SHORT® Dental Implants: Does Size Really Matter?

Hello and welcome to this podcast on short dental implants. My name is Bill Schaeffer, and another title for this could be Does Size Really Matter? And I want to say right at the outset that I have absolutely no financial interest in any implant system other than that I place implants. I’m not a paid consultant or a paid lecturer at all. Okay, does size really matter? Well, I’m going to start by telling you what people have told me for years and that’s that short implants simply don’t work. And when you look at x rays of them it’s easy to see why, these short stubby implants with big long crowns of them, it’s obvious when you look at them that they’re never going to work long term, and there’s plenty of evidence to back that up. This is a paper from nineteen ninety nine and it’s a comprehensive review of the literature, a paper looking at lots of other papers, and it says implant loss increased with short implants. Here’s another review of the literature, Lars Sennerby in 1998, and again high failure rates are associated with the use of short implants. Here’s a paper from two thousand, it looked at almost three thousand implants, followed them up for three years and found that a third of the shortest implants failed. Can you imagine what that would mean for your business if a third of your implants failed? It’s pretty clear that short implants don’t work, right? Wrong, of course wrong, otherwise I wouldn’t be giving this podcast. Not only do short implants work, but they work really, really well. On the left is the image I showed you at the beginning, and here’s the same implant eight years post op. Eight years post op and nine years post op. You’ll see lots and lots of other short implants with long term follow ups. The truth is that implants are getting shorter. No longer do we place the eighteen and twenty millimeters long implants that were the norm five to ten years ago. Anyone that’s been in this business for a long while will remember being taught by cortical fixation. When we learnt that placing implants between the mental foramen, had to drill right the way through, through the bottom cortex so we could engage the bottom of the mandible with our implant to get bicortical fixation. Not only do we not do that now, if we saw someone doing it, it would seem negligent in a normal sized mandible. So, if implants are getting shorter, why is that? Well, there are two main reasons, and the first is that we understand a lot more about how they work. Let me show you what I mean. This is an illustration, a drawing of an implant. It’s not any particular model, make, type or size, it’s just a screw type implant with a crown on top. I’m going to make it really easy for you to visualise this, I’m going to make it a diagrammatic implant. If we apply a force to that crown, the implant will want to rotate around an axis somewhere along its length, and it will be prevented from doing so by applying compression to the bone, as shown by these contour lines. The highest amount of compression, if you like the most damaging bit, will be in the middle of those contour lines. But the thing that I want you to see from this image is that there are large parts of the surface of that implant that are not being used for the distribution of compressive forces, for want of any other word “wasted” areas. If we take that implant and make it twice as long, and again we apply a force to it, it will again want to rotate and will again to prevent it from doing so by compression within the bone, and again the highest and most damaging forces will be in the centre of those contour lines. But the thing I’d like you to see from comparing these two pictures is that the biggest difference is not the surface area over which those compressive forces are distributed, but those wasted areas. You can probably imagine this best by imagining a very long implant. Imagine one that’s a normal diameter, say four millimeters wide, really long, maybe a meter long or a mile long, or infinitely long, and it’s integrated nicely in bone and it’s got a crown on top. If you apply a force to that crown, do you really think that those compressive forces are going to be distributed infinitely over that implant so you don’t get any crestal compression? Of course you’ll get crestal compression, and I hope that should be obvious. Making an implant ever longer, longer and longer does not make the forces distributed to the bone less, less and less. Is that the biggest reason why implants are getting shorter? No, the biggest reason is that we’ve got improved implant surfaces, and by that I mean roughened surfaces. I’m not going to talk to you about the biology of a roughened surface and how one roughened surface increases the transcription of messenger RNA and osteoblasts compared with another one, because really I don’t understand that. It’s over my head. I’m a simple guy and I like to think in simple terms. For me a roughened surface merely increases the surface area of the implant to which bone can fuse. That means directly that a shorter roughened implant can achieve the same bone implant contact as a longer machined one. It also means that