Get ready for the best summary of bridges you ever heard, including diving deep in to this mystical design of bridgework called ‘fixed-movable’ bridge.
You cannot search about Bridge Design on Google without landing on the great content that Prof Paul Tipton has released.
Protrusive Dental Pearl: where to place your grooves for crowns and bridges?
Crowns: place grooves mesial or distal, or mesial AND distal. Ideally in tooth and not in core material (we elaborate in the episode). Why mesial and distal for crowns and bridges? The forces will be transmitted bucco-lingually on a crown – therefore grooves perpendicular to this force vector to resist it would be mesial/distal.
How about for bridges then?
For conventional bridges the grooves are placed buccal or lingual, or buccal AND lingual.
This is because the forces are now acting antero-posteriorly on the bridge via forces on the pontic(s). The buccal/lingual grooves will resist antero-posterior forces.
Prof Tipton and I discuss:
- The benefits of fixed-movable bridges (such as negating the need for parallel preps of abutments)
- The contraindications of Fixed-Moveable bridges (such mobility of abutments)
- Why fixed-moveable bridges should be the default design
- Myth-busting Ante’s law
- What is the maximum span of fixed-moveable bridgework?
- What are the rules that govern cantilever bridges?
- what about mesial cantilever vs distal cantilever? Why is Distal cantilever worse, and is there any evidence to back this up?
- The steps in planning for Bridges: 1. Design anterior bridgework first 2. Choose your abutment teeth 3. What Design? (F-F, F-M, Cantilever?) and 4. Type of retainers for the abutments (Adhesive retainer, conventional crown, onlay etc)
- We discuss an actual case and live planning for a Fixed-Movable bridge
- Where is the fixed-movable attachment housed? Anterior or posterior? Inside the abutment or outside of it?
- The one thing you must do when placing Fixed-moveable bridges or you would have wasted the time and effort:
Remove a small portion of the male component – about 0.25mm on average
If you enjoyed this episode, you will like the complete denture tips given by Dr Mark Bishop – check it out!
Click below for full episode transcript:Opening Snippet: For me, this is 100%. Okay? I know we should never say 100% in dentistry for 99% that the fixed movable attachment is always on the distal aspects of the anterior retainer...
Jaz’s Introduction: Hello everyone and welcome to another episode this time with Professor Paul Tipton. Listen, if you’ve ever been a student, or in your foundation year, and you want to find out more about fixed prosthodontics, you turned to Google and you start searching about bridges. You can’t get very far on Google without coming across Paul Tipton’s papers. In this episode by the way is absolutely full of bridge work gems, which I think are so helpful. So we’re going to talk about all things fixed movable bridges, the common mistake areas that dentists make when it comes to bridge work and bridge design. We also talk about grooves, so my Protrusive Dental pearl for you is when you’re placing grooves for crowns, placed them mesial and distal. When you’re placing grooves for bridges, placed them buccal and lingual or buccal or lingual. Same with the mesial distal is mesial or distal or mesial and distal. And so does that make sense? We go into in more depth. So to find out exactly why those rules exist, then you have to listen all the way to the end of the episode. Because towards the end of the episode, we discuss all that. But there’s so many gems in them. The meat and potatoes of the episode is basically about fixed movable bridge work, the nuances of it, when to choose it, what are the contraindications to fixed movable bridge work? It’s actually interesting actually that fixed movable bridge work is their default design. Prof. Paul Tipton says actually you shouldn’t be finding reasons not to do it and and therefore settle for fixed fix. Whereas in dental school we don’t really get taught or certainly in my experiences that we didn’t really get taught that much. And I never placed a fixed movable at Dental School. So I hope you find this episode useful. And I’ll join you in the outro.
