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.
