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Journal of Prosthetic Dentistry
Research and Education|Articles in Press

Comparison between digital superimposition and microcomputed tomography methods of fit assessment of removable partial denture frameworks

Open AccessPublished:March 06, 2023DOI:https://doi.org/10.1016/j.prosdent.2023.02.002

      Abstract

      Statement of problem

      The fit of removable partial denture frameworks should be assessed to optimize clinical adaptation. Potential discrepancies between framework and supporting structures are typically precisely measured with negative subtracts and high-resolution equipment. The growth of computer-aided engineering technology allows the development of new methods for the direct evaluation of discrepancies. However, how the methods compare is unclear.

      Purpose

      The purpose of this in vitro study was to compare 2 digital methods of fit assessment based on direct digital superimposition and microcomputed tomography indirect analysis.

      Material and methods

      Twelve cobalt-chromium removable partial denture frameworks were fabricated by conventional lost-wax casting or additive manufacturing techniques. The thickness of the gap between occlusal rests and respective definitive cast rest seats (n=34) was evaluated by using 2 different digital methods. Silicone elastomer impressions of the gaps were obtained, and microcomputed tomography measurements were used as controls for validation purposes. Digitization of the framework, the respective definitive cast, and the combination was followed by digital superimposition and direct measurements with the Geomagic Control X software program. Because normality and homogeneity of variance were not verified (Shapiro-Wilk and Levene tests, P<.05), the data were analyzed with Wilcoxon signed rank and Spearman correlation tests (α=.05).

      Results

      The thicknesses measured by microcomputed tomography (median=242 μm) and digital superimposition (median=236 μm) did not reveal statistically significant differences (P=.180). A positive correlation (ρ=0.612) was detected between the 2 methods of assessing fit.

      Conclusions

      The frameworks presented median gap thicknesses under the limit of clinical acceptability without differences between the proposed methods. The digital superimposition method was determined to be as acceptable as the high-resolution microcomputed tomography method for assessing removable partial denture framework fit.
      Clinical Implications
      The fit of removable partial denture frameworks can be assessed in the dental laboratory with a high-precision digital superimposition method. The use of this quality control for framework production could reduce chair time for adaptation, prevent complications, and improve patient satisfaction.
      Removable partial dentures (RPDs) are provided to replace teeth, improving mastication, phonetics, and esthetics, as well as patient quality of life, with an excellent cost-benefit ratio.
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      Thus, assessing frameworks in the dental laboratory could optimize clinical fit, decrease chair time, and ensure a successful prosthesis.
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      Clinical performance of removable partial dentures: a retrospective clinical study.
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      Accuracy of removable partial denture framework fabricated by casting with a 3D printed pattern and selective laser sintering.
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      Relationship between the standards of removable partial denture construction, clinical acceptability, and patient satisfaction.
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      Preliminary clinical application of removable partial denture frameworks fabricated using computer-aided design and rapid prototyping techniques.
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      Comparison of digital and conventional methods of fit evaluation of partial removable dental prosthesis frameworks fabricated by selective laser melting.
      These sensitive techniques can lead to errors because of the low dimension and resilience of the impression materials.
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      The fit accuracy of removable partial denture metal frameworks using conventional and 3D printed techniques: an in vitro study.
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      • Williams R.J.
      • Rafik T.
      • Al-Hourani Z.
      An electronic method for measuring the fit of removable partial denture frameworks to dental casts.
      ,
      • Ye H.
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      • Li M.
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      Preliminary clinical application of removable partial denture frameworks fabricated using computer-aided design and rapid prototyping techniques.
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      • Chen H.
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      Microcomputed tomography a noninvasive method to evaluate the fit of a restoration as compared to conventional replica technique.
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      Fit accuracy of removable partial denture metal frameworks produced by CAD-CAM – clinical study.
      The development of high-resolution scanners and computer-aided engineering software programs for dental laboratories has allowed new methods of directly measuring 3-dimensional (3D) discrepancies, such as digital superimposition, without an intermediate substrate.
      • Diwan R.
      • Talic Y.
      • Omar N.
      • Sadiq W.
      The effect of storage time of removable partial denture wax pattern on the accuracy of fit of the cast framework.
      ,
      • Han S.H.
      • Sadr A.
      • Tagami J.
      • Park S.H.
      Non-destructive evaluation of an internal adaptation of resin composite restoration with swept-source optical coherence tomography and micro-CT.
      ,
      • Tasaka A.
      • Okano H.
      • Shimizu T.
      • Kato Y.
      • Higuchi S.
      • Yamashita S.
      Influence of reinforcement bar on accuracy of removable partial denture framework fabricated by casting with a 3D-printed pattern and selective laser sintering.
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      However, studies validating the digital superimposition method of measuring the fit accuracy of RPD frameworks are sparse.
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      • Tulunoglu I.
      A critically appraised topic review of computer-aided design/computer-aided machining of removable partial denture frameworks.
      The purpose of this in vitro study was to compare 2 digital methods of assessing the discrepancies between the occlusal rests of RPD frameworks and their respective cast rest seats. The null hypotheses were that the quantification of the discrepancy of RPD frameworks would not be affected by the method of assessment used and that no correlation between μCT and digital superimposition methods would be found in the RPD framework fit evaluation.

