The Closed Lock

Greetings again! The following is one of a series of articles on various aspects of dentistry derived from my years of experience in a TMD head, neck and facial pain practice.

THE CLOSED LOCK: Sometimes it isn’t trismus!

Learn to recognize the closed lock. It’s unusual, but it’s also critically important that you make the differential diagnosis very quickly.

Let me tell you a story about Abram. Abram is a 69 year old man who came to see me last month. Abram didn’t come in with a little pain, Abram was cross-eyed with pain, crazy with pain, barely able to stand his pain. And he’d taken Oxycontin. Abram couldn’t open his mouth more than 5 or 6 millimeters. Abram was too drugged to drive. He could hardly walk.

Abram had had root canal treatment on a lower molar two to three weeks prior to his visit with me. The day after the endodontic procedure, he could not open his mouth. Okay, we’ve all seen that before. Trismus after an inferior alveolar block isn’t that uncommon. Give it a few days, some ibuprofen, maybe ice or heat packs and the patient will be fine. But a few days later, Abram wasn’t ok. He could not open his mouth and he was in tremendous pain.

So, what’s going on here? And what do you do about it?

The true closed lock: One of the consequences of a total anterior disc displacement is the true closed lock. This is a relatively rare situation. In fact, during many years in general dentistry, I never saw even one. Now that my practice is primarily focused on TMJ problems, I see these patients fairly often. In fact, I’ve seen and unlocked as many as three in one day.

The major take-home lesson from this section is differential diagnosis. A person who has a true closed lock will generally have a maximum interincisal opening of 25 mm or less. Bear in mind that if the patient has an anterior open bite, you need to subtract the amount of open bite from the measurement of interincisal opening.

In the case of trismus, or severe muscle spasm, a little finger pressure between upper and lower anterior teeth will produce at least a few mm of additional opening. This is termed a “soft end feel.” However, with a true closed lock there is a hard end feel. You will not see any greater opening with finger pressure.

So, if your patient has difficulty opening, has maximum opening of less than 25 mm and there’s a hard end feel, that is, you can’t produce any greater opening with thumb and finger pressure, then that patient almost certainly has a closed lock of the TMJ. The lock is usually unilateral although I have seen both TMJs completely lock at the same time.

To be blunt and unacademic about this—if your patient has closed lock of the TMJ, don’t screw around! It can only get worse and more difficult to treat.

I was visiting with an oral surgeon last week and she mentioned that she was going to be seeing the patient of an endodontist in town. The endodontist had called her office because one of his patients could not open after endo treatment. When asked how long the patient had been locked closed, the endodontist told her it had been about a month. The patient and the endodontist both expected the problem to resolve itself. That wasn’t happening.

“The truth is,” the oral surgeon said, “I think this has been going on two or three months, not just one. He just didn’t want to say it. I’m going to send the patient to you. Think you can unlock it?”

“If it’s really been three months, this person is probably going to need surgery. In that case, I’ll send her right back to you.”

For the patient with closed lock, time is of the essence. On average, I see the patient with closed lock about two weeks after the problem occurs. Why? Because the dentist and patient both believe they are dealing with a trismus that will correct itself in time. It seems to take about two weeks before there is realization that something more is going on. At two weeks, the unlock procedure is fairly straightforward.

After six weeks, adhesions begin to form in the joint space and the unlock becomes much more difficult. Sometime between three and four months of a TMJ in true closed lock, surgery may be the only option.

Back to Abram’s story. A couple of weeks after he locked closed, a local oral surgeon referred him to me. During those two weeks there had been a few futile attempts to unlock him. He’d tried physical therapy and had even been to a hospital emergency room. When he came to me, I did joint imaging and a physical evaluation. I explained how the dislocation caused the lock of the TMJ and also how it is unlocked. I then injected the right superior joint space with lidocaine and manually unlocked it. Manual unlocking usually requires two thumbs on lower molars, but I could only get an index finger in his mouth—remember maximum opening was 5-6 mm. I manipulated the mandible down and to the left (he was locked on the right side) with my index finger. He opened to 35 mm immediately. A few days later, he was opening 38 mm and a couple of weeks later he was opening more than 50 mm with no pain.

If you’ve done a procedure on a patient who then reports he or she can’t open, please have your patient in for an evaluation. Opening 25 mm or less? Hard end feel? That’s a closed lock. I do not recommend you try to unlock it yourself unless you’ve had some training. Most of the time, the joint itself will be exquisitely tender to any pressure and will need to be anesthetized. Most metropolitan areas should have a couple of practitioners who can unlock the joint. Many of these patients then require follow-up care to insure the joint stabilizes, although some do not.

Nobody in your town can do this? Check with the American Academy of Craniofacial Pain ( The website’s referral area will help you find the practice nearest you that can handle the closed lock patient. The organization also has two meetings annually, offers a mini-residency that is excellent and you should be able to learn many aspects of TMJ treatment, including how to properly inject the joint and do the unlock if you’re interested in learning how to do this yourself.

The main point is don’t wait for the closed lock to get better. Early treatment is fairly quick and uneventful. Waiting even a few weeks allows the problem to worsen and make surgery the only option.

As concerned as I am for the patient with a closed lock, I tend to be just as concerned for the dentist who may have caused it. None of us want to do any harm or cause any condition to worsen. Dentistry is tough enough physically and emotionally without this kind of added stress. In my experience, almost every patient who has locked closed after a dental procedure had signs and/or symptoms that a problem was already brewing. Wouldn’t it be nice to know who you should not work on? Stay tuned for the next installment on spotting the suspects.

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