Welcome to this webinar on the Fundamental Concepts of Device Design. My name is Trish Braga, and it's my privilege to serve as the Educational Director at the AADSM. My goal with this webinar is to introduce a strategy of device design for you to at least consider, not necessarily to adopt hook, line, and sinker, but to use as a starting point possibly, or fold into your own decision-making process, your own formula for making decisions. It's always been my theory that dentists who are experienced in dental sleep medicine have this algorithm built in. They possibly unconsciously, but I think they follow that when designing a device. Typically, their decisions are based upon their mistakes, their hard-earned experiences, what worked before, what didn't work out so great, and they likely go through this little internal checklist in their minds. At least that's what I noticed that I was doing when I was talking to my patients about what device we should be using. When dentists new to dental sleep medicine ask that pretty common question, what device do you like, what device is your go-to device, what device should I use, I started paying much more attention to how I was making decisions in my own office. On top of that, it's really, truly amazing how many devices are developed and released into the market each year, so hopefully understanding these fundamental principles, you can apply this to any device. Any practitioner could use this experienced or inexperienced really to sort out advantages and disadvantages. Let's begin. I don't have any conflicts. My objectives are, well, we'll start with how the devices work, what decisions need to be considered, and how one decision leads to another, then we'll talk about the forces applied by the devices and the impact that that can have on the dentician, and we'll finish with a possible decision-making strategy or algorithm, if you will, that's circular in nature. Not a terrible generalization to say that all oral appliances used for sleep-related breathing disorders do the same thing. Doctors probably don't agree with that statement, but what I mean is it's a foundational concept that all MADs, mandibular advancement devices, function to protrude and stabilize, hold the mandible forward, and thereby improve the size, the shape, the geometry, the patency of the airway. This is, of course, how they reduce this air resistance, and they improve breathing. There was a group of dentists led by a Dr. Scherr, Steve Scherr. They developed a working definition for oral appliances that looked at existing research. This was 2014, and they coined the description, mandibular advancement device. That's the term we'll use today. It was hoped that with this definition and description, it would support future research on effectiveness of these devices. His team excluded tongue retention devices from the conversation because there wasn't enough evidence to support their use, and I'm going to be excluding that from this conversation today. Now, a trip to the annual meeting or any meeting where you see exhibitors can overwhelm anybody, seasoned or unseasoned, and that's because of this variety of new devices that's released to the market each year. It's my wish that with this webinar, it will help any dentist evaluate any device that he or she happens to be holding in his or her hands at any time, virtually anywhere, and then we'll take it a step further because a clinician can then design their devices with the advantageous features for that specific patient that they're thinking of, thereby improving comfort and hopefully compliance. So what I'm really trying to say here is that this is a design strategy. I don't want to talk about selection. I don't want to really think about selection. This is about design. So I've added some references here to support the concepts behind positioning and stabilizing the mandible for you to consider for future study, and I've added a visual here, but of course it's important to understand that every patient has a unique physiology and anatomy, and forward movement of the mandible has differing effects from individual to individual. So what we see on the left here is this large volume of tongue. I'm going to use my pointer attached to the hyoid bone, but the tongue is really not attached very tightly to anything. The hyoid bone itself is not attached tightly to anything. So therefore this tongue mass, which in this patient is quite large, has a lot of ability to close back here in the oral pharynx. On the right-hand side, we see that there is a mandibular advancement device in place. The mandible is protruded now past end-to-end, and we see in this particular patient, because of their anatomy or their physiology, it has made an improvement, at least while they're awake, in the size of their airway. So next, if you attended the Mastery Program, I'd like to remind you of this document that describes and classifies oral appliance design decisions in a more specific way. It's really just a resource to help newer practitioners start thinking about these decisions as they examine the mouth. If you have not attended the Mastery Program or ever seen this document, it doesn't matter, as I'll be covering the bulk of what's in this document here in this webinar. Also, you probably know there are more than four categories of decisions in that document, but we'll only be discussing the first four today because, really, these comprise the fundamental principles. Now