In vivo Accuracy Comparison of Residual Ridge between Digital and Conventional Impressions in the Partially Edentulous Maxilla

In vivo Accuracy Comparison of Residual Ridge between Digital and Conventional Impressions in the Partially Edentulous Maxilla | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article In vivo Accuracy Comparison of Residual Ridge between Digital and Conventional Impressions in the Partially Edentulous Maxilla Shijie Zhang, Shuai Hu, Qing Fang, Jianxiang Tao This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6604947/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Purpose : This in vivo study aims to compare the accuracy of residual ridge between digital and conventional impressions in the partially edentulous maxilla. Methods: Forty-four patients with the partially edentulous maxilla were included in the study. Digital impression were obtained using an intraoral scanner (TRIOS2, 3Shape), while conventionalpressure impression were poured with type 4 gypsum and models were scanned using a desktop scanner (Shining 3D). The total deviation and deviations at Point P (Incisive papilla) between two scans were first measured by Geomagic Control X software. The deviations at three points of residual ridge: Point M (mesial), Point C (center), Point D (distal) were then measured. Results: The total deviation and deviation at Point P between the two scans was 0.008 mm and 0.069 mm, respectively. The total deviation and deviation at Point P exhibited no significant difference among patients. For the residual ridge of non-distal extension, the deviations showed no significant difference among Point M, Point C and Point D (0.032mm, 0.044 mm and 0.034 mm, respectively). For the distal extension, the deviation at the Point D and Point C (0.136 mm and 0.082 mm respectively) was significantly greater than that at Point D (0.027mm). The deviations of distal extension increased with the number of missing teeth. Conclusion: The deviation of distal extension was much greater than the total deviation between digital and conventional impressions. This study provided the reference value for the conversion from digital anatomic impressions to digital pressure impressions. Partially edentulous digital impression conventional impressions accuracy Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Digital impression technology is widely utilized in prosthodontic treatments, such as implant prosthodontics and fixed prosthodontics due to simplified processes, patient comfort, operation efficiency [ 1 – 3 ]. Recently, digital impression technology is also gradually applied to the fabrication of removable partial denture models [ 4 – 6 ]. However, several challenges remain [ 7 – 9 ]. One such challenge is the inability to create pressure impressions, which can compromise the precision and fit of removable denture abutments. This, in turn, can result in excessive pressure pain on the abutment teeth and food impaction on the denture tissue surface [ 10 , 11 ]. Conventional impressions place pressure on the residual ridge and can induce the morphology change of a residual ridge [ 12 ]. On the other hand, digital impression never places any pressure on the residual ridge because it is a non-contact system [ 13 ]. If the accurate data of the morphology deviations at residual ridge between digital and conventional impressions be obtained, data modification subsequent to the digital impression taking could be applied to reproduce the morphology of the residual ridge achieved by conventional impression, it would be a potential breakthrough. Previous in vitro studies compared the dimensional accuracy of conventional impressions with that of digital impressions, and investigated the trueness of intraoral scanning in different partially edentulous conditions [ 14 – 16 ]. However, in vitro partially edentulous model could not simulate the true situation of residual ridge such as compressibility of the alveolar mucosa. An in vivo study investigated the morphological difference of the residual ridge top under the first molar artificial tooth between digital and conventional impressions in the partially edentulous mandible of Kennedy Class I and II[ 17 ]. The stress-bearing region of maxilla is much larger than that of the mandible. Therefore, the deviation of the residual ridge between digital and conventional impressions in the partially edentulous maxilla might be different from that in the partially edentulous mandible. In the in vivo study, the digital impression and conventional impression were taken on the partially edentulous maxilla. The accuracy of residual ridge between digital and conventional impressions was examined, the relationship between the accuracy and the number of missing teeth was also investigated. 2. Materials and Methods 2.1 Participants Patients with the partially edentulous maxilla, who visited the Department of Prosthodontics at the Affiliated Stomatological Hospital of Tongji University between September 2022 and August 2024, were selected. All participants met the indications for removable partial denture restoration. The inclusion criteria were as follows: edentulous maxillary ridge for more than three months, absence of periodontitis, stable remaining teeth, no severe alveolar ridge resorption, no prominent bone protrusions, no limitation in mouth opening or temporomandibular joint disorders, no severe systemic diseases, and good compliance. All participants signed informed consent forms and underwent preliminary examinations, including radiographic assessments. This study was approved by the Medical Ethics Committee of the Affiliated Stomatological Hospital of Tongji University, with approval number [2023]-SR-38. 2.2 Materials Intraoral digital impression scanner (3Shape, Denmark); red impression compound (Changzhi, China); silicone rubber impression material (heavy body: tray type, Express STD; light body: Imprint II Garant Type 3, 3M, USA); type 4 gypsum (Die Stone, Heraeus, Germany); extraoral window scan scanner (Shining 3D, China). 2.3 Digital Impression Intraoral image data of maxillary dentition defects were collected from 44 patients by the same prosthodontist using a 3Shape intraoral scanner, adhering to standard intraoral scanning procedures suggested by manufacturers. The removable partial denture impressions made using this method are referred to as digital impression scans (Fig. 1 a). 