EN ISO 23298:2023
(Main)Dentistry - Test methods for machining accuracy of computer-aided milling machines (ISO 23298:2023)
Dentistry - Test methods for machining accuracy of computer-aided milling machines (ISO 23298:2023)
This document specifies the test methods to evaluate the machining accuracy of computer-aided milling machines as a part of dental CAD/CAM systems, which fabricate dental restorations, such as inlays, crowns and bridges.
Zahnheilkunde - Prüfverfahren zur Bewertung der Genauigkeit von computergesteuerten Fräsmaschinen (ISO 23298:2023)
Dieses Dokument legt die Prüfverfahren zur Beurteilung der Fertigungsgenauigkeit von computergesteuerten Fräsmaschinen als Komponenten eines dentalen CAD/CAM-Systems fest, mit denen dentale Restaurationen, wie Inlays, Kronen und Brücken, gefertigt werden.
Médecine bucco-dentaire - Méthodes d'essai pour l'exactitude d'usinage des fraiseuses à commande numérique (ISO 23298:2023)
Le présent document spécifie les méthodes d’essai permettant d’évaluer l’exactitude d’usinage des fraiseuses à commande numérique utilisées au sein de systèmes dentaires de CFAO pour fabriquer des restaurations dentaires, telles que des couronnes, des bridges et des inlays.
Zobozdravstvo - Preskusne metode za natančnost obdelave računalniško podprtih strojev za rezkanje (ISO 23298:2023)
Ta dokument določa preskusne metode za vrednotenje natančnosti obdelave računalniško podprtih strojev za rezkanje v okviru zobnih sistemov CAD/CAM, ki izdelujejo zobne zalivke, npr. inleji, prevleke in mostički.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2023
Zobozdravstvo - Preskusne metode za natančnost obdelave računalniško podprtih
strojev za rezkanje (ISO 23298:2023)
Dentistry - Test methods for machining accuracy of computer-aided milling machines
(ISO 23298:2023)
Zahnheilkunde - Prüfverfahren zur Bewertung der Genauigkeit von computergesteuerten
Fräsmaschinen (ISO 23298:2023)
Médecine bucco-dentaire - Méthodes d'essai pour l'exactitude d'usinage des fraiseuses
à commande numérique (ISO 23298:2023)
Ta slovenski standard je istoveten z: EN ISO 23298:2023
ICS:
11.060.01 Zobozdravstvo na splošno Dentistry in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 23298
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2023
EUROPÄISCHE NORM
ICS 11.060.01
English Version
Dentistry - Test methods for machining accuracy of
computer-aided milling machines (ISO 23298:2023)
Médecine bucco-dentaire - Méthodes d'essai pour Zahnheilkunde - Prüfverfahren zur Bewertung der
l'exactitude d'usinage des fraiseuses à commande Genauigkeit von computergesteuerten Fräsmaschinen
numérique (ISO 23298:2023) (ISO 23298:2023)
This European Standard was approved by CEN on 30 April 2023.
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
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 23298:2023 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 23298:2023) 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 2023, and conflicting national standards
shall be withdrawn at the latest by December 2023.
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.
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 23298:2023 has been approved by CEN as EN ISO 23298:2023 without any modification.
INTERNATIONAL ISO
STANDARD 23298
First edition
2023-05
Dentistry — Test methods for
machining accuracy of computer-
aided milling machines
Médecine bucco-dentaire — Méthodes d’essai pour l’exactitude
d’usinage des fraiseuses à commande numérique
Reference number
ISO 23298:2023(E)
ISO 23298:2023(E)
© ISO 2023
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 23298:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General . 2
5 Test methods . 2
5.1 Metal die method . 2
5.1.1 Target restorations. 2
5.1.2 Apparatus . 2
5.1.3 Measurement of metal dies . 5
5.1.4 Preparation of three-dimensional data . 5
5.1.5 Machining of restorations . 7
5.1.6 Evaluation of accuracy . 8
5.2 Test methods for software method . 13
5.2.1 General .13
5.2.2 Test object . . 15
5.2.3 Equipment and apparatus . 18
5.2.4 Machining of specimens . 18
5.2.5 Measurement . 20
5.2.6 Data alignment procedures . 21
5.2.7 Data analysis procedure . 22
5.2.8 Calculation of total errors . 25
6 Test report .26
6.1 General information.26
6.2 Specific information. 27
6.2.1 Die method . 27
6.2.2 Software method. 27
6.3 Averaged characteristic accuracy values. 27
6.3.1 Die method . 27
6.3.2 Software method.28
Annex A (informative) Flow chart of test method .29
Annex B (normative) Measurement of die set(s) and preparation of CAD data of target
restoration(s) . . .31
Annex C (informative) Contents of test reports .41
Bibliography .46
iii
ISO 23298:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 106, Dentistry, Subcommittee SC 9, Dental
CAD/CAM systems, 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 first edition of ISO 23298 cancels and replaces ISO/TR 18845:2017, which has been technically
revised.
