Medical

Communication

Biosci. Biotech. Res. Comm. 10(4): 790-796 (2017)

Dimentional accuracy of intraoral and laboratory

scanners: A literature review

Iman Sha ei

, Mehran Bahrami

and Saied Nokar

Prosthetic Department, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran

Assistant Professor, Dental Research Center, Department of Prosthodontics, School of Dentistry, Tehran

University of Medical Sciences, North Amirabad Ave, Tehran, Iran

Associate Professor, Department of Prosthodontics, Dental Research Center, Tehran University of Medical

Sciences, Tehran, Iran

ABSTRACT

Restoration of dental implants remains one of the most challenging aspects of implant dentistry. Although it is

not clear whether prosthetic mis t could affect osseointegration, mechanical complications of implant-supported

prostheses can be avoided by achieving a good passive  t between the framework and the implants. Passive  t is a

dif cult concept to de ne. Obtaining absolute passive  t of the prosthetic framework on implants has been reported

to be nearly impossible. Dimentional accuracy of intraoral and laboratory scanners play deniable role on producing

desirable restorations. So, the aim of the current research was to determine dimentional accuracy of intraoral and

laboratory scanners using the PubMed and Medline database English literature by the terms “Dimentional accuracy”,

“Intraoral”, Laboratory scanners”.

KEY WORDS: DIMENTIONAL ACCURACY, INTRAORAL SCANNERS, LABORATORY SCANNERS, DIGITAL IMPRESSION, TRUNESS, PRECISION,

CAD CAM PROSTHODONTICS

790

ARTICLE INFORMATION:

*Corresponding Author: snir2500@yahoo.com

Received 30

Sep, 2017

Accepted after revision 1

Dec, 2017

BBRC Print ISSN: 0974-6455

Online ISSN: 2321-4007 CODEN: USA BBRCBA

Thomson Reuters ISI ESC and Crossref Indexed Journal

NAAS Journal Score 2017: 4.31 Cosmos IF: 4.006

reserved.

Online Contents Available at:

http//www.bbrc.in/

DOI: 10.21786/bbrc/10.4/26

INTRODUCTION

Technique of computer aided design and computer aided

manufacturing (CAD/CAM) is used to produce ceramic

restorations such as all-ceramic crowns and  xed dental

prostheses since decades ago (Su et al. 2015). Numer-

ous CAD/CAM systems are capable of designing and

fabricating prostheses on plaster cast made from con-

ventional silicone impressions (Mo¨rmann, 2006). Non-

standard operation during impression taking and defor-

mation of clinical material will affect the accuracy of

plaster model, consequently affecting the accuracy of

three-dimensionalmodels (3D) model data and prosthe-

ses quality (Stimmelmayr et al. 2012). So, it is desirable

Iman Sha ei et al.

to develop a facility which can take digital impressions

directly from oral cavity to eliminate error and also

economize on impression materials used in conventional

impression procedures. The primery digital intraoral

impression system commercially available was CEREC 1

system (Rekow, 2006). Laboratory digitizing starts with

a conventional impression that is poured, and the leads

model is digitized, using one of numerous optical or

mechanical systems (Beuer et al. 2004). Also, some sys-

tems offer the possibility to scan the impression directly

without cast fabrication (Güth et al. 2013).

In addition, discomfort for the patient like sweat-

ing, gagging, pain and partially inconvenient taste is

a known issue associated with conventional impression

taking. In these situations, this instability and discom-

fort factor might be avoided by direct data capturing,

which represents a logical direct access to dental CAD/

CAM (Steinhäuser-Andresen et al. 2011). To date few

published literature exists on the performance of digital

intraoral impression system, especially concerning the

accuracy and precision of intraoral scanners. So, the aim

of the current research was to determine dimentional

accuracy of intraoral and laboratory scanners.

MATERIAL AND METHODS

The keywords used for the literature search for this

review was peer-reviewed articles following key-words:

Dimentional accuracy × Intraoral scanners and Labo-

ratory scanners. Among them, the papers were  t the

criteria selected and available full-text articles read.

Related articles were also scrutinized. Hand search was

also driven. The search was carried out using Biological

Abstracts, Chemical Abstracts, and the data bank of the

PubMed and Medline database updated to 2017. The ref-

erences found in the search were then studied in detail.