I think of it as kind of a circular design. There's like this connectedness between these decisions, and it lends itself to circular decision-making with the primary purpose of making a patient happy, comfortable, successful. And then, if not entirely happy, then at least not unhappy. So I'm going to start with the first fundamental principle, which is materials. Construction materials, and there will be a little bit of discussion on the manufacturing process as we go through this. We can divide it into three general categories, acrylics, metals, and nylons. Acrylics, a material that dentists are very comfortable using. Metals, also very familiar territory. And the nylons, which are part of the biocompatible polymer group. So if we zoom in now on just the acrylics, they're essentially identical to that which we use for partial dentures. These are polymethyl methacrylates. They have the advantage of being easy to adjust or repair, chair-side, even to accommodate dental anatomy changes in the event that maybe some restorative work is done while a patient has an existing device. It's pretty rugged, of course, if adequately thick, but may feel hard to the patient, may feel tight or hard to their teeth. Polymethyl methacrylate can be altered chemically then also to provide varying degrees of rigidity versus flexibility, and even to take on some thermal properties. So such as, well, for example, as becoming flexible at warmer temperatures, meaning like hot tap water, even at mouth temperature. So let's talk about the rigid PMMA. When we begin to consider the manufacturing process, our first option is a historically very common salt and pepper technique performed by a technician in a laboratory. This is an additive process, of course. It also commonly uses metal clasps for retention that are embedded into the acrylic, ball clasps, for example. Alternatively, there is a process of fabricating a block of acrylic under strictly controlled conditions, yielding a uniform density and arguably very free from any impurities. In this latter instance, a precise digitally driven milling process results in the desired shape or the design shape. This is a subtractive process then and has become quite popular of late. This precision may result in improved fit, maybe a more polished surface finish, while eliminating weak areas or fault lines that can occur with the old salt and pepper techniques. Salt and pepper, in contrast, is technique sensitive and may potentially introduce these varying densities, which then, of course, can lead to weakness or fault lines. A second and quite common option in the PMMA family is to have a device made of a rigid shell but with a flexible liner. The flexible liner has a softer feel to the teeth, patients tend to like that, and it rebounds into anatomical undercuts for retention purposes. But it tends to absorb stain, so it can retain odor, absorb odor more readily than hard acrylics for sure. These are often described as laminates. Sometimes they're called flex, sometimes I've heard them called hard soft, and we know manufacturers use different proprietary names for these flexible acrylics. Then the third is what we'll call today the thermals, the third category of materials in this acrylic family. They have thermal properties, and there are two common options currently available that I know of. The first is a laminate that employs a rigid acrylic shell, but it uses a thermal resin that is fluid and remoldable if it's heated to 160 degrees. The advantage here is that a clinician can reheat, remold anytime they want, any number of times, and as you might imagine, it's terrifically useful when a patient is planning restorative changes. It can be very, very retentive also in instances where there are short clinical crowns or lack of undercuts in just the dental morphology. There's another thermal option that is a single phase then, a single phase PMMA, and it becomes a little more flexible when run under hot water, like hot tap water, and that assists patients in inserting the device into the mouth because then it will flex. It remains somewhat flexible at mouth temperature as well, so it might have a softer feel. The other advantage is, of course, this ability to flex into undercuts as it's warmed up and put in without needing the assistance of ball clasps or C-clasps. So technically, the thermal option that's fluid at 160 degrees, we're going to be calling that thermal resin, and the thermal option that is a single phase and just gets softer in hot tap water or at mouth temperature, we're going to call that thermal acrylic. So if you were holding an acrylic device in your hands, it'd be difficult to distinguish what kind of acrylic you're holding. A giveaway that an oral appliance is made salt and pepper, from the salt and pepper technique, is the presence of metal ball clasps for retention. However, being able to identify an unknown material isn't particularly critical anyway. Since we're designing these devices and we're requesting materials on our lab scripts, so we know what we're asking for when it comes back. It's only if you're wandering around the aisles of a vendor booth somewhere that you might not be able to tell, and then you really just need to ask the vendor, like, what kind of material is this, and what material choices do I have for this design of device? Here, an absence of internal ball clasps could be a clue that the device is milled from solid block, but again, it can be