ISO/TR 20896-2:2023
(Main)Dentistry — Digital impression devices — Part 2: Methods for assessing accuracy for implanted devices
Dentistry — Digital impression devices — Part 2: Methods for assessing accuracy for implanted devices
This document describes methods of acquiring and analysing data from which the accuracy of a numerical model of the geometry of the mucosa and implant bodies in the jaw of a patient can be assessed.
Médecine bucco-dentaire — Dispositifs d'empreinte numérique — Partie 2: Méthodes d'évaluation de l'exactitude de dispositifs implantés
Le présent document décrit des méthodes de collecte et d’analyse des données à partir desquelles l’exactitude d'un modèle numérique de la géométrie de la muqueuse et des implants dentaires dans la mâchoire d'un patient peut être évaluée.
General Information
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Standards Content (Sample)
ISO/TC 106/SC 9 N 229
Date: 2022-03-30
ISO/TR 20896--2:2022(E)
ISO TC 106/SC 9/WG 3
Secretariat: JISC
Dentistry — Digital impression devices — Part 2: Methods for assessing the accuracy of scanning
for implanted devices
First edition
Date: 2022-09-13
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ISO/TR 20896-2:2022(E)
© ISO 2022
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ISO/TR 20896-2:2022(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
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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.
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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).
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.
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ISO/TR 20896-2:2022(E)
Introduction
Dental CAD/CAM systems that produce indirect dental restorations require a 3-dimensional digitized
description, often called a digital impression, of the patient's dentition as a starting point for the design
and fabrication of inlays, crowns, bridges and larger prosthetic or orthodontic appliances. The device
that acquires and digitizes the 3-dimensional metrology data must be sufficiently accurate to enable the
manufacture of a clinically acceptable restoration.
This document describes possible test methods for evaluating the accuracy of digital impression devices
designed for direct oral scanning of implant bodies, intended as support for prosthetic appliances to
replace a patient's dentition, in order to obtain a digital impression. It is a complement to Part 1 (ISO
20896-1), which is a standard for assessingassesses the accuracy of digital impression devices from
which a digital impression of a patient’s dentition can be created. A companion standard, ISO 12836,
provides test methods for assessing the accuracy of fixed devices for digitizing physical impressions or
models/casts made from such impressions. Separate standards were deemed necessary after it became
apparent that two of the test objects described in ISO 12836 were unsuited for successful interpretation
of data acquired with a digital impression device.
Assessment of the accuracy of digital impression devices for a full-arch test object as described in Part 1
or similar tests has revealed that intra-oral, digital impression devices are intrinsically limited in
accuracy to taking impressions of just a few teeth. Furthermore, experience and experiments with these
devices to create a digital impression after the placement of single implants, indicate that a scan body
fitted to the implant body allows an accuracy in position and orientation at least as good as for a tooth
preparation. Implants are however also an indicated treatment for fully or partially edentulous patients.
For such indications, several implant bodies are placed in the upper or lower jaw. Scanning technology
is developing rapidly, to overcome inaccuracies that occur when scanning an edentulous patient. One
hindrance to the development of a relevant method of assessing accuracy for this clinical case is the lack
of a mechanically stable material that can adequately represent mucosal tissue in a test object.
This document reviews the theory and techniques employed to exploit scan bodies to overcome the
challenges of scanning edentulous mucosal tissue by optical methods.
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ISO/TR 20896-2:2022(E)
Dentistry — Digital impression devices — Part 2: Methods for
assessing the accuracy of scanning for implanted devices
1 Scope
This document describes methods of acquiring and analysing data from which the accuracy of a
numerical model of the geometry of the mucosa and implant bodies in the jaw of a patient can be
assessed.
[1]
NOTE 1 ISO 20896-1 specifies test methods for the assessment of accuracy of digitizing devices used
intra-orally on patients with complete or almost complete dentition.
[2]
NOTE 2 ISO 12836 specifies the test methods for the assessment of accuracy of digitizing devices
used in a dental laboratory.
32 Normative references
There are no normative references in this document.
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 16443:2014, Dentistry — Vocabulary for dental implants systems and related procedure
ISO 18739, Dentistry — Vocabulary of process chain for CAD/CAM systems
ISO 20896-1, Dentistry — Digital impression devices — Part 1: Methods for assessing accuracy
ISO/IEC Guide 98-3:2008, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty
in measurement (GUM:1995)
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated
terms (VIM)
43 Terms and definitions
[3] [4]
For the purposes of this document, the terms and definitions given in ISO 1942 ,, ISO 3534-1 ,, ISO
[5] [6] [7] [1] [8] [9]
5725-1 ,, ISO 16443 ,, ISO 18739 ,, ISO 20896-1 ,, ISO/IEC Guide 98-3 ,, ISO/IEC Guide 99 and
the following apply.
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ISO/TR 20896-2:2022(E)
ISO and IEC maintain terminologicalterminology 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
digital impression data
set of numerical coordinates providing a three-dimensional representation of the surfaces of teeth and
surrounding tissue acquired directly from the patient by a digital impression device and presented in a
format suited to a computer-aided dental design and manufacturing (CAD/CAM) process
Note 1 to entry: A digital impression data set can be supplemented by data on surface colour.
Note 2 to entry: A set of digital impression data isare distinct from a virtual model as defined in ISO 18739. A
virtual model is produced by design or similar software.
3.2
external reliability
confidence interval for an estimated dimension after eliminating gross errors (3.3) in the data as
detected by the digitizing system's software
Note 1 to entry: External reliability is evaluated by propagation of uncertainties as estimated from the redundancy
(3.7) in an accepted data set, as described in Annex D.
3.3
gross error
error in an observation arising from partial failure or incorrect calibration of a measurement device,
incorrect pattern recognition or data interpretation and leading to unacceptable error of measurement
in the digital impression
Note 1 to entry: Detection and elimination of gross errors is an essential function of the registration software for a
digital impression device.
3.4
intra-oral calibration appliance
extended scan body (3.9) that is scanned together with the mucosa, residual dentition and other scan
bodies and provides internal calibration of digital impression data. (3.1)
3.5
position of interest
coordinates of a feature on an implant body that define the placement of the implant body
Note 1 to entry: The feature can be defined by the symmetry of the implant body, for example, its axis. It lies on a
surface of the body that is accessible when placed in a jaw.
3.6
range image
two-dimensional array of data on the distances from the scanning device to the surfaces being scanned
Note 1 to entry: The array indices define direction with respect to the axis of the scanning device for which the
distance applies.
3.7
redundancy
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ISO/TR 20896-2:2022(E)
difference between the number of observations judged to be validly measured and the number of
parameters that need to be estimated to calibrate and describe movement of the scanning device and to
produce digital impression data (3.1)
Note 1 to entry: The software of a digitizing device may exploit redundancy to perform an assessment of raw data
in order to detect gross errors (3.3) by statistical testing. (see Annex D)).
