Mechanical Performance of Veneering-ceramics on Zirconia: Layering, Pressing or Multilayering?

Methods: Zirconia frameworks (IPS e.max ZirCAD, IvoclarVivadent) (InLab, Sirona) fabricated in the form of crowns, bars and discs (N=90, n=10) were veneered with one of the veneering methods: a) Layering (L) (IPSe.maxCeram), b) Pressing (P) (IPSe.maxZirPress) and c) Multilayering (M) (IPSe.maxCAD). For crown specimens (N=60) stainless steel dies (1mm chamfer) were scanned (InEos-Sirona). Multilayering was performed for M and reduced design (1mm) was applied for L and P for veneer support. For bar (1.5mmx5mmx25mm) and disc specimens (2.5mmx2.5mm), zirconia blocks were sectioned and sintered. Nano-fluorapatite ceramic was layered and fired for L, fluorapatite-ceramic was pressed for P and lithium-disilicate ceramic was fused with zirconia by a thixotropic glass-ceramic (Crystall/Connect) and then sintered for crystallization of IPSe.max CAD for M. Crowns were then cemented (RelyX luting cement, 3MEspe). All specimens were stored in 37°C, 100% moisture for 24h. Mechanical tests were performed (0.5mm/min). Fractured specimens were examined with SEM and FEA (Abaqus 6.10-1) was performed. Data were statistically analyzed (ANOVA, Tukey’s, α=0.05)

Results: The mean FR values (N) of M (4408±608) and L (4322±462) were not significant (p>0.05) but P (2506±593) showed the lowest results (p<0.001). The mean FS values (MPa) between M (583±62) and P (565±54) were not significant (p>0.05) but L (428±41) showed significantly lower results (p<0.001). The mean SBS values (MPa) of M (49±6) was significantly higher (p<0.001) and no difference was found between L (27±6) and P (29±7) (p>0.05). SEM revealed predominantly cohesive failures in zirconia for M and adhesive failures between veneer and core for P and L. Results were verified by FEA.

Conclusions: Multilayering veneering ceramic on zirconia with reduced framework design may reduce ceramic chipping.