EN ISO 6872:2015

Dentistry - Ceramic materials (ISO 6872:2015)

ISO 6872:2015 specifies the requirements and the corresponding test methods for dental ceramic materials for fixed all-ceramic and metal-ceramic restorations and prostheses.

Zahnheilkunde - Keramische Werkstoffe (ISO 6872:2015)

Diese Internationale Norm legt die Anforderungen und die dazugehörigen Prüfverfahren für dentalkeramische Werkstoffe fest, die zur Herstellung von festsitzenden vollkeramischen und metallkeramischen Restaurationen sowie von herausnehmbarem Zahnersatz verwendet werden.

Médecine bucco-dentaire - Matériaux céramiques (ISO 6872:2015)

L'ISO 6872:2015 spécifie les exigences et les méthodes d'essai correspondantes relatives aux matériaux céramiques dentaires pour les restaurations et les prothèses tout céramique et céramo-métallique.

Zobozdravstvo - Keramični materiali (ISO 6872:2015)

Ta mednarodni standard določa zahteve in ustrezne preskusne metode za zobozdravstvene keramične materiale za fiksna izključno keramična ter kovinsko-keramična popravila in proteze.

General Information

• Status: Withdrawn
• Publication Date: 09-Jun-2015
• Withdrawal Date: 13-Apr-2025
• ICS: 11.060.10 - Dental materials
• Technical Committee: CEN/TC 55 - Dentistry
• Drafting Committee: CEN/TC 55 - Dentistry
• Current Stage: 9960 - Withdrawal effective - Withdrawal
• Start Date: 21-Aug-2024
• Completion Date: 14-Apr-2025
• Directive: 93/42/EEC - Council Directive 93/42/EEC of 14 June 1993 concerning medical devices
• Ref Project: SIST EN ISO 6872:2015 - Dentistry - Ceramic materials (ISO 6872:2015)

Relations

• Replaces: EN ISO 6872:2008 - Dentistry - Ceramic materials (ISO 6872:2008)
• Effective Date: 25-Jul-2012
• Replaced By: EN ISO 6872:2024 - Dentistry - Ceramic materials (ISO 6872:2024)
• Effective Date: 28-Jan-2023
• Amended By: EN ISO 6872:2015/A1:2018 - Dentistry - Ceramic materials (ISO 6872:2015/Amd 1:2018)
• Effective Date: 26-Jul-2017

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2015
1DGRPHãþD
SIST EN ISO 6872:2008
=RER]GUDYVWYR.HUDPLþQLPDWHULDOL,62
Dentistry - Ceramic materials (ISO 6872:2015)
Zahnheilkunde - Keramische Werkstoffe (ISO 6872:2015)
Médecine bucco-dentaire - Matériaux céramiques (ISO 6872:2015)
Ta slovenski standard je istoveten z: EN ISO 6872:2015
ICS:
11.060.10 =RERWHKQLþQLPDWHULDOL Dental materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 6872
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2015
ICS 11.060.10 Supersedes EN ISO 6872:2008
English Version
Dentistry - Ceramic materials (ISO 6872:2015)
Médecine bucco-dentaire - Matériaux céramiques (ISO Zahnheilkunde - Keramische Werkstoffe (ISO 6872:2015)
6872:2015)
This European Standard was approved by CEN on 23 April 2015.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2015 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6872:2015 E
worldwide for CEN national Members.

Contents Page
Foreword .3
Foreword
This document (EN ISO 6872:2015) 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 December 2015, and conflicting national standards shall be withdrawn
at the latest by December 2015.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 6872:2008.
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, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Endorsement notice
The text of ISO 6872:2015 has been approved by CEN as EN ISO 6872:2015 without any modification.

INTERNATIONAL ISO
STANDARD 6872
Fourth edition
2015-06-01
Dentistry — Ceramic materials
Médecine bucco-dentaire — Matériaux céramiques
Reference number
ISO 6872:2015(E)
©
ISO 2015
ISO 6872:2015(E)
© ISO 2015, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2015 – All rights reserved

