What Is the Best Method to Capture a Flawless Traditional Impression?
Sabiha Bunek, DDS | Brian Harris, DDS | Lee Ann Brady, DMD
Sabiha Bunek, DDS, is the editor-in-chief and chief executive officer of Dental Advisor and maintains a private practice in Ann Arbor, Michigan.
Brian Harris, DDS, creator of the Smile Virtual Consult platform, is a recognized speaker on topics related to cosmetic dentistry and technology and maintains multiple private practices in Phoenix, Arizona.
Lee Ann Brady, DMD, a nationally recognized educator, lecturer, writer, and practitioner, maintains a private practice in Glendale, Arizona.
Sabiha Bunek, DDS: Due to the nature of what we do at Dental Advisor, I have used several of the products/tools on the market and found that ensuring a predictable impression every time requires the use of quality materials, proper management of the soft tissue, and the implementation of accessories to help provide more control and precision during light body application.
When it comes to impression material selection, clinicians should not make purchasing decisions based on cost alone. Although there are some good low-cost impression materials on the market, the higher-cost products tend to be more reliable and consistent, which is reflected in their price point. I've used lower-end impression materials before, and the savings can be a wash if the detail and accuracy are not to my standards and the impression needs to be retaken.
More important than material selection is achieving hemostasis and properly managing the soft tissue. In order to ensure the excellent marginal fit of restorations, all captured tooth margins need to be free from bleeding and moisture and visibly clear. When mild retraction and/or hemostasis are needed, I prefer to use a 15% aluminum chloride retraction paste (eg, Traxodent®, Premier; Astringent Retraction Paste, 3M); when moderate retraction is required, I prefer cord packing; and with deep margins, I utilize a diode laser (eg, Picasso Lite Plus, AMD; NV® PRO3 Microlaser, DenMat).
After a high-quality impression material is selected and hemostasis/retraction are achieved, time should be invested in the actual technique of impression-taking. A couple of years ago, I incorporated an intraoral auto-mix syringe dispenser into my technique, and it has significantly improved the detail and accuracy of my impressions. The small size of the disposable syringe allows for precise application of the wash material, right at the sulcus, and alleviates hand stress as well. The traditional gun systems that utilize 50-mL cartridges are bulky, and I find that with my smaller hand size, the light body material is hard to extrude while trying to maneuver around teeth and preparations. Some syringes that I prefer are the Better Faster Cheaper Syringe (Ho Dental), the Mojo II™ Syringe (Zest Dental Solutions), and the Intra-Oral Syringe (3M).
Brian Harris, DDS: My process for taking a "traditional impression" is much different than that of other clinicians because I have not packed cord for a final impression in more than 14 years. For the way that I practice, I have come to believe that it is an unnecessary step in the impression-taking process. That may seem like dental blasphemy to some practitioners, but hopefully, I can explain this change in thinking in a way that allows them to see things differently when it comes to final impressions in dentistry. The whole purpose of taking a final impression is to capture accurate margins so that your lab can fabricate a good-fitting restoration; therefore, the key to a flawless final impression is a flawless preparation design. As long as the lab can see your margins clearly, they can do their job. Taking an extra few minutes to properly prepare that single crown or even longer to finish preparing a 10-unit veneer case will result in smooth, continuous margins and surrounding tissue that is healthy and has not been chewed up by the diamond bur.
Once your preparation design is finished, use an impression material that is thin enough to inject into the natural sulcus of the tooth and capture an ideal margin without the need for cord. After trying many products throughout the years, the one that works best for me in my practice is Take 1™ Advanced™ impression material (Kerr Dental). It allows me to capture accurate impressions on the first try nearly every time. Ideal preparations lead to ideal impressions, both of which are needed for ideal cementation of the final product.
When capturing impressions for single-unit crowns with subgingival margins in the presence of bleeding tissue, my method is still the same. First, achieve hemostasis, and then use an impression material that is thin enough to flow around the tooth and into the existing sulcus to capture the ideal margin. After creating an ideal preparation, the secret to capturing an accurate impression is in the consistency of the impression material. If you can find the right consistency, the impression-making process will become predictable in your practice.
Lee Ann Brady, DMD: Capturing an exquisite final impression is the goal every time, and getting this result can be one of the most challenging things that we routinely do in dentistry. To meet this challenge, we must be masterful at handling the materials and taking the impression, but we must also properly manage the oral environment. For crown and bridge impressions, this process should always start with tissue management.
Tissue management begins before tooth preparation. For many patients, old restorations with poor margins compromise hygiene and the gingival tissues are irritated and inflamed at the time of preparation. Prior to beginning the restorative therapy, one of the best tools that I have to optimize soft-tissue health is a chlorhexidine varnish application (ie, Cervitec® Plus, Ivoclar Vivadent). When we recommend that a tooth be crowned, if the soft tissue is currently inflamed, we place chlorhexidine varnish and the tissue health is vastly improved by the time we take impressions.
In addition, tooth preparation itself can result in difficulty managing the tissue. When clinically appropriate, my preference is always to leave the margins supragingival. My second choice is equigingival, where the margins are right at the crest of the tissue. If the margins need to be placed subgingivally, I want to avoid preparing the tooth and cutting the tissue because then I have to manage bleeding. For these cases, my initial margin is located equigingivally, but then I place a primary retraction cord to move the tissue out of the way. This allows me to then drop the margin to a subgingival level with minimal trauma to the tissue.
Once the teeth are prepared, retraction creates a space for the impression material to go past the margin apically, capturing the proper emergence profile of the restoration. There are many ways to retract prior to an impression. Personally, I prefer to place a second or "top" cord with a larger diameter than the primary cord that I placed to facilitate subgingival preparation. If the tissue is bleeding after the placement of the top cord, I use retraction paste (ie, Astringent Retraction Paste, 3M ESPE) as a hemostatic agent. This allows for the optimal control of bleeding without negatively impacting the set of my impression materials or staining the preparation or gingival tissues.
When it is time to take the final impression, I have my assistant load the tray with heavy body material (Flexitime®, Kulzer) while I wet the top cord so I do not cause bleeding upon removal. After the area is thoroughly dried to allow for proper contact of the impression material with the tooth and tissue surfaces, I inject Flexitime® Correct Flow (Kulzer) and then seat the impression tray.