SIST EN ISO 20795-2:2013

SLOVENSKI STANDARD
01-junij-2013
1DGRPHãþD
SIST EN ISO 20795-2:2010
Zobozdravstvo - Osnovni polimeri - 2. del: Ortodontski osnovni polimeri (ISO
20795-2:2013)
Dentistry - Base polymers - Part 2: Orthodontic base polymers (ISO 20795-2:2013)
Zahnheilkunde - Kunststoffe - Teil 2: Kieferorthopädische Kunststoffe (ISO 20795-
2:2013)
Médecine bucco-dentaire - Polymères de base - Partie 2: Polymères pour base
orthodontique (ISO 20795-2:2013)
Ta slovenski standard je istoveten z: EN ISO 20795-2:2013
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 20795-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2013
ICS 11.060.10 Supersedes EN ISO 20795-2:2010
English Version
Dentistry - Base polymers - Part 2: Orthodontic base polymers
(ISO 20795-2:2013)
Médecine bucco-dentaire - Polymères de base - Partie 2: Zahnheilkunde - Kunststoffe - Teil 2: Kieferorthopädische
Polymères pour base orthodontique (ISO 20795-2:2013) Kunststoffe (ISO 20795-2:2013)
This European Standard was approved by CEN on 5 February 2013.

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

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2013 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20795-2:2013: E
worldwide for CEN national Members.

Contents Page
Foreword . 3

Foreword
This document (EN ISO 20795-2:2013) 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 September 2013, and conflicting national standards shall be
withdrawn at the latest by September 2013.
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 20795-2:2010.
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 20795-2:2013 has been approved by CEN as EN ISO 20795-2:2013 without any modification.

INTERNATIONAL ISO
STANDARD 20795-2
Second edition
2013-03-01
Dentistry — Base polymers —
Part 2:
Orthodontic base polymers
Médecine bucco-dentaire — Polymères de base —
Partie 2: Polymères pour base orthodontique
Reference number
ISO 20795-2:2013(E)
©
ISO 2013
ISO 20795-2:2013(E)
© ISO 2013
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.
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Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
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Published in Switzerland
ii © ISO 2013 – All rights reserved

ISO 20795-2:2013(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Classification . 2
5 Requirements . 2
5.1 Unpolymerized material . 2
5.2 Polymerized material . 3
6 Sampling . 5
7 Preparation of specimen plates and test specimens . 5
7.1 Laboratory environment . 5
7.2 Procedures . 5
7.3 Special equipment . 5
8 Test methods . 5
8.1 Inspection for compliance determination . 5
8.2 Colour . 6
8.3 Polishability, freedom from porosity, ultimate flexural strength, and flexural modulus . 6
8.4 Fracture toughness with a modified bending test .10
8.5 Residual methyl methacrylate monomer .14
8.6 Plasticiser(s), where applicable .19
8.7 Water sorption and solubility .23
9 Requirements for labelling, marking, packaging, and instructions supplied
by manufacturer .26
9.1 Packaging .26
9.2 Marking of outer packages and containers .26
9.3 Manufacturer’s instructions .27
Annex A (normative) HPLC method for determination of MMA content .28
Bibliography .31
ISO 20795-2:2013(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International
Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies
casting a vote.
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.
ISO 20795-2 was prepared by Technical Committee ISO/TC 106, Dentistry, Subcommittee SC 2,
Prosthodontic materials.
This second edition cancels and replaces the first edition (ISO 20795-2:2010), which has been
technically revised.
ISO 20795 consists of the following parts, under the general title Dentistry — Base polymers:
— Part 1: Denture base polymers
— Part 2: Orthodontic base polymers
iv © ISO 2013 – All rights reserved