hard to tell. These materials keep changing. Solid block tends to be clear, salt and pepper tends to be colored, commonly pink, I've seen it blue, but that's changing all the time. Digitally milled, controlled, cured devices sometimes have this telltale milling line visible on very close inspection, but that's unreliable as well. But a scan from an electronic microscope demonstrates the difference in surface between the salt and pepper technique on the left and the solid block milled on the right. It's pretty dramatic. So the solid block tends not to collect as much bacteria or stain, maybe easier to clean. If one were holding a device with a hard outer shell and a flexible liner, that what we're calling laminate, there would be an absence of clasps as well, but to be sure, you'd really need to take something hard and press it into that inner liner to feel if it has any flex to it, if it's flexible, if there's some give to it, that's one way to tell. So here on the left, we see what I'm calling the thermal resin liner within a hard acrylic shell. It has a characteristically white opaque appearance at room temperature and at mouth temperature too, but when it's heated to 160 degrees or thereabouts, it becomes fluid and clear. The one on the right is single phase. So the one on the left is laminate. The one on the right is single phase thermal acrylic that's heated in hot water and then warmed like that before seeding. One clue again is the absence of ball clasps or other retentive clasps, but you can't tell by looking to know for sure, of course, you'd have to have ordered it or ask the manufacturer. So the next material classification is the metals, and they are often used in combination with acrylics because they provide so much strength. All metal devices are relatively uncommon currently due to the expense involved in casting precious alloys like we do for partial dentures. On the other hand, metals are commonly used in propulsion mechanisms. Let's see, they're used to reinforce acrylics for better strength or as retention clasps or as a means of attaching orthodontic elastics to a device. I'll show you some examples of that coming up. This though is an example of a relatively new device that is primarily metal in construction, and it does demonstrate a clear advantage of offering strength without too much bulk. So now this brings us to the evolving area of biocompatible polymers. The most common on the market is nylon, manufactured through a printing process. These are pretty easy to spot because they have this characteristic white opaque appearance. They are incredibly light, very flexible, and very durable. This makes them tougher to adjust chair side though, tougher than acrylics are, but they do snap nicely into undercuts, and you can increase or decrease the retention somewhat By warming them in hot water or with a torch, or by crimping them with a hot instrument, they are BPA and phthalate free, and so not proven to cause any allergic reactions. So you'll often hear to them, but refer to as surgical grade nylon. Okay, so why are materials so important then? Why do I call them the fundamental principle of device design? Well, simply put, the materials lend properties to the device that can be an advantage or a disadvantage depending upon the patient and their individual needs. Certainly if a patient has an allergy to an acrylic monomer or to a particular metal, that would stop a clinician from going to that particular device design. But short of an allergy, a choice of a material largely involves a decision about retention. Strength and thickness also come into play during those decisions, as well, with stronger materials lending themselves then to thinner and less bulky device designs, which is often advantageous. So first and most obviously, there is a great downside risk to not identifying a patient's allergies before a material choice is made. Acrylic devices often have metal hardware, too, so this needs to be considered. Although less common, patients can be allergic to acrylics, especially the monomer component. Controlled cured blocks of PMMA that are used for those milling or mill devices that we talked about, they have much less monomer available, and so, of course, nylon allergies are very rare. So this now brings us to the relationship between material choices and retention choices. To me, this is a critical, critical step in device design. It involves a thorough examination of the patient's mouth, their dentition. I consider retention to also be a fundamental principle of device design. Having a non-retentive device is arguably as bad as designing a device to which the patient is allergic, as you can't wear it. It's pretty simple. Devices retain by either flexion into undercuts or by frictional resistance to displacement or a combination of both of those. Anatomical undercuts beyond the height of convexity on individual teeth or into interproximal spaces provide a retentive opportunity for these flexible materials. This includes flexible acrylics, thermal acrylics, metal ball clasps or other kinds of metal clasps, and flexible nylons. Sometimes tooth angulation and arch form confound a path of draw, so a device needs to have a full arch flexure so that it can pass beyond lingually tipped teeth, as in this case, especially those molars. We see lingual arch collapse much more commonly on the lower, I think. On the maxilla, it's more common to see molars flaring facially, second molars in