|Year : 2020 | Volume
| Issue : 1 | Page : 27-37
Accuracy of an intraoral digital impression: A review
Kanchan Aswani, Sattyam Wankhade, Arun Khalikar, Suryakant Deogade
Department of Prosthodontics and Crown and Bridge, Government Dental College and Hospital, Nagpur, Maharashtra, India
|Date of Submission||04-Sep-2019|
|Date of Decision||30-Oct-2019|
|Date of Acceptance||02-Jan-2020|
|Date of Web Publication||27-Jan-2020|
Dr. Kanchan Aswani
Department of Prosthodontics and Crown and Bridge, Government Dental College and Hospital, Nagpur, Maharashtra
Source of Support: None, Conflict of Interest: None
Intraoral scanners (IOSs) are used for capturing the direct optical impressions in dentistry. The development of three-dimensional technology and the trend of increasing the use of IOSs in dental office routine lead to the need to assess the accuracy of intraoral digital impressions. The aim of this review was to assess the accuracy of the different IOS and the effect of different variables on the accuracy outcome. An electronic search using PubMed with specific keywords to obtain potential references for review. A search of MEDLINE (PubMed) identified 507 articles. After title and abstract screening, 412 articles were excluded for not meeting the inclusion criteria and discarding duplicate references. Ninety-five articles were followed for full screening; only 24 articles were included in the final analysis.
The studies indicated a variable outcome of the different IOS systems. While the accuracy of IOS systems appears to be promising and comparable to conventional methods, they are still vulnerable to inaccuracies.
Keywords: Accuracy, digital impression, intraoral scanner, optical impression
|How to cite this article:|
Aswani K, Wankhade S, Khalikar A, Deogade S. Accuracy of an intraoral digital impression: A review. J Indian Prosthodont Soc 2020;20:27-37
|How to cite this URL:|
Aswani K, Wankhade S, Khalikar A, Deogade S. Accuracy of an intraoral digital impression: A review. J Indian Prosthodont Soc [serial online] 2020 [cited 2020 Nov 26];20:27-37. Available from: https://www.j-ips.org/text.asp?2020/20/1/27/276832
| Introduction|| |
Progress in digital dentistry has not only popularized the concepts of computer-aided design (CAD) and computer-aided manufacturing (CAM) but also created the provision for more efficacious and predictable therapeutic outcomes.
Obtaining three-dimensional images have accentuated the accuracy of the conventional prosthetic options and also provides for the virtual definition of various treatment strategies and to digitally design and fabricate varied types of restorations. Based on the type of tissue scanned, various principles and technologies have been developed and are being applied. The predicaments associated with conventional impression procedures have further highlighted the applications of intraoral scanners (IOSs). The intraoral digital scanning has been perceived as a more rapid and convenient technique from the perspective of both the dentists and the patients.
Digital intraoral scanning has provided numerous benefits such as real-time visualization, easy repeatability, selective capture of the relevant areas, no need to disinfect and clean dental impressions and impression trays, cast pouring, no wear of the model, rapid communication and availability.,,,,,,
Many CAD-CAM systems are available in the market for chairside digital impression and prosthesis fabrication.,,, Different IOSs by the numbers of company are increasing that offer user-friendly, perceived as pleasant for the patient, and time efficient,
Dental impressions, either conventional or digital, are primarily aimed at obtaining an imprint of one or more prepared teeth, the adjacent and antagonist as well, in conjunction with the inter-occlusal record relationship. Thus, the reproducibility of the impression is a core criterion that reflects the definitive outcome of the planned restoration. Apart from the operational and clinical differences (speed of use, need of powder, and size of the tips) and cost (purchase and management) of various scanners, the essential aspect to be considered must be the quality of the data derived from scanning, which is defined as “accuracy.” Accuracy is the consolidation of two elements, both essential and complementary; “trueness” and “precision.” The term “trueness” refers to the ability of a measurement to match the actual value of the quantity being measured. Precision is defined as the ability of a measurement to be consistently repeated, or simply put, the ability of the scanner to derive repeatable outcomes when applied in varied measurements of the same object.
Different scanning techniques are been implemented in different IOSs that may yield different scanning accuracies. Therefore, the purpose of this review was to compare the accuracy of different IOSs and the effect of different variables on the accuracy outcome.
| I Study Design and Methods|| |
An electronic search of literature was performed using a PubMed database of Medline. Applying the PICO format of population = tooth/teeth/arch; intervention = IOS technique(s); comparison = alternative impression technique(s); and outcome = accuracy, was done to define the search question. The search was aimed to collect the articles that investigated the accuracy of IOS for teeth/arch published until 2018.
