Written by Richard L. Brown, Jr, DDS Wednesday, 30 September 2009 19:00
Perhaps no procedure done on a routine basis in dentistry contains more uncertainty and yet of holds more importance for the outcome of care than that of the dental impression. Every dentist and dental office team member has at some point anxiously awaited to see if the fruit of their labor has been captured correctly in the negative form of an impression. While in the state of unknown, each goes through a mental checklist of all the choices made to get to this point. Is the preparation correct, is the tray correct, is this the best technique for the situation at hand, did the tissue get managed properly, and finally was the material the proper one? While each of these variables is a topic of discussion, the material choice is the one that influences all the others in some form or another and perhaps can make the biggest difference.
There is great confusion out there about the types of materials, their clinically relevant properties, and their usage. This is further compounded by the fact that there are some 40 plus brands of one type of impression material distributed by some nearly 30 separate companies.1 The marketing barrage that accompanies these products is sometimes overwhelming.
The purpose of this article is to highlight the use of a new elastomeric impression material that takes advantage of the best properties of both a polyethers and a vinyl polysiloxane (VPS). This new impression material can be used in multiple/different situations, and, in the author’s opinion, should help to clear up the picture of the material of choice for dental final impressions.
BRIEF HISTORY OF ELASTOMERIC IMPRESSION MATERIALS
The dental impression has evolved over the past 3 decades from a cumbersome, labor intensive, ill-tasting event to a relatively simple experience which can be predictably accurate if a system for success exists. Polysulfides were the first elastomeric impression materials.2 For over 30 years, these remained the primary elastomeric material of choice until polyethers burst on the scene with their improved hydrophilicity. Polyethers then became the material of choice for many practitioners.3 Polyethers still had challenges due to poor taste, relatively low tear-strength, rigidity upon removal, and difficulty in mixing. This led to the development of the first condensation-reaction silicones and then VPS in the 1970s. These materials had excellent tear strength, great dimensional stable, a good or neutral taste, and were more flexible and not subject to plastic deformation upon removal. They had one glaring deficiency in that they are extremely hydrophobic. Over the years, surfactants and scavengers have been added to this class of impression materials to reduce the contact angle, and to make them less hydrophobic, with a great deal of success. However, by their nature, they are still hydrophobic they hate water!
Consequently, and until recently, we have been left with 2 good choices for elastomeric impressions: polyether―with its excellent hydrophilic qualities and great flow, but with slow recovery, rigidness, a low tear strength; and VPS―with its great stability, high tear strength, and excellent recovery, but with a hydrophobic nature.4
UNIQUE VPES IMPRESSION MATERIAL INTRODUCED
Figure 1. Multiple viscosities (EXA’lence [GC America]) of the new vinyl polyether silicone (VPES) impression material shown.
|Figure 2. Shark Fin Test.|
A new elastomeric impression material, (EXA’lence [GC America] (Figure 1) that takes the best of polyether and VPS materials and virtually eliminates their weaknesses, has been recently introduced. It is being referred to as a vinyl polyether silicone (VPES). This new material has the tear strength and dimensional stability of VPS, and yet the wettability and flow of polyether. It is available in multiple viscosities, and with multiple setting times that will allow it to be used in nearly every application. It can easily be disinfected without distortion and is gypsum friendly at the dental laboratory. According to flow tests, it is better than virtually all materials on the market as measured by the traditional “shark fin” test. Testing indicates that in every viscosity it outperforms other popular products now available, and the extra light-bodied viscosity reached an impressive 17.0 mm (Figure 2).5 Tear strengths of this material have also been demonstrated to be higher than the available VPS materials, and at or better than polyethers, even in their lowest viscosities.5
The end result is a level of detail that produces an outstanding restoration which fit’s precisely. In the author’s opinion, VPES is a new impression material that will simplify your material selection. I have found that our impressions are taken more easily, without modifying our basic techniques. The remainder of this article will address the clinical use of this new VPES impression material.
Figure 3. Comprehensive orthodontic treatment.
Figure 4. Anterior view: Post-ortho.
Figure 5. Lateral view: Post-ortho.
Figure 6. Anterior view: Provisionals.
