Dentistry - Digital impression devices - Part 1: Methods for assessing accuracy (ISO 20896-1:2019)

This document specifies test methods and procedures for assessing the accuracy of a three dimensional numerical description of intra-oral surfaces acquired directly from a patient with a hand-held scanning device. The test methods are not applicable to ultrasonic, radiographic or magnetic resonance imaging methods.
NOTE       ISO 12836 specifies the test methods for the assessment of accuracy of digitizing devices that use a fixed or a mechanically guided scanning device.

Zahnheilkunde - Digitale Abformgeräte - Teil 1: Verfahren zur Bewertung der Genauigkeit (ISO 20896-1:2019)

Dieses Dokument legt Prüfverfahren und Vorgehensweisen zur Beurteilung der Genauigkeit einer dreidimensionalen, numerischen Beschreibung von intraoralen Oberflächen, die mit einem handgehaltenen Scanner direkt am Patienten erfasst werden, fest. Die Prüfverfahren gelten nicht für Ultraschall-, Röntgen- oder Magnetresonanz-Bildgebungsverfahren.
ANMERKUNG ISO 12836 legt die Prüfverfahren für die Beurteilung der Genauigkeit von Digitalisierungsgeräten fest, die einen fest stehenden oder einen mechanisch geführten Scanner verwenden.

Médecine bucco-dentaire - Dispositifs d'empreinte numérique - Partie 1: Méthodes d'évaluation de l'exactitude (ISO 20896-1:2019)

Le présent document spécifie des méthodes d'essai et des modes opératoires d'évaluation de l'exactitude d'une description numérique tridimensionnelle de surfaces intrabuccales acquises directement à partir d'un patient à l'aide d'un dispositif de balayage manuel. Les méthodes d'essai ne sont pas applicables aux méthodes d'imagerie par résonance ultrasonore, radiographique ou magnétique.
NOTE       L'ISO 12836 spécifie les méthodes d'essai destinées à évaluer l'exactitude des dispositifs de numérisation qui utilisent un dispositif de balayage fixe ou guidé mécaniquement.

Zobozdravstvo - Digitalni pripomočki za sisteme - 1. del: Metode za ugotavljanje točnosti (ISO 20896-1:2019)

Ta standard opisuje preskusne metode, ki se uporabljajo za ocenjevanje ponovljivosti, obnovljivosti in točnosti dentalnih naprav za 3D-meroslovje. Standard se uporablja za zobozdravstvene sisteme CAD/CAM na mestu zdravljenja. Področje uporabe tega dokumenta ne vključuje edinstvenih sistemov z drugimi specifičnimi uporabami 3D-meroslovja na področju zobozdravstva, kot so na primer 3D-računalniška tomografija, slikanje z magnetno resonanco in stereofotogrametrija.

General Information

Status
Published
Publication Date
01-Oct-2019
Withdrawal Date
29-Apr-2020
Technical Committee
Drafting Committee
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Start Date
02-Oct-2019
Completion Date
02-Oct-2019

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SLOVENSKI STANDARD
SIST EN ISO 20896-1:2020
01-januar-2020
Zobozdravstvo - Digitalni pripomočki za sisteme - 1. del: Metode za ugotavljanje
točnosti (ISO 20896-1:2019)
Dentistry - Digital impression devices - Part 1: Methods for assessing accuracy (ISO
20896-1:2019)
Zahnheilkunde - Digitale Abformgeräte - Teil 1: Verfahren zur Bewertung der
Genauigkeit (ISO 20896-1:2019)
Médecine bucco-dentaire - Dispositifs d'empreinte numérique - Partie 1: Méthodes
d'évaluation de l'exactitude (ISO 20896-1:2019)
Ta slovenski standard je istoveten z: EN ISO 20896-1:2019
ICS:
11.060.01 Zobozdravstvo na splošno Dentistry in general
35.240.10 Računalniško podprto Computer-aided design
snovanje (načrtovanje, (CAD)
oblikovanje) (CAD)
SIST EN ISO 20896-1:2020 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 20896-1:2020

