Hi, I'm Dr. Ivan Valcaringhi, and I'll be demonstrating calibration techniques for propulsion mechanisms used in MADs or mandibular advancement devices. We'll begin with a description of the components of a mandibular advancement device so that we are all using the same nomenclature. Then we'll review the styles of propulsion mechanisms based upon the advancement strategies they employ. Finally, we'll get into the specifics of calibration steps. The portion of the device that attaches itself to the dental arches or teeth is often called a splint or a tray. To avoid confusion, we'll use the term tray. The tray itself may be made of various materials, but today we will be looking at examples of PMMA or polymethyl methacrylate, thermoplastic polymer, and nylon. The tray generally covers the entire occlusal surface of both arches and wraps around the most distal molars. By convention, the upper tray is considered the stationary tray since it is attached to the maxilla, which of course isn't movable relative to the skull. The lower tray, therefore, is considered the movable tray, and the relationship between the two trays is determined by a propulsion mechanism that exerts protrusive forces on the lower movable tray. If the upper stationary tray has a propulsion mechanism that anchors toward the maxillary anterior and pulls the mandible forward, we refer to that as a traction device. The propulsion attachment to the lower tray can be at the midline or bilaterally in the lower posterior. We would refer to these as attached midline traction or attached bilateral traction, respectively. If the upper stationary tray has a propulsion mechanism that pushes the mandible forward, then we refer to this as a compression device. It may push the lower tray forward with a telescoping arm. This we call attached bilateral compression. Some devices are constructed as two separate and unattached trays. When placed on the dental arches, the upper stationary tray pushes or holds the mandible forward with arms that interlock when the patient closes together. We refer to this as unattached bilateral interlocking, but it should be noted that this style of device also uses compressive force. They can be advanced with an expansion screw or with a series of trays fabricated in progressively more advanced positions. Next we should consider some advancement strategies. Generally, calibration is a way to gradually protrude the position of the mandible relative to the maxilla. For compression devices that push the mandible forward, the protrusive mechanism gradually increases in length by a turn of the screw or by replacement of one piece for a longer piece. A telescopic herped arm is an example of a compressive arm that lengthens with the turn of a screw. An expansion screw also gets longer with successive turns. Conversely, traction devices that pull the mandible forward achieve mandibular protrusion by gradually shortening the length of the connection between upper and lower trays. Although in some cases, there can also be forward movement of propulsion mechanism to achieve greater traction and advancement. All of this is just meant to help you become familiar with different device protrusive advancement strategies. I'm going to demonstrate the attached bilateral compression category of devices with a device that uses two multi-piece metal arms commonly referred to as telescoping herps arms. We can see that orientation of the herps arms functions in concert with the temporal mandibular joint movements. And this allows the mouth to swing open and freely. Therefore, elastic attachments are often added to encourage and maintain mouth closure during sleep. You can also see that the herps arms allow some lateral movement of the mandible, but this can vary based upon the design of the telescoping arm and the shape of the dental arches. If you are selecting this type of propulsion in hopes of providing some freedom of lateral movement, it is important to discuss this with the manufacturer during the design process. Now take a closer look. We see that when the arm is removed from the tray, it is made up of several components. First, a sliding tube and rod that lengthen when the patient opens their mouth. Some devices only have a small printed plus or minus sign printed on the arm itself. In order to secure the arm to the device, the pivot is embedded into the splint during manufacturing. The hex screw passes through the eyelet and is tightened down into the pivot. It is important to understand that the eyelet is larger in diameter than the pivot and the screw that retains it. This is the mechanism that allows for a certain amount of play side to side with lateral movement of the herps arm. This in turn allows for lateral movement of the mandible when the appliance is in the mouth. For purposes of treating sleep apnea, the arm can be gradually lengthened or calibrated. It is typical to have a calibration nut and a calibration tool to advance the mandible. It is common for the calibration nut to have four equally spaced keyholes around its perimeter. The device I'll be using today has a hexagonal calibration nut without keyholes, but it uses the same rotating mechanism for arm lengthening and therefore mandibular advancement. In either case, as advancement occurs, screw threads will become visible demonstrating advancement has occurred. To advance this device, the calibration tool or wrench is fitted into the hex shaped calibration nut. The calibration wrench is then rotated in the direction of the arrow printed on the acrylic. You will notice that the arrow on one side points up while the arrow on the other side points down. With this rotation, the arm will lengthen. The ratio of turns to length varies from manufacturer to manufacturer, of course. Let me demonstrate. Each 90 degree turn of the key, which is a quarter turn of the calibration nut, generally advances the arm between a fifth to a tenth of a millimeter, so it will take about five to ten turns to equal one millimeter of advancement. Calibration range may also vary depending upon the