Creating Precision Restorations Using a Hand-Dispensed Polyether

Clinicians are faced with many choices when determining which materials to use for taking impressions. The situation is made more intricate in light of the fact that each type of material offers different strengths and features, and the procedure and handling recommendations for each material can vary. However, some materials have now been around long enough to establish a significant track record of success. With materials such as these, innovations in features and delivery options can help make them even more useful in our practices.

Figure 1. Preoperative photo, post-orthodontic treatment. The orthodontist was unable to create enough room for the placement of implants in the positions of the congenitally missing teeth (Teeth Nos. 5, 7, and 10).

Figure 2. Left lateral view of space for tooth No. 10.

Figure 3. Right lateral view of missing teeth Nos. 5 and 7.

Figure 4. Tooth No. 11 prepped for crown with cantilevered bridge.

Figure 5. Teeth Nos. 4 and 6 following preparation.

Figure 6. Final maxillary impression upon removal. Note the excellent blending of the light body and tray materials with no tearing.

Figure 7. Exceptional detail capture is made possible by the polyether’s (Impregum Soft Polyether Tray Impression Material [3M ESPE]) hydrophilicity and flow properties. Note the excellent capture of subgingival detail and margins.

Figure 8. Right lateral view of the completed restorations (Lava [3M ESPE]).

Figure 9. Left lateral view of the final result.

Figure 10. Final view of the patient’s completed maxillary arch.

POLYETHERS: A BRIEF OVERVIEW
Polyethers, introduced in the 1960s, have long been popular with clinicians for providing outstanding accuracy and dimensional stability. Most importantly, however, polyethers have proven themselves reliable in their ability to produce restorations that fit precisely even in challenging clinical situations. This performance is largely due to the material’s initial hydrophilicity, which allows the material to capture accurate impressions in the presence of moisture. In addition to hydrophilicity, polyether’s structural makeup makes the material thixotropic an important characteristic contributing to the material’s high reliability.


Refinements to the material, since its original introduction, have made current polyethers significantly easier to handle than previous formulations. In 2000, Impregum Soft (3M ESPE) was introduced. This polyether material is easier to remove from the mouth and its taste and smell are much improved when compared to the early versions of Impregum. While vinyl polysiloxane (VPS) impression materials have gained ground with some clinicians for their convenience and toughness, polyether offers the advantages of its hydrophilicity, thixotropy, flow properties, and unique setting behavior, contributing to its usefulness in clinical settings.

Hand-Dispensed Polyether Introduced
Polyether materials have previously been only available for use with automatic mixing systems, or in tubes via hand-mixing. Recently, a polyether (Impregum Soft Polyether Tray Impression Material), that can be dispensed from hand-dispensed cartridge mixing system, has been introduced. The material can be used with either a heavy body/light body impression technique, or a monophase technique using a medium body viscosity. This new delivery system allows dentists to achieve the easy and convenient dispensing style of a VPS with the clinical benefits of a polyether. This system is ideal for dentists who have not yet made the investment in an automatic mixing unit, or who are limited to using an automix unit only in selected operatories, the ability to easily use polyether in a portable system.

POLYETHER’S UNIQUE PROPERTIES
Hydrophilicity

Hydrophilicity is a standout characteristic of polyether. While VPS impression materials are actually water-repellent by nature (surfactants are added to increase the “hydrophilicity” of these materials), polyether’s chemical makeup allows it to remain moisture tolerant throughout its working and setting time. In practice, this results in an easier path to void-free impressions. This is due to the fact that when an impression material with a surfactant comes into contact with moisture, the surfactant then has to travel to the surface of the material. The “migration” time needed for this chemical process inhibits VPS materials from reaching a point of fully effective hydrophilicity during their material working time, and this delay in the action of the material can lead to inaccurate, voided impressions.