because most implant systems have only had roughened surfaces for ten years or less, any literature reviews before about two thousand and three are going to be reviewing research mainly on machined implants. We’ll see the importance of that later. We’re talking about short implants, how short is short? Well if you look it up in the dictionary you’ll get fifty nine different definitions, but if you look at the one in relation to distance means short is defined as small in length. And that’s really unhelpful, because what that means is that short can be whatever you decide is small in length for your implant practice. If you’re someone that routinely places eighteen and twenty millimeters long implants, then a twelve millimeters implant will seem really short for you. But if you publish research and you describe an implant as short, you have to define what you mean by that. Over the years there have been papers that have defined short as being fourteen millimeters or less, twelve or less, ten or less, eight or less, and now more and more papers are defining short implants as six millimeters or less. Let’s look at the Bicon short implants. Bicon at the moment have three short implants, two of them are six millimeters long, and one of them is six millimeters wide but just less than six millimeters long. It is wider than it is long, and that’s pretty freaky to begin with. Secondly, it’s almost spherical in shape. And as they’re spherical, how on earth can they work? Because that seems the most crazy shape to make an implant. And what I mean by that is, here’s the image again of our standard implant, let’s make it diagrammatic, let’s put a force on it, it’s going to want to rotate, and it’s going to be prevented from rotation because it’s long, thin, and can apply compression. If you have a round implant and you apply a force to it, it’s going to roll over. And if you have a short round implant, well that’s certainly going to roll over, right? Well, a Bicon implant isn’t just spherical, it’s finned, and if we apply a force to it, it is going to want to rotate, and let’s zoom in here for a moment, but it’s going to be prevented from rotation by compression on the top left as seen by the green arrow on the bottom right. But because this is round in general shape, it will not only be able to apply compression to the bone in those regions, but over the whole of its length. Not only that, but because these fins are three-dimensional and not two dimensional, the whole of the surface area of that implant will be able to distribute those compressive forces, something that’s quite useful when you’re talking about short implants, which by definition are not going to have as much surface area as a longer implant. Now I want to make it clear that exactly the same thing happens with a screw type implant, but only to a degree that depends on the depth of the threads and length of the implant. The deeper these threads of the screw, the closer they resemble fins, the more they will be able to distribute these forces. The shorter the implant, the less wasted area you’re going to get, and the more of that implant length that will be able to distribute those forces. Implant companies have recognised this. These are five different makes of implants, all of which are beginning to get deeper and deeper threads. Short implants are obviously most useful in situations where there isn’t much height or bone, and by that what I mean is the posterior mandible and the posterior maxilla. If you’re not going to use short implants in those situations, what are your other options? Well let’s start with the posterior mandible. And I am not talking about someone like Jean who has so much bone that you could place fourteen millimeters implants and never come close to the nerve. I’m talking about someone like Patricia who has very limited height of bone in the left side of her mandible. Let’s zoom in a little bit. She’s got lots of bone in front of the nerve, but very, very little bone above it. What are your options? Well, first thing you can do is you can cantileve. You can place one or two implants in front of the mental foramen and you can cantilever a bridge off the back of it. I have no problems with that, that’s a perfectly reasonable option. However, it’s not always possible to cantilever. What if she didn’t have any missing teeth anterior to her mental foramen? There’d be nothing to cantilever your bridge off. So it’s not always a feasible option. Your second option is you can put a block graft on top of the ridge to increase height. Take a bit of bone from the hip, or the chin, or the back of the jaw, or the calvarium and screw it on top of the ridge. The downside is you’ve got to take that bone from somewhere, and that hurt and there’s morbidity associated with it. You’ve then got to try and get soft tissue closure that is tension free over the top, and that’s very challenging. If you don’t get tension free good closure and you end up with a bit of wound breakdown, saliva and food will go right down on top of your block graft and you’re going to lose it. Also, patient can’t wear her denture whilst that block graft is developing a blood supply, and even if they don’t