      Material and methods

      Twelve different cobalt-chromium RPD frameworks were produced by conventional lost-wax casting or additive manufacturing techniques to fit 12 different definitive stone casts. The inclusion criteria were that the framework included both sides of the dental arch and at least 1 occlusal rest per quadrant. The RPD fit was assessed by measuring the gap between the occlusal rests of the 12 frameworks and their respective cast rest seats. Two methods were used to measure each gap: an indirect method through μCT measurement of silicone specimens (used as control) and a direct measurement after digital superimposition as proposed by the authors.
      The sample size (n=34 occlusal rests) was estimated with a power analysis to provide statistical significance (α=.05) at a power of 80%, based on pilot study data.
      • Conceição P.R.
      • Pinto R.
      • Marques D.
      • et al.
      Fit accuracy assessment of RPD metal framework by digital superimposition.
      The gap on each occlusal rest was evaluated once by using 2 assessment methods. For the μCT indirect method, an impression was made of the gap between each occlusal rest and the respective cast rest seat. The rest seat was cleaned with a prophylaxis brush (Prophylaxis Brushlet RA 060 Soft; Edenta AG) and filled with polyvinyl siloxane impression material (V-Posil Light Fast Set; VOCO GmbH). The metal framework was positioned and maintained until the complete polymerization of the impression material. After the removal of the framework, each silicone specimen was detached from the definitive cast, verified for the presence of surface pores and irregularities, and shaped with a scalpel blade (Aesculap blade #15; Aesculap, Inc) to remove excess material. The specimen was then positioned on the sample holder of a μCT system (Skyscanner 1174; Bruker SA/NV) with orthodontic wax (Protection wax; Dentaurum GmbH & Co KG) and scanned with the following parameters: 50 KV, 800 μA, 6.6-μm image pixel size, 5500 milliseconds exposure time, 0.9-degree rotation step, and no aluminum filter. Then, specific software programs were used to reconstruct (NRecon Server Local v1.7; Bruker SA/NV) and spatially position (DataViewer v1.5; Bruker SA/NV) the scanned grayscale image. The 9-point area defined in the digital superimposition method represented the volume of interest (Fig. 1). After performing the segmentation of the original reconstructed image, the mean thickness of the specimen was directly calculated in micrometer by a software program (CTAnalyser software, v1.18; Bruker SA/NV) and represented the thickness of the gap on each occlusal rest. Furthermore, the calculated thickness was confirmed through a 2-dimensional measurement of at least 3 transverse segments of the specimen (Fig. 2).
      Figure thumbnail gr1
      Figure 1A, Volume of interest of silicone specimen digitized by microcomputed tomography in coronal (COR), sagittal (SAG), and transversal (TRA) planes. B, Nine points defined by Geomagic Control X software program.
      Figure thumbnail gr2
      Figure 2Two-dimensional thickness measurement of specimen transversal segment to confirm total mean thickness.
