Hello, I'm Dr. David Schwartz. Today, I'm going to demonstrate a polyvinyl siloxane impression technique that can be used for fabrication of an oral appliance. There are a variety of techniques and materials that can be used successfully. Although there's an industry shift toward digital impressions, there still remain certain circumstances when an analog impression has value. And of course, there are many clinicians who do not have access to digital scanners or who just prefer using physical impression materials. There are too many material options to list here, but choices for analog impressions can be broken down into two general categories. Water-based materials like alginate, which is an irreversible hydrocolloid, and elastomeric materials such as polyvinyl siloxane or PVS. Alginate is a single-phase material with a straightforward impression technique very familiar to all dental personnel. But techniques for PVS vary and can be accomplished with both single or dual-step procedures. The two-step process I've chosen to demonstrate today has some notable advantages. First, the slower set times associated with the PVS material allow dental staff that are unfamiliar with full-arch impressions for oral appliance therapy to identify and correct errors in the first step. And second, the heavy body material in the first step functions almost like a custom tray. The benefit here is that it provides for equal distribution of the second light-bodied step, which is meant to capture necessary detail. But the truth is that any material or technique that results in an accurate impression of the teeth and surrounding structures can be used successfully for the fabrication of oral appliances. Before we begin, I want to point out a few capture requirements that are unique to impressions used for fabrication of mandibular advancement devices. Capturing detailed tooth anatomy is not enough. In addition to define CEJs, interproximal areas, and the distals of the most posterior teeth, it is also very important that the impression material extend a minimum of five millimeters beyond the gingival tissue crest in order for the laboratory to build a model or base that extends beyond the teeth. Without this, it can be difficult to contour and finish the device edges. It is also advantageous to extend impression materials into vestibules, particularly maxillary and mandibular buckle vestibules, which often house the device advancement apparatus or compliance monitors. If a patient is partially edentulous, then extension also needs to include any tissue area that will bear the weight of the device or help retain the device by creating a soft tissue seal. The first step is to select a tray that fits the arch width and length. The tray should be adequately perforated to prevent the set material from pulling away from the tray and introducing distortion. Next, check to be sure the tray seats completely and does not bind on the teeth or attached gingival tissues. There should be adequate space within the tray for a uniform thickness of material. This is at least three millimeters in all dimensions. The tray should cover the entire occlusal surface and extend over the distal of the second molars. Sometimes the correct width of tray does not cover the entire occlusal, in which case it should be modified by adding material such as stick compound or rope wax. When trying in the upper tray, be careful that the ends of the tray do not interfere with the coronoid process of the mandible, which could prevent full seating. Having tried in and selected the correct tray, it is fine to use any two-part PVS system of your liking. It is just important to know the set times. This one has a set time of four minutes. You'll need compatible measuring scoops, a light body dispenser, and separating film. I use the measuring scoops provided by the manufacturer to dispense equal amounts of base and accelerator, according to the manufacturer's directions. Wearing a non-latex glove, I will mix these together until the two colors are blended as one. The manufacturer's instructions recommend that my working time is two minutes, but I want to do this as quickly as possible. Shaping it into a log, I can load it easily into the tray and use finger pressure to form a channel that roughly mimics the dental arch. Then I loosely wrap the tray with separating film. I want to center the tray, making sure that the handle is aligned with the patient's midline, and insert it with firm pressure that is equal side to side and anterior to posterior. Once I feel it is seated appropriately, I will immediately remove it from the mouth and examine the material for equal distribution around the arch. So this is my first step completed and I've removed the separating film. I have equal material on all sides of the dental arch with adequate extension over all occlusal surfaces. I can see a channel around all the teeth that effectively forms a custom tray. The perforated stock tray is not visible through the material in any area, which is good. If it was, it would indicate inadequate thickness of the heavy body material for bench stability in that area. But since this is a two-step process, identifying any problems at this point would allow me to quickly redo the first step. I also want to be sure that the distal of the impression forms a dam to prevent overflow of the light-bodied second step. If it doesn't, I can easily remold the material in that area before proceeding to the second light-bodied step. Only about a minute has passed since I first started mixing the heavy body material. The manufacturer tells me I have to wait four minutes for a full set of the second step in the patient's mouth. By the time I remove it, both the first and second step materials will be completely set. Again, working quickly, I fill the trough created by my first step with the light-bodied material. Now, when I return it to the mouth, I need to keep the patient informed of how much time has elapsed and how much longer it must stay in their mouth. While the first heavy body material requires firm pressure during seeding to mold it around the dental arch, this second step is quite light and does not require firm pressure when used in two steps like I'm demonstrating today. Instead, I want to focus on keeping equal pressure side to side and anterior to posterior during the entire set process. Staying connected to the patient in this way also has the advantage of allowing me to assure the patient that I will be removing it precisely at the right time and not one minute longer. Since impressions of this nature create a great deal of suction, it's generally necessary to release the impression on one side at a time. So here's my final impression. We can see that I have adequate and equal material thickness around the arches. The impressions show crisp cervical detail. There is extension beyond the CEJ of at least 5 millimeters and well into the buccal vestibules. There are no pulls or voids or separation from the tray. This is a successful impression. This material is bench stable and can be sent to the laboratory for fabrication of an oral appliance. I want to stress that to date there was no substantial evidence that any particular material or technique is more accurate than any other, but this technique is proposed as a useful way to train clinicians and staff members who are unfamiliar with PBS materials. By separating the process into two steps, a novice clinician is able to assess capture requirements in the first step before proceeding to the second. I hope you found this presentation to be of assistance to you in making clinical choices about materials and ensuring that impressions appropriately capture critical details before being sent to laboratories. Thank you for joining me.

polyvinyl siloxane impression technique

oral appliance fabrication

analog impressions

water-based materials

elastomeric materials