Sintered composite crown: Avoiding chipping in zirconium oxide frameworks

Anja Liebermann, Reza Saeidi Pour, Stefan Frei, Otto Prandtner, Annett Kieschnick

The so-called “major” and “minor” chipping (flaking) of the veneering ceramic are common complications in all-ceramic restorations with zirconium oxide frameworks. In the case of larger chips, the affected restoration may need to be replaced. Digital veneering offers new possibilities here. The digitally created veneer is combined with the framework using a sintered composite technology, for example.

Zirconia and the risk of chipping

Zirconium oxide - stabilized with 3 mol% yttrium (3Y-TZP) - offers high mechanical properties and excellent biocompatibility. However, the material also has limitations. In many cases, the opaque appearance entails the need for a ceramic veneer and therefore the risk of the veneering ceramic chipping. Chipping is usually caused by

• a discrepancy in the thermal expansion coefficients between veneering ceramic and zirconium oxide,
• incorrect firing parameters,
• incorrect scaffolding design or
• a low bending strength of the veneering ceramic (around 120 MPa).

To avoid chipping, various techniques for veneering with ceramic are described. These include:

1. manual veneering using powder-liquid,
2. overpressing technique,
3. Sinter composite technology and
4. adhesive bonding.

The first variant has disadvantages due to possible porosities within the veneer. Failure of the first and second methods (around 4% to 28%) is also frequently reported in the literature.

Digital delusion 

In order to solve the problems and reduce the risk of chipping, new digital veneering methods have been developed, such as: B. the Lava Digital Veneering system (3M), the rapid layer technology (VITA Zahnfabrik) and the CAD-on technology (Ivoclar Vivadent). All of these systems take advantage of computer-aided design of a fully contoured restoration in a first step (CAD). The data is then split into two data sets (file splitting):

• a data set for computer-aided manufacturing (CAM) of the zirconium oxide framework and
• the other for the CAM production of the corresponding veneering material components.

The first system was developed for single crowns and uses a separately milled, pre-sintered silicate ceramic veneer. A glass ceramic powder (“fusing ceramic”) is used to fuse the veneering material with the zirconium oxide framework using a glass solder (DCM hotbond fusio). The second technique uses feldspar ceramic (Vita Mark II, VITA Zahnfabrik), which is adhesively bonded to the zirconium oxide framework surface. However, due to direct bonding, no corrections to the color or shape of the veneering material are possible through further firing. The third technique uses lithium disilicate blanks (IPS e.max CAD, Ivoclar Vivadent) using CAD/CAM technology, which are then bonded to the zirconium oxide framework using a low-melting glass ceramic powder. Both of the latter techniques increase mechanical strength and reduce the risk of chipping compared to conventional veneering techniques.

The images shown here show various sinter composite techniques with dental technology processes based on a patient case (dentist: Dr. Reza Saeidi Pour, ZTM Otto Prandtner). www.rezottoproduction.com

Publication sintered composite crown

In a publication, the team of authors discusses lithium disilicate ceramic veneers for zirconium oxide frameworks. The possibilities for reliable, aesthetic veneering in the posterior region as well as the option of repairs in the event of extensive chipping of conventional veneering ceramics are described. In addition to the mechanical advantages of sintered composite crowns by reducing chipping, the highly aesthetic effect of the restorations is particularly important. The natural tooth is imitated with a dentin core in the form of a zirconium oxide framework and a “coat of tooth enamel” made of opalescent lithium disilicate (HT blank). The procedure can therefore also be used very well in the front tooth area.