Professor Paul Tipton, thanks so much for coming on the Protrusive Dental podcast. How are you today? [Prof Paul]
Yeah, good. Thank you. Yeah, looking forward to sunny day. Hopefully, we’ll have some good weather today. [Jaz]
Good weather and a good chat ahead. So for those listening in the future years, we’re coming to the end of lockdown. We’re starting to get back into work. You’ve been doing great things in the education, part of your teaching, educating dentists all over the world, which is usually what you do. This time, using the power of the internet. I saw your video right at the beginning of lockdown that got thousands of views, you know, saying that, you know, let’s make a difference. Let’s provide some education. So how has that journey been for you providing education, you know, pretty much on almost a daily basis. [Prof Paul]
It’s been pretty tiring. We had four people who are working for me. So at the moment, we’ve got sort of, obviously no income because we’re not doing courses. But rather than furlough all the stuff we put our four main guys with this to work doing something else for the profession. So what we’ve been doing is trying to give free webinars, free education to the profession during this time. And in some days, I think it was today we’ve got three webinars on one at 9 o’clock, one at 1 o’clock and one at 3 o’clock. [Jaz]
All bases covered. And I have to say the caliber of the speakers you’ve had on have been great, and I think is wonderful, what you put on for everyone. So you know on behalf of the profession. Thank you. But today, we want to touch on something that I know very dear to you. And I can only assume that because the reason I want to speak about this topic is as a student, I remember googling about bridges. And you can’t get very far on Google, by Googling about fixed prosthodontics and bridges without seeing your name plastered everywhere, and seeing your papers that you’ve posted on your website and stuff. So you are definitely someone who would be a great person speak about this. You know, we could have picked up many of topics that we could have, but let’s just hone in on one. And that’s bridges. So the first question I’m gonna ask you Prof is, I think and tell me if I’m wrong, it’s my perception, I see that, from what I understand people who used to do the masters courses at Eastman, for example, in the 60s and 70s. It used to be lots of fancy bridge work and whatnot. And then implants came along, and then we went more as a profession more towards implants. But do you think now that perhaps dentists are becoming a bit more cases selective about the implant cases, and that the role of bridges has become, has resurfaced again? Is that a fair comment? [Prof Paul]
Yeah, I think that’s a very fair comment. I think it’s happened. Everything in your life, Jaz, if you live long enough, everything in your life comes full circle. I mean, everything, flat houses come back into fashion. We can talk about something that you were talking to Jason about verti preps, suddenly they’re back you’ve yet in the 60s and 70s. There have been done so everything comes back around. And I think the major stumbling block for implants has been in the last 10 years, the rise of peri-implantitis. And if we look maybe 10 to 20 years ago, we would have taken the brand of art studies. And we’d say to our patients, yes, you’ve got 90% success rate over 15 years, there’s no reason why that should not last 20, 30, 40 years. That’s all changed. Talk to any implantologists, who are worth their salt now, and ask them the question, how long is my implant going to last? And most of them will be saying, well, maybe 15 years. I’m not gonna say anything more than that, because we don’t know. And that’s our problem. So that brings it then into the realms of bridge design as well, because I wouldn’t be doing a bridge for somebody unless they really pushed me without saying this should last 15 years plus, it’s fixed prosthodontics. I do my fixed prosthodontics from a science base, we know what works in the science, and therefore there’s no reason why my fixed prosthodontist should not last a minimum of 15 years. So I think we’ve got this now lovely situation where bridge work and implants will probably be lasting the same amount of time. So we can be very selective with which cases are the right ones to do. And you say, you’ve got a missing six and a low sinus. Do you put the patient through sinus grafting and an implant when the seven behinds got a large MOD and the five imprints got a large MOD, for instance? Or is it better long term to do a fixed bridge there or fixed movable bridge and take the patients away from having the surgery? So I think your questions are fabulous one, and I think yes, implants are going down a little bit, bridges are coming up. And now we can be very case selective. Or one major problem, however, is that people don’t understand bridge design. It’s not taught. And therefore you know that there’s myself obviously that lecture about it, and probably one or two more, but not that many, until you go through university. And most of the time, the University guys are still saying Antes law, and Ante’s law got [debunk] several years ago. So it’s not taught. [Jaz]
So true. And then that’s why when I was googling about to find out more knowledge about bridges, and that’s when I learned about you Prof. And that’s where you came into my radar. And I’ve been to a couple of your educational events, which is very, very good. And that’s what we can explore further in bridge design. So, you know, you’re someone who’s been educating dentists for several years. What is the most common area of lack of knowledge, let’s say or the common myth that you want to bust? Or the weakness area? I mean, yes, in general, you’ve touched on very nicely there that Yeah, bridges are not taught as well as they perhaps should be ante’s law. So ante law could be one of them. Are there any other misconceptions that young dentist may have? Because of the lack of training about bridges that really might annoy you? [Prof Paul]
