Graded structures for damage resistant and aesthetic all-ceramic restorations

Zhang, Yu; Kim, Jae-Won

doi:10.1016/j.dental.2009.01.002

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Volume 25, Issue 6 , Pages 781-790, June 2009

Graded structures for damage resistant and aesthetic all-ceramic restorations

Department of Biomaterials and Biomimetics, New York University College of Dentistry, New York University, New York, USA

Received 21 July 2008; received in revised form 22 December 2008; accepted 2 January 2009.

Abstract

Objectives

Clinical studies revealed several performance deficiencies with alumina- and zirconia-based all-ceramic restorations: fracture; poor aesthetic properties of ceramic cores (particularly zirconia cores); and difficulty in achieving a strong ceramic–resin-based cement bond. We aim to address these issues by developing a functionally graded glass/zirconia/glass (G/Z/G) structure with improved damage resistance, aesthetics, and cementation properties.

Methods

Using a glass powder composition developed in our laboratory and a commercial fine zirconia powder, we have successfully fabricated functionally graded G/Z/G structures. The microstructures of G/Z/G were examined utilizing a scanning electron microscopy (SEM). The crystalline phases present in G/Z/G were identified by X-ray diffraction (XRD). Young's modulus and hardness of G/Z/G were derived from nanoindentations. Critical loads for cementation radial fracture in G/Z/G plates (20mm×20mm, 1.5 or 0.4mm thick) bonded to polycarbonate substrates were determined by loading with a spherical indenter. Parallel studies were conducted on homogeneous yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) controls.

Results

The G/Z/G structure consists of an outer surface aesthetic glass layer, a graded glass–Y-TZP layer, and a dense Y-TZP interior. The Young's modulus and hardness increase from surface to interior following power-law relations. For G/Z/G plates of 1.5 and 0.4mm thick, critical loads for cementation radial fracture were 1990±107N (mean±S.D., n=6) and 227±20N (mean±S.D., n=6), respectively, which were ∼30 and 50% higher than those for their monolithic Y-TZP counterparts (1388±90N for 1.5mm and 113±10N for 0.4mm thick; mean±S.D., n=6 for each thickness). A 1-sample t-test revealed significant difference (p<0.001) in critical loads for radial fracture of G/Z/G and homogeneous Y-TZP for both specimen thicknesses.

Significance

Our results indicate that functionally graded G/Z/G structures exhibit improved damage resistance, aesthetics, and potentially cementation properties compared to homogeneous Y-TZP.

Keywords: Dental ceramic, Zirconia, Graded structures, Aesthetics, Damage resistance