The main changes are as follows:
— the type of document has been changed from Technical Report to International Standard;
— two test methods have been specified using metal dies and software as the normative test methods;
— the selection guidance of test methods has been clarified;
— the details of the procedures of both test methods based on the inter-laboratory test have been
revised.
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.
iv
ISO 23298:2023(E)
Introduction
Dental CAD/CAM systems have been successfully used for the fabrication of indirect dental restorations
such as inlays, crowns and bridges. The accuracy of these restorations is one of the most important
factors for their clinical success. This document provides standardized test methods to evaluate the
machining accuracy of computer-aided milling machines which are used as a part of dental CAD/CAM
systems and the information to be provided by the manufacturer. Flow charts of the test methods are
given in Figures A.1 and A.2.
There are two methods using metal dies or software to evaluate machining accuracy of the target
restoration(s). Either or both test methods should be selected to evaluate the machining accuracy.
v
INTERNATIONAL STANDARD ISO 23298:2023(E)
Dentistry — Test methods for machining accuracy of
computer-aided milling machines
1 Scope
This document specifies the test methods to evaluate the machining accuracy of computer-aided milling
machines as a part of dental CAD/CAM systems, which fabricate dental restorations, such as inlays,
crowns and bridges.
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 18739, Dentistry — Vocabulary of process chain for CAD/CAM systems
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1942, ISO 18739 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
computer-aided milling machine
computer-aided machining device designed for subtractive manufacturing of dental prostheses using
rotary instruments for cutting and grinding
3.2
blank
material to be machined by a computer-aided milling machine (3.1)
Note 1 to entry: A blank can be a block (3.3) or a disc (3.4).
3.3
block
cuboidal material with holding device to be machined by a computer-aided milling machine (3.1)
3.4
disc
flat circular-shaped material to be machined by a computer-aided milling machine (3.1)
3.5
stock material
material blanks (3.2) that are in stock to be machined by a computer-aided milling machine (3.1)
ISO 23298:2023(E)
4 General
There are two methods to evaluate accuracy of the target restoration(s). The accuracy of target
restoration(s) shall be evaluated using one or both of the test methods described in Clause 5. The
test method(s) selected and corresponding results shall be provided in the instructions for use, the
technical manual or other means. When the machining accuracy is affected by the material, appropriate
material(s) shall be tested. Testing shall be performed on each material type that the manufacturer
indicates for use by the device. The metal die method (5.1) is a measurement method based on the
marginal adaptability of a machined restoration to a master die. Measurements obtained using this
method can be used to assess the adaptability at restoration margins. The software method (5.2) is
a measurement method based on a comparison of the scanned file of a milled restoration to a master
manufacturing file using reverse engineering software. Measurements obtained using this method can
be used to assess restoration margin, intaglio and external surface accuracy.
5 Test methods
5.1 Metal die method
5.1.1 Target restorations
Three types of restorations are the targets of this test method:
a) class II inlay,
b) crown, and
c) four-unit bridge.
Choose the restoration type(s) specified in the manufacturer’s instructions for use and technical
manual. If any of the restoration types are not specified by the manufacturer’s technical manual for the
equipment being tested, this restoration type shall be eliminated from the test procedure.
NOTE This test method is designed by adopting the same principle as the examination method of clinical
marginal adaptation. The clinical adaptation is examined by checking the discrepancy between the restoration
and the cavity margin or between it and the shoulder margin of the abutment.