A 44-year-old woman presented for restoration while in comprehensive orthodontic care with a chief complaint of discolored, poorly shaped teeth. She desired to have a more attractive smile (Figure 3). The maxillary teeth exhibited significant anterior inclination, uneven gingival crest heights, and recession areas. An additional aesthetic challenge was present due to the irregular size of the existing provisionals, the unknown tooth structure present, and shape of the of the existing preparations.
After multiple finishing visits with the orthodontists, the orthodontic appliances were removed and the patient presented with the multiple spaces and unaesthetic restorations (Figures 4 and 5). Clinical crown lengthening was performed with osseous recontouring. and new provisional restorations based upon a diagnostic wax-up of face-bow mounted stone models on a semi-adjustable articulator were created (Figure 6).
Figure 7. Anterior view: Preparations.
Figure 8. Full-arch VPES impression.
Figure 9. Close-up view of VPES impression.
Figure 10. Gypsum cast: Note the occlusal detail obtained with the use of the VPES impression material.
Figure 11. Postoperative anterior view.
|Figure 12. Postoperative lateral view.|
After 4 months of healing time, the provisionals were removed and the preparations were refined for final impressions (Figure 7). At this time, stock (custom-moldable) plastic impression trays (Strong-Massad Denplant Impression Tray [Global Dental Impression Trays]) were selected These trays provide a very accurate dental impression by allowing an equal thickness of the impression material in a stock tray, without having to fabricate a custom tray.6-8 The final impression was made with the new VPES (EXA’lence) heavy-bodied material, and (EXA’lence) the extra light-bodied viscosity, in a simultaneous one-step technique. Note the excellent marginal detail, flow, and easily readable, intact finish lines (Figures 8 and 9).
Next, an occlusal registration (Occlufast Rock [Zhermack]) and an opposing alginate impression were made, along with a face-bow for use in mounting the case on a semi-adjustable articulator. The impression was poured in dental stone and the dies trimmed for scanning and the fabrication of zirconium oxide based all-ceramic restorations (Procera [Nobel Biocare USA]). Note the exceptional detail of the occlusal surfaces on the stone casts and the finish line. These details helped to ensure well-fitting restorations (Figure 10) with accurate intercuspation and guidance. The outcome was a more attractive final smile for the patient meeting her chief complaint (Figures 11 and 12).
Over the years, very few advances have occurred in the area of dental impression materials. Manufacturers have attempted to modify and improve existing impression materials creating a stream of products, that by their nature, still presented with some of the same basic weaknesses as originally introduced. While the future of dentistry and dental materials may lie in the digital realm, it will take time to make that complete journey. Since this new VPES technology takes advantage of all the best properties of everything currently available, regardless of the technique or delivery method that is employed for final impressions, this versatile material makes it both easy and reliable to obtain consistent accurate impressions.
Special thanks to Mr. Tom Sano, CDT, G and H Dental Arts, Torrance, CA, for the fine dental laboratory work done in this case, and also for the years of personal friendship.
- Cowie RR. Understanding impression materials and techniques. Dent Today. 2007;26:108, 110-111.
- Coy HD. The selection and purpose of dental restorative materials in operative dentistry. Dent Clin N Amer. 1957;1:65-80.
- Schulein TM. Significant events in the history of operative dentistry. J Hist Dent. 2005;53:63-72.
- Craig RG, Hanks CT. Restorative Dental Materials. 7th ed. St. Louis, Mo: Mosby; 1985:253-302.
- Testing data on file at GC America, Inc, Alsip, Ill; 800-323-7063.
- Eames WB, Sieweke JC, Wallace SW. Elastomeric impression materials: effect of bulk on accuracy. J Prosthet Dent. 1979;41:304-307.
- Shillingburg HT, Hobo S, Whitsett LD. Fundamentals of Fixed Prosthodontics. 2nd ed. Chicago, Ill: Quintessence Publishing Co; 1981:228.
- Massad J, Strong S. Hidden cost in removable overdentures. Dental Economics. 2008;98:46-50.
Cagna DR, Massad JJ. Vinyl polysiloxane impression material in removable prosthodontics. Part 2: Immediate denture and reline impressions. Compend Contin Educ Dent. 2007;28:519-526.
Massad JJ, Cagna DR. Vinyl polysiloxane impression material in removable prosthodontics. Part 1: edentulous impressions. Compend Contin Educ Dent. 2007;28:452-459.
Disclosure: Dr. Brown receives consulting fees from GC America.
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