The firing procedure influences properties of a zirconia core ceramic

High-strength ceramics for dental restoration are used as an understructure (core) that subsequently is covered by veneering ceramic. The veneering process involves a firing procedure at high temperatures at least once, usually two to five times. The aim of this study was to investigate whether these firing procedures affect the mechanical properties of a zirconia ceramic. Methods Thirty-three specimens of an industrially sintered yttria-stabilized zirconia ceramic (DC Zircon, DCS Dental AG, Allschwil, Switzerland) were cut into bars (1.2 mm × 4 mm × 20 mm). One set of specimens (n = 13) remained untreated (controls). Another set of specimens (n = 10) was heat-treated once, corresponding to the first step of the veneering process. The third set of specimens (n = 10) was heat-treated five times to mimic the full veneering process. Flexural strength, microhardness, dimensions and surface roughness were measured. The fracture patterns were assessed by light microscopy. Results The untreated specimens showed a statistically significant higher flexural strength (20%) and microhardness (9%) than both of the test groups (p ≤ 0.001). No significant differences were found for fracture patterns, dimensions or surface roughness. Significance The heat treatment associated with the veneering procedure on a zirconia core material reduced the flexural strength of the core after the first firing. Subsequent firings were not detrimental to the properties measured.