5.1.2 Apparatus
5.1.2.1 Metal dies
Two types of metal dies given in Figure 1 (class II inlay) and Figure 2 (crown and four-unit bridge
dies) are used both for the preparation of three-dimensional data (manufacturing data set) and the
evaluation of the accuracy of restorations. Dies shall be constructed based on the drawings in Figure 1
and Figure 2. These dies consist of a non-malleable base part and one or more removable structure(s)
used for the evaluation of accuracy.
The diameter of the removable occlusal part, measured at the transition between the occlusal part and
the abutment, shall be not less than the diameter of the abutment at this transition and the difference of
diameter shall be not more than 10 μm.
The surface roughness (S ) of the die, excepting the surfaces which do not come in contact with the test
a
specimens/machined restorations, shall be less than 2 μm. Refer to ISO 25178-2 and other parts for test
methods.
If a mark for reference point is necessary, either a groove or a ridge, or both, may be placed on the part,
but shall be placed so as to not influence the evaluation of the results.
ISO 23298:2023(E)
The removable occlusal part and removable shoulder are used for preparation of three-dimensional
data, but not used for evaluation of accuracy.
1)
NOTE An example of the machining device to fabricate the dies is VERTICAL CENTER NEXUS 410B .
Dimensions in millimetres
Key
1 base part
2 removable part
3 positioning pin
4 fixing screw
Figure 1 — Die for class II inlay specimen
1) VERTICAL CENTER NEXUS 410B is the trade name of a product supplied by Yamazaki Mazak. This information
is given for the convenience of users of this document and does not constitute an endorsement by ISO of the product
named. Equivalent products may be used if they can be shown to lead to the same results.
ISO 23298:2023(E)
Dimensions in millimetres
Key
1 base part 4 removable shoulder
2 abutment h height of the removable shoulder
s
3 removable occlusal part
The recommended size of the height of the removable shoulder is (3,6 ± 0,05) mm.
Figure 2 — Die for the crown and bridge specimen
ISO 23298:2023(E)
5.1.2.2 Measuring devices used for metal dies
Measuring devices with accuracy of ≤2 μm shall be used for measurement of metal dies (5.1.3).
Coordinate measuring machine (CMM) can be useful to measure the size of a die.
2)
NOTE An example of a CMM is America Strato-Apex 574 .
5.1.2.3 Measuring devices used for discrepancy measurement
Measuring devices with accuracy of ≤5 μm shall be used for discrepancy measurement in 5.1.4. Three-
dimensional measuring microscopes, displacement meters and digital micrometers can be used.
5.1.3 Measurement of metal dies
Each die shall be measured using a measuring device specified in 5.1.2.2 to confirm the shape and
dimensions specified in Figure 1 or Figure 2. The specified dimensions of constructed die necessary
to prepare CAD data shall be measured in accordance with Annex B. The measured data are used to
prepare the three-dimensional data (see 5.1.4).
In case of a metal die for crown and bridge specimen, the height of the removable shoulder (h in
s
Figure 2), and the height from the upper surface of the removable shoulder (Key 4 in Figure 2) to the
upper surface of the removable occlusal part (Key 3 in Figure 2) shall be measured.
5.1.4 Preparation of three-dimensional data
5.1.4.1 General
The surface to be in contact with the metal die of each specimen type is determined by the measurements
of the dies made in 5.1.3. The external surfaces of each specimen type are determined by 5.1.4.2 and
5.1.4.3.
5.1.4.2 Class II inlay
The shapes and sizes of test specimen of class II inlay shall conform to the cavity of metal die (see
Figure 1). The occlusal and proximal surfaces shall be the same planes with the corresponding surface
of the metal die.
5.1.4.3 Crown and bridges
The shapes and sizes of test specimen of the crown and the bridge shall conform to Figure 3 (crown)
and Figure 4 (bridge). A mark to distinguish direction when placing the restoration on the metal die
shall be made on the top surface of the crown. In case of bridges, the mark shall be made on either
crown.
5.1.4.4 Preparation of CAD data (STL data)
To fabricate the target restorations, CAD data (STL data) for each of the restorations specified in 5.1.4.2
and 5.1.4.3 shall be prepared in accordance with Annex B. This CAD data shall then be processed by
CAM software to prepare the manufacturing data set.
The dimensions of any surfaces in contact with the die surfaces are obtained from the measuring
process in 5.1.3. Other dimensions are determined from Figure 3 and Figure 4.
