Diagnosing Structural Compromise in Teeth with the 1-2-3-4 Risk Assessment

The most minimally invasive dentistry is early diagnosis and treatment. Dr. David Alleman created the 1-2-3-4 risk assessment so he could better diagnose teeth that were at risk of fracture or decay to prevent large fractures or carious lesions under the restoration. In this episode, Dr. Alleman discusses research into the structural integrity of different preparations and how practitioners can use this research to prevent cracks and marginal leakage before they pose a risk to the tooth.

Articles referenced in this episode:

• Larson TD, Douglas WH, Geistfeld RE. Effect of prepared cavities on the strength of teeth. Oper Dent. 1981(6)2-5.
• Wang RZ, Weiner S. Stain-structure relations in human teeth using Moire fringes. J of Biomechanics. 1998;31:135-141.

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Transcript

0:36

Welcome to season four, episode two of the Six Lessons podcast. In this podcast, we want to introduce you to concepts that can make you a better dentist and make your patients more satisfied happy with their treatments. But in this lesson, we want to talk about a very important portion of the six lessons that we call the 1234 risk assessment. And so whenever we look at a tooth that has a restoration, we want to say, is this tooth healthy? Is this tooth functioning properly. And are there risks that in the future could cause this tooth to have defects that would lead to decay or fracture? So the risk assessment is for a tooth that is at risk of fracture or decay. And the real synthesis of this came in several steps. But I received some training in traditional mechanical dentistry. Prosthodontics from John Kois And John Kois introduced me to an article that was published in 1981. that article, 1981, by Doctor Larson. I knew him, my reputation. He was a mentor of Pascal Magne at University of Minnesota, but Doctor Larson and his team Geitsfeld and Douglas, Douglas was Magne’s mentor William Douglas. They said, what happens to a tooth once you put a traditional filling in And so they took my cusps and they filled them, and they found out that a natural tooth had a resistance to fracture of 500 pounds. Wow. That's a lot of force to put on a bicuspid to get it to fracture. It took 500 but then they put an occlusal amalgam that was just 1.5mm in width. That's the ideal G.V. black prep that you're taught in dental school. 1.5mm Isthmus was enough to get into dentin and they felt like that foundation of dentin was more important because it gave you enough depth to have what's called retention form and resistance form from being dislodged. It had a shape, basically a square shape, as all dentists know. So these G.V. black preps had very sharp line angles and those line angles from an engineering point of view, or very deleterious for stress distribution, because they concentrate stress at those sharp angles. Now, it wasn't known really, until steel the turn of the century when steel ships were made. They found out that if you put a angle on a door or an angle on a window on a ship, unlike a house that has a little bit of give, a shift is made out of metal concentrated the stress on those windows that were square and on those doors that were square. And these metal ships didn't have the forgiveness. They didn't have the toughness of the great wooden ships of the previous two centuries in the British Navy. And these metal ships cracked in half. I mean, big ships crack right in the middle, and they see the crack at the bottom, and they go up and they say, oh, that crack started right here on this window. And so they said maybe. And they knew the engineers would have the better answer. Maybe we need to change the shape of those windows instead of square that had the stress concentration on the angles they started to make round windows. Those are called portholes I think. And then all of the doors on ships have round edges. They don't have straight doors like houses. They have these curves. Why? Because a curve stress distributes these micro movements around the whole door frame. And they didn't crack after they did Wow. 100 years ago. Unfortunately, 50 years after that, when airplanes started to become more commercial, they found out that they had the same problem with airplanes. So airplane windows need to be an airplane. Doors need to be curved on the sides. Okay. So this is a major change in tooth preparation, So it went from a normal tooth, 500 pounds per square inch to break. If you had an isthmus that was 1.5. Now it only took 300 to break. Well, that's a reduction. But it's, you know, a little more than half the half the strength of a normal tooth. But then what they did is they only made the isthmus a half millimeter wider. That's just the thickness of your fingernail. when they did that, they lost another 20%. So you went from 300 to 200 pounds per square inch, could break a tooth. Now that it was had this preparation, which would be a a fairly moderate G.V. black preparation, not ideal, but still an ideal preparation. You lose 40% of your fracture resistance, a little wider preparation, which is so common in every dental practice. These fillings now subtracted 60% of the fracture resistance. And this was the beginning of a tooth that would break. And that fracture resistance became related almost 20 years later to decay. That was underneath these restorations or in a crack that had started. that was published in a paper by Graeme Milicich Tim Rainey in 2000. Now, I learned about the science from Larson and Douglas in 1998. So I was a little late to the science there, but again, only two years later, I'm diligently reading the literature, both traditional mechanical literature on operative dentistry and prosthodontics and now adhesive dentistry. That was introduced to me in 1995 by Ray Bertolotti And the name became prominent because he was a prominent speaker in New Zealand and Australia, and Tim Rainey was considered the father of minimally invasive dentistry in the United States, and he promoted air abrasion instead of rotary burrs as a way to prepare a tooth. And it works really well for very small cavities. It doesn't work that well for large cavities, but still, minimally invasive dentistry is one end of the spectrum. Biomimetic restorative