ISO/TS 17988:2020

Dentistry - Corrosion test methods for dental amalgam

This document gives the details of test procedures for evaluating the corrosion resistance of dental amalgam formed from products that are within the scopes of ISO 24234 and ISO 20749. This document is not applicable to other metallic materials in which an alloy powder reacts with a liquid alloy to produce a solid metallic material intended for dental restoration.

Médecine bucco-dentaire — Essais de corrosion des amalgames dentaires

General Information

• Status: Published
• Publication Date: 19-Mar-2020
• ICS: 11.060.10 - Dental materials
• Technical Committee: ISO/TC 106/SC 1 - Filling and restorative materials
• Drafting Committee: ISO/TC 106/SC 1/WG 7 - Dental amalgam
• Current Stage: 9093 - International Standard confirmed
• Start Date: 06-Jul-2023
• Completion Date: 13-Dec-2025

Relations

• Revises: ISO/TS 17988:2014 - Dentistry - Corrosion test methods for dental amalgam
• Effective Date: 20-Jan-2018

Overview

ISO/TS 17988:2020 - Dentistry - Corrosion test methods for dental amalgam - provides detailed laboratory procedures for evaluating the corrosion resistance of dental amalgam. The technical specification defines three accelerated, comparative test methods (immersion, potentiostatic and Hertzian-loading strength‑reduction) intended to produce measurable differences between dental amalgam products within a short time. The scope covers amalgam products within ISO 24234 and ISO 20749 and excludes other metallic restorative materials produced by reactive alloy powder/liquid systems. Results are for comparative performance evaluation and are not appropriate as biocompatibility claims.

Key topics and technical requirements

• Test methods: Three principal procedures are specified:
  • Immersion test - evaluates metal ion and mercury vapour release during exposure to defined solutions.
  • Potentiostatic test - uses electrochemical control (potentiostat) to quantify charge transport and corrosion behavior.
  • Hertzian‑loading strength‑reduction test - combines mechanical loading with corrosive exposure (artificial saliva) to assess strength loss.
• Test‑piece preparation:
  • Cylindrical test‑pieces for immersion and potentiostatic tests; disc‑shaped test‑pieces for Hertzian tests.
  • Detailed instructions on mixing, moulds, packing, finishing and conditioning to ensure repeatability.
• Reagents and solutions:
  • Specified reagents and preparations (e.g., 0.1 mol/L lactic acid for immersion; defined artificial saliva formulation for Hertzian testing).
• Apparatus and instrumentation:
  • Requirements for corrosion cells, temperature control, potentiostat, reference electrode probe, mercury vapour analyser, coulometer or data‑logging systems.
• Sampling, data processing and reporting:
  • Procedures for sampling, cleaning, assembly of test apparatus, data acquisition, calculation of total charge transported and standardized test reports.
• Limitations:
  • Designed for comparative laboratory evaluation; explicitly not for biocompatibility claims.

Applications and who uses it

ISO/TS 17988:2020 is directly applicable to:

• Dental materials manufacturers - to benchmark corrosion resistance during product development and quality control.
• Testing laboratories and conformity assessors - for standardized evaluation of amalgam corrosion performance.
• Regulatory agencies and standards bodies - to interpret comparative corrosion data for product dossiers.
• Dental researchers and academic labs - to compare new alloy formulations and study degradation mechanisms. Practical outcomes include optimized alloy formulations, controlled production tolerances, and reproducible corrosion performance data for regulatory and product comparison purposes.

Related standards

• ISO 24234 and ISO 20749 - product standards referenced in the scope (amalgam product definitions and requirements).
• Prepared by ISO/TC 106 (Dentistry); consult these related standards when implementing ISO/TS 17988:2020 to ensure full compliance with product scope and sampling requirements.

Keywords: ISO/TS 17988:2020, dental amalgam, corrosion test methods, corrosion resistance, potentiostatic test, immersion test, Hertzian-loading, artificial saliva, mercury vapour analyser, dental materials testing.

