Date of Award
Spring 1988
Document Type
Thesis - Restricted
Degree Name
Master of Science (MS)
Department
Dentistry
First Advisor
Brantley, William A.
Second Advisor
Dhuru, Virendra B.
Third Advisor
Ziebert, Gerald J.
Abstract
The plane strain fracture toughness (KIc) of two high-alumina core ceramics, Cerestore and Vitadur, was measured at room temperature by three methods. The single edge notch (SEN) specimen method was used to measure the fracture toughness of both ceramics in air, deionized water and artificial saliva. The short rod and indentation methods were used for Cerestore and Vitadur, respectively, in air. X-ray diffraction analysis and scanning electron microscopy were performed to identify the crystalline phases in the two ceramics and to examine the microstructural features of the fracture surfaces. The fracture toughness values obtained for Cerestore by the SEN method were 1.89 MPa.m 1/2 in air, 1.58 MPa.m 1/2 in deionized water and 1.63 MPa.m 1/2 in artificial saliva. There were no significant differences between fracture toughness values for the three different environments. The short rod method yielded a value of 1.91 MPa.m 1/2, in good agreement with the SEN method. For Vitadur fracture toughness values of 1.75 MPa.m 1/2 in air, 1.18 MPa.m 1/2 in deionized water and 1.54 MPa.m 1/2 in artificial saliva were obtained by the SEN method. The value of 1.18 MPa.m 1/2 obtained in deionized water was significantly different at the p< 0.01 level from the values obtained in air and artificial saliva. A fracture toughness in air of 1.67 MPa.m 1/2 was provided by the indentation method. X-ray diffraction analysts showed the presence of Al 203 and Mg0 in the green Cerestore ceramic. After firing, the peaks corresponding to Mg0 were eliminated while peaks corresponding to magnesium aluminate spinel (MgA1204) were found; crystalline barium aluminum silicate was also present in minor amounts. Vitadur showed x-ray diffraction peaks corresponding principally to Al 203, and other peaks were attributed to possible ternary and higher order phases. Scanning electron micrographs indicated that fracture involved a combination of intergranular and transgranular modes for Cerestore. Substantial porosity, estimated at 5-10%, was present in this ceramic after firing. For Vitadur the fracture mode was predominantly transgranular, and considerably less porosity was evident compared to Cerestore. Optical photomicrographs showed that cracks emanating from indentations in Vitadur propagated indiscriminately through the matrix and alumina particles. In Cerestore cracks could not be measured at the tips of indentations due to their interaction with pores and other microstructural features.
Recommended Citation
Mante, Francis, "Fracture Toughness of Dental Ceramics" (1988). Master's Theses (1922-2009) Access restricted to Marquette Campus. 5426.
https://epublications.marquette.edu/theses/5426