particular. So it's important to get back there to the second molars in particular to take a good look. Nylons work quite well in these instances as they often have this cross arch flexibility, as I've put in this slide. This is somewhat dependent, though, on the bulk and the geometry of their design at the midline, at the dental midline. The one we see here has a simple flat band at the midline, which allows for a lot of cross arch flexure, and that can be a design decision. Parallel to surfaces lend themselves, then, to frictional retention, particularly in the absence of undercuts. Back in the day, before we had these wonderful dental bonding cements for dentistry, this was the same strategy employed for all full crown preparations. We know that a narrow path of draw created by near parallel walls resists displacement. Both the arch form and the individual tooth shape should be evaluated because frictional resistance from parallel surfaces can occur across the arch, too, say, from the buccal surfaces on the right to the buccal surfaces on the left, not just from buccal surface to lingual surface on any individual tooth. Mill devices really excel with this frictional strategy due to the precision of their fabrication. Thermal acrylics that are molded chair side, the ones we referred to earlier as thermal resins, you'll remember they become fluid at 160 degrees, oh, 160 degrees also work well, although you need to be very careful not to let that material get too hard before removal from the mouth, because obviously that can get locked into undercuts. So let's just consider for a minute a patient that is a Bruxer or a Clencher, so we're looking for strength here. Strength becomes a very important consideration, but strength and weakness, or I'm sorry, strength and thickness go together, so we have to consider those at the same time. If a thin or lightweight device is a high priority, then a stronger material should be considered, such as nylon or metal. Conversely, looking at it the other way, if acrylic is the most desired material, plans for an increased thickness or maybe a metal reinforcement should be part of the design process. This then leads us to a discussion about vertical dimension. Vertical dimension, or interarch dimension of the device. If we need strength and we pursue it by increasing thickness then we are affecting the interocclusal dimension of the patient's device. You can see how these decisions have this way of chasing each other, hence the circular decision making that I alluded to at the beginning. But wait, it doesn't stop there. If a device thickness is creating more vertical height than desired or is comfortable for that particular patient, sometimes it can trigger a decision to design the device with less occlusal coverage, or what we call extension toward the distal teeth. If one does not extend the materials all the way to the most posterior teeth, the bite will not be opened as far, won't be forced opened as far. But I probably have lost you at this point, so I wanna show you some pictures that could illustrate what I'm trying to say. Here's what I mean. This is a protrusive bite taken on a patient with an exaggerated curve of speed. If we don't look past the anterior teeth during our exam, we wouldn't know that this was a problem back there. So we need to assume, in this case, some minimum thickness of material depending upon the material chosen. So we've got 3.61 in this slide. So, for example, a laminate is likely to have a required minimum thickness that is greater than a hard single-phase acrylic or nylon. Now, we have to also assume that the mandible is gonna track forward protrusively roughly along a horizontal line or along these lines drawn in this slide. So you can see that this would bring the cusp tips of number 17 closer and closer to the cusp tips of number 14 and 15 as the mandible protrudes. So we can immediately conclude that we don't have enough occlusal vertical clearance to place adequate thickness of material beyond or distal to this red vertical line. Here's another example. We have adequate vertical dimension to extend our device all the way back to the occlusal of number 17, the picture that's on the right. But on the patient's right side, which is the picture on the left, we cannot extend beyond number 31. 32 is hyper-erupted there and tipped. Maybe a little bit on the mesial occlusal of 32, we could put material there, but there isn't enough space to cover the distal and the distal marginal ridge and wrap the distal of 32. And yet here's another one, another extension decision. This one's showing how extension is related to vertical dimension and to material thickness. If we cover number 15, which is the picture on the right, then the bite has to be open not only enough to accommodate the necessary thickness of material we've chosen. And for example purposes, we could say we need four millimeters of minimum thickness between the teeth. Then we also have to account for the hyper-eruption of that number 15. So if we say that's about three millimeters of hyper-eruption past the occlusal plane, then we will require the four millimeters of minimum thickness plus the additional three millimeters of hyper-eruption allotment, and that brings us to seven millimeters of opening. So thickness and extension tie into each other. They go together, hence like this circle. Now sometimes an extension decision can lead us into a decision on propulsion as well. Propulsion