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SIST EN ISO 20896-1:2020


EN ISO 20896-1
EUROPEAN STANDARD

NORME EUROPÉENNE

October 2019
EUROPÄISCHE NORM
ICS 11.060.01
English Version

Dentistry - Digital impression devices - Part 1: Methods for
assessing accuracy (ISO 20896-1:2019)
Médecine bucco-dentaire - Dispositifs d'empreinte Zahnheilkunde - Genauigkeit von handgehaltenen
numérique - Partie 1: Méthodes d'évaluation de Scanner für CAD/CAM-Systeme am Behandlungsstuhl
l'exactitude (ISO 20896-1:2019) (ISO 20896-1:2019)
This European Standard was approved by CEN on 27 July 2019.

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, Turkey 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
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20896-1:2019 E
worldwide for CEN national Members.

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SIST EN ISO 20896-1:2020
EN ISO 20896-1:2019 (E)
Contents Page
European foreword . 3

2

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SIST EN ISO 20896-1:2020
EN ISO 20896-1:2019 (E)
European foreword
This document (EN ISO 20896-1:2019) 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 April 2020, and conflicting national standards shall be
withdrawn at the latest by April 2020.
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.
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, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 20896-1:2019 has been approved by CEN as EN ISO 20896-1:2019 without any
modification.


3

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SIST EN ISO 20896-1:2020

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SIST EN ISO 20896-1:2020
INTERNATIONAL ISO
STANDARD 20896-1
First edition
2019-08
Dentistry — Digital impression
devices —
Part 1:
Methods for assessing accuracy
Médecine bucco-dentaire — Dispositifs d'empreinte numérique —
Partie 1: Méthodes d'évaluation de l'exactitude
Reference number
ISO 20896-1:2019(E)
©
ISO 2019

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SIST EN ISO 20896-1:2020
ISO 20896-1:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
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
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

---------------------- Page: 8 ----------------------
SIST EN ISO 20896-1:2020
ISO 20896-1:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 3
4.1 General . 3
4.2 Reference measurement of test objects . 3
5 Test Methods . 4
5.1 Test objects . 4
5.1.1 General. 4
5.1.2 Preparation . 4
5.1.3 Measurement of reference values . 4
5.2 Test conditions . 5
5.2.1 Ambient conditions . 5
5.2.2 Scanning pattern . 5
5.2.3 Scanning time . 5
5.2.4 Number of scans . 5
5.3 Processing of the digital impression . 5
5.3.1 General. 5
5.3.2 Dimensions of interest . 5
5.3.3 Determination of dimensions . 5
5.4 Assessment of accur acy . 6
5.4.1 Statistical analysis . . 6
5.4.2 Expression of bias . 6
5.4.3 Expression of accuracy . 6
6 Test Report . 7
6.1 General . 7
6.2 Device . 7
6.3 Test object . 7
6.4 Test method . 7
6.5 Test results. 8
Annex A (normative) Test object — Crown preparation . 9
Annex B (normative) Test object — Inlay preparation .11
Annex C (normative) Test object — Full arch .13
Bibliography .15
© ISO 2019 – All rights reserved iii

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SIST EN ISO 20896-1:2020
ISO 20896-1:2019(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.
A list of all parts in the ISO 20896 series can be found on the ISO website.
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 2019 – All rights reserved

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SIST EN ISO 20896-1:2020
ISO 20896-1:2019(E)

Introduction
Dental CAD/CAM systems that produce indirect dental restorations require a three dimensional
digitized description, often called a digital impression, of a patient's dentition as a starting point for the
design and fabrication of inlays, crowns, bridges and larger fixed or removable appliances. The device
that digitizes the three dimensional surface shall be sufficiently accurate to enable the design and
manufacture of a clinically acceptable restoration.
This document describes test methods for evaluating the accuracy of digitizing devices that acquire
data by direct scanning of a patient's dentition with a manually guided; that is hand-held, device in
order to obtain a digital impression. A companion document, ISO 12836, provides test methods for
assessing the accuracy of fixed devices for digitizing physical impressions or models cast from such
impressions. Separate standards were deemed necessary after it became apparent that two of the test
objects described in ISO 12836 are unsuited for successful interpretation of data acquired from these
objects with a hand-held scanning device.
NOTE Testing conducted outside the oral cavity on objects that are ideal − in having both surface
characteristics suitable for a given scanning technology and sufficient recognizable features for registration
algorithms to function well − will give a better result than can be achieved under less ideal, clinical conditions.
© ISO 2019 – All rights reserved v

