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CDEN0310

I 23 opinion _ impression materials I cosmeticdentistry 3_2010 fore, another way of describing ‘hydrokinetic’ would be ‘hydrophobic’. In other words, this prod- uct essentially returns to the early days when all VPS materials were hydrophobic. The RRL also tested this product, but the manufacturer did not specify another product as a control. This makes interpreting the data more difficult, although there were virtually no differences between the experimental groups, indicating that this product will perform as the manufacturer claims it will. Does any of this matter when you are trying to take an accurate impression? Well, if the sulcus is filledwithfluid,includingblood,thatisobscuring your margin, then it could definitely make a dif- ference. If you are using a supremely hydrophilic material, you hope that the product will literally soak up the fluid similar to a sponge and, at the same time, register the impression. On the other hand, if the material is hydroki- netic,theaimistomovethefluidoutofthesulcus first and then capture the margin. Is this a better strategy? The answer is probably yes, since there is less chance that the fluid will distort the mate- rial, as it may do if it was absorbed. But if this strategy is preferred, why have virtually all man- ufacturers opted for the hydrophilic route? One reason could be the mob mentality. If it works for one company, then other companies produce the same item with some slight tweaks. Another reason is that the concept flies in the face of the trend. Hydrophilic is the in concept, from bonding agents to cement to sealants. Why should impression materials be any different? And hydrophilic PE followed in the successful footprints of hydrophilic hydrocolloid. Finally, only one company thought of it. Soshouldyouswitchtoahydrokineticimpres- sion material? Not necessarily. There are numer- ousotherfactorstoconsider,suchasworkingand setting time, flow and availability in different delivery systems. All these criteria may be as or even more important than hydrophilicity. And,ofcourse,noneofthismattersatallifyou use proper soft-tissue management BEFORE you even lay a diamond on the tooth. Preventing a bloody sulcus is much more effective than having to deal with it after the fact. This is my own per- sonal mantra. I obsess over tissue management. However, although this is an admirable goal, it doesn’t always happen. Therefore, finding an impression material that will be ‘forgiving’ has significant value. This is why PE continues to garner kudos from its devotees—these products tend to be less sensitive to moisture and have a terrific ability to wet out the preparation under adverse conditions. _Viscosity and flow This is an issue that goes back to how you pre- fertotakeanimpression.Ipersonallypreferavery light body/heavy body combination. Therefore, I look for a light body material that syringes easily andflowswellwithoutbeingtoorunny,combined with a heavy body tray material that will push the syringe material firmly against the preparation and, at the same time, not run down the patient’s throat. Less popular is a monophase material for both the syringe and tray. But very low viscosity syringe materials com- bined with heavy body tray materials is not new, although the RRL tests on flow using the Shark Fin device developed by 3M ESPE have found more re- cent selections with high flow. This means if you’re likeme,younolongerhavetostickwithoneortwo brands to get better flow in your syringe material. _Hardness/stiffness With the increasing popularity of closed- mouth impressions, especially with sideless trays, a more rigid or stiff material should work better by providing lateral support, although to my knowledge, this has never been shown in a clini- cal comparison. Nevertheless, there have been a few materials that the RRL has measured using a digital durometer that are indeed stiffer than the rest. Just don’t be tempted to use a very rigid material for a full-arch impression, especially if youareusingawell-fittingcustomtray—youmay need a ‘knee-on-chest’ manœuvre to remove it from a patient’s mouth! _Dispensing options Another area with some significant changes is mixing/dispensing. The hand-mixing of tube- based products in the past has been largely re- placed with cartridge-based products mixed and dispensed using a ubiquitous automix gun. How- ever, these guns are no longer exactly cutting edge, look like you bought them in a home-im- provement store, and can make filling a full-arch tray a real challenge for an auxiliary due to the hand and forearm strength required for heavy body materials. To overcome the disadvantages of guns, ESPE introduced the first electronic mixer in 1995.