Fracture Toughness of Nine Lab Multi-Layered Zirconias Disc Materials

Objectives: To examine fracture toughness of nine commercially available dental lab multi-layered zirconias disc materials.
Methods: Nine lab zirconia materials were tested: Group 1: Zolid Bion, Group 2: Luxor Z True Natural, Group 3: DDcube ONE ML, Group 4: Nacera Pearl Natural, Group 5: priti Multi Translucent Plus, Group 6: UpCERA explore, Group 7: Copra Supreme Hyperion, Group 8: IPS e.max^®ZirCAD Prime Esthetic, and Group 9: IPS e.max^®ZirCAD Prime. Ten bars (36mm x 4mm x 3 mm post-sintered) were milled from the center of the puck height (core) using a PrograMill PM7 with PrograMill CAM V5.0.017.00 software. Prior to sintering, specimens were dried at 150^○C for 30 minutes. All specimens from a group were sintered together according to the manufacturer’s instructions in a Programat S2 furnace. 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 Macro 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 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 and averaged for a precrack length.

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: 3.19±0.11; Group2: 3.45±0.10; Group3: 3.99±0.18; Group4: 4.55±0.14; Group5: 4.03±0.19; Group6: 4.50±0.17; Group7: 3.66±0.12; Group8: 3.62±0.17; and Group9: 5.07±0.17. Using ANOVA (p≤0.05), the statistically different means are displayed in Table 1 with the different groups denoted by different letters.
Conclusions: Within the bounds of this study, the IPS e.max ZirCAD Prime zirconia material had the highest core fracture toughness with the Zolid Bion having the lowest.