ISO 20795-2:2013(E)
Introduction
Polymeric materials based on methacrylates have been widely used in the construction of both active
and passive removable orthodontic appliances for many years. These removable appliances are mainly
used in the orthodontic treatment of children. The method of preparing the polymeric part of the
orthodontic appliance has several potential problems. Depending on the polymerization process and
polymer/monomer mixing ratio, the polymer part of the removable orthodontic appliance may be
weaker than if conventional flasking and heat systems of polymerization were used. There may be a
greater risk that an appliance will have more residual substances such as monomers than a conventional
heat-cured denture base polymer. In addition, a high monomer content of the polymer/monomer mix
may cause increased contraction on polymerization.
Specific qualitative and quantitative requirements for freedom from biological hazard are not included
in this part of ISO 20795, but it is recommended that, in assessing possible biological or toxicological
hazards, reference be made to ISO 10993-1 and ISO 7405.
INTERNATIONAL STANDARD ISO 20795-2:2013(E)
Dentistry — Base polymers —
Part 2:
Orthodontic base polymers
1 Scope
This part of ISO 20795 is applicable to orthodontic base polymers and copolymers used in the
construction of both active and passive orthodontic appliances and specifies their requirements. It
also specifies test methods to be used in determining compliance with these requirements. It further
specifies requirements with respect to packaging and marking the products and to the instructions to
be supplied for use of these materials.
2 Normative references
The following referenced documents are indispensable for the application 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 7491, Dental materials — Determination of colour stability
ISO 8601, Data elements and interchange formats — Information interchange — Representation of
dates and times
ISO 20795-1:2008, Dentistry — Base polymers — Part 1: Denture base polymers
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1942 and the following apply.
3.1
autopolymerizable materials
products having polymerization initiated by chemical means and not requiring application of
temperatures above 65 °C to complete the polymerization
3.2
build up technique
spray on technique
gradual addition of increments of powder and liquid on the master cast until the desired shape is attained
3.3
immediate container
container that is in direct contact with the 〈orthodontic〉 base materials
3.4
light activated polymers
products having polymerization initiated by the application of energy from an external radiation source,
such as visible light
ISO 20795-2:2013(E)
3.5
liquid
monomeric liquid to be mixed with polymeric particles to form a mouldable dough or fluid resin mixture
used for forming 〈orthodontic〉 bases
3.6
orthodontic base
polymer part of the 〈orthodontic〉 appliance
3.7
outer packaging
labelled container or wrapping within which other containers are packed
3.8
powder
polymeric particles to be mixed with monomeric liquid to form a mouldable dough or fluid resin mixture
used for forming 〈orthodontic〉 bases
3.9
processing
procedure of preparing a solid 〈orthodontic〉 base polymer plate and/or specimen by polymerization or
injection
3.10
thermoplastic material
hard 〈orthodontic〉 polymeric material that can be softened by application of heat to make it mouldable,
and then returned to the hardened state upon cooling
4 Classification
Orthodontic base polymers covered by this part of ISO 20795 are categorized into the following types:
— Type 1: autopolymerizable materials;
— Type 2: light-activated materials;
— Type 3: thermoplastic materials.
5 Requirements
5.1 Unpolymerized material
5.1.1 Liquid component
5.1.1.1 General
The liquid shall consist essentially of monomeric material compatible with the powder.
5.1.1.2 Homogeneity
The liquid shall be free of deposit or sediment that can be observed by visual inspection (see 8.1.1).
5.1.2 Solid components
The solid or semi-solid components shall be free of extraneous material that can be observed by visual
inspection (see 8.1.1).
2 © ISO 2013 – All rights reserved

