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Journal of Prosthetic Dentistry

Evaluation of complete-arch implant scanning with 5 different intraoral scanners in terms of trueness and operator experience

Open AccessPublished:April 05, 2021DOI:https://doi.org/10.1016/j.prosdent.2021.01.013

      Abstract

      Statement of problem

      The intraoral scanning of the edentulous arch might be challenging for an inexperienced operator because of the large mucosal area and the use of scan bodies.

      Purpose

      The purpose of this ex vivo study was to compare the trueness of 5 intraoral scanners in replicating implant scan bodies and soft tissues in an edentulous maxilla and to investigate the effects of operator experience.

      Material and methods

      The maxilla was resected from a fresh cadaver, 5 implants placed, and a reference scan made. Eight scans were made by experienced operators and 8 by an inexperienced operator with each scanner (iTero Element 2, Medit i500, Primescan, TRIOS 3, TRIOS 4). The implant platform deviation was measured after complete surface alignment and after scan body alignment. Deviation data were analyzed with a generalized linear mixed model (α=.05).

      Results

      After complete surface alignment, the mean ±standard deviation implant platform deviation was higher for the inexperienced operator (421 ±25 μm) than for experienced ones (191 ±12 μm, P<.001) for all scanners. After scan body alignment, no significant differences were found between operators for Element 2, Primescan, and TRIOS 3. The experienced operators produced a lower deviation for TRIOS 4 (35 ±3.3 μm versus 54 ±3.1 μm, P<.001), but higher deviation for i500 (68 ±4.1 μm versus 57 ±3.6 μm, P<.05). The scanner ranking was Element 2 (63 ±4.1 μm), i500 (57 ±3.6 μm, P=.443), TRIOS 4 (54 ±3.1 μm, P=.591), TRIOS 3 (40 ±3.1 μm, P<.01), Primescan (27 ±1.6 μm, P<.001) for the inexperienced operator and i500 (68 ±4.1 μm), Element 2 (58 ±4.0 μm, P=.141), TRIOS 3 (41 ±2.8 μm, P<.001), TRIOS 4 (35 ±3.3 μm, P=.205), Primescan (28 ±1.8 μm, P=.141) for the experienced operators.

