|Year : 2022 | Volume
| Issue : 3 | Page : 279-287
Accuracy between intraoral and extraoral scanning: Three-dimensional deviation and effect of distance between implants from two scanning methods
Ana Larisse Carneiro Pereira, Henrique Vieira Melo Segundo, Luiz Carlos Alves Júnior, Adriano Rocha Germano, Adriana Da Fonte Porto Carreiro
Department of Dentistry, Federal University of Rio Grande Do Norte (UFRN), Natal, Rio Grande do Norte, Brazil
|Date of Submission||01-Mar-2022|
|Date of Decision||14-May-2022|
|Date of Acceptance||19-May-2022|
|Date of Web Publication||18-Jul-2022|
Adriana Da Fonte Porto Carreiro
Department of Dentistry, Federal University of Rio Grande Do Norte (UFRN), AV. Senador Salgado Filho, 1787, Lagoa Nova, Natal 59056-000, Rio Grande Do Norte
Source of Support: None, Conflict of Interest: None
Aim: Evaluate the accuracy between the intraoral and extraoral scanning regarding the three dimensional (3D) deviation and distances between the implants, through 2 scanning methods.
Settings and Design: An in vitro study.
Materials and Methods: An edentulous mandibular model was used to install four implants and abutments, recommending 6 distances between the implants. Scans were performed using an intraoral (SI) and extraoral (SE) scanner for each studied group: Scanning with the scan bodies (SB) and device (SD) (n = 10). The files were imported into a surface evaluation program to assess 3D deviations and measure distances between implants.
Statistical Analysis: Precision was assessed as the difference between files (Kruskal–Wallis test), while trueness was assessed from the difference between scans, applying the Wilcoxon and Mann–Whitney test.
Results: As for the 3D deviations, SI showed accuracy, for the faces and positions of the implants in relation to the SE, in both scanning methods (P < 0.05). Regarding the capture of distances between implants, the SD scan obtained better trueness than the SB group (P < 0.05).
Conclusion: We concluded that the type and scanning methods used did not influence the 3D deviations, while for distances, scanning with the device had better trueness.
Keywords: Dental implant, dimensional measurement accuracy, edentulous, protheses supported-implant, three-dimensional
|How to cite this article:|
Pereira AL, Segundo HV, Júnior LC, Germano AR, Carreiro AD. Accuracy between intraoral and extraoral scanning: Three-dimensional deviation and effect of distance between implants from two scanning methods. J Indian Prosthodont Soc 2022;22:279-87
|How to cite this URL:|
Pereira AL, Segundo HV, Júnior LC, Germano AR, Carreiro AD. Accuracy between intraoral and extraoral scanning: Three-dimensional deviation and effect of distance between implants from two scanning methods. J Indian Prosthodont Soc [serial online] 2022 [cited 2022 Aug 11];22:279-87. Available from: https://www.j-ips.org/text.asp?2022/22/3/279/351274
| Introduction|| |
The introduction of technological innovations in dentistry provided the possibility of obtaining the topography of the oral cavity with greater speed, comfort and patient satisfaction, in view of the elimination of inconvenient steps of the conventional method. Computer-aided design (CAD) and computer-aided manufacturing, together with intraoral scanners, have been used with predictability for the manufacture of monolithic restorations, removable partial dentures,, unitary,,, and fixed partials on implants. Differently, the digitization of total edentulous arches and the position of multiple implants is a limiting factor for intraoral scanners, which is due to the presence of homogeneous areas, associated with edentulous arches, and also the large extensions of space between the implants., As a result, the inaccuracy of the virtual images is linked to errors of distance, and angulation of the implants.
Therefore, the alternative would be to digitize the plaster model, obtained by conventional molding, using an extraoral scanner (laboratory) for then projection of the prosthesis. Previous studies comparing the accuracy between different intraoral and extraoral scanners were carried out from the perspective of total edentulous arches,,, total dentate,,, and multiple implants between teeth. For total edentulous arches rehabilitated with multiple implants, the evaluations consisted of investigating the accuracy of intraoral scanners based on the conventional molding,,,, or coordinate measuring machine, and even by a totally conventional workflow for making the final prosthesis.
Software programs for the analysis of three-dimensional (3D) deviations have been used to determine the displacement of implants and identify the error in transferring their positions to the virtual environment., However, none of the previous studies evaluated the displacement of implants by face and position, but rather, considering the position of the implants in the complete model.
