Article_5_2_5

                   COMPUTERIZED DENTAL PROSTHETICS
                   INTRAORAL SCANS FOR CAD/CAM APPLICATION
Original Article
                   Judit Borbély1a*, Alexandra Czigola1b, Viktoria Vitai1b, Ivett Róth1b, Péter Hermann1c
                   1
                       Department of Prosthodontics, Faculty of Dentistry, Semmelweis University, H-1088 Budapest, Hungary

                   a
                     DMD, PhD, Associate Professor
                   b
                     DMD, Resident of Department of Prosthodontics
                   c
                    DMD, MSc, PhD, Professor and Head of Department of Prosthodontics, Vice-Rector for Education Affairs of Semmelweis Univeristy, Budapest, Hungary


                   ABSTRACT                                                   DOI: 10.25241/stomaeduj.2018.5(2).art.5
                                                                                                                                                    OPEN ACCESS This is an
                   Introduction: There is no doubt the world of dentistry is rapidly changing. Digital innovations                                  Open Access article under the CC
                   are replacing our traditional techniques. Dentists need to keep up with the speed of today's                                     BY-NC 4.0 license.

                   ever changing digital world.                                                                                                     Peer-Reviewed Article

                   The aim of the paper is to educate about the concept of digital dentistry, its advantages                                     Citation: Borbély J, Czigola A, Vitai V,
                   and limitations, and to provide an overview of digital impression taking procedures and the                                   Róth I, Hermann P. Intraoral scans for
                                                                                                                                                 CAD/CAM application. Stoma Edu J.
                   digital workflow for CAD/CAM application.                                                                                     2018;5(2):110-117.
                   Materials and methods: The Department of Prosthodontics, Faculty of Dentistry,                                                Academic Editor: Gerwin V.
                   Semmelweis University (SU) published a series of articles in Hungarian dental paper as part of                                Arnetzl, DMD, Arnetzl Dental Compe-
                                                                                                                                                 tence, A-8041 Graz, Austria
                   the continuing education program to educate Hungarian dentists at the postgraduate level.
                   Digital technologies and their novel materials are also introduced into the SU undergraduate                                  Received: May 15, 2018
                                                                                                                                                 Revised: May 24, 2018
                   dental curricula. A Bachelor of Science (BSc) digital dental designer training program is                                     Acccepted: June 06, 2018
                   also aimed at the Faculty of Dentistry SU in cooperation with the Neumann University of                                       Published: June 07, 2018

                   Technology and Economics to modernizate the classic profession of dental technician. This                                     *Corresponding author: Assoc.
                   paper gives a summary of the basic knowledge published in digital dentistry series.                                           Professor Judit Borbély, DMD, PhD,
                                                                                                                                                 Department of Prosthodontics, Faculty
                   Results: The CAD/CAM technology offers a quick and comfortable experience to the patients                                     of Dentistry, Semmelweis University
                   and an efficient workflow to the dentist and dental technicians. The learning curve is steep                                  Budapest, Szentkirályi u. 47, H-1088
                                                                                                                                                 Budapest, Hungary Tel/Fax: (36-1)
                   to adopt that new technology both in the dental office and on the laboratory side. Educated                                   4591500 / 59338, e-mail: borbely.
                                                                                                                                                 judit@dent.semmelweis-univ.hu
                   dental students and digital designers have the potential to keep pace with the digital era
                   change.                                                                                                                       Copyright: © 2018 the Editorial
                                                                                                                                                 Council for the Stomatology Edu
                   Keywords: CAD/CAM, scanner, intraoral, workflow, dental impression technics.                                                  Journal.


