Written by S. Randy Werrin, DDS Friday, 28 February 2003 19:00
When treating patients who require indirect restorations (eg, full- and partial-coverage crowns, inlays, and onlays), accurate impressions are the cornerstone of restorative success and the key to communication between the dentist and the laboratory. Additionally, quickly achieving an accurate impression the first time, every time, enhances practice profitability by saving time and preventing the need for retakes or the insertion of less-than-satisfactory restorations. Clearly, to be successful in today’s high-pressure, high patient-demand environment, clinicians must provide aesthetic restorative dental care that is more efficient than ever before.1
Today, dentists prescribe and place a significant number of indirect restorations and, as a result, they are required to take more impressions, most of which are for one or two units. Given the current philosophy toward more conservative treatment approaches, the quadrant closed-mouth impression technique—or dual-arch impression technique—is ideally suited for today’s indirect restorative procedures and has been reported to ensure more accurate intercuspal relationships than mounted casts from full-arch impressions.2 This technique enables clinicians to take an impression of the prepared tooth, the opposing teeth, and the habitual centric occlusion all at once, thereby reducing chair time, expense, effort, and error because it requires fewer steps.3
This article describes a technique and combination of materials for producing an excellent record of the master impression, counter impression, and bite registration simultaneously. By using this armamentarium to obtain a closed-mouth impression, clinicians can quickly and easily obtain an accurate impression for indirect restorations in an efficient manner.
This technique utilizes the Wide Body Posterior Triple Tray (Premier Dental Products), Virtual VPS Bite Registration material, and VPS Automatic Dispenser (Ivoclar Vivadent).
Passivity of fit is imperative when obtaining accurate impressions. Therefore, the Wide Body Posterior Triple Tray (Figure 1)—one of a total of 7 designs—features thin, loose mesh and low tapered walls that help avoid tissue impingement. As with other designs of the disposable Triple Tray, size, strength, and comparatively low cost offer improvements over previously introduced double-arch trays.4 The Wide Body Posterior Triple Tray is longer and wider than previous designs and captures up to 6 teeth. Ideal for all one-unit and two-unit posterior impressions, the Wide Body Posterior Triple Tray saves clinicians time compared with separate impression-making procedures. Additionally, patients appreciate the disposability of the Triple Tray versus reusable trays for sanitary considerations.
When using the Triple Tray, the patient closes into full intercuspation. The tray does not distort because of the pliable and permeable webbing that permits complete closure into habitual centric occlusion, helping to ensure impression accuracy. In particular, in the July 2000 issue of the CRA Newsletter, Dr. Gordon Christensen reported that the Triple Tray mesh (wafer) thickness was 0.0015 in and the water sorption was 0.001 g, commenting that “Triple Tray absorbed [the] least water and has [the] thinnest wafer.”5
The new Virtual VPS impression system (Figure 2) features a Bite Registration material with a unique filler technology that provides reduced resistance and allows the patient to easily bite through the material, creating an extremely accurate impression. Further, with proven wettability in the mouth for lower contact angles and better adaptation to the surface, Virtual impression materials demonstrate excellent adaptation to moist tooth structure and tissue (where hydrophilicity is most important), and outstanding dimensional stability.
The setting phase of the Virtual VPS impression materials is temperature-activated. As a result, whether the clinician chooses to use all or a portion of the “working time,” the Virtual impression material moves rapidly into the “setting” phase immediately upon inserting the Wide Body Posterior Triple Tray into the mouth.
It is this shorter transition period of the Virtual impression material—combined with the integrity and one-procedure ability of the Wide Body Posterior Triple Tray and the ease and simplicity of the Virtual Auto-matic Dispenser gun—that saves clinicians time and reduces the risk of distortion once the tray has been seated. The Automatic Dispenser—which features a one-touch, total-control handle—takes the stress and hand fatigue out of the impression procedure and enables dental professionals to control the flow of the material into the tray. When placed in the oral environment, the “Fast Set” orange Virtual Bite Registration material will set within 1 minute.