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SIST EN ISO 20896-1:2020

---------------------- Page: 12 ----------------------
SIST EN ISO 20896-1:2020
INTERNATIONAL STANDARD ISO 20896-1:2019(E)
Dentistry — Digital impression devices —
Part 1:
Methods for assessing accuracy
1 Scope
This document specifies test methods and procedures for assessing the accuracy of a three dimensional
numerical description of intra-oral surfaces acquired directly from a patient with a hand-held scanning
device. The test methods are not applicable to ultrasonic, radiographic or magnetic resonance imaging
methods.
NOTE ISO 12836 specifies the test methods for the assessment of accuracy of digitizing devices that use a
fixed or a mechanically guided scanning device.
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 3534-1, Statistics — Vocabulary and symbols — Part 1: General statistical terms and terms used in
probability
ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General
principles and definitions
ISO 6873:2013, Dentistry — Gypsum products
ISO 18739:2016, Dentistry — Vocabulary of process chain for CAD/CAM systems
ISO 20795-1, Dentistry — Base polymers — Part 1: Denture base polymers
ISO 22112, Dentistry — Artificial teeth for dental prostheses
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated
terms (VIM)
ISO/IEC Guide 98-3:2008, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
me a s ur ement (GUM: 1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions from ISO 1942, ISO 3534-1, ISO 5725-1,
ISO 18739, ISO/IEC Guide 99, ISO/IEC Guide 98-3, 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 http: //www .electropedia .org/
© ISO 2019 – All rights reserved 1

---------------------- Page: 13 ----------------------
SIST EN ISO 20896-1:2020
ISO 20896-1:2019(E)

3.1
accuracy
closeness of agreement between a test result and an accepted reference value
[SOURCE: ISO 18739:2016, 3.2.1]
Note 1 to entry: Accuracy is a qualitative concept. For the purpose of this document accuracy is to be expressed
as specified in 5.4.3.
3.2
bias
expectation of the difference between test results and an accepted reference value
[SOURCE: ISO 3534-1:2006, 1.33, modified to specify test results and reference value]
Note 1 to entry: For the purpose of this document bias is to be expressed as given in 5.4.2.
3.3
digital impression
acquisition of a data set with the numerical three dimensional representation of the surfaces from the
patient directly, or the outcome of such an acquisition
[SOURCE: ISO 18739:2016, 3.1.20, modified]
Note 1 to entry: This definition extends ISO 18739:2016, 3.1.20 to include the outcome of data acquisition.
Note 2 to entry: A digital impression may be supplemented by data on surface colour.
Note 3 to entry: A digital impression is distinct from a virtual model as defined in ISO 18739:2016, 3.1.40. A
virtual model is the graphical output from design or similar software; a digital impression is the input to this
software.
3.4
digital impression device
combination of a hand-held scanning device (3.6) suited for use in the oral cavity, and computer hardware
and software that outputs a numerical, three dimensional description of scanned surfaces
3.5
dimension of interest
distance between features of a test object that are required to be both measured independently as a
reference or true value and estimated by the digital impression d
...