dentistry. On the other end. If you have small, small lesions, then you have mostly tooth support. But once you get to that point where you've lost 50% of the God given creation of the two ability to resist fracture, then we say that tooth is structurally compromised. Now in traditional prosthodontics, that's when they would put a crown on the tooth. Well, I had a problem with that because I, with my own practice, knew that the chances of a tooth having sensitivity that wouldn't go away, that eventually would lead to a root canal and a full coverage crown, were the treatments that I had done routinely for 17 years, and these were the source of the catastrophic failures. I knew that once I put a crown on a tooth, I had more root canals that would come from those treatments. And then once I'd had a root canal and a crown, then I that was the source of the catastrophic failures. So these treatments that were driving me to not really enjoy dentistry and led me to decide not to be a dentist after 17 years, once I was introduced to adhesive dentistry, I started to look at the literature. In this literature always went back to some basic principles about movements. And these movements in a tooth are so small you can't see them with your human eye, but they are measured and they're measured with the devices called a strain gauge. And a strain gauge has the ability to measure these very small movements. But the small movements, let's say 100 microns, well, you know, your fingernail is 500 microns. It's one fifth to thickness of your fingernail. Can you see that kind of movement? Well, when I was younger, I had better eyes. I probably imagine that I could see that kind of movement. But that 100 micron movement is what a tooth does on each side of a filling. There's about 180 micron movement, and the kind of split beside each side of a silver filling would have about 90 to 100 opening. Well, the bacteria is only one micron thick. so the infection of that gap is very easy. And it's fed with the normal carbohydrates that a person eats. so this recurrent decay that I was familiar with in traditional operative dentistry under amalgams and then under composites that I had seen other dentists do. And then I started to do them, and I was aware that this was going to have the same problems, because these gaps you can't see, particularly in a composite, you can see them faster than the amalgam because the amalgam is dark and then the gap what is becomes, starts to become infected is also Then you got the tooth, it's lighter, but in a composite you would have the light composite. Then a dark line would develop after 4 or 5 years, and then you would see that gap. And this is what dentist around the world see is normal. And they accept it. then they have what do they do when the composite fails. Well, the same thing. They do a crown. And when that fails they do a root canal. When that fails to extract the tooth, do an implant. But stopping this circle of retreat to me all went back eventually to my microbiology major, where I knew how big bacteria were. And I knew what they did, I knew how to keep bacteria out of the body. And that's by keeping them in mouth, but not inside the body. Now the tooth is kind of like right on the edge between the outside of the body, which is your mouth, your esophagus, your stomach, your intestine. That's all considered in biological biologic terms outside the body. once they pass into what's called the connective tissue. So if you cut yourself, peel some skin, you got some blood. That's what connective tissue is. All of your bones and muscles and joints are connected, and they're connected with tissues that have access to blood. Because blood is the way you detect bacteria infection there, the way that they distribute the inflammatory responses. And so the pulp is connective tissue. Once the bacteria gets into the pulp its inside your body. And that can lead to other complications. If the tooth becomes abscessed when the pulp dies. I mean, trying not to teach you what you already know, but if you really have a passion to stop a tooth becoming abscessed which is millions and billions of white blood cells that are phagocytizing millions and billions of bacteria, the best way is to stop any bacteria from getting into the pulp in the first place. So you don't have a response. You don't have an immune response that the body is trying to get rid And so the risk assessment starts with measuring the isthmus. That's the first number that I So I said okay Douglas. And Larson says that if the isthmus is greater than two millimeters then you are losing 60% of the structural integrity of the tooth. So we're going to give that a name. Structural compromise. And John Kois use that phrase structural compromise. But how about other measurements? The other measurements came when the literature showed that 90% of your failures come at the bottom of the boxes of a class two restoration. Why is that? There's more movements in the bottom than there are at the top. Why is that? There's more flexibility in the tooth at the bottom, and it squishes a little The rigidity of the tooth increases from subject areas up to the enamel, stiff on top, more squishy on the bottom, and all of a sudden that box at the bottom. That's the place where the more than 100 micron openings happen, and the bacteria have an easier way to replicate and cause decay. And so how do you measure that depth of the box? And there were some articles by Jack Ferracane and Tom Hilton that showed about the and the length of teeth. There are some teeth that are short, some teeth that are long, but basically the short teeth have a DEJ at about four millimeters long, teeth have a DJ and approximately about six millimeters. And so the part of the tooth that connects the route to the crown called the CEJ So that cementoenamel junction has a ring of two millimeters of enamel that are very important because they actually connected to side to side and distribute the forces of occlusion in the middle of the tooth. And that information came in 1998 Just happen to have a copy of it. So this article right here was done not by dentists but by engineers. And they started to see that teeth. Once you put forces on them, they had the ability to change the directions of the forces. This is called the Moire