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Table of Contents
ORIGINAL ARTICLE
Year : 2021  |  Volume : 11  |  Issue : 1  |  Page : 11-16

Comparison of reliability and validity of measurements on digital study models made with scann three-dimensional smartphone software and plaster models: In vitro study


Department of Prosthodontics and Crown and Bridge, Adhiparasakthi Dental College and Hospital, Melmaruvathur, Tamil Nadu, India

Date of Submission03-Sep-2019
Date of Acceptance02-Feb-2021
Date of Web Publication22-Apr-2021

Correspondence Address:
Dr. K Prabhu
Department of Prosthodontics and Crown and Bridge, Adhiparasakthi Dental College and Hospital, Melmaruvathur, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jid.jid_37_19

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   Abstract 


Aim: The aim of this study was to compare traditional manual model analysis with a digital caliper with the virtual model analysis of digitalized plaster models. Settings and Study Design: This was a comparative in vitro study. Materials and Methods: Randomly ten plaster models of prosthodontics patients in permanent dentition were analyzed. Manual analyses were performed with a diagnostic digital caliper and smartphone-assisted analysis after digitization of the plaster models using SCANN 3D software. The reliability and efficiency of digital models are to be analyzed by comparing measurements made on plaster and digital cast. Statistical Analysis Used: Difference and standard deviation were used for statistical analysis. Results: By comparing the linear transverse measurements, the data reveal that the mean values of the tooth width from the manual method were larger than the values from the digital method. The standard deviation was significantly high in the first premolar region, in manual method, and high in the second premolar region in digital measurements. With the digital method, the examiner found low values with the digital method. The time needed for the creation of 3D models from photogrammetry software will more and tedious and needs a learning curve. Conclusion: Models created by Scann 3D software with the help of a smartphone appear to be an adequate and reliable alternative to the conventional method of model analysis.

Keywords: Linear transverse measurements, model analysis, photogrammetry, SCANN 3D, virtual


How to cite this article:
Prabhu K, Venkatesan N, Kirubakaran A, Karthick V C, Imithiyas M, Karthick R. Comparison of reliability and validity of measurements on digital study models made with scann three-dimensional smartphone software and plaster models: In vitro study. J Interdiscip Dentistry 2021;11:11-6

How to cite this URL:
Prabhu K, Venkatesan N, Kirubakaran A, Karthick V C, Imithiyas M, Karthick R. Comparison of reliability and validity of measurements on digital study models made with scann three-dimensional smartphone software and plaster models: In vitro study. J Interdiscip Dentistry [serial online] 2021 [cited 2021 Jul 25];11:11-6. Available from: https://www.jidonline.com/text.asp?2021/11/1/11/314180




   Clinical Relevance to Interdisciplinary Dentistry Top


Digital models are used in all divisions of dentistry especially in prosthodontics and orthodontics in treatment planing and prosthesis fabrication.


   Introduction Top


The plaster models have been an essential part of patient records for various dental treatments. They are a valuable tool for diagnosis and treatments, and it is widely used but often associated with some problems such as storage, breakage, and loss.

The manufacturing of dental models to be used for CAD/CAM systems in prosthetic dentistry has been used for some decades. Digital dental casts can be virtually analyzed with the advantage of clear landmarks at different magnifications and accurate cross-sectional images.

Clinicians seeking to overcome the shortcomings of conventional elastomeric impressions have implemented digital impressions as an adjunct or replacement for elastomeric impression materials. One advantage gained from digital impression technology is the ability to use digital magnification and quality control tools to highlight defective areas and provide guidance on how to capture missing areas of the digital impression.[1]

In 1999, Align Technology introduced OrthoCad, which is a digital model service, based on a proprietary scanning process of plaster models. Three years later, GeoDigm introduced “e-models,” a digitalization service for plaster models using nondestructive laser scanning. Several studies have been performed to compare digital model analyses with the so-called “gold standard,” which means the manual measurement of plaster models with a caliper. Measurements with OrthoCad models or e-models seem to be generally as precise and reliable as measurements made with plaster models.[1]

In 2011, Fleming et al. performed a systematic review of the literature focused on the comparisons between measurements on digital models and measurements with digital calipers on plaster models.[2] The authors stated that “digital models offer a high degree of validity when compared to direct measurement on plaster models.”

