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CDEN0310

24 I I opinion _ impression materials There have been tweaks and speed improvements in these machines, which have been cloned by a handfulofcompetitorsovertheensuing15years, but the overall design is largely the same as the original version. For syringe materials, at least two VPS prod- ucts have unidose versions. While I like unidose packaging,itdoesn’tseemtohavecaughtonwith impression materials and has not been a real factor in product selection. _Intra-oral working time Our thirst for speed has resulted in the avail- ability of a number of very fast setting materials, which can be a real time-saver when you impress one or two teeth. The problem is when you try to stretch the use of fast-set materials for more than the aforementioned one to two units. The intra-oral working time of these fast-set materials then becomes a major issue. Unfortunately, the working times provided by manufacturers are typically determined at room temperature. While this provides somewhat of a comparison between products, it doesn’t really give you much indication about how much time you have between the inception of syringing the material around your preparation and when you need to seat the tray. For example, if you aretakingaten-unitimpression,howmuchtime do you have from when you syringe material around the first preparation and when you need to seat the tray? This is critical to know because the material syringed around the first of the ten preparations is already starting to set, which is accelerated by the heat and moisture of the mouth. If it sets too fast, the tray material will not bond adequately to the syringe material and you’ll most likely end up with wrinkles or other types of distortion. To my knowledge, there are only two extended working time VPS materials on the market, both of which were introduced in recent years. For large cases, it would be prudent to consider using one of them. _Tear strength If you have ever removed an impression from a patient’s mouth and found that it has torn on a critical marginal area, you know how important this property is. I recently took an impression for ten veneers in a patient who had open gingival embrasures. Normally, I would block out these embrasures from the lingual to prevent the im- pression material from locking into them and tearing on the way out of the mouth. But I was using an ‘improved’ formula of a well-known material that had claims of high tear strength. Therefore, on this case, I decided to go for it and dispense with the block-out procedure. Sure enough, the impression tore. I took a second im- pression and it also tore. The guru of tear-strength testing in my opin- ionisDrAlanBoghosian,amemberoftheREALITY Editorial Team. Dr Boghosian and his colleague recently completed a test of eight impression materials for the RRL. The material I used that tore in the mouth scored in the middle of the pack, not quite matching the strength forecast by the manufacturer. To be fair, even though the impressions I took did indeed tear, the mar- gins were still captured and the veneers seated beautifully. Nevertheless, since a torn impression can ruin an otherwise perfect effort, it would be wise not to tempt fate and block-out areas that could cause tears, such as the aforementioned open embrasures, assuming, of course, these areas don’t need to be captured. _What to use? Many aspects of taking an impression are per- sonal. For example, you get to select the material that meets your flow and set-time requirements. But beyond that, don’t get too caught up with marketing slogans such as “vinyl polyether sili- cone” or “polyeasier”. There are still only two real classes of impression material, same as they’ve been for the past 28 years. And remember—no impressionmaterialcandoitall.Togetthebestof allworlds,youprobablyneedtostocktwoorthree different types to cover all clinical situations as efficiently and productively as possible._ Editorialnote:ThisarticleoriginallyappearedintheMarch/ April 2010 issue of General Dentistry. It is published with permission by the Academy of General Dentistry. © 2010 bytheAcademyofGeneralDentistry.Allrightsreserved. cosmeticdentistry 3_2010 Dr Michael B.Miller is President of the REALITY Publishing Company and Editor-in-Chief of its publications.He also maintains a general practice in Houston,Texas,USA. Website:www.realityesthetics.com cosmeticdentistry _about the author