                   1. Introduction                                                                most appropriate techniques, systems or materials [1].
                   The widespread use of digital technology is to                                 Chatham et al. surveyed the undergraduate curricula
                   transform our everyday life: computers and digital                             of the UK dental schools in 2014 to determine the
                   devices offer an easier, faster and more economical                            degree to which digital dental technologies have been
                   alternative to conventional methods. The digital                               introduced. Sixteen schools were surveyed and 11
                   revolution also has an impact on dental procedures.                            replied. 55% of those schools did teach digital dental
                   It is a fact that dentistry changes and undergoes                              technology, 50% gave lectures or demonstrations
                   dramatic developments. In order to meet the patients’                          while the other 50% allowed practical involvement by
                   requirements, it is important to expand our dental                             the student. Seventy-three percent of the schools that
                   knowledge to digital technologies.                                             replied had dental laboratories using some, but not all
                   Present day dental students grow up in a world of digital                      the digital dental technology techniques [1].
                   innova­tion and technology, so the need to include
                   digital technology in their curriculum is evident for                          1.1. Aim
                   them [1]. However the dental curriculum has not really                         The aim of this paper is basic digital education. To
                   changed in 50 years. It has not been revised. Much has                         discuss the concept of digital dentistry, its advantages
                   been added to what dentists must know, considering                             and limitations, and to provide an overview of digital
                   digital technology, there are all those new technologies,                      impression-taking procedures, to clarify the basic steps
                   new CAD/CAM materials etc. but the curriculum                                  of the digital workflow, to introduce the direct method
                   has not been changed [2]. Most practicing dentists                             of intraoral scanning to construct a virtual cast for CAD/
                   received their professional training before the advent                         CAM application. The purpose of the paper also includes
                   of the digital dental technology. Once they become                             clarifying the difference between chairside and labside
                   interested in the new technologies and in developing                           systems, discuss the features of intraoral impression-
                   new skills they demand continuing education courses.                           taking such as accuracy, the time factor and the patient’s
                   There is a severe need to include digital dentistry                            subjective comfort, to present comparative data on
                   in the undergraduate and postgraduate education                                the precision of digital impressions made by intraoral
                   programs. If digital technologies and their novel                              scanners to laboratory scanning of conventional casts
                   materials are not introduced into the dental curricula                         and to compare the traditional impression-taking
                   dentists and technicians will not fully understand the                         method to the digital one and provide a short summary
                   range of new technologies available to them and will                           on the advantages and difficulties of the scanning
                   not be able to make informed decisions regarding the                           procedure.



 110                                                                              Stoma Edu J. 2018;5(2): 110-117                 http://www.stomaeduj.com
                                                                          INTRAORAL SCANS FOR CAD/CAM APPLICATION




                                                                                                                                                Original Article
2. Material and methods
The Department of Prosthodontics, Faculty of Den-
tistry, Semmelweis University has been working with
digital impression-taking systems since 2011. Digital
technologies and their novel materials have been in-
troduced into the department’s undergraduate dental
curricula. A Bachelor of Science digital dental designer
training program is also aimed at the Faculty of Dentist-
ry SU in cooperation with the Neumann University of
Technology and Economics to modernizate the classic
profession of dental technician. A series of articles has
been published in the Hungarian dental paper in 2017
as part of the continuing education program to edu-
cate Hungarian dentists about digital dentistry. This pa-
per gives a summary of the digital dentistry series.

                                                                   Figure 1. Dental students practice digital impression taking at the De-
3. Results                                                        partment of Prosthodontics of Semmelweis University, Budapest.
In 2018 all four Hungarian dental schools teach digital
technology, they give lectures and demostrations
and 50% have also practical training. All four dental
laboratories of those schools use some digital
techniques (Fig. 1). Dental technology educational
programs are faced with serious challenges, including
rapid changes in technology, inadequate funding
for educational programs, and the need to develop
curricula that reflect current industry needs [3]. The
high cost to purchase equipment and the investment
of time and expense in staff training encourages non-
university educational systems and trainings.
Manufacturers and commercial dental laboratories
offer a selection of continuing education courses for
international dentists. Some courses are accredited
by universities and the participants are awarded
certificates and European Credit Transfer System (ECTS)             Figure 2. Laboratory scanner creates a 3-dimensional set of points by in-
credits [4]. Online knowledge centers and webinars                formation of sectioned cast or impression.
provided by manufacturers offer promising new
opportunity for self-education [5].
Digital technology introduced new nomenclature for
dental procedures: digital workflow, CAD/CAM systems,
indirect CAD/CAM impression technique, direct CAD/
CAM impression technique, digital impressions,
virtual casts, intraoral scanners, close or open systems,
charside or labside systems. These elements are drafted
in italics in the following text.

