June 2010, Volume 6, Issue 6
Published by AEGIS Communications
Esthetic Lower Restorations
Creating beautiful restorations begins with using a reliable and convenient impression material.
Making an accurate impression is probably one of the most challenging tasks dentists have to perform daily. An ideal impression material enables dentists to predictably make highly accurate impressions while offering flexibility and convenience in its delivery and use.
In the author’s 23 years in dentistry, he has had the opportunity to experiment with many different kinds of impression materials, and has come to use 3M ESPE Impregum™ Soft Polyether Impression Material (3M ESPE, http://www.3mespe.com/greatimpressions) as the primary material in his office. As a polyether, the Impregum material offers the clinical characteristics necessary to deliver highly accurate impressions and outstanding restorations. In addition, the recent introduction of a new dispensing method for the material increases its convenience. Previously, Impregum material was primarily dispensed from an automatic mixing system. While this provides a consistent and quickly dispensed mix, it also has the possibility of limiting the number of operatories in an office that can be used for impressioning, as some dentists do not wish to go to the expense of equipping all of their operatories with a mixer. The author always found that having his assistant fill the tray with the automatic mixer while out of the operatory resulted in difficulties determining when to syringe the lighter-body wash. However, Impregum material recently became available in a handheld cartridge dispenser, which makes a significant difference in its convenience and portability between operatories. While the author has had experience using other materials that are difficult to dispense from a gun, the Impregum material flows nicely and his assistant has no problems with it.
Just like everyone else, the author hates retaking impressions (and the patients hate it even more), but Impregum material’s reliability gives him confidence in capturing the margins and subgingival detail, often of six to 14 units, the very first time. The six-unit lower anterior case presented below demonstrates a clinical situation in which the properties of Impregum helped to create a highly accurate impression and great fitting restorations that needed no adjusting.
Nine years prior to his visit to the author’s office, the 57-year-old patient had veneers and reverse three-quarter porcelain crowns placed on teeth Nos. 22 through 27. Subsequently, he had undergone several root canals and had chipped several of the crowns. Additionally, dark stains had developed around the root areas of several of the restorations (Figure 1). As a dentist himself, the patient was motivated to address these esthetic and functional issues. It was determined that all of the existing restorations would be replaced with new reverse three-quarter crowns. This allowed the original preparations for the existing crowns to be maintained, and a more conservative approach than full crowns could be used to replace the veneers while covering the endodontic access openings on the lingual.
At the impressioning visit, the old restorations were removed and x-rays were taken. In this case, the margins were close to equigingival or slightly subgingival; therefore, it was not necessary to place retraction cord except on one area of tooth No. 25. The author believes that this is a major benefit to using polyether; if a margin is close to the gum line he often does not worry about packing cord, because he feels confident that the material will flow into the areas it needs to. This is a great time saver and decreases the chance of postoperative sensitivity the patient might experience from the trauma to the gingival tissues during cord placement.
The preparations were finished and photographs were taken for shade selection (Figure 2 and Figure 3). Additionally, the bite record was taken. To take the full-arch impression, the assistant used the cartridge dispenser to load an adhesive-treated tray with Impregum Soft polyether tray impression material as the author syringed wash material around the preparations. After syringing, air was lightly blown around the wash material on the preparations to break the surface tension. Before seating the tray, a small amount of wash was dispensed into the top of the tray material. The tray was seated with a straight vertical path of insertion and held in place for 3 minutes and 15 seconds.
After the full setting time had elapsed, the tray was removed and the author examined the impression with loupes to ensure that the margins were clear (Figure 4). After confirming the impression had been accurately captured, Protemp™ Plus Temporization Material (3M ESPE) was used to create the temporaries (Figure 5). The patient reported that the temporaries felt very smooth and comfortable.
Six weeks later, the patient returned to the office for placement of the final restorations (Figure 6). The crowns were tried in and an excellent fit was confirmed; no interproximal or occlusal adjustments were necessary because of the use of a great impression material and excellent laboratory fabrication. Minor characterization (done in the office and arranged with the laboratory) was performed to lower the color value to match the existing restorations, and the new restorations were then seated with RelyX™ Veneer Cement (3M ESPE) (Figure 7, Figure 8, Figure 9). The patient was very satisfied with the final appearance (Figure 10).