Yeah, I think, if we just go back a little bit, the bridge will involve doing usually not always usually a full crown preparation, or a fairly largest preparation. The first myth is that all young dentists are taught from a very early age, it appears that if you do a crown prep, then you’re going to have 20 to 30% of those going on by, Okay? And I want to just throw that away, not even [Jaz]
touching on the Saunders and Saunders, sort of paper and whatnot. [Prof Paul]
Yeah, that’s not the science. The science shows, as those studies are done without teeth being vitality tested before they were crowned. Now, if your vitality test before crowning, and you’re quite stringent with those vitality tests, and if you get a non vital response, you do a root filling, that drops down to about 5 to 6%. And that’s some French studies that the French are quite big on root filling before they do crown work. But they’ve got some good studies there. So that’s the first myth. And that drags itself then into fixed bridge work, whereby dentists don’t want to do a bridge because they’re worried about the tooth losing its vitality. [Jaz]
Well, you know that saying Prof.? Crowns, kill teeth. Bridges kill them faster. Is there any truth to that? [Prof Paul]
There can be if it’s not done properly again. So we then come a little bit more into the nuances. And I suppose one of the myths is that all bridges should be fixed, fixed. And I teach an awful lot about fixed movable bridges. And one of the great aspects about fixed movable is that you don’t have to get both abutments parallel. So you’ve got your typical missing a lower six, you five’s looking like that, you’re seven’s looking like that. To put a fixed bridge in you have to now really over prepare that seven. Okay? But what we’re talking about more and more, and this has been around for a long time, fixed movable isn’t something new, but again, [Jaz]
but it’s not taught. I was never taught about it. [Prof Paul]
Prepare it down to it’s long access. So we know how one path of insertion for one tooth one path of insertion for the other. The joint together with the stress breaker called the fix movable part. And that means that you don’t have to over prepare is now just like doing two crowns. Now you can’t do that for every single case. But when I lecture to my, my students, I go and say to them, you’ve probably been taught that you’re going to do a posterior bridge today for the patients. You’ve been taught that some posterior bridges should be fixed movable, but you can’t think why, therefore, you’re doing as a fixed, fixed bridge. Okay, I think that the, the thought process goes to a lot of dentists mind, I would like them to choose the opposite scenario. Okay, to get a complete shift, and say it’s a posterior bridge, it is there for fixed movable, and there are one or two reasons why it should be fixed, fixed. And if they do that, you’ll have far better success rates long term than just doing everything fixed fixed. [Jaz]
Well, let’s just emphasize what you said that I think what you said there was really great. So by default, when we’re thinking about bridgework, that what you’re saying is that the default option actually should be the fixed movable, and you should have to justify the few reasons where perhaps thoses that’s not suitable and should be going for fixed fixed. So which are those couple of reasons, but actually, we should be doing fixed, fixed and not the default. And I’m gonna we’ll get into a bit more about the nuances of fixed mobile, but what are the contraindications to fixed movable? [Prof Paul]
The major contraindication is mobility. So if one tooth is mobile, then it should be fixed, fixed. Otherwise, by having two abutments together, on one of them’s mobile, you’ll get an increase in mobility. So that’s the major one, there are some smaller ones such as the fixed movable usually means there’s going to be metal showing in the joint, which to some patient, especially in the lower jaw, maybe a contraindication. If the opposing tooth to the Pontic, or distal abutment, isn’t there, then the fix moveable can actually over erupt as a contraindication. And the other one is length of span. So very, very long bridges are not ideal to be fixed, movable, because that puts too much stress on the distal abutment. [Jaz]
Is that like a ratio? For example, can you do let’s say we got a lower right four and you’re missing the lower right five and six. 4:7? Is that the limit? Or would you say? [Prof Paul]
Generally, we would say that, again, very generalization of all three unit, posterior bridges, fixed movable, all five and six unit posterior bridges fixed fixed. The four unit is the transition area, where we have to look at other things such as mobility, such as the quality of the abutments, et cetera. [Jaz]
Brilliant, well, then before we go into a bit more on fixed mobile, what you haven’t mentioned yet is a cantilever. So what are your thoughts on conventional cantilever bridges? Let’s say we have a missing six and you’ve got a heavily restored seven and the five is unrestored? Yes. You could do a fixed movable I’m sure. But what about the you know risk? Canterlevering after seven to replace the six? Are you concerned about the talking? We’ll talk about mesial versus distal cantilever as well. Tell us about your thoughts on cantilever bridges. [Prof Paul]
