Modulus Mapping of Layered Dental Ceramics Using Nanoindentation

Objectives: The aim of this study was to test the modulus of elasticity (MOE) changes across the interface of layered dental ceramics using nanoindentation.

Methods: Yttria stabilised zirconia core material (KaVo Everest, Germany) specimens (10mm length x 5mm width x 0.5mm depth) were either coated with IPS e-max Zirliner (Ivoclar-Vivadent) (Group-1) or left as sintered (Group-2). Both groups were then veneered with a pressable glass-ceramic (IPS e-max ZirPress, Ivoclar-Vivadent) to a total depth of 1.5mm and finished using the recommended firing cycles. Specimens were polished interfacially (1um finish). The MOE was tested across the polished interfaces using a nanoindentation system (UMIS-CSIRO 2000, ASI, Australia) with a spherical indenter (nominal tip radius: 5um). The multiple-point unload testing regimen was employed. Preliminary testing was performed using 3 loads (10mN, 30mN, 50mN) to establish an optimal load. MOE data for Groups 1 and 2 were compared for statistical differences (Tukey's multiple comparison tests, p<0.05). MOE mappings of the areas tested were produced from the nanoindentation data. All materials used were characterized using Scanning Electron Microscopy (SEM) and X-ray powder diffraction (XRD).

Results: Group 1 and 2 mean (±SD) MOE values were significantly different (p<0.05) only at the 40um position (veneer).

 

Indent positioning	Mean MOE±SD (GPa)
	Group 1(n=60)	Group 2(n=60)
80um, Zirconia	217.4±6.2 a	218.1±5.9 a
40um, Zirconia	219.5±7.5 a	220.8±4.9 a
Interface	131±25.4 b	175.4±18.5 b
40um, Veneer	62.5±2.7 c	71.1±0.6 d
80um, Veneer	71.5±0.9 d	73.4±2.2 d

(Different superscript letters indicate significant differences between and within groups).

XRD and SEM characterization of a zirconia sample showed a bulk tetragonal phase and fine grain crystal structure. Veneering materials were characterized as amorphous.

Conclusion: The lower MOE values were associated with the presence of the interlayer. Nanoindentation is considered a useful complementary tool for the evaluation of dental ceramic interfaces.