The CAD data shall be prepared to ensure that the restoration meets the die without an allowance for
cement space.
2) STRATO-Apex 574 is the trade name of a product supplied by Mitsutoyo. This information is given for the
convenience of users of this document and does not constitute an endorsement by ISO of the product named.
Equivalent products may be used if they can be shown to lead to the same results.
ISO 23298:2023(E)
Dimensions in millimetres
Key
1 base part
2 abutment
3 removable occlusal part
4 removable shoulder
5 test specimen
6 mark to distinguish direction
Figure 3 — Test specimen of the crown
ISO 23298:2023(E)
Dimensions in millimetres
Key
1 base part
2 abutment
3 test specimen
4 mark to distinguish direction
Figure 4 — Test specimen of the bridge
5.1.5 Machining of restorations
The prepared manufacturing data set shall be input into the computer-aided milling machine following
the manufacturer’s instruction. The CAM software shall use the same configuration and parameters
as is usually delivered. The target restoration shall be machined using the material specimen (blank)
following the manufacturer’s instruction.
NOTE 1 A manufacturer refers to a natural person actually manufacturing a computer-aided milling machine,
or a natural person supplying necessary information to use the computer-aided milling machine.
The target restoration shall be the same size of the prepared manufacturing data set. CAM software
contains a scaling factor to compensate for shrinkage of material during an additional process such as
sintering. The CAM software scaling factor used in this test shall be 1,00.
This test is carried out using a computer-aided milling machine maintained according to the
manufacturer’s instruction.
The evaluation of accuracy (see 5.1.6) is carried out using the restoration without any after treatment
such as a sintering process. If any support structures are necessary for fabrication, they shall not be
positioned on the surface contacting the die and shall be removed before the measurement.
NOTE 2 Support structures are carefully removed using an appropriate rotary instrument such as a carbide
laboratory cutter.
ISO 23298:2023(E)
Fabricate six specimens for each of the target restorations.
5.1.6 Evaluation of accuracy
5.1.6.1 General
The accuracy of the restorations is expressed by the discrepancy between the margin of a restoration
and baseline (cavity margin for inlays and the abutment shoulder for the crown and bridge).
The measurement of discrepancy is carried out using a measuring device specified in 5.1.2.3. The
measured value shall be expressed in millimetre to three decimal places. After each measurement, the
surface of metal die shall be cleaned to remove all particles and dust.
When two or more dies for each restoration type are prepared, evaluation of accuracy shall always be
performed using restorations prepared from measurement data specific to that die set.
5.1.6.2 Class II inlay
Place the inlay in the cavity of a metal die and apply a load of (25 ± 1) N, distributed evenly on the
centres of occlusal and proximal surfaces simultaneously. Round edges of the loading tip are preferred.
Remove the load after (30 ± 1) s and examine where the margin of the inlay is located.
V-shaped or M-shaped pressing device having inner corner of 90° and width of (4,5 ± 0,2) mm shall be
used for applying the load onto the occlusal and proximal surfaces of inlay simultaneously.
If necessary, the removable part of the inlay die should be retained with the fixation screw. See Figure 1.
NOTE The use of weighing paper or a thin elastomeric sheet can be used at the interface of the loading tip
and inlay specimen.
When the occlusal margin of the inlay is located higher than the occlusal baseline (occlusal margin
of the die cavity), measure the discrepancy between the inlay margin and the occlusal baseline [L
A+
in Figure 5 a)]. Similarly, when the proximal margin of the inlay extends past the proximal baseline
(proximal margin of the die cavity), measure the discrepancy between the inlay margin and the proximal
baseline [L in Figure 5 b)]. The measured values for both occlusal and the proximal discrepancies are
B+
expressed as positive values.
When the occlusal and proximal margins of the inlay are located at the same level of the baseline or
beneath the baseline, remove the base part (Key 2 in Figure 5) and place the inlay in the removable part
(Key 1 in Figure 5). Apply a load of (25 ± 1) N, distributed evenly on the occlusal and proximal surfaces
simultaneously, and remove it after (30 ± 1) s. Measure the discrepancies between the occlusal inlay
margin and the occlusal baseline [L and L in Figure 5 c)] and between the proximal inlay margin
A− B−
and the proximal baseline [L in Figure 5 d)]. The measured values are expressed as negative values. If
B−
the inlay margin is located at the same level of the baseline, the discrepancy is 0,000 mm.
