BS EN ISO 24234:2015

This standard BS EN ISO 24234:2015 Dentistry. Dental amalgam is classified in these ICS categories:

• 11.060.10 Dental materials

Title (MODIFIED)

This has been changed from Dentistry – Mercury and alloys for dental amalgam to Dentistry – Dental amalgam, which more accurately reflects the content of the standard.

1 Scope (MODIFIED)

Dental mercury supplied in undivided quantities that would produce many restorations (i.e. bulk mercury) no longer complies with the standard and it has been deleted from the Scope.

This packaging format has the potential for a major spillage event, one that is unacceptable. Dental mercury supplied pre-capsulated (with the appropriate mass of dental amalgam alloy powder) or in unit dose sachets (for use with amalgam alloy tablets or free flowing dental amalgam alloy powder) are the only formats of packaging that can comply.

2 Normative references (MODIFIED)

Four of the five deletions from the list had been required for evaluating bulk mercury which has been removed from the standard. One addition to the list is a document that was formerly in the Bibliography. The other addition is required for a new clause (7.2.3) introduced for labelling dental mercury for shipping. These are the changes:

ISO 3585, Borosilicate glass 3.3 – Properties DELETED

ISO 3696, Water for laboratory use – Specification and test methods DELETED

ISO 4793, Laboratory sintered filters – Porosity grading, classification and designation DELETED

ISO 8282, Dental equipment – Mercury and alloy mixers and dispensers DELETED

ISO 8601, Data elements and interchange formats – Information exchange – Representation of dates and times DELETED

Globally Harmonized System of Classification and Labelling of Chemicals (GHS).United Nations, NewYork and Geneva, 5^th Edition, 2010, ISBN 92-1-116840-6 ADDED

UN Recommendations on the Transport of Dangerous Goods, Model Regulations. United Nations, New York and Geneva, 18^th Edition, 2013, ISBN 978-9211931466 ADDED

3 Terms and Definitions (MODIFIED)

Because the supply of bulk mercury has been removed from the Scope, it is no longer necessary to set a requirement for the purity of mercury and have a test method to determine this. As a consequence the definition “Tailing” is redundant and has been deleted.

The term “Primary container” has been deleted.

4 Requirements

Nine requirements have been reduced to five. Two of those deleted are associated with bulk mercury, which is no longer in the Scope and the other two are considered no longer essential. This shortening and simplification is a welcome change.

Using their ISO 24234:2004 clause numbering, the requirements that have been deleted are:

• 4.1 General;

• 4.3 Biocompatibility;

• 4.5 The contamination of mercury by water, oil and foreign material;

• 4.6 Purity of mercury – free pouring.

As a consequence, the remaining requirements have been renumbered:

ISO 24234:2004		ISO 24234:2015
4.2	Chemical composition of the alloy	4.1	Chemical composition and purity of the dental amalgam alloy
4.4	Foreign material and large particles in the alloy powder	4.2	Foreign material and large particles in the dental amalgam alloy powder
4.7	Variability of preproportioned masses	4.3	The accuracy and variability of pre-proportioned masses
4.8	Properties of the amalgam	4.4	Properties of the dental amalgam
4.9	Appearance of the mixed amalgam before setting	4.5	Appearance of the mixed dental amalgam before setting

4.4 Properties of the dental amalgam (MODIFIED)

Dental amalgam suffers from mechanical failures and because its purpose is to provide biting surfaces, adequate (fracture) strength is required. Achieving full strength takes more than a day as a consequence of the setting reaction. Therefore, early strength (at 1h) as well as full strength (at 24h) is important. Raising the requirements for these, from 80 MPa to 100 MPa and from 300MPa to 350MPa, respectively, is expected to reduce the incidence of fracture. Dimensional change takes place during setting. Because the restoration is placed in a cavity in a rigid brittle material (tooth enamel and dentine) this property has to be controlled. Excessive contraction will open the margin of the restoration (if it is unbonded) or create high tensile forces on the adhesive (if it is bonded). Excessive expansion risks fracture of the weakened tooth. The revision reduces the permitted dimensional change from between -0,1% and +0,2% to between -0,1% and +0,15%. These values reflect the performance of modern products.

If, by setting higher requirements, failures are reduced (and the average life of the amalgam restoration is increased) less mercury waste is produced through fewer repairs, which is consistent with the aim of the Minamata Convention.

5 Sampling (MODIFIED)

The requirement to acquire a specific mass of mercury (50 g), is replaced with the requirement to acquire an adequate number of capsules or sachets. This is more appropriate following the deletion of bulk mercury.

6 Test methods (MODIFIED)

The deleted requirements 4.5 and 4.6 required test methods to determine compliance. Their deletion makes these test methods redundant and they have also been deleted. Thus (using their ISO 24234:2004 clause numbering) these test methods have been deleted:

• 6.3 Contamination of mercury by water, oil and foreign material;

• 6.4 Free pouring of mercury.

As a consequence, the following test methods have been renumbered:

ISO 24234:2004		ISO 24234:2015
6.5	Determination of variability of preproportioned masses	6.3	Determination of the accuracy and variability of pre-proportioned masses
6.6	Preparation of test specimens to determine compliance with the requirements for creep, dimensional change and compressive strength	6.4	Preparation of test-pieces to determine compliance with the requirements for creep, dimensional change during hardening, and compressive strength
6.7	Determination of creep	6.5	Determination of creep
6.8	Determination of dimensional change during hardening	6.6	Determination of dimensional change during hardening
6.9	Determination of compressive strength	6.7	Determination of compressive strength
6.10	Appearance of the mixed amalgam before setting	6.8	Appearance of the mixed dental amalgam before setting

7 Marking, labelling and packaging

7.1 Packaging (MODIFIED)

With the removal of bulk mercury from the Scope, paragraph two of the previous, 2004, edition (which gives a containment requirement for dropping a bottle of bulk mercury) is redundant and has been deleted.

