The veneering of zirconium oxide plays an important role in aesthetically high-quality and long-lasting dental restorations. A research team from the Department of Prosthetics at the LMU Munich has investigated the influence of various firing trays and firing supports on the mechanical properties of high- and low-fusing veneering ceramics.
Mechanical properties of high- and low-fusing zirconium oxide veneering ceramics and the influence of different firing supports
Zirconia has become an important component of dentistry and is indispensable in prosthetic applications. Despite good mechanical properties and high biocompatibility, the monolithic use of zirconium oxide is limited due to its inherent opacity. New generations of zirconium oxide offer improved translucency due to higher cubic crystal contents, but in many cases a veneering ceramic is still required for aesthetically demanding restorations. The firing parameters of the zirconium oxide veneering ceramic have a decisive influence on the optical and mechanical properties of the restorations and have been analyzed in numerous studies and appropriate firing procedures have been recommended.1 For example, a slow cooling rate was recommended to reduce residual stresses.2,3,4
Zirconia veneering: influencing parameters
The firing furnace is not the only component of the firing process, but auxiliary components such as firing trays and firing supports are also used. The use of these auxiliary components can be particularly critical when producing aesthetic restorations such as veneers, which can be produced using layering techniques in addition to digital technologies. Studies on the influence of different firing trays and firing supports on the mechanical properties of veneering ceramics are only available to a limited extent. The study presented here aimed to
- the influence of the ceramic type,
- different firing carriers and firing bases on the density,
- the shrinkage,
- the biaxial bending strength,
- the Martens hardness and
- the elastic penetration modulus
of two veneering ceramics for zirconium oxide with different melting temperatures. In this extract from the overall study, partial results are presented.
Material and method
Disc-shaped test specimens (Fig. 1) made of
- a high-melting point (HFZ) and
- a low-fusing (STR) veneering ceramic (both estetic ceram ag, Triesen, Liechtenstein)
for zirconium oxide and divided into 10 groups (n = 12) based on the firing trays and supports used. The test specimens were fired according to the veneering ceramic used and its melting temperature and then density, shrinkage, biaxial bending strength, Martens hardness and penetration modulus were measured and evaluated.
Results
Ceramic type (high-fusing or low-fusing), firing tray and firing support influenced the mechanical properties of the tested veneering ceramics for zirconium oxide.
The high-fusing veneering ceramics usually had higher mechanical properties than the low-fusing veneering ceramics.
Firing the tested veneering ceramics for zirconium oxide on a round, small, honeycomb-shaped cordierite firing tray (RSC) with firing cotton predominantly resulted in higher mechanical properties.
All test specimens showed a flexural strength of more than 50 MPa, which corresponds to the ISO minimum value for veneering ceramics of crown frameworks or adhesively cemented monolithic single-tooth restorations in the anterior region.
Examination
Detailed results, analyses and evaluations can be found in the following study: Hoffmann M, Coldea A, Dönmez MB, Meinen J, Stawarczyk B. Mechanical Properties of High- and Low-Fusing Zirconia Veneering Ceramics Fired on Different Trays and Substrates. Materials 2024, 17, 2261.