For both cases, measurements with and without base part, the measurement shall be carried out at three
points for the occlusal discrepancy [see Figure 5 e)] and at four points for the proximal discrepancy [see
Figure 5 f)]. A discrepancy shall be measured as horizontal discrepancy judging from the top.
NOTE 3 When a measuring microscope is used, the discrepancy in the Z-direction in the vertical direction
cannot be precisely measured because of its poor focusing accuracy.
The measured discrepancy data (three points for the occlusal discrepancy and four points for the
proximal discrepancy) of one inlay are averaged to represent the discrepancy of that inlay. Calculate
the average of the six representative discrepancy values and the standard deviations to express the
accuracy of the inlay.
ISO 23298:2023(E)
a) Occlusal discrepancy with base part b) Proximal discrepancy with base part
c) Occlusal and proximal discrepancy d) Proximal discrepancy measurements without
measurements without base part base part
e) Measurement points for occlusal f) Measurement points for proximal discrepancy
discrepancy
Key
1 removable part
2 base part
3 inlay
L discrepancy between the occlusal baseline and the inlay margin which is higher than the occlusal baseline
A+
L discrepancy between the occlusal baseline and the inlay margin which is lower than the occlusal baseline
A−
L discrepancy between the proximal baseline and the inlay margin which locates outside of the proximal baseline
B+
L discrepancy between the proximal baseline and the inlay margin which locates inside of the proximal baseline
B−
Figure 5 — Discrepancy measurement of class II inlay
ISO 23298:2023(E)
5.1.6.3 Crown
Remove the removable occlusal part (Key 3 in Figure 2) and the removable shoulder (Key 4 in Figure 2)
from the metal die. Place the crown on the abutment of a metal die (Key 2 in Figure 2) referencing
the mark which distinguishes the direction on the upper surface of crown, [see 5.1.4.3 and Figure 6
e)]. Each crown to be measured shall be oriented in the same direction. Apply a load of (25 ± 1) N for
(30 ± 1) s, distributed evenly across the occlusal surface of a crown. The abutment of metal die used
for the preparation of design data shall be used. Remove the load and measure the apparent vertical
discrepancy without the removal part (L ) between the second baseline (Key 6 in Figure 6) and the
By
margin of the crown.
The apparent vertical discrepancy (L ) shall be measured at four points (margin at the centre of medial,
By
distal, buccal and lingual surfaces) specified in Figure 6 e) for each crown.
The vertical discrepancy (L or L in Figure 6) between the margin of the crown and the baseline
Ay+ Ay−
(Key 3 in Figure 6) is obtained by subtracting the height of the removable shoulder (Key 4 in Figure 2)
from L . When the crown margin is located higher than the baseline (Key 3 in Figure 6), the vertical
By
discrepancy [L in Figure 6 a)] between the crown margin and the baseline is expressed as a positive
Ay+
value. When the crown margin is located lower than the baseline (Key 3 in Figure 6), the vertical
discrepancy [L in Figure 6 b)] between the crown margin and the baseline is expressed as a negative
Ay−
value. When the crown margin is located on the baseline, the vertical discrepancy is 0,000.
The vertical discrepancy (L or L ) shall be averaged to represent the vertical discrepancy of that
Ay+ Ay−
crown.
When the crown margin is located higher than the baseline (Key 3 in Figure 6), calculate the lateral
accuracy (L ) using Formula (1).
Ly+
When the crown margin is located lower than the baseline (Key 3 in Figure 6) or at it, calculate the
lateral accuracy (L ) using Formula (2).
Ly−
LD×−()D
da b
g= ×100 (1)
Dh×
aa
LD×−()D
eb a
g= ×100 (2)
Dh×
aa
where
D is the diameter of abutment at the baseline [see Figure 6 c) and d)];
a
D is the diameter of abutment at the top line [see Figure 6 c) and d)];
b
h is the height of abutment [see Figure 6 c) and d)];
a
L is the vertical discrepancy [see L in Figure 6 c)];
d Ay+
L is the vertical discrepancy [see L in Figure 6 d)];
e Ay−
g is the lateral accuracy (L or L ) (%).