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 17988
Second edition
2020-03
Dentistry — Corrosion test methods
for dental amalgam
Médecine bucco-dentaire — Essais de corrosion des amalgames
dentaires
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
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ii © ISO 2020 – All rights reserved

Contents Page
Foreword .v
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Sampling . 3
5 Preparation of dental amalgam test-pieces . 4
5.1 General . 4
5.1.1 Temperature . 4
5.1.2 Mixing . 4
5.2 Cylindrical test-pieces for use in the immersion and potentiostatic corrosion test
procedures . 4
5.2.1 Mass of dental amalgam to be mixed . 4
5.2.2 Apparatus for the preparation of dental amalgam cylindrical test-pieces . 4
5.2.3 Packing . 8
5.3 Disc-shaped test-pieces for use in the Hertzian-loading strength-reduction test . 9
5.3.1 Apparatus for the preparation of dental amalgam disc-shaped test-pieces . 9
5.3.2 Materials and tolerances for construction of the mould . 9
5.3.3 Packing the mould, removal of test-piece and inspection for surface defects .10
6 Determination of the resistance to corrosion by the immersion procedure .10
6.1 Principle .10
6.2 Reagents for the test solution and cleaning the apparatus.10
6.3 Apparatus .13
6.4 Mercury vapour analyser requirements .14
6.5 Cleaning the glassware .15
6.6 Assembly of the immersion corrosion test apparatus .15
6.7 Test-piece production .15
6.8 Preparation of the 0,1 mol/l lactic acid solution .16
6.9 Finishing the dental amalgam test-piece.16
6.10 Test procedure .16
6.10.1 First determination .16
6.10.2 Second determination .17
6.11 Analysis to determine the metal ion and mercury vapour release .18
6.12 Test report .18
7 Determination of the corrosion by the potentiostatic procedure .19
7.1 Principle .19
7.2 Test-piece preparation .19
7.3 Corrosion test cell requirements .20
7.3.1 Corrosion cell .20
7.3.2 Temperature control . .20
7.3.3 Volume of the electrolyte .20
7.4 Reference electrode probe requirements .20
7.4.1 Reference electrode and its control .20
7.4.2 Temperature of the reference electrode .20
7.4.3 Positioning of the reference electrode .20
7.5 Potentiostat requirements .21
7.6 Reagents.21
7.7 Preparation of the electrolyte .21
7.8 Test procedure .21
7.9 Data acquisition and processing .21
7.9.1 General.21
7.9.2 Computer-controlled potentiostat .22
7.9.3 Coulometer .22
7.9.4 Data-logging and integration .22
7.10 Calculation of the total charge transported .22
7.10.1 Test-pieces embedded by casting without masking.22
7.10.2 Test-pieces embedded by casting with masking .22
7.11 Test report .22
8 Determination of the resistance to corrosion by the Hertzian-loading strength-
reduction test .23
8.1 Principle .23
8.2 Test solution (artificial saliva) .23
8.2.1 Reagents .23
8.2.2 Stock solutions .24
8.2.3 Test solution (artificial saliva) .24
8.3 Test-piece production and procedure for test-piece conditioning .24
8.3.1 Apparatus .24
8.3.2 Control test-pieces .25
8.3.3 Corrosion test-pieces .25
8.3.4 Replacement test-pieces .26
8.4 Mechanical testing .26
8.4.1 Apparatus for mechanical testing .26
8.4.2 Procedure .26
8.5 Treatment of data .28
8.6 Test report .28
Bibliography .30
iv © ISO 2020 – All rights reserved

