Impression Materials

Gary Radz, DDS

With more than 60 different brands available from over 30 different manufacturers, the selection of impression materials is almost too great for even the best of clinicians to fully absorb. From the variety in available chemistries including polyvinyl siloxanes (PVS), polyethers and addition silicones, to the selection of viscosities and set times; how does the dentist go about choosing the right materials? To aid the dentist with the process of comparing and selecting the right materials for his or her practice, a comprehensive chart is provided here for a quick comparison of all the major materials with their basic performance specifications, breadth of line, delivery options and price.More importantly, this Buyer's Guide seeks to provide the dentist with more than just the technical specifications of these products; there are other considerations to the product selection process that can and most likely will influence the buying decision.

Ultimately,what really matters is whether the impression produced is of high enough quality to provide a great fitting restoration. Until a material is evaluated all the way through the delivery of the final restoration, the end result cannot be truly determined. The literature is filled with information on the differences in chemistries as well as the various techniques for impression taking with all the necessary steps to ensure an accurate impression; addressing these topics is not the objective here.What is at issue is how the selection of an impression material brand impacts the success of indirect restorations and the clinical needs of the dental practice. The answer really lies in how diligent a dentist is with keeping a clean, dry field and selecting the appropriate materials, viscosities, and set times, as well as the proper type and size of tray for each and every impression that is taken. It is a balancing act each time, for sure. One of the most effective ways to ensure that a final impression will yield a great fitting indirect restoration is to thoroughly inspect it for marginal detail, bubbles or voids, drags and pulls before sending it off to the lab.

Under ideal conditions, most impression materials will yield a satisfactory result; however, impressions are taken on a daily basis under less than ideal conditions and this is where the variation in clinical success can occur between material types and even brands. The more hydrophilic a material is, the more forgiving it will be with regard to the presence of moisture. The greater the hardness of a material, the less prone it will be to distortion.Distortion can also be minimized by selecting the appropriate trays and abiding by the proper working/setting times for a given material. However, though the dentist may prefer the most hydrophilic materials with the highest Durometer hardness, there are also issues of patient comfort and acceptance to consider. These are affected by taste as well as set time and may, in many cases, dictate the choice of materials.There is a time, a place, and a clinical or laboratory application for most, if not all of the materials available. What is important when choosing an impression material is whether the material suits the particular needs of the practice and delivers the desired results.

The needs of most practices are primarily dictated by applications, personal preferences, and the clinical needs of the primary patient base. Whether a practice takes impressions for crown and bridge restorative work, implants and/or for making some of its own prosthetics or mouth guards will likely guide the decision whether vinyl polysiloxane (VPS), polyether, and/or alginate materials are maintained in inventory. The decision regarding a specific brand will likely be driven by a combination of factors, including, but not limited to:

• Preferred technique(s) that may dictate the need for specific viscosities such as tray and wash materials and/or putty.
• Preferred handling characteristics often influenced by specific material flowability and consistency.
• Available flavors, especially if children are frequently treated.
• Delivery method/packaging, if, for example, tabletop auto-mix dispensers are routinely used.

The materials with the highest Durometer scores, the best hydrophilicity, and the shortest setting time will naturally stand out in the following comparison chart.However, these attributes rarely come all together in one material. As a result, tradeoffs- most likely driven by preferences- will often be made until the right materials to meet the application needs of the practice are identified. One thing is certain: whatever the needs of any individual practice, given the pure range of available materials there is an impression material that is well suited for the job and will deliver the desired results.

Click to view table.