ISO 20795-2:2013(E)
5.2 Polymerized material
5.2.1 Biocompatibility
Specific qualitative and quantitative requirements for freedom from biological hazard are not included
in this part of ISO 20795, but it is recommended that, in assessing possible biological or toxicological
hazards, reference be made to ISO 10993-1 and ISO 7405.
5.2.2 Surface characteristics
5.2.2.1 When processed in the manner recommended by the manufacturer and in contact with materials
recommended by the manufacturer, orthodontic base polymer test specimens prepared in accordance
with 8.5.2 and 8.6.3 shall have a smooth, hard, and glossy surface (see 8.1.1).
5.2.2.2 The test specimens for residual methyl methacrylate monomer (see 8.5) and the specimens
for water sorption and solubility testing (see 8.7) shall retain their form without visible distortion after
processing (see 8.1.1).
5.2.2.3 When polished in accordance with 8.3.1.4, the specimen plates shall present a smooth surface
with a high gloss (see 8.1.1).
5.2.3 Shape capability
When prepared in accordance with the manufacturer’s instructions, all types of orthodontic base
polymers shall produce a test specimen plate (see 8.3.1.4) with defined edges and dimensions as given
in Figure 1.
Dimensions in millimetres
NOTE Dimensional tolerance shall be ± 1 mm.
Figure 1 — Model of the specimen plate (see 8.3.1.2.1)
5.2.4 Colour
The colour of a test specimen strip prepared in accordance with 8.3.2.3 shall be as stated by the
manufacturer when tested and inspected in accordance with 8.1.1 and 8.2.
Coloured orthodontic base polymers shall be evenly pigmented and/or coloured.
ISO 20795-2:2013(E)
Transparent orthodontic base polymers shall be transparent or clear.
5.2.5 Freedom from porosity
When prepared in accordance with 8.3.2.3, the test specimen strips shall not show pores that can be
observed by visual inspection (see 8.1.1).
5.2.6 Ultimate flexural strength
When determined in accordance with 8.3.2.5, the ultimate flexural strength shall be not less than
50 MPa (see Table 1).
5.2.7 Flexural modulus
When determined in accordance with 8.3.2.5, the flexural modulus of the processed orthodontic base
polymer shall be at least 1 500 MPa (see Table 1).
5.2.8 Maximum stress intensity factor
When determined in accordance with 8.4, the maximum stress intensity factor shall be at least
1/2
1,1 MPa⋅m (see Table 1).
5.2.9 Total fracture work
When determined in accordance with 8.4, the total fracture work shall be at least 250 J/m (see Table 1).
5.2.10 Residual methyl methacrylate monomer
When orthodontic base polymers are prepared and tested in accordance with 8.5, the following shall
apply (see Table 1).
The maximum mass fraction of residual methyl methacrylate is 5 % for all three types of orthodontic
base polymers.
The residual methyl methacrylate content claimed by the manufacturer [see 9.3 b)] shall not exceed the
stated value by more than 0,2 % mass fraction when tested in accordance with 8.5.
5.2.11 Plasticizers
If the orthodontic base polymer contains extractable phthalate plasticizer(s), identify and quantify the
plasticizer(s) as percent mass fraction determined in accordance with 8.6. The content shall not exceed
the stated value by more than 10 % (see Table 1).
5.2.12 Water sorption
When the processed polymer is tested in accordance with 8.7, the increase in mass per volume (water
sorption) shall not exceed 32 µg/mm (see Table 1).
5.2.13 Water solubility
When the processed polymer is tested in accordance with 8.7, the loss in mass per volume (water
solubility) shall not exceed 5 µg/mm (see Table 1).
4 © ISO 2013 – All rights reserved