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 non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 106, Dentistry, Subcommittee SC 1, Filling
and restorative materials.
This second edition cancels and replaces the first edition (ISO/TS 17988:2014), which has been
technically revised. The main changes to the previous edition are as follows:
— The scope has been extended to include products that are within the scope of ISO 20749.
— Clause 3 includes additional terms and definitions.
— Clause 4: quantities required for the production of test-pieces for each of the three test procedures
are given now as the mass of dental amalgam alloy per test-piece, in place of the total mass of
dental amalgam alloy for the complete test (i.e. the estimated quantity for all test-pieces including
permitted replacements).
— 5.2.2.2 and 5.3.2: the parameter R has replaced R to specify surface roughness on steel moulds.
a k
— 5.3.2: the surface roughness of the tapered hole in the Hertzian-indentation strength-reduction
test-piece mould has been revised.
— 8.3.1.1 and 8.3.1.2: two additional items have been added to the list of apparatus.
— 8.3.1.4: blood dilution vials without protuberances on the interior base surface might not be
available. A means by which the required flat surface can be created has been added.
— 8.3.4 and 8.4.2.2: a technical addition has been made to the procedure. Instructions are given for
replacing test-pieces from which invalid results had been produced. Also, advice is given to make
the maximum number of permitted replacements at the time that the actual test-pieces are made (to
avoid a possible 31-day delay should a result be invalid and a replacement test-piece be required).
— 8.4.2.2: instructions are given to inspect the substrate disc and to replace it if damage is observed.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
vi © ISO 2020 – All rights reserved

Introduction
This document gives the practical details of three test methods for the measurement of the resistance
to corrosion of dental amalgam. These corrosion test methods are laboratory procedures for
evaluating the relative performances of dental amalgam alloy products. They are designed to produce
a measurable effect (and differences between products) within a relatively short time period, a time
period appropriate for a comparative laboratory evaluation.
The results of these tests should not be used for any biocompatibility claims, for which their use is
inappropriate.
Should other corrosion test procedures emerge in time as suitable for application in comparative
evaluations of dental amalgam products, they will be included in future editions of this document.
TECHNICAL SPECIFICATION ISO/TS 17988:2020(E)
Dentistry — Corrosion test methods for dental amalgam
1 Scope
This document gives the details of test procedures for evaluating the corrosion resistance of dental
amalgam formed from products that are within the scopes of ISO 24234 and ISO 20749.
This document is not applicable to other metallic materials in which an alloy powder reacts with a
liquid alloy to produce a solid metallic material intended for dental restoration.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 286-2, Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes —
Part 2: Tables of standard tolerance classes and limit deviations for holes and shafts
ISO 1942, Dentistry — Vocabulary
