SIST EN ISO 6872:2024

SLOVENSKI STANDARD
01-oktober-2024
Nadomešča:
SIST EN ISO 6872:2015
SIST EN ISO 6872:2015/A1:2018
Zobozdravstvo - Keramični materiali (ISO 6872:2024)
Dentistry - Ceramic materials (ISO 6872:2024)
Zahnheilkunde - Keramische Werkstoffe (ISO 6872:2024)
Médecine bucco-dentaire - Matériaux céramiques (ISO 6872:2024)
Ta slovenski standard je istoveten z: EN ISO 6872:2024
ICS:
11.060.10 Zobotehnični materiali Dental materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 6872
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2024
EUROPÄISCHE NORM
ICS 11.060.10 Supersedes EN ISO 6872:2015, EN ISO
6872:2015/A1:2018
English Version
Dentistry - Ceramic materials (ISO 6872:2024)
Médecine bucco-dentaire - Matériaux céramiques (ISO Zahnheilkunde - Keramische Werkstoffe (ISO
6872:2024) 6872:2024)
This European Standard was approved by CEN on 2 August 2024.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6872:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 6872:2024) has been prepared by Technical Committee ISO/TC 106 "Dentistry"
in collaboration with Technical Committee CEN/TC 55 “Dentistry” the secretariat of which is held by
DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by February 2025, and conflicting national standards
shall be withdrawn at the latest by February 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 6872:2015, EN ISO 6872:2015/A1:2018.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 6872:2024 has been approved by CEN as EN ISO 6872:2024 without any modification.

International
Standard
ISO 6872
Fifth edition
Dentistry — Ceramic materials
2024-08
Médecine bucco-dentaire — Matériaux céramiques
Reference number
ISO 6872:2024(en) © ISO 2024
ISO 6872:2024(en)
© ISO 2024
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 on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 6872:2024(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Material .1
3.2 Processing .2
3.3 Properties .3
4 Types, classes, and their identification. 3
5 Requirements . 4
5.1 Uniformity .4
5.2 Freedom from extraneous materials .5
5.3 Mixing and condensation properties of type I ceramics .5
5.4 Physical and chemical properties .5
5.5 Shrinkage factor .5
6 Sampling . 5
6.1 Type I ceramics .5
6.2 Type II ceramics.5
7 Test methods . 6
7.1 Preparation of test specimens .6
7.1.1 General .6
7.1.2 Components of test specimens (type I ceramics) .6
7.1.3 Apparatus for mixing .6
7.1.4 Method of mixing .6
7.1.5 Procedure for specimen fabrication .6
7.1.6 Firing .6
7.2 Radioactivity of dental ceramic .7
7.2.1 Preparation of samples .7
7.2.2 Counting procedure .7
7.2.3 Assessment of results .7
7.3 Flexural strength.7
7.3.1 General .7
7.3.2 Three-point and four-point flexure tests .7
7.3.3 Biaxial flexure test (piston-on-three-ball test) .10
7.4 Linear thermal expansion coefficient . 12
7.4.1 Apparatus . 12
7.4.2 Preparing of test specimens (type I and type II ceramics) . 13
7.4.3 Dilatometric measurement . 13
7.4.4 Assessment of results . 13
7.5 Glass transition temperature . 13
7.5.1 Operating procedure . 13
7.5.2 Assessment of results .14
7.6 Chemical solubility .14
7.6.1 Reagent .14
7.6.2 Apparatus .14
7.6.3 Preparation of test specimens . 15
7.6.4 Procedure . 15
7.6.5 Calculation and assessment of results . 15
8 Information and instructions .15
8.1 Information . . 15
8.1.1 General . 15
8.1.2 Type I ceramics . 15

iii
ISO 6872:2024(en)
8.1.3 Type II ceramics .16
8.2 Instructions for use .16
9 Packaging, marking, and labelling .16
9.1 Packaging .16
9.2 Marking and labelling .16
Annex A (informative) Fracture toughness .18
Annex B (informative) Weibull statistics .25
Annex C (informative) Protocol to assess the hydrothermal stability of yttria-stabilized
tetragonal zirconia (Y-TZP) .27
Bibliography .31

iv
ISO 6872:2024(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 2,
Prosthodontic materials, in collaboration with the European Committee for Standardization (CEN) Technical
Committee CEN/TC 55, Dentistry, in accordance with the Agreement on technical cooperation between ISO
and CEN (Vienna Agreement).
This fifth edition cancels and replaces the fourth edition (ISO 6872:2015), which has been technically
revised. It also incorporates the Amendment ISO 6872:2015/Amd 1:2018.
The main changes are as follows:
— Annex C on protocol to assess the hydrothermal stability of yttria-stabilized tetragonal zirconia (Y-TZP)
has been added.
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.

