Fabian Leopold Alois Strohmayr
Fifth year, group 15INTRAORAL SCANNER: A SYSTEMATIC REVIEW OF
CURRENT LITERATURE
Master’s thesis
Thesis supervisor: Lect. Eglė Ivanauskienė
Annex No. 3
LITHUANIAN UNIVERSITY OF HEALTH SCIENCES MEDICAL ACADEMY
FACULTY OF ODONTOLOGY PROSTHODONTICS CLINIC
INTRAORAL SCANNER: A SYSTEMATIC REVIEW OF CURRENT LITERATURE
The thesis was done
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Annex No. 8 Kaunas 2019
EVALUATION TABLE OF THE MASTER’S THESIS
OF THE TYPE OF SYSTEMIC REVIEW OF SCIENTIFIC LITERATURE
Evaluation: ...
Reviewer: ... (scientific degree, name and surname)
Reviewing date: ... No. MT parts MT evaluation aspects Compliance with MT requirements and evaluation Yes Partially No 1 Summary (0.5 point)
Is summary informative and in compliance withthe
thesis content and requirements? 0.3 0.1 0 2 Are keywords in compliance with the thesis essence? 0.2 0.1 0
3
Introduc- tion, aim and tasks (1 point)
Are the novelty, relevance and significance of the work
justified in the introduction of the thesis? 0.4 0.2 0 4 Are the problem, hypothesis, aim and tasks formed
clearly and properly? 0.4 0.2 0
5 Are the aim and tasks interrelated? 0.2 0.1 0
6 Selection criteria of the studies, search methods and strategy (3.4 points)
Is the protocol of systemic review present? 0.6 0.3 0
7
Were the eligibility criteria of articles for the selected protocol determined (e.g., year, language, publication condition, etc.) 0.4 0.2 0 8
Are all the information sources (databases with dates of coverage, contact with study authorsto identify
additional studies) described and is the last search day indicated? 0.2 0.1 0 9
Is the electronic search strategy described in such a way that it could be repeated (year of search, the lastsearchday; keywords and their combinations; number of found and selected articles according to the combinations of keywords)? 0.4 0.1 0
10 Is the selection process of studies (screening, eligibility, included in systemic review or, if
applicable, included in the meta-analysis) described? 0.4 0.2 0
11
Is the data extraction method from the articles (types of investigations, participants,interventions, analysed factors, indexes) described?
0.4 0.2 0 12
Are all the variables (for which data were sought and any assumptions and simplifications made) listed and defined? 0.4 0.2 0
13 Are the methods, which were used to evaluate the risk
of bias of individual studies and how this 0.2 0.1 0
information is to be used in data synthesis, described?
14 Were the principal summary measures (risk ratio,
difference in means) stated? 0.4 0.2 0
15 Systemiza- tion and analysis of data (2.2 points)
Is the number of studies screened: included upon assessment for eligibility and excluded upon giving the reasons in each stage of exclusion presented?
0.6 0.3 0
16 Are the characteristics of studies presented in the included articles, according to which the data were extracted (e.g., study size, follow-up period, type of respondents) presented? 0.6 0.3 0
17 Are the evaluations of beneficial or harmful outcomes for each study presented? (a) simple summary data for each intervention group; b) effect estimates and confidence intervals)
0.4 0.2 0 18
Are the extracted and systemized data from studies presented in the tables according to individual tasks?
0.6 0.3 0 19 Discussion (1.4 points)
Are the main findings summarized and is their
relevance indicated? 0.4 0.2 0
20 Are the limitations of the performed systemic review
discussed? 0.4 0.2 0
21 Does author present the interpretation of the results? 0.4 0.2 0
22
Conclusions (0.5 points)
Do the conclusions reflect the topic, aim and tasks of
the Master’s thesis? 0.2 0.1 0
23 Are the conclusions based on the analysed material? 0.2 0.1 0
24 Are the conclusions clear and laconic? 0.1 0.1 0
25
References (1 point)
Is the references list formed according to the
requirements? 0.4 0.2 0
26
Are the links of the references to the text correct? Are the literature sources cited correctly and precisely?
0.2 0.1 0
27 Is the scientific level of references suitable for Master’s
thesis? 0.2 0.1 0
28
Do the cited sources not older than 10 years old form at least 70% of sources, and the not older than 5 years – at least 40%? 0.2 0.1 0
Additional sections, which may increase the collected number of points 29 Annexes Do the presented annexes help to understand the
analysed topic? +0.2 +0.1 0 30 Practical recommen- dations
Are the practical recommendations suggested and are they related to the received results?
+0.4 +0.2 0 31
Were additional methods of data analysis and their results used and described (sensitivity analyses, meta-regression)? +1 +0.5 0 32
Was meta-analysis applied? Are the selected statistical methods indicated? Are the results of each meta-analysispresented? +2 +1 0
General requirements, non-compliance with which reduce the number of points 33 General requirements
Is the thesis volume sufficient (excluding annexes)?
15-20 pages (-2 points)
<15pages (-5points) 34 Is the thesis volume increased artificially? -2 points -1 point
35 Does the thesis structure satisfy the requirements of Master’s thesis?
-1 point -2 points
36 Is the thesis written in correctlanguage, scientifically, logically andlaconically?
-0.5 point -1 points
37 Are there any grammatical, styleor computer
literacy-relatedmistakes? -2 points -1 points
38 Is text consistent, integral, and are the volumes of its structural parts balanced?
-0.2 point -0.5 points
39 Amount of plagiarism in the thesis. >20% (not evaluated) 40 Is the content (names of sections and sub-
sections and enumeration of pages) in compliance with the thesis structure and aims?
-0.2 point
-0.5 points
41 Are the names of the thesis parts in compliance with the text? Are the titles of sections and sub-sections distinguished logically and correctly?