The general advantages of virtual models, e.g., less storage space, lower costs, instant accessibility, and transfer anywhere in the world for instant referral or consultation.

Due to the advantages and the development of fast and accurate intraoral scanners, it is foreseeable that virtual models will replace plaster models in the medium term.[2] Accordingly, the software for virtual model analysis will become more important and should deliver results that are at least as reliable and valid as those from plaster model analysis.

However, digital impressions also have disadvantages, and when compared with elastomeric impressions, the potential exists for greater distortion of the digital impression, possibly due to poor technique or the limitations of the specific scanning technology.

Trueness describes how far the measurement deviates from the actual dimensions of the measured object. Therefore, a scanner with high trueness indicates that the scanner delivers a result that is close or equal to the actual dimensions of the object being scanned.

Ender et al. found that for complete arch treatments, conventional impressions were significantly more accurate than digital impressions. Furthermore, Flugge et al. found the precision of intraoral scanners decreased with an increasing distance between the scan bodies.[3]

However, intraoral scanners and extraoral scanners require large infrastructure and investment and it is beyond the reach of a general dentist for the next decade in a developing country like India. Hence, a cost-effective scanner with an open-ended file output like STL would be the ideal way to move forward.

Photogrammetry is the art and science of extracting three-dimensional (3D) information from photographs. The process involves taking overlapping photographs of an object, structure, or space and converting them into 2D or 3D digital models.[4] Photogrammetry is often used by surveyors, architects, engineers, and contractors to create topographic maps, meshes, point clouds, or drawings based on the real world.

Photogrammetry is divided into two types. Aerial photogrammetry is the process of utilizing aircraft to produce aerial photography that can be turned into a 3D model or mapped digitally. Close-range photogrammetry is when images are captured using a handheld camera or with a camera mounted to a tripod. The output of this method is not to create topographic maps but rather to make 3D models of a smaller object.

SCANN3D is an app used to create 3D models available for android-based smartphones. This app takes multiple photos a minimum of 20 images of any object to create a 3D model.

Hence, the study aimed to compare traditional manual model analysis with a digital caliper with the virtual model analysis of digitalized plaster models. The virtual model was made with SCANN3D photogrammetry software and pictures were taken by a smartphone and the 3D model was also created in the smartphone.


   Materials and Methods Top


Sample size calculation

Using G-Power (G-Power 3.1.9.2, Franz Faul, University of Kiel, Kiel, Germany), power and sample sizes were calculated. Power calculation for the digital and manual value groups of linear measurements revealed that a sample size of 7 would have a power of 95% to detect a difference in means of 2 mm.

Inclusion and exclusion criteria

The criteria for inclusion were a fully erupted permanent dentition, with a similar shape of the models, with a base parallel to the occlusal plane, and full integrity of the model: cracked or damaged models were not used. Models with bonded retainers, appliances, attachments, or prostheses were excluded.

This study compares traditional manual model analysis with the virtual model analysis of digitalized plaster models. The virtual model was made with photogrammetry software and pictures were taken by a smartphone and the 3D model was also created in the smartphone. Randomly ten plaster models of Prosthodontics patients in permanent dentition were selected based on the inclusion and exclusion criteria mentioned below and they were analyzed. Manual analyses were performed with a diagnostic digital caliper and smartphone-assisted analysis after digitization of the plaster models using Scann3D. SCANN3D app takes multiple photos minimum of 20 images of any object to create a 3D model [Figure 1]. The distance between the phone and cast was standardized using a tripod stand and cast kept at a distance of 30 mm as the average focal length for most smartphone ranges from 28 to 34 mm.[1] Once the 3D model is created by the software, the model can be exported as STL format. This 3D model is analyzed for arch width in premolar and molar areas for comparison with manual model analysis using MeshLab software. The reliability and efficiency of digital models are to be analyzed by comparing measurements made on plaster and digital cast.[5] Each model set was anonymized with a number and then digitalized using a Scann3D software (SmartMobileVision, Nádorliget u. 7/c, Budapest, 1117, HU) [Figure 2] and [Figure 3]. The maxillary and the mandibular casts were assigned the following titles and anonymized (U1– U5), (L1-L5).
Figure 1: Photos used for creating three.dimensional models

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Figure 2: Lower cast three.dimensional model

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Figure 3: Upper cast three.dimensional model

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Arch width analysis

Inter first premolar and second premolar widths of maxillary and mandibular arches

Distance is attained from buccal cusp tip to the buccal cusp tip of the contralateral side [Figure 4] and [Figure 5].
Figure 4: Measurement in three-dimensional model using MeshLab

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Figure 5: Measurement in three-dimensional model in MeshLab

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Inter molar widths of maxillary and mandibular arches

Distance is attained from the mesiobuccal cusp tip of the right side to the left side [Figure 4] and [Figure 5].