HISTORY OF DIGITAL SYSTEMS IN DENTISTRY

To achieve a correct adaptation between the prosthe-

sis and the implants, the  rst step is to obtain a highly

accurate impression. Many clinical factors affect the

accuracy of the impressions, such as tray type, impres-

sion technique, impression material used and its particu-

lar hydrophobic or hydrophilic characteristics, mixing

methods and impression disinfection. Impressions can

be made at either the implant level or the abutment level

(Giménez et al. 2015). Computer-aided design/computer

aided manufacturing (CAD/CAM) systems have evolved

over the last two decades and have been used by dental

health professionals for over twenty years (Duret et al.

1998). Francois Duret introduced CAD/CAM in restora-

tive dentistry (Priest, 2005). One of the main lines of

implementation was the intraoperative use for dental

restoration using prefabricated ceramic monoblocks

(Mörmann, 2004). Dental CAD/CAM’s evolution over

the past30 years has centered on the chairside market,

beginning with CEREC® (Sirona). This is in part because

the appeal of the CAD/CAM concept is that it offers

dental professionals and their patients the convenience

of same-day dentistry (Davidowitz and Kotick, 2011).

A further development in CAD/CAM technology is the

transition from closed  le format to open access  le

systems, which opens up access to a much wider range

of manufacturing technology such that the most appro-

priate manufacturing processes and associated materials

can be selected (van Noort, 2012).

The CAD/CAM systems have been used mostly for

the manufacturing of prosthetic  xed restorations, such

as inlays, onlays, veneers and crowns. During the last

decade technological developments in these systems

have provided alternative restorations using differ-

ent materials such as porcelain, composite resin and

metallic blocks, which could not be prosecuted previ-

ously because of technical limitations. To date several

optical impression systems have been developed with

which direct impressions could be made in the oral cav-

ity including Cerec AC (Sirona, Behnheim), Lava Chair-

side Oral Scanner (Lava COS, 3 M ESPE), E4D Dentist

(D4D Technologies, LLC) and iTero (Cadent, Carlstadt)

(Giménez et al. 2015). Despite numerous advantages

introduced for dental implants, several challenges, since

excellent accuracy is a prerequisite to achieve proper  t

of the subsequent prosthesis (Giménez et al. 2014). There

is scarce information on the accuracy of intraoral digi-

tal impression systems for dental implants including the

implant-related factors and other clinical aspects such as

the experience of the operator.

APPLICATION OF SCANNERS IN DENTISTRY

For the acquisition of digital images of teeth, different

procedures have been described: digitization of plaster

casts, digitization of impressions, and intraoral digi-

tal impressions (Morris et al. 2010). Digital work  ow

has been proposed to improve treatment planning, give

higher ef ciency, and allow new methods of produc-

tion and new treatment concepts (Galovska et al. 2012).

Data storage and reproducibility are facilitated, and

treatment documentation and communication between

professionals as well as between dentists and patients

have become more convenient (Al Mortadi et al. 2012).

Currently, there are a major digital impression devices:

iTero (Align Technologies, San Jose, Calif), Lava COS

(3M ESPE, Seefeld, Germany), and Trios (3Shape, Copen-

hagen, Denmark) for image acquisition; and CEREC AC

(Sirona, Bensheim, Germany) and E4D (D4D Technolo-

gies, Richardson, Tex) for digital imaging and in-of ce

manufacturing (Flugge et al. 2013). All scanning devices

BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS DIMENTIONAL ACCURACY OF INTRAORAL AND LABORATORY SCANNERS 791

Iman Sha ei et al.

need drying and powdering of intraoral surfaces (CEREC,

E4D, Lava COS). Also, digital impressions are acquired

without contact to the gingival tissues (Ender and Mehl,

2011). Direct acquisitions systems have been constantly

improved because this are less invasive, quicker and

more precise than the conventional methods. Besides the

digital image can be easily store for a long time (Ramsey

and Ritter, 2012).

TYPES OF INDIRECT IMPRESSIONS

Lost-wax

Lost-wax is the traditional technique for fabricating the

metal substructure is the lost-wax technique and using

various metal alloys for casting (Ucar et al. 2009). Con-

ventionally, wax patterns were fabricated with wax and

waxing instruments for example the popular PKT instru-

ments. Wax is used to make the patterns because it can

be conveniently manipulated, precisely shaped and can

also be completely eliminated from the mold by heat-

ing. The fabrication of the wax pattern is the most criti-

cal and labor-intensive step in making the porcelain

fused-metal crown (Vojdani et al. 2013). To fabricate a

restoration prepared using the lost-wax technique, the

dentist must  rst make an impression and the impres-

sion appointment may be uncomfortable for the patient

because of the retraction procedure and need for anes-

thesia. Subsequently, time is required by the dental labo-

ratory technician for careful pouring of the stone die or

cast from the impression, preparation of the cast, then

fabrication of the wax pattern, investing, and casting.