Ly+ Ly−
Calculate the average of the six representative lateral accuracies (%) and the standard deviation to
express the accuracy of the crown.
ISO 23298:2023(E)
a) Vertical discrepancy, L , measurement of b) Vertical discrepancy, L , measurement of
Ay+ Ay−
crown when its margin locates higher than the crown when its margin locates lower than the
baseline baseline or at it
c) Lateral discrepancy, L , of crown d) Lateral discrepancy, L , of crown
Ly+ Ly−
e) Measurement points (margin at the centre of medial, distal, buccal and lingual surfaces)
Key
1 metal die 4 second baseline (lower plane of the removable
shoulder)
2 crown 5 mark to distinguish direction
3 baseline (upper plane of the removable shoulder) D diameter of abutment at the baseline
a
h height of abutment D diameter of abutment at the top line
a b
h height of the removable shoulder which is the distance between the baseline and the second baseline
s
L vertical discrepancy of crown when its margin is higher than the baseline, which is used as d in Formula (1)
Ay+
L vertical discrepancy of crown when its margin is lower than the baseline, which is used as e in Formula (2)
Ay−
L measured vertical discrepancy of crown without removable parts
By
L lateral discrepancy when its margin locates higher than the baseline
Ly+
L lateral discrepancy when its margin locates lower than the baseline or at it
Ly−
Figure 6 — Discrepancy measurement of the crown
ISO 23298:2023(E)
5.1.6.4 Four-unit bridge
Remove the removable occlusal part (Key 3 in Figure 2) and the removable shoulder (Key 4 in Figure 2)
from the metal die. Place both crowns on the abutments of a metal die (Key 2 in Figure 2) referencing
the mark which distinguishes the direction on the upper surface of the bridge, [see 5.1.4.3 and Figure 7
c)]. Each bridge measured shall be oriented in the same direction. Apply a load of (25 ± 1) N, distributed
evenly across the occlusal surface of the two crowns for (30 ± 1) s. The total load is approximately 50 N.
Remove the load and measure the apparent vertical discrepancy (L ) between the second baseline
Dy
(Key 4 in Figure 7) and the margin of the crowns.
The apparent vertical discrepancy (L ) shall be measured at three points for each of two crowns [see
Dy
Figure 7 c)] of one bridge.
The vertical discrepancy (L or L in Figure 7) between the margin of the crown and the baseline
Cy+ Cy−
(Key 3 in Figure 7) is obtained by subtracting the height of the removable shoulder (h in Figure 7)
s
from L . The vertical discrepancy (L or L in Figure 7) between the margin of the crown and
Dy Cy+ Cy−
the baseline (Key 3 in Figure 7) is obtained by subtracting the height of the removable shoulder (h
s
in Figure 7) from L . When the crown margin is located higher than the baseline (Key 3 in Figure 7),
Dy
the vertical discrepancy [L in Figure 7 a)] between the crown margin and the baseline is expressed
Cy+
as a positive value. When the crown margin is located lower than the baseline (Key 3 in Figure 7), the
vertical discrepancy [L in Figure 7 b)] between the crown margin and the baseline is expressed as
Cy−
a negative value. When the crown margin is located on the baseline, the vertical discrepancy is 0,000.
Obtain the average of the six measured values of vertical discrepancy (L or L ) in total to represent
Cy+ Cy−
the discrepancy of that bridge.
Calculate the average of the six representative discrepancy values and the standard deviation to
express the accuracy of the four-unit bridge.
ISO 23298:2023(E)
a) Discrepancy measurement when its margin b) Discrepancy measurement when its margin
locates higher than the baseline locates lower than the baseline
c) Measurement points
Key
1 base part
2 bridge
3 baseline (upper plane of the removable shoulder)
4 second baseline (lower plane of the removable shoulder)
5 mark to distinguish direction
h height of the removable shoulder which is the distance between the baseline and the second baseline
s
L vertical discrepancy between the margin of the crown and the baseline
Cy+
L vertical discrepancy between the margin of the crown and the baseline
Cy−
L apparent vertical discrepancy between the second baseline and the margin of the crowns
Dy
Figure 7 — Discrepancy measurement of the four-unit bridge
5.2 Test methods for software method
5.2.1 General
Four test objects are the targets of the test methods for software method:
a) crown,
b) short span bridge,
ISO 23298:2023(E)
c) medium span bridge, and
d) cross-arch bridge.
