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 result in 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.

Long Term Opioid Use and Dental Local Anesthesia

Norco opioid pain medication used by dentists

Norco – a common opioid pain medication

As a busy private practice dental office, we are constantly doing dentistry, which involves injections of local anesthesia. Like all dentists, we occasionally encounter a patient and/or tooth that is difficult to get numb. Along this theme, an increasingly common phenomenon we are observing involves difficulty in getting patients numb who are long time users of opioids (often called narcotics).

A common situation is a patient with chronic pain who has been taking an opioid type painkiller long term (such as Percocet, Oxycodone, Oxycontin, etc.). A dental procedure that requires effective local anesthesia is attempted on that patient. During the procedure, it is learned rather quickly that the patient is having difficulty either getting completely numb and/or staying numb. Why is that?

Opioids, Narcotics, Pain Pills, Etc.

The term opioid is derived from the word opium, which is a component of the opium poppy. The raw opium can be processed to produce morphine or heroin – both of which are powerful pain relievers. The term opioid simply means a medication that acts on the opioid receptor.

Opium poppy, the basis for narcotics

The opium poppy – the flower from which morphine and heroin are derived. Image courtesy wikipedia.

Millions of Americans take opioids for both acute and/or chronic pain. For those individuals who take them long term for chronic pain, a tolerance will develop, requiring larger doses. Large doses of opioids taken over time can lead to many long term effects. Many of those effects – constipation, dry mouth, etc. – are well documented. What is not well documented nor well researched is how long term use of these painkillers impacts the effectiveness of local anesthesia.

Long Term Opioid Use and Dental Local Anesthesia

Unfortunately, there is very little “official” information available for practicing dentists and dental students on which to rely. The most widely read and cited textbook on local anesthesia for dentists – A Handbook of Local Anesthesia – by Dr. Stanley Malamed – makes no mention of this phenomenon.

Lidocaine is less effective in opioid users.

Multiple studies have shown lidocaine is less effective in opioid users.

However, a survey of recent research has shown multiple articles which directly and/or indirectly give support to this phenomenon:

  • In this article, opium abusers were compared to non-abusers in their response to lidocaine (lidocaine has replaced novocaine as the local anesthetic of choice in dentistry). The abusers were found to require a longer amount of time for the lidocaine to work. And in addition, a greater amount of lidocaine was required.
  • In this study involving rats, the administration of morphine (an opioid) resulted in a decrease in the potency of lidocaine.
  • In another study involving opium vs. non opium users, chronic users experienced a shorter duration of local anesthesia than non users.

In fact, there is a specific term for a related phenomenon, which is Opioid Induced Hyperalgesia. Basically, those individuals who are chronic users can become MORE sensitive to painful stimuli.

However, despite all of these studies, there remains to be seen a widely accepted theory for a mechanism behind the local anesthesia resistance seen in these individuals.

What This Means for Dental Patients

Unfortunately, because this phenomenon is somewhat new and not well documented, not all dentists are aware of these issues. Some tips:

  • Make sure your dentist is aware of your history. This includes patient with a past history of abuse who are on maintenance doses of naloxone or methadone.
  • Don’t be afraid to say “I’m not numb” or “I can feel this.”
  • If you are still uncomfortable, consider switching offices.

As a modern dental office, we’ve had success treating patients on chronic opioids with either buffered local anesthesia and/or IV sedation. So there are solutions out there – you just have to go out and find them.