ISO 3585, Borosilicate glass 3.3 — Properties
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4287, Geometrical Product Specifications (GPS) — Surface texture: Profile method — Terms, definitions
and surface texture parameters
ISO 6344-1, Coated abrasives — Grain size analysis — Part 1: Grain size distribution test
ISO 7488, Dentistry — Mixing machines for dental amalgam
ISO 13897, Dentistry — Dental amalgam reusable mixing-capsules
ISO 24234, Dentistry — Dental amalgam
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1942 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
dental amalgam alloy
alloy in fine particles, composed mainly of silver, tin and copper, which when mixed with dental mercury
produces a dental amalgam for dental restoration
[SOURCE: ISO 20749:2017, 3.1]
3.2
dental mercury
mercury supplied for use in the preparation of dental amalgam
[SOURCE: ISO 20749:2017, 3.2]
3.3
pre-capsulated product
product supplied in a sealed capsule that contains measured amounts of dental amalgam alloy powder
and dental mercury with masses that are appropriate for the production of a mass of dental amalgam
that is considered to be suitable for a single small or medium size restoration in a single tooth
Note 1 to entry: The dental amalgam alloy powder and dental mercury are separated by a barrier that is broken
immediately prior to mixing, allowing their contact. The capsule remains sealed until mixing has been completed.
[SOURCE: ISO 20749:2017, 3.3]
3.4
dental amalgam alloy tablet
quantity of dental amalgam alloy powder that has been compressed to form a single entity for the
purpose of providing a pre-dosed quantity of the alloy that, when mixed with an appropriate mass of
dental mercury, produces a mass of dental amalgam that is considered to be suitable for a single small
or medium size restoration in a single tooth
Note 1 to entry: During mixing the tablet is intended to break apart, forming a fine powder.
[SOURCE: ISO/TS 20746:2016, 3.4]
3.5
dental mercury sachet
measured quantity of dental mercury supplied in a sachet (for use in a reusable mixing capsule) in a
mass that, when mixed with an appropriate mass of dental amalgam alloy powder, produces a mass
of dental amalgam that is considered to be suitable for a single small or medium size restoration in a
single tooth
Note 1 to entry: The sachet is intended to rupture during mixing to allow the dental mercury to come into contact
with the dental amalgam alloy powder.
Note 2 to entry: The dental mercury sachet is also known as a dental mercury pillow.
[SOURCE: ISO/TS 20746:2016, 3.5, modified — Note 2 to entry added.]
3.6
immersion corrosion test
test in which a test-piece of known surface area is immersed in a specified solution (at a specified
temperature) for a defined period of time to determine quantitatively the elemental release into the
solution and thereby allow a comparison of the corrosion resistance between this and other products of
a similar type
3.7
potentiostatic corrosion test
test in which a test-piece of known surface area is immersed in a specified electrolyte (at a specified
temperature) with a set potential applied for a defined period of time during which the corrosion
current is recorded, integrated and then normalized by the anodic surface area and time to produce the
total charge transported per unit of area in a unit of time [units C/(cm .d)]
2 © ISO 2020 – All rights reserved