v
ISO 6872:2024(en)
Introduction
Specific qualitative and quantitative requirements for freedom from biological hazard are not included in
this document, but it is recommended that in assessing possible biological or toxicological hazards, reference
be made to ISO 10993-1 and ISO 7405.

vi
International Standard ISO 6872:2024(en)
Dentistry — Ceramic materials
1 Scope
This document specifies the requirements, recommendations and the corresponding test methods for dental
ceramic materials for fixed all-ceramic and metal-ceramic restorations and prostheses.
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 1942, Dentistry — Vocabulary
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 13078, Dentistry — Dental furnace — Test method for temperature measurement with separate
thermocouple
ISO 13078-2, Dentistry — Dental furnace — Part 2: Test method for evaluation of furnace programme via
firing glaze
ISO 13078-3, Dentistry — Dental furnace — Part 3: Test method for the evaluation of high temperature sintering
furnace measurement with a separate thermocouple
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 terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Material
3.1.1
chromatic dentine ceramic
dentine ceramic having a high strength or saturation of the hue (colour)
3.1.2
dental ceramic
ceramic material prepared for use in the fabrication of dental prostheses and restorations
3.1.3
dentine ceramic
slightly translucent, pigmented dental ceramic (3.1.2) used to simulate the natural appearance of dentine in
a dental ceramic restoration or dental prosthesis

ISO 6872:2024(en)
3.1.4
enamel ceramic
slightly translucent, pigmented dental ceramic (3.1.2) used to simulate the natural enamel in a dental ceramic
restoration or dental prosthesis
3.1.5
fluorescent ceramic
dental ceramic (3.1.2) material that absorbs radiant energy and emits it in the form of radiant energy of a
different wavelength band all or most of whose wavelengths exceed that of the absorbed energy
EXAMPLE Absorption of ultraviolet light with emission of blue light.
3.1.6
glass-ceramic
dental ceramic (3.1.2) material formed by the action of heat treatment on a glass in order to cause initiation
and growth of a wholly or predominantly crystalline microstructure
3.1.7
modelling fluid
liquid with which a dental ceramic (3.1.2) powder is mixed in order to shape or model it into its required
form prior to firing
3.1.8
modifying enamel ceramic
enamel ceramic (3.1.4) used to modify the surface contour of a restoration, for example, add a contact, often
fired at a lower temperature than the enamel ceramic or dentine ceramic (3.1.3)
3.1.9
monolithic ceramic
dental ceramic (3.1.2) that is substantially made of a single uniform material
Note 1 to entry: A thin layer of glaze ceramic (staining technique) can be applied.
3.1.10
opalescent enamel ceramic
enamel ceramic (3.1.4) containing microfine particulates, with a refractive index significantly different from
the ceramic matrix in which they are incorporated
Note 1 to entry: This material scatters shorter wavelengths of light (e.g. blue) and transmits longer wavelengths of
light (e.g. red).
3.1.11
pressable ingot
dental ceramic (3.1.2), in the form of a pellet or ingot, designed for use in a specialised furnace which enables
the ingot to be injected, cast or pressed into a mould prepared through the lost wax technique
3.2 Processing
3.2.1
condensation
process for dental ceramic (3.1.2) whereby a slurry of dental ceramic powder is vibrated to compact the
powder prior to sintering
3.2.2
firing
process whereby heat and potentially other process parameters (e.g. mechanical or gas pressure) are applied
to a ceramic powder or powder compact in order to densify the ceramic into its required form.