-0.2 point
-0.5 points
42 Are there explanations of the key terms and abbreviations (if needed)?
-0.2 point -0.5 points
43
Is the quality of the thesis typography (quality of printing, visual aids, binding) good?
-0.2 point
-0.5 points
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TABLE OF CONTENTS
ANNEX No. 3 ………... 3
EVALUATION TABLE OF THE MASTER’S THESIS OF THE TYPE OF SYSTEMIC REVIEW OF SCIENTIFIC LITERATURE (Annex No. 8) ... 4 SUMMARY ………. 9
ABBREVIATION LIST ………... 10
INTRODUCTION ………... 12
1 CRITERIA FOR SELECTION OF ARTICLES AND SEARCH METHODS AND STRATEGY ………... 14 2 DATA SYSTEMING AND ANALYSIS ………. 16
3 RESULTS 17 3.1 INTRAORAL SCANNER FEATURES ………. 17
3.2 THE DIGITAL IMPRESSION IN COMPARISON TO THE CONVENTIONAL IMPRESSION ………. 19 3.3 CLINICAL APPLICATIONS OF DIGITAL IMPRESSIONS ……… 21
3.3.1 ORTHODONTICS FIELD ………... 21
3.3.2 PROSTHODONTICS FIELD ………... 22
3.3.3 IMPLANTOLOGY FIELD ……….. 23
4 DISCUSSION OF THE RESULTS ………. 25
4. 1 ACKNOWLEDGEMENTS ……….. 30
4. 2 CONFLICT OF INTERESTS ……….. 30
CONCLUSIONS ………. 31
REFERENCES ……… 33
ANNEXES ………... 38 EVALUATION FORM OF THE MASTER’S THESIS FOR THE
MEMBER OF DEFENCE COMMITTEE (Annex No. 10) ………. 39
INTRAORAL SCANNER: A SYSTEMATIC REVIEW OF CURRENT LITERATURE
SUMMARY
Aim: To evaluate the mechanisms and differences of commercially available intraoral scanners. Objectives:
1. To update the knowledge of the differences behind commercially available intraoral scanners. 2. To compare the digital impression to the conventional impression.
3. To shed a light on clinical applications of current intraoral scanners.
4. To describe different factors that could influence the measurements when evaluating the accuracy of intraoral scanner.
Methodology: this was a Systematic Literature review where searches were conducted using several databases PubMed, Cochrane, Ovid Medline, Scopus, TechStreet and IADR Abstracts. The period has covered the last 5 years. The search period lasted two months and the last search date was last search data was on the 28th of February of 2019. All the articles that could be obtained as full text have been assessed. The search was performed in accordance with PRISMA statement and articles were selected according to predetermined inclusion criteria. The only qualitative assessment was, that in vivo studies were assed with a higher quality than in vitro studies. Keywords were matched to database indexing terms. 57 studies were selected and analysed to carry out this Final Master Thesis.
Results and conclusions: Intraoral scanner are clinical acceptable for short term scans. In terms of full arch, partially edentulous and full edentulous impression the conventional impression should be still clinically preferred.
Intraoral scanning is in none of the found applications unanimity gold standard.
The intra oral scanner has a wide field of possible applications, but still has to become clinical standard.
Factors influencing the scan result were found, still more research is needed to connect it to a specific scanner system and therefore improve the scan results further.
Keywords: "intraoral scanner", "oral scanner", "digital impression", “CAD/CAM”, "accuracy intraoral scanner", "comparison of intraoral scanner".
APD Avalanche photodiode AWS Active wavefront sampling CAD Computer-aided design
CAM Computer-aided manufacturing CBCT Cone-beam computed tomography CLSM Confocal laser scanner microscopy C.O.S Chairside Oral Scanner
CT Computer tomography
DICOM Digital Imaging and
Communications in Medicine D.W.I.S Dental Wings Intraoral Scanner FDM Full dentate model
FEM Fully edentulous model FLA Finish line accuracy FLD Finish line distinctiveness IOS Intraoral scanner
ISO International Organisation for Standardization
OBJ Object code
PEM Partially edentulous model PLY Polygon file
PMT Photo multiplier tube SD Standard deviation
STL Standard tessellation language SWS Static wavefront sampling 3D Three-dimensional
2D Two-dimensional
VSE Vinylsiloxanether
INTRODUCTION
Prior to the 19th century, missing teeth were replaced via the employment of various materials, such as gold wire and wood and ivory blocks; later the method evolved through the usage of rigid dental plaster, which was used intraorally to document the intraoral status.
It was not till 1930, when the first hydrocolloids came up: agar and alginates. They had massive advantages over the gypsum: more accurate, more comfortable for the patient, faster and less mistake prone. Nevertheless, they have some disadvantages, such as their fast shrinkage and distortion over time, they are not highly accurate and taking an impression is not entirely comfortable for the patient. Moreover, agar has the downside that it needs to be heated to become fluid and cooled to become solid, requiring special impression trays with water cooling. On the other hand, alginate is easier to handle than agar, hence its wider utilization. Consequently, the search for a better impression material continues.
In 1950, synthetic elastomers were introduced in dentistry. During the decades of 1960 and 1970 new materials were introduced, being these: dental polyether and silicone (type 1 and 2); nevertheless, with the idea of improving their accuracy, in 1980 a hybrid between polyether and silicone was developed. However, still had some disadvantages, being discomfort for the patient; mistake prone due to its long chain procedure, which includes volumetric changes and expansion of the gypsum, and difficulty to operate, therefore, still inaccurate. Experienced technicians are needed to equalize these small deviations [1]. As a result, conventional impression seems susceptible to fail. Nonetheless, digital impression seems to overcome the conventional method in some of these points.
