Ag 1 20kn

The compressive moduli of ACG-HT and ACG-NHT groups were measured on a universal mechanical testing machine equipped with 100 N sensor (AG-I 20 kN, SHIMADZU, Kyoto, Japan). The machine was set and calibrated according to the manufacture's protocol. Samples of each group were prepared in the same size (8.0 mm diameter, 4.0 mm height). Samples with flat surfaces were selected as test specimens. A solid compression plate was used for mechanical compressive strength test. The small tare load of 0.010 N was applied to ensure the same degree of initial compression. The compression ratio was preset at 65% for all samples based on the preliminary study results. When the compression ratio was over 65%, porous structures were fully compressed and compressive force increased significantly before breakdown of samples. The samples were compressed at a speed of 0.2 mm/min. All data were collected and analyzed with Trapezium X software (SHIMADZU).

Before static fracture testing, each sample was fixed on a jig that allowed force to be applied in the direction of the tooth axis (TOKYO GIKEN, Tokyo, Japan). The position of the sample and the contact points were then adjusted to obtain 2 even points of contact with a semi-circular stainless-steel indenter on the occlusal surface. The indenter was chosen based on the assumption that the cusps of the opposing tooth measured 3 mm in diameter. The contact points were evaluated using occlusal registration paper (GC, Tokyo, Japan). A sample mounted on a jig and samples with different morphologies after contact point adjustment are shown in Figs. 3 and4, respectively.
Static fracture testing of the samples was performed by fixing the jig on a universal testing machine (AG-I 20kN, SHIMADZU, Kyoto, Japan). A load was applied to the CAD/CAM crown at a cross-head speed of 0.5 mm/min until it fractured, and the load applied at the point of fracture was recorded as the fracture load value.

After 7 days, shear bond strength was measured using a universal testing machine (AG-I 20kN, Shimadzu, Kyoto, Japan) with a crosshead speed of 1 mm/min. Ten samples were fabricated for each condition. An ANOVA and Tukey's HSD test were used for the statistical analysis (p<0.05).