prEN ISO 23298

Dentistry - Test methods for machining accuracy of computer-aided milling machines (ISO/FDIS 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, e.g. inlays, crowns and bridges.

Zahnheilkunde - Prüfverfahren zur Bewertung der Genauigkeit von computergesteuerten Fräsmaschinen (ISO/FDIS 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/FDIS 23298:2023)

Zobozdravstvo - Preskusne metode za natančnost obdelave računalniško podprtih strojev za rezkanje (ISO/DIS 23298:2021)

General Information

• Status: Not Published
• Publication Date: 02-Oct-2023
• ICS: 11.060.01 - Dentistry in general
• Technical Committee: CEN/TC 55 - Dentistry
• Drafting Committee: CEN/TC 55 - Dentistry
• Current Stage: 5020 - Submission to Vote - Formal Approval
• Start Date: 02-Feb-2023
• Completion Date: 02-Feb-2023
• Ref Project: oSIST prEN ISO 23298:2022 - Dentistry - Test methods for machining accuracy of computer-aided milling machines (ISO/DIS 23298:2021)

Standards Content (Sample)

SLOVENSKI STANDARD
oSIST prEN ISO 23298:2022
01-februar-2022
Zobozdravstvo - Preskusne metode za natančnost obdelave računalniško podprtih
strojev za rezkanje (ISO/DIS 23298:2021)

Dentistry - Test methods for machining accuracy of computer-aided milling machines

(ISO/DIS 23298:2021)

Zahnheilkunde - Prüfverfahren zur Bewertung der Genauigkeit von computergesteuerten

Fräsmaschinen (ISO/DIS 23298:2021)

Médecine bucco-dentaire - Méthodes d'essai pour l'exactitude d'usinage des fraiseuses

à commande numérique (ISO/DIS 23298:2021)
Ta slovenski standard je istoveten z: prEN ISO 23298
ICS:
11.060.01 Zobozdravstvo na splošno Dentistry in general
oSIST prEN ISO 23298:2022 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 23298:2022
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oSIST prEN ISO 23298:2022
DRAFT INTERNATIONAL STANDARD
ISO/DIS 23298
ISO/TC 106/SC 9 Secretariat: JISC
Voting begins on: Voting terminates on:
2021-12-10 2022-03-04
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
ICS: 11.060.01
This document is circulated as received from the committee secretariat.
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
ISO/CEN PARALLEL PROCESSING
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 23298:2021(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2021
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oSIST prEN ISO 23298:2022
ISO/DIS 23298:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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
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Phone: [phone]
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Website: www.iso.org
Published in Switzerland
© ISO 2021 – All rights reserved
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oSIST prEN ISO 23298:2022
ISO/DIS 23298:2021(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 E valuation of accuracy .................................................................................................................................................. 8

5.2 Test methods for software method ................................................................................................................................... 14

5.2.1 General ..................................................................................................................................................................................... 14

5.2.2 Test object .................. .................................................... ........................................................................................................ 15

5.2.3 Equipment and apparatus ....................................................................................................................................... 18

5.2.4 Machining of specimens ............................................................................................................................................ 19

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........................................................................................................................................................................26

6.2.1 Die method ............................................................................................................................................................................ 26

6.2.2 Software method............................................................................................................................................................. 27

6.3 Averaged characteristic accuracy values..................................................................................................................... 27

6.3.1 Die method ............................................................................................................................................................................ 27

6.3.2 Software method............................................................................................................................................................. 27

Annex A (informative) Flow chart of test method ..............................................................................................................................28

Annex B (normative) Measurement of die set(s) and preparation of CAD data of target

restoration(s) ......... .................................................................................................................................. .............................................................30

Annex C (informative) Contents of test report .......................................................................................................................................40

Bibliography ............................................................................................................................................................................................................................ 44

iii
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oSIST prEN ISO 23298:2022
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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 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 the following

URL: www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 106, Dentistry, Subcommittee SC 9, Dental

CAD/CAD systems.

This document cancels and replaces ISO/TR 18845:2017 which have been technically revised.

The main changes compared to ISO/TR 18845:2017 are as follows:

— changing the type of document from Technical Report (TR) to International Standard (IS);

— specifying two test methods using metal dies and software as the normative test methods;

— clarification of selection guidance of test methods;

— revision of the detail procedures of both test methods based on the inter-laboratory test.

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.
© ISO 2021 – All rights reserved
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oSIST prEN ISO 23298:2022
ISO/DIS 23298:2021(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. A flow chart of test method is shown

in Annex A.

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.