In 1973, Dr. Duret presented his thesis “Optical Impression”, later he patented the first computer-aided design and computer-aided manufacturing (CAD/CAM) device, which was able to produce a crown in 4 hours. Following, in 1980, Dr. Mörmann and Marco Brandestini introduced the first digital oral scanner. This laid the fundamentals for CERECs, which led to the first commercially available CAD/ CAM system for dental restorations in 1987. Since then, many companies have recognized its potential and have started to produce their own intraoral scanner (IOS). As a result, a competition between industries occurred, which resulted in more user friendly and accurate IOS [2].
Although the many technological advancements in CAD/CAM technology and their increasing popularity, it is still not the standard technology used in taking impressions [3].
The objective of this master thesis is to answer the following questions: are there differences between current intraoral scanner systems?, what are the differences between the digital and
conventional impression systems?, what are the current clinical applications of intraoral scanners? and what factors could affect the results of intraoral scanners?
HYPOTHESIS
Digital IOS are comparable to the conventional impression method in all aspects and can be used for the same clinical applications.
AIM
To evaluate the mechanisms and differences of commercial available intraoral scanners.
OBJECTIVES
1. To update the knowledge of the differences behind commercially available intraoral scanners.
2. To compare the digital impression to the conventional impression. 3. To shed a light on clinical applications of current intraoral scanners.
4. To describe different factors that could influence the measurements when evaluating the accuracy of intraoral scanner.
1. CRITERIA FOR SELECTION OF ARTICLES AND SEARCH
METHODS AND STRATEGY INTRAORAL SCANNER
FEATURES
• Article eligibility criteria: well written, verifiable, broad coverage, neutral and stable. • Criteria for adding articles: right topic, stable, English or German language.
• Criteria for rejecting articles: not older than 5 years, reviews and experimental studies.
Nedelcu et al. [4] suggested that it poses a challenge to compare the results of existing studies, because of the heterogeneity of each study in terms of design, execution and material properties.
Müller et al. [5] established a significant difference in the accuracy of the Trios pod scanner, when the scan strategy was changed, which agrees Park et al. [6] results. In addition, Prudence et al. [1] demonstrated that there is a statistical difference in the accuracy of IOS using powder and
adjustments in the intaglio surface. Nevertheless, he achieved better results for the Omnican (powder free, according to the manufacturer) by using powdering and adjustments in the intaglio surface. This is in concordance with Nedelcu et al. [4], who found a significant difference between the accuracy of coating and non-coating IOS. Furthermore, was able to demonstrate that there is a statistical difference between the results, depending on what material was scanned. On the other hand, Li et al. [7]
researched the influence of object translucency on the scanning accuracy of a powder-free IOS, concluding that an increased translucency leads to a decreased accuracy. Moreover, the temperature at which the scan is performed could slightly influence the result after ISO-12836 specifications [6]. Imburgia et al. [2] suggested that the more edentulous areas are, the lower the accuracy is, which he demonstrated by reporting that PEM scans were more accurate than FEM scans.
Rödiger et al. [8] proved that there is a significant difference in the materials used in the CAD/CAM process in regards to the marginal fit of the produced coping. For this purpose, he evaluated the marginal gaps of titanium, chrome-cobalt, zirconia and glass ceramic copings. His results showed that titanium had the lowest mean marginal gap, but a high standard deviation (SD) value. On the other hand, glass ceramic had the highest mean marginal gap, but a lower SD allowing it to perform for all tests below the 120 mark. Furthermore, another two studies suggested that the stitching process of some IOS can influence the scan result, in which collected images are stitched together to acquire a 3D image. However, this calculating process is mistake prone, either because the images itself are faulty or through the image modification small inaccuracies develop, which lowers the precision [4, 9].
Haddadi et al. [10] established that the use of different software versions can significantly influence the scan result. In addition, according to Hayama et al. [11] another influencing factor can be the scanner head size, suggesting a difference in accuracy depending on which scanner head was used. He concluded that the use of a bigger scanner head size would increase the accuracy of the scan results [11].
Giminez et al. [12] reported a tendency between the scan results of experienced with inexperienced operators, in which the experienced operators achieved better results.
2. DATA SYSTEMING AND ANALYSIS
The updating knowledge about intraoral scanners is of great amplitude. For selecting the literature, the following databases were used: PubMed, Cochrane, Ovid Medline, Scopus, TechStreet and IADR Abstracts. The terms used were: "intraoral scanner", "oral scanner", "digital impression", “CAD/CAM”, "accuracy intraoral scanner", "comparison of intraoral scanner". Keywords were matched to database indexing terms.
The research selection scheme was performed according to PRISMA requirements: 329 original articles were obtained. Later, filters were applied to the articles: be human, not older than five years and written in English or German language, 87 articles were excluded because of the language and topic. Then the remaining 242 articles were further assessed regarding eligibility, 93 articles were excluded as they did not fulfil the required criteria for verifiable, broad coverage, neutrality and stability. After that, the sparing 149 articles were additionally filtered according their topics and relevance for this Master’s Thesis. Literature reviews, letters and meta-analysis were excluded. After that, 57 studies were selected and analysed to carry out this Final Master Thesis. Following the selection of the articles, the remaining articles were divided into specific topics: comparison of intraoral scanner (9 articles), comparison of digital and conventional impression (12 articles), factors influencing scan results (7 articles), prosthodontics (21 articles) and orthodontics (8 articles).
However, some of the articles could be used in more than one topic. Moreover, the author evaluated the quality of in vivo and in vitro studies.
