Veneering Methods Affect Zirconia-Veneer Adhesion and Fracture Strength

Method: Zirconia frameworks [IPSe.maxZirCAD,IvoclarVivadent (I); In-CeramYZ,VITA (V)] were prepared (InLab-Sirona) as crowns, bars and discs (N=180,n=10) and veneered with one of the following methods: a)CAD-on(CD) (IPSe.maxCAD-lithium-disilicate; MarkII-feldspathic), b)Layering(L) (IPSe.maxCeram-Nano-fluorapatite; VM9-feldspathic), c)Pressing(P) (IPSe.maxZirPress-fluorapatite; PM9-feldspathic). For crowns (N=60) stainless steel dies (chamfer: 1mm) were scanned (InEos). Multilayering for CD and reduced design (1mm) for L and P were performed. Bars(1.5x5x25mm³) and discs(2.5x2.5mm²) were sectioned from zirconia blocks. Framework were veneered according to each manufacturer`s instructions. Crowns were cemented(RelyX) and specimens were stored in 100% humidity at 37°C for 24h. Mechanical tests were performed in a universal testing machine(0.5mm/min). Data were analyzed using ANOVA, Tukey’s, Bonferroni-tests(α=0.05). In addition, fractography (SEM) and FEA (Simufact.forming v11.0) analyses were made.

Result: The lowest FR values(N±SD) were obtained in V-CD group (L:6102±1519,P:4117±1083,CD:1900±254)(p=0.00) followed by I-P group (P:2506±593,CD:4408±608,L:4322±462)(p=0.00). Mean values for I-CD, V-L and V-P were significantly higher than V-CD(p=0.00), I-L(p=0.02) and I-P(p=0.01) combinations. Mean SBS values(MPa±SD) for CD(49±6) were significantly higher in group I (L:27±5,P:29±7)(p=0.00) and CD(24±4) being significantly lower in V (L:35±6,P:32±6)(p<0.002). The differences between I-CD and V-CD and I-L and V-L were significant. Mean FS values(MPa±SD) of L(428±41) were significantly lower (CD:583±62,P:565±54)(p=0.00) than that of group I but it was not significant in V (CD:496±96,L:496±36,P:538±72)(p>0.05). The differences between I-CD and V-CD were significant while V-L had significantly higher values than I-L. SEM of FR revealed adhesive failures for V-CD and cohesive failures within ceramic for I-L. Cohesive failures within ceramic and zirconia were seen in I-CD, V-L and V-P. FEA verified the results.

Conclusion: Zirconia framework can best be veneered with CAD-on produced lithium-disilicate. Reduced zirconia frameworks with feldspathic ceramics can be recommended when layering or pressing veneering ceramics to reduce ceramic fracture.