2.4 Conventional Impression Conventional pressure impressions were obtained using silicone rubber impression material, red paste, and a metal steel tray. These impressions were poured with type 4 gypsum. The plaster models were scanned with an extraoral window scanner, and the data were saved in STL format, referred to as conventional impression scans (Fig. 1 b). 2.5 Measuring the accuracy and Data Analysis The digital impression scans and conventional impression scans STL files were imported into a surface matching software (Geomagic Contro X; 3D Systems, Rock Hill, SC) using the best-fitting alignment method. The dimensional differences between digital impression scans and corresponding conventional impression scans were compared (conventional impression scans as reference). The total deviation and deviations at Point IP (Incisive papilla) between two scans were first measured. The deviations at three points of residual ridge: Point M (mesial), Point C (center), Point D (distal) were also measured (Fig. 1 c). The residual ridges were divided into Distal extension and Non distal extension. The definitions of Point M, Point C and Point D were showed in Table 1 . Table 1 Measurement site and sample size Sites Definition n Point M The crest of residual ridge 2mm far from the mesial remaining tooth 69 Point D Non distal extension: the crest of residual ridge 2mm far from the distal remaining tooth 28 Distal extension: maxillary tuberosity 2mm far from pterygomaxilay notch 41 Point C The midpoint between Point M and Point D in the crest of residual ridge 69 Point P Incisive papilla 44 The methodology and results of the study were reviewed by an independent statistician. The sample size was calculated a priori based on the detection of a minimum clinically relevant difference of 25% at an α level of 0.05 and 80% power (i.e., the risk of a type I and type II error was 5% and 20%, respectively). A total of 44 observations from each partially edentulous conditions were determined in present study. One-way ANOVA and independent samples t-test were used to detect statistical significance for deviations between digital impressions and conventional impressions. Linear regression models were constructed to assess the association between the number of missing teeth and the deviation. For the above all tests, P-values < 0.05 were considered significant. 3. Results 3.1 Participants and residual ridge A total of 44 participants (24 female, 20 male; mean age 65.2 ± 9.7 years) were enrolled in this study. The detailed number of residual ridge was presented in Table 1 . 3.2 The total deviation and deviation at Point P between two scans Under the best-fit alignment, the total deviation between the two scans was 0.008 ± 0.003 mm, and the deviation at Point P were 0.069 ± 0.014 mm. Both the total deviation and the positional at Point P showed no significant difference among participants ( P > 0.05, Table 2 ). Correlation analysis found no significant correlation between the deviation and the number of missing teeth for both total deviation and deviation at Point P ( P > 0.05, Fig. 2 ), suggesting the number of missing teeth did not affect the total deviation and the deviation Point P. Table 2 Result of total deviation and deviation at Point P between two scans, X ± SEM Scans Total deviation(mm) Point P (mm) Deviation 0.008 ± 0.003 0.069 ± 0.014 F 1.963 0.716 P 0.082 0.727 3.3 The deviation of residual ridges between two scans Conventional pressure impressions could induce the morphology change of residual ridges. Therefore, the deviation of residual ridges between two scans was investigated in detail. For Non distal extension, there was no significant difference in the deviation of residual ridges among Point M, Point C, and Point D (0.032mm, 0.044 mm and 0.034 mm, respectively, Fig. 3 ). However, for the distal extension, the deviation at the Point D and Point C (0.136 mm and 0.082 mm respectively) was significantly greater than that at Point M (0.027mm) ( P < 0.05, Fig. 3 ). The deviation of residual ridges for distal extension was also compared with that for Non distal extension. The deviation at Point D and Point C for distal extension respectively was significantly greater than that for Non distal extension, which suggested that the location of residual ridge effected its deviation between two scans. 3.4 The relationship between the deviation of residual ridges and the number of missing teeth The precision of digital impressions decreased as the number of missing teeth increased. The number of missing teeth might influence the deviation of residual ridges between two scans. The relationship between the deviation of residual ridges and the number of missing teeth was investigated (Distal extension, Fig. 4 ; Non distal extension, Fig. 5 ). For distal extension, the deviation of the Point M, Point C, and Point D increased with the number of missing teeth. There was a linear relationship between the deviation at Point M, Point C, and Point D and the number of missing teeth (Fig. 4 ). However, for Non distal extension, there is no linear relationship between the deviation of residual ridges and the number of missing teeth. ( P >0.05 Fig. 5 ) 4. Discussion Currently, the fabrication of removable partial dentures (RPDs) involves a combination of traditional and digital methods [ 18 , 19 ]. The rehabilitation of the partially edentulous using RPDs typically requires a series of processes such as taking traditional pressure impressions, pouring gypsum models, scanning these models, and subsequent computer-aided design/computer-aided manufacturing (CAD/CAM) based on the scanned data. However, this workflow has not yet achieved full digitalization [ 6 , 20 , 21 ]. Conventional pressure impression techniques capture the oral mucosa under appropriate compression to ensure uniform stress distribution across the edentulous mucosa and abutment teeth [ 22 ]. In contrast, intraoral digital impression technology only captures the mucosal state of the residual ridges without any applied pressure. The objective of this in vivo study is to directly compare the accuracy between digital and conventional impressions in the partially edentulous, especially the accuracy of residual ridge. Therefore, present study did not investigate the trueness of different impression technique on in-vitro partially edentulous model as previous studies [ 23 – 25 ]. In present study, the total deviation between two scans was only 0.008 mm, much smaller than the deviation of the Point P and residual ridge. This suggested that the total deviation could not reflect detailed deviation of a particular site. As to residual ridges, the