Okay, so, generally cantilevers work very well. So cantilever bridge work is the only bridge work where we now design it going back to Ante’s law. Okay, so Ante’s law is going out of the window. Apart from cantilever bridge, it’s quite a nice resume of Ante’s law. We know that periodontal ligament space of the abutment to should be equal to or greater than the teeth that were being replaced. Interestingly, in Ante’s law, Ante also talks about fixed movable bridges. And that is the 1926 paper. And it’s movables being advocated by Ante, nobody picks up on that. But if you read the paper, he talks, every single posterior bridge, ideally should be fixed, movable, so that’s the sign. So we know that cantilever has worked very well. But we now have to go by Ante’s law. So at the front of the mouth, fine, we’ll have done central upper central lateral upper canine no problem. As we go to the back of the mouth, the only realistic time where a cantilever would be okay, from Ante’s law point of view, would be a premolar of a lower. So I’m very comfortable doing a five upper six, or if the fives missing and the six has come forward of four upper six. So we’ll move on to your question, which is the six upper seven. So what’s been found with those is that and these are Swedish studies longer and people like that. They found that It depends what’s in the opposing jaw. Because if you have a six coming off a seven, and you have a lower six, which is there, it’s not splinted to anything it can over erupt, what will tend to happen over a period of time is the lower six will over up by a few microns, that’s all. And the Pontic will then be in hyper occlusion as the context in hyper occlusion, then that will put a torquing force on the distal abutment. And there’s a possibility that we can start to get orthodontic movement of that seven due to the over eruption of the six. So one of the ways in which you could do i’m not saying don’t do these, one of the ways in which you can do this is to continually go back every six months, and adjust either the lower six tooth, or the upper six Pontic. Keep it in that hypo, not hyper occlusion. Another way would be, let’s just say for instance, the lower tooth is a bridge pontic or bridge abutment, it can’t over erupt, and therefore Yes, you can do a six off a seven, keep the six gently out of occlusion or again, occlusion and you don’t get the overeruption. So you can do these, it very much depends on what’s happening in the opposing jaw. [Jaz]
Just to clarify on that, if you have a lower six, and we’re worried about it over erupting into an upper six pontic, then if we design it so that it’s very light contact in MIP and no excursions. Why is it that they still over erupt? [Prof Paul]
If we look at vertical dimension, generally, teeth are always over erupting. So we have these compensating mechanisms that are going on all the time. We have this we love a little bit of tooth wear, and we have an over eruption. So that’s alveolar bone growth. As you mentioned, deposition, happens all the time throughout life, slows down in the older patient much more quick in the younger patient. So everything I’m doing, if I’ve got an older patient, I’ve got a much greater chance of being able to work with that patient to stop the over eruption because it’s not happening quickly. So what happens is we bite on the upper Pontic. Okay? and straightaway the upper Pontic will move slightly, because we’re biting on it with a bolus of food. Okay? t will stay there, it will spring back at some stage, but we will also have then a micron or two of over eruption. So this over a period of time has a cumulative effect on those compensation mechanisms just going on all the time. [Jaz]
I love your fantastic direct good answers. I’m really enjoying this chapter. Okay, so one thing I spent a long time researching once one time was to find the evidence base for mesial cantilevers versus distal cantilevers. Because in a mechanical and physics viewpoint, it makes sense that distal cantilevers are not great, especially posteriorly, or those torquing forces. It just it doesn’t make sense. And I think it might be I’m guessing it might be one of the things that will never really get evidence for. And it’s a bit like you we know that we don’t need evidence that if you jump out an airplane without a parachute, that sort of thing. Am I right in thinking that actually that we don’t need evidence for that? Or we’ll never be able to get evidence for such a study like that, and that distal cantilevers by the nature of the forces are, tend to be avoided? [Prof Paul]
Yeah, I think that there’s certain things in dentistry, we’re never going to be able to prove, as you say, just that we can’t prove them also means we can’t disprove them. So it doesn’t mean because we can’t prove something that it’s not right. And sometimes you might look at it completely differently, say, Okay, you go ahead and disprove me, you can’t disprove me, therefore what I’m doing is Okay, so we’ve got that sort of status quo in science generally. So we’ve got two things happening with the Mesial Cantilever vs Distal Cantilever. The first and obvious thing is, the further back in the mouth, we go forces increase, we get closer to our joint, we get closer to the fulcrum we get increase in stress, and we have the potential for the Nutcracker effect, class two leverage which will increase forces on the tooth. If the tooth happens to be a Pontic, there’s going to be more force on there and therefore more bending force on the abutment tooth, that’s number one. And number two, we have something called Mesial drift, and all our teeth are mesially drifting throughout life. That’s why as we get older, we tend to get a little bit more imbrication of our lower teeth. That’s why when we lose a lower six the seven tilts forwards it doesn’t tilt backwards. So with the mesial drift, mesial cantilever sort of fits in without mesial force that the tooth is used to having. They’re not used, the teeth are not used to having a distal cantilever force. So those two things together leads me out I think other people to suggest that we do distal cantilevers, but we have to increase the abutment numbers and the root surface area of our abutment teeth when we’re doing a distal cantilever. But all we have to say to our patient, this is not a brilliant idea. Maybe in these instances, implants are far better if the patient can’t have an implant, okay, for whatever reason, we have to go with what the science tells us. And what’s important again there is to try to stop any over eruption from recurring. [Jaz]
