Objectives: The purpose of this study was to investigate the change of the indentation crack length in resin-bonded ceramics when the indentations were imprinted at several points in the ceramics. Methods: Ceramic disks sized 2.0-mm-thick X 15-mm-diameter were fabricated using two leucite-reinforced ceramics, IPS Empress (Ivoclar-Vivadent) and Finesse (Dentsply Ceramco), one lithia-based ceramic, IPS Empress 2 (Ivoclar-Vivadent), and one mica-based ceramic, OCC (Olympus Optical Co.). The ceramic disks were bonded to resin composite disks (Clearfil DC Core, Kuraray Medical) using a resin cement (Panavia F, Kuraray Medical). The bonded specimens were sectioned perpendicularly. Micro-Vickers indentations were imprinted in the polished ceramic sections at distances of 40, 70, 90, 190, 340 and 490 mm from the ceramic/resin interface at a load of 4.9 N for 10 s. The lengths between two ends of the cracks running along the interface were measured. Resulting data were statistically analyzed by two-way ANOVA and Fisher's PLSD at p < 0.05. Results: Means and s.d. in mm are listed in the table.

	40 mm	70 mm	90 mm	190 mm	340 mm	490 mm
Empress	123.0 (7.2)	75.1 (7.1)	62.1 (4.7)	66.5 (3.9)	59.8 (4.2)	61.1 (6.6)
Finesse	180.9 (32.6)	104.2 (22.1)	98.2 (16.1)	81.9 (12.7)	79.7 (11.9)	77.2 (6.8)
Empress 2	170.1 (15.2)	77.0 (12.4)	58.5 (7.8)	54.0 (8.2)	56.6 (7.9)	60.8 (6.2)
OCC	186.0 (7.1)	74.8 (3.2)	68.3 (2.8)	62.2 (1.6)	60.5 (4.3)	63.1 (2.7)

In each ceramic, the crack length at 40 mm was significantly longer than those at the other points. Difference was recognized in the order of crack lengths between at 40 mm and at 490 mm. Conclusion: Behavior of the indentation crack near the interface (40 mm) is different from that at the inner part (490 mm) of the ceramic materials.

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