Accuracy of Intraorally Scanned Denture Impressions Compared to Conventional Border-Molded Impressions: An In Vivo Study
Phase: NA
Conditions: Edentulism, Complete Dentures, Digital Impression Accuracy, Dental Impression Techniques
Sponsor: Mohammed Bin Rashid University of Medicine and Health Sciences

 
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Research Proposal  
 
 
 
Accuracy of intraorally scanned denture impressions 
compared to conventional border moulded impressions- an in 
vivo study. 
 
 
 
Principal Investigator:  
Fatemeh Amir Rad  
Assistant Professor, Department of Prosthodontics  
Email: fatemeh.amirrad@mbru.ac.ae 
 
Co-investigator: 
Ahmed Fareed AlArayedh   
Resident Doctor, Department of Prosthodontics 
Email: Ahmed.alarayedh@students.mbru.ac.ae 
 
Co-investigator: 
Keyvan Moharamzadeh  
Professor in Endodontics, Department of Prosthodontics 
Associate Dean - Education  
Email: keyvan.moharamzadeh@mbru.ac.ae 
 
 
 
 
Last revised: 25 August 2024 
 
 
 

 
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Introduction 
 
The field of digital dentistry has seen significant breakthroughs and technological 
developments, making it one of the most up-to-date areas of practice for dental professionals. 
Extensive research is being conducted in the rapidly growing field of digital dentistry, with a 
particular focus on restorative dentistry. Digital scanning as part of the computer aided 
designed or computer aided manufacture (CAD/CAM) systems, has been introduced to 
dentistry in the middle of the 1980’s. Intraoral scanning devices have gained wide usage in the 
treatment of single crowns, multiple fixed unit prosthesis, and more recently, in the field of 
implants and complete denture prosthetics (Gan et al., 2016).  
The advent of intra oral scanners aimed to provide a smoother experience for the patient, and 
streamline the work flow by reducing the complications associated with using conventional 
tray-based impressions (Mörmann, 2006). Accordingly, dental practice has increasingly 
adopted digital technology, such as intraoral scanners (IOS), due to several advantages it offers 
over traditional impression techniques. These include reduced laboratory and chairside time 
and steps, as well as the ability to implement a fully digital manufacturing process (Zarone et 
al., 2020).  
CAD/CAM technique has lately been used for the fabrication of complete dentures. Systematic 
review of in vitro studies by Wang et al. (2021) found that the accuracy of digital complete 
dentures is comparable to that of conventional complete dentures. Current research on digital 
dentures has shown that they require fewer clinical appointments and shortened time spent in 
the dental chair compared to conventional complete dentures. This can be particularly 
beneficial for edentulous geriatric patients who may find it difficult to spend extended hours 
on the dental chair. Furthermore, digital dentures may result in better patient satisfaction and 
clinical outcomes (Casucci et al., 2023). However, it is important to acknowledge the lack of 

 
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adequate evidence addressing the efficacy of digital scanners for complete edentulous arches 
in a clinical setting. 
Literature review 
Digital vs conventional impressions 
The selection of the technique and material used by clinicians to take an impression of the 
tissues that support the denture is crucial for ensuring proper fit and function. This includes 
achieving the correct extension and adaptation during both static and dynamic movements, 
which ultimately affects how well the denture stays in place. Incorporating IOS technology in 
removable prosthodontics has certain advantages and challenges. The direct intraoral scanning 
technique eliminates the need for physical impressions, thereby eliminating errors caused by 
distortion of elastomeric conventional impressions, inconsistencies in the water/powder ratio, 
and improper storage conditions of impressions or gypsum casts (Gan et al., 2016). However, 
many clinicians use conventional impression techniques for complete edentulous patients 
because the elastomeric material used in these techniques can record not only the edentulous 
arch but also the dynamic and static movements of mucosal soft tissues. These functional 
movements of the vestibular mucosa in relation to border molding and muscle activities, which 
are essential for shaping and extending the margins of the prosthesis, are difficult to capture 
with an IOS (Chebib et al., 2019, Casucci et al., 2023).  
Furthermore, the incorporation of digital technology in clinical practice comes with additional 
constraints. For instance, there is a learning curve associated with acquiring the skills to 
effectively use this technology. Moreover, the acquisition of an IOS device can be costly. The 
superiority of digital impression over the conventional method is still a subject of controversy. 
Therefore, the conventional method remains the dominant technique in the field of removable 
prosthodontics (Casucci et al., 2023, Zarone et al., 2020). To favor one strategy over the other, 
it is necessary to have evidence-based research. 