3.8
reference impression data
set of three-dimensional coordinates acquired by a digital impression device or a combination of
scanning device and digitizing device that represent the surfaces to a better precision than that of the
device being assessed
3.9
scan body
implant impression post with a numerically defined geometric shape from which the position and
orientation of an implant body can be determined in a scanning procedure
54 Literature review
Intra-oral scanning builds on 170 years of development in photogrammetry. It belongs to the branch
[12] [4]
known as close-range photogrammetry and where it represents very close-range . In the confines
of the mouth, a scanning device requires miniature components with their attendant need for continual
re-calibration in the face of considerable image distortion.
Articles relevant to assessing accuracy in scanning in the oral cavity to produce digital impression data
for existing dentition or an edentulous jaw were searched by the key wordskeywords: “intra-oral
scanning” and “accuracy”. Of an initial list totalling 158 articles from the period 2013 to June 2020, sub-
lists for those concentrating on scanning an edentulous jaw (29 articles) and those scanning a full arch
with full or partial dentition (59 articles) were chosen for review. Figure 1 shows the number of articles
by year of publication. Many studies compare digitizing devices from several manufacturers.
Intra-oral scanning ; accuracy
40
35
30
25
20
15
10
5
0
2020 2019 2018 2017 2016 2015 2014 2013
Edentulous Full-arch Other
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ISO/TR 20896-2:2022(E)
Key
edentulous
full-arch
other
Figure 1 – — Refereed articles with search key wordskeywords “intra-oral scanning” and
“accuracy”
The diversity of methods and variety of statistics employed show that consensus on appropriate
methods of benchmarking digital impression devices would benefit both device manufacturers, their
customers and, in some jurisdictions, regulatory authorities.
65 Assessment of accuracy
6.15.1 General
6.1.15.1.1 Clinical quality
Since digital impression data are the input to the process of designing and manufacturing, a dental
prosthetic appliance, its accuracy, within clinically acceptable tolerances, is a quality factor to be
controlled. When a prosthesis is placed on two or more prepared teeth, a clinical requirement on
uncertainty in separation of critical features is that it be less than approximately 100 µm. When placing
a prosthetic appliance on two or more implant abutments, the requirement on accuracy is more
stringent.
6.1.25.1.2 Sources of uncertainty
Digital impression devices that rely solely on numerical registration methods to combine a large
number of small range images of three-dimensional surfaces into a large model are subject to
uncertainties. These arise from the registration of overlapping range images where the uncertainty
depends on the number of data elements in the overlap. The uncertainty increases as it is propagated
across a scanned region, leading to large uncertainties in relative positions and orientations derived for
features at the extreme ends of a scanning pattern. For full-arch scanning, the accuracy has been shown
to be unacceptably poor, but techniques are evolving to improve accuracy. It is therefore desirable that
standard methods for comparing techniques and instrumentation be available by providing measures of
interest by which accuracy can be assessed.
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6.1.35.1.3 Auxiliary methods
Some solutions for reducing uncertainties employ auxiliary methods of measurement or calibration.
These can be both intra- and extra-oral. The auxiliary data are utilisedutilized either directly in the
registration of range images or employed in a separate numerical algorithm to correct for distortion in
the digital impression data. In order to be utilisedutilized directly, the results or data from auxiliary
measurements are available prior to taking the digital impression data.
6.25.2 Accuracy
6.2.15.2.1 General
Accuracy is a general concept that includes both trueness and precision or reliability. Operational
procedures for estimating trueness, precision and reliability are presented as means for assessing
accuracy.
6.2.25.2.2 Trueness
For digital impression data, the operations by which trueness is assessed can be of two types:
a) Direct comparison with independent, calibrated measurements of particular measures of interest.:
these measures are distances or angles relative to a reference plane which itself is defined by the
dentition, as in Annex A or by one or more auxiliary devices.
b) Estimation of a goodness-of-fit statistic derived from overall comparison with reference impression
data.: this method of assessment frequently disguises serious discrepancies that are of limited
spatial extent. It is therefore recommended that assessmentAssessments employing this
methodology can require the digital impression data to fit reference impression data at a clinically
relevant, limited, contiguous subset of points at or near one extreme of the scanning pattern, for
example, a scan body, and then determine the quality of fit of a similar feature (for example,e.g. a
second scan body) near the opposite extreme.
Goodness-of-fit statistics expressed in the units of the measures of interest give the user a clearer
basis for comparison than those expressed as in relative terms; i.e. as percentages.
Clinically, trueness is ultimately determined when a prosthetic appliance, which has been designed and
manufactured from the digital impression data, is placed in the patient’s mouth. Quality management
[10[2]
procedures and systems can build up data records that, on review, allow assessment of trueness of
the digital impressions upon which prosthesis design and manufacturing are based.
6.2.35.2.3 Precision
By precision is meant that repeated measurements with the digital impression device agree to within a
nominated tolerance regardless of operator, provided the scanning is performed within the guidelines
supplied with the device. Assessments of precision are of two types:
a) Repeated measurements of measures of interest and evaluation of statistics that describe
variability, as described in Part 1, This is a Type A evaluation of uncertainty.
The precision of this determination is expressed as standard uncertainty σ. When the precision in a
value is derived from the standard deviation S of n repeated measurements, the standard
uncertainty is:
σ = S/√n
b) Deduction from knowledge of the design and mode of operation of the scanning device and the
algorithms employed to extract a digital impression from raw data. This is a Type B evaluation of
uncertainty.
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ISO/TR 20896-2:2022(E)
6.2.45.2.4 5.2.4 External reliability
Determination of reliability (see Annex D) assesses the precision of given digital impression data
derived from a single scanning procedure. It provides a measure of the contribution of errors in
observations to uncertainties in the digital impression data. The determination of reliability exploits the
excess over the minimum necessary number of measurements, or redundancy, in the data acquired in
the course of a single scanning procedure, and employs it either
a) within the scanning and registration algorithm to indicate when adequate data have been acquired
to achieve a given precision, or
b) in post-analysis to detect and eliminate gross errors arising from unpredictable sources and then to
estimate the residual uncertainties.
6.35.3 Test objects
6.3.15.3.1 General
Test objects are material models of dentition or edentulous tissue on one jaw employed for assessing
the accuracy of a digital impression device. When scanned in order to assess the accuracy of a digital
impression device, the scanning pattern conforms to that used in a clinical situation.
The principles outlined in this document for assessing precision and accuracy, are not compatible with
the exploitation of the dimensions for the proposed scan body. The scan body design in Annex A
includes features intended to be measured independently as noted in Clause B.3., in order to build up a
redundant set of observations that maycan be assessed for external reliability by the method ofin
Annex D.
