To the dentist: are you cementing crowns that are just out of occlusion? I know it’s a fairly common practice, and is even advocated in some circles (see my article Last Tooth Standing). There was a time, when I was just a boy in dentistry, a young pup starting out, when I would tell the lab to leave crowns just shy of occlusion. It seemed to beat grinding them in, which I saw as the only alternative.
But in my TMJ practice, I’m seeing a downside; and I’m seeing it often. Within the last month, I’ve seen two patients suffer a good deal of pain as a result of the practice of seating crowns that are just a bit out of occlusion.
One of those patients was a young man referred by a local oral surgeon. The oral surgeon was puzzled by the patient’s TMJ-type pain and wanted to see if I could determine the cause. At the intake interview the man said, “My best time, my most pain-free time, is when I first wake up in the morning. I wake up with no pain at all. No tension at all! But then, as the day goes on, the pain comes and gets worse and worse and is fairly bad after dinner. The pain is right here.” He sticks his index finger against his right masseter muscle to show me. “Then I go to bed, and no pain.”
At this point he’s already told me a lot. Do you think he’s a nighttime bruxer or clencher? Right. I don’t think so either.
Now, his story becomes more interesting. “My dentist has done a bunch of crowns over the last 3 or 4 years, all on the right side. I’ve noticed that when I get a new crown, it doesn’t quite touch when I bite down. I’m guessing he does that so that when I start chewing on the new crown, it doesn’t bother me. The new crowns are always comfortable right away. Pretty smart, right?”
My wife, Andrea, always present for these new patient interviews, gives me a look. I know what she’s thinking. She’s read Last Tooth Standing.
“You’re telling me that all these crowns were done on the right side?”
“Yes,” he says.
We move to a treatment room and I start the exam and do imaging of the TM joints. Dentition: normal class I occlusion, normal overbite and overjet, four PFM crowns upper right (Nos. 2,3,4,5) and one PFM lower right (#30). Range of motion normal. Areas painful to palpation? Only the right masseter muscle. Joint noises recorded with JVA by Bioresearch are very slight and within normal limits. Temporomandibular joint images are normal.
And then I do T-scan. Here’s the result with the patient fully closed in centric occlusion.
Obviously there is very heavy occlusion on the left side and very light contact on the right. In fact, the molars on the right side are not in contact at all.
So what are we seeing here? Five teeth, all on the right side, were restored with crowns—one at a time over a period of a few years. According to the patient (and I believe him) all were left just out of occlusion at cementation. Well, won’t the teeth supra-erupt and bring the crowns into occlusion within a short time? The answer apparently is, don’t count on it!
I review the patient’s joint films with him and point out the very normal arrangement of condyles in their glenoid fossae. CO equals CR, i.e. when the patient closes normally, the TM joints are in centric relation by today’s definition.
Then I show him T-scan print outs “You have close to eighty percent of your biting force on the left side and twenty percent on the right. Every time you close, your brain, your motor cortex, is telling your masseter muscles to contract until the teeth come together. But, oops! The right side teeth never come together. And this right cheek muscle, the one that’s sore, just keeps on trying. It tries all day long. The good news is that you don’t have a joint problem. The bad news is your dentist is going to have to pick a couple of crowns to re-do. Get them into contact when you close, and that muscle pain will go away.
“My dentist said maybe I need a night guard.”
“You don’t have any nighttime pain and you said your most pain-free time is first thing in the morning, right?”
So, what’s a night guard going to do for you?”
“Oh, right. Not too much, huh?”
Correct. A night guard will do nothing for this person except possibly make him worse.
I understand that as a dentist you don’t want to do a lot of adjustment on crowns when they come back from the lab. One solution is to request that the technician place a layer of foil relief over the opposing tooth or teeth. And that approach will work—for a while. But if you do several crowns on the same side over a period of time, you’ll eventually take away that one last holding cusp and create a very unbalanced occlusion.
Forty-plus years ago, back in my dental school days, we were instructed to do excellent full arch impressions of both arches, even when just doing a single crown. A few instructors—certainly a minority—approved a technique of doing a quadrant “bite tray” for single crowns, stating that full arch precision models amounted to overkill when doing a single crown. One day, the chairman of the department, watching me do that kind of impression for a crown said, “I know that technique is officially approved, but I don’t like it. Eventually it will get you in trouble. Just do the full arch models, even if it seems like too much trouble. Do what you can to get the occlusion exactly right.” It took years to see the wisdom of his words, and now I see dentists landing in all kinds of grief by not heeding them.
Last Tooth Standing isn’t just a myth. Gradually taking away a naturally balanced occlusion is creating one of those mysteries of TMJ type pain. And often, it isn’t the TM joints at all—just the muscles’ reaction to getting the bite way out of balance. You can get away with leaving a crown or two just out of occlusion. But eventually, one last crown done that way will send the patient over the edge. Just food for thought.