Manual measurements on plaster casts were done for the following parameters: upper jaw transversal width between buccal cusps of first molars (maximum IMW, i.e., intermolar width), inter premolar width, and of canines (maximum ICW, i.e., intercanine width).

The smartphone used for 3D model creation was Samsung galaxy S9+, it has an 18 MP camera with optical stabilization that has 6 gb ram, and a snapdragon 845 processor. Scann3D software was downloaded and installed on the phone for the analysis. According to the software requirements, at least 20 images which are overlapping are required for the 3D model creation.

The distance between the phone and cast was standardized using a tripod stand and cast kept at a distance of 30 mm as the average focal length for most smartphone ranges from 28 to 34 mm. Once the 3D model is created by the software, the model can be exported.

MeshLab software, an open-source software, free to download was used for 3D model analysis. Before linear measurement analysis, the software has to be calibrated for the particular camera.

All the three measurements are analyzed for 10 casts and tabulated for statistical analysis. Documented data were captured in a Microsoft Excel file and processed for descriptive statistics [Table 1].
Table 1: Statistical data

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The null hypothesis was defined as no difference between the manual and smartphone-based digital methods. The standard deviation, mean, was calculated for each method.

P values were calculated for each measured parameter. P < 0.05 was taken as statistically significant, corresponding to the rejection of the null hypothesis.


   Results Top


By comparing the linear transverse measurements, the data reveal that

  1. The mean values of the tooth width from the manual method were larger than the values from the digital method
  2. The standard deviation was significantly high in the first premolar region, in manual method and high in the second premolar region in digital measurements
  3. With the digital method, the examiner found low values with the digital method
  4. The largest deviation was noted in the first premolar region due to a deviation of more than 2.5 mm in UPPER2 and LOWER4, although the reason for this large deviation is not clear.


Time needed for model analysis

  1. The time needed for manual model analysis was 2–3 min
  2. The time needed for digital measurement was <2 min, but the creation of 3D models from photogrammetry software will take from 10 to 15 min.



   Discussion Top


The introduction of digital models in dentistry has various advantages, such as less chair time, digital documentation, and greater accuracy of the prosthesis. Most digital model creation softwares and hardwares are too costly due to which mass adaptation of this technology is not possible in the current scenario.

Several studies have compared digital and manual model analysis. In these studies, it was found that when the scanner and software were from the same company, the workflow was much simpler and easy to master. There are software programs that can work with compatible scanners, but calibrating the software for different scanner has been difficult to master and workflow becomes complex.[1],[2],[3],[6]

Photogrammetry-based softwares are present in the market for many years although not used in dentistry because of its complex process of creating 3D models and they are technique sensitive and difficult to master. A smartphone-based photogrammetry software that processes the image was taken by the smartphone by itself and converting it into 3D model was recently launched called the SCANN 3D.

Software programs such as 3DF ZEPHYR and TRNIO which are photogrammetry-based softwares are available for the past 3 years in multiple platforms. 3DF ZEPHYR uses the smartphone to take photos and the photos are transferred to the computer-based software for conversion of images to 3D model. TRNIO on the other hand uses smartphone-based photo collection but a cloud-based image processing system for 3D model creation. Hence, SCANN3D is the first photogrammetry-based software to capture and process in the smartphone itself.

In the present study, 3D models of plaster cast created by SCANN3D software were compared with manual analysis with a digital caliper.

To obtain data for a full dental arch, both intraoral and extraoral scanning methods can be used. The direct intraoral scanning technique has been used and researched extensively for both diagnostic and treatment procedures.[7] The intraoral scanner-based systems have been shown to have sufficient reliability in prosthodontics but are still not used in daily practice due to the high cost of purchasing the scanner and software and support systems required for the software.