      For the digital superimposition method, the metal framework was coated with scanning spray (Zirko Scanspray; Zirkonzahn GmbH), and the definitive stone cast and the combination were digitized with an image assembly software program (Modellier; Zirkonzahn GmbH) installed in a scanner system (Arti S600; Zirkonzahn GmbH), producing 3 individual standard tessellation language (STL) files.
      • Conceição P.R.
      • Franco M.
      • Alves N.
      • Portugal J.
      • Neves C.B.
      Fit accuracy of removable partial denture metal frameworks produced by CAD-CAM – clinical study.
      ,
      • da Silva Marques D.N.
      • Marques Pinto R.J.
      • Alves R.V.A.A.
      • Baratieri L.N.
      • da Mata A.D.S.P.
      • Caramês J.M.M.
      Soft tissue replication in single unit implant impressions - A three dimensional clinical study.
      Each file was positioned with the best-fit tools of a software program (Geomagic Control X, v2018; 3D Systems Inc) by using the combined image as a reference (Fig. 3). A grid of 10 virtual planes was created by using the plane tool of the program and the 9 points identified where those planes intersected at each of the occlusal rest and rest seat surfaces. The distance of each pair of points was measured, and the mean of the 9 distances represented the thickness of the gap on each occlusal rest (Fig. 4).
      Figure thumbnail gr3
      Figure 3Digital superimposition of framework, definitive cast, and combination images by using Geomagic Control X software tools. A, Point selection to transform alignment. B, Selection of areas to make best fit. C, Image of combination after superimposition.
      Figure thumbnail gr4
      Figure 4Fit assessment method after digital superimposition. A, Grid resulting from 10 built planes with overlapping of 9 points projected on each structure surface. B, Nine points projected on cast rest seat. C, Nine points projected on lower surface of occlusal rest. D, Distance (mm) between each pair of points projected on each structure.
      A single researcher (P.C.) collected the data after training with experienced researchers (D.M. and M.F.) and tested for reproducibility at a 1-week interval. The distribution of the margin of error was 2.9% for the digital superimposition method and 4.3% for the μCT method.
      The data were analyzed by using a statistical software program (IBM SPSS Statistics, v25; IBM Corp). The descriptive analysis was determined. Because normality and homogeneity of variance were not verified (Shapiro-Wilk and Levene tests, P<.05), the data were submitted to related-samples Wilcoxon signed rank and Spearman correlation tests with a scatter plot examination (α=.05).

      Results

      A total of 34 occlusal rests were present in the 12 RPD frameworks, with a mean of 2.8 occlusal rests, a minimum number of 2 rests, and a maximum number of 4 occlusal rests per framework. Similar distributions of the thickness data were obtained by digital superimposition (median=236 μm) and by μCT (median=242 μm) methods (Fig. 5), without statistically significant differences between methods (P=.180). A positive correlation (ρ=0.612) was observed between the 2 assessment methods, which was confirmed by examination of the scatter plot (Fig. 6).
      Figure thumbnail gr5
      Figure 5Box plot representation of gap thicknesses (μm) measured by assessment methods under study.
      Figure thumbnail gr6
      Figure 6Scatter plot of thicknesses (μm) of gaps between occlusal rests and respective cast rest seats obtained by assessment methods under study.

