Fracture Toughness of Five Chairside Multi-Layered Zirconias Blocks

Objectives: To examine SEPB fracture toughness of of five chairside multi-layered zirconias block materials.
Methods: Five chairside zirconia materials were tested: Group 1: Katana^TM STML, Group 2: Katana^TM ONE, Group 3: CEREC Zirconia Plus, Group 4: IPS e.max^®ZirCAD MT Multi, and Group 5: IPS e.max^®ZirCAD Prime Block. Bridge blocks of each material were cut using a Buehler ISOMet saw the full length of the bridge block. Only the core portion of the blocks was used to produce specimens. The cross section of the bars was 3mm x 4mm post-sintered. Prior to sintering, the specimens were dried at 150^οC for 30 minutes. Each bar was individually sintered according to the manufacturer’s instructions in a chairside furnace recommended by the manufacturer. Using the SEPB tested method, the fully sintered bars were indented with three equally spaced indents across the center of the bar using 5 or 10 kg loads using a Marco Vickers Hardness Tester. The bars were then placed in bridge indentation precracking fixture as described in ASTM Standard C 1421 and loaded in an Instron Universal testing machine (33R4204) at a crosshead speed of 0.25 mm/min until a crack was heard or until 10 kN were obtained. The specimen was then backlit to examine for a crack. The specimens were then loaded in a 30 mm 3-point flexure loading fixture until failure at a crosshead speed of 1 mm/min. After fracture three equa-spaced measurements were made of the crack depth at 80x using an Olympus SZX12 optical microscope.

The fracture toughness was calculated using:

K_IC=(P_fS/bW^3/2)f(a/W)
where

f(a/W)=(3/2)(a/W)^1/2(1.964-2.837a/W+13.711a²/W²-23.250a³/W³+24.129a⁴/W⁴)

where

P_f=Failure load(N), S=Support span(m), B=Thickness(m), W=Width(m) and a=Precrack length
Results: The fracture toughness, K_IC(MPa●m^0.5), for each group is: Group1: 2.49±0.20; Group2: 3.54±2.20; Group3: 3.63±0.28; Group4: 3.86±0.12; and Group5: 4.54±0.22. Using ANOVA (p≤0.05) and Tukey HSD, Group 5 was statistical higher than all the other groups while Group 1 was statistically lower than all the other groups.
Conclusions: Within the bounds of this study, the IPS e.max^®ZirCAD Prime Block zirconia produced the highest core SEPB facture toughness while the Katana^TM STML produced the lowest value.