The extraoral or laboratory scanners are used more in dental laboratories than in a clinical environment. These scanners are versatile and have higher accuracy than intraoral scanners.[4] Extraoral scanners utilize various techniques such as laser scanning, structured light scanning and active wavefront sampling. However, no photogrammetry-based systems are currently available for dental purpose.[8]

In this study both for the first time, a completely smartphone-based photogrammetry software was used for creating a 3D model of a patient's diagnostic cast. The trueness of the 3D model created was assessed using MeshLab software. Interpremolar and intermolar width was measured by both digital and manual methods using a digital caliper.

During the digital analysis of the cast, identifying the correct landmark in the cast was a difficulty in this study, which has also been reported in other studies.[5],[3],[1],[4] In the statistical analysis, it was seen that the standard deviation was larger in the premolar region in one of the samples can be attributed to this reason. Other authors who have encountered these variations in the model have been attributed the cause to the learning curve, especially in digital measurements. One other reason can be the process of 3D model creation itself any defect in the photograph such as shadows and low light can create inaccuracies in the models created, which is an inherent deficiency of the photogrammetry technique.

According to statistical analysis, measurements made with digital technique on 3D models have more deviation in the first premolar region. In other studies, the deviation was noted more in posterior areas, especially in the molar region which they attribute to the software which is inbuilt by the manufacturer or some error in calibration of software by the manufacturer.

Time taken to measure digital models was significantly lower when compared to manual methods. However, the time taken for creating a 3D model is significantly high due to the complex photogrammetry process.[9]

This study only compares a single photogrammetry software that can create 3D models with manual model analysis. Variables such as the efficiency of different software and different smartphones which have different image acquisition capabilities were not analyzed. For better inference of smartphone-based 3D model creation and its efficiency, these data should also be compared with digital models created by laboratory or intraoral scanners for future studies.


   Conclusion Top


Three-dimensional models created by Scann 3D software with the help of a smartphone appear to be an adequate and reliable alternative to the conventional method of model analysis. In spite of hardware and software limitations present due to the software being used in smartphone and software still has some bugs, this software system based on a smartphone can be a viable alternative to a costly intraoral and intraoral scanner. Further development of this technique for various dental applications should be done to improve efficiency.

Financial support and sponsorship

This study was financially supported by Adhiparasakthi Charitable Medical and Educational Trust.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Reuschl RP, Heuer W, Stiesch M. Reliability and validity of measurements on digital study models and plaster models. Eur J Orthod 2016;38:22-6.  Back to cited text no. 1
    
2.
Fleming PS, Marinho V, Johal A. Orthodontic measurements on digital study models compared with plaster models: A systematic review. Orthod Craniofac Res 2011;14:1-16.  Back to cited text no. 2
    
3.
Flugge TV, Schlager S, Nelson K, Nahles S, Metzger MC. Precision of intraoral digital dental impressions with iTero and extraoral digitization with the iTero and a model scanner. Am J Orthod Dentofac Orthop 2013;144:471-8.  Back to cited text no. 3
    
4.
Renne W, Ludlow M, Fryml J, Schurch Z, Mennito A, Kessler R, et al. Evaluation of the accuracy of 7 digital scanners: An in vitro analysis based on 3-dimensional comparisons. J Prosthet Dent 2017;9:24-30.  Back to cited text no. 4
    
5.
Dalstra M, Melsen B. From alginate impressions to digital virtual models: Accuracy and reproducibility. J Orthod 2009;36:36-41.  Back to cited text no. 5
    
6.
Gracco A, Buranello M, Cozzani M, Siciliani G. Digital and plaster models: A comparison of measurements and times. Prog Orthod 2007;8:252-9.  Back to cited text no. 6
    
7.
Okunami TR, Kusnoto B, BeGole E, Evans CA, Sadowsky C, Fadavi S. Assessing the American board of orthodontics objective grading system: Digital vs. plaster dental casts. Am J Orthod Dentofac Orthop 2007;131:51-6.  Back to cited text no. 7
    
8.
Hunter WS, Priest WR. Errors and discrepancies in measurement of tooth size. J Dent Res 1960;39:405-14.  Back to cited text no. 8
    
9.
Watanabe-Kanno GA, Abrão J, Miasiro H Jr., Sánchez-Ayala A, Lagravère MO. Reproducibility, reliability and validity of measurements obtained from Cecile3 digital models. Braz Oral Res 2009;23:288-95.  Back to cited text no. 9
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1]



 

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