|Figure 1. Wide Body Posterior Triple Tray.||Figure 2. After tooth preparation and tissue management, the Virtual VPS fast-set Bite Registration material should be loaded into the handheld, cordless, rechargeable dispenser gun.|
|Figure 3. The Bite Registration material is then loaded into both sides of the tray.||Figure 4. The Bite Registration material is loaded around the prepared tooth or teeth.|
|Figure 5. Once the Triple Tray is positioned into the mouth, the patient is instructed to close into full habitual centric occlusion.||Figure 6. When the material is set, the impression is removed and verified for accuracy and detail before being sent to the laboratory.|
The technique described next offers the advantages of reduced armamentarium and time to complete—only 60 to 90 seconds per impression. Below are the clinical protocol and tips that will ensure clinical success using the closed-mouth technique and materials described previously.
(1) During the onset of anesthesia, test the Triple Tray (Figure 1) for passive fit. Notes:
•Passive fit is essential to obtain an accurate impression. If the clinician is concerned that unusual oral anatomy will cause impingement, this technique should not be used.
•Confirming that the tray size fits before initiating the impression-taking procedure helps avoid having to retake the impression.
•The patient should close into habitual centric occlusion while the tray is unloaded.
(2) After tooth preparation and tissue management, the Virtual VPS fast-set Bite Registration material should be loaded into the handheld, cordless, rechargeable dispenser gun (Figure 2), then into both sides of the Wide Body Posterior Triple Tray by using the fastest setting on the gun (setting No. 6) (Figure 3), and around the prepared tooth (Figure 4). Notes:
•Ensuring a dry field is essential to obtaining accurate impressions; therefore, placing a cheek patch (Richmond Reflective Shield) prior to drying the teeth ensures that if the cheek falls back, the prepared dentition will not get wet. It also helps compress the impression material and contributes to a neater impression.
•A Triple Tray not filled sufficiently with the Virtual impression material results in a model that is poor in quality and possibly unusable by the laboratory technician.
•The Virtual material, unlike other products, is so dense that it displaces blood, fluid, or debris from around the teeth, ensuring a clean and accurate impression. Further, the material demonstrates a better contact angle, so dentists need not worry about their “neatness” when placing the Bite Registration material. For these reasons combined, this impression technique using Virtual is far less technique-sensitive.
(3) The loaded Triple Tray is positioned carefully in the mouth, and the patient is instructed to close into full habitual centric occlusion (Figure 5). Note:
•Complete intercuspation should be verified by checking each side of the arch; tapping gently under the patient’s chin or guiding the chin ensures complete closure.
(4) When the material is set—within 60 seconds—the impression is removed and verified for accuracy, detail, and/or signs of impingement (Figure 6) before forwarding to the laboratory.
Accurate impressions depend on technique as well as the optimal material characteristics of the impression system and armamentarium selected. The selection of an impression material with sufficient density, fast set time to eliminate voids, and adequate adaptation to the moist oral environment, combined with the use of a nondistorting, time-saving impression tray, can facilitate the accurate duplication of hard and soft tissues for the fabrication of accurately fitting restorations. Further, for dental patients with gagging problems and/or those fearful of dental materials “running down their throat,” this technique is particularly valuable.
The technique and materials described afford dental professionals the ability to integrate a user-friendly and readily available approach to impression to achieve outstanding indirect restorative results.
1. Werrin Sr. The origin of a new impression tray. Independent Dent. 2001;3:78-83.
2. Parker MH, Cameron SM, Hughbanks JC, et al. Comparison of occlusal contacts in maximum intercuspation for two impression techniques. J Prosthet Dent. 1997;78:255-259.
3. Werrin, SR. The 2-minute impression technique. Quintessence Int. 1996;27:179-181.
4. Christensen G. A new simple double-arch impression tray. Clin Res Assoc Newsletter. 1981;5:4.
5. Christensen G. CRA Status Report. Posteriour double - arch in pression trays. Clin Res Assoc Newsletter. 2000;July:2.
Dr. Werrin is in private practice in Pittsburgh, Pa, and is associate professor of restorative dentistry at the University of Pittsburgh. He can be reached by visiting the Web site dentalpgh.com.
Disclosure: Dr. Werrin is the inventor of 6 Premier Posterior Triple Trays.
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