Dr. James Braun, DDS, MS

	The concept of taking an impression may be simple, but there are a number of factors that can cause a less than an ideal impression, resulting in a retake that requires more time, more product, and ultimately, a dent in profitability.

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Considering the number of potential complications that can arise during the impression-taking process, this article will detail how to avoid common impressioning issues. While every material and technique presents its own sensitivities, these guidelines can help clinicians consistently achieve high-quality impressions. 

Ensuring a clear and moisture-free margin is an essential first step in capturing a detailed impression. First, retraction paste or cord should be dispensed or placed around the gum area to ensure a well-defined marginal area. Figure 1 demonstrates the clean margins achieved using a retraction paste (

) prior to the impression-taking procedure. In this instance, the product dispenser’s fine tip fits into the sulcus, providing improved interproximal delivery. 

The retraction process is especially helpful with shallow preparations, and while this first step is not often discussed, it has an important impact on final treatment success.

Begin by confirming there are no issues with contamination in the mouth, such as blood, saliva or chemical contaminants, which may be present if the surrounding gum area is not adequately displaced. To help keep the tongue displaced and prevent saliva from pooling, clinicians may elect to use a slide injector before taking an impression (

Prepared view of No 30 which displays well-defined margins

In this particular case, tooth No. 30 was prepared for a resin nano ceramic restoration (3M™ ESPE™ 

). Once a dry and clean area was achieved, and soft tissue was not in contact with the margins, the impression was taken with a high-quality impression material. In this case, 3M™ ESPE™ 

Imprint™ 4 VPS Super Quick Impression Material

) was used, which takes only 75 seconds to set. This material is used in about 85% of our clinical workload, and its bright colors and sharp contrast ensures the detail captured in the impression is easy to see. 

The impression is void-free with superior detail capture

Advancements in impression materials such as faster set times and high color contrast allow clinicians to be more efficient, saving time and money in the long run. Finding a high-quality impression material that can be utilized in a number of situations also helps reduce inventory. While bargain options might be appealing, impression material is a product category that dentists cannot afford to shortcut. 

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Continue to the next page to learn more about the solutions offered by 3M ESPE Imprint 4.

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A quick set time is an added benefit of an advanced impression material, but ensuring the product also allows for enough working time is critical to ensure a clinician’s technique is not compromised. Consequently, any good impressioning technique must include an understanding of the chosen material’s working and setting times. 

An ideal impression material should flow quickly and effectively, allowing for plenty of working time to inject the light body material on the prepared tooth. A single-use intral-oral syringe (3M ESPE) is especially helpful to dispense the light body material, as it is lightweight, easy to use and significantly cuts down on product waste. The light body material should flow over the prepared tooth easily while being able to accurately adapt to the configuration of the tooth. 

Simultaneously, the supporting heavy body material is dispensed into an impression tray and then into the mouth once the light body material has been syringed around the prepared tooth (or on top of the heavy body material, if a dental assistant is not available). To fill the tray quickly and easily, some clinicians and assistants prefer to use an automatic mixing unit such as 3M™ ESPE™ 

, which allows for faster dispensing of material while ensuring ideal mix and control.  

After 75 seconds, the stabilized impression was easily removed. It showed no voids, air traps, creases, folds or other defects, as shown in Figure 2. Thanks to a quick setting time, the entire impression-taking process was completed in less than 2 minutes. 

For those impressions that do result in error, dentists are all too familiar with the pain of having to retake the impression altogether – a process that is not pleasant for the dentist or patient. By choosing a reliable impression material and mastering the technique, the need for a retake has been avoided in this case, resulting in a very accurate impression. 

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Patient comfort can also be an issue when capturing an impression, so it is important that dentists do not work with an excessive amount of material that can potentially cause gagging. The tray should be full, but without excess material in the arch of the impression tray, ensuring optimal patient comfort.  

The time to take an impression also matters from a patient perspective. Ensuring a fast and easy patient experience makes all the difference when they are debating scheduling their next visit.

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Continue to the next page to see the results of the final restoration.

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After removal of the impression, it was sent to the dental laboratory and a stone model was created 

. The model reflects very distinct margins capable of being reproduced from the impression, critical for any type of restoration.

In this case, once the finished crown was returned from the lab, it was placed on the restored tooth 

. There was no need to adjust the all-ceramic crown, as it fit perfectly. The restoration was durable and esthetically pleasing in the mouth, providing the patient both great form and function. 

Getting an impression right the first time is often easier said than done. By choosing the best materials available, dentists can alleviate the stress of having to perform one or even multiple retakes. However, the most important part of an impression is the end result – in this case, a perfectly fitting crown leaving the patient happy and healthy.  

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 graduated from the D.D.S. program at the University of Michigan and then earned a Masters degree in Prosthodontics. He has practiced in his hometown of Saginaw, Mich., for more than 25 years, and also has offered seminars at a great number of national and international meetings. 

Articles

 The concept of taking an impression may be simple, but there are a number of factors that can cause a less than an ideal impression, resulting in a retake that requires more time, more product, and ultimately, a dent in profitability.

How to ensure a high-quality impression on the first take

Dr. James Braun explains how liner/base materials can help provide dentists with extra assurance that restorations will be long-lasting and sensitivity free.