      Conclusions

      Mucosal alignment greatly overestimated the platform deviation. The intraoral scanners showed different trueness during the complete-arch implant scanning. The operator experience improved the trueness of the edentulous mucosa but not implant platform deviation.
      Clinical Implications
      Experience is beneficial when scanning complete maxillary soft tissue but distortion is still high. However, by excluding the soft tissue to simulate the digital workflow for an implant-supported prosthesis, the implant platform trueness of the Primescan could be within the clinically acceptable range.
      The trueness of intraoral scanners for edentulous complete-arch scans with scan bodies has been investigated with a wide range of deviation from 31 μm to 810 μm, depending on the scanner type and measurement method.
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      Factors that influence the accuracy of complete-arch scanning include the number and type of scan bodies and their location and angulation.
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      Operator experience has been reported to improve the precision but not trueness of the TRIOS 3 (3Shape A/S) and CEREC Omnicam (Dentsply Sirona) scanners for a partially dentate arch with 3 implants.
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      • Gimenez B.
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      • Pradies G.
      Accuracy of a digital impression system based on parallel confocal laser technology for implants with consideration of operator experience and implant angulation and depth.
      but with the LAVA COS (3M) system, experienced users were reported to produce scans with significantly better accuracy.
      • Gimenez B.
      • Ozcan M.
      • Martinez-Rus F.
      • Pradies G.
      Accuracy of a digital impression system based on active wavefront sampling technology for implants considering operator experience, implant angulation, and depth.
      No effect of experience was reported on trueness for a gypsum cast with 4 scan bodies with the Carestream CS 3600 or with the TRIOS 3 scanners.
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      Trueness of intraoral scanners considering operator experience and three different implant scenarios: a preliminary report.
      These studies used complete surface alignment, including the edentulous mucosa and the scan bodies, with the deviation being measured on the complete surface. The best-fit algorithm minimizes surface distances
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      and does not recognize identical points. Therefore, the surface deviation resulted in a significantly lower deviation than between identical points of the 2 dentate digital casts.
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      A novel method for complex three-dimensional evaluation of intraoral scanner accuracy.
      In an edentulous arch, there is a large mucosal surface with few details. Thus, the superimposition might cause even less approximation of identical structures. However, the framework misfit occurs at the platform level, which is determined by the misalignment of the scan bodies.
      • Mangano F.G.
      • Admakin O.
      • Bonacina M.
      • Lerner H.
      • Rutkunas V.
      • Mangano C.
      Trueness of 12 intraoral scanners in the full-arch implant impression: a comparative in vitro study.
      ,
      • Imburgia M.
      • Kois J.
      • Marino E.
      • Lerner H.
      • Mangano F.G.
      Continuous scan strategy (CSS): a novel technique to improve the accuracy of intraoral digital impressions.
      Previous attempts have been made to overcome this problem either by applying scan body alignment
      • Mangano F.G.
      • Admakin O.
      • Bonacina M.
      • Lerner H.