      Discussion

      This in vitro study aimed to compare 2 digital methods of assessing the fit of RPD frameworks based on digital superimposition and μCT analysis (control). Because a positive correlation was found, the digital superimposition method appeared to be acceptable for assessing the fit of RPD frameworks.
      Assessment of fit is an essential step in controlling the quality of the framework production and ensuring the appropriate function of the prosthesis.
      • Bajunaid S.O.
      • Altwaim B.
      • Alhassan M.
      • Alammari R.
      The fit accuracy of removable partial denture metal frameworks using conventional and 3D printed techniques: an in vitro study.
      ,
      • Williams R.J.
      • Rafik T.
      • Al-Hourani Z.
      An electronic method for measuring the fit of removable partial denture frameworks to dental casts.
      The fit is based on the intimate contact and residual discrepancies between the RPD framework and the supporting teeth.
      • Ye H.
      • Ning J.
      • Li M.
      • et al.
      Preliminary clinical application of removable partial denture frameworks fabricated using computer-aided design and rapid prototyping techniques.
      ,
      • Lang L.A.
      • Tulunoglu I.
      A critically appraised topic review of computer-aided design/computer-aided machining of removable partial denture frameworks.
      Specifically, the design and fabrication standards of the RPD mean that stability and support of the framework are achieved when all rests are seated.
      • Frank R.P.
      • Brudvik J.S.
      • Leroux B.
      • Milgrom P.
      • Hawkins N.
      Relationship between the standards of removable partial denture construction, clinical acceptability, and patient satisfaction.
      ,
      • Etman M.
      • Bikey D.
      Clinical performance of removable partial dentures: a retrospective clinical study.
      ,
      • Ye H.
      • Ning J.
      • Li M.
      • et al.
      Preliminary clinical application of removable partial denture frameworks fabricated using computer-aided design and rapid prototyping techniques.
      ,
      • Tasaka A.
      • Okano H.
      • Shimizu T.
      • Kato Y.
      • Higuchi S.
      • Yamashita S.
      Influence of reinforcement bar on accuracy of removable partial denture framework fabricated by casting with a 3D-printed pattern and selective laser sintering.
      Therefore, the present study focused on the discrepancy between the occlusal rests and the respective rest seats.
      • Williams R.J.
      • Rafik T.
      • Al-Hourani Z.
      An electronic method for measuring the fit of removable partial denture frameworks to dental casts.
      • Tasaka A.
      • Shimizu T.
      • Kato Y.
      • et al.
      Accuracy of removable partial denture framework fabricated by casting with a 3D printed pattern and selective laser sintering.
      • Williams R.J.
      • Bibb R.
      • Rafik T.
      A technique for fabricating patterns for removable partial denture frameworks using digitized casts and electronic surveying.
      In the present study, an impression of the gap between each occlusal rest and rest seat allowed an indirect quantitative assessment of the discrepancy. The impression material used was polyvinyl siloxane, a silicone elastomer material better than acrylic resin to reproduce details.
      • Bajunaid S.O.
      • Altwaim B.
      • Alhassan M.
      • Alammari R.
      The fit accuracy of removable partial denture metal frameworks using conventional and 3D printed techniques: an in vitro study.
      ,
      • Ye H.
      • Ning J.
      • Li M.
      • et al.
      Preliminary clinical application of removable partial denture frameworks fabricated using computer-aided design and rapid prototyping techniques.
      ,
      • Soltanzadeh P.
      • Suprono M.S.
      • Kattadiyil M.T.
      • Goodacre C.
      • Gregorius W.
      An in vitro investigation of accuracy and fit of conventional and CAD/CAM removable partial denture frameworks.
      ,
      • Diwan R.
      • Talic Y.
      • Omar N.
      • Sadiq W.
      The effect of storage time of removable partial denture wax pattern on the accuracy of fit of the cast framework.
      Furthermore, digital technology was used to analyze the impression specimens, as it permitted a complete and reproducible analysis by preserving the specimens.