3. RESULTS
3. 1 INTRAORAL SCANNER FEATURES
In order to mention the features of IOS, we should start by looking at its evolution, and so as to do that, we should start by the history of the CAD/CAM system. In 1984, the first CAD/CAM
chairside developed by Cerec produced inlays with a marginal discrepancy of 140 to 256μm. Only ten years later, the Cerec 2 was already able to produce full crowns with a marginal fit of 50 to 150μm. Both Cerecs used two-dimensional (2D) imaging, until 2003, when the Cerec 3 was developed and upgraded to three-dimensional (3D) imaging. The change from 2D to 3D images, increased the
accuracy of the CAD/CAM system, so that nowadays marginal fit values of 40μm were described [1]. But, actually, how is a 3D image created? To acquire 3D images commercially available IOS uses either confocal laser scanner microscopy (CLSM), triangulation techniques, optical coherent tomography, accordion fringe interferometry and active wavefront sampling or a subtle variation of those aforementioned. Then, the achieved 3D image is processed by a scanning software, which
creates points cloud. These point clouds are then connected to triangles; however, each scanner can use a different number of triangles to reproduce the same image. In addition, a mesh of triangles can be regular and irregular, achieving the irregular arrangement a higher accuracy in specific needed sectors [2].
In comparison to the current IOS, which uses video image acquisition, the first IOS mostly used camera image acquisition, in which the picture is taken by an auto-shutter and for a specific programmed moment. For instance, in the bluecam, the auto-shutter is triggered when the camera touches the teeth. However, if the camera is moved in this precise moment, the later image will appear blurred; thus, so as to achieve a clear image, normally more than one attempt is needed, meaning that this method is time and skill dependent. Contrarily, with video image acquisition you have a
continuous video, which decreases the noise in the image through shaking [3, 4].
An additional important feature of IOS is the time needed to take an impression. Patzelt et al. [5] demonstrates that there is a significant difference between the time needed to take an oral
impression by the different IOS systems. Moreover, he described that on the one hand, the Cerec system with camera acquisition was the fastest method in recording a single abutment, and on the other hand, the Lava C.O.S with video acquisition was the fastest in recording a full arch [5]. This is in agreement with Treesh et al. [6], which declared that the scan times of continuous capture scanners were faster than the single capture scanners. Nonetheless, there are other factors playing a role in the image acquisition, like the size of the scan, software and handling and calculating power [5].
Furthermore, powdering was employed in some early systems so as to decrease the tooth surface reflection; for this purpose, titanium oxide powder was used. Besides, at that time, only a single colour of light was used, hence the use of powdering. For instance, the bluecam used blue LED, which emitted only blue light; this was problematic for surfaces with different light reflectivity, since the discrepancy between the light reflections could produce an unclear image. Therefore, titanium oxide powder was used, as produces a uniform surface diminishing the variations in reflection. Nowadays, newer developed systems use different ranges of lights, like the Omnicam, which uses white LED emitting red, green and blue light, allowing the use of different light wavelengths for a much clearer image acquisition with less variables. Moreover, the white LED allows to deal with a wider range of surface reflectivity [3, 4].
A further subject that should be mentioned is that most systems became “opened”, meaning that the data is saved in an open format (like Standard tessellation language (STL), Object code (OBJ), Polygon file (PLY)), which can be immediately used by any CAD system. The STL is the standard system used, whether the OBJ is exclusively used by wavefront IOS and the PLY files are used for colour information [7]. In comparison, the “closed” system has only the reference proprietary format as output, which is encoded to be only opened by a software of the same manufacturer. Nevertheless, some manufacturers offer to convert the files into an “opened” format for a charge, but this may result in the loss of quality and information. Therefore, the clearly advantage of the “open” system is the freedom of use and financial charge. On the other hand, the “closed” system is more user friendly as it uses the same software. Nonetheless, Mangano et al. [2] explains that both systems have their
advantages and proposes that some newer systems let the user choose if the file should be saved in an open or close format.
Table 1. Evaluation of intraoral scanner features, 2019 [7-12]
Feature Advantages Disadvantages
Image acquisition Camera
Video
-
Faster, user-friendly
Many images, many are blurred
-
Coating Powder
Powder-free
Less reflected light Pleasant, less mistake prone
Unpleasant, mistake prone -
File Format “Opened”
“Closed” Combined
More variable, cheaper Easier to handle Advantages from both
formats Requires expertise Dependent on fees - Colour 134 121 +13 Caries detector 202 210 -10
3. 2 THE DIGITAL IMPRESSION IN COMPARISON TO THE CONVENTIONAL IMPRESSION
When comparing the digital cast to a conventional cast, we see that the digital has some advantages over the conventional, such as more efficient data storage and retrieval, increased diagnostic versatility, easier transferability, easier customization, superior durability and decreased processing time [8, 9]. But, on the other hand, the conventional impression has shown some resistance in the private practice sector, since it is accurate, well accepted and inexpensive [9, 10]. Nevertheless, conventional impressions have been reported as unpleasant and burdensome for the patient [9].
Five in vivo [11-16] and one in vitro [5] studies compared the efficiency and patient’s
preference of both digital and conventional impression. The results of these studies are in opposition, since four studies [5, 11, 13, 14] concluded that the patients preferred the digital impression, whereas the conventional impression was chosen by only one study [15]. Furthermore, two studies reported patient’s discomfort during the digital impression, because of the large scanner head [15, 16]. Interestingly both studies came to different conclusions, being that one study described more comfortable the digital impression [16], while in contrast the other reported the conventional impression method [15]. However, only one study tested in vivo the patient’s preferences in prosthodontics, establishing that the digital impression had a higher patient satisfaction when impressions for single crowns were made [14].
Burzynsky et al. [9] evaluated the patient’s time perception. All impression methods were rated faster than expected, suggesting that the iTero group was perceived as the fastest. On the other hand, when assessing the chair-side time the alginate was the fastest, followed by the iTero with no
significant difference, nonetheless, the Trios was established as the slowest showing a significant difference in comparison to the other two methods [16]. This conclusion contradicts some findings of the current literature, which proposes that the digital impression requires less time than the
conventional impression [5, 14]. In addition, the results from Burzynsky et al. [9] can be explained since was only considered the chair-time and preparation and processing times were excluded. This is in agreement with the results obtained by Patzelt et al. [14] and Grünheid et al. [15] concluding that the conventional impression had shorter chair-time, but when considering the full-time method, the digital group was faster [15].
