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News Releases 2014

A world first! Combining high strength, superior toughness and hydrothermal resistance
New Flexible Zirconia Developed
Expanding into dental materials and other fields

June 4, 2014
Kuraray Noritake Dental Inc.
(The Kuraray Group)

Kuraray Noritake Dental Inc. (Head office: Chiyoda-ku, Tokyo; President: Sadaaki Matsuyama) has developed a highly durable zirconia that possesses both high strength and superior toughness. We are pursuing the marketing of this new and unique product in the dental material and other fields.

1.Characteristics of the Material

Although the yttria partially stabilized zirconia currently in wide use is very strong, it possesses the fragility which is characteristic of ceramics. Zirconia is also known to gradually weaken over time as the crystal structure changes from a tetragonal phase to a monoclinic one when exposed to hydrothermal condition*1.
Kuraray Noritake Dental improved the raw materials and manufacturing processes, aiming to develop a highly reliable ceramic material. We succeeded in developing a new type of zirconia that has both higher flexural strength and fracture toughness*2 and, when exposed to hydrothermal condition, its crystal structure does not change to a monoclinic phase, a common cause of compromised strength. In addition, the product does not need to be subjected to Hot Isostatic Pressing.

  • *1 Tested under ISO 13356:2008
  • *2 Resistance to extending cracks: higher number means more difficult to break
Comparison with Existing Products
Examined Property Unit Conventional Zirconia New Product
Three-point flexural strength MPa (megapascal) 900~1,200 1,500
Fracture toughness MPa√m (megapascal square root meter) 4~5 12
Ratio of monoclinic phase (accelerated aging test) %(percent) 80 <1

The above data is based on comparative data obtained by Kuraray Noritake Dental

Since the new product has higher flexural strength and fracture toughness than conventional zirconia, it exhibits such characteristics as the ability to withstand being deformed to a high degree without fracturing. The photo at right shows a side view of a 0.2 mm thickness by 4.0 mm width plate of the new product being subjected to a three-point flexural strength test. The test plate was dyed red to make it more visible.
The conventional zirconia fractured at the 4 mm mark compared with the starting horizontal position. The new product, however, maintained its integrity until it was pressed into a 6 mm arc, confirming its high fracture toughness.

Accelerated aging test (the ratio of monoclinic phase corresponds to the rate of deterioration)

In the accelerated aging test (ISO 13356:2008), the ratio of strength-reducing monoclinic phase in conventional zirconia rose from 0% to 12% after five hours and all the way to 80% after 15 hours. The newly developed product, on the other hand, maintained a nearly 0% ratio of monoclinic phase even after 200 hours of testing, proving it is an exceptionally durable material.

2.Potential Applications

Mainly dental materials, prosthetic joints and general industrial applications.

Company Outline
Company Name Kuraray Noritake Dental Inc.
Established October 1, 2001
Head Office Otemachi 1-1-3, Chiyoda-ku, Tokyo
Representative Sadaaki Matsuyama
Capital ¥300 million; Kuraray Co., Ltd.: 66.7%; Noritake Co., Limited: 33.3%
Number of Employees 386
Businesses Dental adhesives and fillings, ceramics and toughened resins for crowns, dental plaster, dental CAD/CAM devices, etc.

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