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

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Status
Published
Publication Date
19-Mar-2020
Current Stage
6060 - International Standard published
Start Date
13-Feb-2020
Completion Date
20-Mar-2020
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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/TS 17988:2020(E)
ISO 2020
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ISO/TS 17988:2020(E)
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© ISO 2020

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ii © ISO 2020 – All rights reserved
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ISO/TS 17988:2020(E)
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

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ISO/TS 17988:2020(E)

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
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ISO/TS 17988:2020(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 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.

© ISO 2020 – All rights reserved v
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ISO/TS 17988:2020(E)

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
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ISO/TS 17988:2020(E)
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.

© ISO 2020 – All rights reserved vii
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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]
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ISO/TS 17988:2020(E)
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)]
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ISO/TS 17988:2020(E)
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.
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ISO/TS 17988:2020(E)

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.
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ISO/TS 17988:2020(E)
Key
1 holder
2 spacer no. 1
3 spacer no. 2
...

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