Bench mastery: Esthetic and efficient monolithic zirconia crowns

As more and more dentists begin to implement digital scanning technology in the office, laboratories stand to reap the benefits of this conversion as well.

The right digital scanning system not only reduces remakes, it can also save numerous steps at the laboratory. Furthermore, digital scans are now moving beyond just crown and bridge workflows to encompass many more technologies and products.

At D&S Dental Laboratory, we work with a number of dentists who use the -simplifying the workflow in the lab dramatically. There is no need to pour a stone model, and the greater accuracy of crowns produced with the system means that less time is spent on adjustments and remakes. Our experience has demonstrated that the marginal fit and overall fit of crowns made with this technology are far superior to those made with traditional impression techniques.

As 3M’s system has evolved, so have the potential workflows that its digital scans can be used for. The 3M True Definition Scanner is an open system that produces industry-standard STL files that can be used by the lab with almost unlimited options for design, materials and production based on what’s clinically appropriate for each case. There are also “Trusted Connections,” which mean the trusted workflow to various products has been technically and clinically validated to perform well with the 3M True Definition Scanner, opening the door to CAD/CAM, digital implant and orthodontic appliance workflows.

Check out the following video to view the step-by-step case:

High-performance zirconia
Beyond the advancements in digital scanning that have improved lab efficiency, new materials from 3M ESPE are saving time as well. Our lab has now transitioned from classic 3M™ ESPE™ Lava™ Zirconia to 3M™ ESPE™ Lava™ Plus High Translucency Zirconia. This new generation of zirconia still has the strength the original was known for, and it allows for thin-walled restorations that preserve tooth structure.

The improved esthetics of this material enable labs to create very lifelike monolithic restorations or to stack or press porcelain for a traditional layered restoration. The greater level of translucency is made possible by high-quality processing of the zirconia to minimize impurities and structural defects. Our lab has found this high-quality processing contributes to fewer problems with fracturing during the milling process. The alumina content is also lower than in classic Lava zirconia with the distribution improved in order to maintain aging stability.   

Esthetically speaking, another standout aspect of this material is the fact that it has a direct match to the most common VITA® Classical A1-D4 shades and has a conversion for the VITA SYSTEM 3D Master® Shades. The material also offers its own bleached shades. 3M ESPE has engineered dyeing liquids for this system that are specifically tailored to the microstructure of the zirconia, contributing to an excellent and predictable color match. The combination of coloration possibilities and the high translucency of the material mean that labs can achieve outstanding esthetics, regardless of whether they are creating veneered or monolithic restorations.

The case shown here demonstrates the use of the 3M True Definition Scanner and Lava Plus zirconia in a very representative monolithic crown case.

At the dental office1. The patient had a large MOD amalgam restoration with recurrent caries. Due to the size of the restoration, its location in the mouth, and the patient’s bruxism, it was determined that treatment with a monolithic Lava Plus zirconia crown would be most appropriate. The amalgam and caries were removed and the tooth was prepared for the crown. The 3M True Definition Scanner was then used to capture a digital scan of the mouth. After reviewing the scan for completion, the prescription was submitted to the laboratory via the 3M™ Connection Center.

At the lab2. Once the lab received the scan, software was used to mark the margins. The scan was then imported into Lava Design software and the full contour design was created.
3. The CAM file was calculated by the software and assigned to a Lava Plus zirconia block. The crown was then milled.
4. Once milling was complete, the block was removed from the mill and a highspeed fine diamond bur was used to cut the crown from the block. The sprues were smoothed and the green state Lava Plus crown was cleaned to remove any excess dust.
5. To stain the crown, a mixture of W3 and A1 Lava Plus shading liquids were applied with a brush to the incisal half of the crown. Color markers were used to track where the incisal shade was placed. The entire crown was then immersed for two minutes in the body shade of Lava Plus shading liquid. The crown was then carefully removed and excess liquid was blotted from the surface.
6. The crown was placed on a sintering tray and fired. Our laboratory has found that Lava Plus zirconia is able to produce consistent results with a fast firing cycle of just four hours, which includes drying and cooling time.  
7. After firing was complete, final contouring and characterization were performed, including final finishing of the margins and minor adjustments to interproximal and occlusal contacts. The final shade is confirmed and the crown is prepared to be returned to the dentist for final seating.

Conclusion
The efficient workflow described here is very typical for a case utilizing the 3M True Definition Scanner and Lava Plus zirconia. With a highly accurate digital impression and an esthetic and strong monolithic crown, workflows are simplified for both the dentist and the laboratory. In the end, the patient benefits from a natural-looking restoration that will stand up to wear in the mouth and continue looking great for the long term.

About the authorJed Miller, CDT, is the CAD/CAM manager and ceramist at D&S Dental Laboratory in Waunakee, Wis. He earned a degree from Luther College with a major in ceramics. He has been a dental technician for 10 years and currently focuses on implementing technology and production processes to maximize workflow at D&S. Jed has been involved with 3M™ ESPE™ Lava™ Plus High Translucency Zirconia since its initial beta testing and has consulted for 3M ESPE internationally.

Video: 3M ESPE's udated 3M True Definition Scanner software improves digital impression abilities