      • Bajunaid S.O.
      • Altwaim B.
      • Alhassan M.
      • Alammari R.
      The fit accuracy of removable partial denture metal frameworks using conventional and 3D printed techniques: an in vitro study.
      ,
      • Ye H.
      • Ning J.
      • Li M.
      • et al.
      Preliminary clinical application of removable partial denture frameworks fabricated using computer-aided design and rapid prototyping techniques.
      ,
      • El-Khamisy N.E.
      • Habib A.H.
      • El-Mekawy N.E.
      • Emera R.M.
      Digital versus conventional design for mandibular distal extension RPD: A study of passivity of RPD components and principal abutment alveolar bone height changes.
      ,
      • Chen H.
      • Li H.
      • Zhao Y.
      • Zhang X.
      • Wang Y.
      • Lyu P.
      Adaptation of removable partial denture frameworks fabricated by selective laser melting.
      ,
      • Muehlemann E.
      • Orzcan M.
      Accuracy of removable partial denture frameworks fabricated using conventional and digital technologies.
      ,
      • Conceição P.R.
      • Franco M.
      • Alves N.
      • Portugal J.
      • Neves C.B.
      Fit accuracy of removable partial denture metal frameworks produced by CAD-CAM – clinical study.
      ,
      • Oh K.C.
      • Yun B.S.
      • Kim J.H.
      Accuracy of metal 3D printed frameworks for removable partial dentures evaluated by digital superimposition.
      Some digital techniques, with photography or microscopy, have shown limitations in the 360-degree analysis of the specimens, namely in measuring hidden locations.
      • Bajunaid S.O.
      • Altwaim B.
      • Alhassan M.
      • Alammari R.
      The fit accuracy of removable partial denture metal frameworks using conventional and 3D printed techniques: an in vitro study.
      ,
      • El-Khamisy N.E.
      • Habib A.H.
      • El-Mekawy N.E.
      • Emera R.M.
      Digital versus conventional design for mandibular distal extension RPD: A study of passivity of RPD components and principal abutment alveolar bone height changes.
      Another technique based on digital superimposition of the specimens requires several scans to provide high-precision levels of measurement.
      • Chen H.
      • Li H.
      • Zhao Y.
      • Zhang X.
      • Wang Y.
      • Lyu P.
      Adaptation of removable partial denture frameworks fabricated by selective laser melting.
      ,
      • Conceição P.R.
      • Pinto R.
      • Marques D.
      • et al.
      Fit accuracy assessment of RPD metal framework by digital superimposition.
      Therefore, the present study used μCT, the standard for analysis in various fields of biomedical science.
      • Ram S.M.
      • Ranadive N.M.
      • Nadgere J.B.
      Microcomputed tomography a noninvasive method to evaluate the fit of a restoration as compared to conventional replica technique.
      ,
      • Han S.H.
      • Sadr A.
      • Tagami J.
      • Park S.H.
      Non-destructive evaluation of an internal adaptation of resin composite restoration with swept-source optical coherence tomography and micro-CT.
      ,
      • Jackson N.
      • Assad M.
      • Vollmer D.
      • Stanley J.
      • Chagnon M.
      Histopathological evaluation of orthopedic medical devices: the state-of.the art in animal models, imaging, and histomorphometry techniques.
      This high-precision and high-resolution technique provides a complete analysis of low-dimension specimens from a single scan.
      • Ram S.M.
      • Ranadive N.M.
      • Nadgere J.B.
      Microcomputed tomography a noninvasive method to evaluate the fit of a restoration as compared to conventional replica technique.
      ,
      • Han S.H.
      • Sadr A.
      • Tagami J.
      • Park S.H.
      Non-destructive evaluation of an internal adaptation of resin composite restoration with swept-source optical coherence tomography and micro-CT.
      ,
      • Jackson N.
      • Assad M.
      • Vollmer D.
      • Stanley J.
      • Chagnon M.
      Histopathological evaluation of orthopedic medical devices: the state-of.the art in animal models, imaging, and histomorphometry techniques.
      ,
      • Conceição P.R.
      • Franco M.
      • Alves N.
      • Portugal J.
      • Neves C.B.
      Fit accuracy of removable partial denture metal frameworks produced by CAD-CAM – clinical study.