and attachment, I bundle those together. So like around the circle we go. And this is what I found myself doing actually for my patients, by the way. Sometimes thinking out loud and including them in the decision making, we go around the circle once and then in simple cases you're satisfied, but if you're not satisfied and you get around the circle, then you have to go around again until you hammer out the conflicts you have between these fundamental principles. Here we have an extension decision that is independent of vertical dimension, but does call into question the unique extension requirements of any given propulsion mechanism. You can see that on this blue splint material, it extends well beyond the teeth onto the attached tissue. You can just barely see the CEJ of I think tooth like number four and five and six there, just ahead of the advancement mechanism. But the size of these buccal exostoses, that's gonna limit that extension beyond the teeth. Think also maybe about like a dorsal, a bilateral interlocking propulsion mechanism with a dorsal fin. If that fin was too tall, that could be quite uncomfortable as well depending upon where it was placed relative to those buccal exostoses. Now finally, let's turn our discussion towards propulsion. Sometimes this is referred to as mechanism of action. I personally believe that decisions about propulsion, while important, are no more or less important than any other decision in these fundamentals that we make. And it generally isn't the decision I would make first or discuss first with the patient anyway. I think of materials as the first fundamental property and I generally start there. However, propulsion is important in terms of the forces it applies and where those forces focus. And it can call into a person's dexterity as well or maybe even whether they sleep on their side. And of course, if Medicare benefits are going to be used, a PDAC list restricts the devices it will cover largely based on propulsion. PDAC, you probably know, stands for Pricing, Data Analysis, and Coding. Device manufacturers have to apply to be on this list. I find it amusing that in that definition of oral appliances for OSA article, that was Dr. Sher, they comment in that article that Medicare is using a definition of acceptable oral appliance that is based on, and here I'm using air quotes, serendipity rather than science. I kind of like that they put that in the article. All right, moving on. When you think about how a device works to protrude and stabilize the mandible, it can first be divided into two categories overall, attached and unattached. This refers to whether the upper and the lower splints remain attached to each other when removed from the mouth. To date, Medicare requires that the upper and lower splints be attached when removed from the mouth. Next, we get into whether the device works by pushing or pulling. The maxillary splint is considered the stationary splint. So if you consider the maxilla, the one that stays still, the propulsion either uses compression to push the mandible forward, or it uses traction to pull the mandible forward and hold it forward. Before we go further, I want to show you some examples. The nomenclature we're using here today is based upon this work that was done by Essek in his article, which was published in 2016, not that long ago. These graphics represent, these come from that article, these graphic representations. In addition to the descriptions that you can see in the black font, where it says midline push-pull, bilateral push, bilateral interlocking or fastened, bilateral pull. So these descriptions really have worked their way into the lexicon of dentists like Medicine Dentist pretty rapidly. The nomenclature I'm using today is just an attempt to be used as a little more descriptively accurate or maybe more meaningful. What I'm using today is in green font, attached midline traction, attached bilateral compression, unattached bilateral interlocking, and attached bilateral traction. So this is the attached midline traction. This graphic shows, oh, and this one appears on the PDAC list. If we think of the maxillary splint, again, as the stationary splint, because it's attached to the maxilla, then it's easy to visualize the mechanism located at the front midline is pulling the mandible forward and holding the mandible forward. Therefore, we've referred to that as traction. Distal vectors are concentrated in the maxillary anterior and mesial or forward forces are also focused in the mandibular anterior. For this propulsion design, there is clinical significance to its upper to lower attachment. It's easy to kind of imagine that if a patient did not have retentive anterior teeth, upper or lower, the device would dislodge when the patient tried to open their mouth or maybe yawned in the middle of the night. The devices that are currently available with this propulsion tend to utilize a large key, though, as seen in this picture at the bottom center. The size of that key makes it easier for patients with limited dexterity. That's something to keep in mind. And it allows the device to be advanced while it's still inserted in the mouth on the teeth. Most other designs tend to be advanced outside of the mouth before it's inserted and placed on the teeth. This then is the attached bilateral compression propulsion. It uses a telescoping arm, commonly called a Herbst arm. The arm anchors on the stationary maxillary splint, and it pushes