September 2011, Volume 7, Issue 8
Published by AEGIS Communications
Digital Dentistry and the Lab-Doctor Relationship
Increase productivity with digital impressioning.
By Jim Grant, DDS; Don Albensi, CDT
Digital dentistry has enabled a dramatic transformation in the relationship between dentists and the laboratory. As a subset of this trend, digital impressioning has perhaps been one of the most significant factors in this changing relationship. However, the increasing popularity of these systems and the influx of information about them may have many dentists and laboratory technicians confused about their capabilities and purposes.
One important distinction to make when discussing digital impressioning systems is whether the system is designed for in-office or laboratory milling. In-office milling systems have been on the market for many years, and many dentists have already made their choices about whether or not they care to make milling and other laboratory tasks part of their practices. For those who prefer to focus on dentistry, digital impression systems that export data to the laboratory can be a valuable tool.
It is well established that laboratory technicians feel many conventional impressions are of poor quality.1,2 The variables of each case and the time constraints in many practices simply prevent dentists from capturing perfect impressions consistently. Additionally, patients typically find the impression-taking procedure deeply uncomfortable, and many even gag on the tray.3
As an alternative to this process, a digital-impressioning device offers many benefits. The authors are experienced in working with the 3M™ ESPE™ Lava™ Chairside Oral Scanner C.O.S. (www.3MESPE.com/LavaCOS); another such system is the Cadent iTero™ (www.cadentinc.com). In the case of the Lava C.O.S., the device captures a continuous video image of the patient’s mouth with a 14-oz intraoral wand fitted with a 13.2-mm lens. This video captures approximately 24 million data points per arch and models the image back on a chairside monitor as it is being scanned. This instant review mechanism allows the dentist to critically examine the impression as it is being captured and make any necessary corrections while the patient is still in the chair.
Early reviews and studies on the system have been promising. Data shows that restorations made with this digital impressioning device exhibit a better overall fit than those made with traditional impression materials, as well as a greater number of accurate interproximal contacts, better stability, better margins, and more precise occlusion.4 Seating times for crowns made with the system have averaged 41% faster than those made traditionally,5 and the rate of remakes due to marginal fit is 80% below the industry average.6
In a clinical trial conducted by a leading research publication, clinicians used both the digital impressioning system and a conventional vinyl polysiloxane material to capture impressions. Restorations were then created according to the appropriate workflow for each system, and doctors were asked to evaluate the resulting restorations and select one to seat. Of the selected restorations in this blind trial, 83% were fabricated with the Lava C.O.S., offering additional validation of its accuracy.7
A significant component of the digital workflow for this system is the model produced from the digital impression. These models are created at the manufacturer’s facility with a stereolithography (SLA) apparatus, which prints them, layer by layer, in a photosensitive polymer resin, and then ships them to the laboratory. This saves the laboratory the time involved in the traditional model-making procedure and results in a highly accurate and durable model. Once at the laboratory, the model can be used with a wide variety of restorative options and materials. Additionally, if the final restoration is made with Lava™ zirconia, this can be manufactured at the same time as the model, reducing turnaround time even further.
The authors’ lab, Albensi Laboratories, has gone an additional step in using digital impressioning by developing a process that allows the laboratory to turn around a single lithium-disilicate posterior crown in 48 hours. These crowns can be produced at a price that is competitive with an overseas outsourcer, highlighting the potential of digital tools for helping laboratories improve productivity. Using the PG-Pro™ process, when a digital impression arrives at the laboratory, technicians use 3Shape (www.3shapedental.com) software to design the restoration in just a few minutes. This is a part of the qualified open-architecture platform that allows for more flexibility for Lava C.O.S. users.
A batch of restorations is sent to the 3D printer at the end of the day, and when staff members arrive the next day, the batch of wax copies is ready to be finished. The white support material is removed and restorations are sent to their appropriate departments. To prepare for the press technique, the restorations are sprued onto a ring, and the ring is invested. A speed burnout is then performed, and the lithium-disilicate material is pressed. Once pressed, the ring is divested and the individual restorations are separated. The restorations are then contoured, followed by staining and glazing by a ceramist. At 2:30 on the second day, the restoration is ready to be shipped back to the dentist.
As demonstrated by these workflows, digital impressions give laboratories and dentists considerable flexibility in the type of restorations they produce. What remains consistent is the accuracy of the data, whether it is used to fabricate a model, or to directly design a restoration. Using these tools, laboratories and dentists can communicate in ways that were never possible before, reducing the chance for errors and creating work that satisfies the laboratory, dentist, and patient. The following case demonstrates the workflow for creating a zirconia restoration using digital impression-taking technology.