      The direct measurement of the gaps avoids distortions of the impression materials used in indirect methods.
      • Ye H.
      • Ning J.
      • Li M.
      • et al.
      Preliminary clinical application of removable partial denture frameworks fabricated using computer-aided design and rapid prototyping techniques.
      ,
      • Arnold C.
      • Hey J.
      • Schweyen R.
      • Setz J.M.
      Accuracy of CAD-CAM-fabricated removable partial dentures.
      The most frequently used direct method has been based on visual inspection but provides unreliable qualitative information, is limited to the border of the framework structures, and is prone to subjectivity and human error.
      • Frank R.P.
      • Brudvik J.S.
      • Leroux B.
      • Milgrom P.
      • Hawkins N.
      Relationship between the standards of removable partial denture construction, clinical acceptability, and patient satisfaction.
      ,
      • Ye H.
      • Ning J.
      • Li M.
      • et al.
      Preliminary clinical application of removable partial denture frameworks fabricated using computer-aided design and rapid prototyping techniques.
      • Tregerman I.
      • Renne W.
      • Kelly A.
      • Wilson D.
      Evaluation of removable partial denture frameworks fabricated using 3 different techniques.
      • Chen G.X.
      • Zeng X.Y.
      • Wang Z.M.
      • Guan K.
      • Peng C.W.
      Fabrication of removable partial denture framework by selective laser melting.
      The development of the digital design and production of restorations in the dental laboratory have expanded the direct methods of assessing the quantitative gap. Previous studies
      • Almufleh B.
      • Emami E.
      • Alageel O.
      • et al.
      Patient satisfaction with laser-sintered removable partial dentures: a crossover pilot clinical trial.
      ,
      • Tasaka A.
      • Okano H.
      • Shimizu T.
      • Kato Y.
      • Higuchi S.
      • Yamashita S.
      Influence of reinforcement bar on accuracy of removable partial denture framework fabricated by casting with a 3D-printed pattern and selective laser sintering.
      ,
      • Peng P.W.
      • Hsu C.Y.
      • Huang H.Y.
      • Chao J.C.
      • Lee W.F.
      Trueness of removable partial denture frameworks additively manufactured with selective laser melting.
      ,
      • Hwang S.
      • An S.
      • Robles U.
      • Rumpf R.C.
      Process parameter optimization for removable partial denture frameworks manufactured by selective laser melting.
      compared the digitized framework with the STL design but did not consider the relationship with the supporting structures, which is essential for a successful prosthesis.
      The present study proposed a method that applied the digital principles of a triple scan,
      • da Silva Marques D.N.
      • Marques Pinto R.J.
      • Alves R.V.A.A.
      • Baratieri L.N.
      • da Mata A.D.S.P.
      • Caramês J.M.M.
      Soft tissue replication in single unit implant impressions - A three dimensional clinical study.
      followed by digital superimposition with a specific software program. A precise evaluation of discrepancies was made possible by measuring the selected distances between 2 points in a defined axis. In addition, this method avoided impingements of the RPD framework on the definitive cast because of incorrect overlap, as with techniques that evaluate a range of distances in a color map.
      • Alabdullah S.A.
      • Hannam A.G.
      • Wyatt C.C.
      • McCullagh A.P.G.
      • Aleksejuniene J.
      • Mostafa N.Z.
      Comparison of digital and conventional methods of fit evaluation of partial removable dental prosthesis frameworks fabricated by selective laser melting.
      ,
      • Tasaka A.
      • Okano H.
      • Shimizu T.
      • Kato Y.
      • Higuchi S.
      • Yamashita S.
      Influence of reinforcement bar on accuracy of removable partial denture framework fabricated by casting with a 3D-printed pattern and selective laser sintering.
      ,
      • Rokhshad R.
      • Tehrani A.M.
      • Nahidi R.
      • Zarbakhsh A.
      Fit of removable partial denture frameworks fabricated from 3D-printed patterns versus the conventional method: an in vitro comparison.