deviation at the Point D and Point C for distal extension was significantly greater than that at Point M, also significantly greater than that for Non distal extension. Furthermore, the deviation of the distal extension increased with the number of missing teeth. These indicates that digital impression could not fully replicate conventional pressure impression, mainly in residual ridge of distal extension. This phenomenon is primarily due to the compression and subsequent depression of the mucosa in the residual ridge of distal extension during conventional pressure impression [ 20 , 26 ]. Additionally, this may be related to the characteristic of precision for digital impression. Intraoral digital impression technology is based on the superimposition of multiple images [ 27 , 28 ]. The anatomical features of the edentulous area, such as the smooth mucosa on the residual ridge, lack distinct and fixed anatomical reference points [ 29 – 32 ]. Compared with hard tissues like teeth, the residual ridge is more difficult to be captured in high-quality images by intraoral scanning [ 33 , 34 ]. As the scanning area of the distal extension extends, cumulative deviation induced by the overlapping of each frame increases [ 29 ]. There are several methods to enhance the accuracy of digital impressions for edentulous regions. One is adding reference markers[ 8 ]. Reference markers can be placed at problematic overlap areas, the Incisive papilla region, and along the alveolar ridge in longer edentulous spans [ 32 , 35 ]. Alternative scanning paths, such as “Z” or “S” shape s[ 16 , 25 , 36 ], can also improve image stitching and overlapping issues. Additionally, biting the occlusal silicone rubber in the edentulous area is used to simulate functional occlusion, once removing the occlusal silicone rubber, quickly completing the mucosal scan is recommended to achieve the digital pressure impressions[ 37 ]. Vahidi’s study[ 26 ] compared tissue displacement resulting from different techniques and impression materials for distal-extension ridges. The vertical displacement in the mucosa of the residual ridge of distal extension was estimated to be around 200 µm. The deviation at Point D of the distal extension between digital and conventional impressions in this study was 136µm, smaller than their results. In Vahidi’s study[ 26 ], distal extension of the partially edentulous mandible was investigated while the partially edentulous maxilla was examined in present study. Palate might lead to the smaller subsidence of distal extension for maxilla than that for mandible. Ishioka’s study[ 17 ] reported the 90.3µm vertical displacement of the residual ridge between digital and conventional impressions in the partially edentulous mandible, which was smaller than the deviation at Point D of the distal extension in our study. However, the recorded location in Ishioka’s study was the residual ridge under the first molar artificial tooth, not the Point D of the distal extension in our study. This study provided the reference value for the conversion from digital anatomic impressions to digital pressure impressions. By collecting the deviation of the residual ridges between digital and conventional impressions, expanding the sample size and establishing a standardized software model database, it is possible to design the subsidence of the mucosa in residual ridges directly on the digital impression through algorithm, achieving a direct conversion from digital anatomic impressions to digital pressure impressions. This approach facilitates the custom design and fabrication of removable partial dentures. However, further expansion of the sample size and software is necessary to enhance the reference value and establish a standard database. Declarations Data availability The original contributions presented in the study are included in the article. Acknowledgements The authors gratefully acknowledge all patients who participated in the study. Finding Supported by grants from the National Natural Science Foundation of China (Grant No. 81970962) and the Shanghai Municipal Commission of Health and Family Planning (No. 202340063) to J. T. Data availability The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request. Ethics approval and consent to participate All methods were conducted in accordance with the relevant guidelines and regulations, including the Declaration of Helsinki. All participants signed informed consent forms and underwent preliminary examinations, including radiographic assessments. This study was approved by the Medical Ethics Committee of the Affiliated Stomatological Hospital of Tongji University, with approval number [2023]-SR-38. Consent for publication Written informed consent was obtained prior to the participation of this patient. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6604947","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":492042284,"identity":"018f4d15-bab2-4870-8b50-7cc26c962678","order_by":0,"name":"Shijie Zhang","email":"","orcid":"","institution":"Stomatological Hospital and Dental School, Tongji University","correspondingAuthor":false,"prefix":"","firstName":"Shijie","middleName":"","lastName":"Zhang","suffix":""},{"id":492042286,"identity":"f4d1dd4b-5805-4765-8ed3-50088f9d968b","order_by":1,"name":"Shuai Hu","email":"","orcid":"","institution":"Shanghai Engineering Research Center of Tooth Restoration and Regeneration \u0026 Tongji Research Institute of Stomatology \u0026 Department of Prosthodontics","correspondingAuthor":false,"prefix":"","firstName":"Shuai","middleName":"","lastName":"Hu","suffix":""},{"id":492042288,"identity":"21ebb93c-6996-4e0e-b356-5fcc2ccb12ab","order_by":2,"name":"Qing Fang","email":"","orcid":"","institution":"Stomatological Hospital and Dental School, Tongji University","correspondingAuthor":false,"prefix":"","firstName":"Qing","middleName":"","lastName":"Fang","suffix":""},{"id":492042290,"identity":"ce461557-f491-42fb-90ab-b984463eaedf","order_by":3,"name":"Jianxiang Tao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABDUlEQVRIiWNgGAWjYJACAyBOYOBhYHwA4jE2AwkePMp5wFoSwFqYDQ4Qq4UBqoVN4gCqMHZgz374QDHvD5s8fp4zZtUfKu7YNbcDXfi2jUHeHJctPGkJhjMS0oole3vMbhw48yy5sZmB2XBuG4PhzgZcDssxMPiQcDhxw3kesxsH2w4nA/3CJs3bxpBgcACHFv43BgYJUC0FUC3sv/FqkYDZcrbHjAGoxQ5kCzNeLTeeAf2SlpY4s+dYscSZM4cTGJsZmyXnnJMw3IBDC3t/8jFjHhubxH6e5I0fKioO2xv2Hz744U2ZjTwuW4CAzQCZl7ixgbEBSEvgVA8EzA+Qefby+NSOglEwCkbBiAQAYxVc1YXyeuUAAAAASUVORK5CYII=","orcid":"","institution":"Shanghai Engineering Research Center of Tooth Restoration and Regeneration \u0026 Tongji Research Institute of Stomatology \u0026 Department of Prosthodontics","correspondingAuthor":true,"prefix":"","firstName":"Jianxiang","middleName":"","lastName":"Tao","suffix":""}],"badges":[],"createdAt":"2025-05-06 16:08:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6604947/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6604947/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":88014554,"identity":"02dcb374-71f8-41b1-9129-7e4dfc9d8762","added_by":"auto","created_at":"2025-07-31 12:42:20","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1811941,"visible":true,"origin":"","legend":"\u003cp\u003eAcquisition and fitting of Digital and Conventional Impression Scans. a: Digital Impression; b:Conventional pressure impressions; c:The best-fitting alignment method. Point P: Incisive papilla; Point M: mesialof residual ridge; Point C: center of residual ridge; Point D: distal of residual ridge.