ISO 20795-2:2013(E)
Table 1 — Summary of requirements described in 5.2.6 to 5.2.13
Requirements Flexural properties Fracture toughness Residual Phthalate Water Water
methyl plasticizers sorption solubil-
Ultimate Flexural Maxi- Total
methacrylate ity
flexural modulus mum fracture
monomer
strength stress work
intensity
factor
σ E K W w w
max f sp sl
1/2 2 3 3
MPa MPa MPa m J/m Percent mass Percent µg/mm µg/mm
min. min. min. min. fraction mass frac- max. max.
max. tion max.
All types 50 1 500 1,1 250 5 Maximum 32 5
10 % above
stated
a
value
a
For example, if the manufacturer states a percent mass fraction of 5 % of phthalate plasticizers, the content shall not be
more than 5,5 %.
6 Sampling
The test sample shall consist of a retail package, or packages, containing sufficient material to carry out
the specified tests, plus an allowance for any necessary repetition of the tests. If more than one package
is required, all material shall be of the same batch.
7 Preparation of specimen plates and test specimens
7.1 Laboratory environment
Prepare and test specimens and specimen plates at (23 ± 2) °C and (50 ± 10) % relative humidity, unless
otherwise specified in this part of ISO 20795 or in the manufacturer’s instructions.
7.2 Procedures
Prepare, manipulate, and process materials for making the test specimens and specimen plates using the
equipment and procedures recommended in the manufacturer’s instructions (see 9.3), unless otherwise
specified in this part of ISO 20795.
From materials requiring a mixture of two or more ingredients, prepare separate mixes for each test
specimen or specimen plate.
7.3 Special equipment
Any special equipment specified by the manufacturer for processing a material shall be made available
by the manufacturer.
8 Test methods
8.1 Inspection for compliance determination
8.1.1 Visual inspection
Observe the test samples by visual inspection in order to determine compliance with the requirements
laid down in 5.1.1.2 and 5.1.2.
ISO 20795-2:2013(E)
Observe the test specimen(s) by visual inspection in order to determine compliance with the requirements
laid down in 5.2.2.1, 5.2.2.2, and 5.2.5 and inspect for colour (see 5.2.4) in accordance with ISO 7491.
Observe the test specimen plate(s) by visual inspection in order to determine compliance with the
requirements laid down in 5.2.2.3 and 5.2.3.
Inspect visually to determine compliance with Clause 9.
8.1.2 Expression of results
Report whether the liquid components pass or fail (see 5.1.1.2).
Report whether the solid components pass or fail (see 5.1.2).
Report whether the surfaces of the orthodontic base polymer specimens have a smooth, hard, and glossy
surface (see 5.2.2.1) and whether the specimens pass or fail.
Report whether the form of specimens is retained without distortion and whether the specimens pass
or fail (see 5.2.2.2).
Report whether the specimen plates have a smooth surface with a high gloss after polishing and whether
the specimen plate passes or fails (see 5.2.2.3).
Report whether the specimen plate has defined edges and whether the specimen plate passes or fails
(see 5.2.3).
Report whether the material passes or fails the requirements for labelling, marking, packaging, and
instructions (see Clause 9).
8.2 Colour
8.2.1 General
Compare a specimen strip prepared in accordance with 8.3.2.3 for compliance with 5.2.4. Inspect its
colour visually (see 8.1.1) for compliance with the manufacturer’s statement [see 9.2.1 c) and 9.2.2 c)].
8.2.2 Expression of results
Report whether the material passes or fails (see 5.2.4) when tested in accordance with ISO 7491.
8.3 Polishability, freedom from porosity, ultimate flexural strength, and flexural modulus
8.3.1 Polishability
8.3.1.1 Materials
8.3.1.1.1 Wet pumice for polishing, having a grain size of approximately 10 µm to 20 µm.
8.3.1.2 Apparatus
8.3.1.2.1 Model of the specimen plate, in metal or polymer (see Figure 1).
8.3.1.2.2 Denture flask, capable of accommodating the test specimen plate so that the corners are not
less than 5 mm from the walls of the flask.
8.3.1.2.3 Equipment for processing the orthodontic base resin, including gypsum or hydrocolloid
investment system [see 9.3 j)].
6 © ISO 2013 – All rights reserved

