Page 24 - DT Vol 15 No 3

24 I aesthetics DENTAL TECHNOLOGY, JULY-SEPTEMBER 2025

HARMONY: MULTILAYER ZIRCONIA IN DAILY USE IN

THE LABORATORY SELECTION CRITERIA

CARSTEN FISCHER

The modern daily life of the laboratory is characterized by a wide variety of materials
and products. Especially in the case of relatively new materials (e.g., zirconium
oxide), however, the choice can become difficult. This article discusses zirconium
multilayer and highlights the essential factors to consider when choosing. The
focus is on the production of beams for microstratification, where the term truss
is imprecise in this context. Eighty to ninety percent of a multilayer restoration
is zirconium oxide. This forms the base for shaping and staining. Therefore, the
choice and the exact colour are of great importance. In the laboratory, we still work
according to a conventional colour scale (classical Vita colour scale). But does a
zirconium oxide A3 really correspond to the A3 of the colour scale?

THE HISTORY OF ZIRCONIUM OXIDE
The history of zirconium oxide is marked by important milestones. In the beginning, Fig 1: Visualization of microstratification with the example of an anterior
zirconium oxide was an opaque material. Later, efforts were made to give the crown. Base made of zirconium oxide which imparts shape and
material a basic colour similar to that of the teeth (beige, cream, white, etc.). Then colour aesthetically finalized with a thin layer of ceramic from veneer.
translucency came into play, giving the material more naturalness. Today, the focus Image published for the first time in Quintessenz Zahntechnik (edition
is on multilayered zirconium oxides. With these multilayered zirconium oxides, the 09/2022)
dental laboratory has at its disposal an instrument that ideally integrates calibration
well. This scale offers the potential to mimic the diversity of optical-luminous
properties and the interplay between opacity and translucency that we know from
the natural tooth. But not all manufacturers succeed in achieving a harmonious
result.

ZIRCONIUM OXIDE ≠ ZIRCONIUM OXIDE
Just as a table of alloys integrates different gold alloys, zirconium oxides also vary
in detail and have significant differences. It seems absurd to think that the dental
laboratory must adapt to each manufacturer’s zirconium oxide. Rather, zirconium
oxide should keep pace with the times.
SITUATION
The modern dental laboratory produces all-ceramic restorations routinely and Fig 2: Individually produced shade samples (Colour Index) for anterior
economically. While highly trained specialists are able to use the various shades of teeth made of zirconia original (here ArgenZ HT+ Multilayer). Note:
all-ceramic materials freely and create beautiful restorations, a standard laboratory Due to volume variation, we recommend separate colour samples for
requires restorations to be made with relative ease. This calls for zirconium oxides premolars and molars
that work in a reliable manner. Ceramics departments are staffed by skilled people
who want to use their experience to produce esthetic restorations reproducibly and current generation. In our daily laboratory work, we use a multilayer
efficiently. Their work is largely based on the classic Vita shade guide (Vita Classic). zirconium oxide of the type 4Y-TZP (ArgenZ HT+ Multilayer,
Although an increasing number of patients are visiting the laboratory, the Vita Argen Dental).
colour scale will continue to be the main basis for colour communication. However,
it is precisely here that a great disharmony arises between the classical colour scale THE VENEER
and the designation of zirconia colours. For a long time, layering was considered the “bottleneck” of
all-ceramic restorations. Soon, a desire was expressed to make
SEEMINGLY EQUAL zirconium oxide suitable for monolithic fabrication. Later, with
Apparently equal things do not function in the same way. At first glance, zirconium the introduction of the first multilayer zirconium oxides in 2013,
oxides hardly stand out at all—they look like a simple white disk. But what do they monolithic restorations could avoid the sensitive “bottleneck”
actually contain? This is where we need our “table (of alloys) of zirconium oxides.” (chipping).
Zirconium oxides differ mainly in their mechanical and optical properties. Aesthetic finalization is based on the original multicolour
First of all, it is necessary to differentiate the various “eras,” which requires structure of the zirconium oxide and, if necessary, can be enhanced
considering the production formula. The base is usually tetragonal zirconium oxide with surface staining or partial layering similar to a veneer.
(TZP, tetragonal zirconia polycrystal), to which the manufacturer adds stabilizers Further development has led to the optimization of the materials,
(e.g., yttrium oxide). By changing the yttrium oxide content, the manufacturer including new working concepts, followed by the next milestone:
controls the properties of zirconium oxide. The material is adapted to the respective microstratification.
indication (e.g., high translucency, high strength). Types of zirconium oxide are
commonly classified according to generations. The most obvious differences are MICROSTRATIFICATION AS REBIRTH OF PARTIAL
found in flexural strength (between 750 MPa and 1,500 MPa) and in the degree of CLADDING?
translucency (from highly translucent to opaque). Microstratification is not a rebirth of partial cladding but an
• 1st/2nd generation: zirconia 3Y-TZP independent technique. Although the application of a thin layer
• 3rd generation: zirconia 5Y-TZP of veneer is not new, microstratification cannot be compared with
• 4th generation: zirconia 4Y-TZP the traditional partial veneer. Micro-layering is performed with
• Multi-generation zirconia specially designed ceramic materials. Both zirconium oxide and
Experience shows that it is advantageous to work with zirconium oxide of the veneering ceramics are suitable for this purpose.