Dr. Mrinmayee Tushar Thakur, Dr. Naisargi Shah, Dr. Anshul Khanna, Dr. Ashutosh Pai, Dr. Rutuparn Sasane, Dr. Nikita Gharat
Professor and Head of Department,
Department of Prosthodontics, Crown & Bridge.,
T.P.C.T’s Terna Dental College, Navi Mumbai
Aim : This scoping review aims to evaluate the accuracy of digital impressions obtained from the intraoral scanners and extraoral scanners as a part of the pilot study for an anticipated systematic review.
Design and setting : The Arksey and O’Malley methodological framework.
Materials and methodology: An electronic systematic search was conducted in the PubMed database for articles published from 1st January 2006 to 31st July 2020. A combination of MeSH terms, Query and free-text terms was used. The population, intervention, comparisons, and outcomes (PICO) format was applied to formulate a research question. The outcome parameters were the trueness and/or precision for the accuracy of digital impressions.
The PICO details: Population: digital impressions obtained from scanners,
Intervention: Digital impressions obtained from the intraoral scanner,
Comparison : Digital impressions obtained from the extraoral scanner,
Outcome : Accuracy in terms of trueness and/or precision.
Results : 5 articles were identified after applying the inclusion and exclusion criteria and were included in this scoping review. The accuracy shown by the intraoral and extraoral scanners both lies within the clinically acceptable range. However, the intraoral scanners are more accurate than the extraoral scanners.
Conclusion : There seems to be a difference in the accuracy of digital impressions obtained from intraoral and extraoral scanners. A more detailed search of the available literature is required, preferably a systematic review, to draw a more definitive conclusion regarding the accuracy of the digital impressions.
Keywords : digital impressions, intraoral scanners, extraoral scanners, accuracy, trueness, precision
Citations : Thakur M, Shah N, Khanna A, Pai A, Sasane R, Gharat N. Comparison of Intraoral and Extraoral Scanners based on Trueness and/or Precision - A Scoping Review. J Prosthodont Dent Mater 2021;2(1):11-16.
Digital dental technology is increasingly becoming an integral part of the modern prosthodontic practice. Application of Computer-aided design/ computer-aided manufacturing (CAD/CAM) have provided high-quality dental restorations.1 The digital workflow consists of image acquisitions, data processing, and digital manufacturing. Precision in these steps results in the accurate adaptation of the restorations and prosthesis.
The image acquisition devices include intraoral scanners and extraoral scanners, that capture the details of a patient’s intraoral tissues and convert it to 3D data. The 3D data can be further edited using CAD software.3 New developments in the scanners have led to the advancement and success of image acquisition technology. As digital impression systems continue to upgrade, they may prove to be a better alternative to conventional impression techniques.4 Recording with digital scanners is easier, faster, and more accurate. The other advantages include less storage space, ease of accessibility, reproducibility, and transferability of the digital images between the clinic and dental lab, eliminating the laboratory production steps which may cause a misfit.5 The literature contains few studies comparing the digital accuracy of impressions constructed using intraoral and extraoral scanners. However, there is no clear consensus available.
Arksey and O’Malley (2005)6,7 identified various reasons for conducting a scoping review to examine the extent, range and nature of research activity to determine the value of undertaking a full systematic review, summarize and disseminate research findings and identify gaps in the existing literature. This scoping review focuses on the first step of a digital workflow that is to evaluate the accuracy of digital impressions obtained from the intraoral and extraoral scanners. This scoping review was conducted as a part of the pilot search for an anticipated systematic review.
Methodology: The Arksey and O’Malley methodological framework was followed for this scoping review (Figure 1)
Stage 1: Identifying the research question
The research question defined for this scoping review was, “Does the type of Scanning Technique (Intraoral or Extraoral) affect the Accuracy based on Trueness and/or Precision of Digital Impression?”
PICO Criteria was established based on the research question as follows.
POPULATION: Digital Impression obtained by digital scanners.
INTERVENTION: Digital Impression obtained by Intraoral Scanners.
COMPARISON: Digital impression obtained by Extraoral scanners.
OUTCOME: Accuracy for Digital Impression. Outcome parameters were assessed by trueness and precision of impression.
Stage 2: Identifying relevant studies
An electronic search of the PubMed database for articles published from 1st January 2006 to 31st July 2020 was conducted. The search was conducted using a combination of various controlled vocabulary terms (i.e., MeSH terms) as well as free text terms related to the research question. The MeSH terms used were Dental Impression technique, Data measurement accuracy and Data accuracy. The free text terms used were Digital Impression, Intraoral Scanners, Extraoral Scanners, Accuracy, Trueness and Precision. Various combinations of the MeSH terms and the free text terms were used to conduct the searches.