3.8
Hertzian-loading strength-reduction test
test in which a test-piece is immersed for a defined period of time in a specified solution (at a specified
temperature) in a way that creates crevice corrosion conditions on one surface, after which it is removed
from the solution and fractured with the force to do this then compared with the force to fracture an
identical test-piece subjected to ageing in air at the same temperature
Note 1 to entry: Fracture is initiated from the surface subjected to crevice corrosion conditions and proceeds by
radial crack growth.
3.9
radial cracking
fracture pattern of a Hertzian-loaded test-piece in which (more or less) planar cracks form along radii,
normal to the face of the disc shaped test-piece, thus dissecting it into two or more sectors
Note 1 to entry: Such radial cracks initiate on the test surface of the test-piece and propagate through the disc to
produce approximately equiangular dissection in most cases.
EXAMPLE Some radial fracture patterns in disc shaped test-pieces are illustrated here.

[SOURCE: ISO/TS 20746:2016, 3.8]
3.10
top surface
surface of the disc shaped test-piece that has been produced by carving back unset amalgam that is
above the level of the mould until the surface of the test-piece is flat and level with that mould surface
[SOURCE: ISO/TS 20746:2016, 3.6]
3.11
test surface
surface of the disc shaped test-piece that has been produced by contact with the polished glass plate
when the mixed amalgam is packed into the mould
[SOURCE: ISO/TS 20746:2016, 3.7]
3.12
mixing machine for dental amalgam
DEPRECATED: amalgamator
electrically powered mixing machine that operates using an oscillating action for mixing dental
amalgam alloy and dental mercury (in a capsule) to produce a dental amalgam
4 Sampling
Products shall be procured in packages that have been produced for retail.
For pre-capsulated dental amalgam products, procure a sufficient number of capsules from a single lot.
For dental amalgam alloy in the form of a powder supplied in bulk or as dental amalgam alloy tablets,
procure sufficient dental amalgam alloy and a sufficient number of dental mercury sachets from single
lots. The dental mercury sachets shall conform to ISO 24234.
NOTE In this context, “sufficient” is deemed to be the quantity to make the required number of test-pieces
and the maximum number of test-pieces allowed to replace any that are rejected.
For the immersion corrosion procedure (see Clause 6), at least 1,5 g of dental amalgam alloy is required
per test-piece.
For the potentiostatic corrosion procedure (see Clause 7), at least 1,5 g of dental amalgam alloy is
required per test-piece.
For the Hertzian-loading strength-reduction procedure (see Clause 8), at least 3,5 g of dental amalgam
alloy is required per test-piece.
5 Preparation of dental amalgam test-pieces
5.1 General
5.1.1 Temperature
Prepare test-pieces at (23 ± 2) °C.
5.1.2 Mixing
For a dental amalgam alloy product supplied either as tablets or as a free-flowing powder in bulk, the
ratio by mass of the dental amalgam alloy to the mass of dental mercury should be that recommended by
the manufacturer. Use a reusable mixing-capsule (with a pestle, if needed) that conforms to ISO 13897.
Use any other mixing accessory that is required, as recommended by the manufacturer. If more than
one mix is required to make the test-piece, produce these mixes simultaneously using equipment of the
same type for each mix. However, if the last mix can be produced within the working time of the first
mix, mixing these masses sequentially on a single piece of equipment is permitted.
For pre-capsulated products, use as many capsules as are needed. Mix the contents of the capsules
either simultaneously using the same number of mixing machines for dental amalgam of the same type,
or sequentially on a single mixing machine for dental amalgam. (The latter is permitted, provided the
mixing of the last capsule is completed before the end of the working time of the first.) If necessary, use
only a portion of the dental amalgam mix from one of these capsules.
Use a mixing machine for dental amalgam that conforms to ISO 7488 and that is recommended for mixing
the dental amalgam alloy product with dental mercury or mixing the pre-capsulated product. Use the
mixing machine settings and mixing time that are recommended by the manufacturer of the dental
amalgam alloy or pre-capsulated product (for the mass of dental amalgam alloy that is being mixed).
5.2 Cylindrical test-pieces for use in the immersion and potentiostatic corrosion test
procedures
5.2.1 Mass of dental amalgam to be mixed
Mix a mass of the dental amalgam at least sufficient to make a cylindrical test-piece (8 ± 1) mm in length
after packing into the die shown in Figure 1.
NOTE The mass of a dental amalgam cylinder that is 4 mm in diameter and 8 mm in length is
approximately 1,2 g.
5.2.2 Apparatus for the preparation of dental amalgam cylindrical test-pieces
5.2.2.1 General
Use the apparatus as shown in Figures 1 to 4.
4 © ISO 2020 – All rights reserved

Key
1 holder
2 spacer no. 1
3 spacer no. 2
4 plunger no. 2
5 test-piece
6 die
7 plunger no. 1
NOTE The dimensions for each of the components are given in the figures that follow.
Figure 1 — Vertical section through the apparatus for making dental amalgam cylindrical test-
pieces, showing the assembled apparatus with a test-piece in place
Dimensions in millimetres
Key
1 slot
Figure 2 — The holder
6 © ISO 2020 – All rights reserved