ISO 6872:2015(E)
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 . 3
3.3 Properties . 4
4 Types, classes, and their identification . 4
5 Requirements . 6
5.1 Uniformity . 6
5.2 Freedom from extraneous materials. 6
5.3 Mixing and condensation properties of type I ceramics . 6
5.4 Physical and chemical properties . 6
5.5 Biocompatibility . 6
5.6 Shrinkage factor . 6
6 Sampling . 6
6.1 Type I ceramics . 6
6.2 Type II ceramics . 7
7 Test methods . 7
7.1 Preparation of test specimens . 7
7.1.1 Components of test specimens (type I ceramics) . 7
7.1.2 Apparatus for mixing . 7
7.1.3 Method of mixing . 7
7.1.4 Procedure for specimen fabrication . 7
7.1.5 Firing . 8
7.2 Radioactivity of dental ceramic . 8
7.2.1 Preparation of samples . 8
7.2.2 Counting procedure. 8
7.2.3 Assessment of results . 8
7.3 Flexural strength . 8
7.3.1 Three-point and four-point bending tests . 8
7.3.2 Biaxial flexure test (piston-on-three-ball test) .12
7.4 Linear thermal expansion coefficient .14
7.4.1 Apparatus .14
7.4.2 Preparing of test specimens (type I and type II ceramics) .14
7.4.3 Dilatometric measurement .14
7.4.4 Assessment of results .14
7.5 Glass transition temperature .14
7.5.1 Operating procedure .14
7.5.2 Assessment of results .15
7.6 Chemical solubility .15
7.6.1 Reagent . .15
7.6.2 Apparatus .15
7.6.3 Preparation of test specimens .16
7.6.4 Procedure .16
7.6.5 Calculation and assessment of results .16
8 Information and instructions .16
8.1 Information .16
8.1.1 General.16
8.1.2 Type I Ceramics .16
ISO 6872:2015(E)
8.1.3 Type II ceramics .16
8.2 Instructions for use .17
9 Packaging, marking, and labelling .17
9.1 Packaging .17
9.2 Marking and labelling .17
Annex A (informative) Fracture toughness .19
Annex B (informative) Weibull statistics .26
Bibliography .28
iv © ISO 2015 – All rights reserved

ISO 6872:2015(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 on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 106, Dentistry, Subcommittee SC 2,
Prosthodontic materials.
This fourth edition cancels and replaces the third edition (ISO 6872:2008), which has been technically
revised with the following changes:
— new edition of ISO 23146:2012 for fracture toughness by SEVNB has been added as an alternative in
Annex A. It has a rigorous procedure developed by ISO/TC 206, Fine ceramics;
— a restriction on the use of the SEVNB method for fracture toughness determination for 3Y-TZP has
been added. In most cases, the notch cannot be made sharp enough with a razor blade;
— maximum chamfer size on bend bars has been reduced for the case of the thin specimens;
— recommendations to grind lengthwise were added to the bend bar preparation step in 7.3.1.2.2;
— the Y equations for SEVNB fracture toughness in 3–point have been refined and expanded to cover
more configurations;
— modification to Table 1 changing “aesthetic” to “monolithic”.
ISO 6872:2015(E)
Introduction
Specific qualitative and quantitative requirements for freedom from biological hazard are not included
in this International Standard, but it is recommended that in assessing possible biological or toxicological
hazards, reference be made to ISO 10993-1 and ISO 7405.
vi © ISO 2015 – All rights reserved

INTERNATIONAL STANDARD ISO 6872:2015(E)
Dentistry — Ceramic materials
1 Scope
This International Standard specifies the requirements 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, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 1942, Dentistry — Vocabulary
ISO 13078, Dentistry — Dental furnace — Test method for temperature measurement with separate thermocouple
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1942 and the following apply.
3.1 Material
3.1.1
addition ceramic
add-on ceramic
correction ceramic
dental ceramic material which is fired at a reduced temperature and is normally applied to restore
contact areas on a dental restoration or prosthesis
3.1.2
aesthetic ceramic
dental porcelain (3.1.5) or glass ceramic (3.1.10) having appropriate translucency and colour used to
mimic the optical properties of natural teeth
3.1.3
chromatic dentin ceramic
dentine ceramic having a high strength or saturation of the hue (color)
3.1.4
dental ceramic
inorganic, non-metallic material which is specifically formulated for use when processed according to
the manufacturers’ instructions to form the whole or part of a dental restoration or prosthesis
3.1.5
dental porcelain
predominantly, glassy dental ceramic (3.1.4) material used mainly for aesthetics in a dental restoration
or prosthesis
3.1.6
dentine ceramic
dental ceramic (3.1.4) material used to form the overall shape and basic colour of a dental restoration or
prosthesis simulating the natural tooth dentine
ISO 6872:2015(E)
3.1.7
enamel ceramic
dental ceramic (3.1.4) material used to overlay, either partially or wholly, the dentine ceramic (3.1.6)
and also, to form the more translucent incisal third of a dental restoration or prosthesis simulating the
natural tooth enamel
3.1.8
flame-sprayed dental ceramic
dental ceramic core or substructure layer formed via the technique of flame-spraying
3.1.9
fluorescent ceramic
dental ceramic (3.1.4) 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.
3.1.10
glass ceramic (dental)
dental ceramic (3.1.4) 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
3.1.11
glass-infiltrated dental ceramic
dental ceramic core or substructure layer which is porous and is subsequently densified by the
infiltration of specialised glass at elevated temperature
3.1.12
glaze ceramic
dental ceramic (3.1.4) material which is overlayed and fired at a lower temperature compared to dentine
ceramic (3.1.6) or enamel ceramic (3.1.7) to produce a thin coherent sealed surface, the level of gloss
being determined by the firing conditions
3.1.13
liner
dental ceramic (3.1.4) material used on all ceramic substructure forming a layer that provides a
background colour upon which dentine or opaceous dentine can be applied to achieve overall aesthetics
3.1.14
modelling fluid
liquid with which a dental ceramic powder is mixed in order to shape or model it into its required form
prior to firing
3.1.15
modifying enamel ceramic
enamel ceramic (3.1.7) 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
3.1.16
monolithic ceramic
dental ceramic (3.1.4) that is substantially made of a single uniform material
Note 1 to entry: A thin layer of glaze (3.3.4) (staining technique) can be applied.
3.1.17
opaceous dentine ceramic
dental ceramic (3.1.4) material having a higher opacity than a dentine ceramic (3.1.6) material, but which
can still be used to contribute to the overall shape and basic colour of a dental restoration or prosthesis
simulating the natural tooth dentine
2 © ISO 2015 – All rights reserved