wear a denture, you will still lose about half of the height of bone you have put on there. So if you don’t use a block graft, what else can you do? Well you can do osseodistraction. You can make three cuts right the way through the whole thickness of the mandible and use a distraction device to lift that floating segment of bone up. It’s quite fashionable and sexy at the moment. The downside is you’re only going to be doing this where there isn’t much height of bone above the nerve, and when you’re making those cuts you don’t have x-ray vision. Yeah, sure you’ll have taken x rays, maybe a CT scan before you start the surgery, but you’re still making those cuts above the nerve without x-ray vision when there isn’t much height or bone above it. Finally, need enough height of bone above the nerve to actually connect the distraction device, and if you’ve got enough height of bone for that, you’ve got enough height of bone for a short implant. Next option is you can move the nerve out of the way. Nerve repositioning. Cut through the bone, take the nerve out, and have it coming out through the bone further back. Removes your problem. You can drill all the way down to the lower border of the mandible, where you can get your bicortical fixation if you wanted it. The downside is that if you look at the larger series of nerve repositioning, where they looked at the sensory disturbance following it of the lower lip, twenty three percent of patients are going to have numbness for more than six months, and five percent, one in twenty of patients are going to have permanent numbness to some degree. So if you’re not going to do any of these four options, what can you use? Well of course you can use short implants, that’s what this podcast is about. That’s what I did for Patricia. This is my pilot hole stage, you better believe I took a check x-ray. And there’s the nerve. And here are the implants placed. Placed on the fifth of July two thousand and four, it’s about as close as I want to get to that nerve. And here it is January two thousand and seven, more than two years post restoration, and again no bone loss, safely above the nerve. Let’s move on to the posterior maxilla. And this is Justin. I really like Justin, he’s a lovely guy. Doesn’t brush his teeth enough, but he’s a lovely guy. One of the reasons he’s lovely is he keeps coming back for more implants. These are three Bicon implants that I placed on the left side of his mandible. Since this x-ray was taken, I’ve replaced these two teeth with Bicons, but I’m talking about this region in the posterior maxilla. Let’s get a close-up of it. Six millimeters at the front of the space, six millimeters at the back and a little bit less in the middle. What are your options? Well, first option is you can do a lateral sinus graft. We all know what these are. You make a cut in the gum and lift it away from the lateral wall of the sinus. Drill through the bone but not through the membrane beneath, lift that window inside, creating a space where you can pack loads of bone in. I’ve done hundreds of these. The downsides are that it’s quite big surgery for the patient. They don’t like it. They get bruised, they get swollen. Do I mind about that? Not really. Second thing is you’ve got to wait a long while for this graft to become vascularised, a living part of the patient, either before you put the implants in or to integrate two implants placed at the same time. It takes time, it delays the treatment. Do I mind about that? Not too much. What I mind about lateral sinus grafts is that they can get infected. Of course we give patients antibiotics during and after the procedure, and we mix antibiotics with the graft material. But despite all of that, three percent of lateral sinus grafts will get an infection, of which you can settle down two thirds with a third of course of antibiotics. But one percent of all lateral sinus grafts get an infection that you cannot settle down, and you’ve got to take all of that graft material back out. It’s a bad day at the office. So, if you’re not going to do a lateral sinus graft, what can you do? Well, you can do an internal sinus lift, also known as the Summers technique or an osteotome lift. Again, this is relatively straightforward to do if the sinus floor is flat, but it’s very challenging if the sinus floor is at an angle like it is in the premolar region. It’s very difficult to spot, let alone treat a membrane tear if you get one, and the amount of height gain you can get is usually quite limited. Three-five millimeters is about as much you can ever get. If you’re not going to use those two techniques, your only other option is short implants. That’s what I did for Justin here. I placed two 6×5.7 millimeters Bicon implants without any kind of sinus grafting. Here we are one and a half years later, and we are two and a half years later. Single unsplinted molar crowns in the posterior maxilla, where we know the bone is poor, in a distal extension situation where we know the forces are greater, without any crestal bone loss. Okay, short implants obviously have some advantages over all these bone grafting techniques. They are that there is no increased morbidity, you’re