Date of Completion

6-15-2019

Embargo Period

12-7-2019

Advisors

Dr. J. Robert Kelly, Dr. Avinash Bidra, Dr. Patchnee Rungruanganunt, Dr. Jon Goldberg

Field of Study

Dental Science

Degree

Master of Dental Science

Open Access

Campus Access

Abstract

1. STATEMENT OF PROBLEM: Zirconia and lithium discilicate are the most popular ceramic restorative materials today. The use of monolithic zirconia ceramics had been often limited to posterior restorations due to their opaque optical properties. Many manufacturers have developed more translucent zirconia stabilized by 4 and 5 mol% yttria, and the use of translucent zirconia ceramics has become popular today. There is a lack of clinical data regarding the longevity of translucent zirconia restorations. Thus, in-vitro data that reflect clinical behavior are needed. Flexural strength values are often used to compare the mechanical properties of different ceramic materials. However, fracture toughness, as an “inherent” property of ceramics, may suggest more meaningful comparisons that appears to better predict clinical behavior of ceramic materials.

Among several different testing methods, the single edge V-notch beam (SEVNB) method is widely used to measure fracture toughness due to its relative simplicity. However, both engineering and dental ceramic standards caution against the use of the SEVNB method for fracture toughness testing of zirconia stabilized by 3 mol% yttria, and they remain silent with respect to testing of more recently introduced translucent zirconia. This is due to the difficulty of creating a sharp starter crack for zirconia ceramics.

2. Purpose: The primary purpose of this study is to measure the fracture toughness of 3, 4, and 5 mol% yttria stabilized zirconia (3Y, 4Y, 5Y-TZP) in comparison to lithium disilicate glass-ceramics using a modified version of SEVNB method by hopefully creating an appropriately sharp starter crack with focused ion beam (FIB) milling technology.

3. MATERIALS & METHODS: Fracture toughness of zirconia ceramics and lithium disilicate ceramics were measured using SEVNB method following the Annex of ISO 6872:2015. FIB technology was used as a modification in an attempt to create a sharp starter crack.

4. Results: The fracture toughness values of 4, 5Y-TZP ceramics were significantly higher than that of lithium disilicate glass ceramics, but significantly lower than that of 3Y-TZP (p < 0.05). The current methodology, however, seems to still over-estimate the fracture toughness values of 3Y-TZP.

5. Conclusions: The translucent zirconia specimens showed superior mechanical properties compared to lithium disilicate. The starter crack created by ion-beam milling was not sharp enough to allow the SEVNB protocol to obtain an accurate measure for 3Y-TZP.

Major Advisor

Dr. J. Robert Kelly

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