\u003c/p\u003e","description":"","filename":"Fig.1.png","url":"https://assets-eu.researchsquare.com/files/rs-6604947/v1/660ee78f0d07ceaf6c6b6838.png"},{"id":88014562,"identity":"61e9aebc-4440-4f0f-bc08-1a1e1b0eee1c","added_by":"auto","created_at":"2025-07-31 12:42:20","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1446763,"visible":true,"origin":"","legend":"\u003cp\u003eThe total deviation and deviation at Point P for different number of missing teeth.\u003c/p\u003e","description":"","filename":"Fig.2.png","url":"https://assets-eu.researchsquare.com/files/rs-6604947/v1/ca84e1c2a4706b2cc38e6a0f.png"},{"id":88014669,"identity":"5bb720cd-57ce-45ac-9c15-fbb904152caa","added_by":"auto","created_at":"2025-07-31 12:50:20","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":298506,"visible":true,"origin":"","legend":"\u003cp\u003eThe deviation of residual ridges between two scans. ns: no significant difference; *:\u003cem\u003eP\u003c/em\u003e＜0.05; **:\u003cem\u003eP\u003c/em\u003e＜0.01.\u003c/p\u003e","description":"","filename":"Fig.3.png","url":"https://assets-eu.researchsquare.com/files/rs-6604947/v1/34b349a80ab851e94be2163d.png"},{"id":88014557,"identity":"069745c3-875c-4ede-8a0c-e46ecb45e067","added_by":"auto","created_at":"2025-07-31 12:42:20","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1075534,"visible":true,"origin":"","legend":"\u003cp\u003eThe relationship between the deviation of residual ridges and the number of missing teeth for distal extension.\u003c/p\u003e","description":"","filename":"Fig.4.png","url":"https://assets-eu.researchsquare.com/files/rs-6604947/v1/5e9ebbfa3ffbbb2084779791.png"},{"id":88014671,"identity":"571f1b5b-8829-474b-8679-3d1203c60de8","added_by":"auto","created_at":"2025-07-31 12:50:20","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":844568,"visible":true,"origin":"","legend":"\u003cp\u003eThe relationship between the deviation of residual ridges and the number of missing teeth for non-distal extension.\u003c/p\u003e","description":"","filename":"Fig.5.png","url":"https://assets-eu.researchsquare.com/files/rs-6604947/v1/cdce7f468928ff52c3cb4eb2.png"},{"id":93903939,"identity":"04c40f0d-9e80-41fa-aee6-26cff5c9f8b7","added_by":"auto","created_at":"2025-10-20 06:32:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5830349,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6604947/v1/7d7f8616-17f5-47cf-87f0-a08c8fcdcbf2.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"In vivo Accuracy Comparison of Residual Ridge between Digital and Conventional Impressions in the Partially Edentulous Maxilla","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eDigital impression technology is widely utilized in prosthodontic treatments, such as implant prosthodontics and fixed prosthodontics due to simplified processes, patient comfort, operation efficiency [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Recently, digital impression technology is also gradually applied to the fabrication of removable partial denture models [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. However, several challenges remain [\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. One such challenge is the inability to create pressure impressions, which can compromise the precision and fit of removable denture abutments. This, in turn, can result in excessive pressure pain on the abutment teeth and food impaction on the denture tissue surface [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eConventional impressions place pressure on the residual ridge and can induce the morphology change of a residual ridge [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. On the other hand, digital impression never places any pressure on the residual ridge because it is a non-contact system [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. If the accurate data of the morphology deviations at residual ridge between digital and conventional impressions be obtained, data modification subsequent to the digital impression taking could be applied to reproduce the morphology of the residual ridge achieved by conventional impression, it would be a potential breakthrough. Previous in vitro studies compared the dimensional accuracy of conventional impressions with that of digital impressions, and investigated the trueness of intraoral scanning in different partially edentulous conditions [\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. However, in vitro partially edentulous model could not simulate the true situation of residual ridge such as compressibility of the alveolar mucosa. An in vivo study investigated the morphological difference of the residual ridge top under the first molar artificial tooth between digital and conventional impressions in the partially edentulous mandible of Kennedy Class I and II[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The stress-bearing region of maxilla is much larger than that of the mandible. Therefore, the deviation of the residual ridge between digital and conventional impressions in the partially edentulous maxilla might be different from that in the partially edentulous mandible.\u003c/p\u003e\u003cp\u003eIn the in vivo study, the digital impression and conventional impression were taken on the partially edentulous maxilla. The accuracy of residual ridge between digital and conventional impressions was examined, the relationship between the accuracy and the number of missing teeth was also investigated.