The properties of the impression material used in this case help to explain its reliability and accuracy, which contributed greatly to the final result. First among these properties is the material’s hydrophilicity. This is one of the key characteristics that make polyether so accurate.1 To demonstrate the hydrophilic properties of impression materials, studies compare the contact angles of water droplets on unset materials. When comparing polyether and vinyl polysiloxane (VPS) via this method, results have shown that the water droplet on the polyether material exhibits a lower contact angle, meaning the moisture has been displaced to a greater extent due to the material’s higher level of hydrophilicity.2
An additional characteristic of polyether is its thixotropy, or its ability to change viscosity under stress.1 When the material is being dispensed into a tray or injected, it flows easily. It quickly returns to a viscous state, however, when no force is being applied to it, helping to prevent oozing away from the tooth preparation.1 Once the material’s working time is complete, it polymerizes into a strong lattice structure. This is what is referred to as the material’s “snap-set” characteristic, meaning that it will not start to set until the end of the working time, but at that point, it sets immediately. Because of this characteristic, it is vital to leave the material in place for its full working time. Many times dentists remove impressions early, creating distortions in the material simply because they did not wait until it was fully set.
In cases with undercut areas or a deep sulcus, polyether’s excellent flowability is an especially vital quality, as the material is able to reach key areas without a high level of pressure being applied. Tests have shown that the flow properties for Impregum material remain nearly constant throughout its working time, and that it performs better than VPS both at the beginning and the end of the materials’ working times.3 That is why for multiple-unit cases, where it may take longer to syringe the wash and place the tray, the author likes to use Impregum material. These results hold for the cartridge-dispensed material as well as the traditional automixed material.4
In impressioning, using an excellent material is vital, but it is only the first step. There are several other measures that the author employs, and teaches as well, to help ensure an accurate impression. Selecting the proper tray size is an important step. If the tray is too small, it may prevent complete setting of the tray, it may not capture all of the teeth needed in the impression, and it may cause distortion of the material from rubbing the tissue. If the tray is too large it will be difficult to get into the patient’s mouth and be uncomfortable for him or her and, again, it may cause distortion from rubbing the intraoral tissue. It is also important that the tray is placed soon after the light-body material has been syringed around the preparations. The dentist and the assistant filling the tray must consciously determine when it is best for the dentist to begin syringing the light-body material.
Another important component is holding the tray in place. The author has observed many dentists instructing patients to simply bite down on the tray, but patients can sometimes bite down too hard and bottom out on the tray, ruining the impression or, just as bad, causing the tray to rock as the back teeth hit the tray as they close. Transferring the hold to an assistant can also be risky, as it may allow the tray to shift. Therefore, in the author’s practice he manually holds the tray in place during the material’s setting time until it has achieved its initial set before allowing the assistant to hold the tray. At no time is the patient allowed to close on the tray.
Allowing the material to set for the full time is another key factor in preventing distortions. Polyether’s snap-set behavior is very helpful for allowing additional working time when doing multiple-unit cases, but it also makes it especially important to allow the entire setting time to elapse before attempting to remove the tray. The author recommends setting a timer to help ensure that the full time has passed before removing the tray.
Finally, thoroughly checking the impression after removal is a simple and vital part of the process. The author makes sure to confirm that the wash and tray materials have blended well, with no demarcation between one and the other. Then, he recommends using loupes to examine the margins of the preparations. Taking the time to thoroughly examine the impression is far preferable to hearing later from the laboratory that the impression is unsuitable and the patient will have to be called back.
Using a quality impression material and the technique covered here, dentists can feel more confident that they will capture an accurate impression the first time they take it, and have superbly fitting restorations no matter how many units are involved. As this case demonstrates, multiple lower restorations can have a significant esthetic impact, and this high-quality impression material played a key role in creating outstanding restorations.
The author would like to thank Dr. Arthur A. Tomaro for his cooperation and input, and Bob Clark of Williams Dental Laboratory for his excellent laboratory work.
The author has received material support from 3M ESPE.
1. 3M ESPE Impregum Technical Product Profile. Available at: http://solutions.3m.com/wps/portal/3M/en_US/3M-ESPE/dental-professionals/products/category/impression/impregum-penta-soft-quick-step/.
2. Klettke T, Kuppermann B, Führer C, Richter B. “Hydrophilicity of Precision Impression Materials During Working Time,” CED/IADR, Istanbul, 2004; submitted for publication.
3. 3M ESPE Impression Materials Update. Studies show clinical advantages in using innovative “Soft” polyether vs. vinyl polysiloxane. 2004.
4. Durack JL, Hudson C, Kuppermann B, Klettke T. Flow of Impression Materials During Working Time. Espertise™ Scientific Facts 2008. IADR #3191;2008.
About the Author
Michael Miyasaki, DDS
Las Vegas, Nevada