SLOVENSKI STANDARD
oSIST prEN ISO 20896:2018
01-julij-2018
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20896:2018)
Zahnheilkunde - Genauigkeit von handgehaltenen Scanner für CAD/CAM-Systeme am
Behandlungsstuhl (ISO/DIS 20896:2018)
Médecine bucco-dentaire - Précision du balayage des dispositifs portatifs pour systèmes
CAO/FAO de fauteuils dentaires (ISO/DIS 20896:2018)
Ta slovenski standard je istoveten z: prEN ISO 20896
ICS:
11.060.01 Zobozdravstvo na splošno Dentistry in general
35.240.10 5DþXQDOQLãNRSRGSUWR Computer-aided design
VQRYDQMH QDþUWRYDQMH (CAD)
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---------------------- Page: 1 ----------------------
oSIST prEN ISO 20896:2018

---------------------- Page: 2 ----------------------
oSIST prEN ISO 20896:2018
DRAFT INTERNATIONAL STANDARD
ISO/DIS 20896
ISO/TC 106/SC 9 Secretariat: JISC
Voting begins on: Voting terminates on:
2018-04-19 2018-07-12
Dentistry — Digital impression devices — Methods for
assessing accuracy
Médecine bucco-dentaire — Précision du balayage des dispositifs portatifs pour systèmes CAO/FAO de
fauteuils dentaires
ICS: 11.060.01
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
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 20896:2018(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 2018

---------------------- Page: 3 ----------------------
oSIST prEN ISO 20896:2018
ISO/DIS 20896:2018(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2018
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
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

---------------------- Page: 4 ----------------------
oSIST prEN ISO 20896:2018
ISO/DIS 20896:2018(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 4
4.1 General . 4
4.2 Reference measurement of test objects . 4
5 Test Methods . 4
5.1 Test objects . 4
5.1.1 General. 4
5.1.2 Preparation . 5
5.1.3 Measurement of reference values . 5
5.2 Test conditions . 5
5.2.1 Ambient conditions . 5
5.2.2 Scanning pattern . 5
5.2.3 Scanning time . 5
5.2.4 Number of Scans . 5
5.3 Processing of the digital impression . 5
5.3.1 Dimensions of interest . 6
5.4 Assessment of accur acy . 6
5.4.1 Statistical analysis . . 6
5.4.2 Expression of bias . 6
5.4.3 Expression of accuracy . 6
5.4.4 Consistency with external reliability . 7
6 Test Report . 7
6.1 General . 7
6.2 Device . 7
6.3 Test object . 7
6.4 Test method . 8
6.5 Test results. 8
6.6 Test data . 8
Annex A (normative) Test Object - Crown Preparation . 9
Annex B (normative) Test object - Inlay preparation .11
Annex C (normative) Test object - Full arch .13
Annex D (informative) Guidance on Evaluating Precision and External Reliability .15
Bibliography .18
© ISO 2018 – All rights reserved iii

---------------------- Page: 5 ----------------------
oSIST prEN ISO 20896:2018
ISO/DIS 20896:2018(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO's adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www .iso .org/ iso/ foreword .html.
The committee responsible for this document is Technical Committee ISO/TC 106, Dentistry,
Subcommittee SC 9, Dental CAD/CAM Systems.
iv © ISO 2018 – All rights reserved

---------------------- Page: 6 ----------------------
oSIST prEN ISO 20896:2018
ISO/DIS 20896:2018(E)

Introduction
Dental CAD/CAM systems that produce indirect dental restorations require a 3-dimensional digitized
description, often called a digital impression, of a patient's dentition as a starting point for the design
and fabrication of inlays, crowns, bridges and larger fixed or removable appliances. The device that
acquires and digitizes the 3-dimensional metrology data shall be sufficiently accurate to enable the
design and manufacture of a clinically acceptable restoration.
This document describes test methods for evaluating the accuracy of digitizing devices that acquire
data by direct scanning of a patient's dentition with a manually guided; that is hand-held, device in
order to obtain a digital impression. A companion document, ISO 12836, provides test methods for
assessing the accuracy of fixed devices for digitizing physical impressions or models cast from such
impressions. Separate standards were deemed necessary after it became apparent that two of the test
objects described in ISO 12836 are unsuited for successful interpretation of data acquired from these
objects with a hand-held scanning device.
It is to be noted that testing conducted outside the oral cavity on objects that are ideal − in having both
surface characteristics suitable for a given scanning technology and sufficient recognizable features for
registration algorithms to function well − will give a better result than can be achieved under less ideal,
clinical conditions. As a first stage in developing standard methods for estimating and representing the
degradation in precision that arises in the clinical use of digitizing devices, this document includes an
informative annex on the evaluation of external reliability.
© ISO 2018 – All rights reserved v