A female patient presented with old composite fillings on teeth Nos. 13 and 20, both of which were failing due to recurrent decay. The teeth were carefully prepared with chamfer margins to facilitate the scanning process. A size 00 retraction cord was placed subgingivally below the margin and left in place during the scan. A titanium-dioxide powder was then lightly sprayed on the teeth and the digital impression system was used to scan the preparations and the bite. The images were reviewed on the chairside monitor to confirm their accuracy, and a digital prescription for Lava zirconia restorations was submitted to the laboratory.
At the laboratory, the scan was reviewed in a virtual articulator. The software allows the technician to see the preparation in a cross-section, a two-dimensional view, or a three-dimensional view for marking of the margins and cutting of the dies. These steps were completed, and the case was sent to 3M ESPE for model manufacturing. At the same time, the restorations were digitally designed and sent for milling of the zirconia copings. Once the SLA model arrived at the laboratory, it was used in the final characterization steps.
At the dental office, both crowns were tried on to confirm fit. After it was determined that no adjustments were necessary, the crowns were seated with 3M™ ESPE™ RelyX™ Unicem 2 Automix Self-Adhesive Resin Cement in a process that took just 2 to 3 minutes per tooth (Figure 1 and Figure 2). A radiograph then confirmed the excellent fit of both restorations (Figure 3). Interestingly, the same radiograph also shows a fairly typical fit of a traditional crown on tooth No. 19, directly adjacent to the new work. The image displays shadowing and a gap in fit, which is what many dentists have found they have to accept when using traditional impression materials.
The degree of accuracy shown in this case is typical for the Lava C.O.S., as it captures data that is accurate in the range of 6 µm to 12 µm—smaller than a human hair (50 µm). This level of accuracy has an immense impact on the relationship between the dentist and laboratory, as it removes much of the guesswork and many of the steps involved in creating a traditional restoration. The ability to see the digital image as it is being captured gives the dentist the opportunity to review and modify it, if needed, before uploading it to the laboratory. The manufacturer has also taken helpful steps to assist dentists during their learning curve with the device, providing on-site training and detailed reviews of each case with feedback reports during the user’s first months (Figure 4).
The increased productivity and accuracy enabled by digital impressioning is something all laboratories should take advantage of and encourage clients to adopt. Albensi Laboratories is currently undertaking several programs to educate dentists on these technologies. Dentists in the laboratory’s area are regularly invited to attend open houses to learn about the system, and the laboratory has also invested in a unit that is sent to outlying areas to give dentists the opportunity to evaluate it in a hands-on environment during “lunch-and-learn” sessions.
For laboratories, digital impression systems open up new opportunities for productivity and efficient workflows. For dentists, digital impression systems provide an opportunity to increase practice incomes. These factors alone make it critical for laboratories to participate in this digital revolution, but an added benefit that is almost as important is the potential for improving relationships with clients. With the guesswork about the quality of an impression removed, laboratories can concentrate on fabricating highly accurate restorations. At the dental office, clinicians can then seat the restorations without the need for adjustments that damage the esthetic work done by the laboratory. In the end, the patient’s experience is improved at both the impression appointment and the seating. With this new tool for collaboration, dentists and laboratories can create restorations that have a true “wow” factor.
1. Christensen GJ. Laboratories want better impressions. J Am Dent Assoc. 2007;138:527-529.
2. Christensen GJ. The state of fixed prosthodontic impressions: Room for improvement. J Am Dent Assoc. 2005;136:343-346.
3. Christensen GJ. The challenge to conventional impressions. J Am Dent Assoc. 2008;139:347-349.
4. Farah JW, Brown L. Comparison of the fit of crowns based on digital impressions with 3M ESPE Lava Chairside Oral Scanner C.O.S. vs. traditional impressions. The Dental Advisor Research Report. June 2009; No. 22.
5. Data on file, 3M ESPE.
6. Hirayama H, Chang YC. Fit of zirconia copings generated from a digital impression technique and a conventional impression technique. Tufts University of Dental Medicine Master’s Thesis. Published as Espertise Scientific Facts.
7. Will digital imaging replace VPS impressions? Gordon J. Christensen Clinicians Report. April 2010.
About the Authors
Jim Grant, DDS
Colorado Springs, Colorado
Don Albensi, CDT