Dentistry — Corrosion tests for amalgam

ISO/TS 17576:2004 provides two test methods and concomitant protocols to determine the corrosive behaviour of dental amalgams and their tendency to release mercury vapour during corrosion. The methods measure 1) the integrated current in a potentiostatic corrosion test and 2) the amount of released ions and mercury vapour in a static immersion test. ISO/TS 17576:2004 is not intended to set limits for the relevant parameters in the two tests described.

Art dentaire — Essais de corrosion des amalgames

General Information

Status
Withdrawn
Publication Date
06-Jan-2004
Withdrawal Date
06-Jan-2004
Current Stage
9599 - Withdrawal of International Standard
Start Date
16-Jan-2008
Completion Date
16-Jan-2008
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TECHNICAL ISO/TS
SPECIFICATION 17576
First edition
2004-01-15
Dentistry — Corrosion tests for amalgam
Art dentaire — Essais de corrosion des amalgames
Reference number
ISO/TS 17576:2004(E)
ISO 2004
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ISO/TS 17576:2004(E)
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ii © ISO 2004 – All rights reserved
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ISO/TS 17576:2004(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

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International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

In other circumstances, particularly when there is an urgent market requirement for such documents, a

technical committee may decide to publish other types of normative document:

 an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in

an ISO working group and is accepted for publication if it is approved by more than 50 % of the members

of the parent committee casting a vote;

 an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical

committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting

a vote.

An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a

further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is

confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an

International Standard or be withdrawn.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO/TS 17576 was prepared by Technical Committee ISO/TC 106, Dentistry, Subcommittee SC 1, Filling and

restorative materials.
© ISO 2004 – All rights reserved iii
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ISO/TS 17576:2004(E)
Introduction

The development of this Technical Specification is the result of worldwide demand for test methods to

determine acceptability of dental amalgams for oral restorations in relation to corrosion and mercury vapour.

The test methods described in ISO 10271 are intended for dental metallic materials and are not suitable for

amalgams, due to the risk of formation of precipitates during the test. Furthermore, ISO 10271 does not cover

measurement of mercury vapour liberated during corrosion of amalgam.
iv © ISO 2004 – All rights reserved
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TECHNICAL SPECIFICATION ISO/TS 17576:2004(E)
Dentistry — Corrosion tests for amalgam
1 Scope

This Technical Specification provides two test methods and concomitant protocols to determine the corrosive

behaviour of dental amalgams and their tendency to release mercury vapour during corrosion. The methods

measure 1) the integrated current in a potentiostatic corrosion test and 2) the amount of released ions and

mercury vapour in a static immersion test.

This Technical Specification is not intended to set limits for the relevant parameters in the two tests described.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.
ISO 1559:1995, Dental materials — Alloys for dental amalgam
ISO 3585:1998, Borosilicate glass 3.3 — Properties

ISO 3696:1987, Water for analytical laboratory use — Specification and test methods

ISO 10271:2001, Dental metallic materials — Corrosion test methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
amalgam
alloy of mercury with one or more other metals
3.2
corrosion

deterioration of an amalgam by chemical or electrochemical reaction with its environment

NOTE This deterioration is manifest in the loss in mass of the amalgam, with a release of constituent elements or the

formation of an adherent film of reaction products.
3.3
electrolyte
liquid that contains ions whose combination allows the conduction of electricity
3.4
immersion test

test in which the sample is exposed to a corrosive solution without application of variable mechanical stresses

to the sample
3.5
potentiostatic test
test in which the electrode potential is kept constant
© ISO 2004 – All rights reserved 1
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ISO/TS 17576:2004(E)
4 Test methods
4.1 Potentiostatic corrosion test for dental amalgam
4.1.1 Specimen preparation

Prepare an amalgam specimen of the type for the measurement of compression strength, in accordance with

ISO 1559. Condition in air at (37 ± 2) °C for (7,0 ± 0,1) days.
Attach an insulated lead to the specimen for connection to the potentiostat.

Cover the connecting lead junction and all surfaces except one end of the specimen with an insulating

material, preferably by casting in epoxy resin. The temperature rise during setting of the resin shall not exceed

15 °C. This material shall not dissolve in or react with the electrolyte.

Wet-grind the exposed end of the specimen uniformly to ASTM 600 or FEPA 1200 using silicon carbide

surface abrasive paper. Wash with distilled water.

Eliminate the crevice between the amalgam and the embedding materials by casting or masking.

The testing laboratory may develop its own method of specimen preparation, provided the above procedures

are included and the conditions are met.
4.1.2 Reagents
4.1.2.1 Electrolyte, of volume W 300 ml.

Make up a fresh solution of NaCl [c(NaCl = 0,154 mol/l)] by adding (9,0 ± 0,1) g analytical grade NaCl to

600 ml water (ISO 3696, Grade 2), then make up this solution to (1000,0 ± 0,5) ml.