ISO 6872:2024(en)
3.2.3
sintering
process of densification and consolidation of a green body by the application of heat with resulting joining of
ceramic particles and increasing contact interfaces due to atom movement within and between the ceramic
grains of the developing polycrystalline microstructure
Note 1 to entry: Sintering may take place either directly or through the agency of a secondary phase (e.g. reaction
sintering and liquid-phase sintering).
[SOURCE: ISO 20507:2022, 3.2.69]
3.3 Properties
3.3.1
class of dental ceramic
classification of a dental ceramic (3.1.2) material in accordance with its intended function
3.3.2
fracture toughness
conventional fracture mechanics parameter indicating the resistance of a material to crack extension
(propagation)
3.3.3
glass transition temperature
T
g
approximate midpoint of the temperature range over which a glass transforms between elastic and
viscoelastic behaviour characterized by the onset of a rapid change in its coefficient of thermal expansion
3.3.4
glaze
surface appearance obtained when the gloss is clinically and aesthetically acceptable
4 Types, classes, and their identification
For the purposes of this document, dental ceramics are designated into two types.
— Type I: Ceramic products that are provided as powders, pastes, or aerosols.
— Type II: All other forms of ceramic products.
Ceramics are divided into five classes in accordance with their intended clinical use and in accordance with
the descriptions in Table 1. If colour is added to a ceramic powder for identification purposes, then the colour
coding given in Table 2 is recommended.

ISO 6872:2024(en)
Table 1 — Classification of ceramics for restorations and fixed prostheses by intended clinical use
and required values of mechanical and chemical properties
Mechanical and chemical properties
Flexural strength Chemical solubility
Class Recommended clinical indications 2
[MPa]
[μg/cm ]
minimum value for
(see 7.6)
mean (see 7.3)
a) Monolithic ceramic for single-unit anterior 50 < 100
1 prostheses, veneers, inlays, or onlays
adhesively cemented.
b) Ceramic for coverage of a metal framework 50 < 100

or a ceramic substructure.
a) Monolithic ceramic for single-unit anterior 100 < 100
or posterior prostheses adhesively cemented.
b) Fully covered substructure ceramic for 100 < 2 000
single-unit anterior or posterior prostheses
adhesively cemented.
a) Monolithic ceramic for single-unit anterior 300 < 100
or posterior prostheses and for three-unit
prostheses not involving molar restoration
adhesively or non-adhesively cemented.
b) Fully covered substructure for single-unit 300 < 2 000
anterior or posterior prostheses and for
three-unit prostheses not involving molar
restoration adhesively or non-adhesively
cemented.
a) Monolithic ceramic for three-unit 500 < 100
prostheses involving molar restoration.
b) Partially or fully covered substructure for 500 < 2 000
three-unit prostheses involving molar
restoration.
Monolithic ceramic for prostheses involving 800 < 100
5 partially or fully covered substructure for four or
more units.
Table 2 — Recommended colour coding for the identification of type I dental ceramic powders
Material Colour coding
Dentine ceramic Pink
Enamel ceramic Blue
Fluorescent ceramic Yellow
Highly chromatic dentine ceramic Orange
Opalescent enamel ceramic Blue-green
Modifying enamel ceramic Purple
(e.g. translucent, clear)
5 Requirements
5.1 Uniformity
The inorganic pigment(s) used to produce the colour of a fired dental ceramic and any organic colourants
(for colour coding) shall be uniformly dispersed throughout the dental ceramic material and in powdered
ceramic products, no segregation of the pigment(s) shall take place when the powder is mixed as in 7.1.4.
Check by visual inspection.
ISO 6872:2024(en)
5.2 Freedom from extraneous materials
5.2.1 Dental ceramic materials shall be free from extraneous materials when assessed by visual
inspection.
−1 238
5.2.2 Dental ceramic materials shall not have an activity concentration of more than 1,0 Bq⋅g of U.
Test in accordance with 7.2.
5.2.3 Any colourants used to colour code the ceramic powder, as per Table 2, are recommended to be food-
quality organic materials.
5.3 Mixing and condensation properties of type I ceramics
When mixed as in 7.1.4 with water or the modelling fluid recommended by the manufacturer, a dental
ceramic powder shall neither form lumps, nor granules, when assessed by visual inspection.
The paste formed shall be suitable for making the indicated restorations and prostheses by condensation of
successive layers. When the paste is condensed, as in 7.1.4, it shall neither crack, nor crumble, when assessed
by visual inspection during drying.
5.4 Physical and chemical properties
The physical and chemical properties of ceramic test specimens tested in accordance with the relevant
methods detailed for type I and type II ceramics in Clause 7 shall comply with the requirements specified
in Table 1. In addition to the required physical and chemical properties, there are other important physical
and chemical properties that can be reported, including fracture toughness (Annex A), strength distribution
parameters (Annex B), and hydrothermal stability (Annex C). The coefficient of thermal expansion of the
−6 −1
ceramics shall not deviate by more than 0,5 × 10 K from the value stated by the manufacturer (see 8.2.2).
The glass transition temperature of the ceramics shall not deviate by more than 20 °C from the value stated
by the manufacturer (see 8.2.2).
5.5 Shrinkage factor
The absolute uncertainty of measurement of the shrinkage factor by which the dimensions of the partially
sintered material is to be divided (as provided under 9.2.2 c) shall be ±0,002.
6 Sampling
6.1 Type I ceramics
Use retail packages from the same batch containing enough material to carry out the specified tests plus an
allowance for repeated tests, if necessary. Where there is more than one shade of a dental ceramic, perform
test with a colour/shade most commonly used. All of the materials tested shall be of the same lot.
Sufficient quantities of essential modelling fluids shall be obtained if their use is recommended by the
manufacturers. The quantities shall be those recommended by the manufacturer concerned.
6.2 Type II ceramics
All of the materials procured for testing in accordance with this document shall be of the same lot. Where
there is more than one shade of a dental ceramic, perform test with a colour/shade most commonly used.