      • Rutkunas V.
      • Mangano C.
      Trueness of 12 intraoral scanners in the full-arch implant impression: a comparative in vitro study.
      ,
      • Huang R.
      • Liu Y.
      • Huang B.
      • Zhang C.
      • Chen Z.
      • Li Z.
      Improved scanning accuracy with newly designed scan bodies: An in vitro study comparing digital versus conventional impression techniques for complete-arch implant rehabilitation.
      or by measuring the scan body deviation,
      • Di Fiore A.
      • Meneghello R.
      • Graiff L.
      • Savio G.
      • Vigolo P.
      • Monaco C.
      • et al.
      Full arch digital scanning systems performances for implant-supported fixed dental prostheses: a comparative study of 8 intraoral scanners.
      ,
      • Roig E.
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      • et al.
      In vitro comparison of the accuracy of four intraoral scanners and three conventional impression methods for two neighboring implants.
      but the 2 methods have not been combined. Furthermore, these studies measured the deviation on the visible part of the scan body; therefore, they might not estimate the displacement of the implant platform.
      The accuracy of intraoral scanners has been reported to depend on the physical composition of the substrate.
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      • Culp A.
      • et al.
      The effect different substrates have on the trueness and precision of eight different intraoral scanners.
      Therefore, basing a study on a human specimen is more clinically relevant than studies on gypsum casts or plastic models.
      • Bilmenoglu C.
      • Cilingir A.
      • Geckili O.
      • Bilhan H.
      • Bilgin T.
      In vitro comparison of trueness of 10 intraoral scanners for implant-supported complete-arch fixed dental prostheses.
      • Mangano F.G.
      • Admakin O.
      • Bonacina M.
      • Lerner H.
      • Rutkunas V.
      • Mangano C.
      Trueness of 12 intraoral scanners in the full-arch implant impression: a comparative in vitro study.
      • Mizumoto R.M.
      • Yilmaz B.
      • McGlumphy Jr., E.A.
      • Seidt J.
      • Johnston W.M.
      Accuracy of different digital scanning techniques and scan bodies for complete-arch implant-supported prostheses.
      • Sami T.
      • Goldstein G.
      • Vafiadis D.
      • Absher T.
      An in vitro 3D evaluation of the accuracy of 4 intraoral optical scanners on a 6-implant model.
      • Mangano F.G.
      • Veronesi G.
      • Hauschild U.
      • Mijiritsky E.
      • Mangano C.
      Trueness and precision of four intraoral scanners in oral implantology: a comparative in vitro study.
      • Di Fiore A.
      • Meneghello R.
      • Graiff L.
      • Savio G.
      • Vigolo P.
      • Monaco C.
      • et al.
      Full arch digital scanning systems performances for implant-supported fixed dental prostheses: a comparative study of 8 intraoral scanners.
      • Mizumoto R.M.
      • Alp G.
      • Ozcan M.
      • Yilmaz B.
      The effect of scanning the palate and scan body position on the accuracy of complete-arch implant scans.
      A human specimen is more likely to be necessary for analyzing completely edentulous arches where long spans of soft tissue are present beyond the dimension of the frame of capture between scan bodies.
      The aim of the present study was to evaluate the effect of the experience on the trueness of 5 intraoral scanners for complete-arch implant scans of an edentulous cadaveric maxilla. The implant platform deviation was calculated after complete surface alignment and after scan body alignment. The null hypotheses were that no significant differences would be found among the scanner systems and between experienced and inexperienced operators, regardless of the superimposition technique.