The evaluation of both variables is fundamental for a better predictability of making a framework with passive adjustment, once quantifying how much the 3D discrepancy of the virtual image can imply in the materialization of the final prosthetic work. In this sense, there is still a need to studies that evaluate the 3D deviation considering the implant, as well as the effect of different linear distances in capturing the virtual transfer of the position of multiple implants, based on the comparison between intraoral and extraoral scanning and scanning methods.
Therefore, it is proposed to carry out this in vitro study with the objective of evaluating the accuracy (precision and trueness) between the intraoral and extraoral scanning, regarding the 3D deviation and distances between the implants, through two scanning methods. The null hypothesis consisted in showing that there is no difference between the intraoral and extraoral scans, either with the digitizing bodies or the device, regarding the 3D deviations and distances between the implants.
| Materials and Methods|| |
A rigid polyurethane total edentulous mandibular model with gingival simulation (Edentulous mandible with gum; Nacional Bones) [Figure 1] was used as the master model for this study. Prior to the preparation of this model, the position of the implants was coded according to their distribution in the arch, being: (1) right posterior, (2) right anterior, (3) left anterior, and (4) left posterior. Afterward, with the aid of a digital caliper (150 Mn Mtx; Mtx) and permanent pen for marking surfaces, six distances were linearly determined, (D1: 1–2; 16 mm), (D2: 1–3; 23.5 mm), (D3: 1–4; 40.2 mm), (D4: 2–3; 9.0 mm), (D5: 2–4; 26.2 mm), (D6: 3–4; 22 mm), which determined the location of the four implants in the regions of the right lateral incisor, right mandibular first premolar and their respective contralateral positions.
Implants with external hexagon connection (H. E.4.1 mm × 3.75 mm) (Neodent; Straumann) and Conical Mini Abutments (Neodent; Straumman) were selected for this study. With the aid of a 4.1 mm trephine drill (Neodent; Straumman) adapted to the implant engine (Neodent; Straumann) an adaptation of direct access to the bone was performed, followed by drills: Spear, for milling and initial access, which provided space for the others: Ø2.0, Ø2/3, and Ø3.0 (sequence recommended by the manufacturer), with a final torque of 45Ncm. Afterward, the Mini Conical Abutments (Neodent; Straumman) with a gingival height of 1 mm, angle of 0° and diameter Ø4.1 mm, with torque of 32Ncm were installed.
With the master model prepared, it was submitted to four scanning steps: (1) extraoral scanning with the scan bodies (SE-SB), (2) intraoral scanning with the SB (SI-SB) [Figure 2], (3) extraoral scanning with the device attached to the scan bodies (SE-SD) and (4) intraoral scanning with the device attached to the scan bodies (SI-SD) [Figure 3]. The intraoral scans performed with the device coupled to the digitization bodies have three parts: Pin with ball-shaped fixation, fixation support, and cylindrical union bar, which was assembled during the digitization act.
|Figure 3: Master model with the device attached to the scan bodies (SD). SD: Scan device|
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For each group mentioned above, 10 scans were performed, all obtained by a single operator, whose intraoral (SI) scans were performed by an intraoral scanner (TRIOS; 3Shape A/S) and the extraoral (SE), a bench scanner (S600 ARTI Scan; Zirkonzahn). For this, four marking points along the model were made, following the position of the implants, buccal and lingual, to facilitate the recognition of the region to be digitized by the scanner. The master model was fixed on the mobile table of the bench scanner (S600 ARTI Scan; Zirkonzahn) and the set (table/model) on a flat surface, using the following scanning technique: Occlusal face of the right end of the arch, continuing to the left contralateral area, extending to the buccal face, and finally to the lingual face.
After the digitization step, the scans were stored in standard tessellation language (STL) format in the digital library of the scanner software program used and renamed (study group name; 1–10), following the order in which the scanning. The STL files were submitted to the two dependent variables of this study: 3D deviation and distance between the implants, which were evaluated using an inspection software program (GOM Inspect; GOM GmbH).