ISO 6872:2024(en)
7 Test methods
7.1 Preparation of test specimens
7.1.1 General
For detailed instructions, see the individual test methods.
For type I ceramics (unless otherwise stated or inconsistent with the text), the apparatus detailed in 7.1.2
along with the conditions for mixing, condensation, and firing (7.1.3, 7.1.4, and 7.1.5) apply to all of the test
methods.
7.1.2 Components of test specimens (type I ceramics)
The liquid used in the preparation of test specimens shall be water that complies with the requirements for
grade 3 water (ISO 3696) or, when applicable, the modelling fluid recommended by the manufacturer of the
dental ceramic powder. The required amount of powder shall be taken from the appropriate pool of powder
obtained in accordance with 6.1.
7.1.3 Apparatus for mixing
All apparatus for mixing shall be clean and dry.
7.1.3.1 Glass slab or mixing palette.
7.1.3.2 Spatula, made from material that is not readily abraded by the dental ceramic powder (glass
is recommended). Instruments used for the mixing procedure shall be made of materials that do not
contaminate the ceramic material.
7.1.3.3 Open multipart mould, from which the condensed specimen can be removed without distortion.
7.1.3.4 Vibration system (table or mechanical brush), capable of vibrating at a frequency of 50 Hz to
60 Hz or in accordance with the manufacturer’s instructions.
7.1.4 Method of mixing
Combine the water or modelling liquid and the ceramic powder in the proportions recommended by the
manufacturer. Avoid vigorous mixing which will tend to incorporate air bubbles with the paste and, both
during and after mixing, examine for compliance with 5.1 and 5.2.
7.1.5 Procedure for specimen fabrication
Overfill the mould with dental ceramic paste and vibrate. When excess liquid appears at the free surface
of the specimen, place a paper tissue (or similar absorbent material) on the surface of the specimen and
remove the excess liquid continually by replacing the tissue as soon as it becomes saturated with liquid.
Continue vibration and absorption until no further liquid can be removed and then level the free surface
of the condensed specimen by means of a suitable instrument (a bevelled glass microscope slide is ideal for
this purpose). After removing the specimen from the mould, place it on a firing tray, dry it, and check for
compliance with 5.3.
NOTE Other forming methods such as dry pressing are acceptable for specimen fabrication.
7.1.6 Firing
Position the specimens in the furnace so that they will be uniformly fired on a substrate to which they will
not adhere and from which there will be no pick-up of material. Obtain guidance from the manufacturer for
the firing of test specimens. These specimens should be fired in accordance with manufacturer’s instructions