Another important factor to considered, is the time needed for rescans or retakes of an
impression. Lee et al. [17] showed a time difference of up to 10 minutes in favour of the digital group. The impressions were performed by inexperienced second-year dental students onto other students, later both group were asked about their perception of both techniques. The majority concluded that the digital technique was easier to perform [17]; thus, indicating that the digital impression is in general
well-accepted by the dentist as well as by the dental patient and has, in terms of comfort, efficiency and handling, slight advantages over the conventional impression [15].
Nonetheless, all the advantages of digital scanners would not be relevant, if their accuracy and efficiency was not comparable to conventional impression [15]. However, before being able to speak about the accuracy of IOS, a definition of accuracy should be given. Many authors defined it by using the International Organisation for Standardization (ISO) 5725, which describes accuracy by two measurements: trueness and precision [18-21]. Precision describes how close repeated scans are to each other, the higher the precision of IOS is, the more predictable is its measurement. Trueness describes how exact the measurement is to the real dimensions of an object [18-22]. Trueness and precision of conventional impressions were normally assessed by measuring the changes between the original master model and the model from the impression material. In vivo, normally, the fit of the restoration is evaluated to make a conclusion of the impression material trueness. Moreover, repeated impressions can be made from one arch and can be compared with each other so as to establish the precision of the to be tested material [18]. In addition, they have shown a high level of accuracy [18, 19].
Ender et al. [18] compared in an in vivo study the trueness and precision of five conventional impression systems with seven digital impression systems. The models from conventional impressions were scanned and saved as a STL file. The digital impression scan was saved as well as STL files, thus, the scan data could be superimposed using a best fit algorithm. Ender et al. [18] concluded that the conventional group showed the highest accuracy, with exception of the alginate group. However, the digital group achieved equal and even higher precision values than the alginate test group.
Nonetheless, vinylsiloxanether (VSE) and direct scannable vinylsiloxanether (VSES) achieved the best values in precision and the digital group achieved also good values in precision, but suffered, in terms of trueness, local deviations [18]. This in concordance with the results of two other studies, which came to similar results [23, 24]. One study compared digital impressions to polyvynil siloxane impressions [24] and the other study compared digital impression to impregum, both concluding that the conventional impression is still more accurate for full-arch impressions [23, 24]. Nedelcu et al. [25] performed an in vivo study, in which the digital group of 3m and Trios showed higher accuracy than the impregum impression; however, no statistical difference between these two groups was found [25].
3. 3 CLINICAL APPLICATIONS OF DIGITAL IMPRESSIONS
Nowadays, researches manifest that the longer the scan is, the lessen accurate the IOS are [25-27]. Park et al. [26] analysed the accuracy of four different IOS, in terms of the distance of the scan’s starting point, establishing that all four IOS were more inaccurate the further the starting point was. Therefore, concluding that IOS are accurate for short distances, but inaccurate for full arch scans [26, 28]. On the other hand, Nedelcu et al. [25] tested in vivo the accuracy of three IOS with an implant scan body, proving that IOS are clinically acceptable when restoring up to ten units without extended edentulous spans.
IOS are applicable in the fields of orthodontics, prosthodontics and implantology [25-47] (Table 2).
Table 2. Enrolment in local colleges [25-47]
Field Applications Remark
General General applicable for up to
10 units scans Digital patient
Comparable to conventional impression
Can be used in many fields: orthodontics, prosthodontics, implantology, surgery, etc.
Orthodontics - Diagnosis
- Treatment planning - Documentation
Higher chance of clinical error
Prosthodontics - Single restorations or
partial fixed restorations - Complete dentures
- Crown shows good marginal fit
- Usable, but with restrictions
Implantology - Guided implantology
- Implant impression
- IOS data more reliable than CBCT data
- Usable, but with restrictions (i. e.: edentulous areas)
3. 3. 1 Orthodontics field
Carmadella et al. [29] demonstrated that the measurements of digital casts have a higher chance of clinically relevant error than the measurements from the conventional casts; however, paradoxically he assumed that the Trios colour could be used to replace the conventional impression. Nonetheless, Manuelli et al. [30] compared the intercanine and intermolar measurements of
reporting a statistical significant difference between the measurements, no clinically significant difference was found, as the difference was less than 0.1mm. That was defended by Sfondrini et al. [13] as he concluded that IOS are able to produce digital models useful in the clinical practice for diagnosis, treatment planning and documentation of treatment outcomes.
Furthermore, it is now possible to merge IOS, cone-beam computed tomography (CBCT) and face scans so as to create a digital patient. This requires the successful superimposition of three different formats: the STL, the PLY or OBJ formats used by IOS; the Digital Imaging and
Communications in Medicine (DICOM) format used by CBCT, and OBJ files from facial scan [31-33]. Joda et al. [31] proposed a successful technique of superimposing this data creating a virtual patient. This technology can be useful in the field of orthodontics, for example in orthognathic surgery, in the creation of surgical guidelines, in the placement of orthodontic mini-screws and in the exposure of ectopic teeth. In addition, it has the advantage that the root position can be visualized throughout the whole treatment, simply by scanning the teeth instead of performing multiple computer tomography (CT) scans, avoiding the patient unnecessary exposure to radiation [32].
This technique has a wide range of applications in different fields. In dentistry and medicine is useful in the matters of simulating treatment planning and discovering patient’s expectations, facilitates a more effective patient-doctor communication and the achievement of high-precision anatomical documentation, keeping in mind that is a non-invasive imaging technique, hence its implementation in dental education. Besides, it is very helpful in maxillofacial and plastic surgery fields [31].