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Participants\u003c/h2\u003e\u003cp\u003ePatients with the partially edentulous maxilla, who visited the Department of Prosthodontics at the Affiliated Stomatological Hospital of Tongji University between September 2022 and August 2024, were selected. All participants met the indications for removable partial denture restoration. The inclusion criteria were as follows: edentulous maxillary ridge for more than three months, absence of periodontitis, stable remaining teeth, no severe alveolar ridge resorption, no prominent bone protrusions, no limitation in mouth opening or temporomandibular joint disorders, no severe systemic diseases, and good compliance. All participants signed informed consent forms and underwent preliminary examinations, including radiographic assessments. This study was approved by the Medical Ethics Committee of the Affiliated Stomatological Hospital of Tongji University, with approval number [2023]-SR-38.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Materials\u003c/h2\u003e\u003cp\u003eIntraoral digital impression scanner (3Shape, Denmark); red impression compound (Changzhi, China); silicone rubber impression material (heavy body: tray type, Express STD; light body: Imprint II Garant Type 3, 3M, USA); type 4 gypsum (Die Stone, Heraeus, Germany); extraoral window scan scanner (Shining 3D, China).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Digital Impression\u003c/h2\u003e\u003cp\u003eIntraoral image data of maxillary dentition defects were collected from 44 patients by the same prosthodontist using a 3Shape intraoral scanner, adhering to standard intraoral scanning procedures suggested by manufacturers. The removable partial denture impressions made using this method are referred to as digital impression scans (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Conventional Impression\u003c/h2\u003e\u003cp\u003eConventional pressure impressions were obtained using silicone rubber impression material, red paste, and a metal steel tray. These impressions were poured with type 4 gypsum. The plaster models were scanned with an extraoral window scanner, and the data were saved in STL format, referred to as conventional impression scans (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Measuring the accuracy and Data Analysis\u003c/h2\u003e\u003cp\u003eThe digital impression scans and conventional impression scans STL files were imported into a surface matching software (Geomagic Contro X; 3D Systems, Rock Hill, SC) using the best-fitting alignment method. The dimensional differences between digital impression scans and corresponding conventional impression scans were compared (conventional impression scans as reference). The total deviation and deviations at Point IP (Incisive papilla) between two scans were first measured. The deviations at three points of residual ridge: Point M (mesial), Point C (center), Point D (distal) were also measured (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). The residual ridges were divided into Distal extension and Non distal extension. The definitions of Point M, Point C and Point D were showed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eMeasurement site and sample size\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSites\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDefinition\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePoint M\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eThe crest of residual ridge 2mm far from the mesial remaining tooth\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e69\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003ePoint D\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNon distal extension: the crest of residual ridge 2mm far from the distal remaining tooth\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDistal extension: maxillary tuberosity 2mm far from pterygomaxilay notch\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e41\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePoint C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eThe midpoint between Point M and Point D in the crest of residual ridge\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e69\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePoint P\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eIncisive papilla\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e44\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e The methodology and results of the study were reviewed by an independent statistician. The sample size was calculated a priori based on the detection of a minimum clinically relevant difference of 25% at an α level of 0.05 and 80% power (i.e., the risk of a type I and type II error was 5% and 20%, respectively). A total of 44 observations from each partially edentulous conditions were determined in present study.\u003c/p\u003e\u003cp\u003eOne-way ANOVA and independent samples t-test were used to detect statistical significance for deviations between digital impressions and conventional impressions. Linear regression models were constructed to assess the association between the number of missing teeth and the deviation. For the above all tests, P-values\u0026thinsp;\u0026lt;\u0026thinsp;0.05 were considered significant.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Participants and residual ridge\u003c/h2\u003e\u003cp\u003eA total of 44 participants (24 female, 20 male; mean age 65.2\u0026thinsp;\u0026plusmn;\u0026thinsp;9.7 years) were enrolled in this study. The detailed number of residual ridge was presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2 The total deviation and deviation at Point P between two scans\u003c/h2\u003e\u003cp\u003eUnder the best-fit alignment, the total deviation between the two scans was 0.008\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003 mm, and the deviation at Point P were 0.069\u0026thinsp;\u0026plusmn;\u0026thinsp;0.014 mm. Both the total deviation and the positional at Point P showed no significant difference among participants (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Correlation analysis found no significant correlation between the deviation and the number of missing teeth for both total deviation and deviation at Point P (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), suggesting the number of missing teeth did not affect the total deviation and the deviation Point P.