---------------------- Page: 7 ----------------------
oSIST prEN ISO 20896:2018

---------------------- Page: 8 ----------------------
oSIST prEN ISO 20896:2018
DRAFT INTERNATIONAL STANDARD ISO/DIS 20896:2018(E)
Dentistry — Digital impression devices — Methods for
assessing accuracy
1 Scope
This document specifies test methods and procedures for assessing the accuracy and external reliability
of a three-dimensional numerical description of intra-oral surfaces acquired directly from a patient
with a hand-held scanning device. The test methods are not applicable to ultrasonic, radiographic or
magnetic resonance imaging methods.
Note: ISO 12836:2015 specifies the test methods for the assessment of accuracy of digitizing devices
that use a fixed or a mechanically guided scanning device.
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 3534-1 Statistics — Vocabulary and symbols -- Part 1: General statistical terms and terms used in
probability
ISO 5725-1 Accuracy (trueness and precision) of measurement methods and results — Part 1: General
principles and definitions
ISO 6873:2013, Dentistry — Gypsum Products
ISO 12836 Dentistry — Digitizing devices for CAD/CAM systems for indirect dental restorations — Test
methods for assessing accuracy
ISO 18739 Dentistry — Vocabulary of process chain for CAD/CAM systems ISO 20795-1, Dentistry —
Base polymers — Part 1: Denture base polymers
ISO 22112 Dentistry — Artificial teeth for dental prostheses
ISO/IEC Guide 99 International vocabulary of metrology — Basic and general concepts and associated
terms (VIM)
ISO/IEC Guide 98-3:2008 Uncertainty of measurement — Part 3: Guide to the expression of uncertainty
in measurement (GUM: 1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions from ISO 1942, ISO 3534-1, ISO 5725-1,
ISO 18739, ISO/IEC Guide 99, ISO/IEC Guide 98-3, and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
IEC Electropedia: available at http:// www .electropedia .org/
ISO Online browsing platform: available at http:// www .iso .org/ obp
© ISO 2018 – All rights reserved 1

---------------------- Page: 9 ----------------------
oSIST prEN ISO 20896:2018
ISO/DIS 20896:2018(E)