      Material AND methods

      A fresh cadaver head with a completely edentulous maxilla was procured for this study compliant with the Institutional Review Board for Human Research in the Medical University of South Carolina. The maxilla was resected immediately from the specimen which included both hard and soft tissue and the keratinized and mucosal tissues present. To maintain the fidelity of the specimen, preservatives were not applied during the study.
      Five endosseous ASTRA TECH EV dental implants (Ø4.2×13 mm) were placed in the maxilla by an experienced surgeon (Z.E.) in an optimal restorative configuration. A torque of at least 25 Ncm was achieved at each site. Five intraoral Ø4.2-mm scan bodies (Atlantis Intraoral FLO IO-P-03; ASTRA TECH) were attached to the implants (Fig. 1). The specimen was coated with scanning preparation spray (CEREC Optispray; Dentsply Sirona) as per the protocol established for the use of the industrial scanner (ATOS Capsule scanner; GOM GmbH) to obtain a standardized reference scan. As per the manufacturer (GOM GmbH), it has a precision deviation of 3 μm to 15 μm. Five different intraoral scanners were compared (Table 1). With each scanning system, 16 scans were made in total: 8 by an experienced operator and 8 by an inexperienced operator. The inexperienced operator (G.R.) was a dental student without prior experience with any of the systems. However, this user received a lecture on complete-arch scanning. The 4 experienced operators had extensive experience, including intraoral complete arch scanning, with each system (Z.E. for Element 2, A.M. for i500, M.L. for Primescan, W.R. for the TRIOS systems). All operators followed the manufacturers' recommended scan patterns. Scanners were used in a stratified randomization order. The maxilla was kept on ice to prevent degradation or dimensional changes of the specimen during the scanning process. It was removed for each scan and was returned to the ice between scans. Apart from those made with the Element 2, all scans were processed by the software program associated with each scanner and were directly exported as standard tessellation language (STL) files. For the Element 2, STL files were downloaded from the manufacturer webpage (myitero.com, Align Technology) after processing was performed off-site by the company.
      Figure thumbnail gr1
      Figure 1Five endosseous ASTRA TECH EV dental implants installed into completely edentulous human maxilla. Ø4.2×5.5-mm scan bodies (Atlantis IO FLO P-O3, ASTRA TECH) attached to implants.
      Table 1Intraoral scanner and software versions used
      Intraoral ScannerSoftware VersionManufacturer
      iTero Element 21.9.3.7Align Technology
      Medit i5001.2.0.3Medit Corp
      Primescan5.0.1Dentsply Sirona
      TRIOS 31.6.9.13Shape A/S
      TRIOS 41.18.3.53Shape A/S
      The superimposition and measurement were made in 2 different ways on each scan. The STL files of the master scan and intraoral scan were imported into a comprehensive metrology program (GOM Inspect software; GOM GmbH) individually and aligned by the best-fit algorithm considering all the surface points. Cylinders were fitted onto the cylindriform lower part of each scan body by the Gaussian best-fit method (Fig. 2). The coordinates of the axes of 2 cylinders were exported, and the 2 vectors of the axes were linearly extrapolated in 3 dimension by the length of the scan body, which was 5.5 mm from the top of the cylindrical part to the implant platform. The 3-dimensional deviation was calculated between the endpoint of the 2 vectors by the 3-dimensional Pythagoras term. The angle between the axes of the 2 cylinders within a scan body was also calculated. In the second method, the 5 scan bodies were selected, and the 2 scans were aligned, considering only the scan bodies' surfaces. The deviations in the platform and the angle between cylinders were calculated similarly to the first method. Each scan had 5 scan bodies, and for statistical analysis, these values were averaged.
      Figure thumbnail gr2
      Figure 2Measurement method of platform deviation. A, Master scan and actual scans aligned by minimizing differences (closest point algorithm). B, Moved away from each other for demonstration purpose to make deviance between 2 fitted cylinders visible. C, Surface comparison map of scan body. Mean surface deviation 0.210 mm, platform 0.290 mm.
      The data were exported into a statistical software program (IBM SPSS Statistics for Windows, v24.0; IBM Corp) for statistical evaluation. Data in the text and the figures are presented as mean and standard error of the mean. Data were analyzed with a generalized linear mixed model with a gamma distribution and log-link function approach with restricted maximum likelihood estimation. Scanners and experience were the main comparative factors, with their interactions integrated into the model. Four models were run separately, 2 for the platform deviation and 2 for the angulation after either complete surface alignment or after scan body alignment. The P values were adjusted by the Bonferroni method for pairwise comparison (α=.05). Correlations between the 2 deviation values measured were assessed by the Spearman rank correlation coefficient (r).

