A novel etching technique for surface treatment of zirconia ceramics to improve adhesion of resin-based luting cements

Figures & data

Table 1. Groups listed with abbreviation and surface treatment procedure.

Abbreviation	Roughening treatment	Surface behavior
SBU	Sandblasting, 110 μm alumina	unsilanized
SBS	Sandblasting, 110 μm alumina	silanized
EKPU	Etched, K[FHF] powder	unsilanized
EKPS	Etched, K[FHF] powder	silanized
EAPU	Etched, NH4[FHF] powder	unsilanized
EAPS	Etched, NH4 [FHF] powder	silanized
EKSU	Etched, K[FHF] slurry	unsilanized
EKSS	Etched, K[FHF] slurry	silanized
EASU	Etched, NH4[FHF] slurry	unsilanized
EASS	Etched, NH4[FHF] slurry	silanized

Figure 1. Schematic view of etching process. Diffusion of active etching agents in the melt and to the solid zirconia surface with simultaneous diffusion of etching products, fluorozirconates, from the zirconia surface and into the melt.

Figure 2. Schematic illustration of combination of materials (zirconia bonded to zirconia ceramic).

Table 2. Mean shear bond strength values of all groups tested along with the standard deviation.

Specimen group	Shear bondstrength (n = 10)(MPa)	Standard deviation(MPa)
SBU	5.4^a	1.7
SBS	26.2^b	7.4
EKPU	34.7^b	8.3
EKPS	31.2^b	7.5
EAPU	45.6^b	11.3
EAPS	31.9^b	11.1
EKSU	38.8^b	7.9
EKSS	42.7^b	12.7
EASU	37.3^b	11.5
EASS	40.3^b	10.1

Superscripts indicate statistically indistinguishable groups as found by F-test (a/b, p < 0.05).

Figure 3. SEM images of the zirconia disc specimens (reference) after different surface treatments (a) Sandblasted; (b) K[FHF] powder, etched; (c) K[FHF] slurry, etched; (d) NH₄[FHF] powder etched; (e) NH₄[FHF] slurry etched.

Figure 4. SEM images of the zirconia disc specimens after shear bond measurements (a) EKPS (b) EKPU and (c) EKSU.

Figure 5. SEM images of the fracture surfaces of zirconia disc and rod specimens after shear bond testing measurements. Light areas are thin layers and darker areas are thicker layers of bonding resin cement. (a) SBS zirconia disc, contact area at the upper part; (b) SBS zirconia rod, contact area at the upper part; (c) EASS zirconia disc, contact area; (d) EASS zirconia rod, contact area.

Figure 6. Rietveld fit to XRD data for Y-TZP specimens after different surface treatments. (a) Polished; (b) Sandblasted; (c) K[FHF] slurry etched; (d) NH₄[FHF] slurry etched. Upper plots showing observed and calculated intensities, lower plot shows the difference for the samples. *Monoclinic peak.

Table 3. Results of quantitative and crystallite size analysis by the Rietveld method.

	Weight (%)			Crystallite Size (nm)
Sample	Monoclinic	Tetragonal	Cubic	Monoclinic	Tetragonal	Cubic	Rwp
POL	0	86	14	–	304.2	175.6	24.1
EKPU	2	79	19	49.5^a	225.6	50.9	24.3
EKSU	2	80	18	48.5^a	231.6	55.5	24.7
EAPU	1	83	15	56.5^a	267.4	112.9	23.9
EASU	1	83	16	55.0^a	262.9	111.7	24.0
SBU	15	56	29	14.0	61.6	10.6	17.6

Approximate uncertainty in weight percentages= ±3%, crystallite sizes ±10 nm.

Rwp is a reliability factor (weight profile factor).

EKPU: K[FHF] powder etched; EKSU: K[FHF] slurry etched; EAPU: NH₄[FHF] powder etched; EASU: NH₄[FHF] slurry etched; POL: polished; SBU: sandblasted (110 μm 2 bar).

^a These crystallite size values are not much reliable due to the low weight fraction of the monoclinic phase present and they are calculated from a single tiny peak.

Figure 7. FT-IR spectra of (a) etched surface product and (b) K₂[ZrF₆] in the region 510–460 cm⁻¹. The figures on the absorption peaks represent wavenumbers and peak areas.

Figure 8. FT-IR spectra for (a) etched surface product and (b) K₂[ZrF₆] in the region 500–200 cm⁻¹.