ISO 6872:2015(E)
3.1.18
opalescent enamel ceramic
enamel ceramic (3.1.7) material that scatters shorter wavelengths of light (e.g. blue) and transmits longer
wavelengths of light (e.g. red)
3.1.19
opaque dental ceramic
dental ceramic (3.1.4) material which when applied to a metallic substructure, according to the
manufacturer’s instructions, acts to bond to the metal surface forming a layer that provides a
background colour and interface upon which other dental ceramic materials can be applied to achieve
overall aesthetics
3.1.20
shoulder ceramic
margin ceramic
dental ceramic (3.1.4) material used to form shape and colour at the marginal area of the dental
restoration or prosthesis simulating natural tooth dentine in this area
3.1.21
stain ceramic
dental ceramic powder or paste which is normally intensely coloured and which is formulated to be
used either internally or externally during the build-up of a dental restoration or prosthesis to simulate
details within or on the surface as are found in natural teeth
3.1.22
substructure (core) dental ceramic
predominantly, polycrystalline dental ceramic material that forms a supporting substructure upon
which one or more layers of dental ceramic (3.1.4) or dental polymer material are applied, either partially
or totally, to form a dental restoration or prosthesis
3.2 Processing
3.2.1
air firing dental ceramic
firing of dental ceramics (3.1.4) under ambient atmospheric pressure
3.2.2
dental CAD/CAM
computer-aided design/computer-aided manufacture (CAD/CAM) procedures to manufacture a dental
restoration or prosthesis normally including the following stages: a) a digital scanning procedure of the
model, wax-up, or intra-orally to produce a 3D data set; b) software manipulation of the 3D data set to
design the prosthesis; c) a computer-directed machine tool that performs the manufacturing process
3.2.3
condensation of dental ceramic
powder process whereby a slurry of dental ceramic powder is vibrated to compact the powder prior to
sintering
3.2.4
injectable, castable, or pressable dental ceramic
dental ceramic (3.1.4) material, normally in the form of a pellet or ingot (often pre-sintered), designed for
use in a specialised furnace which enables the ingot to be injected/cast/pressed into a mould prepared
through the lost wax technique
ISO 6872:2015(E)
3.2.5
sintering of a dental ceramic
process whereby heat and potentially other process parameters, for example, mechanical or gas
pressure, are applied to a ceramic powder or powder compact in order to densify the ceramic into its
required form
Note 1 to entry: “Firing” and “sintering” are used interchangeably in this International Standard (“firing”
connoting the application of heat to drive sintering).
3.2.6
vacuum firing dental ceramic
firing of dental ceramics (3.1.4) at reduced pressure (i.e. under vacuum) to yield the required density and
associated aesthetics especially the degree of translucency
Note 1 to entry: Dental ceramics for vacuum firing have a specific particle size distribution to reduce the
entrapment of porosity.
3.3 Properties
3.3.1
class of dental ceramic
classification of a dental ceramic (3.1.4) material according to 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
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 International Standard, 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 according to their intended clinical use and according to the
descriptions in Table 1. If colour is added to a ceramic powder for identification purposes, the colour
coding given in Table 2 is recommended.
4 © ISO 2015 – All rights reserved