manufacturer. In a similar fashion, if the clinician decides to reduce the advancement of the mandible, the calibration wrench is rotated in the opposite direction of the arrow, and in some cases toward the negative sign printed on the arm. In any event, calibration may continue until the limit of the arm range is reached, at which point the calibration nut will no longer turn. This is normally about five millimeters. Let's take a look at one of these devices described as midline traction. The propulsion mechanism is positioned anteriorly at the midline, locks together the upper and lower trays before it is inserted into the mouth. Taking a closer look, the calibration mechanism consists of an advancement screw and a hook located centrally. On the facial aspect of the calibration mechanism, there is a keyhole for the adjustment key. If the hook is positioned on the upper, it connects into a lingual keyhole attached to the mandibular tray. If the hook is positioned on the lower tray, it then interlocks with a wire on the upper tray. To advance the midline traction device, place the adjustment key in the keyhole and rotate the adjustment key clockwise 180 degrees. Let me demonstrate. Each 180 degree turn advances the hook protrusively a quarter of a millimeter for a ratio of four to one or four turns for each millimeter. Therefore, two complete 360 degree rotations will advance the appliance one millimeter. Naturally, turning the key in the opposite direction will retrude the mandibular position in an equivalent fashion. You can see that the position of the keyhole lends itself to advancement turns even when the device is positioned in the mouth. And the size of the key makes it a bit easier to hold and manipulate if a patient's eyesight or dexterity are a consideration. When we discuss calibration of an unattached bilateral interlocking device style of propulsion, we will consider two methods, expansion of an advancement screw and iterative changes of device trays with sequentially more protrusive relationships in the interlocking arms. Let's begin with a device often referred to as a dorsal device that uses an expansion screw. Here you will see the propulsion mechanism that advances the device. It consists of an advancement arm on the lower tray that is shaped like a dorsal fin positioned near the premolars and a calibration or advancement mechanism anchored towards the distal of the upper tray. With very close inspection, you can see the calibration mechanism consists of two acrylic blocks joined by three horizontal metal connectors. The block positioned most posteriorly is manufactured as part of the tray and is therefore immobile. The anteriorly positioned block, which can also be called the advancement block, is designed to slide forward on the metal connectors as the middle expansion screw is rotated. When the device is inserted in the patient's mouth with the jaws closed, the advancement block rests against the posterior side of the dorsal fin. You can see here the advancement block and the dorsal fin both have a bevel or angled face where the two nicely fit against each other. The significance of this angle is that it allows the mandible to rotate downward and backwards without much resistance. Therefore there is often a need to use orthodontic elastics to apply gentle closing pressure. Similar to some telescoping HERPS arms, there are four key holes in the calibration nut distributed equally around the perimeter. Two should always be visible at any given time. To advance the device, the calibration tool is inserted into the keyhole, the one that is closest to the base of the directional arrow, or in some instances furthest from the plus sign. The calibration tool is then rotated in a direction of the arrow and towards the plus sign. Rotation should proceed until there is a hard stop. Since there are four keyholes equally spaced around the calibration nut, one rotational advancement is the equivalent of a quarter turn. With each quarter turn of the advancement screw, the advancement block will move between a fifth and a tenth of a millimeter anteriorly away from the posterior block so it will take about five to ten turns to advance this mechanism one millimeter. This varies from manufacturer to manufacturer. In a similar fashion, if a clinician decides to reduce the advancement of the mandible, the calibration tool is inserted in the keyhole that is closest to the tip of the directional arrow or plus sign and rotated in the opposite direction. Some clinicians may request that the lab set the propulsion apparatus at the desired bite, but with one millimeter available to retrude the propulsion block. This is referred to as the setback. This would then allow some adjustments to retrude the mandible if the initial position was too aggressive or difficult for the patient to acclimate. When the advancement block reaches its most protrusive position, the key will no longer turn the calibration nut. This is another device referred to as an unattached bilateral interlocking that uses an iterative strategy for advancement. The design of this particular device is proprietary, however, it is likely that other manufacturers will begin to use this iterative approach in future designs so that it is useful to be familiar with the concepts of this propulsion mechanism. It is digitally designed, then manufactured via a milling process starting with a controlled cure solid block of polymethyl methacrylate or PMMA. This allows for efficient manufacturing of multiple identical trays that have small incremental changes in the position of the propulsion arms. I will be demonstrating how consecutive tray changes will increase the mandibular protrusion. The propulsion mechanism consists of two interlocking arms that nest against each other when placed in the patient's mouth. These arms are generally fabricated with a 90 degree angle to the tray. The arm on the maxillary tray is positioned posteriorly adjacent to the molars and extends downward past the occlusal surface. The interlocking arm of the mandibular tray is positioned more