Brilliant, thank you so much. I think that’s a common question we find, you know, Mesial Cantilever, Distal Cantilever base, I think you’ve answered that very succinctly. So then the last part of the podcast, so we’re gonna focus in on something that you’re very passionate about educating because honestly, the if you actually type in on Facebook, fixed movable bridges, it’s just, you just educating dentists on the various threads for dentist by dentist, dentist UK, Australian threads, American you name it, Indian threads, you’re just there. And you’re always you know, helping people out, actually design it that way, design it this way. So it’s great to see. So I know there’s limitations. Obviously, we’re doing this video component, a lot of people listen to the podcast, there are some limitations. And I urge everyone to check out the content that you put out there is really great on fixed movable bridges, some cases that you’ve posted before as well, but we can maybe tackle some of the nuances. For example, let’s talk about, let’s make it tangible, let’s talk about scenario and how you would design it. Let’s say we have a missing upper right four and five, we have the six which is got a large MO composite. And the canine is got a small, conveniently at small distal composite. Missing premolar we’ve got canine and first molar both restored to some degree. How would you design it in the sense that where would the male part of the connective be? Where would the female part be? Any advantages of doing it a different ways? If we’ve talking about in that scenario, if that’s okay? [Prof Paul]
Sure. The first thing that we would decide so when we do bridge work, and when we do bridge design, we have to go through a scenario whereby we go through treatment planning, we come up with what we think is the ideal. So [Jaz]
actually, you know what I’m gonna do something, I’m going to show you a photo I’m actually ever scenario that can show you that is this scenario that I’ve just remembered. So that will be really cool for people watching. Sory to stop you there prof. I think add more value. Okay, so can you see that? [Prof Paul]
Yes I can. [Jaz]
So there’s the canine and it has got a small distal composite. There’s the first molar, it’s got an actually a DO not an MO composite. So it’s fairly close. Is that the sort of thing that you had in mind when i described the case? Brilliant. So that’s a little visual for people to get that people are visually minded. So yeah, please do carry on about how you were saying how he would actually plan and think about bridgework. [Prof Paul]
Yeah, so so we plan a case. First of all, we have four stages in planning the case. Okay, number one is, if we’ve got bridgework, potentially in other areas of the mouth, we design the anterior bridge first, and then the posterior bridge later. Okay? So that’s number one, always designed from the front going backwards. Number two, is to choose your abutment teeth. Certain abutment teeth are not great teeth, such as mobile teeth, such as post crowns where there’s no ferrule, and it may well be that you decide that you’re going to take a tooth out and make a longer bridge that will have a better success rate than keeping a poor abutment. The next one is to go and design the actual design itself of the bridge. So is it going to be fixed, moveable? Fixed, fixed? Cantilever? Multiple abutments? Coping design, that sort of thing. And the final one, then is to go and design or choose the actual retainer type. And is that going to be a crown, three quarter crown, inlay, onlay, Maryland wing, etc, etc. So that’s the way in which we’ll take every single case. So in this case, it is no other bridge work. So we’re just going to design that bridge work. We look at the abutments the three is healthy, the six is healthy. So we have no problems there. We now go and look at the design. So the design is going to be dependent upon mobility. So is the six mobile? No. /-no mobility/ Three mobile? No. So that gives us the opportunity to go fixed fixed or fixed movable. The next thing we’ll do then is, again, look at root support. Are they short roots? Are they long roots? I presume the six and the three have got reasonably good roots. In which case then you have the scenario, do we go fixed, fixed or fixed movable? There’s no contract indications to fix movable and therefore we go back to some of our studies which show that fixed movables because they have a stress breaker, there’ll be less stress on the abutment teeth, less chance of fracturing off, less stress on the cement lut, less chance of cementation failure, less stress on the porcelain, therefore less chance porcelain fracturing. And we go back to some of the studies that say those potential for failures can add up to about 50% of all the failures that occur in bridges, versus what’s the percentage of failure occurs in bridges due to occlusal overload. And that’s about 6%. So your way up the two things here, and you come to the conclusion. What I would do, the fixed moveable would be the better long term solution. Now, if any of those teeth were mobile, straight into fixed, fixed, okay? So we’re into fixed movable the final stage then is to go and decide what our retainers are going to be. And we know from our retainers, that the best long term retainer for success is a full crown. However, as we know, full crowns can be very detrimental to tooth destruction, etc. So can we get away with other types of retainer? And we look at the science that says in fixed movables, there’s not as much stress on the cement lut, therefore, we can go with retainers, which are not as retentive as a full crown, and therefore not as destructive. So for me during this, I’d look at the six and say, that six looks as though it’s got a pretty hefty composite. Looking at that six looks as though those buccal walls are not that thick, therefore I’m probably going to go and do a full crown on that six, that would be my thought process. Distal composite, we know that inlays, for instance, or a Maryland wing would be a reduction in the amount of tooth destruction. So it’s going to be a little bit easier for the patient, easier for the enamel of the tooth itself, if you don’t go and traumatize it as much. So for me, I’ve now got the situation, shall I use a distal gold inlay? Or should I use a Maryland wing? The Maryland wing is going to obviously change somewhat my guidance. And it may well be I look at that and say, you know what the patient doesn’t have canine guidance, the canines aren’t contacted. And therefore I’d like to put something onto the palatal aspect to give contact and give guidance. Another part would