As such, considerable force may be required to remove the impression from the mouth or the stone cast.Īddition polyvinyl siloxane impression materials have four types of viscosity to suit different needs. Polyether impression materials have adequate tear resistance and good elastic properties, but they have high elastic modulus and are relatively rigid when set. It is also messy to handle and has an unpleasant odor. Polysulfide is a relatively unpopular impression material because of its long setting time. Addition polyvinyl siloxane has superior results for accuracy and dimensional stability compared with condensation polyvinyl siloxane, and research indicates that addition polyvinyl siloxane remains unchanged over time, allowing impressions to be poured days after they were recorded. Further, this impression material does not have polymerization shrinkage like that of condensation polyvinyl siloxane, so that it produces a highly stable impression because no by-products are released during polymerization. There are currently four types of elastomeric impression materials used for crown and bridge work in dentistry: polysulfide, condensation polyvinyl siloxane, addition polyvinyl siloxane, and polyether.Īt present, addition polyvinyl siloxane is widely used because of its high accuracy, good dimensional stability, good elastic properties, high tear strength, excellent recovery from deformation on removal, and short working and setting time. Synthetic elastomeric impression materials were first introduced in the late 1950s and became popular because they improved on the existing hydrocolloid impression materials in two aspects, namely dimensional stability and inadequate tear resistance associated with the hydrocolloid material used at that time. Impression materials that exhibit good dimensional stability and accuracy are necessary to record the fine details of hard and l tissues and obtain biologically, mechanically, functionally, and esthetically acceptable restorations. The ability to record the tooth preparation accurately during the impression stage is critical for producing well-fitting crowns and bridges.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |