Newsletter | December 2023
Per Vult von Steyern
Professor and CEO
When translucent zirconium-dioxide (zirconia) was launched in 2009 for monolithic and semi-monolithic crowns and FDPs, as an alternative to traditional veneered zirconia, the given clinical recommendations were based on the properties of the first generation of translucent zirconia. Since then, several new zirconia options have occurred on the market e.g. high translucent, ultra-high translucent zirconia and multi-layer options that that combine different translucencies in different layers of the material.
The degree of translucency is mainly determined by the yttria content, from 3 mol % in traditional zirconia to 3 – 7 mol % in translucent zirconia (3YSZ – 7YSZ). The higher the yttria content, the more translucency is gained, but at the cost of a substantial decrease in strength and toughness.
Early recommendations for how to prepare teeth for monolithic translucent zirconia crowns and FDPs were often a preparation design with a 0.5 mm deep cervical chamfer. That recommendation was based on the first generation of translucent zirconia with 3 mol % yttria and a reduced aluminum-oxide content compared to the traditional 3Y-TZP zirconia, a type of zirconia with moderate translucency and relatively unchanged strength and toughness compared to the latter.
If adopting the same preparation design for e.g. crowns made of the less strong, less tough 4YSZ -7YSZ zirconia materials, especially in the high-load premolar- and molar regions, they will not withstand the functional loads they are subjected to without compensation for the lack of strength with increased cervical dimensions. Hence, current recommendations suggest a preparation design with a chamfer depth of 0.8 mm – 1.0 mm for those materials.
In November 2023, NIOM-researchers gave presentations at the Swedish and Finnish National Dental Conventions where they highlighted the importance of adopting new recommendations for tooth-preparation when using high or ultra-high translucent zirconia materials. The material manufacturer’s recommendations give information on this, but it is important to decide what material to use already prior to preparation. When an impression is sent to the dental laboratory, it is often too late to make changes if a more translucent material is better suited than the initially planned. If a less translucent material is sufficient, then the cervical preparation might be unnecessarily deep, wasting sound tooth structure.
Hence, NIOM recommends dentists to communicate with their dental technicians about what material to use, depending on the clinical case, and to check the recommended cervical dimensions in the manufacturer’s recommendations prior to preparation.
Example of customized recommendations from one manufacturer:
Please watch our webinar below to learn more about this topic.
Mina Sagen and Per Vult von Steyern