not having to cut bone out of somewhere else, you’re not having to move nerves and make people numb, you’re not having to risk infections. There is no increased treatment time. You don’t have to wait for the graft to heal, the osteodistracted segment to consolidate, or the block graft to develop a blood supply. There are no problems with temporisation. Bury the implants and let them wear a denture if that’s the only option. But they can, that’s not a problem to do. It’s routine implant dentistry and what I mean by that is, it’s done by you. You’re not sending the patient to the scary oral surgeon to do the scary bone grafting. If you are able to drill a standard length hole for a standard length implant, you can drill a hole shorter for a short implant. And finally, and please don’t make too little of this, it’s less expensive. Bone grafting costs money, bone grafting is always expensive, and if you are talking about just an area for one or two implants, it can push the cost of treatment outside what is affordable for the patient. So clearly from this page you can see that there are a number of advantages to short implants, but are they really as attractive as they look, or is there something that we’re missing? Is this a misuse of implants? Is it something that’s going to turn around and bite us in the butt? In other words, do they work? Well this is a brilliant paper written in two thousand and six, and it also is a literature review, but it’s a literature review over a long period, sixteen years of papers, and they define a short implant as eight millimeters or less in bone. And they’re quite honest, they say. A relatively high number of these studies, twelve of them, indicated an increased failure rate with short implants. But recent publications, almost double the number, showed survival rates of short implants exactly equal to those obtained with longer implants. Articles dedicated to short implants published in the last three years reported survival rates ranging from at worst ninety four point six percent to ninety nine point four percent. The worst paper they could find showed a survival rate that’s already comparable with normal length implants. It goes on to try and explain why you get these differences in these two groups of papers, and it says that they may be explained by differences in the implant surface properties. Of the twelve studies that showed an increased failure rate with short implants, eleven of them used machined surfaces, and the remainder used mainly machined and a few HAs. Is a seven year life table analysis. From two thousand and four shorter implants did not fail more than longer ones, but this is my favourite paper. Two thousand and eight, recent paper, it looked at almost three hundred patients and over five hundred short implants, and Look at that survival rate, ninety nine point two percent survival rates for short implants. I can show you more and more papers showing that short implants work, but you don’t want to see them, you want to see more examples. So let’s do that. Middle implant was placed in February nineteen ninety seven, so that’s five point five years on, that’s eight years on. Let’s take a look at that implant. That’s the bottom of the implant, that’s the top of the implant, that’s the top of the crown, so that’s the crown root ratio. Something’s wrong here. If we look at a natural tooth, even one that’s got some recession, the root is longer than the crown, but for our implant the crown is a lot longer than the implant. Both implants were placed in April ninety seven, seven point five years on, that’s nine years on. Crown, root ratio. Crown is a lot longer than the root. Implant placed in the posterior maxilla where we know the bone is poor. Seven years on, eight years on, wait for it, eleven years on. A single unsplinted molar crown in the posterior maxilla showing no bone loss over eleven years, and look at the crown root ratio. Crown is a lot longer than the implant, and if you look at all the other natural teeth that you can see there, their crowns are much shorter than their roots. The implant crowns much longer than the implant. Single unsplinted molar, seven years on, eight years on, look at the crown root ratio, it’s wrong. Both implants, that’s five years on, look at the crown root ratio and compare it to the tooth next door. Look how little bone this implant was placed into, and yet there it is three years on and four years on showing no bone loss. Look at the crown ratio, a single unsplinted molar crown in a distal extension situation where we know the forces are highest, in the posterior maxilla where we know the bone is worst, still looking great even with a crown root ratio like that. But this is my favorite one, I love this. What a screw up, look at the placement of that implant. It’s been placed at a crazy angle, so you’ve got off axis loading, a big mesial cantilever on a single unsplinted molar implant in a distal extension situation. This cannot work, everything we know from conventional dentistry tells us this is doomed to failure. And yet here it is seven years on, eight years on, both of these x rays are ten years on. And finally this is eleven years on, and when