3. 3. 2 Prosthodontics field
In the field of prosthodontics, a good marginal fit and internal fit of the later fixed restoration is of high importance to achieve a high rate of long term success [33, 34]. To which paragraph belongs? However, there is no clinical definition about what exactly the maximal marginal deviation should be so as to be assessed as a successful treatment. McLean and von Fraunhofer proposed the value as 120μm, after examining over 1000 marginal gaps in a 5 years period [33, 35]. Moreover, several studies analysed the influence of IOS on the marginal fit of crowns, describing a clinical acceptable marginal fit of crowns fabricated by digital scans [14, 36-39].
Currently, just few studies describe the use of IOS when fabricating complete dentures. Goodacre et al. [40] proposed a technique to fabricate a complete denture and implant overdenture; also, the patient reported to be pleased with the retention, stability and aesthetic of his new denture. However, the study has some limitations, which are that the denture was not completely new
fabricated, since the existing dentures were scanned and used to create the new ones. This results in an agreement with Clark et al. [41], who suggested a similar technique able to fabricate two complete dentures. As well, the existing dentures were scanned and the new printed copies were used as a
custom tray to achieve a better retention than the existing dentures. He concluded: “Most steps of the conventional denture workflow now have digital alternatives—even auxiliary procedures, including denture duplication and processed record bases”.
When comparing fabricated restorations by conventional or digital impression, on the one hand, two studies found no significant difference [14, 36], on the other hand, three studies reported that the digital impression achieved better results than the conventional [25, 36]. Berrendero et al. [36] reported that “digital impression provided a lower mean gap value for three of the four measurement points, in comparison with conventional impressions and gypsum casts scanned with a standard benchtop laboratory scanner”. However, Nedelcu et al. [21] reported a higher finish line accuracy (FLA) and better finish line distinctiveness (FLD) in the digital test group. Nonetheless, it should be mention that this study was an in vitro experiment and the finish line, was except for two locations, supragingival. Accordingly, the clinical reality may prove as a more challenging setup [21].
Notwithstanding, Sarkominon et al. [14] performed an in vivo experiment resulting in no significant difference between the digital and conventional group.
3. 3. 3 Implantology field
Joda et al. [31] declared that computer-assisted implant guided-surgery in combination with 3D planning software offers an additional tool in a prosthetic oriented digital treatment concept, which considers the individual situation of each patient. In addition, Brand et al. [42] compared the accuracy of implant position in guided surgery, based either on CBCT or IOS data, concluding that the implant position showed a higher accuracy by IOS, thus, being a more feasible diagnostic alternative.
Nonetheless, a highly true and precise digital model is needed when manufacturing implant-supported prosthetic rehabilitation, since clinical relevant errors can lead to a decreased long-term success rates of implant supported prosthesis or of the implant itself, for instance loosening of screws, cracking of aesthetic components and framework fractures, which all can affect the success of the prosthetic components [43].
Studies concerning the accuracy of IOS have reported clinical acceptable values concerning the accuracy of IOS in short span scans [25, 44]. However, Nedelcu et al. [25] was the only in vivo study that found clinically acceptable accuracy for up to ten units scans, in which one of the units was implant abutment. Fukuzawa et al. [44] came to the same conclusion, as he tested the accuracy of IOS on two models with an opposing difference between the implant posts. When the distance between the implant abutments was extended to twofold, the rate of change in the distance error almost doubled. These results are in agreement with Imburgia et al. [45] as he tested the accuracy of four IOS
(CS3600, Trios3, Omnicam and TrueDefinition) on two different models: partially edentulous model (PEM) with three implants and fully edentulous model (FEM), both were out of gypsum with a gingiva
mask around the implant. The models were scanned, five times each, with a reference scanner for the specific IOS. Later the scans were superimposed so as to achieve values of trueness and precision of the tested scanner. A significance difference regarding trueness was found between the tested IOS, CS3600 showed the best values in trueness, as well as for PEM and FEM group (Table 3). To sum up, all scanners showed a significant difference between their values for the PEM and FEM group, and the accuracy of all tested digital impression systems were higher in the FEM than in the PEM group [50]. Nonetheless, Ajioka et al. [46] concluded that for impressions on a PEM model with two implant abutments on position 35# and 36# the error of the digital impression was greater than the one of conventional impression. In addition, study shows that longer healing abutments increase the accuracy of angulations measurements [46].
Ciocca et al. [43] digitally scanned a FEM model with 6 implant abutments. In comparison to Giminez et al. [47], the abutment surface was reduced to single spatial points, which were then superimposed by a best-fit software, concluding that the average 3D position error of the digital impression was 0.041 ± 0.023mm to 0.082 ± 0.030mm, which is in accordance with previous studies and suggests a clinically acceptable level of accuracy [43]. However, even edentulous areas in a full-arch digital impression may generate errors due to the collimation process that uses geometrical repair points [48]. On the other hand, Iturrate et al. [28] proposed the use of an auxiliary device, which could increase the accuracy of the implant abutment scans in full edentulous arches. An in vivo study
compared full arch screw-retained maxillary rehabilitations produced by both digital and conventional impressions, in which 50 metal framework prosthesis were screwed onto 6 implants and the
bar-implant accuracy was radiologically estimated. The bone resorption was documented for a period of 24 months, resulting in that the digital group had a mean bone loss of 1.11 ± 0.54mm compared to 1.07 ± 0.66mm of the conventional. The bar-implant accuracy was reported to be high and no voids were found. Therefore, it was concluded that no statistical significance was found in the success rate of full arch screw-retained maxillary rehabilitations fabricated by means of conventional or digital
impressions [48].