6.3.25.3.2 Single implant
Annex A describes a test object and measures of interest for assessing accuracy when scanning a single
implant body with an attached scan body.
6.3.35.3.3 Multiple implants
Annex B describes a test object with more than one implant where design of a clinically acceptable
prosthetic device requires accuracy in relative position and orientation.
6.45.4 Reference measurement of test objects
6.4.15.4.1 Calibrated measures of interest
The dimensions of interest of the test object as designated in Annex B and Annex C are determined by
an independent, calibrated measurement traceable to the internationally adopted standard of length.
The values obtained are considered the true values for the dimensions of interest. The conditions of
temperature and humidity under which the determination is made are measured and recorded.
Where precision is obtained from a Type B evaluation of standard uncertainty as defined by ISO/IEC
Guide 98-3 (GUM: :2008) §, 4.3, an appropriate conversion to standard uncertainty is cited.
The standard uncertainty in the reference values of the measures of interest is not greater than one-
fifth of (i.e. 0,2 times) the accuracy expected, required or claimed for the digitizing device.
6.4.25.4.2 Independent scanning device
Where trueness is assessed according to 5.2.2 b), or precision according to 5.2.3 b), the independent
scanning device is capable of creating reference impression data to a precision with a standard
uncertainty no greater than one-half the accuracy expected, required or claimed for the digitizing device
being assessed.
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ISO/TR 20896-2:2022(E)
6.55.5 Auxiliary devices
6.5.15.5.1 General
The purpose of an auxiliary measurement of the geometry of the dentition or mucosal surface is to
allow closure of the linear series of scanning frames acquired by a digital impression device during a
scanning procedure. The auxiliary measurement provides additional and more precise data on the
relative positions within the scan pattern. The following clauses describe methods mentioned in
published reports.
6.5.25.5.2 Calliper measurement
Caliper measurement can provide an independent estimate of the distance between an identifiable
feature on each implant scan body on the scanning pattern. The distance between such features is in the
range (40 ± ± 20) mm and the uncertainty in this dimension required for clinical acceptability is
100 µm (at 95 % confidence limit). Since, however, This distance measurement has to imposeimposes a
significant constraint within the registration algorithm, anif its uncertainty is less than or equal to
50 µm is recommended.
6.5.35.5.3 Extra-oral photogrammetry
For measuring implant positions and orientations, a device that acquires data in a single range image on
distance and angular direction to specially designed scan bodies. In one implementation, the scan body
has a flag-like superstructure, which is patterned to allow their orientation to be interpreted from a
single optical image or a pair of stereographic images.
For this technique to improve to the accuracy of digital impression data, the resolution of the extra-oral
data acquisition device must allow feature identification over approximately 40 mm at a distance of
(100 ± 20) mm to provide a precision of 0,025 mm. To achieve this, features within an angular range of
(25 ± 11)° need)° are to be resolved to one part in two thousand. This requires up to 6000 6 000 sensor
elements in the lateral direction, where a minimum of three elements is required to identify a feature.
76 Accuracy assessment methods
7.16.1 Measures of interest
7.1.16.1.1 General
The measures of interest are defined by positions and directions in an appropriate reference system.
Recommended reference systems are described in Annex A and Annex B.
7.1.26.1.2 Position of interest
The recommended position of interest for an implant body is the point where the axis of implant body
intersects the connecting interface. The geometrical description of the surface of a scan body takes this
point as its origin.
NOTE 1 : The term connecting interface is defined in ISO 16443:2014, 3.2.8
NOTE 2 : Where an implant body is designed to receive an abutment screw, the position of interest can be
defined as the intersection of the axis of the implant body with the surface of the implant body to which the
abutment matches.
7.26.2 Assessment of trueness
7.2.16.2.1 Single implant
Annex A describes a test object and measures of interest for assessing accuracy when scanning a single
implant body with an attached scan body.
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ISO/TR 20896-2:2022(E)
7.2.26.2.2 Multiple implants
The principles for the design and calibration of test objects designed to assess the accuracy of a digital
impression device and auxiliary devices are outlined in Annex A and Annex B. Additional measures of
interest are given in Annex C.
For assessment of trueness according to 4.1.1 a), it is recommended that the measures of interest beare
extracted from the digital impression data and compared directly with the corresponding reference
values.
For assessment of trueness according to 4.1.1 b),
a) The digital impression data acquired by the digital impression device and the reference impression
data are registered to minimize the goodness-of-fit statistic over the surface of one scan body (at
one end of the scanning range where more than two scan bodies are scanned) and the mucosal
surface. The goodness of fit is recorded.
b) The goodness of fit for the surface of the neighbouring scan body in the digital impression and in
the reference impression is then evaluated and recorded.
Where more than two scan bodies are scanned,
c) the digital impression data are then registered to minimize the goodness-of-fit statistic over both
the first and successive, neighbouring scan bodies, and the minimum goodness of fit evaluated and
recorded.
d) steps 2 and 3 are repeated for the surfaces of further neighbouring scan bodies, each time including
only previously assessed scan bodies in the registration.
Trueness is evaluated as the difference between the goodness of fit for the ultimate scan body as
evaluated at step in 6.2.2 b) and the goodness of fit evaluated in step 1.6.2.2 a).
7.36.3 Assessment of precision
7.3.16.3.1 Repeated scanning procedures
For assessment of precision, the recommended scanning procedure is performed at least five (5) times
according to the instructions provided for the given indication as described in 6.2. Precision is
expressed as the largest standard uncertainty evaluated for the measures of interest or in the goodness
of fit.
Data from all repetitions of the scanning procedure are included in the estimation of the standard
uncertainty. Exclusion is allowed if the digitizing device itself identifies a scanning procedure as
improperly or inadequately performed.
7.3.26.3.2 Design analysis
Since the major source of uncertainty in intra-oral scanning is registration of successive range images,
the uncertainty in the relative orientation angles and displacements of overlapping frames can be
evaluated from the numbers of data in two orthogonal directions in each overlap. The uncertainty
estimation includes the number of data required to identify features in the overlap.
Where registration is based on overall shape of the scanned surface within an overlap, and determined
by minimizing a goodness-of-fit statistic, the residual misfit is propagated to estimate uncertainties in
the change between overlapping range images in:
a) three angles describing camera rotation, and
b) three components of camera displacement.
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ISO/TR 20896-2:2022(E)
The uncertainty estimates derived above is then propagated to derive the uncertainty in relative
positions and orientations of scan bodies separated as described for the clinical indication for which
assessment of precision is required.