I first looked at these I thought ah that’s the same x-ray, if you look carefully they’re not. Eleven years on, single unsplinted molar crown on a distal extension situation with a crazy off axis loading and a mesial cantilever with no bone loss. I don’t even know where you would measure the crown root ratio to, do you measure it to here, Do you measure it to there? I don’t know, but it doesn’t matter. Okay, these crown root ratios are crazy, how on earth can they possibly work? Because if we look at conventional dental teaching, we’re taught that you need a crown root ratio of one to one point five as a good abutment for a bridge, and really you shouldn’t use anything with a crown root ratio of less than one to one. This is a natural tooth. It’s got a crown root ratio of 1:2 or half to one. If we lose some bone and we get a crown root ratio of 1:1, that is the maximum crown root ratio that is advised to support a bridge. If we lose some more bone and we get a crown root ratio of one point five to one, I don’t think anyone would be wanting to put a bridge on this as a long term solution for a patient. By definition, a short implant is going to have an unfavourable crown implant or crown root ratio. But do the crown root ratio rules of natural teeth apply to implants? This is one of my favourite papers, because it really messes with your mind. This is a ten year prospective study done in two thousand and seven, so it’s a recent paper. It looked at almost two hundred Straumann implants and followed them up for ten years, and it looked specifically at the crown implant ratio and its impact on crestal bone levels. It divided the implants into three groups, a crown root ratio of less than one, crown root ratio between one and one point nine nine, and a crown root ratio of two or more. More than a quarter of those implants were in that last group. And look at this, implant restorations with a high crown root ratio showed significantly less than implant restorations with a low crown implant. Less, crazier your crown root ratio, the better your crestal bone! Goes on to say that implant restorations with high clinical or anatomical crown implant ratios do not demonstrate lower survival or success rates compared with implants with low crown implant ratios. As a result, can use crown root ratios of two to three successfully in the posterior region of the mouth. The worse your crown root ratio, the better your crestal bone. That goes against everything we’ve been taught in dentistry. Well, if these crown root ratio rules of natural teeth don’t apply to implants, why don’t they? Then there are three reasons for it. The first is conical roots versus cylindrical implants, and I know some people use tapered implants, we’ll discuss that. A natural tooth has a conical root, it’s tapered, particularly near the apex. If you lose half of the length of the root from bone, you have lost well more than half of the bony support, because you’re now down into that tapered area that has very little surface area. This implant is half the length of this implant, but it has half the bone, not well less than half the bone. Subtle, but it is important. Health versus disease. Both of these are in bone to the same amount, but this is supposed to be in that much bone. This is supposed to be in that much bone. Is where we come onto tapered implants. You don’t place a tapered implant just to the taper, you place a tapered implant right up to the platform where it is supposed to be, whether it’s a long tapered implant or a short tapered implant. Now those two reasons are kind of important, but are they the most important reason? Of course not. The most important reason is that implants do not have a periodontal ligament, they are osseointegrated, effectively in ankylosis. We’ll understand the importance of that now. Imagine a natural tooth, and trying to take out a natural premolar tooth with a pair of forceps. We’ve all done it. How do you do it? Well, stand behind the patient, you grip the head in one hand, you apply the forceps with the other, and you begin to apply some force. And because the natural tooth has a periodontal ligament, it’s got a bit of give, it’s got a bit of movement straight away. So you start rocking it backwards and forwards, a bit harder and a bit harder, maybe even a figure of eights, and eventually before you know it you can roll that tooth out sideways. We’ve all done it, it’s easy. Let’s now imagine not taking out a healthy natural premolar, but an ankylosed one. You stand behind the patient, grip the tooth with the forceps, apply some force and crack. You will break the top off that tooth. You cannot take out an ankylosed tooth with a pair of forceps, long before the bone root interface breaks down you’ll snap the crown right off. How do you take out an ankylosed tooth? You cut it out. I’d now like to think not a lot about taking out an ankylosed tooth, but taking out effectively an ankylosed and osseointegrated implant. Let’s imagine you’ve got a really strong implant with a really strongly bound crown on top of it. Stand behind the patient, grip the implant crown with your forceps and give it some. I don’t care how strong you are, you cannot