Dr. Matt Croley discusses adaptable impression materials
Impression taking is a critical and yet commonly overlooked function of a busy dental practice, and choosing the right impression material for each case can be challenging. While it’s certainly true that the type of material you choose doesn’t completely dictate the accuracy of the impression (many human factors are involved here too), selecting the appropriate impression material for each case is an important part of the process that can help ensure the best clinical outcomes and a more efficient practice. Especially in larger practices, honing in on the right materials for your cases can also help limit the amount of inventory you carry. Generally, I utilize a go-to material for what I like to call “everyday impressions,” and a second for more challenging cases that require the finest detail or longer working times, such as implant cases.
Choosing impression material
Almost all patients will need an impression at some point for diagnostic purposes — standard procedures that happen in your practice on a daily basis. For these “everyday” cases, I utilize a vinyl polysiloxane (VPS) material because it allows for sufficient time to load and seat the impression tray. Many clinicians utilize an alginate for similar cases, but it’s important to remember that alginate needs to be poured immediately if you want an accurate result. It also limits the options for multiple pours, and the material’s viscosity can mean that the accuracy of soft tissue areas could be compromised.
Taking better “everyday” impressions
VPS materials offer the kind of accuracy that you might need for diagnostic and preliminary casts, and they can be poured later if the lab can’t get to it in a timely manner. With a VPS material, there’s no “stressful race against the clock.” The material I utilize in my practice, Imprint™ 4 VPS Impression Material from 3M, also has one of the shortest intraoral setting times on the market. This means my patients are able to get out of the chair faster and with a better overall experience. I also recommend the use of an intraoral syringe because I can prepare for cases by prefilling up to 12 hours in advance without the material setting, allowing me to be more efficient during practice hours. In my practice, we use the 3M™ Intra-oral Syringe.
Another benefit over an alginate material is that VPS materials are not mixed by hand, which reduces steps, waste, and cleanup time.
Impression taking for challenging cases
For cases that offer bigger challenges or the need for finer precision (which, in my practice, comes up quite often), I turn to a polyether material — 3M™ Impregum™ Polyether Impression Material. This class of impression material offers superior moisture tolerance for void-free impressions, even in wet environments.1 We all know that the mouth presents a constantly moist environment, regardless of steps taken to reduce wetness with air, cotton rolls, and more. Impregum™ offers high precision due to the inherent hydrophilic composition of the material. This makes the material very forgiving when sulcus control is challenging due to blood and saliva contamination around the margin.
Another advantage of a polyether material is sustained flowability throughout a long working time. The long working time allows the material to flow into tough spots to capture fine details for precision impressions. A final feature of Impregum™ Polyether material that I appreciate is its unique snap-set behavior. Impregum™ Polyether will not start setting before the working time ends, and when it does, it does so immediately. It allows constant flow behavior during the entire working time. Flowability, long working time, and moisture control are the three key reasons I choose Impregum™ for many of my implant impression cases.
A 66-year-old female patient presented with pain in tooth No. 3. An X-ray confirmed that the tooth had been previously endodontically treated with a root canal and a crown. Several treatment options were discussed to address the pain, including retreatment of the root canal, removal of the tooth, a three-unit bridge, or a single-unit crown over implant.
The patient selected the single-unit crown over implant because it offered maximum predictability and strength over time. The patient was referred to an oral surgery practice for tooth removal and bone grafting. After 3 months of healing time, the patient returned to the oral surgeon for placement of a Nobel Biocare® Replace Select™ 5.0 mm tapered implant. After 4 months and ample time for osseointegration and healing time, the patient returned for impressions and to discuss a final treatment plan (Figure 1). Because strength was a priority over esthetics based on the positioning of the affected tooth, the final treatment plan included a screw-retained crown with UCLA abutment, which would also minimize the risk for peri-implantitis.
Impressions were taken with Impregum™ Soft Polyether Impression Material from 3M (Figure 2). This particular impression material was selected because it offers excellent moisture tolerance in wet environments, and the flowability continues even with a longer working time. The rigidity of the material makes it excellent for use in a tray, while the flowability helps for flowing around the implant impression post. To prevent distortion, the impression tray should be removed by first loosening it on the opposite side of the implants (moved slowly with an up-and-down and side-to-side motion) with the area to be restored being removed last. The impressions were then shipped to the lab, models were created (Figures 3-5), and the final restoration was received. The patient returned for final seating, and few minimal occlusal adjustments were made, with the initial restoration showing excellent marginal fit (Figures 6-7). Once the abutment was torqued to 35 Ncm, a cotton pellet was placed over the abutment and the access opening filled with Filtek™ Supreme Ultra Universal Restorative. Despite a tight interocclusal space, the accuracy of the impression-taking process led to a restoration with excellent fit.
With nearly 10 years of clinical experience with polyether impression material, I’ve continued to see satisfactory results, minimal retakes, and very few crown/restoration remakes, allowing me to maintain efficiency while providing the best possible patient outcomes. While VPS impression material has a place in my practice for indications such as preliminary impressions and dentures, polyether impression materials continue to be key for the majority of my impression-taking needs. In the end, it really comes down to which material works most predictably in your hands, and how “tricky” or involved a particular case may be, and I appreciate having both materials on hand to ensure that I can easily adapt to the right material for the right case.
- Walker MP, Petrie CS, Haj-Ali R, Spencer P, Dumas C, Williams K. Moisture effect on polyether and polyvinyl-siloxane dimensional accuracy and detail reproduction. J Prosthodont. 2005;14(3):158-163.