fringe test forces that come straight down. Once they get to the bottom half of the tooth, they start to distribute the stresses and the tooth squishes out a little bit. That's called an isotropic expansion. This straight down force. This is called an anisotropic distribution of forces. And that is handled really well by enamel. But enamel doesn't do much stress distribution doesn't have that squishing us. And so the Wang and Weiner showed to make a tooth act like a tooth, you have to have some materials that that portion of the tooth that's on the bottom. And the best materials we had were composites. But 1998, 2000, when these concepts are being talked about by Graeme Milicich and Rainey in their paper in 2000, it gave me another clue into diagnosing these areas that may become infected or start cracks. And that is they showed us that a crack on a marginal ridge after a class one restoration. When you do the class one restoration, you won't see a crack in the marginal but after a number of years you will see cracks there. then those cracks can be traced to recurrent decay, which they gave a name of occlusal effect caries. And the name that they gave to the crack on the marginal ridge was peripheral rim fracture, and the peripheral rim fracture and occlusal effect caries When I read that in 2000 and explained a very common phenomenon that I had in my first 1718 years of practice, and that was would see a patient that for years would have no inner proximal decay, and then they would show up and they would have several class two lesions. Inner proximal lesions shows on the bite wing X-ray. I would just immediately say you need to brush and floss better. And by the time I started to say floss, I looked at their teeth and there was no plaque. Now, usually if a patient just brushes and flushes right before they come to the dentist, you have an idea that, well, the teeth are cleaned today, but you know the gums are a little bit red. But these patients were consistently patients with good hygiene. But now we had a class two lesion that needed to be treated. It was a mystery to me until I read that paper in 2000, and I understood that decay was coming from the inside of the tooth, not from the outside plaque accumulation that was diminished into the dentin. It was actually an infection in the dentin that was starting to diminish the enamel. And the occlusal effect caries. That was coined by Milicich. And rainy became a very strong diagnostic tool for me. From that day till now, I've had the opportunity to give many courses with Tim Rainey and Graeme Milicich around the world. There still active there, still alive. Tim's a little bit older. He's in his 80s now, but Graeme had a near fatal bike accident a few years ago, so he's not practicing dentistry, but he has survived, and I respect and always give credit to them and all the courses that we give for these contributions that they have given us in the early diagnosis that leads to early treatment, that makes adhesive dentistry more effective anyway. So the peripheral rim fracture, that's what we look for. One fracture on an on a marginal ridge. We ask the patient, do you have any sensitivity sweet cold or biting, which would indicate that that crack not only is an enamel but has passed the DJ and now is into the sensitive part of the tooth. The dentin, the second number two, the 1234 risk assessment. First cracking the marginal ridge. Second is how wide is the estimates? Two millimeters. If it's less, the tooth. Is the restorations being held by the tooth substantially. And then number three is can you have a thin cusp without a wide isthmus. And the answer is yes. You can have a groove that goes to the side. The dentists restored the groove towards the side. It's the minimal isthmus. But the thinness of the cusp now means that the pulp is not hydrating that cusp and is prone to fracture. those fracture numbers came from several studies. those several studies showed us that 80% of the fractures were on lower molars, lingual of lower molars, or the buckle of upper molars. And so those studies showed us that if you have a thin cusp, that cusp is going to be prone to fracture because it's not hydrated. Plus, if it doesn't have a holding cost, the micro movements will be exaggerated. We call that a tension cusp, where the lingual cusps that are not being held by a central fossa they'll move towards the tongue. The buckle costs and upper molar will move towards the cheek. They're not held by a fossa, but the lingual cusp of an upper molar is held by the fossa of the lower molar, and buckle cusp of the lower molars being held by the central fossa the upper molar. So these cusps move sideways more than these central, what we call holding cusps. So that's one, two, three, four. And the fourth is that four millimeter. The average between the short teeth and the long teeth is four millimeters. Once you a box that's more than four millimeters, you are not very often going to have enough enamel to hold a bevel that can increase the bond strength in the bottom of that box. Some long teeth do have enough to bevel, but the general 90% of the time you will not have And so you treat a box is deeper than four as a butt joint, and you use the technology that we've developed for lesson for to hold that bond long term. And so far we haven't had any reported recurrent decays or initiation of fractures in these prepared deep boxes. And some of these boxes have very, very Okay. So 1234 look for a fracture on a marginal ridge. Look for an isthmus greater than two. Look for a cusp. It's less than three millimeters. And look for a box that's deeper than four. If any one of those signs or symptoms are are noted, just write it in the chart then talk to the patient about this tooth is at risk of fracture and decay. If you're kind of proactive and want to prevent that from happening, then it's better to treat these situations earlier rather than later. that's the whole discussion of trying to make an early diagnosis in an early treatment, instead of reacting to a later, more difficult or a more catastrophic situation developing in the two. So early diagnosis, early treatment, that's the foundation of minimally invasive dentistry. And it's relative biomimetic restorative dentistry. Until next time, get bonded. Stay bonded.