In the analysis of the 3D deviations, the discrepancy between the extraoral and intraoral scans was evaluated. For this, the files corresponding to the extraoral scan (SE) were imported into the software in the “Body CAD” format and the files of the intraoral scan (SI) in “Mesh,” i.e., SE-SB with SI-SB, as well as, SE-SD with SI-SD. Afterward, using the three-point alignment and best fit methodology, the two files were superimposed, using the entry of the screws from the scanning bodies as a coincident point between the files. Then, a comparison analysis of the superimposed surfaces was performed with a maximum distance of 0.200 mm between the files. With the projection of the 3D comparison map, deviation labels were projected on the faces (mesial, distal, buccal, and lingual) of each implant to extract the discrepancy values between the files. For this variable, 40 faces were measured per group, totaling 160 for the 4 groups [Figure 4].
|Figure 4: (a) Projection of two virtual cylinders for three-dimensional capture of the position of two implants. (b) Analysis of the three-dimensional deviation between the extraoral and intraoral scans per face|
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As for the analysis of the distances between the implants, the six predefined distances were measured before the installation of the implants for the four groups (SE-SB, SE-SD, SI-SB, and SI-SD). For this, the model obtained by the extraoral scan of each intraoral scan was used as a digital table, given its absence in the software used, to standardize the insertion axis of the files for evaluation. Therefore, as reported for the analysis of 3D deviations, the files were superimposed, and then the cylinders were projected for each digitizing body, forming a vertical central line inside each cylinder, this point being used to draw the lines of measurement between implants. Therefore, assuming that the model has four implants and each group contains 10 STL files, then 6 distances were measured, totaling 60 per group and 240 for the four groups [Figure 5].
All analyzes were performed by a single operator (H. V. M. S.) and reviewed by a second evaluator (A. F. P. C.), three times for each face and measured distance, in the 10 STL files of each group. From that, an average was obtained and the analyzes of this study were carried out from it. The Intraclass Correlation Coefficient was applied to both variables, showing “good” value power for 3D deviations (0.731) and “excellent” value power for the distance between implants (SE-SB: 1.000; SE-SD: 1.000; SI-SB: 1.000; SI-SD: 1.000).
Data were tabulated and analyzed using statistical software (IBM SPSS Statistics, v22.0; IBM Corp, Chicago, EUA). Initially, the Kolmogorov–Smirnov test was performed to estimate the normality of the data, which did not show normal distribution. Descriptive analysis was based on the median (x̄) and quartile 25 (Q25) and 75 (Q75). In assessing precision for the two dependent variables of this study, the difference between the chronological sequence of the STL files was considered, regardless of face, position, and distance between the implants. For this, we used the nonparametric Kruskal–Wallis test with Dunn's posttest. As for trueness, for the two dependent variables of this study, the difference between intraoral and extraoral scanning was evaluated, considering the faces, position, and distance between the implants. For this, the nonparametric Wilcoxon test was used to compare the intraoral with the extraoral of the same scanning method and the Mann–Whitney test to compare the four scans. In carrying out all tests, a significance level of 5% was adopted.
| Results|| |
3D deviations are shown for precision [Figure 6] and [Figure 7] and trueness [Table 1] and [Table 2]. For the precision of 3D deviations, when comparing the scan sequence (STL1-10 files), no statistically significant differences were identified between extraoral and intraoral scanning for both scanning methods. When comparing the order in which the STL files were obtained between the types of scans and scans, differences were also not found (STL1: P = 0.379; STL2: P = 0.605; STL3: P = 0.438; STL4: P = 0.052; STL5: P = 0.256; STL6: P = 0.535; STL7: P = 0.301; STL8: P = 0.641; STL9: P = 0.717; STL10: P = 0.301). The faces, with the exception of the buccal face [Table 1] and the position of the implants [Table 2], did not influence the trueness of the 3D deviations.
|Figure 6: Precision of three-dimensional deviations between SE and SI only with the SB (P = 0.449). SE: Scanning extraoral, SI: Scanning intraoral, SB: Scan bodies|
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|Figure 7: Precision of three-dimensional deviations between SE and SI with the device coupled to the scan bodies (SD) (P = 0.081). SE: Scanning extraoral, SI: Scanning intraoral, SD: Scan device|
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|Table 1: Trueness values by implant faces between groups (extraoral and intraoral scanning with the device attached to the scanning bodies and extraoral and intraoral scanning with scan bodies only)|
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|Table 2: Trueness values per implant between groups (extraoral and intraoral scanning with scan bodies only e extraoral and intraoral scanning with the device attached to the scanning bodies)|
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The distances between the implants are shown for precision [Figure 8] and trueness [Table 3]. As for precision, an analysis was performed considering each measured distance and STL file. For each distance, it was observed that when comparing the scans for each type of scan, statistically differences were found in the distances: D1 when comparing SE (P = 0.009) and SI (P = 0.092) scans, D2 for SI (P = 0.017), D3 for SE (P = 0.013), D4 for SI (P = 0.005), D5 for SE (P = 0.092) and SI (P = 0.028), and D6 for SE (P = 0.037) and SI (P = 0.005). In the other evaluations, no significant difference was observed (D2: SE-SD × SE-SB/P = 0.333; D3: SI-SD × SI-SB/P = 0.203; D4: SE-SD × SE-SB/P = 0.285).