The hydrophilicity properties of polyether and VPS impression materials have been illustrated in studies which measure the contact angles of water droplets on unset materials. The polyether in these studies shows greater hydrophilicity, illustrated with a lower contact angle, meaning the material has displaced moisture better than others.1 Further testing has bolstered these findings, with researchers demonstrating that polyether is the most accurate and reliable material for recording grooves on moist surfaces,2 and also that polyether shows “significantly higher detail impression reproducibility on a wet surface as compared to all other impression materials.”3 These characteristics illustrate why polyether is preferred over VPS for outstanding performance in the presence of moisture. The initial hydrophilicity and detail reproduction help the polyether material deliver excellent marginal accuracy and integrity in clinical settings. 

Flow Properties
An additional advantage offered by polyether material is that of its flow properties, which help the product flow to critical areas without a high amount of pressure being exerted. This characteristic is especially helpful in cases with undercut areas or with a deep sulcus. The “shark fin” test is most frequently used to measure flow properties, via a process in which the impression material is injected into a small receptacle, a fin-shaped mold is placed over it, and a weight is added that represents the pressure applied to the material during clinical use. The weight slowly sinks into the material for the specified setting time, after which the height of the resulting “fin” is measured. A taller fin represents better flow properties with this method. The results of this test for Impregum Soft impression material show that it outperforms VPS at both the beginning and end of its working time, exhibiting significantly better flow properties. Results show the flow properties for Impregum remain almost constant throughout the entire working time of the material.4 Additional findings on the cartridge-dispensed polyether are consistent with this data. A study comparing the flow of Impregum Soft Polyether Tray Impression Material delivered from the hand dispenser versus commercial VPS impression materials found that the polyether material showed higher flow than the VPS tested.5

Structural Viscosity and Snap-Set Behavior
Complementing its hydrophilicity and flow properties, polyether’s structural makeup also results in thixotropy, meaning it changes viscosity under stress. This characteristic adds to the reliability of a polyether, as its viscosity is reduced at increased shearing speeds; such as those that occur when the material is being injected or applied to the tray. However, when no stress is being exerted, the material quickly returns to a highly viscous state which prevents it from oozing out of the tray or away from the tooth preparation. This property is the result of the triglycerides used in polyethers. Triglygerides form a 3-dimensional (3-D) lattice that harbors its liquid parts, giving the material the required stability. Under stress, the crystals in the material align evenly and its flowability increases, but once the pressure is released the 3-D lattice is restored, the material reverts to its original viscosity.


The makeup of polyether is such that even under minimal outside forces, its high degree of flowability is exhibited, giving it ideal handling properties for the clinical setting. After its brief setting time is complete, the material polymerizes into a strong lattice structure, giving the material ideal elastic behavior. This “snap-set” characteristic means that polyether will not start setting until the end of its working time. In addition, when it does set, it does so immediately. This characteristic helps polyether deliver excellent detail without distortion, using a variety of impression making techniques. This forgiving behavior of polyether is just one more quality that helps to set it apart from a VPS material. 

These clinical qualities help explain why dentists rely on polyether to capture consistently detailed and accurate impressions, especially in larger multi-unit (3 or more) crown and bridge cases. 

The benefits of the material’s chemical makeup, its portability and ease of use, and also its extended working time are illustrated in the following case report. 

CASE REPORT
A 19-year-old female patient presented with congenitally missing teeth Nos. 5, 7, and 10 (Figure 1). The patient had previously undergone orthodontic treatment in hopes of creating space for implants to be placed. Unfortunately, the orthodontist encountered problems with the roots of the teeth and was unable to torque the existing teeth enough to create adequate space for implants (Figures 2 and 3). Following this treatment attempt, the patient was seeking another option for filling in the missing spaces in order to achieve a more aesthetic smile.


