The evaluation of shear bond strength between different all ceramic substructures and superstructures and the bonding effect of liner application

The aim of this in vitro study is to evaluate the effects of liner surface treatment on the shear bond strength between zirconia and lithium disilicate substructures and superstructure ceramics. In this study, for every 20 all ceramic substructures 10 mm. diameter and 4 mm. height, totally 60 samples were evaluated. Noritake Alliance Y-TZP presintered blocks were used to prepare zirconia substructures. IPS e.maxPress ingots and IPS e.maxCAD blocks were used to prepare lithium disilicate substructures. Zirconia specimens were fabricated using YenaDent CAM unit and sintered. IPS e.maxPress lithium disilicate specimens were obtained using the lost-wax hot pressing technique. IPS e.maxCAD lithium disilicate blocks were fabricated using YenaDent CAM unit and crystallized. All groups were then divided into 2 subgroups according to the liner surface treatment (n=10). The specimens were sandblasted with Al2O3, additionally lithium disilicate specimens were etched with hydrofluoric acid. A custom made acrylic index prepared to veneer the all ceramic substructures. With acrylic index, 5mm. diameter and 3 mm. height veneering ceramics were layered on all ceramic substructures. VITA VM9 powder-liquid slurry was placed on zirconia and IPS e.maxCeram powder-liquid slurry veneering ceramic was placed on lithium disilicate substructures. All specimens were then subjected to shear bond strength test using a universal testing machine at 1 mm/min speed. Fracture patterns of all specimens were evaluated under a scanning electron microscope (SEM) and classified as adhesive, cohesive or combined (combination of adhesive and cohesive fractures) patterns. Data were statistically analyzed using the Kolmogorov Smirnov, Levene, Kruskal Wallis, Mann Whitney U, Chi-Squared tests and Two-Way Variance Analysis (p<0,017). Within comparisons of shear bond strength values among liner applied substructure groups were statistically insignificant (p=0,595). Within comparisons of not applied liner groups, shear bond strength values of zirconia and IPS e.maxCAD groups were statistically lower than IPS e.maxPress groups (p<0,001). Shear bond strengths of zirconia and IPS e.maxCAD groups were statistically insignificant (p=0,304). The comparisons of fracture patterns on liner applied and not applied zirconia, IPS e.maxCAD, IPS e.maxPress substructures was statistically insignificant (p=1,000; p=0,303; p=0,650 respectively).While adhesive fracture pattern was not demonstrated in any of the groups, cohesive and combined patterns was seen in all groups. In conclusion, within the limitations of this in vitro study, within comparisons of not applied liner groups, the bonding between pressable IPS e.maxPress substructure and veneering ceramic was seen to be higher. Liner application does not effect the bonding between substructure and superstructure. Key Words: Zirconia, lithium disilicate, shear bond strength, liner, scanning electron microscobe (SEM)