What influence does high-speed sintering of zirconium oxide have on the accuracy (correctness, reproducibility) and fit of restorations? A study at the 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 restorations to bridges. Traditionally, the restorations have to be subjected to a sintering process after the digital manufacturing process (CAD/CAM milling). There are now three different sintering protocols, which differ, among other things, in the length of the sintering time:
- Conventional sintering
- Speed sintering
- High-speed sintering
High-speed sintering processes are currently the focus of scientific research. High-speed sintering is intended to shorten the sintering process, which normally takes several hours. A current study is presented below that deals with the topic of high-speed sintering. What impact does the shortened process have on different restoration geometries? The topic was examined as part of a study at the LMU and is summarized here.
Aim of the investigation
The aim of this study was to analyze the influence of high-speed sintering on the accuracy (correctness and reproducibility) and fit of various monolithic 4Y-TZP zirconia (4 mol% yttria stabilized tetragonal zirconia) restorations.
material and methods
The single-tooth restorations as well as three-unit conventional bridges and cantilever bridges (N = 108, n = 12) were made from the following zirconium oxide 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 approx. 20 Minutes as well as two conventionally sintered 4Y-TZP materials with the sintering temperature of 1450 ° C and a duration of the sintering process of approx. 10h
- Multi-layer (Zolid Gen-X, Amann Girrbach, ZMLC)
- Monochromatic 4Y-TZP (Ceramill Zolid HT+ PS, Amann Girrbach, ZMOC)
All test 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 = .05).
Results
The tripartite restorations made from the high-speed sintered multi-layer 4Y-TZP ZMLH showed reduced accuracy compared to ZMLC (p ≤ 0.008). Marginal and general fit were not clinically significantly affected by high-speed sintering (p = 0.154 – 0.877).
High-speed sintering of zirconia: conclusion
High-speed sintering affected the accuracy of 4Y-TZP monolithic single-tooth restorations and three-unit bridges of various designs. However, no clinically relevant influence on the fit could be observed.