and holds the mandible forward with compressive forces. Therefore, the distal forces focus in the upper posterior, and they focus in the, and anterior forces actually focus on the lower anterior. So, and at this point, I should point out that a well-fitting rigid splint will actually distribute all of those forces we're talking about throughout all the teeth to which it is fitted. It's just that the forces are more focused in these areas, but they're not confined to these areas. So, these are some examples of this telescoping compression arm. The telescoping feature allows the, it's like a tube and a rod. So, it allows the patient to move forward without restraint. The angle of the arm, the way it attaches, which hinges on both of its connections to the splints, allows the patient to open their jaw without resistance. So, this is comfortable for patients, especially claustrophobic patients, but it doesn't adequately stabilize the mandible, meaning it doesn't keep the mandible closed. Therefore, it's pretty common with this style to use elastics to prevent the patient from flopping open at night and rotating posteriorly. So, now let's look at this attached bilateral traction. The first thing you might wanna notice is that the propulsion arm is perpendicular to the arm of that compression device that we just looked at in the last slide. Since the maxillary splint is our stationary splint, we see that traction is used to pull and hold the mandible forward, and the forces are focused differently than the device we just reviewed. Distal forces focus on the maxillary anterior and mesial forces focus on the mandibular posterior. The angle of this propulsion arm actually resists patient opening. It also pulls a patient slightly more protrusively if they do open. So that's a good feature from the standpoint of preventing airway collapse, but it does require that there be adequate retention, especially to the upper anterior and to the lower posterior teeth. So it's common for lower molars to have short clinical crowns, so be aware of tooth morphology choosing this propulsion mechanism. Depending upon where the traction arm is attached or how the splint is designed, the forces change position of course. Here, lower center, the forces focus on the midline, maxillary midline. Here on the lower right and lower left, the forces focus near the upper canines. Finally, we will talk about an unattached bilateral interlocking. It should technically, maybe, also be called bilateral compression, but because we see that the upper splint is pushing the lower splint forward with the interlocking arms, that is indeed compression, and the force vectors are very similar to the attached bilateral compression propulsion, but it has become convention to call this interlocking. So we're going to be calling this bilateral interlocking for today's purposes. When those interlocking arms have a triangular shape, like this one on the lower left, we've referred to it as a dorsal style. There's many manufacturers of that dorsal style. The lower arm conventionally forms a 70 degree angle, and this slope angle allows the mandible to rotate open pretty comfortably. Again, patients like this, especially those claustrophobic patients, but just like in the bilateral compression style, the Herbst style, we often use elastics to keep a patient closed. With 90 degree interlocking arms, there's more friction. There's frictional resistance to opening, and this resistance gets greater the further the mandible is protruded. And here on the lower right, you can even flip that angle into a negative angle, and then there's tremendous resistance to patient opening, and it virtually functions as an attached device for all practical purposes. All right, that said, I'd like to talk to you about this circular thing again. I'm going to take you on a spin and do some decision making, and we'll start with materials and follow the circle clockwise, taking more than one lap if needed, but we're going to start with a very straightforward case. Let me introduce you to your patient. She's bright, capable, 63-year-old, and has a heavily restored mouth. We see a very nice, flat, occlusal plane. That's nice. In the anterior, she has a six-unit bridge retained by four teeth, so the two canines and the two centrals. No buccal exostoses. That's good. She also has a luted three-unit bridge, let's see, in both the upper and lower right posterior. Now, none of these restorations are bonded. They're all luting cement. There are five teeth with root canal treatments, including number nine under that bridge, so that we can assume there's a little brittleness there in that anterior bridge. So, materials. We're going to start by thinking about materials. This patient does not have any allergies, so all three options are going to be open to us. Okay, for retention, then, which is next, there's not much to think about here either, except we want to retain. Well, just as a reminder, we can retain a device with flexion into undercuts, or under tipped teeth across an arch, or by frictional resistance to displacement, like with a crown, or a combination of those. Okay, so let's talk about retention. So, I'm probably going to steer away from the frictional retention as with a mill device, because I'm a little worried about the strength of the teeth under these crowns, not to mention the strength of the luting cements, and I don't want to unknowingly loosen one abutment, say, of a three-unit