Impression-Taking: Overcoming Challenges of a Demanding Oral Environment
A VPS solution without compromise
Stephen D. Poss, DDS
For most general dental practices, fixed prosthetics continue to be a mainstay. The single-unit crown is the third most common procedure in dental offices.1 This can equate to as much as half of billable restorative procedural revenue for an average practice. Several key factors, as discussed below, contribute to the success of this procedure.
What to Consider
First, clinicians should consider the type of restoration that they would like to have fabricated prior to starting the procedure. This includes deciding what type of substrate (eg, PFM, lithium disilicate, zirconia) from which the crown will be fabricated and what preparation design is needed to obtain the desired result. The preparation may require the clinician to manage tissue depending on the location of an existing restoration or decay that must be removed.
These types of considerations can also determine what type of cement protocol should be used. Will the tissue management and margin location allow for an adhesive protocol or use of more traditional cement?
Additionally, office time and overhead are critical components that the clinician must manage, especially in the delivery of a crown-and-bridge. If the procedure is not done precisely, verification of the fit of the crown and occlusal adjustments can add unanticipated extra time to the process. The remake of a crown can be quite costly for the clinician and inconvenient for the patient.
In recent years there has been an increase in the use of retraction paste to manage tissue.2 The trend in using the single-cord retraction method instead of double-cord techniques has created thinner films of impression material around the margin. This can lead to a greater possibility of tearing of the impression material, especially at the margins. Most dental laboratories require multiple pours, which can increase the likelihood of a thin marginal area tearing.
Another concern for obtaining an ideal impression is moisture contamination. Some vinylpolysiloxane (VPS) materials are not very hydrophilic and require the preparation to be dried thoroughly to obtain an accurate impression. Not only is this difficult to achieve—especially on second molars—it is well documented that over-drying the dentin can cause postoperative sensitivity in some patients.3
Performance Under Stress
Aquasil® Ultra (Dentsply Sirona Restorative, www.dentsplysirona.com) has been a foremost VPS impression material for years. Building off of market-leading technology, Dentsply Sirona Restorative is now introducing Aquasil® Ultra+. This new impression material heightens performance for dentists by improving on material hydrophilicity in the intraoral environment and delivering high tear strength when and where it is important, namely in thin cross-sections when the material is being removed from the patient’s mouth. This new material is designed to offer peak performance in even the most challenging of circumstances.
In addition to the high intraoral tear strength of Aquasil Ultra+ that reduces the risk of tears when removing the impression from the mouth, the material also maintains its high tear strength, improving after 24 hours.4 This ensures that the dental laboratory will achieve the same results if multiple pours are needed.
Aquasil Ultra+ also offers high intraoral hydrophilicity, which reduces the risk of voids at the margin, a common occurrence with impression materials due to the presence of moisture when impression-taking. This new material wets out quickly while still in an uncured state as it is syringed around the prepared tooth. As illustrated in Figure 1, water, when placed on an uncured film of impression material, does not wet out as a clinician would want. The contact angle shown is 78°. Figure 2 demonstrates how Aquasil Ultra+ offers dramatic improvement in this performance area, showing a contact angle of just 12°. This test was performed at 80% humidity to replicate the environment in the oral cavity. The increased hydrophilicity will give the clinician a higher degree of marginal detail in the presence of moisture. Intraoral hydrophilicity, speed, delivery, taste, and product selection all combine to make this new material unique.