7.2.1 h) (ISO 24234:2004 clause numbering) (DELETED)

This item, the mixing ratio, is one of the manufacturer’s instructions for use and, as such, it is present in 7.3.1 General instructions for the use of products containing dental amalgam alloy, e), and not appropriate in a list of information on marking and labelling.

7.2.1 l) (ADDED)

Additional pictograms, hazard statements and signal word may be mandatory in the country of sale and this list item acknowledges this. The phraseology used neatly overcomes differences between the demands of national / regional regulatory bodies. Any addition marking shall be in accordance with the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS).

7.2.1 Footnote (DELETED)

With the addition of 7.2.1 l) [see the preceding comment], the footnote that was introduced with ISO 24234:2004/AMD1:2011, Requirements for marking and manufacturer’s instructions concerning mercury is redundant, and as such has been deleted.

7.2.2 Clause title (MODIFIED)

The heading of the clause Safety precautions – packs that contain dental mercury did not reflect the content of the clause and has been revised to become Labelling of a package for a product that contains dental mercury. The content of the clause has been revised.

Figure 6 (MODIFIED)

The background colour (yellow) for the general warning symbol (an exclamation mark in a triangle) was wrong in AMD1:2011. For the meaning intended, the background colour should be white. The correction has been made.

7.2.3 (REVISED)

Previously, this had been a brief fourth level clause 7.2.2.2. With the revision of its content, this has been changed to a level 3 clause, 7.2.3. It had to be rewritten because UN Model Regulations on the Transport of Dangerous Goods is available and is an internationally agreed document. Also with this revision, the UN substance number has been changed. Dental amalgam is classified now as a “mercury-added product” (substance number 3506). Use of the substance number 2809 (pure mercury) would be incorrect.

7.3 Manufacturer’s instructions

7.3.1 (REVISED)

This heading has been revised to become 7.3.1 General instructions for the use of products containing dental amalgam alloy, which more accurately reflects its content. By changing the presentation from two to seven points, there is improved clarity.

Annex A and Annex B (DELETED)

Corrosion resistance is recognized as an important property for all dental alloys, including dental amalgam. Empiricism had been used to establish compositional limits within which dental amalgam alloys will produce amalgams that have acceptable corrosion resistance in a patient’s mouth. This gives the justification for a composition requirement [Requirement 4.1].

Many years ago, the working group of the ISO technical committee recognized that this should be replaced with a validated laboratory test from which a pass/fail value could be set (to follow ISO policy on objective requirements). Although test procedures were developed, a body of data did not exist to set the requirement. Initially a Technical Specification (ISO TS/17576:2004, Dentistry – Corrosion tests for dental amalgam) was published to provide users with the approved test methodologies. Development of this TS was initiated before ISO 24234 was proposed, but met with a series of delays, extending the time before publication. Uncertainty about the continued existence of any TS beyond a specified time led to these tests being added as annexes in ISO 24234:2004, instead of being referenced. There was an expectation that sufficient data would become available to set a requirement and at the first revision of the Standard and these tests would be transferred to Clause 6, Test methods. The TS was allowed to continue in existence until 2008, when it was withdrawn on the grounds of redundancy. Unfortunately, corrosion data has not emerged as a consequence of the uncertain future of amalgam. (The prospect of an amalgam ban resulted in manufacturers directing their research efforts at alternatives and governmental bodies refusing to fund research on amalgam.) As a consequence, in this revision these annexes have been deleted from the standard and placed in a new Technical Specification, ISO/TS 17988:2014, Dentistry – Corrosion test methods for dental amalgam. Should the user of the Standard require to assess corrosion resistance, a recommendation to use ISO/TS 17988 is given in the Introduction.

Bibliography (REVISED)

The books by Luxton [4] and Pourbaix [5] were relevant to the Annexes which have been deleted and as a consequence, they too have been deleted. ISO/TS 17988, Dentistry – Corrosion test methods for dental amalgam has been added.

Relationship with other national standards

BS EN ISO 24234:2015, Dentistry – Dental amalgam contains the requirements by which products can show compliance. There are other standards that are closely linked with determining the performance of dental amalgam. These are:

ISO/TS 17988:2014, Dentistry – Corrosion test methods for dental amalgam,

ISO 7405:2008+AMD1:2013, Dentistry – Evaluation of biocompatibility of medical devices used in dentistry,

and

ISO 10993‑1:2009, Biological evaluation of medical devices – Part 1: Evaluation and testing within a risk management process.

Reviewers This commentary was peer reviewed Graeme Wilson, Dentist. Previous UK Principal Expert on Dental Amalgam, and Professor R G Chadwick, Professor of Operative Dentistry and Dental Materials Science, University of Dundee

Disclaimer This commentary is commissioned text from expert authorities in their industry. It has been commissioned, edited and peer-reviewed before publication but remains the personal opinion of the individual experts who have provided it. It is not official British Standards guidance. Accordingly, BSI cannot accept liability for any direct or indirect loss or damage arising from a reliance on the commentary except to the extent that such liability may not be excluded by law.