The Benefit of Control
Achieving outstanding impressions without retraction cord
Clinical techniques are refined through repetition and reevaluation; the old adage “practice makes perfect” is apposite to improving clinical dentistry. Using repetition to create mastery relates nicely to capturing final crown and bridge impressions because there are many factors the clinician must control to ensure a positive outcome. Some of these factors are dentist-related and can include preparation design, tissue management and fluid control, material selection, type of tray, and timing. Other factors may be patient-related, such as anatomy of the area being impressed, gingival health, occlusion, and anxiety. Adequately controlling these factors can help clinicians successfully complete the impression stage of the fixed prosthodontic procedure.
In a study by Samet and colleagues, it was observed that 89% of fixed partial denture impressions submitted to a dental laboratory had one or more observable errors, with two common errors being voids or tears at the finish line and air bubbles at the finish line.1 The authors’ conclusions indicated that a more thorough evaluation by the dentist of the final impression is needed. More recently, Dr. Gordon Christensen reinforced the notion that operator confidence and technique are vital to successful impression-making saying, “Impression materials can no longer be indicted for restoration inadequacies.”2
Placing retraction cord is a common practice during fixed prosthodontics; one possible reason is to help capture subgingival margins for the fabrication of porcelain-fused-to-metal crowns.3 Besides wanting to hide a metal margin and improve esthetics, reasons for placing margins subgingivally may include the presence of caries or restorative material, fractures, and the need to increase crown height or create adequate ferrule. In these cases, cord is generally needed and useful to create both tissue retraction and fluid control. However, when possible it is sometimes advantageous to keep prep margins supragingival (aka, “high and dry”) to preserve tooth structure, aid in hygiene, and make the impression process and cementation easier. With so many new metal-free crown substrates available, clinicians can now potentially utilize supragingival margins without sacrificing esthetics and strength.
In the author’s clinical practice, less retraction cord is being used for several reasons. The most important reason is that mechanical retraction using cord is traumatic to the surrounding tissue and can cause gingival recession.4,5 Also, because the placement of cord is often painful for the patient, anesthesia is usually required. Next, it is possible to achieve hemostasis, fluid control, and the minimum necessary retraction via chemical means, which is less traumatic compared to using cord.6 Lastly, recent material and equipment advancements allow for more control over the materials used and the precision with which it is placed around the tooth.
Among the factors that the clinician must control during impression-making are selecting the right material and placing it into the mouth. A common method for doing so involves a light-bodied impression material placed around the prepared tooth followed by a more viscous or heavy-bodied material in the impression tray. The light body or wash material is typically syringed around the tooth using a backfilled syringe or via a 50-mL impression gun. This method forces the clinician to do two tasks simultaneously (ie, expressing the material and placing it around the tooth) and can potentially make it difficult to place the wash material precisely into the sulcus or around the tooth being impressed. Also, because of the pistol grip and unwieldy size of the 50-mL gun, placement of wash material may involve simply flooding the area around the tooth.
Recently, DENTSPLY Caulk introduced the Aquasil Ultra Cordless Tissue Managing Impression System to give clinicians more control during impression-making. This system consists of a digit power™ Dispenser, digit power™ unit-dose polyvinyl siloxane impression cartridges, and dedicated polyvinyl siloxane tray material, a regulator that connects to most dental air lines, and an adaptor that allows the system to sit in a tool holder at the dental unit (Figure 1). Instead of depressing a backfill syringe or squeezing the impression gun, clinicians can hold the Dispenser in a pen-style grip (similar to holding a handpiece) and use the rheostat to control the flow of the wash material. Coupled with an ultrafine intraoral tip, the wash material can be placed precisely around the prepared tooth or implant, potentially minimizing the need for retraction cord and mitigating syringing errors such as air entrapment, which can lead to voids or bubbles at the finish line.