Dimensions in millimetres
Figure 3 — Spacer no. 1 (left) and spacer no. 2 (right)
Dimensions in millimetres
Figure 4 — Plunger no. 2 (left), the die (centre) and plunger no. 1 (right)
To assist the operator in judging whether the correct quantity of dental amalgam has been inserted into
the die, for the test-piece to be within the permitted range for length [i.e. (8 ± 1) mm], circumferential
datum lines may be scribed at 11 mm and 13 mm from one end of plunger no. 1. This end shall be
in contact with the dental amalgam. Though such datum lines are not mandatory, their use is
recommended.
The diameters of the plungers are subject to a shaft (or in this case a plunger) clearance (with
a tolerance) of h7 according to ISO 286-2. For a plunger that is nominally 4,000 mm in diameter, its
diameter shall be between 0 μm and 18 μm less than 4,000 mm. Thus, the diameter of the plunger shall
be between 3,982 mm and 4,000 mm.
The diameter of the hole in the die is subject to a clearance (with a tolerance) of F7 according to
ISO 286-2. For a hole that is nominally 4,000 mm in diameter, its diameter shall be between 10 μm and
20 μm more than 4,000 mm. Thus, the diameter of the hole shall be between 4,010 mm and 4,020 mm.
5.2.2.2 Materials and tolerances for construction of the apparatus to make test-pieces
Make the holder and the spacers of cold-rolled or stainless steel. Make the die and the plungers of
hardened tool steel or hardened stainless steel. Hone the working surfaces of the die and the plungers
to a roughness, R , not greater than 6,3 μm when tested in accordance with ISO 4287. Set the limits of
a
clearance between the die and the plungers at F7 and h7, respectively, in accordance with ISO 286-2.
5.2.2.3 Assembly of the apparatus
Assemble the holder, spacers no. 1 and no. 2, the die and plunger no. 2 as shown in Figure 1.
5.2.3 Packing
Place the coherent mass of mixed dental amalgam on top of the die cavity and insert immediately with
several thrusts of a hand instrument for dental amalgam packing that is slightly less than 4 mm in
diameter. Do not express dental mercury during this process. Then insert plunger no. 1 into the die
cavity and proceed, following the schedule given in Table 1.
If plunger no. 1 has circumferential datum lines scribed on its cylindrical surface (at 11 mm and 13 mm
from the end of the plunger that is in contact with the dental amalgam), the test-piece will be within
the permitted (8 ± 1) mm range for length if the 13 mm datum line can be seen and the 11 mm datum
line cannot.
After ejection from the mould, the test-piece should not be trimmed.
Inspect the surfaces of the test-piece for any defects. Use visual inspection without magnification. Carry
out this inspection at an illuminance of at least 1 000 lux and at a distance not exceeding 250 mm. A
person making the inspection shall have nominally normal visual acuity. [Corrective (non-magnifying)
non-tinted lenses may be worn.] If the test-piece is defective, replace it.
Table 1 — Schedule for the production of a dental amalgam cylindrical test-piece
Time
Procedure
s
End of mixing 0
Insert the mixed mass into the die cavity, then plunger no. 1 and apply a force
of (176 ± 13) N to produce a pressure of (14 ± 1) MPa
Release the force and remove spacer no. 2 45
Reapply the force 50
Re-release the force 90
Carefully remove excess dental mercury and eject the test-piece 120
8 © ISO 2020 – All rights reserved

