The Wonders of T-Scan: It’s Amazing What You’re Missing

Dr. HalliganIn my TMJ practice, I see patients daily who have classic symptoms of TMD: painful TM joints, painful muscles of mastication, limited opening, clicking joints and so on. My exam includes joint imaging, joint vibration analysis (JVA by Bioresearch), palpation exam, and T-scan occlusal analysis.

Interestingly, more than 25% of these pain patients do not have a joint problem at all.

So, if there is no internal derangement of the temporomandibular joint, why does the patient have pain? The answer almost always lies in the occlusion, and the most common occlusal problem? Lack of cuspid rise.

Here’s almost everything you need to know about occlusion in a nutshell: When a person closes, all teeth should touch at the same time with about the same occlusal force. And when the person moves the mandible into a right or left excursion, all posterior teeth should disclude immediately.

But here’s the problem: With the old standby, articulating paper, you have no idea of the timing of tooth contact. That is, if one tooth contacts a fraction of a second before any of the others, articulating paper will not indicate this. The patient may even tell you, “Doctor, when I bite down, the left side hits first.” But when you check the occlusion with articulating paper, all the teeth make even marks.

Or the patient may tell you that a tooth is hitting hard. You check and look. Well, all the marks look about the same to you. The tooth the patient is complaining about may even have the smallest mark.

Working side and balancing side interferences? If you take the time to look carefully, articulating paper should pick those up. But even significant interferences can be rather subtle and not easy to see. It can be even harder to get the patient to move the mandible in such a way that the offending teeth contact. People actually learn to subconsciously avoid those areas of contact.

Enter T-scan. Recently I went to a lecture by Dr. Robert Kerstein, a Boston, MA prosthodontist. For the past 25 years he has been doing key research projects on computerized bite analysis. The results of his research is rather telling. His peer reviewed research shows for example that there is no correlation between the size of articulating paper marks and the depth of color in articulating paper marks and the force of occlusal contact. T-scan on the other hand will tell you just how hard—or how lightly—each tooth contacts when the patient closes.

And timing of tooth contacts? Forget about it. Marking paper cannot tell you. Is that important? For implant restorations it can be critical. T-scan will tell you the exact timing of every tooth contact.

How about canine protected occlusion? Do the posteriors disclude upon lateral movement? And do they do so immediately? In fact, do they disclude at all? T-scan answers those questions easily.

Before showing you an example of a problem case, I thought it would be useful for you to see what normal looks like on T-scan:

Normal occlusion on T-scan

This happens to be my centric occlusion. Close enough for government work—actually quite a bit better than that. Now, if you’re unfamiliar with T-scan, you might think normal means exact 50/50 occlusal contact right to left. But that’s actually very unusual. I’ve seen a few patients with that kind of perfection, but it is rare. It’s as unusual as a hole-in-one in golf or a perfect 300 game for a bowler.

Here’s T-scan of my left lateral excursion:

Normal lateral excusions on T-scan

This is how correct cuspid rise looks on T-scan: 100% of contact on the left canine and no other contact at all.

My right lateral excursion:

Normal lateral excusions on T-scan
Above is T-scan of my occlusion as I move into right lateral. Again, that’s perfect. This is the job the cuspids should do. This is what canine protected occlusion means.

Last week, a young woman named Annette came to my office for a TMJ exam. She was referred by a prominent La Jolla dentist for limited opening, ear pain, and facial pain. Range of motion measured 22 mm opening without pain and 35 mm maximum opening with pain—that’s very limited given that normal opening is generally agreed to be between 42 mm and 52 mm without pain. But joint images showed normal TM joints. And joint vibration analysis results were within normal limits.

So, if the TM joints are normal, what’s the problem? Why all the muscle pain? Why such limited range of motion? Let’s look at her T-scans:

Uneven occlusion

Here’s Annette’s centric occlusion (C.O.) or maximum intercuspal position (MIP) if you prefer. Remember, all teeth should occlude with about the same amount of force. Annette’s T-scan isn’t perfect in this regard, although I certainly see much more uneven occlusal contact almost daily. In a note to her dentist I wrote, “In centric occlusion, contact on the left side is a little hard, especially on #14 and #15. However, this is not as much of a problem as her lack of canine guidance.”

Here’s Annette on right lateral excursion:

Lack of cuspid rise

And this, by the way, is what she notices most. She can even point out the teeth. “Back two teeth on the right side,” she says. And she is correct. When Annette goes into right lateral, the lingual slopes of the buccal cusps of #2 and #3 are in hard contact. Those are serious working side interferences and are likely the primary cause of all of Annette’s symptoms. But notice that #15, and to a lesser degree #14, are also contacting. Those are balancing, or non-working, side interferences and also a source of muscle strain and pain.

Now look at left lateral excursion:

Lack of cuspid rise

Obviously, it’s far from perfect. This is lack of normal canine guidance and a source of muscle strain.

One more thing to bear in mind: Sometimes even if there is cuspid rise, there can be a problem with time to disclusion. In other words, the cuspids may actually function to cause disclusion of the posterior teeth, but those posterior cusps may grind across each other for too long a time before separating. T- scan will tell you disclusion time! Try doing that with articulating paper.

So in Annette’s case, I wrote to the dentist and stated that there is no TM joint pathology, and therefore I was not recommending treatment in my office (I do no restorative dentistry in my practice). Instead I offered suggestions for improving cuspid function with restorative dentistry to be done by the referring dentist.

“If your patient is breaking posterior teeth, look at the cuspids.” ~ Dr. Ron Jackson

What are some of the other consequences of working and non-working interferences? Fractured molars, loose teeth, sensitive teeth, tooth mobility. Your patient breaks the lingual cusp off a lower molar? Sure you restore the tooth. But take a look at the cuspids and deal with proper canine guidance or someday down the road your patient will break the restoration too. Don’t say I didn’t warn you.

Annette’s story is a common one. Only two weeks ago, a young woman came to me with a self- diagnosed closed lock of the TMJ. And indeed when I checked range of motion, her maximum opening, even with pain, was 25 mm. Classic closed lock, right? But joint images were normal. And an icy cold spray (Gebauer’s Spray and Stretch) resulted in an increase to 35 mm opening within several seconds. T- scan disclosed total lack of cuspid rise on both right and left sides. Lack of canine guidance had obviously been a problem for some time—perhaps for years. But the strained muscles finally rebelled.

Her dentist has started to correct occlusion and after one visit he sent her back to me for an evaluation. I did new T-scan print-outs for him, but also rechecked range of motion. She opened 40 mm without pain. That’s a pretty nice result for a person with “closed lock” of the TMJ with no TMJ treatment.

For more thoughts on occlusion and equilibration, you may want to refer to my earlier article, Rethinking Equilibration.

Does every dentist need T-scan? I wouldn’t want to practice a day without it. And I believe computerized occlusal analysis will someday be standard of care in restorative dentistry. But can you do without it? Let me simply say this, there are excellent dentists who miss lack of cuspid rise and very uneven occlusal contacts by relying on articulating paper alone. Until you purchase T-scan you will need to be very diligent in your observations of occlusion. And someday, when you purchase T-scan and learn to use it, it will be as mind blowing as when you started using loupes. You won’t believe what you’ve been missing.

(disclaimer— I do not lecture for T-scan and am not paid by them for my endorsement.)

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