Zirconia-parylene multilayer thin-films for enhanced fracture resistance of dental porcelain

Objective: Different thin films have been used in the electronic, thermal, and biomedical industries. Ceramic thin films can be used to improve physical-mechanical properties of certain devices. In this study the effect of different mono/multi-layered films on the strength of a brittle ceramic substrate (dental porcelain) is demonstrated. It is well established that cracks can initiate and/or propagate from the internal surfaces of all-ceramic restorations. Modifying that surface by thin-film deposition may help increase service longevity and clinical applicability. Methods: Specimens were divided into the following groups according to different surface treatments received: uncoated (control group), 10mm yttria-stabilized zirconia (YSZ) thin film, 10mm parylene thin film, 9.75mm YSZ + 0.25mm parylene film, and a multi-layered film (5 layers of 1.25mm YSZ + 0.75mm parylene). Depositions were performed using a radio frequency magnetron sputter system (working pressure of 15mT, 150¨¬C, 30:1 Ar/O2 gas ratio) to produce the YSZ layers and a vapor deposition process to produce the parylene layers. Flexural strength measurements were carried out by three-point bending (span=10mm) in a servo-electric material testing system in DI water (37¨¬C). Results: ANOVA followed by Tukey's statistical test showed that the strength of the brittle substrate significantly increased with the deposition of all types of coatings, showing the greatest increase (~32%) with the multi-layered film. The flexural strength values (MPa ± SD) for the groups were: uncoated- 99.6 (5.0), 10mm (YSZ) thin film-110.7 (6.7), 10mm parylene thin film-112.7 (5.6), 9.75mm YSZ + 0.25mm parylene film-116.4 (6.2), multi-layered film- 131.3 (6.9). Conclusion: It is hypothesized that a multi-layer YSZ/Parylene structure (brittle/ductile) could promote enhanced crack deflection resulting in significant strength enhancement of the brittle porcelain substructure.