Zirconia–parylene multilayer thin films for enhanced fracture resistance of dental ceramics

Abstract

Recent research has shown that the application of specific thin films can enhance the material properties of a laminate construct. In this study, the effect of different mono/multilayered films on the strength of a ceramic specimen is demonstrated. It is well established that cracks can initiate and/or propagate from the internal surfaces of all-ceramic dental restorations. Modifying that surface by thin-film deposition might help increase clinical longevity and applicability. Specimens were divided into the following groups according to different surface treatments received: uncoated (control group), 10 μm yttria-stabilized zirconia (YSZ) thin film, 10 μm parylene thin film, 9.75 μm YSZ + 0.25 μm parylene film, and a multilayered film (five layers of 1.25 μm YSZ + 0.75 μm parylene). Depositions were performed using a radio-frequency magnetron sputter system (working pressure 15 mT, 150 °C, 30:1 Ar/O2 gas ratio) to produce the YSZ layers, and a vapour deposition process was used to produce the parylene layers. Flexural strength measurements were carried out by three-point bending (span = 10 mm) in a servo-electric material testing system in deioinized (DI) water (37 °C). The results showed that the strength of the specimen significantly increased with the deposition of all types of coating, showing the greatest increase with the multilayered film (∼32 per cent). It is hypothesized that a multilayer thin film (brittle/ductile) can promote crack deflection, causing strength enhancement of the brittle construct.