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oSIST prEN ISO 23298:2022
DRAFT INTERNATIONAL STANDARD ISO/DIS 23298:2021(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, e.g. 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

ISO 25178-2, Geometrical product specifications (GPS) — Surface texture: Areal — Part 2: Terms, definitions

and surface texture parameters
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 terminological 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 for machining on a computer-aided milling machine (3.1). It may be a block (3.3) or a disk (3.4)

3.3
block

cuboidal material with holding device for machining on a computer-aided milling machine (3.1)

3.4
disc
disc-shaped material for machining on a computer-aided milling machine (3.1)
3.5
stock material

material blanks (3.2) that are in stock for machining on a computer-aided milling machine (3.1)

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ISO/DIS 23298:2021(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 instruction 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 adaptability at restoration margins. The software method (5.2) is

a measurement method based on a comparison of the scanned file of 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, a) Class II inlay, b) crown and c) four-unit/element bridge, are the targets

of this test method. 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 adopting the same principle as the examination method of clinical

marginal adaptation. The clinical adaptation is examined checking the discrepancy between the restoration and

the cavity margin or between it and the shoulder margin of 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/element

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 metal die and one or more removable

structure(s) used for the evaluation of accuracy.

The diameter of the removable occlusal part shall be not less than the diameter of abutment and the

difference of diameter shall be not more than 10 μm.

The surface roughness (Sa) of the die, excepting the surfaces which do not come in contact with the test

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.

The removal occlusal part and removable shoulder are used for preparation of three-dimensional data,

but not used for evaluation of accuracy.

NOTE An example of the machining device to fabricate the dies is Vertical Center NEXUS 410B.

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oSIST prEN ISO 23298:2022
ISO/DIS 23298:2021(E)
Dimensions in millimetres
Key
1 metal die
2 removable part
3 positioning pin
4 fixing screw
Figure 1 — Die for class II inlay specimen
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oSIST prEN ISO 23298:2022
ISO/DIS 23298:2021(E)
Dimensions in millimetres
Key
1 metal die
2 abutment
3 removable occlusal part
4 removable shoulder
h height of removable shoulder

NOTE The recommended size of the height of removable shoulder (h ) is (3,6 ± 0,05) mm.

Figure 2 — Die for crown and bridge specimen
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oSIST prEN ISO 23298:2022
ISO/DIS 23298:2021(E)
5.1.2.2 Measuring devices to be 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 die.
NOTE An example of a CMM is America Strato-Apex 574.
5.1.2.3 Measuring devices to be 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 the metal die for crown and bridge specimen, the height of removable shoulder (h in Figure 2),

and the height from the upper surface of the removable shoulder (4 in Figure 2) to the upper surface of

the removable occlusal part (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 the sections 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 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, a 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 the

CAM software to prepare the manufacturing data set. The CAD data-shall not be modified by the CAM

software.

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.
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oSIST prEN ISO 23298:2022
ISO/DIS 23298:2021(E)
Dimensions in millimetres
Key
1 metal die
2 abutment
3 removable occlusal part
4 removable shoulder
5 test specimen
6 mark to distinguish direction
Figure 3 — Test specimen of crown
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oSIST prEN ISO 23298:2022
ISO/DIS 23298:2021(E)
Dimensions in millimetres
Key
1 metal die
2 abutment
3 test specimen
4 mark to distinguish direction
Figure 4 — Test specimen of 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 means a natural or legal person actually manufacturing a computer-aided milling

machine or a natural or legal 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 in accordance with the

manufacturer’s instruction.
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oSIST prEN ISO 23298:2022
ISO/DIS 23298:2021(E)

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.
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 abutment shoulder for 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.

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.

The surface of the metal die shall be cleaned after each measurement.
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. 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° with (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 portion of the inlay die should be retained with the fixation screw. See

Figure 1.
NOTE 1 Round edges of the loading tip are preferred.

NOTE 2 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

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 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 metal die (2 in Figure 5) and place the inlay in the removable part

(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 occlusal inlay margin and

A B

the proximal baseline [−L in Figure 5 d)]. The measured values are expressed as negative values. If the

inlay margin is located at the same level of the baseline, the discrepancy is 0,000 mm.

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oSIST prEN ISO 23298:2022
ISO/DIS 23298:2021(E)

For both cases, measurements with and without metal die, 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 When a measuring microscope is used, the discrepancy in the Z-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.
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oSIST prEN ISO 23298:2022
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a) Occlusal discrepancy with metal die b) Proximal discrepancy with metal die

c) Occlusal and proximal discrepancy meas- d) Proximal discrepancy measurements without

urements without metal die metal die

e) Measurement points for occlusal discrep- f) Measurement points for proximal discrepancy

ancy
Key
1 removable part
2 metal die
3 inlay

+L discrepancy between the occlusal baseline and the inlay margin which is higher than the occlusal baseline

-L discrepancy between the occlusal baseline and the inlay margin which is lower than the occlusal baseline

+L discrepancy between the proximal baseline and the inlay margin which locates outside of the proximal baseline

-L discrepancy between the proximal baseline and the inlay margin which locates inside of the proximal baseline

Figure 5 — Discrepancy measurement of class II inlay
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oSIST prEN ISO 23298:2022
ISO/DIS 23298:2021(E)
5.1.6.3 Crown

Remove a removable occlusal part (3 in Figure 2) and a removable shoulder (4 in Figure 2) from the

metal die. Place the crown on the abutment of a metal die (2 in Figure 2) referring the mark, which can

distinguish 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)

...