Table 3. Trueness and precision of four IOS [50]
Scanner Trueness PEM Trueness FEM Precision PEM/FEM
CS3600 45.8μm 60.6μm ± 1.6μm/± 11.7μm
Trios 50.2μm 67.2μm ± 2.5μm/± 6.9μm
Omnicam 58.8μm 66.4μm ± 1.6μm/± 3.9μm
TrueDefinition 61.4μm 106.4μm ± 3.0μm/± 23.1μm
4. DISCUSSION OF THE RESULTS
One of the first methods used to substitute absent teeth was through the usage of gold wire, which threaded together the human and the artificial teeth. Later the technique evolved into carving blocks of wood and ivory so as to accommodate the intraoral contours. All these processes led to a better understanding of the oral tissues, resulting in the development of new impression techniques and materials [53]. However, despite the efforts, rigid dental plaster was used intraorally to record the intraoral situation till the beginning of the 19th century; these had to be intraorally fragmented, just so as to be glued together again extraorally [54].
Since 1930, is the conventional impression is the clinical standard method in dentistry, whereas the digital impression could still not assert itself in the clinical practice [15].
This master thesis has the purpose to update the knowledge about IOS regarding their clinical application and factors influencing the scan’s results, as well as comparing the different IOS systems and the digital impression to the conventional.
There are a series of coincident findings in almost all the articles reviewed:
1. The data obtained by IOS is processed by a scanning software. This software creates a point mesh to acquire a 3D imagen, then the image is transformed into surfaces and triangles are formed between the points. Each scanning system uses a different count of points and triangles to depict the same image. Current literature defines the count of triangles as the triangle
resolution. Correspondent results show that a higher triangle resolution not necessarily means that IOS are more accurate in comparison to another system with a lower triangle resolution [2, 21, 25]. However, Dentsply Sirona developed a software that is able to increase the triangle count at points where high accuracy is needed (finish line) and to reduce it at points where does not need to be so accurate [55].
2. The image or data can be either captured by individual images (camera) or by video sequence. Most of the found literature establishes that scanners operating with video sequence are more accurate, despite image stitching. Moreover, in terms of time efficiency, the current literature suggests that video sequence scanner require less time than individual image scanner [5, 6, 22, 25, 26].
3. Patient’s satisfaction and time efficacy are important factors in the acceptance of an impression system. In regard to that matter, digital impression seems to be better prepared for the dental patient and has less chair time than the conventional method [11-16].
4. Conventional impression shows the best accuracy for full arch impressions, which is in agreement with other findings that state that IOS become more inaccurate the longer the scan is. However, opposite findings were found by Nedelcu et al. [25]; nonetheless, his results could be explained since only ten units instead of the full arch were scanned [10, 18, 23-25].
5. Data acquired from CBCT, facial scan and IOS can be superimposed, creating a digital patient, which has a broad spectrum of applications in various fields, such as in dentistry, medicine, maxillofacial and plastic surgery [31-33].
6. Crowns fabricated by digital scans show an acceptable marginal fit. Therefore, suggesting that the use of IOS is clinical acceptable, when producing crowns or for short span restorations [14, 21, 25, 36-39].
7. Coating or no coating, object translucency and scan strategy are the main factors influencing the results of the scan.
As a result of the different gathered literature and the establishment of the aforementioned coinciding finding, I was able to achieve the objective of this Final Master Thesis by answering the previously stated questions.
Are there differences between current intraoral scanner systems?
In relation to the current literature, it can be affirmatively concluded that there are differences between current IOS systems.
IOS are based on different 3D imaging techniques: CLSM, triangulation techniques, optical coherent tomography, accordion fringe interferometry and active wavefront sampling or a slight modification of those previously mentioned [2, 54]. However, only two studies were found, in which the principles were comprehensively and thoroughly described and conclusions were suggested according to their clinical performances.
Kim et al. [56] compared the trueness mean of the different imagining techniques,
demonstrating that there is a significant difference in regard of the technique employed (Table 3). The study was conducted in vitro, thus, an in vivo study concerning this topic would be interesting.
Additionally, correspondent finding propose that IOS differ also in their image capture principle, displaying the video sequence advantages over the individual image principle in terms of time efficiency and accuracy [5, 6, 22, 25, 56].
On the other hand, triangulation resolution can be different between the different IOS, which may directly influence their accuracy [25]. Throughout the literature I could establish that the most important difference between the various IOS appears to be their dissimilarities in accuracy. When
accuracy is considered, we use the definition of ISO 5725; however, by means of ISO 5725 differences in trueness were found [18-22]. In addition, regarding precision, the results are controversial [2, 10, 25]. Whereas coincident findings from Nedelcu et al. [25] and Imburgia et al. [2] suggest that there is no significant difference in precision, Ender et al. [10] suggest the opposite by establishing a
significant difference in the precision of the different IOS systems.
Furthermore, one more difference would be the need for coating, which is used by IOS systems in regard of different wavelengths [3, 4]. Earlier systems used a single wavelength resulting in high translucent or reflective materials, which could lead to errors in the outcomes. Consequently, arose the need for coating. Nowadays, the materials are coated with a slim titandioxide film that makes the material opaquer [3, 4].
Table 3. Comparison of trueness by data capture principle, mode, and powder coating [56] (Kim R., Park J., Shim J.)
SS-OCT, swept source optical coherence tomography. Superscript letters mean multiple comparison. *P<.01; **P<.05.
What are the differences between the digital and conventional impression systems?
Based on the data found in the current literature differences between conventional and digital impression systems in terms of accuracy, time efficiency and patient’s acceptance were established.
Regarding accuracy, it has been corroborated that the conventional impression is the most accurate when scanning the full arch [18, 23, 24], since the digital impression decreases in accuracy the longer the scan endures [31]. Therefore, for short lasting scans no significant difference between both impression systems was found [14, 36-39].