5.3 Disc-shaped test-pieces for use in the Hertzian-loading strength-reduction test
5.3.1 Apparatus for the preparation of dental amalgam disc-shaped test-pieces
5.3.1.1 Mould as shown in Figure 5.
5.3.1.2 Flat glass plate, with a polished scratch-free surface and square with an edge length greater
than 30 mm.
5.3.1.3 Microscope slide, glass, to provide a straight edge to carve back the dental amalgam.
5.3.1.4 Hand instrument for dental amalgam packing.
5.3.2 Materials and tolerances for construction of the mould
The mould shall be made of hardened tool steel or hardened stainless steel. The upper and lower
surfaces shall be flat and parallel, and have an arithmetic mean roughness value, R , not greater than
a
6,3 μm when tested in accordance with ISO 4287. The hole shall have a taper of (7 ± 2) ° to allow the
amalgam disc to be ejected without undue force when this is applied to the face that has the smaller
diameter. The tapered surface shall be smooth enough not to impede the ejection of the test-piece.
For example, it may be honed to an arithmetic mean roughness value, R , of 6,3 μm (when tested in
a
accordance with ISO 4287).
NOTE 1 For convenience, to distinguish between the two surfaces during test-piece production, a small
engraved mark (set away from the hole) can be made on one of the mould faces.
NOTE 2 The angle of the taper, (7 ± 2) °, is the included angle. The wall of the mould is at an angle of (3,5 ± 1,0) °
with the centre line.
Figure 5 — The mould to produce disc-shaped test-pieces for the Hertzian-loading strength-
reduction test
5.3.3 Packing the mould, removal of test-piece and inspection for surface defects
Place the steel mould on the glass plate with the side that has the greater diameter for the tapered hole
in contact with the plate.
NOTE 1 The surface of the glass plate acts as a matrix for the test surface of the test-piece.
Mix a mass of the dental amalgam sufficient to make a disc-shaped test-piece that is 10 mm in diameter
and 3 mm high after packing into the die shown in Figure 5.
NOTE 2 The mass of a 10 mm diameter dental amalgam disc 3 mm in height is approximately 3,0 g.
Pack the dental amalgam by hand, overfilling slightly. Carve back using the edge of the microscope slide
to produce a flat surface (on the dental amalgam) that is level with that of the mould.
Allow the dental amalgam to set for 10 minutes. Carefully eject the test-piece from the mould by
applying light finger-pressure to the surface of the test-piece that had been carved back (the “top”
surface), while holding the mould in the other hand. Check visually that the test surface is defect-free
everywhere, other than possibly at the margin. Use visual inspection without magnification. Carry out
this inspection at an illuminance of at least 1 000 lux and at a distance not exceeding 250 mm. A person
making the inspection shall have nominally normal visual acuity. [Corrective (non-magnifying) non-
tinted lenses may be worn.] If a defect is detected, reject that test-piece and make a replacement.
To prevent any damage to the test surface during ejection, placing a thick soft pad, such as a number of
dental napkins, under the mould to “catch” the ejected test-piece is recommended.
After ejection do not grind or polish the surfaces of the test-piece.
6 Determination of the resistance to corrosion by the immersion procedure
6.1 Principle
Static immersion corrosion tests, of which this is one, are used extensively in the metals industry to
assess the corrosion resistance of different alloys to a specific potentially corrosive environment.
In its simplest form, the weight loss from a test-piece (immersed for a specified time at a defined
temperature) is measured. The composition of the test solution is relevant to the intended application
but modified to yield a measurable effect in a period of time very much less than the expected service
life. (It is an accelerated test.) It is reliable as a screening test for uniform surface corrosion resistance
under conditions that are static. A static immersion corrosion test does not measure the effect of pitting
corrosion, crevice corrosion or other local corrosion processes.
The test procedure given here was developed specifically for dental amalgam from the static immersion
test used for dental metallic materials (specified in ISO 10271) in which the release of metal ions into
the electrolyte is measured quantitatively by using spectroscopic analysis. (This replaces measurement
of weight loss.) For dental amalgam, the apparatus is also modified to collect any mercury vapour that
might be released. Because dental amalgam has a lower corrosion resistance than, for example, dental
gold alloys, the electrolyte composition is less aggressive.
The data collected is processed to give the release of metallic elements in micrograms per unit of
exposed surface area of the test-pieces and in nanograms of mercury vapour released per unit of
exposed surface area.
6.2 Reagents for the test solution and cleaning the apparatus
6.2.1 Lactic acid solution ≥ 85 % grade.
6.2.2 Water, to Grade 2 as specified in ISO 3696.
10 © ISO 2020 – All rights reserved

6.2.3 Nitric acid, spectroscopic grade.
6.2.4 Ethanol, analytical grade.
Dimensions in millimetres
Key
1 water-bath at (37,0 ± 0,5) °C
2 0,1 mol/l lactic acid solution
3 round-bottomed flask, 250 ml capacity, three parallel necks with ground-glass joints
4 conical ground-glass joint with a cone screw-thread adapter to create and maintain the seal with the glass
rod or tube
5 glass tube (air inlet tube)
6 PVC tubing (1 000 ± 100) mm in length
7 peristaltic pump
8 PVC tubing (500 ± 50) mm in length
9 variable area air-flow meter
10 PVC tubing (150 ± 50) mm in length
11 glass reduction connector
12 © ISO 2020 – All rights reserved