bridge, and then let it start to leak and all that. So, the arch forms, though, are pretty straight, and the teeth are parallel across the arch, so we have a nice path of draw. It appears that flexion past the height of convexity of individual teeth is probably going to be adequate for retention. So, I'm leaning towards this, towards a laminate, a laminate with a hard outer shell and a flexible liner, because that will be gentle to the dentistry when it's removed. Plus, I'm going to coach this patient on how to remove the device slowly, carefully, don't bite it into place. Laminates can bend and distort if they're bit on at funny angles, and furthermore, unlike a nylon device, if the patient does get a new restoration, which doesn't seem unlikely, then the soft liner can be relieved a bit in the office, so it fits, or it can even be sent to the lab and relined. Nylon has to actually be remade if it doesn't fit the new restoration, and it it might go to place, but it might not be retentive. That's the problem with nylon when you get new dental work. So, I have my material. My material is acrylic, and I have my retention mechanism. It's a flexible acrylic liner. So, then what's next? Extension is next. Flat occlusal plane and no exostoses in the way, so I'm going to cover the entire occlusal surface and wrap the distals of the most distal teeth. So, now this helps prevent tooth movement, particularly on the lower arch, where forward forces can open up contacts between the teeth. I'm also going to extend back on to the edentulous space to help support the occlusion and the joint on that right side. Plus, probably this flexible liner will be kind of kind to the edentulous ridge. So, now we're going to get to our propulsion decision. We're thinking about forces, of course. We're thinking about patient dexterity, sleep position, Medicare coverage, and I would ask, where is this patient particularly vulnerable? So, if we look here again with that anterior bridge on natural teeth, I'd say that's pretty delicate. The bridges in the back are a little vulnerable too, I suppose, to dislodging if our retention is too tight or if the patient removes the device carelessly, quickly, you know, meaning if they pull it out fast instead of easing it out. So, she's this perfectly capable woman. She can advance to any propulsion mechanism. That doesn't limit us. She's only 63, so we don't have to really worry about our friends that make the PDAC list. She sleeps on her side, and that can sometimes be a little uncomfortable with the Herbst style propulsion mechanism because they have these pivot arms to which the Herbst arm is attached, which stick out. There's some bulk there that usually has a fair amount of protrusion to it. So, let's look at these propulsion mechanisms then. On the upper left, we have the attached midline traction. Remember that all the forces are concentrated in the anterior, and if the patient should attempt to open with the device in, it will exert dislodging forces on that anterior bridge, and I don't think we want that. Next up, we have the attached bilateral traction. This particular one puts too much pressure on the anterior bridge as well, for my liking, and it's the one that when the patient opens, it concentrates the dislodging forces not just on the upper anterior but also on the lower posterior molars, which is where we have a three-ended bridge as well. So, I'm not liking that one either. Here, on the far right, we have the unattached bilateral interlocking with the dorsal arms, or the fins, I guess you can call them, and these are the 70 degree dorsal angle fins. It has very little resistance to openings, so we don't have to worry so much about dislodging our dental work, but we may need to put elastics on that, plan to have elastics attached. The compression is focused mid-posterior on both sides, so it will distribute, it's well distributed, I would say, and it avoids our most delicate area, which is the anterior bridge. Then, look down here on the lower left, that's the attached bilateral compression. It's on the PDAC list, but we don't care about that for this patient, and like that dorsal device on the upper right, it does not resist opening very much, so it will not pull too hard on our bridges. But again, it would need some elastics, and they have, there's an image with the elastics shown there, but this one actually could be less comfortable for side sleeping. All right, so we've reached this point, there's no right or wrong answer here, obviously, but this is what I would propose. Materials, acrylic laminate, retention, flexible liner, flexible acrylic liner, extension with full occlusal extension, even onto that edentulous ridge that we had, and propulsion, I would lean towards the dorsal style, which is part of that unattached bilateral interlocking group, and I'd have elastics to encourage mouth closure, and I'm done. Patient happy. All right, let's do another case, going on another spin. Okay, now we have a 35 year old man with the history of mouth breathing, an exaggerated curve of speed on his left, an exaggerated curve of Wilson on his right, very narrow arches, and very crowded tongue, very fat tongue on this guy. We have missing teeth, tipped teeth, we have a Maryland bridge there replacing number seven. Again, there are no right or wrong answers here, but let's just go through this circular process. We're going to start with materials, then retention, then we'll go to extension, then