      Results

      The deviation and the angle measured at the implant platform for various scanners after complete surface and scan body alignment are shown in Table 2. After complete surface alignment, a significant interaction between experience and scanner was found in platform deviation (P<.001). With all scanners, the experienced users had significantly lower deviation (all P<.001) (Fig. 3A). Significant differences in trueness were found among the scanners at the implant platform depending on operator experience (Table 3). For the inexperienced operator, the greatest deviation was measured with the Element 2, significantly greater than the i500 and the Primescan, but similar to the TRIOS 3 and the TRIOS 4. The trueness of the i500 was not significantly different from the Primescan or the TRIOS 3, but it was better than the TRIOS 4. No significant differences were found between the Primescan and the TRIOS 3, between the Primescan and the TRIOS 4, or between the TRIOS 3 and 4. For experienced operators, the Element 2 had significantly greater deviation than the i500, the Primescan, the TRIOS 3, and the TRIOS 4. The deviation of i500 was not significantly different compared with the Primescan, TRIOS 3, or TRIOS 4. The Primescan was not significantly different from the TRIOS 3 or TRIOS 4. No difference was found between the TRIOS systems.
      Table 2Deviation and angle in implant platform after different alignment


      Scanners
      ExperienceComplete Surface AlignmentScan Body Alignment
      Platform Deviation (μm)Angle (Degree)Platform Deviation (μm)Angle (Degree)
      MeanSEMMeanSEMMeanSEMMeanSEM
      Element 2Inexperienced490340.740.10634.10.300.03
      Experienced343310.690.09583.90.280.03
      i500Inexperienced375250.380.05573.50.250.02
      Experienced160120.440.06684.00.390.04
      PrimescanInexperienced391300.470.06271.70.100.01
      Experienced157150.360.05281.90.130.01
      TRIOS 3Inexperienced417310.460.06402.90.190.02
      Experienced184180.360.05402.70.200.02
      TRIOS 4Inexperienced442280.560.07543.20.170.02
      Experienced159140.340.04353.40.170.02
      SEM, standard error of mean.
      Figure thumbnail gr3
      Figure 3Implant platform deviation differences between inexperienced and experienced users. A, After complete surface alignment. B, After scan body alignment. ∗Significant differences between inexperienced and experienced users P<.05, ∗∗∗ P<.001.
      Table 3Differences in implant platform deviation among scanners
      ExperienceScannersComplete Surface AlignmentScan Body Alignment
      Platform Devitation (μm)Angle (Degree)Platform Devitation (μm)Angle (Degree)
      MeanSEMP<MeanSEMP<MeanSEMP<MeanSEMP<
      InexperiencedElement 2-i50011524.0010.360.08.0016.55.3.4420.060.03.156
      Element 2-Primescan9928.010.260.08.0136.74.4.0010.200.03.001
      Element 2-TRIOS 37328.0700.280.08.0123.25.0.0010.110.03.001
      Element 2-TRIOS 44823.1860.180.08.1609.85.1.1640.130.03.001
      i500-Primescan-1623.820-0.100.05.33830.23.8.0010.140.02.001
      i500-TRIOS 3-4224.320-0.080.05.43116.74.5.0010.050.03.090
      i500-TRIOS 4-6718.001-0.180.06.053.34.7.4730.080.02.01
      Primescan-TRIOS 3-2628.8200.010.06.813-13.53.4.001-0.090.02.001
      Primescan-TRIOS 4-5223.151-0.080.06.431-26.83.6.001-0.070.02.001
      TRIOS 3-TRIOS 4-2523.820-0.100.06.431-13.34.3.010.020.02.318
      ExperiencedElement 2-i50018328.0010.240.07.01-9.95.5.211-0.110.04.05
      Element 2-Primescan18629.0010.330.07.00129.94.3.0010.140.03.001
      Element 2-TRIOS 315930.0010.330.07.00117.84.7.0010.080.03.05
      Element 2-TRIOS 418428.0010.350.07.00122.95.1.0010.110.03.001
      i500-Primescan3151.0000.090.05.35039.84.4.0010.260.04.001
      i500-TRIOS 3-2417.9080.090.05.35027.74.8.0010.190.04.001
      i500-TRIOS 41141.0000.100.05.18832.85.2.0010.220.04.001
      Primescan-TRIOS 3-2719.9080.000.041.000-12.13.3.001-0.060.02.01
      Primescan-TRIOS 4-2161.0000.020.041.000-7.03.8.211-0.040.02.086
      TRIOS 3-TRIOS 42518.9080.020.041.0005.14.3.2400.030.02.234
      SEM, standard error of mean.