3.1
accuracy
closeness of agreement between a test result and an accepted reference value.
[SOURCE: ISO 18739:2016]
Note 1 to entry: Accuracy is a qualitative concept. For the purpose of this document accuracy is to be expressed
as specified in 5.4.3.
3.2
bias
difference between the expectation of the test results and an accepted reference value.
[SOURCE: ISO 3534-1]
Note 1 to entry: For the purpose of this document bias is to be expressed as given in 5.4.2
3.3
digital impression
acquisition of a data set with the numerical 3-dimensional representation of the surfaces from the
patient directly, or the outcome of such an acquisition.
[SOURCE: ISO 18739:2016, Clause 3.1.20, modified]
Note 1 to entry: This definition extends ISO 18739:2016, Clause 3.1.20 to include the outcome of data acquisition.
Note 2 to entry: A digital impression may be supplemented by data on surface colour.
Note 3 to entry: A digital impression is distinct from a virtual model as defined in ISO 18739:2016, Clause 3.1.40.
A virtual model is the graphical output from design or similar software; a digital impression is the input to this
software.
3.4
digital-impression device
combination of a hand-held scanning device suited for use in the oral cavity, and computer hardware
and software that outputs a numerical, three-dimensional description of scanned surfaces.
3.5
dimension of interest
distance between features of a test object that are required to be both measured independently as a
reference or true value and estimated by the digital impression device using a prescribed scanning
procedure.
3.6
external reliability
confidence interval for an estimated dimension after eliminating gross errors in the data as detected
by the digitizing system's software.
Note 1 to entry: Note to entry: External reliability is evaluated by propagation of uncertainties as estimated from
the redundancy in an accepted dataset, as described in Annex D.
3.7
gross error
observation that can be demonstrated to be inconsistent with other data.
Note 1 to entry: Detection and elimination of gross errors is an essential function of the registration software of
a digitizing device.
Note 2 to entry: A gross error can arise from partial failure of a measurement device, or from incorrect calibration,
pattern recognition or data interpretation.
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3.8
hand-held scanning device
camera or similar sensor which may be moved freely as it captures light reflected or diffusely scattered
from a surface and converts it into a sequence of data from which distances and corresponding
directions to the surface can be determined.
Note 1 to entry: The instrument may have its own source of illumination.
Note 2 to entry: The scanning device may operate by any technology that provides data on range and direction
from the device to the surface.
Note 3 to entry: The values of distances and corresponding directions constitute the raw data for creating the
digital impression.
3.9
observation
single item of data or of information relating items of data.
Note 1 to entry: Examples of observations in intra-oral scanning are: i) a range or a component of direction in an
array of digitized data, ii) the identification of a single feature in two arrays of digitized data.
3.10
precision
the closeness of agreement between independent results of measurement obtained under stipulated
conditions.
Note 1 to entry: Precision is a qualitative concept. The operational definition that applies in this document is the
standard deviation.
[SOURCE: ISO 18739:2016, 3.2.7]
3.11
range
measured distance from the hand-held scanning device to a scanned surface.
3.12
redundancy
3.12.1 total redundancydifference between the number of observations and the number of parameters
in the digital impression and required to describe the movement of the hand-held scanning device.3.12.2
redundancy numberrelative part of an observation which does not contribute significantly to the
estimation of parameters.
Note 1 to entry: Total redundancy is also known as the number of degrees of freedom.
Note 2 to entry: Redundancy numbers range from 0 to 1. A redundancy number near 1 allows an observation to
be controlled for gross error. A redundancy number near zero means that an observation cannot be controlled
for gross error and yet the observation has a direct influence on the parameters.
Note 3 to entry: The sum of redundancy numbers for all observations is equal the total redundancy.
3.13
registration
sub-process in analysis of scanning data in which segments of surface topography derived from data
acquired by a scanning device in successive positions and orientations are matched in order to estimate
the relative translation and rotation of the scanning device.
3.14
scanning pattern
sequence of translations and rotations of a hand-held scanning device relative to the object being
scanned as it acquires data from which to render the surface of the object as a digital impression.
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3.15
scanning procedure
acquisition and analysis of a set of data with a hand-held digitizing device according to a scanning
pattern for the purpose of creating a dental impression.
4 Requirements
4.1 General
The hand-held scanning device shall be driven by software installed in the digitizing device or by
independent software specified by the manufacturer for the digitization and rendering of a digital
impression of the surface of a patient's dentition.
A scanning pattern or patterns for each clinical indication described in the instructions supplied by
the manufacturer shall be applied to scan the test objects described in Annexes A, B and C for the
assessment of accuracy.
If the instructions for use of a hand-held scanning device claim that it is suited to obtain a digital
impression for fabricating a multi-unit fixed dental prosthesis, then two types of test object, conforming
to Annex A and to Annex C shall be employed.
Note Examples of clinical indications are a preparation for an inlay, a single crown, a multi-unit fixed dental
prosthesis, or a full-arch of the dentition of the upper or lower jaw.
4.2 Reference measurement of test objects