12 direction of gas flow
13 glass reduction connector
14 PVC tubing (150 ± 50) mm in length
15 gold-impregnated silica tube mercury vapour trap
16 PVC tubing (150 ± 50) mm in length
17 conical ground-glass joint with a cone adapter to create and maintain the seal with the glass tube
18 water-cooled Liebig condenser with ground-glass joints
19 solid glass rod (suspension rod)
20 conical ground-glass joint
a
21 polychloroprene O-ring to fit the glass rod
22 nylon threads
23 test-pieces
a
Neoprene® is the trade name of a product supplied by Dupont Performance Elastomers L.L.C., Dupont de Nemours
Inc., Wilmington DE, USA. This information is given for the convenience of users of this document and does not
constitute an endorsement by ISO of this product.
NOTE The peristaltic pump recirculates the air during the test.
Figure 6 — Immersion corrosion test apparatus
In Figure 6 the use and positioning of reduction connectors is intended to be schematic. Use such
connectors in such numbers and with sizes as required to attach tubing with appropriate diameters to
the components of the apparatus.
6.3 Apparatus
6.3.1 Flask, of borosilicate glass (in accordance with ISO 3585), having a round bottom, 250 ml
capacity, with three parallel necks and ground-glass conical socket joints.
6.3.2 Inlet tube, of borosilicate glass (in accordance with ISO 3585), with an internal diameter of
(4,0 ± 0,2) mm and approximate length of 150 mm.
6.3.3 Variable area air-flow meter, of borosilicate glass (in accordance with ISO 3585), with a glass
float and a measurement range of 0 ml/min to 10 ml/min.
Other flow measuring instrumentation may be used if it can measure air-flow within the same range.
6.3.4 Peristaltic pump (variable speed), to operate at up to 20 r/min, to provide an air-flow rate of
(5,0 ± 0,3) ml/min through the inlet tube (6.3.2).
6.3.5 Atomic fluorescence mercury vapour analyser that is compatible with the selected mercury
1)
vapour trap (6.3.6) .
6.3.6 Mercury vapour trap (four in number), a commercially manufactured gold-impregnated silica
2)
tubular trap .
1) PSA 10.525 Sir Galahad mercury vapour detector by PS Analytical, Orpington, Kent, UK is an example of a
suitable product available commercially. This information is given for the convenience of users of this document and
does not constitute an endorsement by ISO of this product.
2) Quartz Amasil 30 mg filled by PS Analytical, Orpington, Kent, UK is an example of a suitable mercury vapour
trap available commercially. This information is given for the convenience of users of this document and does not
constitute an endorsement by ISO of this product.
6.3.7 Liebig condenser, straight, water-cooled, of borosilicate glass (in accordance with ISO 3585),
and at least 20 cm in length, with ground-glass joints. (The lower cone end shall fit one of the outer necks
of the flask, 6.3.1).
6.3.8 Cone screw-thread adapter (three in number), of borosilicate glass (in accordance with
ISO 3585) to fit the outer and centre necks of the flask (6.3.1) and the socket end of the condenser (6.3.7).
6.3.9 Solid suspension rod, of borosilicate glass (in accordance with ISO 3585) with a diameter of
(4,0 ± 0,2) mm and approximately 150 mm length.
3)
6.3.10 “O” ring, of polychloroprene , with internal diameter < 3,8 mm, to fit the suspension rod (6.3.9).
6.3.11 Thread, nylon, single-ply, sewing.
6.3.12 PVC tubing, clear plasticized, with internal diameters (3,2 mm to 7,8 mm) and lengths, both as
required.
6.3.13 Reduction connector, of borosilicate glass (in accordance with ISO 3585). Number and size of
these as required.
6.3.14 Analytical facility, AAS, ICP-OES or ICP-MS.
6.3.15 Water bath, with a temperature control to maintain (37,0 ± 0,5) °C.
6.3.16 Beakers (six in number), of borosilicate glass (in accordance with ISO 3585), 250 ml capacity.
6.3.17 Polyethylene gloves.
6.3.18 Volumetric flask with stopper, of borosilicate glass (in accordance with ISO 3585), 1 l capacity.
6.3.19 Beaker of borosilicate glass (in accordance with ISO 3585), 500 ml capacity.
6.4 Mercury vapour analyser requirements
Use a tubular gold-impregnated silica mercury vapour trap with a collection capacity of at least 50 mg
of mercury. To measure the mercury vapour it has collected, use a compatible atomic fluorescence
mercury vapour analyser with a lower detection limit no greater th
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