3.1. Digital workflow
3.1.1. Indirect CAD/CAM method                                      Figure 3. CAM (Computer-Aided Manufacturing) machine milled crowns
The digital workflow starts with a device which is                from zirconia block.
suitable for mapping real forms. Indirect CAD/CAM                 The computer makes the virtual cast that serves as
method is built on conventional impressions. The                  basis for CAD/CAM workflow. During CAD (Computer-
virtual cast is created by digitizing the gypsum cast             Aided Design) the dental technician designs dental
(or the conventional impression) with a laboratory                restorations, most often crowns, veneers, inlays or
scanner [6] (Fig. 2). The virtual cast is a realistic, colorful   onlays and bridges. The CAD software enables the
digital model of the patient’s oral cavity. This method           technician to design the framework of the restorations
has some distorting effects enclosed: conditions of               or the anatomical, final form. Applying CAM (Computer-
impression-taking, material properties of alginate,               Aided Manufacturing) the restorations are milled from
silicone or gypsum (shrinkage of impression material,             solid blocks with dental milling CNC machines (Fig. 3).
dilation or shrinkage of gypsum) and sectioning of                There are different types of materials to mill: ceramics,
casts. Furthermore, the laboratory scanner has some               zirconia, PMMA, metal alloys or titanium.
degree of distortion.
The laboratory scanner creates a 3-dimensional set                3.1.2. Direct CAD/CAM method
of points based on information of the sectioned cast.             The Direct CAD/CAM method means that the digital



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                   INTRAORAL SCANS FOR CAD/CAM APPLICATION



                   data set is created by intraoral scanning. Intraoral
Original Article   scanners are intraoral devices for capturing direct
                   optical impressions [6] (Fig. 4). Intraoral scanners are
                   based on different data capture principles: confocal
                   laser technology, confocal microscopy, triangulation,
                   wavefront sampling, multiscan imaging, stereopho-
                   togrammetic video, accordion fringe interferometry
                   [7,8].
                   It is important that the user takes digital impressions
                   according to the manufacturer’s instructions. This
                   method can eliminate many inaccuracies derived
                   from indirect CAD/CAM impression process. However,
                   the traditional principles of the impression-taking
                   procedure are still alive, soft tissue control and isolation
                   remain basic principles. The scanning process ends
                   with biterecord. There are intraoral scanners which can
                   also determine the tooth-color.
                   The next step following the digital impression-taking
                   procedure is to evaluate the quality of the virtual cast
                   (Fig. 5). Inaccuracies can be eliminated by the dentist
                   directly chairside within this step. The occlusal and axial      Figure 4. Trios intraoral captures optical impressions of the prepared
                   reduction, the insertion direction can be observed on          teeth for the direct CAD/CAM method.
                   the computer screen with built in tools of software.
                   The margin line can also be checked enlarged by the
                   software.
                   Any imperfections of the virtual cast can be corrected
                   without the need to retake the whole impression.
                   Additional images of the areas of interest can be added
                   to previous scan. When satisfied with the impression
                   and resulting virtual cast, it is sent to laboratory with
                   the digital worksheet via e-mail.
                   There are open and closed dental CAD/CAM systems.
                   Closed systems’files can be opened by the manufacturer’s
                   CAD software only. Closed systems are CEREC AC and               Figure 5. Full arch virtual casts in ICP position on computer screen after
                   E4D systems. Most intraoral scanners work with an open         scanning.
                   system and they are compatible with several types
                   of CAD softwers and milling machines (for example
                   3Shape TRIOS, Planmeca PlanScan, CEREC Omnicam,
                   iTero Element, Carestream CS 3500, 3M True Definition,
                   GC Aadva, DWIO Dental Wings, KaVo Lythos, Dentium
                   Rainbow, Zfx IntraScan, MFI Condor IOS, etc) (7).

                   3.2. Direct CAD/CAM workflow
                   3.2.1. Labside system
                   The labside workflow of CAD/CAM technology means
                   The labside workflow of CAD/CAM technology means
                   that the dental technician processes data coming
                   from the dental office. The technician performs the
                   preparatory work on the virtual cast, model occlusion
                   with CAD software and design restoration on the
                   computer screen (Fig. 6).
                   The technician sets the margin line and the space for
                   the cement. After that the framework or the full-contour
                   restoration is designed. The anatomical occlusion surface
                   and contour of the teeth can be made individually. The          Figure 6. Dental technician designs restoration on computer screen with
                   software contains the color of the restoration, so the         CAD software.
                   suitable block is chosen for the milling. Digital planning     the restoration, then data sets are sent for milling to the
                   does not exclude model making. From the digital data           centre. Procera is a well-known example for milling centre.
                   a polimer model can be made by milling, 3D printing or         It is specialised for milling technically sensitive materials
                   with stereolithography (SLA) [9]. The final restoration can    like high strength ceramics and titanium (Figs. 9, 10).
                   be checked on this model (Figs. 7, 8).
                   Another option of the computer-assisted production             3.2.2. Chairside systems
                   is centralised production in a milling centre. In this         We must not forget that initially intraoral scanners were
                   variation, it is possible for the local laboratory to design   developed for chairside solutions (CEREC). The main