Considering the lower unit cost of base metal alloys, a

more economical dental laboratory technique would be

helpful to replace the previously described technique for

preparing cast restorations (Ucar et al. 2009).

Selective laser sintering (SLS) is a manufacturing tech-

nology recently introduced in dentistry. SLS, is one of

the fast prototyping production techniques, uses a high-

temperature laser to beam selectively substructure metal

powder based on the CAD data with the  xed dental pros-

theses design. A thin layer of the beamed area becomes

burnt and the  xed dental prostheses is completed by

laminating these thin layers. The metal-ceramic crown is

formerly one of the most commonly used  xed dental

prostheses and the lower core is mostly produced by the

lost wax technique and casting method. However, SLS

system has several bene ts such as material, time and

expenses saving was well as the production is simpler

compared to the existing methods (Akova et al. 2008).

CEREC

With CEREC 1 and CEREC 2, an opticalscan of the pre-

pared tooth is made with a couple charged device (CCD)

camera, and a 3-dimensional digital image is generated

on the monitor. The restoration is then designed and

milled. With the newer CEREC 3D, the operator records

multiple images within seconds, enabling clinicians to

prepare multiple teeth in the same quadrant and create

a virtual cast for the entire quadrant. The restoration is

then designed and transmitted to a remote milling unit

for fabrication. While the system is milling the  rst res-

toration, the software can virtually seat the restoration

back into the virtual cast to provide the adjacent con-

tact while designing the next restoration (Estafan et al.

2003).

DCS Precident

The DCS Precident system is comprised of a Preciscan

laser scanner and Precimill CAM multitool milling center.

The DCS Dentform software automatically suggests con-

nector sizes and pontic forms for bridges. It can scan 14

dies simultaneously and mill up to 30 framework units

in 1 fully automated operation. Materials used with DCS

include porcelain, glass ceramic, In- Ceram, dense zir-

conia, metals, and  ber- reinforced composites. This

system is one of the few CAD/CAM systems that can

mill titanium and fully dense sintered zirconia (Sjogren

et al. 2004).

Procera

Procera/AllCeram was introduced in 1994 and according

to company data, has produced 3 million units as of May

2004. Procera uses an innovative concept for generating

its alumina and zirconia copings. First, a scanning stylus

acquires 3D images of the master dies that are sent to

the processing center via modem. The processing center

then generates enlarged dies designed to compensate

for the shrinkage of the ceramic material. Copings are

manufactured by dry pressing high-purity alumina pow-

der (>99.9%) against the enlarged dies. These densely

packed copings are then milled to the desired thickness.

Subsequent sintering at 2,000°C imparts maximum den-

sity and strength to the milled copings. The complete

procedure for Procera coping fabrication is very tech-

nique-sensitive because the degree of die enlargement

must precisely match the shrinkage produced by sinter-

ing the alumina or zirconia (Posselt et al. 2003).

Lava

Lava introduced in 2002, Lava uses a laser optical sys-

tem to digitize information from multiple abutment

margins and the edentulous ridge. The Lava CAD soft-

ware automatically  nds the margin and suggests a

pontic. The framework is designed to be 20% larger to

compensate for sintering shrinkage. After the design is

complete, a properly sized semisintered zirconia block

is selected for milling. The block is bar coded to register

the special design of the block. The computer- controlled

792 DIMENTIONAL ACCURACY OF INTRAORAL AND LABORATORY SCANNERS BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

Iman Sha ei et al.

BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS DIMENTIONAL ACCURACY OF INTRAORAL AND LABORATORY SCANNERS 793

precision milling unit can mill out 21 copings or bridge

frameworks without supervision or manual intervention.

Milled frameworks then undergo sintering to attain their

 nal dimensions, density, and strength. The system also

has 8 different shades to color the framework for maxi-

mum esthetics (Bindl et al. 2004).