propulsion, and we'll keep going if we need to. All right, materials, no allergies, but it would be nice to have something thin for this guy, so we do not crowd the tongue any more than it already is. Also remember the exaggerated curves of Wilson and Speed that are going to make us have to open the bite already quite a bit. Thicker materials mean even more opening of vertical dimension, so let's narrow it down to, say, a nylon device or an all-metal device, or if we're going to use an acrylic, maybe it should be as thin as possible, so we'll want to steer away from the laminates and go single phase. All right, next is retention. It appears that the teeth have pretty well-developed anatomy, I would say, and that will provide adequate retention on the upper, but we might want to avoid that Merlin bridge, number seven. On the lower, it's a different story. We're missing teeth and the whole arch form collapses lingually. This might require some cross arch retention. A nylon device is nice for that. It'll fold nicely to capture those lower lingual surfaces and tuck under those. A metal device would have to have some kind of well-designed clasp to grab onto the molars. I don't really see enough parallel surfaces to give us frictional retention, like in a milled acrylic, so if we go acrylic, we'd also need to add clasps to that. Okay, third thing is extension. I don't see any issues here. We need to extend over the entire occlusal and wrap the distal valve of the teeth, and we'll need to open the vertical dimension enough to accomplish that, while being mindful of our curves of Spee and Wilson. We need a flat plane of material thickness that it clears all the undulations introduced by those curves, obviously. Okay, so that brings us to propulsion. Okay, you remember this slide. The attached bilateral compression, this one here on the upper right, and the unattached bilateral interlocking, the lower left, those are going to exert the least dislodging forces when a patient opens, and remember we have a retention concern on the lower, particularly the posterior. So now I have to revisit my material decisions, since nylon and all metal devices do not come in the propulsion styles that I might think are best, and that is when this decision tree becomes a decision circle, and we take another spin and go back to reconsider materials. So if we revisit materials that are available in a bilateral compression or a bilateral interlocking device, and remember I'm hoping to stay away from acrylic laminates because of the added bulk with two materials like that, and an already crowded situation, and plus an uneven occlusal plane, so we're going to narrow, we've got narrow arches and a big tongue and crazy curves of Wilson and Spie. However, both the bilateral compression and the bilateral interlocking are available in milled acrylic. Milled acrylic is thinner, and it can be thinner, and if there are adequate parallel surfaces on the facial for frictional retention, it can even be made lingual-less. So I think that's possible for our upper arch. So if you look at the upper arch there, you could see that buccal and lingual surfaces of all those teeth are fairly parallel, and possibly there's enough retention just on the buccal surfaces to retain the device and make it lingual-less with the exception of not wanting to put any stress on that Maryland bridge, which is number seven. Okay, then extension would be full occlusal, except maybe on the slower molars where I'd only have clasps made. On the lower, I would ask them to survey the models to get as much frictional cross arch retention as they can. Next, I would involve the patient in the propulsion decision. So for a side sleeper, I might suggest steering clear of the Herbst compression arms again, and I'd go with the bilateral interlocking style. I like this case really because it not only shows how one decision leads to the next, but there's often conflict between your choices. So we just continue around the circle multiple times, and that helps a clinician and patient really weigh their decisions against each other, and it involves the patient in the discussion, particularly if you're like me and you think out loud. The important thing to remember is that all devices do essentially the same thing, and it makes it hard to make a wrong decision. However, with great variety of devices available, there are advantages to categorizing and sequencing your decisions. So when experienced dental sleep medicine providers engage on this topic of device design, they really rely on this shared familiarity and their understanding and experience with all the variety of choices that are commercially available. But dentists that are new to the field will often seek advice and want to know which device to use, and by having gone through this circular decision process, I'm hoping you might begin to see that there's certainly no one best device, and the decision should be based upon the unique needs of that patient. It's also my hope that by addressing these four fundamentals of device design that you would become familiar with this shared nomenclature, and then we can have meaningful and fruitful discussions when designing the best device for any given patient going forward. So thank you. Thank you for your attention today. I hope you found this presentation useful.

Trish Braga

Educational Director

AADSM

device design

dental sleep medicine

materials

retention

extension

propulsion