How to achieve long-lasting results with 3M™ ESPE™ Lava™ zirconia, Issue 4

As users of the 3M™ ESPE™ Lava™ system since its introduction, we are strong believers in its esthetic and functional benefits. When properly handled, Lava Zirconia is an extremely reliable and strong material, and its introduction has given dentistry an outstanding alternative to traditional PFM crowns.

As users of the 3M™ ESPE™ Lava™ system since its introduction, we are strong believers in its esthetic and functional benefits. When properly handled, Lava Zirconia is an extremely reliable and strong material, and its introduction has given dentistry an outstanding alternative to traditional PFM crowns.

However, recent anecdotal stories and small scale studies have shown some evidence of issues with chipping and fracture of the porcelain on Lava restorations. Fortunately, the reasons for these issues are now well understood in the industry-improper handling of the material and poor coping design are to blame for the vast majority of failed restorations. These problems can easily be avoided by following the protocols for the material.

Because zirconia heats and cools at a much slower rate than porcelain, it requires different handling in the laboratory. Improper handling can lead to the development of micro fractures in the layering porcelain, which eventually cause shearing. Additionally, some early restorations were not designed to provide proper support of the porcelain, which has led to additional failures. To ensure the success of a Lava restoration, labs and dentists must pay careful attention to a number of factors in the preparation, design and handling of Lava frameworks. Following these protocols will help ensure that Lava restorations perform to their full capabilities. 

Dentists’ considerations

1. Proper Preparation: Ensuring a well-fitting and long-lasting crown begins with the dentist’s preparation. To allow adequate space for the framework and porcelain, a minimum occlusal clearance of 1.5 mm is recommended, and a 1 mm minimum is recommended axially. Additionally, a chamfer prep at the margin is necessary. For dentists utilizing a 3M™ ESPE™ Lava Chairside Oral Scanner C.O.S., blocking out major undercuts is also an important step.

Dentists should also make allowances for patients with very dark teeth. The translucency of Lava zirconia is such that with very dark teeth, the coping may not fully block out the underlying structure. In these cases, an additional .25 to .5 mm in the preparation can allow for a thicker coping.

Some zirconia restorations have developed reputations for being opaque in the gingival third area, which is often due to under-reduction. This is another reason that a 1 to 1.5 mm reduction is so important to the success of the final restoration.

2. Occlusal Relationships: For patients who are heavy bruxers, a Lava restoration can provide additional strength, but it does not take the place of using a nightguard and following other standard procedures. Additionally, some indications of the Lava system (cantilever bridges, inlay bridges, onlay bridges and anterior adhesive bridges) are excluded for bruxism. For approved indications, the laboratory’s role in providing  proper support of the porcelain becomes even more vital.

 3. Communication with the lab: Because the Lava framework has the ability to block out dentin for most patients, it is not as critical that dentists communicate the dentin shade with the laboratory. This applies unless the dentin is extremely dark. What is critical, however, is communicating about the desired final shade. The laboratory has a selection of zirconia framework shades from which to choose, which can help the restoration give a more lifelike result.

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Laboratory considerations

1. Design and Overlay Thickness: When zirconia restorations were first introduced, it seemed that some laboratories thought that since the porcelain was bonded to the zirconia, it did not have to be supported in the way that a traditional PFM does. The fact is that proper support of the porcelain is one of the most important factors in the long term success of the restoration. A uniform ceramic thickness of 1 to 1.5 mm is most successful with Lava restorations, as it is for any restoration. Laboratories that outsource design of their copings should ensure that outsourcing labs are adhering to these guidelines.

The introduction of the Lava C.O.S. is creating new opportunities for labs to simplify and take control of the design of their Lava restorations, even without owning a scanner or milling equipment. The recently introduced  Lava™ CAD workstation will allow labs to design copings using the digital scan captured by the dentist, then send their design to an outsourcing center for milling. This enables the dentist’s laboratory to maintain full control over the design of the framework, allowing them to ensure its proper design.

Under our current procedures, Dr. Weston’s Lava C.O.S. scan (Fig. A) is delivered to both an SLA model manufacturing facility and an Authorized Lava Digital and Manufacturing Center. After 5 to 6 days, Horizon Dental Studio receives the completed model (Fig. B) and coping for application of the porcelain. It’s a very streamlined process that allows the coping and model to be manufactured concurrently and delivered in a timely way.

2. Proper Processing: The root cause of much of the confusion about zirconia failures is that the material conducts heat differently than traditional dental alloys. Dr. Ed McLaren of the UCLA School of Dentistry has developed a specific protocol for processing porcelain (see sidebar), which should be closely followed in order to avoid failure.

Additionally, we have found that in posterior cases or cases with occlusal considerations, pressing to the Lava restorations has helped eliminate any problems. For the majority of anterior restorations, layering with ceramic has remained a fine choice.

3. Final Delivery: Following the guidelines described above, we have found that delivery of the restoration is typically a very straightforward process, particularly in cases in which the impression has been captured with the Lava C.O.S. In the event that any adjustments are necessary, using a low speed fine diamond cooled with water can help prevent any micro fractures in the layering porcelain. Cementation is performed traditionally, and the patient is able to leave with a lifelike and strong restoration (Fig. C).

Lava zirconia has been an invaluable tool for us in the creation of esthetic and high-performing restorations. By adhering to the simple guidelines for handling the material, labs and dentists can ensure that they are delivering restorations of the highest quality, which will serve patients for many years.