Modern Zirconias in Dental Treatments

Abstract Body: All ceramic restorations are highly appreciated by patients, dentists and dental laboratory technicians. Zirconia has significantly changed fixed prosthetics as it was the first reliable option for the posterior region and the first material to fabricate fixed dental prostheses (FDPs). When the first generation of zirconia materials was introduced, the manufacturing process was similar to metal ceramics. A high strength material was used for the substructure while the esthetics and the outer surface were created with veneering porcelain. Numerous studies reported failure of the veneering material of up to 54 % of the restorations after 5 years of clinical service. So this kind of restoration was much more prone to technical failures as metal ceramics. Furthermore the digital fabrication of dental restorations was increased and improved during the last 15 years. Meanwhile the milling of anatomically correct occlusal surfaces is possible with most of the recent computer aided design (CAD)/computer aided manufacturing (CAM) systems. However, zirconia from the first generation was an opaque material with a light transmission of 5 to 10 %. With the growing demand for cost-effective and clinically reliable all-ceramic restorations the next generation of zirconia materials was introduced. Some modifications increased the light transmission up to 30 % while the flexural strength was only minimally reduced to 800 -1100 MPa. The material allows fabricating full-contour posterior crowns and FDPs with a reduced minimum thickness of 0.5 mm according to the manufacturers. Changing the properties again led to the third generation of zirconia materials that is even more translucent and enables to fabricate anterior crowns and theoretically laminate veneers. The light transmission is up to 41 % with a flexural strength of 550 MPa.
The new zirconia materials have the potential to change prosthetics as much as the first generation in the past.