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                                                                     INTRAORAL SCANS FOR CAD/CAM APPLICATION



idea was to make restorations without the need for           scanners were evaluated in terms of trueness and




                                                                                                                                          Original Article
dental laboratory. A chairside system means that every       precision (an acrylic model with the embedded
step of the workflow is in the hands of the dentist.         typodont teeth was scanned and datasets were
Digital impressions are taken in the dental office with      superimposed): 3Shape trios, 3M True Definition, iTero,
an intraoral scanner, designing the restoration is done      CS3500, CEREC Omnicam, Planmeca, Planscan [14].
chairside and even the milling and finishing is done in      The accuracy of virtual data gained from intraoral
the office. Its great advantage is that it offers One Day    scanners is influenced by many factors. For example,
Dentistry. Inlays, onlays, solo crowns can be made for       the palatum and toothless areas do not give enough
patients within a few hours. Monoblocks restorations         information to make a useful digital model [15, 16].
are milled with the CAM unit, which need small               Virtual models obtained by digital impressions were
adjustments (staining, polishing, sintering) before          shown to be more accurate than their conventional
cementation.                                                 counterparts when Polyvinyl-siloxane impressions and
The main difference between those restorations milled        digital impressions with three intraoral scanners (iTero,
by labside and chairside systems are the extension and        Figure 7. Polymer model made by 3D printing from digital data.
the materials used. Chairside systems are made for solo
restorations as mentioned before (veneers, crowns,
inlays, onlays, small full contours), and temporaries.
Labside milling in the dental laboratory or in the milling
centres offers you more options due to the precision
of 5-axis milling and high-strength materials, labside
offers extended prosthetic appliances.

                                                              Figure 8. Polymer models are printed with pins holding the ICP position
4. Discussion                                                and mounted on an adjustable articulator for veneering.
4.1. Features of taking digital impressions - accuracy,
time factor, patient’s comfort
There are numerous factors that can easily describe
the clinical use of the digital impression procedure. The
investigation of some of these factors can be measured
objectively, for example accuracy and scanning time.
This is a well-researched area in literature. Other
features of intraoral scanners can be described with
subjective parameters for example patient’s comfort
and dentist’s satisfaction.

4.1.1. Accuracy of digital impressions
The fit of the final restoration depends on the quality of
the impression, therefore accuracy of intraoral scanners       Figure 9. CAM/Computer Assisted Manufacturing: Blocks for zirconium-
                                                             dioxide frameworks, lithium disilicate monolithic restorations and PMMA
is one of the most important features. Accuracy consists
                                                             temporary restorations.
of trueness and precision. Trueness describes how close
our data are to the original true value. Precision shows
the relative deviation of the repeated measurements
[10] (Fig. 11).
In a blind study, crowns developed using intraoral
scanning technology were preferred over crowns
generated using conventional impressions and
criteria of marginal fit, contacts, occlusion, and
time of adjustment in nearly 70% of cases [11].
It was found that digital quadrant impression methods
achieve a level of precision, comparable to the
conventional impression techniques (precision ranged
from 18.8 to 58.5 μm). However, there are significant
differences in terms of absolute values and deviation
pattern [12].
The direct digitalisation with Lava C.O.S. showed
statistically significantly higher accuracy compared to
the conventional procedure of impression-taking and
indirect digitalisation when datasets were generated
and superimposed by a best fit algorithm. It could
be shown that direct digitalisation accomplished the
most accurate results, followed by digitized polyether         Figure 10. PMMA block manufactured in Roland DG DWX-50 milling
impression, and indirect digitalisation [13].                machine. Advantage of PMMA temporary restorations fabricated by CAD/
According to a study in 2015 the following scanners          CAM technology is that they last long. Polymer’s resistancy is much better
were found acceptable in clinical practice when              than temporary materials used for conventional chairside technique.




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                   INTRAORAL SCANS FOR CAD/CAM APPLICATION



                   CEREC, TRIOS) were made from a PMMA model for
Original Article   comparison [17] (Fig. 12).