 
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Accuracy of digital impressions 
Accuracy consists of two main factors: precision and trueness ISO 5725-1 (2023). Given the 
extensive interest in digital workflow, the focus remains on the accuracy of new impression 
techniques in capturing the necessary data. Precision defines how near repetitive measurements 
are to each other whereas trueness defines how far-off the measurement diverges from the 
actual dimensions of the measured object (Ender and Mehl, 2013).  
 
Figure 1. Illustration of the relationship between trueness, precision, and accuracy, as defined 
by International Standard Organization (ISO, 1994). 
 
With the progress of intra oral scanning technology, the latest generation of scanners show 
enhanced precision and reduced scanning intervals. Over time, both software and hardware 
enhancements in scanners have also been worked on to help in securing the data. While the 
accuracy of an intra oral scanner is influenced by the quality of the scanned image, it also relies 
on the accuracy of superimposing the actual anatomical landmarks, which is dependent on 
algorithms in the scanner for image reconstruction (Srivastava et al., 2023). 
In-vitro studies on accuracy of the digital impressions 
In vitro studies have assessed the accuracy of digital impressions for dentated and partially 
dentated full arches in comparison to conventional impressions. These studies have shown 

 
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various issues, such as the distortion of the digital scans and reduced accuracy, i.e. precision 
and trueness, when compared to conventional impressions (Ender and Mehl, 2013), (Malik et 
al., 2018). Likewise, Zarone et al. (2020), who examined and compared different intraoral 
scanning techniques on a model of completely edentulous maxilla, found that scanning 
complete edentulous arches presents challenges. This is because there are no visible landmarks 
in the larger scanning range of edentulous areas, which makes it difficult to accurately identify 
anatomical reference points.  
Previous studies by Schimmel et al. (2021) examined how the operator's experience influences 
scan accuracy and time. Their results indicate that operators’ experience observed shorter 
scanning times which can improve the accuracy of digital scans. However, they found that 
scans of the fully edentulous mandibular arch showed significantly better trueness when 
performed by inexperienced operators. Similarly, scans of the edentulous maxillary arch 
demonstrated significantly better precision from inexperienced operators. Nonetheless, these 
studies were conducted on edentulous arch models, which do not accurately replicate the actual 
intraoral conditions.  
The technology utilized in scanners varies, resulting in possible differences in accuracy. In a 
study by Nulty (2021), the accuracy of nine IOSs and four lab scanners were compared. The 
result showed that all the scanners had a mean trueness of less than 60-micron deviation. This 
study indicated that the scanning of a completely edentulous arch is more difficult than 
scanning a dentate arch, and it suggests that the accuracy of these scanners in edentulous cases 
should be evaluated in future studies, given the rapid advancements in this a field of  
technology.  
In-vivo studies on digital impressions 
Current intraoral scanning devices have shortcomings with accurately scanning the soft tissue 
under selective pressure and capturing the movement of the soft tissues in denture-bearing 