anteriorly in the premolar area and extends upward past the occlusal surface. When properly fitted in the patient's mouth, the mandibular arm rests in front of the maxillary arm and should rest together with equal pressure on both sides of the mouth. The calibration or advancement of this oral appliance is accomplished by changing upper and lower tray combinations. The increments of the tray combinations may be customized, but generally proceeds at one to two millimeters at a time. Each tray is labeled as to identify the dental arch which it attaches and the number of millimeters of advancement it provides relative to the starting bite position. Let me show you what I mean. This tray is labeled with a U for upper and a zero, indicating it's an upper tray and was manufactured with zero advancement beyond the starting protrusive bite position. This tray is labeled with an L for lower and zero, which again signifies no advancement. When worn together, they replicate the starting protrusive bite position. In this case example, you should be able to see just slight protrusion of the mandible beyond the end to end. Replacing the lower zero tray with one labeled L1 will move the mandible one millimeter forward from the start position. Similarly, subsequent replacement of the upper zero tray for an upper two tray will advance the mandible two millimeters more for a total of three millimeters beyond the start position. Since the protrusive position of the mandible is determined by the sum of the tray advancements, it's important to recognize that in order to advance in a linear position, we jump back and forth between trays. Further advancements or advancement in different increments are accomplished by ordering specific customized tray advancements. Next, I want to demonstrate a group of device styles that use traction to pull the mandible forward. The upper and lower trays are all connected with attached straps or rods and can be referred to as attached bilateral traction. In today's market, these straps may be manufactured from flexible or more rigid materials, but all work on the principle that the shorter the strap, the more forward the mandibular position is. Here are some examples of connectors that can be gradually shortened to achieve protrusive movements. They are commonly made from elastomeric materials or nylon and may also be referred to as straps or links. Let's start with an elastic strap which comes in various lengths. The flexibility allows lateral mandibular movements to some extent. Because it may also lengthen over time with elastomeric fatigue, it should be replaced routinely. One common strategy for device calibration is to use the most flexible band at the particular length first, then proceed to a more rigid version of the same length before attempting further advancement. It is really a simple thing to replace these elastomeric bands and a patient can be provided with a schedule of colors and lengths for titration at home depending on comfort and calibration. Next up we have a nylon band or link that is much more resistant to lengthening fatigue. As a rule, straps fabricated from nylon have some lateral flexibility but do not require the same schedule replacement as the elastic version. Here's another nylon connector that attaches on the maxillary tray only at the front. This is a unique design in that it allows lateral movement of the mandible by sliding through an anterior groove. The strap fits into the groove by identifying an area of its most narrow diameter. The final strap change I'll show you today is a device that uses two nylon straps or rods to attach to 3D printed nylon trays. When you inspect the straps closely, you'll see that they are printed on one side with the length of the strap in millimeters. And in this case, it also says demo. You'll also notice that a triangular attachment and the receiver on both trays fit together precisely in a specific lock and key fit. This key then inserts into a keyhole positioned at the anterior portion of the upper tray and the distal or posterior of the lower tray. The triangular keys must be rotated to fit into a keyhole to then lock in place and must be reversed to change the rods or straps. And the straps are identical, right and left, so they cannot be placed improperly side to side. These can take a bit of dexterity and coordination. I find it easiest to attach the key into the keyhole on the lower tray first. It should be inserted from the medial side of the strap wing and rotated 180 degrees anteriorly to lay forward on the tray. Remember, the embossed writing should face medially. On the left side of the tray, I'll lift the left strap to an almost vertical position. Then I'll lift and rotate the distal end of the upper tray to a vertical orientation as well. Now I can insert the strap key into the keyhole as the triangle properly aligns and drops into place. Securing the left key into place with my left hand and index finger, I am now free to use my right hand to snap the right strap into place on the upper tray and rotate the upper tray back into the position it will take in the mount. Special consideration should be made regarding the manual dexterity of a patient for this type of mandibular advancement appliance. In conclusion, no matter the style of propulsion mechanism, the calibration technique, some dentists elect to advance the device for the patient in the clinic and therefore schedule return visits on regular intervals. Other dentists provide the calibration tool or elements along with written instructions to the patient describing how and when to advance. With any style, it is critical that the patient demonstrates their understanding and ability to advance the device before leaving the clinic. Chairside staff members should be very familiar with all device advancement techniques in order to be well prepared to assist patients who encounter difficulties. Thank you for joining me. I hope you have found this demonstration useful.

calibration techniques

propulsion mechanisms

MADs

trays

traction devices

compression devices