Stage 3: Study selection
Only those studies pertaining to digital impressions of dentulous patients or models, studies having outcome measures in Accuracy, Trueness, and/or Precision were included. Studies involving all different Intraoral and Extraoral scanning software and techniques were included. Also, articles published in the English language were included.
Studies pertaining to Conventional Impression without Digital Intervention, studies involving a comparison between Conventional methods and the Digital impression method, those involving Implant Impressions, Case reports, Magnetic Resonance Imaging (MRI) scans, Ongoing trials were excluded from this scoping review. Also, Studies with a sample size of less than 5 were excluded.
A total of 61 articles were obtained in the searches. 13 articles were included after the title screening, followed by the further exclusion of 5 articles after abstract evaluation. More than 3 articles were excluded after full-text evaluation. 5 articles fulfilled the inclusion and exclusion criteria and were included in this scoping review. (Figure 2)
Stage 4: Charting the data
The data was then extracted from the 5 selected studies and was entered into a Microsoft Excel spreadsheet (Figure 3).
The data items that were extracted and charted were as follows:
2. Year of publication.
3. Study setting.
4. Number of Scans.
5. Impression material used.
6. Accuracy combining Trueness and/or Precision OR individual Trueness and precision values
Stage 5: Collating, summarizing and reporting the results.
Among the Included 5 articles, Flugge et al.8 evaluated precision, Bohner et al.11 evaluated trueness while Vecsei et al.9, Sason et al.12 and Muallah et al.10 evaluated the accuracy of the digital impression. Some studies 9,10 evaluated the accuracy combining trueness and precision values of the digital impression. Flugge et al.8 and Sason et al.12 conducted invivo studies, where they evaluated full arch scans and single tooth scans respectively.
Vescei et al.9, Sason et al.12 and Muallah et al.10 evaluated the linear measurements between the landmarks on the model and compared the accuracy of those measurements. Flugge et al.8 and Bohner et al.11 compared the precision and trueness of the impression by superimposing the scans respectively.
Except for Flugge et al.8, all the other 4 studies 9-12 reported that accuracy digital impressions obtained from intraoral scanners are better than the extraoral scanner. However, according to them the accuracy of the digital impression obtained from the extraoral scanners are also in the acceptable range. It is difficult to draw any conclusion concerning these two digital impression techniques and more studies evaluating the accuracy of digital impressions are required.
Scoping reviews represent an increasingly popular approach to reviewing health research evidence as they represent a great tool to rapidly map the already available literature concerning a particular subject, thereby enabling researchers to identify the research potential and subsequently plan future researches.6,13,14, Similarly, this scoping review was primarily conducted as a part of a pilot search to assess the range and nature of research available, and to determine the necessity to conduct a systematic review on this topic in the future.
The Arksey and O’Malley methodological framework was followed for this scoping review. This was decided based upon the scoping review conducted by Pham MT et al. in which they found that the Arksey and O'Malley (2005) framework had been used in 62.6% (109/174) reviews. Making it the most frequently used framework design for scoping reviews.15 Levac et al. also reported that this framework provided an excellent methodological foundation for conducting scoping reviews.
The advent of CAD-CAM technology has paved the way for a highly precise and efficient digital workflow. An accurate digital impression is essential for the proper fit of the prosthesis. Accuracy (according to ISO 12836: 2012 Definition: 3.1) is the closeness of agreement between a result of a measurement and a true value of the measurement.17 ISO 5725-1 uses two parameters, trueness, and precision to describe the accuracy of a measurement method.
Trueness is the closeness of agreement between the average value obtained from a large series of test results and an accepted reference value (ISO 5725-1:1994 definition 3.7). Precision is the closeness of agreement between independent results of measurement obtained under a stipulated condition (ISO 12836: 2012 definition: 3.8). Both these factors in digital impression can justify the accuracy of an impression made, which in turn will give information about the superiority and reproducibility of the scanning system.
The limitations of this scoping review are that the search was limited to a single database and a select few MeSH terms, and free text terms were used in the search, due to which some of the available literature might have been overlooked. This scoping review also found that the accuracy of the digital impression may be affected by various factors and hence we need to find out various techniques or methods to overcome the difficulties related to these factors. Thus, a systematic review needs to be conducted on this subject to come to a more definitive conclusion.
- Scanning techniques do affect the accuracy of the digital impression.
- Intraoral scanners seem to be accurate when compared to extraoral scanners.
- More in-vivo and in-vitro studies with similar methodology assessing the accuracy of digital scanners are needed .
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17. International Organization for Standardization. ISO 12836:2012: Dentistry - digitizing devices for CAD/CAM systems for indirect dental restorations: test methods for assessing accuracy.
18. Accuracy (trueness and precision) of measurement methods and results. Part 1. General principles and definitions (ISO 5725-1:1994).