Everest

Marketed in 2002, the Everest system consists of scan,

engine, and therm components. In the scanning unit, a

re ection-free gypsum cast is  xed to the turntable and

scanned by a CCD camera in a 1:1 ratio with an accu-

racy of measurement of 20 m. A digital 3D model is

generated by computing 15 point photographs. The res-

toration is then designed on the virtual 3D model with

Windows-based software. Its machining unit has 5-axis

movement that is capable of producing detailed mor-

phology and precise margins from a variety of materi-

als including leucite-reinforced glass ceramics, partially

and fully sintered zirconia, and titanium. Partially sin-

tered zirconia frameworks require additional heat pro-

cessing in its furnace (Blatz et al. 2003).

Cercon

The Cercon System is commonly referred to as a CAM

system because it does not have a CAD component. In

this system, a wax pattern (coping and pontic) with a

minimum thickness of 0.4 mm is made. The system scans

the wax pattern and mills a zirconia bridge coping from

presintered zirconia blanks. The coping is then sintered

in the Cercon heat furnace (1,350°C) for 6 to 8 hours.

A low-fusing, leucite-free Cercon Ceram S veneering

porcelain is used to provide the esthetic contour. In an

in vitro study the marginal adaptation for Cercon all-

ceramic crowns and  xed partial dentures was reported

as 31.3 m and 29.3 m, respectively (Ariko et al. 2003).

INTRAORAL AND LABORATORY SCANNERS

Several intraoral scanners have been introduced in the

recent decades, and an increasing number of dental clin-

ics have decided to adopt these powerful devices for cap-

turing digital impressions (Mangano et al. 2016). Cap-

turing of digital impressions of the dental arches using

this system can done by only a light beam, without the

need of individual trays and materials (alginate, silicone,

polyether) that are traditionally used to take impressions

(Logozzo et al. 2014). Because of the unpleasant proce-

dure, especially for those with a pronounced gag re ex

conventional impressions are generally not appreciated

by patients (Zimmermann et al. 2015). The possibility to

effectively replace conventional impressions is the main

advantage of intraoral digital impressions, which leads

to decrease materials costs (Yuzbasioglu et al. 2014).

Immediate control of the quality of the impression, and

the possibility of obtaining 3D which can be electroni-

cally sent to the laboratory is known as advantages for

this system (Schepke et al. 2015).

Digital impression making has improved this pro-

cess and the ability to evaluate the preparation in real-

rime. Having the capability of acquiring a scan of a

prepared tooth and visualizing it on a computer moni-

tor eliminates the issues associated with conventional

impressions. The dentist is now able to see a magni ed

high-resolution image of exactly what is present in the

oral cavity and not just a negative representation. This

improved visualization enables the dentist to see and

evaluate, in exquisite detail, the quality of the prepa-

rations, while the patient is still in the chair. Factors

such as preparation taper, quality of margins, undercuts,

inter-occlusal clearance, and path of draw can be color-

coded displayed and directly corrected if necessary, and

a new digital impression can be made within seconds.

All of the currently available conventional impression

materials exhibit some degree of dimensional change

that builds distortion and inaccuracy into the  nal res-

toration. Digital impressions can reduce the possibility

of dimensional change (shrinkage) that is evident with

all conventional impression materials. Voids, tears, and

pulls that are routinely experienced with conventional

materials are no longer an issue with digital scans (Geb-

hards et al. 2010).

Laboratory digitizing starts with a conventional

impression that is poured, and the resulting model is

digitized, by using one of several optical or mechanical

systems (Beuer et al. 2008). As well, some systems offer

the possibility to scan the impression directly without

cast fabrication (Quaas et al. 2007). However, in either

instance, the initial step of the highly precise digi-

tal work ow is an analogue impression. Conventional

high precision impression materials, like hydrocolloid,

polyether, polyvinyl or polysul de in combination with

stone casts, offer a well-known procedure to transfer

the clinical situation into the laboratory. However, some

drawbacks are related to the sensitive process steps of

this technique (Haim et al. 2009).

The CAD-CAM system includes three parts, which

correspond to the three basic steps of the process: (I)

First, a device is used to input the existing dental shapes

into the system. This device includes a laser source

(diode) which, through the  rst endoscope, projects light

on the desired picture area. A second endoscope, adja-

cent to the  rst, allows a camera to take pictures in the

mouth. This camera is connected to a system that digi-

tizes the information and correlates the different views

(Duret et al. 1985). (II) The CAD system, including all

necessary hardware and software, allows the operator

to create an electronic model of the impression, display

Iman Sha ei et al.

794 DIMENTIONAL ACCURACY OF INTRAORAL AND LABORATORY SCANNERS BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

it on the screen, an d use it to design the prosthesis.