7.46.4 Expression of accuracy
The accuracy in the measurement of a measure of interest is assessed as the combination of the
th
trueness and the precision. The accuracy in the i measure of interest is evaluated as the greater of the
standard uncertainty in the reference value and root-mean-square difference between the measured
values and the reference value; that is by evaluating the statistic:
n
2
d − d
( )
j ,,i Ri
∑
j=1
s =
i
n
2
𝑛𝑛
∑
�𝑑𝑑 −𝑑𝑑 �
⎛ ⎞
𝑗𝑗,𝑖𝑖 𝑅𝑅,𝑖𝑖
𝑗𝑗=1
�
𝑠𝑠 = max ,𝜎𝜎�𝑑𝑑 �
𝑖𝑖 𝑅𝑅,𝑖𝑖
⎜ ⎟
𝑛𝑛
⎝ ⎠
where
th
si is the accuracy of measurement of the i measure of interest
th th
d is the j measured value of the i measure of interest
j,i
th
d is the reference value for the i measure of interest
R,i
th
σ(d ) is the standard uncertainty in the reference value for the i measure of
R,i
interest
s is the root-mean-square difference between the measured values and reference value for
i
the measure of interest
th th
d is the j measured value of the i measure of interest;
j,i
th
d is the reference value for the i measure of interest.
R,i
7.56.5 Assessment of reliability
The principles of estimating the reliability of a scanning procedure are described in Annex D. Reliability
can be improved by increasing redundancy; that is by performing additional scanning on a different
scanning pattern in order to reveal gross errors that can then be eliminated.
Reliability can also be improved by incorporating independent, auxiliary observations regarding the
scan bodies or implant bodies into the numerical algorithm that minimizes the goodness of
...
FINAL
TECHNICAL ISO/DTR
DRAFT
REPORT 20896-2
ISO/TC 106/SC 9
Dentistry — Digital impression
Secretariat: JISC
devices —
Voting begins on:
2022-09-28
Part 2:
Voting terminates on:
Methods for assessing accuracy for
2022-12-21
implanted devices
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BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/DTR 20896-2:2022(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
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NATIONAL REGULATIONS. © ISO 2022
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ISO/DTR 20896-2:2022(E)
FINAL
TECHNICAL ISO/DTR
DRAFT
REPORT 20896-2
ISO/TC 106/SC 9
Dentistry — Digital impression
Secretariat: JISC
devices —
Voting begins on:
Part 2:
Voting terminates on:
Methods for assessing accuracy for
implanted devices
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NATIONAL REGULATIONS. © ISO 2022
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ISO/DTR 20896-2:2022(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Literature review . 3
5 Assessment of accuracy . 3
5.1 General . 3
5.1.1 Clinical quality . 3
5.1.2 Sources of uncertainty . 4
5.1.3 Auxiliary methods . 4
5.2 Accuracy . 4
5.2.1 General . 4
5.2.2 Trueness . 4
5.2.3 Precision . 5
5.2.4 External reliability . 5
5.3 Test objects . 5
5.3.1 General . 5
5.3.2 Single implant. 5
5.3.3 Multiple implants . 5
5.4 Reference measurement of test objects . 6
5.4.1 Calibrated measures of interest . 6
5.4.2 Independent scanning device. 6
5.5 Auxiliary devices . 6
5.5.1 General . 6
5.5.2 Calliper measurement . 6
5.5.3 Extra-oral photogrammetry . 6
6 Accuracy assessment methods .7
6.1 Measures of interest . 7
6.1.1 General . 7
6.1.2 Position of interest. 7
6.2 A ssessment of trueness . 7
6.2.1 Single implant. 7
6.2.2 Multiple implants . 7
6.3 Assessment of precision . 8
6.3.1 Repeated scanning procedures . 8
6.3.2 Design analysis . 8
6.4 Expression of accuracy. 8
6.5 A ssessment of reliability . 8
7 Test report . 9
7.1 General . 9
7.2 Device . 9
7.3 Test object . 9
7.4 Test method . 10
7.5 Test results . 10
7.6 Test data . 10
Annex A (Informative) Scan body for accuracy assessment .11
Annex B (informative) Test object — Single implant .13
Annex C (informative) Test object — Multiple implants .16
Annex D (informative) Guidance on evaluating precision and external reliability .18
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ISO/DTR 20896-2:2022(E)
Bibliography .22
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ISO/DTR 20896-2:2022(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).
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.
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ISO/DTR 20896-2:2022(E)
Introduction
Dental CAD/CAM systems that produce indirect dental restorations require a 3-dimensional digitized
description, often called a digital impression, of the patient's dentition as a starting point for the design
and fabrication of inlays, crowns, bridges and larger prosthetic or orthodontic appliances. The device
that acquires and digitizes the 3-dimensional metrology data must be sufficiently accurate to enable
the manufacture of a clinically acceptable restoration.
This document describes possible test methods for evaluating the accuracy of digital impression
devices designed for direct oral scanning of implant bodies, intended as support for prosthetic
appliances to replace a patient's dentition, in order to obtain a digital impression. It is a complement to
ISO 20896-1, which assesses the accuracy of digital impression devices from which a digital impression
of a patient’s dentition can be created. A companion standard, ISO 12836, provides test methods for
assessing the accuracy of fixed devices for digitizing physical impressions or models/casts made from
such impressions. Separate standards were deemed necessary after it became apparent that two of the
test objects described in ISO 12836 were unsuited for successful interpretation of data acquired with a
digital impression device.
Assessment of the accuracy of digital impression devices for a full-arch test object as described in Part
1 or similar tests has revealed that intra-oral, digital impression devices are intrinsically limited in
accuracy to taking impressions of just a few teeth. Furthermore, experience and experiments with
these devices to create a digital impression after the placement of single implants, indicate that a scan
body fitted to the implant body allows an accuracy in position and orientation at least as good as for a
tooth preparation. Implants are however also an indicated treatment for fully or partially edentulous
patients. For such indications, several implant bodies are placed in the upper or lower jaw. Scanning
technology is developing rapidly, to overcome inaccuracies that occur when scanning an edentulous
patient. One hindrance to the development of a relevant method of assessing accuracy for this clinical
case is the lack of a mechanically stable material that can adequately represent mucosal tissue in a test
object.
This document reviews the theory and techniques employed to exploit scan bodies to overcome the
challenges of scanning edentulous mucosal tissue by optical methods.
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TECHNICAL REPORT ISO/DTR 20896-2:2022(E)
Dentistry — Digital impression devices —
Part 2:
Methods for assessing accuracy for implanted devices
1 Scope
This document describes methods of acquiring and analysing data from which the accuracy of
a numerical model of the geometry of the mucosa and implant bodies in the jaw of a patient can be
assessed.