Another factor that must be controlled during impression-making is manipulating impression materials within their intraoral working time. The intraoral working time of an impression material is defined as the time when the material should be placed into the mouth and is measured from the start of the mix until the material can no longer be manipulated without introducing distortion or inaccuracy in the final impression.6 The Aquasil Ultra Cordless Tissue Managing Impression System helps control the timing during the impression-making process by safeguarding against errors due to working time/setting time violations. The digit power cartridges are designed so that the entire impression cartridge can be expressed within the material’s intraoral working time while still giving clinicians time to seat the tray properly. The intraoral working time of the single-unit cartridge is 35 seconds and the intraoral working time for the multi-unit cartridge is 1 minute; the working time of the dedicated tray material is approximately 1 minute 15 seconds. Mouth removal times for the single- and multi-unit cartridges are 3 minutes and 4 minutes 30 seconds from the start of mixing, respectively.7
A 39-year-old female patient presented for crown preparations on teeth Nos. 30 and 31 (Figure 2). Tooth No. 30 had a failing porcelain inlay and tooth No. 31 had a large disto-occlusal composite restoration; in both cases, full coverage was indicated. After successful anesthesia using one carpule of 4% Articadent® DENTAL with epinephrine 1:200,000 (DENTSPLY Pharmaceutical, www.dentsply.com), both teeth were prepared for monolithic zirconia crowns using Two-Striper® (Premier, www.premusa.com) diamond burs to achieve 1.0 mm of occlusal clearance, 1.0 to 1.5 mm circumferential clearance, and a slightly supragingival butt joint finish line (Figure 3).
Using a Triotray Pro-Lock Semi-Disposable Dual-Arch Impression Tray (Triodent, www.triodent.com), the final impression with the Aquasil Ultra Cordless Tissue Managing Impression Material was taken without the use of cord or retraction paste. A multi-unit impression cartridge was used and the impression was removed from the mouth after 4 minutes and 30 seconds from the start of mixing (Figure 4). After inspection to verify unequivocal capture of the prepared tooth details, provisionals were fabricated with Integrity Multi-Cure®Temporary Crown and Bridge Material and cemented with Integrity TempGrip® Temporary Cement (DENTSPLY Caulk) (Figure 5 and Figure 6).
Three weeks later, the final restorations on Nos. 30 and 31 were cemented with Calibra Universal Self-Adhesive Resin Cement opaque shade (DENTSPLY Caulk) (Figure 7). Figure 8 shows the completed restorations after cementation.
With the Aquasil Ultra Cordless Tissue Managing Impression System, dentists have a streamlined solution for impression-making that allows easy, precise, and predictable placement of impression material potentially minimizing the need for retraction cord or paste.
1. Samet N, Shohat M, Livny A, Weiss El. A clinical evaluation of fixed partial denture impressions. J Prosthet Dent. 2005;94(2):112-117.
2. Christensen G. Impression materials: need more speed? Clinicians Report. 2014;7(7):1-6.
3. Donovan TE, Gandara BK, Nemetz H. Review and survey of medicaments used with gingival retraction cords. J Prosthet Dent. 1985;53(4):525-531.
4. Ruel J, Schuessler PJ, Malament K, Mori D. Effect of retraction procedures on the periodontium in humans. J Prosthet Dent. 1980;44(5):508-515.
5. Kazemi M, Memarian MA, Loran V. Comparing the effectiveness of two gingival retraction procedures on gingival recession and tissue displacement: clinical study. Research Journal of Biological Sciences. 2009;4(3):335-339.
6. Smeltzer M. An alternative way to use gingival retraction paste. J Am Dent Assoc. 2003;134(11):1485.
7. Terry DA. The impression process: part I—material selection. Pract Proced Aesthet Dent. 2006;18(9):576-578.
8. Aquasil Ultra Cordless Tissue Managing Impression System. Aquasil Ultra Cordless website. www.aquasilultracordless.com/sites/default/files/578051_aucordless_dfu.pdf. Accessed June 25, 2015.
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