ISO 20795-2:2013(E)
8.3.1.2.4 Standard metallographic grinding paper, with a grain size of approximately 30 µm (P500).
NOTE See ISO 6344-1.
8.3.1.2.5 Muslin wheel, with 16 to 36 ply having a diameter of 70 mm to 95 mm and at least 10 mm
between the periphery and the stitching or other reinforcement.
8.3.1.2.6 Unstitched muslin wheel, with 16 to 36 ply having a diameter of 70 mm to 95 mm.
8.3.1.3 Preparation of the mould
For Type 1 and Type 2 polymers, invest the model of the specimen plate (8.3.1.2.1) in the denture flask
(8.3.1.2.2) in accordance with the manufacturer’s instructions.
8.3.1.4 Procedure
Form and process, according to the manufacturer’s instructions, two specimen plates each from a
separate mix. Use the material (8.3.1.1), the apparatus (8.3.1.2), and the mould (see 8.3.1.3). Grind and
polish the surfaces of the specimen plates for no longer than 1 min with pumice (8.3.1.1.1) and with a
wet muslin wheel (8.3.1.2.5) at a circumferential speed of (650 ± 350) m/min.
−1
NOTE A wheel with a diameter of 70 mm rotating at 1 500 min will have a circumferential speed of 329 m/min
−1
and a 100 mm diameter wheel rotating at 3 500 min will have a circumferential speed of 1 100 m/min.
Thereafter polish with an unstitched muslin wheel (8.3.1.2.6) with a polishing compound (8.3.1.1.1).
After polishing and cleaning, examine the polished surfaces for compliance with 5.2.2.3.
8.3.1.4.1 Pass/fail determination
If both specimen plates comply with 5.2.2.3, the material passes.
If both specimen plates fail to comply with 5.2.2.3, the material fails.
If only one of the specimen plates complies, prepare and evaluate three new plates. The material passes
only if all three new plates comply.
8.3.1.5 Expression of results
Report the number of specimen plates evaluated, the number complying, and whether the material passes.
8.3.2 Freedom from porosity, ultimate flexural strength, and flexural modulus
8.3.2.1 Materials
8.3.2.1.1 Two specimen plates, prepared and tested in accordance with 8.3.1.
8.3.2.2 Apparatus
8.3.2.2.1 Motorised saw, or other cutting device, for sectioning the specimen plates.
8.3.2.2.2 Milling machine, or other equipment for air- or water-cooled cutting, so as not to generate
temperatures above 30 °C during shaping of the specimens.
NOTE A machine with a milling head and a sharp carbide edge is suitable.
ISO 20795-2:2013(E)
8.3.2.2.3 Standard metallographic grinding papers, having a grain size of approximately 30 µm
(P500), 18 µm (P1000), and 15 µm (P1200).
NOTE See ISO 6344-1.
8.3.2.2.4 Micrometer screw gauge and/or dial calliper, accurate to 0,01 mm and fitted with
parallel anvils.
8.3.2.2.5 Container, containing water complying with grade 3 of ISO 3696, for storing the specimen
strips at (37 ± 1) °C for pre-test conditioning.
8.3.2.2.6 Testing machine, calibrated to provide a constant displacement rate of (5 ± 1) mm/min and
equipped with instrumentation for measuring the deflection of the specimen to within 0,025 mm.
Take into account for any load exerted by the deflection instrument when calibrating the machine.
8.3.2.2.7 Metal flexural test rig, consisting of a central loading plunger and two polished cylindrical
supports, 3,2 mm in diameter, and at least 10,5 mm long.
The supports shall be parallel to within 0,1 mm and perpendicular to the longitudinal centreline. The
distance between centres of the supports shall be (50 ± 0,1) mm, and the loading plunger shall be
midway between the supports to within 0,1 mm. Include means in the design to prevent misalignment
of the specimen.
8.3.2.2.8 Water bath, for maintaining the specimens wet and at a temperature of (37 ± 1) °C, during testing.
8.3.2.3 Preparation of specimen strips
Prepare six specimen strips. Cut each plate lengthways into three equal strips, 64 mm long,
(10,0 ± 0,2) mm wide, and (3,3 ± 0,2) mm in height. Machine the strips in a milling machine (8.3.2.2.2)
on the edges and equally from both moulded surfaces so that the dimensions remain slightly oversized.
Take care to avoid overheating the specimen. Wet-grind all faces and edges smooth and flat with the
metallographic grinding papers (8.3.2.2.3) to the required width and height. Make three measurements
of the specimen height along the long axis to an accuracy of ± 0,01 mm using a micrometer and/or dial
calliper (8.3.2.2.4). The deviation between the three measurements along the long axis shall be no more
than ± 0,02 mm. The specimen shall be flat and have an even height.
8.3.2.4 Freedom from porosity
8.3.2.4.1 Procedure and pass/fail determination
Prepare six test specimen strips in accordance with 8.3.2.3 and examine for compliance with 5.2.5.
The material passes only if at least five out of six specimen strips comply with the requirement in 5.2.5.
8.3.2.4.2 Expression of results
Report the number of specimen strips complying and whether the material passes.
8.3.2.5 Ultimate flexural strength and flexural modulus
8.3.2.5.1 Procedure
Store five specimen strips, or six in the case of repetition of the test (see 8.3.2.5.2.3 and 8.3.2.5.2.4),
prepared in accordance with 8.3.2.3 and complying with 5.2.5, in the container (8.3.2.2.5) at a
temperature of (37 ± 1) °C for (50 ± 2) h prior to flexural testing. Take a specimen strip from water
storage and immediately lay the flat surface symmetrically on the supports of the flexural test rig
8 © ISO 2013 – All rights reserved