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 16443:2014, Dentistry — Vocabulary for dental implants systems and related procedure
ISO 18739, Dentistry — Vocabulary of process chain for CAD/CAM systems
ISO 20896-1, Dentistry — Digital impression devices — Part 1: Methods for assessing accuracy
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)
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated
terms (VIM)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1942, ISO 3534-1, ISO 5725-1,
ISO 16443, ISO 18739, ISO 20896-1, ISO/IEC Guide 98-3, ISO/IEC Guide 99 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
digital impression data
set of numerical coordinates providing a three-dimensional representation of the surfaces of teeth and
surrounding tissue acquired directly from the patient by a digital impression device and presented in a
format suited to a computer-aided dental design and manufacturing (CAD/CAM) process
Note 1 to entry: A digital impression data set can be supplemented by data on surface colour.
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ISO/DTR 20896-2:2022(E)
Note 2 to entry: A set of digital impression data are distinct from a virtual model as defined in ISO 18739. A
virtual model is produced by design or similar software.
3.2
external reliability
confidence interval for an estimated dimension after eliminating gross errors (3.3) in the data as
detected by the digitizing system's software
Note 1 to entry: External reliability is evaluated by propagation of uncertainties as estimated from the redundancy
(3.7) in an accepted data set, as described in Annex D.
3.3
gross error
error in an observation arising from partial failure or incorrect calibration of a measurement device,
incorrect pattern recognition or data interpretation and leading to unacceptable error of measurement
in the digital impression
Note 1 to entry: Detection and elimination of gross errors is an essential function of the registration software for
a digital impression device.
3.4
intra-oral calibration appliance
extended scan body (3.9) that is scanned together with the mucosa, residual dentition and other scan
bodies and provides internal calibration of digital impression data (3.1)
3.5
position of interest
coordinates of a feature on an implant body that define the placement of the implant body
Note 1 to entry: The feature can be defined by the symmetry of the implant body, for example, its axis. It lies on a
surface of the body that is accessible when placed in a jaw.
3.6
range image
two-dimensional array of data on the distances from the scanning device to the surfaces being scanned
Note 1 to entry: The array indices define direction with respect to the axis of the scanning device for which the
distance applies.
3.7
redundancy
difference between the number of observations judged to be validly measured and the number of
parameters that need to be estimated to calibrate and describe movement of the scanning device and to
produce digital impression data (3.1)
Note 1 to entry: The software of a digitizing device may exploit redundancy to perform an assessment of raw
data in order to detect gross errors (3.3) by statistical testing (see Annex D).
3.8
reference impression data
set of three-dimensional coordinates acquired by a digital impression device or a combination of
scanning device and digitizing device that represent the surfaces to a better precision than that of the
device being assessed
3.9
scan body
implant impression post with a numerically defined geometric shape from which the position and
orientation of an implant body can be determined in a scanning procedure
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ISO/DTR 20896-2:2022(E)
4 Literature review
Intra-oral scanning builds on 170 years of development in photogrammetry. It belongs to the branch
[4]
known as close-range photogrammetry and where it represents very close-range. In the confines of
the mouth, a scanning device requires miniature components with their attendant need for continual
re-calibration in the face of considerable image distortion.
Articles relevant to assessing accuracy in scanning in the oral cavity to produce digital impression data
for existing dentition or an edentulous jaw were searched by the keywords: “intra-oral scanning” and
“accuracy”. Of an initial list totalling 158 articles from the period 2013 to June 2020, sub-lists for those
concentrating on scanning an edentulous jaw (29 articles) and those scanning a full arch with full or
partial dentition (59 articles) were chosen for review. Figure 1 shows the number of articles by year of
publication. Many studies compare digitizing devices from several manufacturers.
Key
edentulous
full-arch
other
Figure 1 — Refereed articles with search keywords “intra-oral scanning” and “accuracy”
The diversity of methods and variety of statistics employed show that consensus on appropriate
methods of benchmarking digital impression devices would benefit both device manufacturers, their
customers and, in some jurisdictions, regulatory authorities.
5 Assessment of ac curacy
5.1 General
5.1.1 Clinical quality
Since digital impression data are the input to the process of designing and manufacturing, a dental
prosthetic appliance, its accuracy, within clinically acceptable tolerances, is a quality factor to be
controlled. When a prosthesis is placed on two or more prepared teeth, a clinical requirement on
uncertainty in separation of critical features is that it be less than approximately 100 µm. When
placing a prosthetic appliance on two or more implant abutments, the requirement on accuracy is more
stringent.
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ISO/DTR 20896-2:2022(E)
5.1.2 Sources of uncertainty
Digital impression devices that rely solely on numerical registration methods to combine a large
number of small range images of three-dimensional surfaces into a large model are subject to
uncertainties. These arise from the registration of overlapping range images where the uncertainty
depends on the number of data elements in the overlap. The uncertainty increases as it is propagated
across a scanned region, leading to large uncertainties in relative positions and orientations derived for
features at the extreme ends of a scanning pattern. For full-arch scanning, the accuracy has been shown
to be unacceptably poor, but techniques are evolving to improve accuracy. It is therefore desirable that
standard methods for comparing techniques and instrumentation be available by providing measures
of interest by which accuracy can be assessed.
5.1.3 Auxiliary methods
Some solutions for reducing uncertainties employ auxiliary methods of measurement or calibration.
These can be both intra- and extra-oral. The auxiliary data are utilized either directly in the registration
of range images or employed in a separate numerical algorithm to correct for distortion in the digital
impression data. In order to be utilized directly, the results or data from auxiliary measurements are
available prior to taking the digital impression data.
5.2 Accuracy
5.2.1 General
Accuracy is a general concept that includes both trueness and precision or reliability. Operational
procedures for estimating trueness, precision and reliability are presented as means for assessing
accuracy.
5.2.2 Trueness
For digital impression data, the operations by which trueness is assessed can be of two types:
a) Direct comparison with independent, calibrated measurements of particular measures of interest:
these measures are distances or angles relative to a reference plane which itself is defined by the
dentition, as in Annex A or by one or more auxiliary devices.
b) Estimation of a goodness-of-fit statistic derived from overall comparison with reference impression
data: this method of assessment frequently disguises serious discrepancies that are of limited
spatial extent. Assessments employing this methodology can require the digital impression data to
fit reference impression data at a clinically relevant, limited, contiguous subset of points at or near
one extreme of the scanning pattern, for example, a scan body, and then determine the quality of fit
of a similar feature (e.g. a second scan body) near the opposite extreme.
Goodness-of-fit statistics expressed in the units of the measures of interest give the user a clearer
basis for comparison than those expressed as in relative terms; i.e. as percentages.
Clinically, trueness is ultimately determined when a prosthetic appliance, which has been designed and
manufactured from the digital impression data, is placed in the patient’s mouth. Quality management
[2]
procedures and systems can build up data records that, on review, allow assessment of trueness of
the digital impressions upon which prosthesis design and manufacturing are based.