 
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areas. In a study conducted by Gan et al. (2016), the accuracy of intraoral digital impressions 
for whole upper jaws, including the full dentitions and palatal soft tissues, was compared. The 
study found that the flexible oral mucosa and smooth tooth surfaces, coated by saliva, can pose 
difficulties for clinicians when taking intraoral digital impression for removable partial 
dentures or complete dentures. Other limitations in terms of anatomical structure and 
accessibility in posterior areas make it challenging to use the IOSs effectively. Hence, these in-
vivo studies reveal additional potential challenges encountered in comparison to the in-vitro 
experiments.  
In a recent systematic review conducted by Casucci et al. (2023), the accuracy, time required, 
and satisfaction of patients were assessed for digital impressions compared to conventional 
impressions taken for removable prostheses on edentulous arches. The review included six 
clinical in vivo studies focusing on accuracy, specifically trueness, while precision was not 
addressed. The review concluded that there is limited scientific evidence available on the use 
of IOS for edentulous arches, particularly in terms of scanning time and patient satisfaction. 
Although, the study determined that digital scanning seems to be a predictable method for 
capturing impression of the attached mucosa in edentulous patients, the studies consistently 
found discrepancies in the peripheral areas, especially the soft palate and the vestibule, 
emphasizing the need for further research investigating the abilities of IOSs in edentulous 
arches and their suitability for removable prostheses. In addition, scanning fully edentulous 
arches may be further complicated due to the presence of mobile tissues and saliva. On the 
other hand, a systematic review that examined clinical studies comparing the accuracy of 
digital impressions to conventional impressions in fixed prosthodontics, found that 
conventional impressions are more accurate than digital impressions in clinical situations 
(Giachetti et al., 2020).  

 
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Alternative contemporary systematic review examining the accuracy of IOSs for recording 
completely edentulous arches, included eight in vivo studies, six of which coincided with the 
previous review, while two were modern found that IOSs provide clinically acceptable digital 
scans. However, the message remains identical, improvements are still needed to aid in 
capturing movable mucosa. In cases with unfavorable ridge anatomy or when denture retention 
is considered necessary through compressing the tissue, digital intraoral scanning is not 
advised. Also, it is recommended that when scanning the vestibule, capturing the entire surface 
area in one scan is suggested to avoid faults. While IOSs can be used in the fabrication of 
complete denture prosthetics for edentulous arches, careful case selection is still crucial 
(Srivastava et al., 2023). 
Effect of scan length and strategy 
The inside of the oral cavity is a small, confined space, which makes it difficult to fully capture 
the entire space just with a few pictures. To acquire a 3D image of the surface inside the oral 
cavity, the scanner takes multiple small "point cloud" shots during the scanning process. 
Furthermore, it combines all those smaller point clouds into one big 3D point cloud. Finally, it 
connects all the points in that cloud to create a smooth, triangulated 3D surface model 
(Waldecker et al., 2024).  
Recent study reported by Waldecker et al. (2024) found that missing upper teeth led to greater 
measurement errors in the 3D scans and longer scanning paths resulted in linearly increasing 
distance deviations. Angular and tooth axis deviations did not increase linearly with longer 
scans. Accuracy of complete-arch intraoral scans based on confocal microscopy versus optical 
triangulation a comparative in vitro study by Moritz Waldecker (2021) found that scanning 
accuracy is reduced as the scan-path length is expanded by comparing short and long distances.  
Recent in-vitro study by Zarone et al. (2020) compared the accuracy of three different scanning 
strategies using a single intraoral scanner, TRIOS 3 (3Shape), on two edentulous maxillary 

 
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reference typodonts - one with defined palatal rugae and one without. The outcomes showed 
that scans performed on the typodont with less distinct anatomical landmarks had better 
accuracy than those made on the typodont with more defined landmarks.  On the smooth 
typodont, there was no difference between the three scanning techniques. However, on the 
wrinkled typodont, the buccal-palatal scanning technique was more accurate than the palatal-
buccal approach, while the S-shaped technique showed no significant difference. The study 
concluded that the scanning strategy had a major impact on the accuracy of scans for the 
completely edentulous maxilla. Limitations of this in-vitro study include the lack of clinically 
relevant factors such as oral temperature, humidity, soft tissue characteristics, and intraoral 
anatomy. Contrary to the previous report,  Kim et al. (2017) studied the effect of an artificial 
landmark on a long edentulous space on the accuracy of intraoral digital impressions an in vitro 
report and concluded that the utilization of an alumina mock landmark enhanced the trueness 
and precision. 
Deviation measurement 
Recent study by Al Hamad and Al-Kaff (2023) found that certain areas of both the upper and 
lower arches showed positive deviations, with a color range of 1.4 to 1.8 mm mainly located 
in the buccal dynamic regions. In the static areas, a mixed outline observed some regions with 
positive deviations, while others had negative deviations. The range for both types of deviations 
in these static areas was 0.2 to 0.4 mm.  
Another research by Masri et al. (2020) evaluating the adaptation of CDs fabricated using IOS 
technique and conventional technique results showed no significant deviations: 
- Overall surface: 0.502 ± 0.035 mm 
- Posterior palatal seal: 0.447 ± 0.089 mm   
- Anterior border seal: 0.659 ± 0.099 mm 
- Ridge crest: 0.579 ± 0.092 mm 