ISO 6872:2024(en)
so that their final density and thermal history is representative of that found for indicated restorations or
prostheses specific for the given test specimen which can be different from the instructions for use.
7.2 Radioactivity of dental ceramic
7.2.1 Preparation of samples
7.2.1.1 Type I ceramics
A 50 g sample, as manufactured, is suitable to be collected as described in 6.1.
7.2.1.2 Type II ceramics
Mill powder using tungsten-carbide milling media or other appropriate media (to avoid contamination by
radioactive species). Sieve and obtain 50 g of powder with a particle size less than 75 μm.
7.2.2 Counting procedure
Use a sample volume of 50 g bulk powder and determine the activity concentration of U by neutron
activation or gamma spectroscopy.
7.2.3 Assessment of results
Each sample tested shall comply with the requirement in 5.2.2.
7.3 Flexural strength
7.3.1 General
Three flexural test methods acceptable are:
a) three-point flexure,
b) four-point flexure, and
c) biaxial flexure (piston-on-three-ball).
7.3.2 Three-point and four-point flexure tests
7.3.2.1 Apparatus
7.3.2.1.1 Universal mechanical testing machine, capable of a crosshead speed of (1 ± 0,5) mm/min and an
ability to measure applied loads with a maximum limit of uncertainty in accordance with ISO 7500-1.
NOTE Usually not more than 5 kN of load is needed.
7.3.2.1.2 Flexural test fixtures
7.3.2.1.2.1 Fixture for three-point flexure, consisting of support rollers (1,5 mm to 5 mm ± 0,2 mm, in
diameter) positioned with their centres 12,0 mm to 40,0 mm (±0,5 mm) apart. The load shall be applied
at the midpoint between the supports by means of a third roller (1,5 mm to 5 mm ± 0,2 mm, in diameter).
Rollers shall be made from hardened steel or other hard material having a hardness greater than 40 HRC
(Rockwell C-scale) and have a smooth surface with a roughness less than 0,5 μm. It is recommended that the
actual spacing between the support roller centres (L) be measured to within 0,1 mm.