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ISO/DTR 20896-2:2022(E)
5.2.3 Precision
By precision is meant that repeated measurements with the digital impression device agree to within a
nominated tolerance regardless of operator, provided the scanning is performed within the guidelines
supplied with the device. Assessments of precision are of two types:
a) Repeated measurements of measures of interest and evaluation of statistics that describe
variability, as described in Part 1, This is a Type A evaluation of uncertainty.
The precision of this determination is expressed as standard uncertainty σ. When the precision
in a value is derived from the standard deviation S of n repeated measurements, the standard
uncertainty is:
σ = S/√n
b) Deduction from knowledge of the design and mode of operation of the scanning device and the
algorithms employed to extract a digital impression from raw data. This is a Type B evaluation of
uncertainty.
5.2.4 External reliability
Determination of reliability (see Annex D) assesses the precision of given digital impression data derived
from a single scanning procedure. It provides a measure of the contribution of errors in observations
to uncertainties in the digital impression data. The determination of reliability exploits the excess over
the minimum necessary number of measurements, or redundancy, in the data acquired in the course of
a single scanning procedure, and employs it either
a) within the scanning and registration algorithm to indicate when adequate data have been acquired
to achieve a given precision, or
b) in post-analysis to detect and eliminate gross errors arising from unpredictable sources and then
to estimate the residual uncertainties.
5.3 Test objects
5.
...
PROJET
RAPPORT ISO/DTR
FINAL
TECHNIQUE 20896-2
ISO/TC 106/SC 9
Médecine bucco-dentaire —
Secrétariat: JISC
Dispositifs d'empreinte numérique —
Début de vote:
2022-09-28
Partie 2:
Vote clos le:
Méthodes d'évaluation de l'exactitude
2022-12-21
de dispositifs implantés
Dentistry — Digital impression devices —
Part 2: Methods for assessing accuracy for implanted devices
LES DESTINATAIRES DU PRÉSENT PROJET SONT
INVITÉS À PRÉSENTER, AVEC LEURS OBSER-
VATIONS, NOTIFICATION DES DROITS DE PRO-
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TATION EXPLICATIVE.
OUTRE LE FAIT D’ÊTRE EXAMINÉS POUR
ÉTABLIR S’ILS SONT ACCEPTABLES À DES FINS
INDUSTRIELLES, TECHNOLOGIQUES ET COM-
Numéro de référence
MERCIALES, AINSI QUE DU POINT DE VUE
ISO/DTR 20896-2:2022(F)
DES UTILISATEURS, LES PROJETS DE NORMES
INTERNATIONALES DOIVENT PARFOIS ÊTRE
CONSIDÉRÉS DU POINT DE VUE DE LEUR POSSI-
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SERVIR DE RÉFÉRENCE DANS LA RÉGLEMENTA-
TION NATIONALE. © ISO 2022
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ISO/DTR 20896-2:2022(F)
PROJET
RAPPORT ISO/DTR
FINAL
TECHNIQUE 20896-2
ISO/TC 106/SC 9
Médecine bucco-dentaire —
Secrétariat: JISC
Dispositifs d'empreinte numérique —
Début de vote:
2022-09-28
Partie 2:
Vote clos le:
Méthodes d'évaluation de l'exactitude
2022-12-21
de dispositifs implantés
Dentistry — Digital impression devices —
Part 2: Methods for assessing accuracy for implanted devices
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TION NATIONALE. © ISO 2022
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ISO/DTR 20896-2:2022(F)
Sommaire Page
Avant-propos .v
Introduction . vi
1 Domaine d’application . 1
2 Références normatives .1
3 Termes et définitions . 1
4 Analyse de la littérature . 3
5 Évaluation de l’exactitude . 4
5.1 Généralités . 4
5.1.1 Qualité clinique . 4
5.1.2 Sources d'incertitude . 4
5.1.3 Méthodes supplémentaires . 4
5.2 Exactitude . 4
5.2.1 Généralités . 4
5.2.2 Justesse . 4
5.2.3 Fidélité . 5
5.2.4 Fiabilité . 5
5.3 Objets d’essai . 5
5.3.1 Généralités . 5
5.3.2 Implant unique . 6
5.3.3 Implants multiples . 6
5.4 Mesurage de référence d’objets d’essai . 6
5.4.1 Dimensions d’intérêt étalonnées . 6
5.4.2 Dispositif de scannage indépendant . 6
5.5 Dispositifs supplémentaires . 6
5.5.1 Généralités . 6
5.5.2 Mesurage à l’aide d’un pied à coulisse . 6
5.5.3 Photogrammétrie extrabuccale . 7
6 Méthodes d’évaluation de l’exactitude . 7
6.1 Dimensions d’intérêt . 7
6.1.1 Généralités . 7
6.1.2 Position d’intérêt . 7
6.2 Évaluation de l’exactitude . . 7
6.2.1 Implant unique . 7
6.2.2 Implants multiples . 7
6.3 Évaluation de la fidélité . 8
6.3.1 Modes opératoires de scannage répétés . 8
6.3.2 Analyse de la conception . 8
6.4 Expression de l’exactitude . 8
6.5 Évaluation de la fiabilité . 9
7 Rapport d’essai . 9
7.1 Généralités . 9
7.2 Dispositif . 9
7.3 Objet d’essai . 10
7.4 Méthode d’essai . 10
7.5 Résultats d'essai . 10
7.6 Données d’essai . 11
Annexe A (informative) Transferts numériques pour l’évaluation de l’exactitude .12
Annexe B (informative) Objet d’essai — Implant unique .14
Annexe C (informative) Objet d’essai — Implants multiples.17
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ISO/DTR 20896-2:2022(F)
Annexe D (informative) Recommandations relatives à l’évaluation de la fidélité et de
la fiabilité .19
Bibliographie .23
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ISO/DTR 20896-2:2022(F)
Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes
nationaux de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est
en général confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude
a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,
gouvernementales et non gouvernementales, en liaison avec l’ISO participent également aux travaux.
L’ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui
concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier de prendre note des différents
critères d'approbation requis pour les différents types de documents ISO. Le présent document
a été rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2
(voir www.iso.org/directives).
L’attention est appelée sur le fait que certains des éléments du présent document peuvent faire l’objet de
droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable
de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant
les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de
l’élaboration du document sont indiqués dans l’Introduction et/ou dans la liste des déclarations de
brevets rédigées par l’ISO (voir www.iso.org/brevets).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données
pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un
engagement.
Pour une explication de la nature volontaire des normes, de la signification des termes et expressions
spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute autre information au sujet de
l’adhésion de l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les
obstacles techniques au commerce (OTC), voir le lien suivant: www.iso.org/iso/fr/avant-propos.html.
