Ion release from three different dental alloys – effect of dynamic loading and toxicity of released elements

Figures & data

Table 1. Comparison of investigated alloys, their compositions and recommended heat treatment specifications.

Alloy type	Trade name, manufacturer, LOT No.	Composition in weight-%	Heat treatment (°C) Oxidation under vacuum/ 4 ×  ceramic firing under vacuum.
Base metal Co–Cr	Wirobond 280 BEGO, Bremen, Germany. LOT: WBA12753	Co: 60.2 Cr: 25 W: 6.2 Mo: 4.8 Ga: 2.9 Mn < 1	No (not recommended)/ Yes (*970)
Base metal Co–Cr	d.Sign 30 Ivoclar Vivadent, Schaan, Liechtenstein. LOT: $RR54002AQ	Co: 60.2 Cr: 30.1 Ga: 3.9, Nb: 3.2 Al, Fe, Li, Mo < 1	Yes (925)/ Yes (*970)
Noble Pd–Ag	Aurolite 2B Aurium Research U.S.A., San Diego, CA, USA. LOT: 6391202	Pd: 59.9 Ag: 26.3 In: 5 Sn: 5 Zn: 2 Au: 1.7 Ru < 1	Yes (1040)/ Yes (*970)

The heat treatment simulation procedures were carried out according to ISO 22674: 2016.

* Highest allowed temperature for simulating ceramics fusing to alloy.

Figure 1. The dynamic corrosion test set-up. A specimen was placed on supporting pins immersed in artificial saliva (corrosive solution, pH= 2.3). The inner chamber, the bending bar and the supporting pins comprise of polyoxymethylene (POM) thermoplastic material. The inner chamber was sealed to prevent evaporation of the corrosive solution. The outer chamber was filled with distilled water set to constant temperature of 37 °C.

Figure 2. Load, displacement (y-axis) and time (x-axis) during cyclic loading of an alloy specimen. The green line shows force (N) applied to a specimen and the blue line shows the corresponding displacement as the alloy deflects. Each minima peak presents the highest values in force and displacement as a result from downward direction. Notice the highest force applied at the last cycle in a series.

Table 2. Summary of selected compounds for cytotoxicity testing.

Chemical compound	Chemical formula	MW (g/mol)
Chromium(III) chloride hexahydrate	CrCl3 × 6H2O	266.45
Cobalt(II) chloride hexahydrate	CoCl2 × 6H2O	237.93
Indium(III) chloride	InCl3	221.18
Molybdenum(IV) oxide	MoO2	127.94
Niobium(V) chloride	NbCl5	270.17
Tin(II) chloride dihydrate	SnCl2 × 2H2O	225.65
Zinc chloride	ZnCl2	136.28
Zinc nitrate hexahydrate	Zn(NO3)2 × 6H2O	297.47
Zinc sulphate heptahydrate	ZnSO4 × 7H2O	287.54

Table 3. Results from the static and dynamic corrosion immersion test analysed by ICP-MS. Mean values (of n = 3) are shown (µg released/cm²)±SD (except “#” where ± refers to max/min values; n = 2).

	Aurolite 2B		Wirobond 280		d.Sign 30
Elements	Static	^#Dynamic	Static	Dynamic	Static	Dynamic
Ag	0.11 ± 0.00	0.15 ± 0.00	–	–	–	–
Al	0.02 ± 0.00	0.02 ± 0.02	–	0.08 ± 0.04	0.01 ± 0.01	0.39 ± 0.33
B	0.09 ± 0.08	0.35 ± 0.19	0.04 ± 0.06	0.06 ± 0.01	0.03 ± 0.04	0.09 ± 0.05
*Co	–	–	15.13 ± 7.18	2.88 ± 2.70	0.49 ± 0.06	0.45 ± 0.11
*Cr	–	–	0.83 ± 0.34	0.81 ± 1.08	0.07 ± 0.01	0.08 ± 0.02
Fe	0.02 ± 0.01	0.02 ± 0.00	0.01 ± 0.01	0.04 ± 0.03	–	0.37 ± 0.48
Ga	–	–	0.42 ± 0.19	0.17 ± 0.19	0.02 ± 0.00	0.02 ± 0.00
*In	2.97 ± 0.23	0.07 ± 0.02	–	–	–	–
Mn	–	–	0.04 ± 0.02	0.01 ± 0.01	–	0.01 ± 0.00
*Mo	–	–	1.79 ± 0.60	0.38 ± 0.28	0.01 ± 0.00	0.01 ± 0.01
*Nb	–	–	–	–	0.14 ± 0.03	0.08 ± 0.05
Ni	–	–	–	0.01 ± 0.00	–	0.01 ± 0.01
Pd	–	0.32 ± 0.00	–	–	–	–
Ru	0.01 ± 0.00	–	–	–	–	–
*Sn	1.88 ± 0.31	0.06 ± 0.00	–	–	–	0.01 ± 0.01
*W	–	–	2.12 ± 0.81	0.47 ± 0.41	–	0.01 ± 0.02
*Zn	9.27 ± 8.34	0.89 ± 0.93	–	0.31 ± 0.31	–	0.43 ± 0.23
Total	14.37 ± 8.08	1.88 ± 0.80	20.38 ± 9.14	5.22 ± 5.04	0.77 ± 0.06	1.96 ± 1.17

Values less than 0.01 µg/cm² are shown as “-“. Au, Be, Li and Cd were analysed but below the detection limit. No significant difference between static and dynamic test was measured for d.Sign (p = 0.15) and Wirobond 280 (p = 0.07). No statistics is performed on Aurolite 2B. None of the measurements suggest higher ion release in the dynamic test compared to the standard static test.

Elements marked with asterisk (*) were chosen for further toxicity testing. (#) Technical fault during run of one sample, thus n = 2.

Figure 3. MTT-test results from the metal elements representing the Pd–Ag alloy (Aurolite© 2B) (n = 3, error bars indicate SD). *Statistical difference (p < .05).

Figure 4. MTT-test results from the metal elements representing the Co–Cr based alloys (Wirobond© 280 and d.Sign© 30) (n = 3, error bars indicate SD). *Statistical difference (p < .05).

Figure 5. MTT-test results of elements combined. 125 µm Zn was combined with different concentration of In and Sn, representing the Pd–Ag alloy. For the Co–Cr alloys, 125 µm Co was combined with different concentrations of Cr, Mo and Nb.