look at it and say, the canines, fantastic, it’s a gorgeous looking tooth, we’ve got great guidance, the patient’s not bruxing, why change that palatal inclination at all. And therefore I’ll go with a distal gold inlay. So that’s my thought process. At the end of the day, no one bridge is right or wrong. All we’re doing when we design bridge work, is we try to get three things into every fixed restoration, we do. We want maximum longevity, we usually want minimum preparation for that. And we want to get as good or aesthetics as we can. So that can be a single crown, it can be all the way up to a 8-10 unit bridge or whatever. Well, those are the three factors. And we’re always looking to try to get those three factors in our favor. Now, what we do find over the years, however, is that no one restoration will satisfy all three. So we have to make a choice. And we have to usually say to our patient, choose to which two out of those three are the most important for you. And then we can design a restoration. So for instance, if I was going to do that bridge, and the patient said, maximum aesthetics, absolutely maximum aesthetics, I’d be probably thinking I’m going to go to zirconia. But that’s going to have to be a fixed fixed bridge. And so I’m going to have to take more tooth tissue away. If the patient said maximum longevity, I’m probably going to go and put a gold crown on the six as an abutment. So we have to work within those three parameters, but also discuss with the patient what they want. [Jaz]
Well, what was the third parameter? Sorry you say longevity, conservation [Prof Paul]
Longevity, minimal prep and aesthetics. We can’t do any restoration we do. We cannot get all three. We don’t have that gorgeous scenario. [Jaz]
Perfect Well, since we’re doing amazing time, and you’ve literally covered a blitz through the bridgework in such a I mean, the nuggets people are going to take home from this bit alone is fantastic. So it’s just a homerun on that final part of the design design process of the nuances of that fixed movable. If the inlay, if the gold inlay is on the canine and that’s facing distally and you have the full coverage retainer on that first molar. How do you then instruct the laboratory to design the male and female components? Because I believe there are a couple of ways to do this. And there are a couple of camps. Can you just talk a little bit about that and where you can find out more information? [Prof Paul]
So for me, this is 100%. Okay, I know we should never say 100% in dentistry, the 99% that the fixed movable attachment is always on the distal aspects of the anterior retainer. Okay? So the anterior retainer, in this case, it’s going to be the canine, it’s going to be gold inlay will house the female, which is the slot. Okay, the male portion, which is the rod that fits into the slot is always connected to the Pontic. And the Pontic is always connected rigidly to the distal abutment. So for me, it’s always in that distal aspect. Now, it depends in that distal aspect whereabouts you put it, you could with this gold inlay idea, you go and drill a box, in your scenario, you’ve got a distal composite. So you’re going to drill that distal composite out, tighten the wall, so there’s a little bit more retentive print inlay, you’ve not lost an awful lot of tooth tissue there. But you’ve got now a box into which the female can be housed. Now the advantage of this is that when the male bites up and down, the road goes into the tube, and the tube, the force is now put down the long axis of that canine so we get really good forces down the long axis. Now the second scenario, not particularly in this case, but if we’re doing say, a crown, a full crown with a female attachment. The second scenario is now that the rod tube, we do not cut a box. So to get the female down the long axis, we have to cut a box. And that box is usually about two millimeters wide, two millimeters deep. Now if that’s a perfectly healthy tube, let’s say the we’re doing using an upper four, and the upper four has an MO but nothing distally. You then say to yourself, should I cut a distal box, a four millimeter square distal box just to house that female so forces can go down the long axis versus if I just do a normal crown preparation, my attachment will now be slightly off axis. So when I bite up and down, there’ll be some off Axis forces. What’s the root like on the four. Does the four have a good root and good bone support? In which case potentially it can take that stress. So again, always on the distal of the anterior abutment, but it can be housed internally, on the edge or externally. The other aspect that we should know about the fixed movable is the technician initially, he buys this from a company such as [Sondra Materia], or something like that. It’s a plastic burnout. And he waxes it into his reconstruction, so that the male actually bottoms out and hits the bottom of the female. So that’s how it’s returned to the dentist. Now as a dentist, as a clinician, we need to therefore take a little bit off the base of the male to allow this movement to occur. So if you just cemented in place without having adjusted the base of the male is now acting on the loan like a fixed fixed. [Jaz]
This is a really key point here. So those listening and watching right now, you have to really hone in on that because that could be a complete waste of you doing the fixed movable. So what Prof is saying you have to remove the base of the male, so that it has that sort of give and that space to actually act as a stress breaker, which is the whole point. That’s a really, really key point. [Prof Paul]
Yep. And we usually take about a quarter of a millimeter off it. And the lovely thing also about fixed movables is that we can selectively put more stress on to one of the abutments. With a fixed fixed bridge, you bite on it both abutments take the stress and therefore if you have one weak abutments there’s no way you can protect it. Now with a fixed movable, if I have a weak abutment, especially if my anterior abutment is weaker, if I take a little bit more than my quarter of a millimeter off, that’s throwing more stress onto my distal abutment protecting my anterior abutment so we can play around with the nuances there and protect teeth to get that extra little bit of longevity even more. [Jaz]