ISO 6872:2024(en)
7.3.2.1.2.2 Fixture for four-point flexure, consisting of 1/4-point test configuration such that the test
piece is loaded by two inner bearing rollers located at 1/4 of the total span (L) from the outer support
bearing rollers (see Figure 1).
Support rollers (1,5 mm to 5 mm ± 0,2 mm, diameter) shall be positioned with their centres apart such that
L = 16,0 mm to 40,0 mm. Rollers shall be made from hardened steel or other hard material having a hardness
greater than 40 HRC (Rockwell C-scale) and have a smooth surface with a roughness less than 0,5 μm. The
two loading rollers of identical material and size to the support rollers shall be located at the quarter points
yielding an inner span (L/2 in Figure 1) of 8,0 mm to 20,0 mm. The loading arrangement shall ensure that
equal forces are applied to the loading rollers and that torsional loading is minimized. It is recommended
that the actual spacing between the roller centres (L for support and L/2 for inner) be measured to within
0,1 mm. It is also recommended that the inner span be centred over the support span to within 0,1 mm.
NOTE Moment arm = L/4
Figure 1 — Schematic of the four-point-1/4-point fixture configuration
7.3.2.2 Preparation of test specimens
7.3.2.2.1 Test specimen dimensions and test parameters
7.3.2.2.1.1 Dimensions:
Specimens for three-point and four-point flexure testing have a rectangular cross section and most
preferably an edge chamfer as per the diagram in Figure 2 and dimensions listed below. The edge chamfer
should be ground or rounded lengthwise along the long axis of the specimen so that grinding damage and
chipping is minimized. The edge chamfer can be ground prior to final sintering if kept within below values
after final sintering.
Specimen dimensions:
Width w = (4 ± 0,2) mm (dimension of the side at right angles to the direction of the applied load)
Thickness b = (2,1 ± 1,1) mm (with 3,0 mm recommended; dimension of the side parallel to the
direction of the applied load)
Chamfer c = (0,12 ± 0,03) mm [with a maximum of 0,10 mm recommended for small thickness
specimens (b < 2,0 mm)]
7.3.2.2.1.2 Test parameters:
Test span:
For four-point flexure; L in millimetres (centre-to-centre distance between outer support roller, see Figure 1.
In the four-point 1/4 configuration specified, the moment arm = L/4).
For three-point flexure; l in millimetres (centre-to-centre distance between support rollers).
Breaking load: P in newtons
ISO 6872:2024(en)
Specimen lengths shall be at least 2b mm longer than the test span (L or l), and the ratio of thickness to
length (b/L or b/l) shall be ≤0,1.
Figure 2 — Specification of indicated dimensions
7.3.2.2.2 Type I ceramics
Prepare at least 10 and preferably 30 specimens of dimensions as specified in 7.3.2.2.1. Use a mould
appropriately sized to allow for dimensional changes resulting from sintering and finishing. Fire the
specimens in accordance with the manufacturer’s instructions modified as needed due to specimen
dimensions. Grind each specimen so as to produce a rectangular test piece as specified in 7.3.2.2.1. Final
grind on diamond-embedded media having a nominal grit size of 30 μm to 40 μm and final polish on media
having 15 μm to 20 μm diamond grit. Grinding of all four long faces should be done lengthwise parallel to the
specimen long axis wherever possible to minimize grinding damage that can alter the strength. Polishing
does not always remove prior grinding damage unless the polishing removes 20 µm to 30 µm of the material.
Ensure that opposing faces of the test pieces are flat and parallel within 0,05 mm. Where appropriate, testing
of specimen “as fired” (without further grinding at the edge or on the surface) should be done so long as the
shape and dimensions are within the limits specified. Thoroughly clean the test pieces ensuring that all
traces of grinding debris are removed.
7.3.2.2.3 Type II ceramics
Prepare in accordance with the manufacturer’s instructions at least 10 and preferably 30 specimens of
dimensions as specified in 7.3.2.2.1. In the case of ceramic material produced for machining, prepare the
specimens from ceramic blocks made by the manufacturer. Grind each specimen to produce test pieces
using the protocol specified in 7.3.2.2.2. Where appropriate, testing of specimen “as fired” (without further
grinding at the edge or on the surface) can be done as long as the shape and dimensions are within the limits
specified.
7.3.2.3 Procedure
Measure the cross-sectional dimensions of each test piece to ±0,01 mm. Then, place a test piece centrally
on the bearers of the test machine so that the load is applied to a 4 mm wide face along a line perpendicular
to the long axis of the test piece and determine to ±0,1 N the load required to break the test piece. Use a
crosshead speed of (1 ± 0,5) mm/min. Repeat the procedure with the remaining test pieces.
7.3.2.4 Calculation of strength
7.3.2.4.1 Three-point flexure
From Formula (1), calculate the flexural strength, σ, in megapascals and report the mean and standard
deviation of the strength data. Means should equal or exceed the requirements listed in Table 1. In addition,

ISO 6872:2024(en)
if at least 15 specimens have been tested, the Weibull characteristic strength and Weibull modulus should be
reported as well, per Annex B.
3Pl
σ = (1)
2wb
where
P is the breaking load, in newtons;
l is the test span (centre-to-centre distance between support rollers), in millimetres;
w is the width of the specimen, i.e. the dimension of the side at right angles to the direction
of the applied load, in millimetres;
b is the thickness of the specimen, i.e. the dimension of the side parallel to the direction
of the applied load, in millimetres.
7.3.2.4.2 Four-point flexure
From Formula (2), calculate the flexural strength, σ, in megapascals and report the mean and standard
deviation of the strength data. Means should equal or exceed the requirements listed in Table 1. In addition,
if at least 15 specimens have been tested, the Weibull characteristic strength and Weibull modulus should be
reported as well, per Annex B.
3PL
σ = (2)
4wb
where
P is the load at failure, in newtons;
L is the centre-to-centre distance between outer support rollers, in millimetres;
w is the width of the specimen, i.e. the dimension of the side at right angles to the direction
of the applied load, in millimetres;
b is the thickness of the sp
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