Different combination of the following terms was applied using Boolean operator of PubMed database:
Teeth/arch, digital impression, optical impression, IOS, and accuracy, to obtain potential references for review. Articles were considered for inclusion criteria if it was published in English language, laboratory or clinical study, evaluating a current IOS system, evaluating scanning accuracy, quantitative results provided, excluding the article other than in English, literature review, article that evaluate the marginal adaptation and fit evaluation of the fabricated restoration, scanning done for digital implant impression or implant-supported prosthesis and duplicates were discarded [Table 1].
| Results|| |
A search of MEDLINE (PubMed) identified 507 articles. After title and abstract screening, 412 articles were excluded for not meeting the inclusion criteria and discarding duplicate references. Ninety-five articles were followed for full screening; only 24 were included in the final analysis.
| Discussion|| |
The purpose of the present review was to determine the accuracy of the different IOSs. The studies included in the review have been mentioned in [Table 2]. Different IOSs evaluated in studies with their respective advantages and disadvantages have been summarized in [Table 3] and [Table 4]. A multitude of factors influences the reproducibility of an IOS, including the scanning technology, data processing algorithm, the choice to use powder, and image acquisition method. Active triangulation, a traditional scanning technology that is frequently utilized, offers the highest trueness. Comparatively, the parallel confocal technology need not require a certain distance for focusing, thus ensuring accurate images irrespective of whether the scanner tip is in contact with the teeth when the oral cavity is scanned. Concurrently, the optical coherence tomography provides for high resolution to procure an image of the micromorphology of the abutment by consolidating the optical interference phenomenon and the confocal microscopy technology. Park reported that restoration type, the preparation outline form, the scanning technology and the application of power affect the accuracy of the IOS.
Hack and Patzelt reported that TRIOS to be the most accurate (trueness ± 0.9 μm and precision 4.5 ± 0.9 μm) when scanned for single tooth compared to the other scanner (True definition, ITero, CS3500, Omnicam, and Planscan) and Omnicam and Planscan to be least accurate. Even Güth et al. results showed that Cerec Bluecam and Omnicam were least accurate in term of trueness compare to other scanners (CS 3500, Zfx Intrascan CEREC AC Bluecam, CEREC AC Omnicam, True Definition) with the True Definition and CS 3500 to be most accurate when used to scan a titanium model for four unitsfixed prosthesis (FPD).
The most critical component in prosthodontics for fixed prosthesis is the finish line accuracy when IOSs are used. Nedelcu et al. studied the finish line distinctness and finish line accuracy in 7 IOSs (3M, CS3500 and CS3600, DWIO, Omnicam, Planscan and TRIOS). TRIOS displayed the highest level of finish line distinctness and together with CS3600, the highest finish line accuracy, DWIO and PLAN, on the other hand, displayed a generally low level of finish line distinctness and finish line accuracy. The author, thus, reached on a consensus that there are sizeable variations between IOSs with both higher and lower finish line distinctness and finish line accuracy. High finish line distinctness had more correlation to high localized finish line resolution, and nonuniform tessellation than to high overall resolution, color output from some scanners may better delineate the finish line due to the contrast provided; but relies on the underlying technology.
In vitro scanning done for a complete arch by Kim et al. using 9 IOS found that median average trueness values were better for TRIOS as compared to the E4D and Zfx IntraScan scanners, which were found to be least accurate for full arch scan. The authors also observed that Fast Scan and True Definition IOSs, which require a powder coating before scanning, exhibited significantly better trueness than IOSs that did not require powdering.
Anotherin vitro study on scanning complete arch model by Ender and Mehl compared the accuracy of digital scanning (Lava COS and CEREC Bluecam) to conventional impressions (Impregum) reported similar trueness between the digital and conventional impressions, whereas the CEREC Bluecam showed significantly higher precision than the conventional and Lava COS. However, Patzelt et al., in their evaluation of 4 IOSs (CEREC Bluecam, iTero, Lava COS, and Zfx Intra Scan), demonstrated that the CEREC Bluecam was the least accurate (trueness 332.9 ± 64.8 μm; precision 99.1 ± 37.4 μm) and highest accuracy was observed with the Lava COS (trueness 38.0 ± 14.3 μm; precision 37.9 ± 19.1 μm). Similar finding was observed by the same author in 2014 while determining the accuracy of CAD/CAM-generated dental casts based on IOS data. Rehmann et al. found recently calibrated Cerec Bluecam had the highest trueness, followed by iTero and Lava COS.
A study by Jeong et al. for the complete arch model, digital impressions obtained by the Omnicam intraoral video scanner were more accurate than those obtained by the Bluecam intraoral still image scanner. In a comparison of the accuracy of Bluecam and Omnicam for single tooth scanning, Lee et al. reported similar precision for the two scanners.