                   4.1.2. Time efficiency (factor) of digital impressions
                   We have found numerous studies comparing the
                   time needed for digital and conventional impression-
                   taking techniques. When investigating the whole
                   treatment time an average of 260 s is needed for a
                   digital impression and 620 s for a conventional one.
                   Bite registration with intraoral scanner took five times
                   less than with the conventional technique [18].
                   Although scanning time extends when there are                   Figure 11. Fit of the final restoration depends on the quality of the im-
                   abutment teeth in the arch. Scanning 1 abutment is 23         pression. Accuracy consists of trueness and precision. Trueness shows how
                   minutes, 2 abutments 22 minutes and the whole arch is         close is our data to the original true value. Precision shows the relative de-
                   13 minutes faster than conventional impression-taking.        viation of repeated measurements.
                   As the number of prepared teeth increases, the time of
                   the intraoral scanning gets closer to the conventional
                   impression-taking time. In these studies participants had
                   experience in taking conventional impressions [19].
                   In Lee and Galucci’s study dental students had no
                   previous experience on taking impressions. Intraoral
                   scanning took half the time of the conventional
                   technique. Consequently, the study shows that without
                   experience intraoral scanning is still a time saving
                   technique. It seems that digital technology reduces
                   patients’ time spent in the dental office [20].

                   4.1.3. Evaluation of the digital impression-taking
                   procedure based on the dentist’s and the patient's
                   subjective comfort
                   In 2016 Joda et al. investigated digital and conventional
                   implant impression procedures. They found the
                   usability and the efficiency of intraoral scanners more
                   favourable by students (88%) and dentists (64%)
                   compared to conventional methods [21].
                                                                                   Figure 12. Less time is needed for a full arch intraoral scan compared to
                   According the previous studies patients prefer digital        the conventional impression taking procedure.
                   impressions to conventional ones. During conventional
                   impressions patients reported breathing difficulties
                   and they felt vulnerable, especially when upper
                   impressions were taken. They were afraid of repeating
                   conventional impressions rather than repeating digital
                   ones [22].
                   Overall both dentists and the patients found it less
                   stressful when impressions were taken digitally.

                   4.2. Intraoral scanning possibilities; advantages and
                   difficulties
                   In the next session we would like to introduce the             Figure 13. Scan bodies are used for implant scanning, they provide the
                                                                                 necessary information for designing the prosthetic appliance.
                   features of the new technology, which can be a benefit
                   or an initial difficulty when we use an intraoral scanner     CAD software in order to plan the digital prosthetic
                   [23].                                                         appliance. Manufacturers have already faced the need
                                                                                 to start production of hybrid scan bodies, which are
                   4.2.1. Difficulties of intraoral scanning                     compatible with different systems.
                   Learning the process of intraoral scanning is not an          If we are not properly informed about the scanners’
                   easy task, it is important to follow the instructions given   features prior to the purchase, it may be an
                   by the manufacturers. Digital impression taking is very       unpleasant surprise that some companies charge a
                   different from conventional impression procedure.             data management fee. In such a case, after scanning
                   During scanning as the scanner-head goes above the            the data, it is entered into the cloud operated by
                   surface of the tooth the software adds new data to the        the company, from which it can only be sent to the
                   images that have already been taken. The inappropriate        laboratory after payment of the fee. However, most
                   use leads to insufficient or inaccurate virtual model.        manufacturers provide an open system, which allows
                   For implant scanning scan bodies are used, which are          to export the STL files for free.
                   supported by the manufacturers (Fig. 13).                     Limitation of intraoral scanners is that they are very
                   These scan bodies should be compatible with the               expensive, however the cost of equipment is expected



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                                                                                        INTRAORAL SCANS FOR CAD/CAM APPLICATION




                                                                                                                                                              Original Article
  Figure 14. When digital impression taken, the virtual model is appearing      Figure 15. Scanned image can be displayed on computer screen and si-
continuously on computer screen. Additional scans are integrated to the        multaneously on dental laboratory devices. It helps communication be-
incomplete (white) areas.                                                      tween lab and dental office.




 Figure 16. Built in software features of intraoral scanners (such as occlusal analysis) make dentists’work lot easier. Some scanners determine tooth shade
and are equipped with intraoral cameras, thus expanding the possibilities of communication between dental lab and dentists.
to decrease in the future as the cost of production of
scanners is declining.