      The null hypothesis that the quantification of the discrepancies of RPD frameworks was not affected by the assessment method could not be rejected because no differences were found between the 2 methods. However, a moderate positive correlation between the digital superimposition and the μCT techniques rejected the null hypothesis that no correlation between μCT and digital superimposition methods would be found. The results indicated that digital superimposition by using the available digital laboratory hardware and software equipment is an acceptable method of quantifying discrepancies during the quality control of the RPD framework production.
      • Soltanzadeh P.
      • Suprono M.S.
      • Kattadiyil M.T.
      • Goodacre C.
      • Gregorius W.
      An in vitro investigation of accuracy and fit of conventional and CAD/CAM removable partial denture frameworks.
      ,
      • Chen H.
      • Li H.
      • Zhao Y.
      • Zhang X.
      • Wang Y.
      • Lyu P.
      Adaptation of removable partial denture frameworks fabricated by selective laser melting.
      ,
      • Tasaka A.
      • Okano H.
      • Shimizu T.
      • Kato Y.
      • Higuchi S.
      • Yamashita S.
      Influence of reinforcement bar on accuracy of removable partial denture framework fabricated by casting with a 3D-printed pattern and selective laser sintering.
      ,
      • da Silva Marques D.N.
      • Marques Pinto R.J.
      • Alves R.V.A.A.
      • Baratieri L.N.
      • da Mata A.D.S.P.
      • Caramês J.M.M.
      Soft tissue replication in single unit implant impressions - A three dimensional clinical study.
      Nevertheless, this direct method should be used with caution in intraoral evaluations of discrepancies, as it requires a high-resolution scanner and a precise technique.
      • Ender A.
      • Attin T.
      • Mehl A.
      In vivo precision of conventional and digital methods of obtaining complete-arch dental impressions.
      ,
      • Lee S.
      • Kim S.
      • Lee J.
      • Cheong C.
      Comparison of intraoral and extraoral digital scanners: evaluation of surface topography and precision.
      Limitations of this study were related to the scanning and best-fit alignment of the structures in the superimposition method. Because of its complex shape, fewer RPD frameworks had to be repositioned for a second scan to digitize the complete information on the upper and lower surfaces of the occlusal rest. In those situations, the final image was achieved by using the scan and match tool of the scanning program. Also, only frameworks with at least 1 occlusal rest per quadrant were included in the study to minimize errors caused by undesirable inclinations. The 3D image acquisition and the value selection in the μCT morphometric analysis are also sensitive techniques. All the procedures were made by the same researcher (P.C.), who was trained and calibrated by experienced researchers (D.M., M.F.) to prevent bias. Furthermore, the mean thickness of each silicone specimen was confirmed by a 2D measurement in at least 3 transverse segments with the tools of CTAnalyser software, v1.18 (Bruker SA/NV) (Fig. 2). Further studies with larger sample sizes are required to verify the validity of these results.

      Conclusions

      Based on the findings of this in vitro study, the following conclusions were drawn:
      • 1.
        The digital superimposition method of quantifying discrepancies between the occlusal rests and their respective cast rest seats had results similar to those of the μCT analysis.
      • 2.
        The positive correlation between the methods determined that the digital superimposition method was as acceptable as the high-resolution μCT method for assessing the fit of removable partial denture frameworks.

      CRediT authorship contribution statement

      Pedro Conceição: Conceptualization, Data curation, Formal analysis, Investigation, Software, Visualization, Writing – original draft. Jaime Portugal: Supervision, Visualization, Writing – review & editing. Margarida Franco: Data curation, Investigation, Methodology, Software, Validation. Nuno M. Alves: Resources, Supervision, Funding acquisition. Duarte Marques: Methodology, Software, Resources, Validation. Cristina B. Neves: Conceptualization, Project administration, Supervision, Writing - review & editing.

      Acknowledgments

      The authors thank VOCO GmbH (Cuxhaven, Germany) for the donation of the impression material and Dr. Ricardo Pinto (FMDUL) for digital support.

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