Nowadays, computer-aided design/computer-aided manufacturing (CAD/CAM) technology is becoming increasingly popular due to fewer clinical sessions, leading to higher patient comfort. ¹ , ² , ³ This technology has been popular since the 1980s and is currently used to manufacture a wide range of dental prostheses such as fixed partial dentures, removable partial frameworks, maxillofacial prostheses, and complete dentures. ⁴ , ⁵ , ⁶ The processing chain of CAD/CAM technology consists of three different steps, namely scanning, designing, and manufacturing of the prosthesis, which can be milled or 3D-printed using different types of materials. ⁷

There are two types of scanners based on the method of fabrication of CAD/CAM crowns: intraoral scanners which directly scan the dental arch and extraoral scanners, scanning either the dental impressions or the laboratory-fabricated casts. Intraoral scanners mainly use the tenets of active triangulation, confocal microscopy, and wave-front sampling. The output of these scanners can be divided into two subgroups of camera image impressions and video image impressions. ⁴ , ⁸ , ⁹ , ¹⁰ , ¹¹ Extraoral scanners are divided into three subgroups, namely laser, structured light, and contact scanners. ⁴ Laser and light scanners produce scans faster and are not influenced by the density of the object. Despite this advantage, these types of scanners are affected by the optical properties of the object being scanned such as shininess of the surface and brightness. Contact scanners use a contact probe touching a cast, which is highly accurate but can potentially damage the scanned surface. The slow scanning speed of this group of scanners is another drawback of this type of scanners. ¹ , ⁴ , ¹² , ¹³ , ¹⁴

Enhancement of accuracy is among the most important goals of digital dentistry, and computer-aided technology can decrease discrepancies which occur during the conventional method of impression making and crown fabrication. ¹⁵ , ¹⁶ , ¹⁷ , ¹⁸ According to different technologies of intraoral and extraoral scanners, different companies produce different types of scanners. There is inconsistent information about the accuracy of crowns made with these systems. Accuracy of scanners consists of precision (how close the repeated measurements are to each other), trueness (how far the measurements are aberrant from the actual dimensions), and marginal adaptation. ¹⁵ , ¹⁹ , ²⁰ , ²¹

The purpose of this study was to compare the accuracy (precision and trueness) of eight dental scanners for dental bridge scanning. The null hypothesis was assumed for this investigation was that there would be no differences between different dental scanners with regard to accuracy.

This in-vitro experimental study compared the accuracy (precision and trueness) of eight dental scanners. The accuracy of Sirona inEos inLab (Dentsply Sirona, USA), Sirona X5 (Dentsply Sirona, USA), Dentium Rainbow™ (Dentium, Korea), imes icore 350I I3D (imes-icore, Germany), Amann Girrbach map 100 (Amann Girrbach, Austria), 3Shape D100 (3shape, Denmark), and 3Shape E3 (3shape, Denmark) was evaluated, and data of each scanner were compared with the data received from the 3shape Trios intraoral scanner (3shape, Denmark) as the reference.

A typodont model (Hossbm, Iran) with a missing maxillary right first molar was prepared for a 3-unit fixed partial denture by a prosthodontist according to the principles of Rosenstiel et al. ⁷ Next, three points were created on the surface of the prepared tooth as reference points. Each scanner performed seven scans of the typodont, and the obtained data were analyzed using 3D-tool software (3D-Tool GmbH and Co., KG, Germany). The abutment length, abutment width, arch length, and interdental distance were measured, as shown in Figure 1. In order to compare the trueness, the prepared typodont was first scanned with 3shape Trios scanner as the reference. This true value was then compared with the measurements made by each scanner. Then, precision was determined based on the differences in values obtained by repeated measurements by each scanner. Figure 1

3D-Tool software and the measurement sequence: (a) Images of abutment with reference points on its surfaces scanned with ATOS scanner. (b) Selecting the measure markup item. (c) Selecting the vortex item. (d) Marking the deepest point on reference area. (e) Measuring the exact distance between the two selected points.