take out a well integrated implant with a pair of forceps. Long before the bone implant interface breaks down, you will either dislocate the mandible, fracture the mandible, fracture the crown, or break the forceps. How do you take out an integrated implant? You cut it out, you trephine it out. A natural tooth is a bit like a post buried in earth. If you don’t have very much of it buried in earth, and a lot sticking it out, can wiggle it really really easily and before you know it, it’s come right out. So a natural tooth with a periodontal ligament has to be buried deeply down in the bone with not much sticking out if it’s going to survive long term. An implant on the other hand is like a post buried in concrete. You don’t need very much length buried in the concrete to be able to withstand forces applied to a very long post sticking out of it. Take this traffic light, maybe one or two feet of this is buried in concrete, twenty feet sticking out the top, and you can drive a Ferrari full speed into it, and that post might scratch, might even bend or buckle a little bit, but you’re not going to rip it out of the concrete. If you think that’s a one off, it’s not. You may bend, you may buckle, you may scratch these posts, but you will not pull them out of the concrete, even driving a car fast into them. Now we’ve seen that you can have a short fat implant, and we know that you can have a long thin implant, but can you have a short thin implant like this one? Because let’s face it, that would be the answer to our prayers. You wouldn’t need much bony width and you wouldn’t need much bone. The end to grafting. But does it work? The answer to that is yes, but mainly no, so we’ll start with a no. Why wouldn’t a short thin implant work well? The first reason is you do need a certain amount of surface area to withstand occlusal forces. You can’t have an implant the size of a pinhead and expect it to withstand chewing forces. But that’s not the important one, the important one is short thin implants break. And where do they break? They break where implants or with break, either at the portion of implant, or in one of the components that holds the whole stack together, one of the screws or posts. In other words, they break somewhere in this region. But why should the short thin implant break in that region when the long thin implant has an identical region within the box? And I like this because it makes you think. The reason is that you don’t place a short thin implant in a situation like this, you place a short thin implant where you don’t have much height of bone, like this, and what that means is the crown that’s put upon it is long, and this short thin implant is simply not strong enough to withstand the forces of leverage applied to it by this long crown. I can hear you saying hang on, that’s crown root ratio, you spent the last ten minutes telling us that crown root ratio didn’t affect implants, now you’re saying it does, you’re contradicting yourself, you’re an idiot, shut up and go home. I am not talking crown height to implant length, I am talking about crown height to implant strength, which is directly related to its diameter. Let me show you what I mean. This short thin implant has exactly the same crown root ratio as this short fat implant, but this short fat implant has thick walls of titanium, big strong screws or posts holding the stack together, and is easily able to withstand the forces of leverage applied to it by a long crown. If we take this long thin implant and bring it down to the same level as the short thin implant, these two have very different crown root ratios, but if this short thin implant is too weak to withstand the forces applied to it by the long crown, then so will this one. And this brings us onto an interesting point. If we take our generic implant, and we overload it to the point of failure, it will break somewhere here. Making this implant longer doesn’t make it stronger, only making it wider makes it stronger. Now, we’ve always been taught in implants, longer is better, longer is better, longer is stronger. It’s not, only wider is stronger. Okay, I did say that short thin implants can work, let me show you when they’ll work. They’ll work in this situation. If this long thin implant is strong enough to withstand the forces applied by a short crown, then so will a short thin implant. Okay, I’m now going to summarize what short implants mean. To your patients they mean that they can avoid bone grafting. They can have treatment that is less painful, with less morbidity, that’s done quicker, that’s done when they can still wear dentures if they need to, treatment that is more affordable for them. What do short implants mean for you? Well it means that you’re going to be putting in a whole load more implants. Patients don’t want bone grafts, patients want teeth, and if you can offer them implants without bone grafting you’ll have a lot more of them coming to your door. The truth of it is short implants work. It’s a fact. Every single piece of recent literature shows that they work exactly as well as longer implants. Bring them into your practice, you’ll enjoy it. My name is Bill Schafer, thank you very much.