4.2.2. Advantages of intraoral scanning
One great advantage is that the virtual model can be
evaluated immediately chairside on the computer
screen and the preparation can be modified if needed
(Fig.14).
Built-in features of the software help to find not properly
scanned surfaces and scan the approximal areas. The
software provides data on adequate material thickness
corresponding to the type of the dental appliance. The                            Figure 17. Digital impressions save the original form and shape of pa-
virtual model can be modified easy and quick, there is                         tient’s teeth. The data can be stored for years and help planning of dental
no need to rescan the whole arch.                                              treatment later.
Scanning is more time-efficient than conventional                              initial status and treatment scans. The final aim is the
impression-taking. No time needed for mixing, setting,                         evaluation of long term changes in the dental status,
disinfection or casting.                                                       such as dental migration, rotation, gingiva recession,
In addition, digital impression taking is an environment-                      abrasions etc. [7, 24] (Fig. 17).
friendly procedure, as it eliminates the large amount                          Data of intraoral scanning can be fused with data of
of hazardous waste generated by conventional                                   other 3 dimensional methods, such as CT and CBCT.
impressions in dental practices. Ease of documentation                         This option opens up completely new perspectives
is an important advantage. Digital models never wipe,                          for diagnosis, treatment plan, and planning of dental
break, wear out. Patient documentation can be stored                           surgeries, already used in orthodontics and dental
digitally on a hard disk or in the cloud and can be                            implantation. Modern undergraduate educational
recalled at any time. (Fig. 15)                                                programs in implant dentistry (including digital
Intraoral scanners have additional functions such as                           prosthetic treatment) can provide proffessional care
color display and intraoral camera. These functions                            and a high treatment quality for the patients [25].
also help patient communication as they make the
lesions visible. Some scanners are able to determine
tooth shade and forward that information to the dental                         5. Conclusions
laboratory (Fig. 16).                                                          Digital dentistry is here to stay and it offers quick and
The scanned data are also an excellent tool for                                comfortable experience to the patients and an efficient
treatment follow up and to evaluate the patients’ dental                       workflow to the dentist and dental technicians. The
status. At the University of Zurich, Zimmermann et al.                         learning curve is steep to adopt that new technology
created a digital database, which records the patient’s                        both in the dental office and on the laboratory side.



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                   To have the potential to keep pace with the digital                             12.   Ender A, Zimmermann M, Attin T, et al. In vivo precision of
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                                                                                                                          Judit BORBÉLY
                                                                                                         DMD, PhD, Associate Professor
                                                                                    Department of Prosthodontics, Faculty of Dentistry
                                                                                                     Semmelweis University Budapest
                                                                                         Szentkirályi u. 47, H-1088 Budapest, Hungary


                   CV
                   Doctor Borbély is an Associate Professor at the Department of Prosthodontics, Semmelweis University, Budapest, Hungary.
                   She graduated from the Dental Faculty of Semmelweis University of Medicine, Budapest, Hungary in 2001, then she began
                   to specialize in prosthodontics. She received her PhD degree in 2008 on visual and digital methods for tooth shade selection.
                   She also works in private practice focusing on prosthodontics and aesthetic dentistry. Since 2011 she has been working with
                   digital impressioning systems. She conducts ongoing clinical research in digital prosthodontics and materials research. She
                   presents lectures, hands-on clinical and postgraduate courses on ceramics, tooth shade selection and intraoral scanning. She
                   is a presidential member of the Hungarian Prosthodontic Association and Hungarian Dental Association, she is a member of
                   Society for Color and Appearance in Dentistry and Hungarian Academy of Esthetic Dentistry.




 116                                                                               Stoma Edu J. 2018;5(2): 110-117                   http://www.stomaeduj.com
                                                          INTRAORAL SCANS FOR CAD/CAM APPLICATION




Questions




                                                                                                    Original Article
1. Intraoral scanners cannot be based on:
qa. Confocal laser technology;
qb. Confocal microscopy;
qc. Triangulation;
qd. Scanning probe microscopy.

2. It is not true for open CAD/CAM systems:
qa. Files can be opened by the manufacturer’s CAD software only;
qb. For example 3Shape Trios and Planmeca Planscan;
qc. It is compatible with several types of CAD softwares;
qd. It is compatible with several types of milling machines.

3. What does accuracy consist of?
qa. Trueness and deviation;
qb. Precision and deviation;
qc. Trueness and precision;
qd. Quality and quantity.

4. Which material cannot be milled by dental CNC machines?
qa. PMMA;
qb. Ceramic;
qc. Titanium;
qd. Gold.




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