The mean and standard deviation of arch length Table 1, crown width of tooth #14 Table 2, crown width of tooth #16 Table 3, interdental distance Table 4, crown length of tooth #14 Table 5, and crown length of tooth #16 Table 6were compared using the one-way ANOVA Table 7.{Table 1}{Table 2}{Table 3}{Table 4}{Table 5}{Table 6}{Table 7}

The mean crown width of tooth #14, crown length of tooth #14, and crown length of tooth #16 were significantly different (P < 0.05) among the test groups. The results of post-hoc Tukey's test showed that the crown width of tooth #14 was significantly different between Sirona inEos and Dentium (P = 0.007), Sirona 25 and Imes icore350i (P = 0.018), and Imes icore350i and Dentium (P = 0.002). The crown length of tooth #14 was significantly different between Sirona inEos and Dentium (P = 0.031), Sirona inEos and Amann Girrbach (P = 0.016), and Sirona inEos and 3Shape E3 (P = 0.012). The crown length of tooth #16 was significantly different between Sirona inEos and Amann Girrbach (P = 0.008).

According to the current results, the reported trueness values for 3Shape Trios, Sirona inEos inLab, Sirona X5, Dentium, Imes icore350i, Amann Girrbach, 3Shape d700, and 3Shape e3 were 63, 45, 71, 67, 70, 53, 38, and 42 μm, respectively, whereas the precision values were 14, 29, 44, 34, 45, 44, 30, and 28 μm, respectively Table 8.{Table 8}

Nowadays, conventional impression making with impression materials is exceedingly replaced with digital impression making utilizing dental scanners. These scanners operate based on different technologies which have some negative and positive points that can affect their accuracy.

This study was conducted to evaluate and compare the accuracy (precision and trueness) of eight dental scanners. On the basis of the results of this study, the null hypothesis regarding the absence of a significant difference in the accuracy of different dental scanners was rejected.

The measured values were higher than the accuracy declared by the manufacturers (10–20 μm). ²² Such different values may be due to differences in sharp angles or smooth surfaces used to assess the scanners.

Different values have been reported in different studies. Persson et al. reported a trueness value of 10 μm for a contact scanner. ²³ DeLong et al. found 18–30 μm discrepancy for structured light scanners. ²⁴ While Del Corso et al. measured a trueness value of 14–21 μm for structured light scanners. ²⁵ In the present study, we found a trueness value of 61 μm for structured light scanners. These differences may be due to the use of different scanners and different preparation of surfaces for scanning.

González de Villaumbrosia et al. showed that laser scanners had the highest trueness (35 μm) and precision (44 μm) and the values were higher than those obtained by light scanners. ¹³ According to their results, none of the scanners had the best-recorded values for all variables and each scanner had higher values for some specific aspects of the scanning procedure. They also showed that the structured light scanners did not present higher values compared to others while they are commonly recommended as the best scanners. The results of the present study were in accordance with those of Gonzalez et al. The 3Shape d700 had the highest trueness and the difference in the trueness value of this scanner and that of structured light scanners was significant. The 3Shape Trios intraoral scanner, utilizing the confocal technology, had the highest precision value among all, which maybe because of the ability to sequentially capture pictures from an object. Superior trueness recorded in our study for 3Shape Trios intraoral scanner was in agreement with the findings of Gonzalez et al. Sirona X5 and i3dcam (Imes icore 350i) structured light scanners had lower precision values among all. Structured light scanners which were used in this study did not show higher values in every aspect.

Most previous studies on this topic have some limitations because only single-tooth scans were used to compare accuracy. ²² In this study, complete-arch scan yielded higher validity and reliability.

Within the limitations of this study, the results showed that the tested scanners had significant differences with each other in terms of trueness and precision. 3Shape D700 extraoral scanner had the highest trueness while the minimum trueness was noted in Sirona X5. The best precision value was recorded for 3shape trios scanner, whereas Imes icore 350i had the worst precision value.

Financial support and sponsorship

This study was financially supported by the Hamedan University of Medical Sciences, Hamadan, Iran.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or non-financial in this article.