Flexural Strength of Translucent Zirconia Restorations Using Two Sintering Systems

Objectives: The aim of this study was to compare the effects of speed sintering on the flexural strength of 5 mol% yttrium partially stabilized tetragonal zirconia polycrystalline (Y-TZP) restorations made in a conventional and speed sintering ovens.
Methods: Three-unit zirconia fixed partial prostheses (FPDs: n=20) were made from a digital impression, and were divided randomly into two groups (10 per group). The first was the long cycle sintering group (LC), which was sintered by the conventional sintering oven (Mihm-Vogt Dental Geratebau GmbH &Co. KG) with heating rate rang 15-30 C^o/min and holding time of 120 min. The second was the short cycle sintering group (SC), ) that was sintered by a short cycle oven (SpeedFire oven, CEREC ,Bensheim, Germany) with heating rate ranging 50-99 C^o/min and holding time of 35 min. After sintering, the flexural strength was measured using a universal testing machine and the values were recorded. The two groups were compared using the Mann-Whitney U test, with the level of significance set at 0.05.
Results: The LC group demonstrated a lower mean flexural strength, 348.03 ± 47.27 Mpa, compared to the SC group, 504.76 ± 211.44 Mpa. The Mann-Whitney U test revealed a statistically significant difference between the two groups (p = 0.04), in which the FPDs sintered by SpeedFire oven exhibited higher flexural strength than the ones sintered in Mihm-Vogt oven.
Conclusions: Within the limitations of this study, 3-unit zirconia FPDs sintered with the short sintering protocol performed superiorly in terms of flexural strength when compared to the long sintering protocol. However, SpeedFire sintered FPDs might not be able to perform clinically as well as advertised by the company (800-1000 MPa) and SpeedFire oven might be more useful in sintering monolithic zirconia crowns rather than FPDs.