temporomandibular (TMJ) joint. Pain in this joint as well as the muscles and ligaments associated with the joint can occur after a dental visit.

Here’s another analogy: imagine standing on the tips of your toes. Now do this for 5 minute intervals several times, with perhaps 30 second breaks in between. Do this for approximately 45 minutes. Don’t you think that the next day, moving that muscle and the joints would be sore? This assumes you are not a ballet dancer.

A cleaning or a filling of moderate duration will be a lot like the above. Lots of straining to keep your mouth open, which can lead to fatigue and soreness in the muscles and joint. This can then result in pain and soreness on opening for several days.

Some Assumptions

We find that one or both of these reasons are responsible for the pain and soreness approximately 99% of the time. There are other circumstances which can include:

  • Infection of either a tooth or an infection at the injection site.
  • Pain after a surgical procedure such as a lower wisdom tooth extraction.
  • Aphthous ulcers (cold sores) in the back of the throat.
  • Upper respiratory infections, etc.
  • And many others.

Of course there can be other explanations. But for the vast majority of the time, the pain is either from the actual injection or in joint after being open for a prolonged period of time.


  1. How long will the discomfort normally last? Is 2 weeks normal?

    • Depending upon the number of injections, 2 weeks of discomfort can occasionally occur.

      • How typical is the pain/tighness, and 24/7 headache after two weeks? I had 5 injections, so I had chalked it up to the aches as described above. But this headache is pretty miserable. I guess I’m looking for hope more than anything. Lol

        • I my opinion, that is pretty unlikely, but not impossible. I am assuming you had several injections to numb a lower back tooth. You could also be clenching at night due to pain/stress associated with the procedure. You can/should follow-up with your dentist.

  2. My first dental appointment was a tooth cleaning, small cavity and lower back molar tooth prep for a crown. I was shot with novocaine and everything went as planned with zero jaw issues after. However, I went back two weeks later for my permanent crown in which I did not want another shot to numb so I could feel the bite of the new tooth. Removing the temp crown was a challenge and my dentist said she could no longer see me suffer and shot me with Novocain again. They got the temp crown removed but the new crown shattered in my mouth while adjusting the bite. I had to have another temp put in and a new tooth ordered. I woke up at 1:30 the next morning with bad jaw soreness but figured it to be expected from the two visits and having my mouth open so long. Well, two weeks later I am still in pain and can’t open my mouth all the way. I can fit two verticle fingers in my mouth. I spoke to my dentist and she said it sounds like the muscle seized up from two shots in two weeks and to do warm compresses and Ibuprofen. I have never had jaw issues and the bite is fine and there is n clicking or cracking noises. I am very scared this will never heal and my mouth will never open all the way again. It seems the more I try home therapy, the more pain it causes. Can you please advise me what to do in this situation? This won’t be permanent, will it? Do I need to see a doctor? Any advice you can give would be appreciated because this is really scaring me right now and my dentist doesn’t seem to be concerned at all.

    • Michele, based on your description, your dentist appears to have given you sound advice. However, if the clicking/cracking is persisting when you go in for you crown cement visit, it is worth mentioning it to her.

      • Michele, I had almost the exact same thing so I am going to take ibuprofen and try to use the warm compress and exercise the jaw muscles like my dentist said. Hopefully my pain will go away and I’ll be able to open my mouth again normally. It’s been about two weeks. Good luck you aren’t alone!

  3. Andrew Jacobberger says

    How Long should this last? I went I for a dental visit to do both a deep clean and fillings on one side and then the next day they did the other side. After, it was fine the first day, but, the second day, felt a lot of pain when opening and closing jaw on the left side. It has been about 5 days after now, and I have been doing heat/cold packs and advil and still is there.

  4. I had all my fillings replaced about two weeks ago. I received four shots since I had all nine fillings done at the same time, so the dentist worked on both sides. A week later I went back because one of the new fillings fell out and my bite needed to be adjusted.

    My jaw and teeth are still in pretty strong pain. It wakes me up at night when the Ibuprofen wears off. Is this normal? On Monday it’ll be exactly two weeks since the first work was done, and a week since I went back to get my bite adjusted and the lost filling replaced.

    I didn’t get any numbing shots when I went back for them to fix my bite and replace the lost filling. Shouldn’t the pain be gone by now or is it too soon?

    Most of the pain does seem to be coming from the areas where I received the shots, and it spreads to the rest of my jaw then into my ears and even my temples.

  5. I had two lower fillings the other day and I’m having soreness when I open my mouth half and cannot open it very wide. After reading this I realize this is normal (especially since I had two injections) but is there anything I can do to improve the soreness?

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