Le présent document a été élaboré par le comité technique CEN/TC 106, Médecine bucco-dentaire,
sous-comité SC 9, Systèmes dentaires de CFAO, en collaboration avec le comité technique ISO/TC 55,
Médecine bucco-dentaire, du Comité européen de normalisation (CEN), conformément à l’Accord de
coopération technique entre l’ISO et le CEN (Accord de Vienne).
Une liste de toutes les parties de la série ISO 20896 se trouve sur le site web de l’ISO.
Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent
document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes
se trouve à l’adresse www.iso.org/fr/members.html.
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ISO/DTR 20896-2:2022(F)
Introduction
Les systèmes dentaires de CFAO qui produisent des restaurations dentaires indirectes nécessitent une
description numérisée tridimensionnelle, souvent appelée empreinte numérique, de la dentition d’un
patient comme point de départ pour la conception et la fabrication d’inlays, de couronnes, de bridges
et de plus gros appareils prothétiques ou orthodontiques. Le dispositif qui collecte et numérise les
données métrologiques tridimensionnelles doit être suffisamment exact pour permettre la fabrication
d’une restauration cliniquement acceptable.
Le présent document décrit des méthodes d’essai pour évaluer l’exactitude des dispositifs d’empreinte
numérique conçus pour le scannage buccal direct d’implants dentaires, destinés à servir de support
pour les appareils prothétiques pour remplacer la dentition d’un patient, afin d’obtenir une empreinte
numérique. Il vient compléter l’ISO 20896-1, qui évalue l’exactitude des dispositifs d’empreinte
numérique à partir desquels une empreinte numérique de la dentition d’un patient peut être créée.
Une norme connexe, l’ISO 12836, fournit des méthodes d’essai destinées à évaluer l’exactitude des
dispositifs fixes pour numériser des empreintes physiques ou des modèles/moules fabriqués à partir de
ces empreintes. Des normes distinctes se sont avérées nécessaires dès lors que deux des objets d’essai
décrits dans l’ISO 12836 se sont révélés inaptes pour interpréter correctement les données collectées
avec un dispositif d’empreinte numérique
L'évaluation de l’exactitude des dispositifs d’empreinte numérique pour un objet d’essai de type arc
complet tel que décrit dans la Partie 1 ou des essais similaires ont révélé que les dispositifs d’empreinte
numérique intrabuccaux sont intrinsèquement limités en termes d’exactitude pour prendre des
empreintes de seulement quelques dents. De plus, l’expérience et les expérimentations avec ces
dispositifs pour créer une empreinte numérique après le placement d’implants unitaires, indiquent
qu’un transfert numérique fixé à un implant dentaire offre une exactitude de position et d’orientation
au moins équivalente à celle d’une préparation dentaire. Toutefois, les implants sont également un
traitement indiqué pour les patients totalement ou partiellement édentés. Pour ces indications,
plusieurs implants dentaires sont placés dans la mâchoire inférieure ou supérieure. La technologie de
scannage progresse rapidement, dans l'objectif d’éliminer les inexactitudes qui se produisent lors du
scannage d'un patient édenté. Un obstacle au développement d’une méthode pertinente d'évaluation de
l’exactitude pour ce cas clinique est l’absence de matériau mécaniquement stable pouvant représenter
adéquatement le tissu muqueux d’un objet d’essai.
Le présent document examine la théorie et les techniques utilisées pour exploiter les transferts
numériques afin de résoudre les problèmes liés au scannage du tissu muqueux de patients édentés par
des méthodes optiques.
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RAPPORT TECHNIQUE ISO/DTR 20896-2:2022(F)
Médecine bucco-dentaire — Dispositifs d'empreinte
numérique —
Partie 2:
Méthodes d'évaluation de l'exactitude de dispositifs
implantés
1 Domaine d’application
Le présent document décrit des méthodes de collecte et d’analyse des données à partir desquelles
l’exactitude d'un modèle numérique de la géométrie de la muqueuse et des implants dentaires dans la
mâchoire d'un patient peut être évaluée.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu’ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références datées, seule l’édition citée s’applique.
Pour les références non datées, la dernière édition du document de référence s'applique (y compris les
éventuels amendements).
ISO 1942, Médecine bucco-dentaire — Vocabulaire
ISO 3534-1, Statistique — Vocabulaire et symboles — Partie 1: Termes statistiques généraux et termes
utilisés en calcul des probabilités
ISO 5725-1, Exactitude (justesse et fidélité) des résultats et méthodes de mesure — Partie 1: Principes
généraux et définitions
ISO 16443:2014, Médecine bucco-dentaire — Vocabulaire des systèmes d'implants dentaires et procédures
associées
ISO 18739, Médecine bucco-dentaire — Vocabulaire de la chaîne de procédé applicable aux systèmes de
CFAO
ISO 20896-1, Médecine bucco-dentaire — Dispositifs d'empreinte numérique — Partie 1: Méthodes
d'évaluation de l'exactitude
Guide ISO/IEC 983:2008, Incertitude de mesure — Partie 3: Guide pour l’expression de l’incertitude de
mesure (GUM: 1995)
Guide ISO/IEC 99, Vocabulaire international de métrologie — Concepts fondamentaux et généraux et
termes associés (VIM)
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions donnés dans l’ISO 1942, l’ISO 3534-1,
l’ISO 5725-1, l’ISO 16443, l’ISO 18739, l’ISO 20896-1, le Guide ISO/IEC 98-3, le Guide ISO/IEC 99, ainsi
que les suivants s’appliquent.
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en
normalisation, consultables aux adresses suivantes:
— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp
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ISO/DTR 20896-2:2022(F)
— IEC Electropedia: disponible à l’adresse https:// www .electropedia .org/
3.1
données d’empreinte numérique
ensemble de coordonnées numériques fournissant une représentation tridimensionnelle des surfaces
des dents et du tissu voisin, collectées directement à partir du patient par un dispositif d’empreinte
numérique et présentées dans un format adapté à un processus de conception et de fabrication assistées
par ordinateur (CFAO)
Note 1 à l'article: Un jeu de données d’empreinte numérique peut être complété par des données sur la couleur de
la surface.
Note 2 à l'article: Un ensemble de données d’empreinte numérique est différent d’un modèle virtuel tel que défini
dans l’ISO 18739. Un modèle virtuel est produit par un logiciel de conception ou par un logiciel similaire.
3.2
fiabilité
intervalle de confiance relatif à une dimension estimée après élimination des erreurs manifestes (3.3)
dans les données telles que détectées par le logiciel du système de numérisation
Note 1 à l'article: La fiabilité est évaluée par la propagation des incertitudes estimée d’après la redondance (3.7)
dans un jeu de données accepté, tel que décrit à l’Annexe D.
