Effect of Thermocycling on Physical Properties of Anterior Full-contour Zirconia Ceramics

Objectives: The aim of this study was to determine the effect of thermocycling on the flexural strength and Vickers hardness of different shades of a high-translucency full-contour zirconia (FCZ) ceramics designed for anterior restorations.
Methods: Twenty rectangular bars each of seven different FCZ ceramic groups 20 mm x 5 mm x 3 mm and twenty discs 2 mm thickness by 6 mm diameter were fabricated according to manufacturer’s instructions. Ten bars and 10 disks of each material were subjected to 40,000 thermal cycles in a Thermocycling machine (SD Mechatronic GMBH, Feldkirchen-Westerham, Germany). Flexural strength of the bars was determined using an Instron Mechanical Testing Machine (Instron 4204, Norwood, MA, USA.) and calculated with standard formulas. Vickers hardness was measured using a LECO Hardness Tester (Model M-400-G1, St. Joseph, Michigan, USA.). Materials used in the study were, Prettau Anterior T0, Prettau Anterior T1, Prettau Anterior T2, Prettau Anterior T3, Prettau Anterior T4, Prettau Anterior BL1 and Prettau Anterior BL2 (Zirkonzahn, Bruneck, Italy).
Results: Flexural strength values range from 1014.4 (123.9) to 617.5 (115) MPa for untreated samples versus 1005.2 (131) to 666.2 (83.9) MPa for thermocycled samples. For both thermocycled and untreated samples, BL2 showed a significantly higher flexural strength (p<0.05). There was no difference in flexural strength between untreated and thermocycled samples. Vickers hardness values ranged from 713.1(30.4) MPa for Prettau Anterior T0 to 681.7(29.0) MPa for Prettau Anterior BL2. There were no significant differences between the different groups/shades. There were no differences in hardness before and after thermal cycling.
Conclusions: For the FCZ ceramics investigated, thermal cycling for the equivalent intraoral period of 4 years did not significantly influence flexural strength or Vickers hardness.