The crown specimen (see Figure 8) has similar dimensions and shape with respect to a molar crown
restoration. It is used as an example for crowns and other smaller-sized restorations. The three bridge
specimens are used to represent examples of short span (see Figure 9), medium span (see Figure 10)
and cross-arch bridges (see Figure 11) which can use different CAM software templates and challenge
the accuracy of the milling machine.
Milling machines can have restrictions on stock material dimensions and thus not be capable of milling
all bridge restoration specimens.
The crown specimen and the largest bridge specimen which fits in the dental mill manufacturer’s
largest stock material shall be used for accuracy evaluation. For example, if a machining device only
accepts small blocks for machining, and only the crown specimen fits in the block, then the crown
specimen is the only specimen milled and measured for accuracy. If the three-unit bridge fits in a block
compatible with the machining device and is indicated by the device manufacturer, then the crown and
three-unit bridge specimen (short span bridge) is milled and measured for accuracy. If a machining
device accepts large disc stock material for machining crowns and cross-arch bridges, then the crown
specimen and only the cross-arch bridge specimens is milled and measured for accuracy.
The single crown specimen has a diameter of about 12,9 mm, and a height of approximately 10 mm.
The design is shaped like a sphere with a cylindrical section. The cylinder walls are conical with a wall
angle of 6° from vertical. The wall thickness of the specimen is 1 mm overall except for one flat plane
which has a wall thickness of 0,75 mm.
The design consists of curved surfaces and flat surfaces, which are used partly for measuring and
partly for placing the support pins to connect the specimen to the stock material. The three lateral flat
surfaces are used for attaching the pins. They are not evenly distributed around the circumference. In
addition, one surface is larger and has a smaller wall thickness to allow clear orientation to the machine
axes.
The three-dimensional data (STL) of the specimen (see Table 1) shall be downloaded from: https://
standards .iso .org/ iso/ 23298/ ed -1/ en, and shall not be generated from the drawings shown in Figure 8
to Figure 11.
ISO 23298:2023(E)
Table 1 — Three-dimensional data (STL) of the specimen
Specimen STL-file Used for
Crown_Specimen.stl Manufacturing
Crown_Specimen_Alignment.stl Alignment procedure
Crown Crown_Specimen_External.stl Analysis of external surface
Crown_Specimen_Intaglio.stl Analysis of intaglio surface
Crown_Specimen_Prepline.stl Analysis of prepline-surface
Short_Span_Bridge_Specimen.stl Manufacturing
Short_Span_Bridge_Specimen_Alignment.stl Alignment procedure
Short span bridge Short_Span_Bridge_Specimen_External.stl Analysis of external surface
Short_Span_Bridge_Specimen_Intaglio.stl Analysis of intaglio surface
Short_Span_Bridge_Specimen_Prepline.stl Analysis of prepline-surface
Medium_Span_Bridge_Specimen.stl Manufacturing
Medium_Span_Bridge_Specimen_Alignment.stl Alignment procedure
Medium span
Medium_Span_Bridge_Specimen_External.stl Analysis of external surface
bridge
Medium_Span_Bridge_Specimen_Intaglio.stl Analysis of intaglio surface
Medium_Span_Bridge_Specimen_Prepline.stl Analysis of prepline-surface
Cross_Arch_Bridge_Specimen.stl Manufacturing
Cross_Arch_Bridge_Specimen_Alignment.stl Alignment procedure
Cross-arch bridge Cross_Arch_Bridge_Specimen_External.stl Analysis of external surface
Cross_Arch_Bridge_Specimen_Intaglio.stl Analysis of intaglio surface
Cross_Arch_Bridge_Specimen_Prepline.stl Analysis of prepline-surface
5.2.2 Test object
5.2.2.1 Crown specimen
To determine crown accuracy, the single crown test specimen (see Figure 8) shall be used.
ISO 23298:2023(E)
Dimensions in millimetres
a) Section A―A b) Bird’s eye perspective
c) Top view d) Bottom view
Figure 8 — Crown specimen
5.2.2.2 Short span bridge specimen
To determine the short span accuracy, the
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