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eResult of total deviation and deviation at Point P between two scans, X\u0026thinsp;\u0026plusmn;\u0026thinsp;SEM\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eScans\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTotal deviation(mm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePoint P\u003c/p\u003e\u003cp\u003e(mm)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDeviation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.008\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.069\u0026thinsp;\u0026plusmn;\u0026thinsp;0.014\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.963\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.716\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.082\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.727\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.3 The deviation of residual ridges between two scans\u003c/h2\u003e\u003cp\u003eConventional pressure impressions could induce the morphology change of residual ridges. Therefore, the deviation of residual ridges between two scans was investigated in detail. For Non distal extension, there was no significant difference in the deviation of residual ridges among Point M, Point C, and Point D (0.032mm, 0.044 mm and 0.034 mm, respectively, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). However, for the distal extension, the deviation at the Point D and Point C (0.136 mm and 0.082 mm respectively) was significantly greater than that at Point M (0.027mm) (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The deviation of residual ridges for distal extension was also compared with that for Non distal extension. The deviation at Point D and Point C for distal extension respectively was significantly greater than that for Non distal extension, which suggested that the location of residual ridge effected its deviation between two scans.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.4 The relationship between the deviation of residual ridges and the number of missing teeth\u003c/h2\u003e\u003cp\u003eThe precision of digital impressions decreased as the number of missing teeth increased. The number of missing teeth might influence the deviation of residual ridges between two scans. The relationship between the deviation of residual ridges and the number of missing teeth was investigated (Distal extension, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e; Non distal extension, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). For distal extension, the deviation of the Point M, Point C, and Point D increased with the number of missing teeth. There was a linear relationship between the deviation at Point M, Point C, and Point D and the number of missing teeth (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). However, for Non distal extension, there is no linear relationship between the deviation of residual ridges and the number of missing teeth. (\u003cem\u003eP\u003c/em\u003e\u0026gt;0.05 Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e)\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eCurrently, the fabrication of removable partial dentures (RPDs) involves a combination of traditional and digital methods [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The rehabilitation of the partially edentulous using RPDs typically requires a series of processes such as taking traditional pressure impressions, pouring gypsum models, scanning these models, and subsequent computer-aided design/computer-aided manufacturing (CAD/CAM) based on the scanned data. However, this workflow has not yet achieved full digitalization [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Conventional pressure impression techniques capture the oral mucosa under appropriate compression to ensure uniform stress distribution across the edentulous mucosa and abutment teeth [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In contrast, intraoral digital impression technology only captures the mucosal state of the residual ridges without any applied pressure. The objective of this in vivo study is to directly compare the accuracy between digital and conventional impressions in the partially edentulous, especially the accuracy of residual ridge. Therefore, present study did not investigate the trueness of different impression technique on in-vitro partially edentulous model as previous studies [\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn present study, the total deviation between two scans was only 0.008 mm, much smaller than the deviation of the Point P and residual ridge. This suggested that the total deviation could not reflect detailed deviation of a particular site. As to residual ridges, the deviation at the Point D and Point C for distal extension was significantly greater than that at Point M, also significantly greater than that for Non distal extension. Furthermore, the deviation of the distal extension increased with the number of missing teeth. These indicates that digital impression could not fully replicate conventional pressure impression, mainly in residual ridge of distal extension. This phenomenon is primarily due to the compression and subsequent depression of the mucosa in the residual ridge of distal extension during conventional pressure impression [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Additionally, this may be related to the characteristic of precision for digital impression. Intraoral digital impression technology is based on the superimposition of multiple images [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The anatomical features of the edentulous area, such as the smooth mucosa on the residual ridge, lack distinct and fixed anatomical reference points [\u003cspan additionalcitationids=\"CR30 CR31\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Compared with hard tissues like teeth, the residual ridge is more difficult to be captured in high-quality images by intraoral scanning [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. As the scanning area of the distal extension extends, cumulative deviation induced by the overlapping of each frame increases [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThere are several methods to enhance the accuracy of digital impressions for edentulous regions. One is adding reference markers[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Reference markers can be placed at problematic overlap areas, the Incisive papilla region, and along the alveolar ridge in longer edentulous spans [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Alternative scanning paths, such as \u0026ldquo;Z\u0026rdquo; or \u0026ldquo;S\u0026rdquo; shape