 
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- Palatal area: 0.357 ± 0.089 mm  
The palatal area appears to be the region with the least deviation, while the highest incidence 
of discrepancy was found to be in the anterior border seal. 
3 Shape Trios scanner 
3Shape is a conspicuous dental scanning company that was founded in 2000 by Tais Clausen 
and Nikolaj Deichmann. Their dental scanners are widely used in dental practices. The way the 
3Shape scanners work explained by Singer (2024) is by shining a light onto the object being 
scanned, like the dentition with soft tissues. The light bounces off the object and gets redirected 
back to a sensor in the scanner. This allows the scanner to capture a sharp, detailed image of 
the scanned surface. Using these individual images, the scanner software then builds a 3D 
digital model of the scanned area. The 3Shape Trios intraoral scanner can capture around 2,500 
of these images per second. From every 100 or so of these individual images, the scanner 
software creates a "sub-scan" - which is broadly a 3D point cloud representation that includes 
color information of what the scanner is capturing. These point clouds are organized into 
triangles.  
 
Aims and Objectives  
Aim 1: 
To compare the trueness of digital impression captured using an intra oral scanner, in a 
completely edentulous arch, in comparison to a conventional impression obtained from the 
same patient. 
Null hypothesis 1: There are no statistically significant differences in trueness between the 
digital and conventional impression techniques for complete edentulous arch. 
Aim 2: 

 
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To compare the precision of the 3 digital impressions for complete edentulous arches obtained 
from the same patient. 
Null hypothesis 2: The digital impressions of a complete edentulous arch would not be different 
when the digital impression is repeated multiple times. 
Null hypothesis 3: The precision of the digital impressions is not different in the maxillary and 
mandibular arch. 
Research question  
Is the accuracy of IOSs similar to conventional border moulded impressions in a completely 
edentulous arch (maxillary or mandibular)?  
Research methodology  
This study proposal will be submitted for Institutional Review Board (IRB) approval it will be 
conducted in agreement with the Declaration of Helsinki of ethical human research practice. 
Prior to participation, each subject will sign an informed consent.  
Each subject provided will sign informed consent prior to participation. All personal 
information collected will be anonymous and securely protected with a study code number. 
There will be no data which could personally identify participants of the research study. Any 
future published work will also be unidentified and will not include any personal information 
regarding the individuals participating in this study. 
Research design 
• A non-randomized clinical trial, in which participants will be recruited and digital and 
conventional impressions will be obtained for them at the same time by the same 
operator. 

 
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Patient Sample   
The determination of the sample size needed will be based on previously reported study the  
trueness of intraoral scanning of edentulous arches: A comparative clinical study by (Al 
Hamad and Al-Kaff, 2023) given RMS (root mean square) means 0.21 and 1.51 and SD 0.03 
and 0.28 respectively for static and dynamic maxillary.  
The sample size calculation formula is expressed as N=2 
(𝑍𝛼/2+𝑍𝛽)2
(𝐸𝑆)2
  where N represents the 
sample size per group. In this case, the standard normal value Zα/2 is 1.96 for a significance 
level α of 0.05, and Zβ is 0.84 for a desired power of 80%. The effect size ES is 0.82, and the 
square of the effect size is 0.7. By replacing these values into the formula, we can calculate the 
sample size for different scenarios. Based on the calculations, a total of 10 participants will be 
recruited, and the control and test impression techniques will be conducted and compared for 
each patient. 
N=2 
(𝑍𝛼/2+𝑍𝛽)2
(𝐸𝑆)2
 
N = sample size per group  
Zα/2 = standard normal value Z-value for a significance α = 0.05 which is 1.96 
Zβ = standard normal Z-value for the power of 80%, which is 0.84  
 
 
 
 
 