After examining the patient, it was determined that the best course of treatment would be the placement of a fixed bridge on teeth Nos. 4 through 7. Teeth Nos. 4 and 6 would serve as abutments, tooth No. 5 would be a standard pontic, and tooth No. 7 would be a cantilevered pontic. Additionally, on the opposite side, we determined to place a crown on No. 11 with a cantilevered pontic in the space for No. 10. While not as ideal a treatment as implants would have been, this plan allowed us to fill in the gaps aesthetically while still leaving teeth Nos. 8 and 9 intact. This conservative approach was possible due to the known strength of the cuspid and the fact that the lateral would not be subjected to bite forces as high as elsewhere in the mouth. Restorations with CAD/CAM zirconium oxide substructures (Lava [3M ESPE]) were selected because of its strength and aesthetics. 

The teeth were prepped (1.5 mm axial reduction) with a diamond chamfer bur (856-016 [Brasseler USA]) (Figures 4 and 5). Then, 2 retraction cords (Ultrapak No. 000 [Ultradent Products]) were placed into the sulci in preparation for the impression, using the double-cord technique. Just before placement of the impression material, the top cord (the second one placed) was removed and Impregum light body impression material was injected into the sulci. A tray was filled with Impregum Soft Polyether Tray Impression Material using the hand operated dispenser, and then placed into the patient’s mouth. In a multi-unit case such as this, the additional working time provided by the impression material is very valuable. The tray was held in place with passive pressure for 4 minutes, and then removed. Upon inspection, the impression appeared very crisp, and the blending of the tray and syringe materials was excellent (Figures 6 and 7). 

Provisionals were fabricated in the mouth with a self-curing bis-acryl (Protemp Plus [3M ESPE]) material, removed, and then luted into place with a temporary cement (Zone [Dux Dental]). The patient was asked to return 2 weeks later for placement of the final restorations. The all-ceramic Lava restorations seated easily due to the high quality polyether impression that gave the dental technicians who worked on the case exactly what they needed to create precise fitting restorations. The patient was very happy with the final result, and was pleased to finally have a beautiful and complete smile (Figures 8 to 10).

CONCLUSION
Proper technique is vital in taking an accurate impression. In addition, the impression material itself is vital for capturing the preparation and other morphological details in a way that will meet the goals of the dentist and the patient. With an outstanding impression material, dentists will have less retakes and intraoral adjustments. Doctors and their dental laboratory teams will also benefit from fewer remakes while creating restorations that are outstanding both aesthetically and functionally.


References

  1. Klettke T, Kuppermann B, Führer C, et al. Hydrophilicity of precision impression materials during working time. Paper presented at: International Association for Dental Research—Continental European Division (IADR-CED); 2004; Istanbul, Turkey.
  2. McCabe J, Carrick T. Impression accuracy when recording impressions of moist surfaces. Paper presented at: International Association for Dental Research—Continental European Division (IADR-CED); July 1, 2006; Brisbane, Australia.
  3. Perry R, Kugel G, Appelin E, et al. Detail reproduction of impression materials on a wet surface. Paper presented at: IADR/CADR/AADR; March 23, 2007; New Orleans, La.
  4. 3M ESPE Impression Materials Update. Studies show clinical advantages in using innovative “soft” polyether vs. vinyl polysiloxane. 2004; Seefeld, Germany.
  5. Durack JL, Hudson C, Kuppermann B, et al. Flow of impression materials during working time. Espertise Scientific Facts 2008. 3M ESPE; Seefeld Germany. Paper presented at: International Association for Dental Research; September 2008; Toronto, Canada.

Dr. Margeas received his DDS from the University of Iowa College of Dentistry in 1986 and completed an AEGD residency in 1987. He is an adjunct professor in the Department of Operative Dentistry at the University of Iowa. He is board-certified by the American Board of Operative Dentistry and is a fellow of the Academy of General Dentistry. He has authored numerous articles on implant and restorative dentistry and lectures on those subjects. He is the director of The Center for Advanced Dental Education and maintains a private practice in Des Moines, Iowa. He can be reached at (515) 277-6358 or via e-mail at rcmarge@aol.com.

 

Disclosure: Dr. Margeas reports no conflicts of interest.