ISO 20795-2:2013(E)
(8.3.2.2.7) immersed in the water bath (8.3.2.2.8). Allow the specimen to come to equilibrium with the
water bath temperature.
Increase the force on the loading plunger from zero, uniformly, using a constant displacement rate of
(5 ± 1) mm/min until the specimen breaks.
8.3.2.5.2 Calculation and expression of results
8.3.2.5.2.1 Ultimate flexural strength
Calculate the ultimate flexural strength, σ, in megapascals using the following equation:
3Fl
σ =
2bh
where
F is the maximum load, in newtons, exerted on the specimen;
l is the distance, in millimetres, between the supports, accurate to ± 0,01 mm;
b is the width, in millimetres, of the specimen measured immediately prior to water storage;
h is the height, in millimetres, of the specimen measured immediately prior to water storage.
8.3.2.5.2.2 Flexural modulus
Calculate the flexural modulus, E, in megapascals using the following equation:
Fl
E=
4bh d
where
F is the load, in newtons, at a point in the straight line portion (with the maximum
slope) of the load/deflection curve;
NOTE For greater accuracy, the straight line can be extended.
d is the deflection, in millimetres, at load F ;
l, b, and h are as defined in 8.3.2.5.2.1.
8.3.2.5.2.3 Pass/fail determination of ultimate flexural strength
If at least four out of five specimens give results not less than 50 MPa, the material is deemed to have
complied with the requirements of 5.2.6.
If at least three of the results are less than 50 MPa, the material is deemed to have failed.
If two of the results are less than 50 MPa, repeat the whole test, but on this occasion, prepare six
specimen strips.
If at least five of the results are not less than 50 MPa on the second occasion, the material is deemed to
have complied with the requirement of 5.2.6.
ISO 20795-2:2013(E)
8.3.2.5.2.4 Pass/fail determination of flexural modulus
If at least four of the results passed the requirement of 5.2.6 on the first occasion, calculate the flexural
modulus according to 8.3.2.5.2.2 for each of the five specimens.
If a second series was tested, calculate the flexural modulus for five of the six specimens from this series only.
If at least four of the results are not less than 1 500 MPa, the material is deemed to have complied with
the requirements of 5.2.7.
If at least three of the results are less than 1 500 MPa, the material is deemed to have failed.
If two of the results are less than 1 500 MPa, repeat the whole test, but on this occasion, prepare six
specimen strips. In this series, at least five results for both ultimate flexural strength and flexural
modulus shall comply with the requirements of 5.2.6 and 5.2.7.
8.3.2.5.2.5 Expression of results
Report the number of specimen strips evaluated, all results for ultimate flexural strength and flexural
modulus with the number of strips complying with the requirements of 5.2.6 and 5.2.7, and whether the
material passes.
8.4 Fracture toughness with a modified bending test
8.4.1 Materials
8.4.1.1 Two specimen plates, prepared and tested in accordance with 8.3.1.
8.4.1.2 Glycerol, technical grade, used as a lubricant.
8.4.2 Apparatus
8.4.2.1 Apparatus as described in 8.3.2.2.2, 8.3.2.2.3, 8.3.2.2.4, 8.3.2.2.5, 8.3.2.2.8 plus the following.
8.4.2.2 Motorised saw or other cutting device, able to section the specimen plates. Preferably
for cutting the pre-crack, a (0,5 ± 0,1) mm diamond sawing blade is needed. The cutting tool shall be
adjustable to a depth of (3,0 ± 0,2) mm.
8.4.2.3 Holding device containing a fixation clamp, to align specimen(s) during pre-cracking and the
sharp blade cutting procedure.
8.4.2.4 Sharp blade, such as scalpel, razor blade, or craft knife with an unbent straight blade.
8.4.2.5 Optical microscope with micrometer scale included, to measure the total length of the crack
(total amount of pre-crack and the sharp notch in millimetres).
8.4.2.6 Container, containing water for conditioning the specimen strips at (23 ± 1) °C.
8.4.2.7 Clean, dry towel.
8.4.2.8 Metal flexural test rig, see 8.3.2.2.7, but with a span length, l , of (32,0 ± 0,1) mm (see 8.4.4.1).
t
10 © ISO 2013 – All rights reserved