ES = 0.82 (effect size) 
(𝐸𝑆)2 = 0.7  
 
Patient selection 
A total of 10 participants, attending Dubai Dental Hospital in collaboration with Mohammed 
Bin Rashid University MBRU, requiring complete denture prothesis treatment or follow up on 
previous prosthesis will be included in the study following the inclusion criteria. In addition, 
any participant who has recently been edentulous (at least 6 weeks) will be involved after 

 
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attaining their approval. Patients speaking Arabic and or English languages will be recruited in 
the study, and prior to any procedure, comprehensive verbal explanations will be provided to 
them. Dentate patients and those un-willing to participate and presenting with gag reflux will 
be excluded from the study.  
Inclusion criteria  
• Patients attending DDH for complete dental prosthesis. 
• Fully edentulous patients  
• All alveolar ridge classifications of Cawood and Howell 1988 (Cawood and Howell, 
1988) 
• Above 18 years old   
• Arabic and English-speaking patients  
• Good physical health (ASA class 1 or 2) 
• Willing to provide informed consent.  
Exclusion criteria 
• Dentate patients  
• Implant attachment supported complete denture.  
• Patients un-willing to participate (non-consented patients)  
• Patients with severe gag reflex  
• 
Patient mentally unstable, drug users or alcoholics  
Primary outcome  
• Compare accuracy of digital scanning by assessment of trueness through measuring 
the differences between the conventional impression technique (control) & IOS 
impression technique (test) of both static and dynamic tissues. 
•  Assessing the precision by measuring the differences between more than one 
superimposed STL file. 
Secondary outcomes 
• Differences in terms of trueness and precision of both maxillary and mandibular 
arches. 

 
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• Difference in terms of trueness and precision of scanned attached and mobile areas. 
Data acquisition 
All impressions will be acquired by a single operator (AA) who has experience in the use of 
intraoral scanners in regular clinical practice and adequately trained to conduct conventional 
and digital impressions, thereby ensuring good intra-investigator reproducibility (Kappa). 
Digital impressions will be the initial step in the impression-taking process, followed by 
conventional impression to standardize the sequence for all participants. Subsequent to relevant 
training, the same investigator will perform each phase of data generation. 
Digital impressions 
Edentulous maxillary and mandibular arches will be scanned using IOS TRIOS 5 (3Shape, 
Copenhagen, Denmark), running on software Unite version 24.1, following the guidelines of 
Prof. Dr. Lo Russo edentulous scanning strategy (Lo Rosso) the manufacturer’s instructions of 
the same scanner.  
The scanning strategy will be done within four stages. Scan sequence for the maxillary 
edentulous arch: 1) the scanning process will initiate from the tuberosity of one side and 
continue along the center of the residual ridge towards the tuberosity of the opposite side. 2) 
coming back to the midline to complete the scan of the palate with smooth zig zag movements. 
3) scanning the buccal aspect of the ridge towards the midline of the incisive foramen of one 
side. 4) scanning the buccal aspect of the ridge towards the midline of the incisive foramen of 
the opposing side of the ridge. The third and fourth stage scanning process, the tip of the intra 
oral scanner device should be slightly rotated facing the vestibular slope of the ridge. (Figure 
2).  
Scan sequence for the mandibular edentulous arch: 1) the scan will begin from one side of the 
retromolar pad area lingually with the scanner slightly tipped, across the ridge towards the 
midline. 2)  scanning process will begin from the midline of the ridge buccally continuing to 

 
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the retromolar pad area of the same side. 3) the scan will restart from the midline of the opposite 
side towards the retromolar area lingually, and the fourth stage will be continued buccally. 
(Figure 2).  
 
 
 
 
 
 
Figure 2. Representation of the scan strategy: A. Maxilla, B. Mandible. Source: Russo 2020, 
Edentulous Scan Strategy available from: https://www.3shape.com/-/media/files/news-
pdf/prof-dr-lo-russo-edentulous-scan-startegy-jan2020.pdfv=8de884d2-7c39-45b7-ae68-
35d43e3c4e29.  
 