On the other hand, throughout the current literature it has been manifested that the digital impression chair-time is shorter than the conventional impression [5, 14]. Nevertheless, it is still controversial the acceptance of one of these methods as the most efficient impression technique [9, 15].
Concerning patient’s acceptance, digital impression method was appointed as the preferred method by the majority of dental patients [5, 11, 13, 14, 16], however, some studies have suggested the contrary, meaning that a percentage of the patients opted for the conventional impression method [15].
What are the current clinical applications of intraoral scanners?
The current literature unanimously acknowledges the use of IOS for short span scans [14, 36-39]. However, this poses an issue: for what distance is IOS clinically acceptable? Nedelcu et al. [25] was able to answer the problem by suggesting that a span up to ten units is satisfactory.
IOS are clinically applicable in diverse fields.
In orthodontics field, the digital impression method is considered useful in the diagnosis, treatment planning and documentation [13, 29, 30]. However, the digital impression has a higher chance of clinical errors and worse accuracy in comparison to the conventional impression system [29].
In prosthodontics, current literature suggests that digital impressions can be used for single restorations or short fixed partial restorations [14, 36-39].
In prosthodontics, current literature suggests that digital impressions can be used for single restorations or short fixed partial restorations [14, 36-39]. Crowns produced by IOS were reported as clinically acceptable by the majority of studies [36-39]. However, it is still problematic to fabricate a completely good fitting denture with IOS data; nevertheless, successful cases have been described, in which an existing prosthesis was replicated and later used as the impression tray or relined.
In implantology, IOS data has been reported as successful in guided implantology. Moreover, IOS was found in vivo clinically acceptable for up to ten unit scans with one implant abutment [25]. On the other hand, in vitro was described as suitable for FEM scans with six implant abutments [43]. Nevertheless, edentulous areas seem to decrease the scan’s accuracy [2], therefore, an auxiliary device is needed to simulate the teeth in these areas, resulting in an increased FEM scan’s accuracy [28]. Furthermore, was reported in vivo the production of full arch screw retained maxillary rehabilitation in up to six implants by digital impression. All implants showed a success rate of 100%, after immediate loading, in a period of two years [47].
Moreover, a digital patient has been created, which is suitable in various fields, such as in orthodontics, surgery, prosthodontics and implantology [31, 32].
What factors could affect the results of intraoral scanners?
The current literature mentions various factors that could influence the scan results: coating, material consistency and texture, scanning strategy, model composition (FEM, PEM and full dentate model full dentate model (FDM)), software version, stitching process, data capture principle, mode and experience of the operator [26, 49, 50-52, 57].
Coating has been suggested to increase the IOS accuracy when the scan system is susceptible to reflection. Moreover, Nedelcu et al. [57] reported that there was no significant difference when changing the size of the coating layer.
Moreover, translucency and/ reflectiveness of the object may alter the scan results, since with an increased objects’ translucency and/or reflectiveness, the less accurate the scan is [49]. Hence the use of coating so as to decrease them.
Müller et al. [48] recorded that the use of different scan strategies leads to significant differences. Furthermore, different software versions may also play a role [51].
Furthermore, the experience of the operator seems to influence the scan’s accuracy; however, there are controversial findings on whether experienced or inexperienced operators achieve the best results [46]. In addition, different model situations had different accuracies, meaning that the accuracy can be influenced in regard of specific spaces, such as for edentulous spaces, in which the accuracy is decreased [2].
4.1 ACKNOWLEDGEMENTS
I dedicate this thesis to my family for their constant support in me.
Further I would like to thank my supervisor Lect. Eglė Ivanauskienė for her advice thought this literature review project.
4. 2 CONFLICT OF INTERESTS
CONCLUSIONS
1. There are differences between current intraoral scanner sytems; following differences could be made out on basis of the current literature; 3D imaging principle, different wavelengths, image capture, principle, time needed for one scan, scanner head, triangle resolution, trueness and precision. Still more research is needed to test their performance in context to their differences.
2. Currently, IOS are clinically acceptable for short spans scans, but when it comes to longer scans and more complicated situations, such as PEM or FEM, the conventional impression is preferred. Since its accuracy, in comparison to the digital impression in these cases, is the best, therefore, exhibiting better results.
3. There is a wide field of possible applications, but applications were digital impression can be seen as clinical standard is limited. In addition, there is no consensus on which particular applications the digital impression should have. It has been described that it can be used in a wide range of fields; however, there is no single study that defines its precise employment. Moreover, as it is being used for various objectives, that can lead to its misuse. For example, it is not like a caries treatment, everybody knows that its treatment is filling; hence its appropriate use and ability to improve the technique, which is opposed to IOS. Thus, a detailed literature should be directed to establish its proper use. However, this objective is difficult to accomplish, since IOS are very expensive, ergo, only few dentists have it complicating the performance of studies and researches.
4. There is no agreement on which factors influence the most the IOS system and the scan’s results, as well as, if there is a specific factor that could affect a particular system. Since the influencing factors are not fully understood and described that hinders the development and improvement of future IOS systems, as no specific factor can be improved.
The Hypothesis was rejected, since digital and conventional impressions are not comparable from a clinical view. The conventional method is still the gold standard method regarding fimpression taking in dentistry.
Therefore, as a dentistry student, I prefer, based on the clinical view, the use of the conventional impression, since it is more accurate and reliable in a wider field of established applications. Nevertheless, I believe that in the coming years IOS will become the gold standard method for impression taking in dentistry, due to their reported advantages over the conventional impression method. This development could occur earlier than expected, as the IOS became cheaper, possibly leading to more buyers and, thus, broader research field, which would improve the accuracy of the further developed IOS. Furthermore, new systems were introduced in the dental fare of 2019, which accuracy and applicability still have to be tested.
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