3.3
erreur manifeste
erreur dans une observation résultant de la défaillance partielle ou de l’étalonnage incorrect d’un
dispositif de mesure, de la reconnaissance incorrecte du modèle ou de l’interprétation incorrecte des
données, et produisant une erreur de mesure inacceptable dans l’empreinte numérique
Note 1 à l'article: La détection et l’élimination des erreurs manifestes sont des fonctions essentielles du logiciel
d’enregistrement d’un dispositif d’empreinte numérique.
3.4
dispositif d'étalonnage intrabuccal
transfert numérique (3.9) déployé, qui est balayé en même temps que la muqueuse, la dentition résiduelle
et d’autres transferts numériques, et qui permet l’étalonnage interne des données d’empreinte numérique
(3.1)
3.5
position d’intérêt
coordonnées d’une caractéristique sur un implant dentaire qui définit le placement de l’implant dentaire
Note 1 à l'article: La caractéristique peut être définie par la symétrie de l’implant dentaire, son axe par exemple.
Elle repose sur une surface de l’implant qui est accessible lorsqu’elle est placée dans une mâchoire.
3.6
image télémétrique
ensemble de données bidimensionnelles sur les distances entre le dispositif de scannage et les surfaces
en cours de scannage
Note 1 à l'article: Les indices de l’ensemble définissent la direction par rapport à l’axe du dispositif de scannage
pour lequel la distance s’applique.
3.7
redondance
différence entre le nombre d’observations jugées mesurées de façon valable et le nombre de paramètres
qui doivent être estimés pour étalonner et décrire le mouvement du dispositif de scannage et pour
produire des données d’empreinte numérique (3.1)
Note 1 à l'article: Le logiciel d'un dispositif de numérisation peut exploiter la redondance pour effectuer une
évaluation des données brutes afin de détecter les erreurs manifestes (3.3) par des essais statistiques (voir
Annexe D).
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ISO/DTR 20896-2:2022(F)
3.8
données d’empreinte de référence
ensemble de coordonnées tridimensionnelles collectées par un dispositif d’empreinte numérique ou
par une combinaison d’un dispositif de scannage et d’un dispositif de numérisation qui représentent les
surfaces avec une plus grande précision que celle obtenue avec le dispositif en cours d'évaluation
3.9
transfert numérique
pilier pour empreinte d’implant ayant une forme géométrique numériquement définie à partir de
laquelle la position et l’orientation d'un implant dentaire peuvent être déterminées lors d’un mode
opératoire de scannage
4 Analyse de la littérature
Le scannage intrabuccal repose sur 170 années de développement en photogrammétrie. Il appartient au
[4]
domaine connu sous le nom de photogrammétrie rapprochée . À l’intérieur de la bouche, un dispositif
de scannage a besoin de composants miniatures qui nécessitent un réétalonnage permanent du fait de
l’importante distorsion d’image.
Les articles traitant de l’évaluation de l’exactitude lors du scannage dans la cavité buccale pour produire
des données d’impression numérique pour la dentition existante ou une mâchoire édentée ont été
consultés à l’aide des mots-clés suivants: «scannage intrabuccal» et «exactitude». Dans la liste initiale
totalisant 158 articles de la période allant de 2013 à juin 2020, des sous-listes d’articles concernant le
scannage d’une mâchoire édentée (29 articles) et d’articles concernant un arc complet avec dentition
complète ou partielle (59 articles) ont été choisis pour être consultés. La Figure 1 illustre le nombre
d’articles par année de publication. De nombreuses études comparent les dispositifs de numérisation de
plusieurs fabricants.
Légende
mâchoire édentée
arc complet
autre
Figure 1 — Articles consultés à l’aide des mots-clés «intrabuccal» et «exactitude»
La diversité des méthodes et des statistiques utilisées montre qu’un consensus sur des méthodes
appropriées d'évaluation des dispositifs d’empreinte numérique serait utile pour les fabricants de
dispositifs, leurs clients et, dans certains pays, les autorités réglementaires.
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ISO/DTR 20896-2:2022(F)
5 Évaluation de l’exactitude
5.1 Généralités
5.1.1 Qualité clinique
Étant donné que les données d’empreinte numérique sont nécessaires au processus de conception et
de fabrication, une prothèse dentaire est un facteur de qualité à contrôler (ainsi que son exactitude
dans les limites de tolérance cliniquement acceptables). Lorsqu’une prothèse est placée sur deux dents
préparées ou plus, une exigence clinique concernant l’incertitude d’espacement des caractéristiques
critiques est que l’espacement doit être inférieur à 100 µm. Lorsqu’une prothèse est placée sur deux
piliers implantaires ou plus, l’exigence concernant l’exactitude est plus contraignante.
5.1.2 Sources d'incertitude
Les dispositifs d’empreinte numérique qui reposent uniquement sur des méthodes d’enregistrement
numérique pour combiner un grand nombre de petites images télémétriques de surfaces
tridimensionnelles en un grand modèle sont sujets à des incertitudes. Ces incertitudes sont dues à
l’enregistrement d’images télémétriques qui se chevauchent, l’incertitude étant fonction du nombre
d’éléments de données dans le chevauchement. L’incertitude augmente à mesure qu’elle se propage dans
une région balayée, ce qui produit d’importantes incertitudes au niveau des positions et orientations
relatives obtenues pour les caractéristiques aux extrémités d’un diagramme de scannage. Pour le
scannage d'un arc complet, l’exactitude s’est avérée trop faible, mais les techniques d’amélioration de
l’exactitude progressent. Il est donc souhaitable de disposer de méthodes normalisées pour comparer
les techniques et les instruments en fournissant des dimensions d’intérêt qui permettent d'évaluer
l’exactitude.
5.1.3 Méthodes supplémentaires
Certaines solutions de réduction des incertitudes utilisent des méthodes supplémentaires de mesure ou
d'étalonnage. Ces méthodes peuvent être intrabuccales et extrabuccales. Les données supplémentaires
sont utilisées soit directement lors de l’enregistrement d’images télémétriques soit dans un algorithme
numérique distinct pour corriger la distorsion dans les données d’empreinte numérique. Pour être
utilisés directement, les résultats ou les données des mesurages supplémentaires sont disponibles
avant d’obtenir les données d’empreinte numérique.
5.2 Exactitude
5.2.1 Généralités
L’exactitude est un concept général qui inclut la justesse et la fidélité ou fiabilité. Les processus
opérationnels qui permettent d’estimer la justesse, la fidélité et la fiabilité sont présentés comme des
moyens d'évaluation de l’exactitude.
5.2.2 Justesse
Pour les données d’empreinte numérique, il existe deux types d’opérations d'évaluation de la justesse:
a) Comparaison directe avec les mesurages étalonnés indépendants des dimensions d’intérêt
particulières: ces mesures sont les distances ou les angles par rapport à un plan de référence
qui est lui-même défini par la dentition, comme à l’Annexe A
...
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