ISO 20795-2:2013(E)
8.4.2.9 Machine for testing, calibrated to provide a constant displacement rate of (1,0 ± 0,2) mm/min
and equipped with instrumentation for measuring the deflection of the specimen to within 0,025 mm.
The recording of the load/deflection curve and the calculation of the integral area under the curve
shall be possible.
When calibrating the machine, take into account any load exerted by the deflection instrument.
8.4.3 Procedure
At least 24 h from the beginning of the curing cycle, wet-grind or machine the plates (8.4.1.1) in a milling
machine (8.3.2.2.2), equally from both mould surfaces, to obtain flat, parallel surfaces, and so that the
thickness of the plates remain slightly oversized. Take care to avoid overheating the specimens.
Cut each plate breadthwise with a cutting device (8.4.2.2) in equal specimen strips 8 mm wide, so that
the dimensions remain slightly oversized compared with the finished specimen strips. Wet-grind all
surfaces smooth and flat with the metallographic grinding papers (8.3.2.2.3) to the required dimensions,
length 39 mm, height, h , (8,0 ± 0,2) mm, and width, b , (4,0 ± 0,2) mm, using grain size 18 µm (P1000)
t t
or 15 µm (P1200).
Fix the specimens lengthwise in the holding device (8.4.2.3) and set a mark exactly on the centreline
midway from the edges of the specimens. Cut the pre-crack with a diamond blade and a saw (8.4.2.2) to
a depth of (3,0 ± 0,2) mm along the marked centreline.
Fix one specimen at a time, in a clamp or holding device (8.4.2.3) so that the specimen cannot be removed
by hand/machine force. Wet the pre-crack with a drop of glycerol (8.4.1.2). Set the sharp blade (8.4.2.4)
on the bottom of the pre-crack and cut the sharp notch with hand/machine pressure and a sliding back
and forth motion.
A notch depth in the range of 100 µm to 400 µm is sufficient. Use an optical microscope (8.4.2.5) to check
the crack depth. It is recommended to test the cutting procedure on a pre-test specimen. Attempting to
further increase the notch depth should not be done. The situation of the notch arrangement is shown
in Figure 2 a). Measure the width, b , and the height, h , of the specimen with a micrometer (8.3.2.2.4).
t t
See Figure 2 b).
Store 10 selected notched specimens in a container with water (8.3.2.2.5) at (37 ± 1) °C for 7 d ± 2 h. Condition
the specimens in a different container of water (8.4.2.6) at (23 ± 1) °C for (60 ± 15) min prior to testing.
After conditioning, remove one specimen strip from the water and dry it with a clean, dry towel (8.4.2.7).
Place the specimen on the supports of the test rig (8.4.2.8). Place the specimen strip with the notch
facing exactly opposite the load plunger [see Figure 2 b)]. Be sure that the notch is placed right in the
centre between the supports.
Increase the force of the loading plunger of the testing machine (8.4.2.9) from zero, using a constant
displacement rate of (1,0 ± 0,2) mm/min, until maximum load is passed and the crack has almost reached
the opposite side of the specimen. The test can be considered finished when the current load is reduced
to 5 % of the maximum load or is less than (1,0 ± 0,2) N.
The recording of the whole load/deflection curve is necessary for calculations. Repeat the test for all 10
conditioned specimens.
After completing the test, measure the depth of the crack, including the sharp notch, a, in Figure 2, next
to the fracture surface with an optical microscope (8.4.2.5).
NOTE Before fracture toughness testing, ink can be introduced into the notch and allowed to dry to improve
identification of the complete notched area.
Determine the total crack length, a, as the average of three measurements (a , a , and a ) of the distance
1 2 3
between the specimen surface and the area fractured in the test. Take these three measurements along
the quarter- and half-width lines (see Figure 3).
ISO 20795-2:2013(E)
a) Notch arrangement
b) Specimen strip with the notch facing exactly opposite to the load plunger
Figure 2 — Fracture toughness test
Key
1 fracture surface
Figure 3 — Determination of the total crack length next to the fracture surface
12 © ISO 2013 – All rights reserved