The dimensions of interest of each test object as designated in Annexes A, B and C shall be determined
by an independent, calibrated measurement technique. The values obtained shall be considered the
true values for the dimensions of interest. The conditions of temperature and humidity under which the
determination is made shall be measured.
The precision of this determination is to be expressed as standard uncertainty σ. When the precision
in a true value is derived from the standard deviation S of n repeated measurements, the standard
uncertainty is:
σ = S/√n.
Where precision is obtained from a Type B evaluation of standard uncertainty as defined by
ISO/IEC Guide 98-3 (GUM: 1995) §4.3, an appropriate conversion to standard uncertainty shall be cited.
The standard uncertainty in the reference values of the dimensions of interest shall be no greater than
one-fifth of (i.e. 0.2 times) the accuracy expected, required or claimed for the digitizing device.
5 Test Methods
5.1 Test objects
5.1.1 General
The test objects described in Annexes A, B and C, against which the results of a digitizing procedure
are compared, have features for which dimensions or separations shall be determined by independent
means. Such features include flat areas, linear structures, straight or curved edges and corners, or
spherical markers.
The test objects may have additional decoration or incisions as necessary for successful registration
and processing of the raw scanning data. Such features shall not obscure or distort surfaces required
for measuring the defined dimensions of interest.
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5.1.2 Preparation
The test object shall be fabricated and prepared for scanning as described below before the dimensions
of interest are determined.
The surfaces of the test objects described in Annex A and B and the gauge spheres described in Annex C
may be rendered light-diffusing by sand-blasting or similar treatment. The surface roughness amplitude
shall be measured and recorded.
Surfaces may be coated or sprayed.
If required in order for the registration stage of data processing to function, the surfaces of the test
objects described in Annexes A and B may be decorated or incised with details that break the mirror
and cylindrical symmetries of the test objects. There shall remain sufficient undecorated and un-incised
area to allow complete determination of the upper and lower circumferences of the cone or conical hole,
and to determine the planes of the upper and lower surfaces of the test object.
5.1.3 Measurement of reference values
The apparatus employed for the independent measurement of dimensions of interest shall be calibrated
to ensure compliance with the accuracy and precision required by 4.2.
The test object or objects shall be measured and the reference values shall be recorded prior to their
use to assess accuracy of a scanning device.
5.2 Test conditions
5.2.1 Ambient conditions
The scanning device shall be evaluated under ambient conditions. The temperature and relative
humidity during measurement shall be measured and recorded.
5.2.2 Scanning pattern
The scanning pattern, including the orientation of the hand-held scanning device, shall reflect the
restrictions that the oral cavity would impose in clinical use.
The scanning device shall be moved freely by hand in accordance with the scanning pattern without
mechanical guidance.
5.2.3 Scanning time
Testing procedures should be completed in an efficient manner typical for the clinical use for which it is
intended. The time taken to complete each scan of a test object should be recorded.
5.2.4 Number of Scans
At least thirty (n = 30) scanning procedures shall be performed on a test object and a digital impression
obtained and measured for each procedure.
Only if an individual scanning procedure fails during acquisition or processing so that a digital
impression is not produced or is not suitable for estimation of the dimensions of interest, shall that
procedure be discarded.
5.3 Processing of the digital impression
The dimensions of interest shall be extracted from the digital impression by software supplied with the
digitizing device. Only if the digitizing device lacks this functionality shall the dimensions of interest be
extracted from the digital impression by independent software.
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If the functionality is available, the redundancy in the raw data should be employed to derive estimates
of external reliability of the dimensions of interest. External reliability should be expressed as a
standard uncertainty. (See Annex D).
5.3.1 Dimensions of interest
5.3.1.1 General
The analysis software of the digital impression device shall be used to analyse each digital impression
as required. If the device's own software does not have this functionality, independent software shall
be used to analyse each digital impression.
5.3.1.2 Determination of dimensions
After the execution of a scanning procedure, the value of each dimension of interest shall be determined
from the digital impression and recorded.
The conical symmetry, the flatness and the parallelism of base and top surfaces of the components in
Annexes A and B, and the sphericity and calibrated diameter of gauge balls in Annex C, may be assumed
in this analysis.
Where the software has the appropriate functionality, an estimate of external reliability in each
estimated value shall be recorded.
5.4 Assessment of ac curacy
5.4.1 Statistical analysis
The individual values of each dimension of interest shall be examined for outliers. These shall be
highlighted, but not discarded unless there is corroborating evidence of measurement failure.
For each dimension of interest, denoted d, the mean and standard deviation S(d ) shall be evaluated
i i
from the n observations of that dimension obtained according to 5.3.1. Each observation shall be
assumed to have equal weighting, even if estimates of external reliability indicate otherwise.
5.4.2 Expression of bias
Bias in the ith dimension of interest shall be expressed as the difference between the mean value
obtained according to 5.4.1 and the corresponding reference value, ob
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