![]() ![]() PVS material can be used in ether a single-stage or two-stage impression technique as new material will bond to already-set material. ![]() A softer material is available that can be injected into the marginal detail, and it is advised this also be placed into undercuts, such as under existing bridges, to prevent the impression from locking intraorally. When excess undercuts are present, it is recommended that these be blocked out. These materials are also stiffer than PVS. As polyether impression materials will not adhere to already-set materials, one cannot reline the impression to capture additional detail therefore the impression must be taken in a single step. ![]() Polyether impression materials are used in a single-step process. The dental auxiliary should have an understanding of how best to use these materials, in various clinical situations. Each of these materials has its proponents and detractors. Impression materials that are recommended for final impressions are in 2 categories: polyether (eg, ImpregumTM, 3MTM ESPETM, and PVS. They do not require immediate pouring and usually have sufficient durability to allow multiple pours from the same impression. In recent years, alginate substitutes have been introduced, which are less expensive medium-body polyvinyl siloxane (PVS) impression materials. In addition, due to the delicacy of the material, multiple pours are not possible as the material typically tears upon separation of the cast from the impression. However, alginate impression materials must be poured immediately because they lose accuracy as they dehydrate. Alginate materials are suited well for preliminary impressions and study models or for bleaching trays, occlusal guards, and other uses for which finite accuracy is not critical. No one impression material fits every clinical situation. This article will address some basics to explain how the appropriate selection of impression material and tray is integral to the end result of the impression. However, the quality of impressions can greatly affect the clinical results. Many dental practices may overlook the importance of good impressions. The appropriate selection of impression material and tray is integral to the end result ![]()
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