      After complete surface alignment, a significant interaction between experience and scanner was found in the angle between the cylinder axes (P<.01). The experienced users had significantly lower angle deviation with Primescan (P<.05), TRIOS 3 (P<.05), and TRIOS 4 (P<.001). No significant difference was observed for Element 2 (P=.556) and i500 (P=.181). For the inexperienced operator, the angle deviation for Element 2 was greater than for i500, for Primescan, for TRIOS 3, but it was similar to TRIOS 4 (Table 3). The i500 had a significantly lower angle deviation than the TRIOS 4. No significant differences were found between i500 and Primescan or TRIOS 3, between Primescan and the 2 TRIOS systems, or between the TRIOS systems. For experienced operators, the angle deviation for Element 2 was greater than for i500, for Primescan, for TRIOS 3, and for TRIOS 4. No significant differences were found between i500 and Primescan, between TRIOS 3 and TRIOS 4, between Primescan and the 2 TRIOS systems, or between the TRIOS systems.
      After scan body alignment, a significant interaction between experience and scanner was found in implant platform deviation (P<.001). The experienced users had significantly lower deviation with TRIOS 4 (P<.001) (Fig. 3B) and greater with i500 (P<.05). With the other scanners, no difference was observed among the operators (Element 2, P=.338; Primescan, P=.558; TRIOS 3, P=.996). Significant differences were found among the scanners, depending on operator experience (Table 3). For the inexperienced operator, the deviation for the Element 2 was greater than for Primescan and for TRIOS 3. It was similar to the i500 and TRIOS 4. The deviation of the i500 was greater than that of Primescan and TRIOS 3, and it was not significantly different from the TRIOS 4. The deviation of Primescan was lower than that of TRIOS 3 and TRIOS 4. TRIOS 3 had a lower deviation than TRIOS 4. For experienced operators, the Element 2 had significantly greater deviation than Primescan, TRIOS 3, and TRIOS 4, but it was similar to the i500. The deviation of i500 was greater than that of Primescan, TRIOS 3, and TRIOS 4. The Primescan was not significantly different from TRIOS 4, but it had a lower deviation than the TRIOS 3. No significant difference was found between the 2 TRIOS systems.
      After scan body alignment, a significant interaction between experience and scanner was found in the angle between the cylinders (P<.01). The experienced users had a significantly lower angle with i500 (P<.001) and Primescan (P<.05). No significant differences were observed with Element 2 (P=.436), TRIOS 3 (P=.828), and TRIOS 4 (P=.966). For the inexperienced operator, Element 2 had the greatest angle deviation. It was significantly greater than that for Primescan, TRIOS 3, and TRIOS 4 (Table 3). It was not significantly different compared with i500. The i500 had a significantly greater angle deviation than the Primescan and TRIOS 4. No significant differences were found between i500 and TRIOS 3. The Primescan had a significantly lower angle deviation than TRIOS 3 and TRIOS 4. No difference was found between the TRIOS systems. For experienced operators, i500 had the greatest angle deviation, and it was significantly greater than Element 2, Primescan, TRIOS 3, and TRIOS 4. Element 2 had a greater angle deviation than Primescan, TRIOS 3, and TRIOS 4. The Primescan had a significantly lower angle deviation than TRIOS 3, but similar to TRIOS 4. No significant differences were found between the 2 TRIOS systems.
      The rankings of the scanners based on the 4 parameters are summarized in Table 4. The overall ranking of the scanners was more explicit in the experienced group than in the inexperienced one. No significant correlation was found in the implant platform deviation between the complete surface alignment and scan body alignment (r=0.20, P=.072).
      Table 4Ranking of scanners based on deviation values
      ExperienceAlignmentDeviation1 (Lowest)2345 (Greatest)
      InexperiencedComplete surfaceImplant platformi500PrimescanTRIOS 3TRIOS 4Element 2
      Scan bodyImplant platformPrimescanTRIOS 3TRIOS 4i500Element 2
      Complete surfaceAnglei500TRIOS 3PrimescanTRIOS 4Element 2
      Scan bodyAnglePrimescanTRIOS 4TRIOS 3i500Element 2
      ExperiencedComplete surfaceImplant platformPrimescanTRIOS 4i500TRIOS 3Element 2
      Scan bodyImplant platformPrimescanTRIOS 4TRIOS 3Element 2i500
      Complete surfaceAngleTRIOS 4PrimescanTRIOS 3i500Element 2
      Scan bodyAnglePrimescanTRIOS 4TRIOS 3Element 2i500
      Same color indicates same scanner. Gray, i500; green, Primescan; yellow, TRIOS 3; pale red, TRIOS 4; blue, Element 2.