Ender and Mehl analyzed the accuracy of four different IOSs and four different impression materials. The results revealed that CEREC Bluecam was the most accurate (trueness 29.4 ± 8.2 μm and precision 19.5 ± 3.9 μm) followed by iTero (trueness 32.4 ± 7.1 μm and precision 36.4 ± 21.6 μm), then Omnicam (trueness 37.3 ± 14.3 μm and precision 35.5 ± 11.4 μm), followed by Lava COS (trueness 44.9 ± 22.4 μm and precision 63.0 ± 21.6 μm). The authors concluded that digital systems with single image stitching (iTero and CEREC Bluecam) showed local deviations at the terminal end of the arch, whereas the video-based systems (CEREC Omnicam and Lava COS) showed compression of the dental arch and also stated that deviations of 100 μm and above across the full arch may lead to inaccurate fitting of the maxilla and mandible, which can be problematic in the case of large rehabilitations. Even other studies had stated that digital impression show distortion of distal aspect when scan for complete arch,,
Treesh et al. in his study of complete arch accuracy with four different IOS (CEREC Bluecam, CEREC Omnicam, TRIOS Color, and Carestream CS 3500) found that TRIOS was most accurate among the scanner and CS3500 was the least whereas Renne et al. had found that CS3500 performs better than the CEREC Bluecam, CEREC Omnicam for full-arch scan, but when the same scanner was used to scan the sextants, CS3500 was less accurate than the two. Authors gave the conclusion that scanners differ regarding the speed, trueness, and precision of sextant scans, with the Planscan and the CEREC Omnicam providing the best combination of speed, trueness, and precision and 3Shape TRIOS for the complete arch scan.
Ali founded differences in trueness between the different scanners (Cerec Bluecam, iTero, Lava COS, and E4D). Most accurate systems were iTero and Lava COS, and the least accuracy was reported for E4D followed by Cerec Bluecam.
Lee found no statistical significance between the TRIOS and iTero scanners. Even Anh et al. results showed the same when comparing the precision of the TRIOS and iTero. However, the scanning strategies have been shown to affect the accuracy.,,
In 2018, Malik et al. observed that conventional full-arch polyvinyl siloxane impressions exhibited higher accuracy compared to two direct optical scanners (TRIOS, 3Shape, and CEREC Omnicam, Sirona). Similar results were found when different scanner used to scan complete arch against the conventional impression in anin vivo studies as well asin vitro studies.,,, Hence, optical scanners seem to perform better in anin vitro environment, and their accuracy seems to be reducedin vivo as patient-specific factors, such as anatomic restrictions, movement, saliva, and soft tissue, contribute toward the accuracy of scan.,
Software version used for scanning can have a significant impact on the accuracy of an IOS. Nedelcu and Persson observed that even the type of material being scanned has a significant impact on the accuracy of the scanner. Greater deviations can be observed in the area of change of curvature, so it is better that grooves, sharp preparation edges, boxes should be avoided. Rounded internal line angles are easier to replicate by the CAM process on the fitting surface of prostheses.
Su and Sun reported decline in the precision of intraoral digital impression with the increase in the area of scanned arch. Precision was clinically acceptable when scanning scope was less than half arch, that means the larger and more complicated the scan area, the lower the accuracy, Therefore, it is difficult to compare individual studies directly to arrive at a general conclusion regarding the accuracy of IOS. Studies done for the digitization of edentulous arch with the IOS found out to be feasible in in vitro, but research is to be needed to recommend the use of the scanners for the digitization of edentulous jaws in vivo.,
For longer span prosthesis, not only recording the tooth surface accurately but also registration of the occlusal relationship is needed, which is difficult to record by IOS after preparation of several teeth. Indeed, studies,,,,,, have demonstrated that fabrication of single unit and short span prostheses (3 or 4 unit prostheses) using an IOS exhibit similar accuracy to prostheses fabricated by conventional techniques.
Digital dentistry is ushering in its popularity due to continued showcase of its potentials; however, much research is imperative to evaluate and compare the clinical accuracy of digital impression techniques for the complete arch. An amalgamation of the digital and conventional approach may provide the added benefits in clinical practice, in specific relation to the treatment strategies planned for each case.
| Conclusion|| |
Digital intraoral impression systems continue to undergo rapid development. Due to the heterogeneity of the data, it was difficult to compare individual studies directly to arrive at a general conclusion regarding the accuracy of IOSs, as different parameters (clinical or laboratory study, scanning for complete arch, partial edentulous arch or single tooth, and accuracy measured in term of resolution) are used to evaluate the accuracy of scanners. The accuracy of IOS is affected by several factors including the scanner technology, use of powder material being scanned, software for scanning, scanning strategy. Intraoral scanning systems, in comparison to conventional impressions, can be reliably used for diagnostic purposes and short-span scanning. However, for whole arch scanning, the IOS is susceptible of more deviation. The studies indicated a variable outcome of the different IOS systems. While the accuracy of IOS systems appears to be promising and comparable to conventional methods, they are still vulnerable to inaccuracies.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]