ISO 6872:2015(E)
Table 1 — Classification of ceramics for fixed prostheses by intended clinical use with required
mechanical and chemical properties
Class Recommended clinical indications Mechanical and chemical properties
Flexural strength
[MPa] Chemical solubility
minimum value for [μg/cm ]
mean (see 7.3.1.4)
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) Partially or fully covered substructure ceramic 100 <2 000
for
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) Partially or fully covered substructure for sin- 300 <2 000
gle-unit
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
partially or fully covered substructure for four or
5 more units or fully covered
substructure for prostheses involving
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)
ISO 6872:2015(E)
5 Requirements
5.1 Uniformity
The inorganic pigment(s) used to produce the colour of a fired dental ceramic and any organic colorants
(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 7.1.3.
Check by visual inspection.
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 7.2.2.
5.2.3 Any colorants 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 7.1.3 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. The coefficient of thermal expansion of the ceramics shall not deviate by more than
−6 −1
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 Biocompatibility
See the introduction for guidance on biocompatibility.
5.6 Shrinkage factor
The absolute accuracy 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 in a class of dental
ceramic, perform test with a colour/shade most commonly used. All of the materials tested shall be of
the same lot.
6 © ISO 2015 – All rights reserved

ISO 6872:2015(E)
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 International Standard shall be of
the same lot.
7 Test methods
7.1 Preparation of test specimens
For detailed instructions, see the individual test methods.
For type I specimens (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
the test methods.
7.1.1 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.
7.1.2 Apparatus for mixing
All apparatus for mixing shall be clean and dry.
7.1.2.1 Glass slab or mixing palette.
7.1.2.2 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.
7.1.2.3 Open multipart mould, from which the condensed specimen can be removed without distortion.
7.1.2.4 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.
7.1.3 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 5.2.1.
7.1.4 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
ISO 6872:2015(E)
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.
7.1.5 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 according to manufacturer’s instructions
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 could 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.
NOTE Those with gamma spectroscopy techniques should be used to screen for adulteration.
7.2.3 Assessment of results
Each sample tested shall comply with the requirement in 5.2.2.
7.3 Flexural strength
Three flexural test methods are acceptable thath are
a) three-point bending,
b) four-point bending, and
c) biaxial flexure (piston-on-three-ball).
7.3.1 Three-point and four-point bending tests
7.3.1.1 Apparatus
7.3.1.1.1 Universal mechanical testing machine, capable of a crosshead speed of (1 ± 0,5) mm/min
and an ability to measure applied loads of between 10 N and [1 000 N or 2 500 N] e.g see ISO 7500-1.
7.3.1.1.2 Flexural test fixtures.
8 © ISO 2015 – All rights reserved

ISO 6872:2015(E)
7.3.1.1.2.1 Fixture for three-point bending, 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 R . It is recommended
a
that the actual spacing between the support roller centres (L) be measured to within 0,1 mm.
7.3.1.1.2.2 Fixture for four-point bending, 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 R . The two loading rollers of identical material and size to the support rollers shall be
a
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.
L/4 L/2
L
Figure 1 — Schematic of the four-point-1/4-point fixture configuration (Note: Moment arm = L/4)
7.3.1.2 Preparation of test specimens
7.3.1.2.1 Test specimen dimensions and test parameters
Dimensions:
Specimens for three-point and four-point bending 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)]
Test parameters:
ISO 6872:2015(E)
Test span:
For four-point bending; 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 bending; l in millimetres (centre-to-centre distance between support rollers).
Breaking load: P in newtons
Specimen lengths shall be at least 2 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.
c
45°
b
w
Figure 2 — Specification of indicated dimensions
7.3.1.2.2 Type I ceramics
Prepare at least 10 and preferably 30 specimens of dimensions as specified in 7.3.1.2.1. 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 7.3.1.2.1. 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 could alter the
strength. Polishing may not necessarily 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) may 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.
7.3.1.2.3 Type II ceramics
Prepare according to the manufacturer’s instructions at least 10 and preferably 30 specimens of
dimensions as specified in 7.3.1.2.1. 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 7.3.1.2.2. Where appropriate, testing of specimen “as fired” (without
further grinding at the edge or on the surface) could be done as long as the shape and dimensions are
within the limits specified.
7.3.1.3 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.
10 © ISO 2015 – All rights reserved

ISO 6872:2015(E)
7.3.1.4 Calculation of strength
7.3.1.4.1 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, if at least 15 specimens have been tested, the Weibull characteristic strength and Weibull
modulus may be repor
...