The CAD system is linked to a proprietary articulator,

called the Access Articulator, which provides the data

relating to the dynamic movements of the jaw. (III) The

CAM system, which includes a numerically controlled

machine tool with four-axis capability. This machine

will automatically mill the prosthesis from conventional

or special materials (Belser et al. 1985).

Comparison of the accuracy of direct and indirect

To date numerous researches have been done on com-

parison of the accuracy of direct and indirect dental

scanners. However, proces and cones reported for each

system, here we highlighted the most signi csnt  nd-

ings of the previous reports. For the precision of direct

digital impression, Guth et al. (2013) compared the 3D

average and standard deviations of intraoral digital

impression (Lava Chairside Oral Scanner) with those

of extraoral desktop scanner (Lava Scan ST laboratory

scanner) in an in-vitro study where a molar and premo-

lar were scanned. It revealed the 3D standard deviations

of 19 µm for the intraoral digital scanner and 31 µm for

the extraoral scanner. Ender and Mehl (2011) compared

the trueness and precision of digital impressions of the

full arch with those of conventional impressions using

a reference scanner on a in-vitro model, and the results

showed that precision was 61.3 ± 17.9 µm for conven-

tional impression, 30.9 ± 7.1 µm for digital impression

with the Cerec Bluecam and 60.1±31.3 µm for digital

impression with Lava C.O.S.

Guth et al. (2013) found that digital impressions made

using Lava C.O.S. were more accurate than a laboratory

scan of a conventional impression and conversion to a

digital  le. Mangano et al. (2016) in research on trueness

and precision of four intraoral scanners in oral implan-

tology revealed in the partially edentulous maxilla, CS

3500 had the best general trueness (47.8 m) and pre-

cision (40.8 m), followed by Trios (trueness 71.2 m,

precision 51.0 m), Zfx Intrascan (trueness 117.0 m,

precision 126.2 m), and Planscan (trueness 233.4 m,

precision219.8 m). With regard to general trueness,

Trios was signi cantly better than Planscan, CS 3500

was signi cantly better than Zfx Intrascan and Planscan

and Zfx Intrascan was signi cantly better than Plans-

can; with regard to general precision, Trios was signi -

cantly better than Zfx Intrascan and Planscan, CS 3500

was signi cantly better than Zfx Intrascan and Planscan

and Zfx Intrascan was signi cantly better than Planscan.

In the totally edentulous maxilla, CS 3500 had the best

performance in terms of general trueness (63.2 m) and

precision (55.2 m), followed by Trios (trueness71.6 m,

precision 67.0 m), Zfx Intrascan (trueness 103.0 m,

precision112.4 m), and Planscan (trueness 253.4 m,

precision 204.2 m). With regard to general trueness,

Trios was signi cantly better than Planscan, CS 3500

was signi cantly better than Zfx Intrascan and Planscan

and Zfx Intrascan was signi cantly better than Planscan

with regard to general precision, Trios was signi cantly

better than Zfx Intrascan and Planscan, CS 3500 was

signi cantly better than Zfx Intrascan and Planscan and

Zfx Intrascan was signi cantly better than Planscan.

Local trueness values con rmed these results (Mangano

et al. 2016).

On Precision of intraoral digital dental impressions

with iTero and extraoral digitization with the iTero and

a model scanner Flugge et al. (2013) reported scanning

with the iTero is less accurate than scanning with the

D250. Intraoral scanning with the iTero is less accurate

than model scanning with the iTero, suggesting that

the intraoral conditions (saliva, limited spacing) con-

tribute to the inaccuracy of a scan. For treatment plan-

ning and manufacturing of tooth-supported appliances,

virtual models created with the iTero can be used. An

extended scanning protocol could improve the scanning

results in some regions. In a study on accuracy 3M Lava

C.O.S., 3Shape D900, Cadent iTero, CEREC Bluecam, and

E4D Dentistdigital impression systems revealed digital

impressions from the Cadent iTero system were the most

accurate (Ali, 2015).

Recently, on comparison of repeatability between

intraoral digital scanner and extraoral digital scan-

ner, Su et al. (2015) revealed precision decreases with

the increased scanning scope. Precision was clinically

acceptable when scanning scope was less than half arch.

Precision of extraoral scanning was acceptable in scan-

ning any scope of arch region. Güth et al. (2013) revealed

the direct digitalisation with Lava C.O.S. showed statisti-

cally signi cantly higher accuracy compared to the con-

ventional procedure of impression taking and indirect

digitalisation.

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