|Figure 8: Analysis of precision between the sequence of scans regarding distances between implants. (a) Extraoral scanning with scan bodies only (P = 1.000). (b) Extraoral scanning with the device attached to the scanning bodies (P = 1.000). (c) Intraoral scanning with scan bodies only (P = 1.000). (d) Intraoral scanning with the device attached to the scanning bodies (P = 1.000). (e) Extraoral scans between SB and SD groups (P = 0.414). (f) Intraoral scans between the SB and SD groups (P = 0.113). SB: Scan bodies. SD: Scan device|
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In the evaluation between the sequence of scans (STL1 10 files), there was no difference in precision [Figure 8]. [Table 3] shows the intraoral scanning with the device coupled to the scan bodies (SD) obtained greater trueness for the six distances compared to scanning only with the SB.
| Discussion|| |
The null hypothesis that there is no difference between intraoral and extraoral scans, either with SB or device, was accepted for the variable 3D deviations and denied for the distances between implants. For 3D deviations, the intraoral and extraoral scans showed precision and truness within an acceptable range for clinical use, in both scanning methods. The distances between the implants and the scanning method no influenced the scanning precision. The intraoral scanning with the device coupled to the SB trueness captured interimplant distances of 9.0–22 mm and 23.5–40.2 mm in a crossed arc, while the scanning with only the SB, interimplant distances of 9 mm and 23.5–26.2 mm in crossed arch, when compared to extraoral scanning.
Most intraoral scanners project a leisure beam onto the object's geometric surface and capture the reflected light through a charge-coupled device. Afterward, the scanner system will calculate the position of the points, for the union of several triangles and formation of the final image. Some factors can influence the quality of this image, such as: Mouth arch curvature, where large curvatures will promote highly dense meshes, while flatter regions have lower mesh density, the scan time, as the greater the area and complexity, the longer the scanning time, leading to lower accuracy, especially when associated with operators with little experience and the surface to be scanned.
In this last aspect, the greatest difficulty in capturing total edentulous arches is due to the lack of reference along the ridge, due to the physiological process of bone resorption triggered by edentulism. In addition, although the presence of multiple implants configures reference points for the intraoral scanner, the loss of follow-up in the recognition of the region between the implants influences the quality of the mesh, especially in view of the large extensions of space. With this, proposals for improving the capture accuracy of such arches have been addressed, all of which promote the union of the scanning bodies and filling the spaces between the implants.,,,, These findings justify the inclusion, in the present study, of a new scanning alternative to improve the position capture accuracy of multiple implants in total edentulous arches.
In the comparative evaluation between intraoral and extraoral scanning, considering the two scanning methods, we observed that scanning with the device coupled to the digitization bodies captured the recommended distances with greater accuracy compared to the scanning with only the SB. Therefore, previous studies, also showed that scans of total edentulous arches rehabilitated with multiple implants, using only SB, lead to large errors in distance and angulation, making these images inaccurate for planning passive framework.
When joining the SB, references are provided for the intraoral scanner between one implant and another, making the process faster and consequently improving the mesh quality. This is how Cappare et al. and Carneiro Pereira et al. showed from clinical studies, in which they used a splinting device or a joining device to obtain images with better accuracy. Tan et al. stated that by decreasing the inter-implant distances, linear distortions regarding the position of the implants can be reduced. In this sense, we showed, as in previous studies, that inter-implant distances from 9.0 mm to 22 mm were accurately captured when the intraoral scan was obtained with the device coupled to the SB, justified by the reduced distances associated with the union device.
Braian and Wennerberg, corroborate the findings of this study by showing that a range of 19 μm to 23 μm for inter-implant distances and 23 μm to 94 μm for crossed arch are the minimum and maximum possible limits to perform an intraoral and get accurate images. However, we disagree about the scanning method, since the authors have found such results for scanning only with the scanning bodies, which was discussed previously about the difficulty of performing such a procedure without any object of edge modulation.
The findings of the present study show a proportional effect of the error in capturing cross-arc distances as inter-implant distances are increased, which justifies the fact that scanning only with the SB presented difficulty in capturing inter-implant distances >9 mm and 26.2 mm in crossed arc. The error also increases due to the increased extension of the area to be scanned, generating a greater number of images, requiring more seams to form the final image, as explained above. Thus, these values can be compared to data from the study by Braian and Wennerberg.