s[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e], can also improve image stitching and overlapping issues. Additionally, biting the occlusal silicone rubber in the edentulous area is used to simulate functional occlusion, once removing the occlusal silicone rubber, quickly completing the mucosal scan is recommended to achieve the digital pressure impressions[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eVahidi\u0026rsquo;s study[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] compared tissue displacement resulting from different techniques and impression materials for distal-extension ridges. The vertical displacement in the mucosa of the residual ridge of distal extension was estimated to be around 200 \u0026micro;m. The deviation at Point D of the distal extension between digital and conventional impressions in this study was 136\u0026micro;m, smaller than their results. In Vahidi\u0026rsquo;s study[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], distal extension of the partially edentulous mandible was investigated while the partially edentulous maxilla was examined in present study. Palate might lead to the smaller subsidence of distal extension for maxilla than that for mandible. Ishioka\u0026rsquo;s study[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] reported the 90.3\u0026micro;m vertical displacement of the residual ridge between digital and conventional impressions in the partially edentulous mandible, which was smaller than the deviation at Point D of the distal extension in our study. However, the recorded location in Ishioka\u0026rsquo;s study was the residual ridge under the first molar artificial tooth, not the Point D of the distal extension in our study.\u003c/p\u003e\u003cp\u003eThis study provided the reference value for the conversion from digital anatomic impressions to digital pressure impressions. By collecting the deviation of the residual ridges between digital and conventional impressions, expanding the sample size and establishing a standardized software model database, it is possible to design the subsidence of the mucosa in residual ridges directly on the digital impression through algorithm, achieving a direct conversion from digital anatomic impressions to digital pressure impressions. This approach facilitates the custom design and fabrication of removable partial dentures. However, further expansion of the sample size and software is necessary to enhance the reference value and establish a standard database.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe original contributions presented in the study are included in the article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge all patients who participated in the study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFinding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSupported by grants from the National Natural Science Foundation of China (Grant No. 81970962) and the Shanghai Municipal Commission of Health and Family Planning (No. 202340063) to J. T.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll methods were conducted in accordance with the relevant guidelines and regulations, including the Declaration of Helsinki. All participants signed informed consent forms and underwent preliminary examinations, including radiographic assessments. This study was approved by the Medical Ethics Committee of the Affiliated Stomatological Hospital of Tongji University, with approval number [2023]-SR-38.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWritten informed consent was obtained prior to the participation of this patient.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eChochlidakis KM, Papaspyridakos P, Geminiani A, Chen C-J, Feng IJ, Ercoli C. Digital versus conventional impressions for fixed prosthodontics: A systematic review and meta-analysis. J Prosthet Dent. 2016;116:184\u0026thinsp;\u0026ndash;\u0026thinsp;90.e12.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRaja SR, Dutta A, Jain SK, Dewan H, Thomas V, Jose AT. In vitro comparative analysis of digital versus conventional impressions in fixed prosthodontics. J Pharm Bioallied Sci. 2024;1:S2700\u0026ndash;2.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSchmidt A, W\u0026ouml;stmann B, Schlenz MA. Accuracy of digital implant impressions in clinical studies: A systematic review. Clin Oral Implant Res. 2022;33:573\u0026ndash;85.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTakaichi A, Fueki K, Murakami N, Ueno T, Inamochi Y, Wada J, et al. A systematic review of digital removable partial dentures. Part II: CAD/CAM framework, artificial teeth, and denture base. J Prosthodont Res. 2022;66:53\u0026ndash;67.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAl-Haj Husain N, \u0026Ouml;zcan M, Schimmel M, Abou-Ayash S. 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Effect of scan-path length on the scanning accuracy of completely dentate and partially edentulous maxillae. J Prosthet Dent. 2022;131:146\u0026ndash;54.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eIshioka Y, Wada J, Kim E-Y, Sakamoto K, Arai Y, Murakami N et al. Morphological Comparison of Residual Ridge in Impression for Removable Partial Denture between Digital and Conventional Techniques: A Preliminary In-Vivo Study. J Clin Med. 2023.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTregerman I, Renne W, Kelly A, Wilson D. Evaluation of removable partial denture frameworks fabricated using 3 different techniques. J Prosthet Dent. 2019;122:390\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCampbell SD, Cooper L, Craddock H, Hyde TP, Nattress B, Pavitt SH, et al. Removable partial dentures: The clinical need for innovation. J Prosthet Dent. 2017;118:273\u0026ndash;80.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFriel T, Waia S. Removable partial dentures for older adults. Prim Dent J. 2020;9:34\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMai HY, Mai H-N, Kim H-J, Lee J, Lee D-H. Accuracy of removable partial denture metal frameworks fabricated by computer-aided design/ computer-aided manufacturing method: a systematic review and meta-analysis. J Evid Based Dent Pract. 2022;22:101681.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eReddy SM, Mohan CA, Vijitha D, Balasubramanian R, Satish A, Kumar M. Pressure produced on the residual maxillary alveolar ridge by different impression materials and tray design: An in vivo study. J Indian Prosthodont Soc. 2013;13:509\u0026ndash;12.