The intraoral scan will be performed 3 times by the principal investigator to assess the 
precision. All scans for the same arch will be taken on the same day. 
Conventional impressions 
During the first visit a preliminary alginate impression (Palgat Plus Quick, 3M ESPE, Milan, 
Italy) of the edentulous arch using a stainless-steel tray (ASA Dental, Milan, Italy) will be 
acquired to create a study model. Afterwards, on the study model, an outline of the working 
A 
B 

 
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area on the model will be drawn to fabricate custom trays specially customized for the patients’ 
edentate arch, by using the product (Photo-tray, Dental Farm Dental Equipment, Italy), which 
is a light-hardening material made from light-curing resin indicated for custom tray 
impressions. Following the manufacturer’s instructions, polymerization of the custom tray in 
an ultra-violet light curing unit (Eclipse Junior, Dentsply, Germany) will take about 20 minutes 
in daylight. Light curing unit will be used to cure the top of the tray on the model, and the 
curing time will take up to 3-5 minutes, subsequently the inside of the tray without the model 
will be cured within 3-5 minutes. Final impression will be recorded conventionally using the 
custom-made photo-tray (Photo-tray, Dental Farm Dental Equipment, Italy), and thermoplastic 
impression compound ‘’green stick’’ for border molding (Kerr, Kerr Corporation, California, 
USA) including a high-accuracy impression material. Specifically, the polyvinylsiloxane 
medium body monophase (Hydrorise Monophase; Zhermack, Badia Polesine Rovigo, Italy), 
which will be used as the "gold standard" reference for the impression. Afterwards the 
impression model will be scanned using the laboratory scanner (Ceramill map400, 
AMANNGIRRBACH, Pforzheim, Germany). The scanning images taken from the impression 
model will be superimposed on the initial intra oral scan taken from the edentulous arch by 
using (Geomagic Control X, Artec 3D System, Morrisville, USA), the trueness will then be 
measured. As trueness protocol requires superimposing the dental models obtained from the 
same subject with different impression methods (conventional impression) and measuring how 
close their readings are to one another. High precision and high trueness will result in high 
accuracy and will be determined by (Geomagic Control X 2022, Artec 3D System, Morrisville, 
USA) following the measurements on the markers.  
Superimposition Software 
Geomagic Control X 2022, Artec 3D System, Morrisville, USA. Offers a comprehensive 
collection of metrology tools for dimensional inspection, surface analysis, and automated 

 
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inspection. This includes capabilities such as best-fit alignment, color mapping, and 
programmed reporting. The software is designed with an innate sensitive interface and 
simplified workflow to make quality measurement processes efficient and user-friendly. 
 
 
 
 
 
 
 
 
                                
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Participants (N=10) 
Consent to Treatment 
(N=10) 
Excluded Candidates: 
•
Dentate 
•
Severe Gag Reflex 
•
Unwilling 
Participants 
•
Implant Attached 
Prosthesis 
Intra Orally 
Scanned as (Test) 
 
3 consecutive 
times  
TRIOS 5 
Maxillary N= 30 
Mandibular N= 30 
Conventional Impression once: 
(Gold standard as control)  
 
Primary impression- Alginate  
 
Secondary impression PVS- 
Using Custom tray  
Maxillary N=10 
Mandibular N=10  
Using Geomagic Control 
X Software 
Impressions Scanned 
(ceramill map400, 
AMANNGIRRBACH, 
Germany).  
Scans saved as STL files, 
superimposition of 3 scans 
to assess Precision.  
Scanned Impression model 
Superimposed on intra oral 
scanned STL file, to assess 
the Trueness.   

 
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Figure 3. Experimental Design: Flowchart illustrating the experimental design with IOS, and 
conventional impressions used. Accuracy evaluation by comparison to reference conventional 
impression and precision evaluation by cross-comparison. 
Data Collection 
Each conventional impression will be scanned once, and three scans will be conducted on each 
arch. Each scan data will be converted to standard tessellation language (STL) file format for 
the purpose of standardization and subsequent digital processing. Each scan will be imported 
individually into a 3D design and analysis software program (Geomagic Control X 2022, 
Geomagic, Morrisville, USA). 
Trueness and Precision Analysis through Deviation Measurement 
Each scan will be divided into dynamic and static regions. The dynamic region will include the 
mobile tissues at the periphery, which serve as the functional border of complete dentures. The 
static region will involve around 2 mm short of the depth of the sulcus, and 2 mm short of 
posterior palatal seal area.  
The areas with maximum deviation will be compared in the following regions: 
Dynamic areas: 
1- Labial sulcus 
2- Buccal sulcus (right and left) 
3- Lingual sulcus in the mandible (right and left) 
4- Post palatal seal area 
5- Hamular notch area 
Static areas: 
1- Palatal rugae 
2- Buccal slopes of the alveolar ridge (right and left) 