Dentistry has seen a number of liner/base materials come and go over the years, and even now, use of a liner is not an everyday practice in many offices. However, proper use of a liner/base can help provide dentists with extra assurance that restorations will be long-lasting and sensitivity free. For this reason, it is important for clinicians to be aware of the materials currently available and the reasons for using each.

The basic function of a liner is to adapt to the internal surfaces of a cavity preparation to create a level surface and compensate for irregularities and defects, which helps in the subsequent placement of the definitive restorative materials. It also helps improve the seal for pulpal protection. When selecting a liner material, dentists typically think of two options: a glass ionomer (GI) or resin-modified glass ionomer (RMGI) liner, or a flowable composite.


	Flowables are sometimes used as a liner in composite restoration cases, or in crown and bridge cases to block out undercuts before taking an impression. In composite restoration situations, these products can be helpful in cases with atypical preparation designs that have undercuts or angulations where the dentist may have a difficult time placing direct composite. In these cases, using a flowable composite as a liner can help the dentist address issues with access and visibility, building the preparation out before filling it with the composite restoration. Some dentists use flowable as an additional layer after adhesive placement to perhaps decrease microleakage.

However, a more classic liner/base material, such as a GI or RMGI, provides clinicians with a tool that suits multiple clinical situations. The chief purpose of these materials is to help protect against post-operative sensitivity, which they accomplish in many ways. They act as a thermal barrier, are antimicrobial, seal the dentin and prevent microleakage, and also provide stress relief in a restoration. Additionally, they do not remove the tooth’s smear layer and are able to bond in a moist environment. On top of their utility in preventing post-operative sensitivity, GI and RMGI liners serve as a renewable source of fluoride under a restoration and help reduce recurrent decay. This is extremely important in areas of deep decay where increased dentinal tissue is lost.

 Vitrebond™ Plus Light Cure Glass Ionomer Liner/Base can be particularly helpful in a case such as a direct composite restoration following deep decay removal.

If, during decay removal, the clinician determines the preparation goes beyond the normal parameters and is approximating pulpal structure, placing a liner/base is paramount.

The liner/base can be placed in the preparation following decay removal and then light cured to establish a sound bond to dentin.

After this, the clinician can place the restoration following normal steps, including using an adhesive. The selective etch technique can be used, with a phosphoric acid used on the enamel, followed by an adhesive such as 3M™ ESPE™ Scotchbond™ Universal Adhesive, and then light curing. (Scotchbond Universal adhesive is appropriate for all etching techniques-selective, self-etch or total-etch.) After this, a direct composite restorative can be used to complete the restoration.

Liner/base materials also may be used in cases involving adolescent or pediatric patients, something that is often overlooked.

With their very large nerve chambers, these patients are potential candidates for sensitivity following restorations. Routinely placing a RMGI liner/base in restorative procedures on these patients can be very helpful in reducing post-operative sensitivity, versus simply restoring with adhesive and composite.


	A RMGI liner/base material performs a number of functions in a restoration that a flowable composite does not. While flowables certainly can be used as liners, dentists should understand their limitations to determine when it is and is not advisable to use them. Clinicians should keep in mind their preferred flowable’s shrinkage properties, as these materials can sometimes shrink up to twice as much as condensable composites. This can result in stress on the adhesive layer and greater potential for microleakage. An additional difficulty with placing flowable as a liner is it can sometimes be challenging to achieve an even layer around the entire internal perimeter of a preparation. Creating proper coverage without pooling and extensions may be more difficult than it seems.

Dentists also sometimes cite the flexural strength achieved by layering flowable with packable composite as a rationale for using flowable as a liner. They say that by placing an assemblage of layers that more or less match the flexural strength of the layers of the tooth as it is built up, this technique can help with stress distribution. However, using a liner/base material, which more closely matches the coefficient of thermal expansion and the flexural capabilities of the tooth structure itself, may achieve this goal more effectively.

In terms of ease of use and versatility, a liner/base like Vitrebond Plus gives dentists a helpful tool as well. The material is non-sticky and very easy to manipulate; it can be easily dragged and placed without tackiness. It is light curable, and has an optimal film thickness that helps it stay where it is placed without pooling. Additionally, it does not require an adhesive underneath it, but achieves both chemical and mechanical adhesion to dentin. As compared to earlier generation glass ionomer materials, its solubility potential is decreased because of the incorporation of resin. Finally, its two-part liquid/paste dispensing system makes it easy to get the proper proportions of base to catalyst.


	In areas of deep decay where post-operative sensitivity is likely to be an issue, the unique chemical and physical characteristics of liner/base materials can help dentists achieve better results than a flowable. In any situation that calls for a liner, clinicians should consider the benefits of a non-shrinking base with high fluoride release that achieves a good bond to dentin. This offers greater benefits to the tooth than a flowable restorative. While flowables are valuable as filler materials to create an easy-to-work-with geometric configuration, in cases of deeper preparations, a RMGI liner/base provides added assurance of minimizing post-op sensitivity and preventing recurrent decay. Because of this, liner/base material should be part of every clinician’s toolkit for regular use.