Submicron Grain Sized Alumina Ceramics for Translucency and Strength

Objectives: The objective of this study is to determine the translucency and flexural strength of submicron grain sized alumina.
Methods: The translucent submicron grain sized alumina ceramic plates were obtained via pressureless sintering followed by Hot Isostatic Pressing. The plates were sectioned into bars specimen approximately 2 × 3 × 25 mm. These bars were tested on a four-point bending fixture attached to an Instron universal testing machine. The grain size of as-prepared plates was characterized using Scanning Electron Microscope on polished and thermally etched sections. The CIE L*, a* and b* parameters of polished plate-shaped specimen referring to the brightness, redness to greenness and yellowness to blueness coordinates were recorded with a dental colorimeter (SpectroShade^TM Micro, MHT Optic Research AG, Switzerland). The translucency parameter (TP) of each specimen was obtained by calculating the color difference between the specimen against the white and the black background, respectively.
Results: SEM images showed that our alumina ceramics consisted of submicron grain with the size around 600-800 nm. The four-point bending strength (mean ± standard error) for the submicron alumina ceramics (n = 5) was 585 ± 28 MPa whereas bending strength for three commercial Y-TZP ceramics (n = 10) were 990 ± 39, 1416 ± 33 and 1076 ± 32 MPa for high-translucency, high-strength and high-surface, respectively. The average TP value of plate-shaped alumina specimen with the thickness of 2.0 mm was 21.99 ± 0.40, which was much higher than those of three commercial Y-TZP ceramics with the same thickness: 11.56 ± 1.21 for high-translucency, 7.33 ± 0.33 for high-strength and 3.57 ± 0.29 for high-surface area.
Conclusions: Submicron grain sized alumina ceramics possess high translucency and good strength, suggesting that these materials have potential applications in restorative dentistry.