 
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3- Palatal slopes of the alveolar ridge in the maxilla (right and left) 
4- Lingual slopes of the alveolar ridge in the mandible (right and left) 
5- Anterior alveolar ridge crest 
6- Posterior alveolar ridge crest (right and left) 
The scan STL files of conventional and digital impressions will be aligned using Geomagic 
software’s Initial and Best-Fit Alignment functions. The software’s Best Fit Alignment feature 
applies an Iterative Closest Point algorithm (ICP) to align the test file to the reference file.  
Accuracy in terms of precision requires the superimposition of multiple scans from the same 
arch. The precision will be evaluated by quantifying the deviation observed after aligning two 
STL datasets of the same arch.  The analysis will involve conducting two-way pairwise 
comparisons between scan 1, 2, and 3 of the same arch. Each comparison will be done twice, 
first with scan 1 as the reference and again with scan 2 as the reference. The mean of deviation 
measures will be determined by calculating the average of the discrepancies. 
To evaluate accuracy in terms of trueness, it is necessary to compare different impression 
methods and assess the agreement between the mean of multiple test results and the reference 
value. Therefore, the IOS scans and the physical impression scans will be compared by 
overlying the scan images. The scan of conventional impression will serve as the reference file. 
The root mean square (RMS) will be calculated as the square root of the average of both 
positive and negative values, according to the formula: 
𝑅𝑀𝑆= √∑𝑖=1
𝑛 (𝑋1, 𝑖−𝑋2)2
√𝑛
 
 
n= total number of measuring points, 
X1,i= the measuring point of the reference data,  
X2,I= the measuring point of the IOSs.  

 
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The trueness analysis will be presented through the color-difference map and the numerical 
values of minimum, maximum, average variation, and RMS. The three-dimensional analysis 
will be finalized by comparing the scans within the defined tolerance range of -100 μm to +100 
μm as minimum and maximum values. Then, the deviation measure for the dynamic, static, 
and the overall areas will be recorded, and the color differences will be displayed and analyzed. 
Statistical Analysis 
The data will be entered into the computer using IBM-SPSS for Windows version 29.0 (SPSS 
Inc., Chicago, IL). Continuous variables will be described by using measures of central 
tendency and measures of dispersion. The Shapiro-Wilk will be used to test the normality of 
the trueness and precision measurements. Independent paired t-test will be used to compare 
measurements between conventional and intraoral scan, if the measurements are normally 
distributed otherwise Wilcoxon will be used as non-parametric test to administrate these 
comparisons. A P-value of less than 0.05 will be considered significant in all statistical 
analyses. 
Significance of this Research Study:  
As society undergoes continuous evolution and life expectancy increases, there is a growing 
demand for innovative and high-quality dental treatment and care. Individuals seek not only 
effective dental solutions but also comfortable, effective, and positive experiences. Technology 
plays a pivotal role in our daily lives, and as clinicians, we recognize the importance of 
continuing education to provide the community with the best possible dental care. The purpose 
of this research study is to explore the advantages and limitations of technological intraoral 
devices. By comparing them to the established gold standard process, we aim to gather valuable 
information that will develop our understanding and knowledge. This will enable us to better 
serve the public by providing them with the most valuable and effective dental care possible. 
The significance of this study lies in its potential to contribute to the advancement of dental 

 
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practices and improve the overall patient experience, aligning with the evolving needs and 
expectations of the community. 
 
 
 
References:  
 
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Part 1: General principles and definitions. International Organization for 
Standardization. 
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Digital Impressions in Edentulous Patients: A Systematic Review for Clinical Evidence. 
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