Comparison of Four Chairside Ceramics With Reduced Firing Cycles

Objectives: To examine the effect of shortened firing cycles on the change in strength of four chairside CAD/CAM materials.
Methods: Eight groups (N=20) of chairside ceramics were milled using a Cerec InLab into cylinders and then cut into discs (14 mm diameter x 1.2 mm thick - post firing). Groups 1,2 IPS e.max®CAD (Ivoclar Vivadent); Groups 3,4 IPS e.max®ZirCAD MT Multi (Ivoclar Vivadent); Groups 5,6: Lava™ Esthetic (3M ESPE) and Groups 7,8 IPS e.maxZirCAD LT (Ivoclar Vivadent).

The un-fired discs were polished through 1200 grit SiC. Groups 1,3,5, and 7 were crystallized/sintered in a Programat® S1 with longer firing cycles according to the manufacturers' standard firing schedule. Groups 2,4,6, and 8 were crystallized/sintered in a Programat CS6 furnace using shorter firing cycles.

The disc specimens were loaded in a piston-on-three ball fixture detailed in ISO 6872 and loaded at a rate of 0.5 mm/minute. The strength values were calculated by:

σ = -0.2387 P(X-Y)/b²

where σ is strength (MPa); P is fracture load (N), X and Y are loading constants derived from loading configuration and Poison’s ratio and b is thickness of specimen.
Results: Biaxial flexure strengths (MPa) were Group 1: 574.6±84.5, Group 2: 598.22±72.3, Group 3: 905.6±95.4, Group 4: 962.9±114.6; Group 5: 962.5±117.4, Group 6: 1064.24±118.5, Group 7: 1209.4±127.6 and Group 8: 1173.0±135.9. One-way univariate analysis of variance (ANOVA) (p < 0.05) with a pairwise analysis of the biaxial flexure strength found no significant difference for each material fired differently. A significant difference was observed between materials.
Conclusions: Within the bounds of this study, no significant difference in biaxial flexure strength was found whether the material was fired using a longer Programat S1 or a shortened Programat CS6 firing cycle.