Mechanical Behavioral Assessment of Zirconia Ceramics Using Vickers Indentation Hardness

Objectives: Previously, as part of a comprehensive study to assess the mechanics and failure mechanisms of zirconia-ceramics, the authors assessed the consistency in flexural-strength of zirconia-ceramic specimens provided by multiple dental-laboratories. The objective of this study was to determine Vickers-hardness-number values for the same zirconia-ceramic specimens and investigate any correlations between the indentation results with the previously determined flexural-strength values.
Methods: In the previous study, 15 dental-laboratories provided one each of both anterior (high-translucency) and posterior (low-translucency) dental-zirconia specimens of A3-shade, processed according to their normal laboratory procedures to specific dimensions(3x4x45mm). After flexural-strength(FS) testing, these specimens were prepared for Vickers-indentation-hardness-tests (VIT) following ASTM C1327. Each specimen was mounted in resin and sequentially ground and polished starting at 80grit and finishing with a 0.3µm alumina-suspension. Five-indents were performed on each sample, at a load of 1kgf for 15s. Indentation images were acquired via reflected-light microscopy at 50X.
VIT generate cracks that emanate from the corners of an indentation. Dimensions of the indents and the consequential cracks were measured and recorded to calculate Vickers-hardness-number(HV) and total-crack-length(TCL), respectively. Analysis of the TCL extending from the Vickers-indentations was performed as detailed in Fig1.
Results: Results of the TCL-analysis showed that the specimens could be divided into 2 main-groups with a distinct crack-length-threshold of 0.06mm between groups: 0Conclusions: HV values were successfully determined on zirconia-ceramic specimens and compared to previously determined FS values showing the specimens could be divided into 2-groups based on TCL-analysis. High FS specimens were correlated with minimal-cracking from indents. Ongoing work is investigating a correlation between the groupings and yttria-content.