As for the comparison between intraoral and extraoral scanning, we showed that the type of scan influenced the precision and trueness of the images obtained by each scanning method. Therefore, the virtual images obtained with the intraoral scan from the device were able to be trueness reproduced by the extraoral scan, for all tested inter-implant and cross-arc distances. Thus, we agree with Ribeiro et al., who showed no difference between intraoral and extraoral scanning in total edentulous arches rehabilitated with multiple implants. On the other hand, we disagree with previous studies that stated that there is a superiority of intraoral scanning over the conventional one,, once dealing with in vitro studies and that no alternative to solve the limitations of intraoral scanners was presented or discussed.
The assessment for 3D deviations was performed to quantitatively identify the discrepancy between the intraoral and extraoral scanning for the two types of scans. For this analysis, the STL files were superimposed at a maximum distance of 0.200 mm, this being the minimum possible provided by the software, as well as using Papaspyridakos et al. From this determination, the direction of the 3D deviation was indicated by positive numbers or negatives of the average displacement, illustrated by a 3D color map. Therefore, the present study showed precision regarding the 3D deviations of the intraoral scans with their respective reference (extraoral) scans, pointing to a reproducibility of the methods in a continuous sequence of ten scans.
However, when assessing trueness, the mean 3D distortion was consistently negative for all faces, with the exception of the buccal face of the SE + SD group, and all implant positions, except for the left anterior implant SE + SB. The signal does not interfere in the interpretation of the data when the same value differs from each other by the signal, being symmetrical in relation to the origin (zero). In this context, a statistically significant difference was found in the vestibular face between the two groups, where SE + SD obtained a distortion (+0.01) closer to the origin than SE + SB of (−0.07), not being considered clinically relevant. This punctual and minimal result may have been triggered by the method used (overlay). This introduces an inaccuracy due to the compensation of positive and negative deviations between the values, which can generate a reduced or increased estimate of the actual deviation of the reference model, being necessary to calculate the root mean square to eliminate this inaccuracy, which does not was possible due to the absence of this tool in the software used in this study.
Although the lack of studies comparing the 3D deviations of two intraoral scanning methods from the extraoral scanning is scarce and makes this discussion difficult, the results of the present study are in agreement with previous in vitro and clinical studies that also evaluated the 3D deviations between the conventional and digital method in mandibular arches with multiple implants. These showed similarity in terms of accuracy between the intraoral and reference scanning,, considering 200 μm as the clinically acceptable limit for digitizing implants in total edentulous arches., All values presented by this study are below this one limit, indicating clinical irrelevance, even not using the same measurement unit.
The in vitro findings of this study allow the clinician to have greater predictability of the final prosthetic work, by noting that the positions of the implants present clinically irrelevant deviations and showing that the biggest problem in the search for passive framework is concentrated in the distances between the implants. From the results found, we observed that if the virtual images obtained by the SB group were used to design a metallic framework, it would present large vertical and horizontal marginal mismatches, which could be minimized if the images provided by intraoral scanning of the SD group were used since there was no difference with extraoral scanning.
Therefore, this in vitro study compares in an innovative way two scanning and scanning methods, through the 3D deviations and distances between the implants, seeking to quantify the 3D discrepancy between the scans and the possible distances to be accurately captured. In addition, it shows that the use of a joining device allows obtaining more accurate 3D images, which can enable the construction of framework with a better fit. Future studies should be conducted to evaluate different quantities of implants, connections, intraoral scanners, angulations, and new alternative techniques to improve the accuracy of the images obtained by intraoral scans of total edentulous arches.
| Conclusion|| |
Based on the results of this in vitro study, the following conclusions were drawn:
- The intraoral scanning, only with the SB and with the device coupled to the SB, showed precision and trueness, in relation to the extraoral scanning for 3D deviations
- The scanning method did not influence the precision of capturing the distances between the implants in the intraoral and extraoral scanning, resulting in greater distance errors in the SB group
- The intraoral scanning with the device attached to the SB accurately captured interimplant distances from 9 mm to 22 mm and 23.5 mm to 40.2 mm in a crossed arc while scanning with only the SB, interimplant distances 9 mm and 23.5–26.2 mm in crossed arch, when compared to extraoral scanning.
CAPES - Coordination for the Improvement of Higher Education Personnel (N°88887.531281/2020-00).
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3]