ISO 20795-2:2013(E)
8.4.4 Calculation and expression of the results
8.4.4.1 Dimensions
Pre-crack a′ = (3,0 ± 0,2) mm
Crack length a (0,1 mm to 0,4 mm longer than a′)
Width b = (4,0 ± 0,2) mm
t
Height h = (8,0 ± 0,2) mm
t
Span length l = (32,0 ± 0,1) mm
t
8.4.4.2 Calculation of the maximum stress intensity factor
Calculate maximum stress intensity factor, K , using the following equation:
max
fP l
max t −3
1/2
K =× 10 MPa m
max
()bh
tt
where
f is a geometrical function dependent on x:
23 2
2    
fx =−31xx,(99 12−−xx)( ,,15 3932+ ,(72xx12+−)(1 x)
()
   
and
xa= h
t
P is the maximum load exerted on the specimen, in newtons;
max
a, h , b , and l are expressed in millimetres (see 8.4.4.1).
t t t
8.4.4.3 Calculation of the total fracture work
Calculate the total fracture work, W , using the following equation. The fracture work is calculated from
f
the integral area of the load/deflection curve.
U
W = ×1000Jm/
f
 
2bh −a
()
tt
 
where
U is the recorded area under the load/deflection curve given by the following equation:
in newton millimetres;
UP= dΔ
∫
Δ is the measured deflection for load, P;
a, b , and h are expressed in millimetres (see 8.4.4.1).
t t
NOTE The area under the load/deflection curve represents the energy required to break the whole specimen.
Dividing this energy by twice the fractured area, the surface energy expressed in joules per square meter is obtained.
ISO 20795-2:2013(E)
8.4.4.4 Pass/fail determination of maximum stress intensity factor
1/2
If at least eight of the results from 10 specimens are not less than 1,1 MPa m , the material complies
with the requirements of 5.2.8.
1/2
If at least six of the results are less than 1,1 MPa m , the material is deemed to have failed.
1/2
If three, four, or five of the results are less than 1,1 MPa m , repeat the whole test, but on this occasion,
prepare 12 specimen strips.
1/2
If at least 10 of the 12 results are not less than 1,1 MPa m on the second occasion, the material complies
with the requirement of 5.2.8.
8.4.4.5 Pass/fail determination of total fracture work
If at least eight of the results from 10 specimens are not less than 250 J/m , the material complies with
the requirements of 5.2.9.
If at least six of the results are less than 250 J/m , the material is deemed to have failed.
If three, four, or five of the results are less than 250 J/m , repeat the whole test, but on this occasion,
prepare 12 specimen strips.
If at least 10 of the 12 results are not less than 250 J/m on the second occasion, the material is deemed
to have complied with the requirement of 5.2.9.
8.4.4.6 Expression of results
Report for the number of specimens evaluated all results for maximum stress intensity factor K and
max
total fracture work W and the number of specimens complying with the requirements of 5.2.8 and 5.2.9,
f
and whether the material passes.
8.5 Residual methyl methacrylate monomer
8.5.1 Principle
Solvent extraction of the methyl methacrylate (MMA) monomer from polymerized orthodontic base
polymers is carried out, followed by chromatographic analyses.
A gas chromatographic (GC) method, high performance liquid chromatography (HPLC) method (see
Annex A), or any other chromatographic method can be used, which gives the same results as with the
methods of this part of ISO 20795. Verify the results by proficiency testing based on the chromatographic
methods described in this part of ISO 20795.
8.5.2 Preparation of test specimen discs
8.5.2.1 Material
8.5.2.1.1 Sheet of polyester film, having a thickness of (50 ± 25) µm, to cover the steel mould (8.5.2.2.1).
8.5.2.2 Apparatus
8.5.2.2.1 Circular stainless steel mould, with a diameter of 50 mm and a depth of (3,0 ± 0,1) mm with
a flat cover.
A similar mould (less deep) is shown in F
...