That is absolutely fantastic, honestly, Prof you’ve given such concise learning points for bridges. I’m absolutely really pleased with all the knowledge I know I’m going to get loads of messages saying “Wow, Prof just gave out all the answers and it’s a great way.” So I’m really happy with all that choice. If you’ve answered every single question I had about bridges. This is a. look this is a complex rule, every scenario, every mouth every every patient is unique so that anytime I give you a scenario And you have his methodological system to go through and design. But at the end of day, every case will be different. And there’ll be some nuance in each case. For those wanting to learn more and go on any hands on training that you might have about this. Can you tell us a bit more about how we can come on to those? [Prof Paul]
Yes. So Tipton Training, as you’re aware, we’ve been doing courses, [PG materials, Diplomas] for many, many years. And we’ve been doing this for, I hate to think it’s about 25 years now. And the courses have obviously evolved as dental science evolves. But we do a full day on bridge design, which is, it is a full date to understand it fully. It’s going through the papers, and I’m a big one for self discovery. I’m not when we do our courses, I don’t like to just lecture to people, I think lecturing is a really poor way of getting knowledge across. So when I went down to the Eastman all those years ago, to do my master’s degree, it was the first time that I’d ever experienced sitting in a group around a table and discussing things and having a mentor lead the discussion. The mentor knew where he wanted to lead it, what everybody else in that room was discovering things for the first time. And that really stays in your mind. So what we do to teach bridge design is we go through about 20 papers, and I leave the discussion, and I let the guys in the room go, ‘Ah, that’s why we’re doing that.’ And that just stayed with people. So it’s a far better education method. So I down bridge design, we have about 10, till two in the afternoon, where we do four hours, it’s a tough day of pure science, the lectures, we then have a lunch break, and then I follow that up with two hours of slides, going through my lecture showing obviously photos, case scenarios, etc. And then we also have a full day on the Phantom head, the operative course that we do at Tipton Training, where they go into the lab, they have webinars before that, so they can get all their information, again, via webinars. And then they spend from 10 o’clock till 5 o’clock, prepping various bridge designs, which we put in front of them. So that’s how we do that. That’s part of our restorative courses. I don’t go and do any other one day courses on bridge design, because I think for bridge design, you have to understand dentistry, as you’re trying to get through there. And you made the point really well, the nuances are key. And the nuances come from and [Jaz]
This is why, Prof I had you on but I realized that you know, a lot of people this might be the first time to learning about fixed movable. I have a very, very young audience. And they may be learning about fixed movables for the first time. So I don’t want anyone to go away thinking that they listened to this podcast episode. And now they can confidently do maybe with some mentorship. Yeah, fair enough. There are some great dentists out there. But I think for those who want to really get to the meat and potatoes to consider, and I like what you said about the ‘aha moments’. I think last year, I went to your Watford one day at the Hilton, amongst other things I’ve been to as well, and that I definitely member having some aha moments there. So I like your teaching style. So I think definitely that’s a takeaway point to make sure that Yeah, you’ve got this introductory knowledge about fixed movables. But you may need to find out more about the nuances because really is about the nuances. I mean, we haven’t even covered about the cementation, and how to do that. So there’s so much practical stuff to learn still. [Prof Paul]
Yep. And with every bridge, we can’t get around. It’s the elephant in the room, the Beagle, occlusion. So occlusion matters hugely, how long that bridge will last, whether you get the guidance, right, whether you get the five principles, the occlusion, whether you managed to get no class two leverage it converted to class three leverage, whether your pontics are discluding or not. So we’ve got that. We’ve got another huge topic, which is tooth preparation. To make sure that you understand resistance, retention form and how with a bridge you need to increase, especially fixed bridge resistance retention form. We’ve got lab techniques, and most dentists, unfortunately, don’t understand lab techniques. And throughout the course, we’re always going on about visit your lab, talk to your lab about lab techniques. As an aside, if you don’t mind me for just a minute, one of the major influences on my life my dental life was going down to the basement and doing my master’s degree. And I was we did my master’s degree it was a two year degree. I went down there three days a week for two years from Manchester. And during the daytime usually from 9 till 1 it was a seminar from 2 till 5-5:30. We did our practical on patients. But then from 5:30 to 9 o’clock we’re in the lab doing our own lab work and this is a huge key. If you look at any successful restorative dentist, prosthodontist around the world, okay named the top 10, they’ve either been trained as a technician first [Christian Coachman], something like that, or they’ve got really good technical ability, and they’ve learned how to do the technical side of things. So again, a take home message to all the young dentists out there is understand what your technician does, you’re in a partnership, you cannot get away from that partnership, he needs to understand what you do, you need to understand what he does. And so the mechanical principles of casting of dealing with fixed movable twigs, how the made die spacer, things like that are so essential, and technicians every single day when they’re doing your lab work, face about 10 or 15 decisions, how they’re going to do your lab work. And they might go down the wrong route or the right route. Okay, I’m very often that’s due to financial constraints, you need to be there saying right route, please, right route, please keep on going on the straight and narrow. And that way you get better long term results [Jaz]