      Discussion

      The null hypotheses were rejected as a significant difference was observed among the scanners and the operators. High deviation on the platform after complete surface alignment suggests that an accurate mucosal scan is problematic, especially for inexperienced users. It also indicates that complete surface distance was minimized by the best-fit algorithm not considering the identical points such as the implant platform. The identical point method could result in higher deviation compared with the surface comparsion method.
      • Vag J.
      • Nagy Z.
      • Simon B.
      • Mikolicz A.
      • Kover E.
      • Mennito A.
      • et al.
      A novel method for complex three-dimensional evaluation of intraoral scanner accuracy.
      This was also suggested by the lack of correlation between the 2 alignment methods. Low deviation and no effect of experience were found after scan body alignment. The scan body surface error could be compensated for by fitting the cylinder, canceling out the effect of experience. This analyzing technique best replicates the digital laboratory workflow
      • Mangano F.G.
      • Admakin O.
      • Bonacina M.
      • Lerner H.
      • Rutkunas V.
      • Mangano C.
      Trueness of 12 intraoral scanners in the full-arch implant impression: a comparative in vitro study.
      ,
      • Huang R.
      • Liu Y.
      • Huang B.
      • Zhang C.
      • Chen Z.
      • Li Z.
      Improved scanning accuracy with newly designed scan bodies: An in vitro study comparing digital versus conventional impression techniques for complete-arch implant rehabilitation.
      ; therefore, these values have more clinical relevance.
      The ranking of the scanner performance was more consistent in the experienced than in the inexperienced group. Two scanners shared the worst (Element 2 and i500) and the best (TRIOS 4 and Primescan), with about twice the difference between them. The recommended 30 μm for passive fit
      • Imburgia M.
      • Kois J.
      • Marino E.
      • Lerner H.
      • Mangano F.G.
      Continuous scan strategy (CSS): a novel technique to improve the accuracy of intraoral digital impressions.
      was only achieved by the Primescan in the present study. However, the recommended value was achieved in a clinical study by splinting the scan bodies together before intraoral scan,
      • Imburgia M.
      • Kois J.
      • Marino E.
      • Lerner H.
      • Mangano F.G.
      Continuous scan strategy (CSS): a novel technique to improve the accuracy of intraoral digital impressions.
      which could decrease the deviation.
      • Huang R.
      • Liu Y.
      • Huang B.
      • Zhang C.
      • Chen Z.
      • Li Z.
      Improved scanning accuracy with newly designed scan bodies: An in vitro study comparing digital versus conventional impression techniques for complete-arch implant rehabilitation.
      ,
      • Iturrate M.
      • Eguiraun H.
      • Etxaniz O.
      • Solaberrieta E.
      Accuracy analysis of complete-arch digital scans in edentulous arches when using an auxiliary geometric device.
      Compared with the present values, the surface deviation of the scan bodies after their alignment was reported to be lower for the i500 (32.2 μm),
      • Mangano F.G.
      • Admakin O.
      • Bonacina M.
      • Lerner H.
      • Rutkunas V.
      • Mangano C.
      Trueness of 12 intraoral scanners in the full-arch implant impression: a comparative in vitro study.
      but it was similar for the Primescan (38.4 μm)
      • Mangano F.G.
      • Admakin O.
      • Bonacina M.
      • Lerner H.
      • Rutkunas V.
      • Mangano C.
      Trueness of 12 intraoral scanners in the full-arch implant impression: a comparative in vitro study.
      and TRIOS 3 (36.4 μm).
      • Bilmenoglu C.
      • Cilingir A.
      • Geckili O.
      • Bilhan H.
      • Bilgin T.
      In vitro comparison of trueness of 10 intraoral scanners for implant-supported complete-arch fixed dental prostheses.
      ,
      • Mangano F.G.
      • Admakin O.
      • Bonacina M.
      • Lerner H.
      • Rutkunas V.
      • Mangano C.
      Trueness of 12 intraoral scanners in the full-arch implant impression: a comparative in vitro study.
      The greater values for axis deviation of the scan bodies after complete surface alignment (ranging from 130 to 220 μm) were found for TRIOS 3,
      • Mizumoto R.M.
      • Yilmaz B.
      • McGlumphy Jr., E.A.
      • Seidt J.
      • Johnston W.M.
      Accuracy of different digital scanning techniques and scan bodies for complete-arch implant-supported prostheses.
      ,
      • Moslemion M.
      • Payaminia L.
      • Jalali H.
      • Alikhasi M.
      Do type and shape of scan bodies affect accuracy and time of digital implant impressions?.