4.1.3 Apparatus
4.1.3.1 Corrosion cell.

Use a three-electrode corrosion cell holding the specimen (working electrode), a reference electrode probe,

and an inert counter-electrode (platinum or carbon is recommended).

4.1.3.2 Temperature control, consisting of a jacket and temperature control/circulator, or a temperature-

controlled bath, capable of maintaining (37,0 ± 0,5) °C in the cell.
4.1.3.3 Reference electrode and its control.

Use any standard reference electrode with a stable potential of known potential difference from a standard

hydrogen electrode (SHE). Control the potential at (0,000 ± 0,002) V vs. a saturated calomel electrode (SCE)

at 25 °C, equivalent to (0,2415 ± 0,002) V (SHE).

The reference potential values for some other common reference electrodes and corresponding values for the

control potential settings are shown in Table 1. Other electrodes can be used based on their known potential

difference from SHE.

4.1.3.4 Electronic potentiostat, capable of a current output W 100 mA, a voltage output W 10 V, and a

potential control accurate and stable to ± 1 mV.

The hardware/software used shall allow either recording the current for 24 h or integrating the current for 24 h.

2 © ISO 2004 – All rights reserved
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ISO/TS 17576:2004(E)
4.1.4 Test set-up
4.1.4.1 Temperature of the reference electrode

Measure the temperature of the reference electrode (4.1.3.3). If necessary, adjust the temperature to

(25 ± 1) °C by the control potential using the temperature coefficient for the given electrode type.

Temperature coefficients and examples of potential correction are shown in Table 1.

Table 1 — Potential settings for different reference electrodes and temperatures
of the reference electrodes
Reference potential Control potential setting
Temperature /V (SHE) /V
Reference Reference
[1]
coefficient
when the temperature of the when the temperature of
electrode type electrolyte
V/K
reference electrode is the reference electrode is
18 °C 25 °C 37 °C 18 °C 25 °C 37 °C
Saturated calomel
Saturated KCl 0,2468 0,2415 0,2325 −0,005 0,000 0,009
−7,50 × 10
(SCE)
1,0 M calomel 1 mol/l KCl 0,2817 0,2800 0,2771 −0,040 −0,039 −0,036
−2,40 × 10
0,1 calomel 0,1 mol/l KCl 0,3342 0,3337 0,3329 −0,093 −0,092 −0,091
−7,00 × 10
0,1 silver chloride 0,1 mol/l KCl 0.2927 0,2881 0,2803 −0,051 −0,047 −0,039
−6,50 × 10
4.1.4.2 Positioning of the reference electrode

During the polarization part of the procedure, place the reference electrode probe close to the working

electrode (amalgam) surface without touching the surface or shielding substantially the specimen surface.

Also, the electrolyte of the reference electrode shall not contaminate the electrolyte in the vicinity of the

amalgam. This is commonly achieved by placing the reference electrode in a separate compartment and

using a “salt-bridge” between the reference electrode compartment and the main cell. The salt-bridge is a tube

filled with the electrolyte and ending in a capillary (“Luggin capillary”), the end of which is placed close to the

tested surface. The tip of the capillary should be at a distance from the amalgam surface equal to about two

outer diameters of the tip.
4.1.5 Test procedure

Fill the corrosion cell (4.1.3.1) with electrolyte (4.1.2.1). Leave the cell open to the atmosphere. However, the

cell should be covered with a lid to prevent excessive evaporation of the electrolyte.

Using the temperature control (4.1.3.2), heat the cell and maintain at a temperature of (37,0 ± 0,5) °C.

Insert the specimen, connect the specimen and electrodes to the potentiostat (4.1.3.4) (no potential control)

and wait (10,0 ± 0,1) min. During this potential stabilization it is advisable to stir the solution, e.g. using a

magnetic stirrer and a stirring bar in the cell.

Record the potential at the end of the (10,0 ± 0,1) min exposure period. Stirring also may be used during this

open-circuit potential measurement.

Set the potentiostat to the appropriate control potential (see Table 1) and time (24 h). Apply the potential and

record or integrate current for (24,0 ± 0,2) h. During this polarization part of the test, the solution should

remain stagnant (no stirring).
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ISO/TS 17576:2004(E)
4.1.6 Data acquisition and processing
a) Coulometer method

A convenient method of data acquisition is to use an electronic current integrator (coulometer) in the

circuit between the potentiostat and the cell. The reading of the coulometer after 24 h of polarization is the

anodic charge.
b) Computer-controlled potentiostat method

An equally convenient procedure is to use a computer-controlled potentiostat with a program for

potentiostatic control and software which allows post-test integration of the recorded current as displayed

on the screen .
c) Data-logging and integration method

If neither a) nor b) is available, record the polarization current using any available data acquisition system.

The integration then can be performed by averaging all the current data and multiplying the average

current, in amperes, by the total exposure time, in seconds (assuming that the time between current

...

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