What is the influence of high-speed sintering of zirconia on the accuracy (trueness and reproducibility) and fit of restorations? An investigation at LMU Munich addressed this highly topical issue and provided exciting findings.
Anja Liebermann, Annett Kieschnick, Bogna Stawarczyk
Zirconia is often used in everyday clinical practice for restorations of various types – from single-tooth to multi-unit restorations. The restorations traditionally have to undergo a sintering process after the digital manufacturing process (CAD/CAM milling). There are now three different sintering protocols, which differ in the duration of the sintering time, among other things:
- Conventional sintering
Currently, High-Speed-Sintering processes are strongly in the focus of scientific investigations. High-Speed-Sintering is intended to shorten the sintering process, which normally takes several hours. In the following, a current investigation is presented which deals with the topic of High-Speed-Sintering. What are the effects of the shortened process on different restoration geometries? The topic was investigated as part of a investigation at the LMU and is summarized here.
Aim of the investigation
This investigation examined the influence of High-Speed-Sintering on the accuracy (trueness and reproducibility) and fit of various monolithic 4Y-TZP zirconia (4 mol% yttria-stabilized tetragonal zirconia) restorations.
Material and methods
Single-tooth restorations and three-unit conventional and cantilever three-unit fixed dental prostheses (N = 108, n = 12) were fabricated from the following zirconia materials:
- High-speed-sintered Multi-Layer 4Y-TZP (Zolid RS, Amann Girrbach, ZMLH) with a sintering temperature of 1580 °C and a duration of the sintering process of approximately 20 minutes and two conventionally sintered 4Y-TZP materials with the sintering temperature of 1450°C and a duration of the sintering process of approximately 10 hours with
- Multi-layer 4Y-TZP (Zolid Gen-X, Amann Girrbach, ZMLC) and
- Monochromatic 4Y-TZP (Ceramill Zolid HT+ PS, Amann Girrbach, ZMOC).
All specimens were scanned. Accuracy, reproducibility and fit were measured using 3D analysis software (GOM). Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests were performed for data analysis (α = 0.05).
The three-unit restorations made of high-speed-sintered multilayer 4Y-TZP ZMLH showed reduced accuracy compared to ZMLC (p ≤ 0.008). Marginal and overall fit were not clinically relevant affected by High-Speed-Sintering (p = 0.154 – 0.877).
High-speed sintering of zirconia: Conclusion
High-Speed-Sintering influenced the accuracy of monolithic 4Y-TZP single-tooth restorations and three-unit fixed dental prostheses of different designs. However, no clinically relevant influence on fit was observed.