      which was similar to the platform deviation in the present study, indicating that increasing the amount of soft tissue in the superimposition increases the deviation. However, Sami et al
      • Sami T.
      • Goldstein G.
      • Vafiadis D.
      • Absher T.
      An in vitro 3D evaluation of the accuracy of 4 intraoral optical scanners on a 6-implant model.
      reported that after scan body alignment, the surface deviation of the scan bodies was 18 times greater (740 μm) for TRIOS than the platform deviation (40 μm) found in the present study. The difference could be explained by calculating the deviation from the surface instead of from the cylinder fit and by using an older software version and by the fact that the root mean square error is more sensitive to outliers than the mean absolute deviation.
      • Chai T.
      • Draxler R.R.
      Root mean square error (RMSE) or mean absolute error (MAE)? – Arguments against avoiding RMSE in the literature.
      All angular deviations were under 0.74 degrees, which should not be clinically relevant, although the clinical acceptance level is unclear.
      • Flugge T.
      • van der Meer W.J.
      • Gonzalez B.G.
      • Vach K.
      • Wismeijer D.
      • Wang P.
      The accuracy of different dental impression techniques for implant-supported dental prostheses: A systematic review and meta-analysis.
      After complete surface alignment without the scan bodies, the angle deviation for TRIOS was 3 times greater
      • Mizumoto R.M.
      • Yilmaz B.
      • McGlumphy Jr., E.A.
      • Seidt J.
      • Johnston W.M.
      Accuracy of different digital scanning techniques and scan bodies for complete-arch implant-supported prostheses.
      than that reported in the present and another study
      • Moslemion M.
      • Payaminia L.
      • Jalali H.
      • Alikhasi M.
      Do type and shape of scan bodies affect accuracy and time of digital implant impressions?.
      with scan body alignment. The angle was smaller for all scanners with the scan body alignment than the complete surface alignment, indicating that complete surface alignment adversely affected the deviation. Scan bodies are long and protrude from the surface; thus, they can help alignment to the proper axis.
      A human specimen should be more realistic than stone or plastic casts, especially for the analysis of a completely edentulous arch. However, limitations of this ex vivo study included that the scanner head better accessed the cadaver tissue than in the oral cavity and cadaver tissue contains less moisture and is immobile. The different ambient light conditions might also have influenced the results.
      • Revilla-Leon M.
      • Jiang P.
      • Sadeghpour M.
      • Piedra-Cascon W.
      • Zandinejad A.
      • Ozcan M.
      • et al.
      Intraoral digital scans: Part 2-influence of ambient scanning light conditions on the mesh quality of different intraoral scanners.
      • Revilla-León M.
      • Jiang P.
      • Sadeghpour M.
      • Piedra-Cascón W.
      • Zandinejad A.
      • Özcan M.
      • et al.
      Intraoral digital scans—Part 1: Influence of ambient scanning light conditions on the accuracy (trueness and precision) of different intraoral scanners.
      • Revilla-Leon M.
      • Subramanian S.G.
      • Ozcan M.
      • Krishnamurthy V.R.
      Clinical study of the influence of ambient light scanning conditions on the accuracy (trueness and precision) of an intraoral scanner.
      Following other studies,
      • Sami T.
      • Goldstein G.
      • Vafiadis D.
      • Absher T.
      An in vitro 3D evaluation of the accuracy of 4 intraoral optical scanners on a 6-implant model.
      ,
      • Vag J.
      • Nagy Z.
      • Simon B.
      • Mikolicz A.
      • Kover E.
      • Mennito A.
      • et al.
      A novel method for complex three-dimensional evaluation of intraoral scanner accuracy.
      the present data also confirmed that the standardization of the parameters should be obligatory in future IOS trueness studies. Further research is necessary to assess the effect of alternative scan body designs, as well as splinting them together.

      Conclusions

      Based on the findings of this ex vivo study, the following conclusions were drawn:
      • 1.
        Experience with intraoral scanners improved the accuracy of superimposition of a complete arch, including the palatal mucosa, but it had little effect on the trueness of the implant platform after excluding the soft tissues.
      • 2.
        The best implant platform trueness was obtained by the Primescan and TRIOS 4 (statistically equivalent), followed by TRIOS 3. The trueness for the i500 and Element 2 was about half that of the Primescan and TRIOS 4.

      Acknowledgments

      The authors thank Dentsply Sirona for supplying complimentary implants.

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