The more you can understand about the technical side, the more you can communicate with your technician in a language that you both understand, because there are different ways of thinking about it. So I completely echo what you’re saying, to have that sort of communication with the laboratory and relationship with the lab, which will really help you because they can make great mentors. But also I say that even though your technician, even the twice your age, will always benefit from your ideas as a dentist as well, because they might come to some of your courses, and then come to your way of thinking and they may have been missing a key point in the technical aspect. So I think they can learn something from us and we can learn a lot from them as well. So I think that’s a great point you raise that. So Prof, before I say goodbye. There’s a one more thing I just remember, I forgot to ask you is when you’re in this is going to be my Protrusive Dental pearl and be like okay, so Prof gave me this pearl for today. And this is when you’re placing grooves for crowns and bridges. Is there a rule in terms of, for example, do the grooves for crowns need to be mesial and distal and for bridges, they need to be buccal and lingual, is there a sort of guideline that we how to, where to place your grooves in certain restorations? Can you please share that with me. [Prof Paul]
So grooves are placed for single crowns and for bridges differently. So first of all, we have to go reason for a groove through retention because of surface area, but it’s mostly for resistance form. So the groove was not stopped the crown being pulled off this way. Okay? The groove will give you resistance form, which means the crown being pushed off from a non axial direction of force. So if we look for more crowns, and you still together, grind from side to side, it’s usually a buccal lingual force that will, that’s the direction buccal lingually. Then we put our grooves at 90 degrees to the direction of force. So for a single crown, we’ll put our groove either mesial or distal, or mesial and distal, that will give us more resistance form. So the question then comes is it mesial? Is it distal? The rule state that you’re better off putting the groove in tooth tissue than you are putting it in restoration, if you put it in restoration, then the resistance form is directly due to the actual resistance form of the restoration, which might not be very good. We’ve all had times where we’ve prepped to tooth taken the impression and the cores come out. So sometimes that’s not brilliant. Next thing is, is your groove parallel sided or tapered? Parallel side will give you more resistance form. Tapered a little bit less. If you’re putting multiple grooves in you got to make sure that those multiple grooves are parallel and not like this. Then we come onto bridges and we look at bridges and we say Okay, first thing grooves for resistance form. What direction of force will bring a bridge off? Now it’s not tense does not to be buccal lingual, it’s now anteroposterior. So the usual thing is we bite on the anterior abutment and the posterior wants to rotate off, so it’s anteroposterior and chanted a good paper [TJAN] looking at the anterior and the posterior abutments the posterior is always under more stress, the cement lut and therefore with a bridge which is going to be a posterior one. I seldom put a groove in the anterior abutment, always put a groove in the posterior abutment. Okay, and now because it’s going to be an anterior posterior direction of force, which brings the bridge off. Okay? Where do we put our grooves? Our grooves are now placed buccal or lingual or buccal and lingual and don’t forget also and important part here. We can also get resistance form, increased retention as well occlusally. So very often we will be doing a bridge prep, a crown prep on a tooth that’s got an occlusal amalgam for goodness sake, take the occlusal amalgam out, make it into an inlay. If it’s an MOD amalgam puts a slot down it. And again, you’re going to get several things, you’re going to get increased rigidity, rigidity is really important with bridgework, you’ll get increased rigidity, you’ll get increased resistance and retention form and the other thing that we find with most crowns and bridges posteriorly. If you look at 100, crown bridges, okay, units, aesthetically, the area where most technicians and dentist struggle is when they’re doing occlusal reduction. They never reduce enough in the central fossa. So if my cusp bang goes like this, the prep cusp bangles are like that. Okay? By putting a groove mesial distally, you’re now allowing the technician to get a really nice deep central fossa, which will also increase aesthetics. So don’t forget the occlusal surface occlusal stuff is really important. [Jaz]
What a fantastic comprehensive reply. Thank you so much. Prof that’s been a really, really educational session. I really appreciate you coming on the show. I know how busy you are. And it’s been a great chat. I’ll let you know when the episode’s out and then for everyone to listen to it as well. I hope you have a lovely summer and I hope you get back into the swing of things with the courses and clinics and whatnot. [Prof Paul]
Thank you very much, Jaz. It’s been a pleasure talking. Any other time happy to do another one. [Jaz]
Thanks so much. [Prof Paul]
Jaz’s Outro: So there we have it loads and loads of bridgework gems as I promised. I hope you found that useful. I’ve had so many superstars on recently honestly, I’ve been quite blessed. So yeah, as always, thanks for listening all the way to the end. I really appreciate it and I’ll join you in the next episode.