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLee J-H, Yun J-H, Han J-S, Yeo I-SL, Yoon H-I. Repeatability of intraoral scanners for complete arch scan of partially edentulous dentitions: An in vitro study. J Clin Med. 2019;8:1187.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMangano FG, Veronesi G, Hauschild U, Mijiritsky E, Mangano C. Trueness and precision of four intraoral scanners in oral implantology: A comparative in vitro study. PLoS ONE. 2016;11:e0163107.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZarone F, Ruggiero G, Ferrari M, Mangano F, Joda T, Sorrentino R. Comparison of different intraoral scanning techniques on the completely edentulous maxilla: An in vitro 3-dimensional comparative analysis. J Prosthet Dent. 2020;124:762e1. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e-.e8\u003c/span\u003e\u003cspan address=\"http://-.e8\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVahidi F. Vertical displacement of distal-extension ridges by different impression techniques. J Prosthet Dent. 1978;40:374\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLogozzo S, Zanetti EM, Franceschini G, Kilpel\u0026auml; A, M\u0026auml;kynen A. Recent advances in dental optics \u0026ndash; Part I: 3D intraoral scanners for restorative dentistry. Opt Lasers Eng. 2014;54:203\u0026ndash;21.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eStefanelli LV, Franchina A, Pranno A, Pellegrino G, Ferri A, Pranno N, et al. Use of intraoral scanners for full dental arches: Could different strategies or overlapping software affect accuracy? Int J Environ Res Public Health. 2021;18:9946.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKontis P, G\u0026uuml;th J-F, Schubert O, Keul C. Accuracy of intraoral scans of edentulous jaws with different generations of intraoral scanners compared to laboratory scans. J Adv Prosthodont. 2021;13:316\u0026ndash;26.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRasaie V, Abduo J, Hashemi S. Accuracy of intraoral scanners for recording the denture bearing areas: A systematic review. J Prosthodont Implant Esthet Reconstr. 2021;30:520\u0026ndash;39.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLeggeri A, Carosi P, Mazzetti V, Arcuri C, Lorenzi C. Techniques to improve the accuracy of intraoral digital impression in complete edentulous arches: A Narrative Review. Appl Sci. 2023;13:7068.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFang J-H, An X, Jeong S-M, Choi B-H. Digital intraoral scanning technique for edentulous jaws. J Prosthet Dent. 2018;11:733\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKattadiyil MT, Mursic Z, AlRumaih H, Goodacre CJ. Intraoral scanning of hard and soft tissues for partial removable dental prosthesis fabrication. J Prosthet Dent. 2014;112:444\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCao R, Zhang S, Li L, Qiu P, Xu H, Cao Y. Accuracy of intraoral scanning versus conventional impressions for partial edentulous patients with maxillary defects. Sci Rep. 2023;13:16773.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShimizu T, Tasaka A, Wadachi J, Yamashita S. A new proposal for improving the accuracy of intraoral scanning for partially edentulous residual ridge. J Prosthodont Res. 2023;67:246\u0026ndash;54.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAbduo J, Elseyoufi M. Accuracy of intraoral scanners: A systematic review of influencing factors. Eur J Prosthodont Restor Dent. 2018;26:101\u0026ndash;21.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHirota Y, Tawada Y, Komatsu S, Watanabe F. Effect of impression holding time and tray removal speed on the dimensional accuracy of impressions for artificial abutment tooth inclined. Odontology. 2021;109:157\u0026ndash;67.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Partially edentulous, digital impression, conventional impressions, accuracy","lastPublishedDoi":"10.21203/rs.3.rs-6604947/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6604947/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003ePurpose\u003c/strong\u003e: This in vivo study aims to compare the accuracy of residual ridge between digital and conventional impressions in the partially edentulous maxilla.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods:\u003c/strong\u003e Forty-four patients with the partially edentulous maxilla were included in the study. Digital impression were obtained using an intraoral scanner (TRIOS2, 3Shape), while conventionalpressure impression were poured with type 4 gypsum and models were scanned using a desktop scanner (Shining 3D). The total deviation and deviations at Point P (Incisive papilla) between two scans were first measured by Geomagic Control X software. The deviations at three points of residual ridge: Point M (mesial), Point C (center), Point D (distal) were then measured.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults:\u003c/strong\u003e The total deviation and deviation at Point P between the two scans was 0.008 mm and 0.069 mm, respectively. The total deviation and deviation at Point P exhibited no significant difference among patients. For the residual ridge of non-distal extension, the deviations showed no significant difference among Point M, Point C and Point D (0.032mm, 0.044 mm and 0.034 mm, respectively). For the distal extension, the deviation at the Point D and Point C (0.136 mm and 0.082 mm respectively) was significantly greater than that at Point D (0.027mm). The deviations of distal extension increased with the number of missing teeth.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e The deviation of distal extension was much greater than the total deviation between digital and conventional impressions. This study provided the reference value for the conversion from digital anatomic impressions to digital pressure impressions.\u003c/p\u003e","manuscriptTitle":"In vivo Accuracy Comparison of Residual Ridge between Digital and Conventional Impressions in the Partially Edentulous Maxilla","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-31 12:42:15","doi":"10.21203/rs.3.rs-6604947/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1b2649d0-46ab-4155-bd25-11e4214aa71c","owner":[],"postedDate":"July 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-20T06:23:49+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-31 12:42:15","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6604947","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6604947","identity":"rs-6604947","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}