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Original Articlehttp://mjiri.iums.ac.ir Medical Journal of the Islamic Republic of Iran (MJIRI)
Iran University of Medical Sciences
____________________________________________________________________________________________________________________1. (Corresponding author) Assistant Professor, Department of Oral and Maxillofacial Medicine, School of Dentistry, Tehran University ofMedical Sciences, Tehran, Iran. [email protected] & maria_koopaie @yahoo.com2. Master of Science in Mechanical Engineering, Department of Mechanical Engineering, Amirkabir University of Technology, Tehran, [email protected]
Three-dimensional simulation of human teeth and its applicationin dental education and research
Maryam Koopaie*1, Sajad Kolahdouz2
Received: 2 April 2016 Accepted: 12 November 2016 Published: 24 December 2016
AbstractBackground: A comprehensive database, comprising geometry and properties of human teeth, is needed for
dentistry education and dental research. The aim of this study was to create a three-dimensional model of humanteeth to improve the dental E-learning and dental research.
Methods: In this study, a cross-section picture of the three-dimensional model of the teeth was used. CT-Scanimages were used in the first method. The space between the cross- sectional images was about 200 to 500 mi-crometers. Hard tissue margin was detected in each image by Matlab (R2009b), as image processing software.The images were transferred to Solidworks 2015 software. Tooth border curve was fitted on B-spline curves,using the least square-curve fitting algorithm. After transferring all curves for each tooth to Solidworks, the sur-face was created based on the surface fitting technique. This surface was meshed in Meshlab-v132 software, andthe optimization of the surface was done based on the remeshing technique. The mechanical properties of theteeth were applied to the dental model.
Results: This study presented a methodology for communication between CT-Scan images and the finite ele-ment and training software through which modeling and simulation of the teeth were performed. In this study,cross-sectional images were used for modeling. According to the findings, the cost and time were reduced com-pared to other studies.
Conclusion: The three-dimensional model method presented in this study facilitated the learning of the dentalstudents and dentists. Based on the three-dimensional model proposed in this study, designing and manufactur-ing the implants and dental prosthesis are possible.
Keywords: Three-Dimensional Modeling, Dental Education, Finite Element Analysis.
Cite this article as: Koopaie M, Kolahdouz S. Three-dimensional simulation of human teeth and its application in dental education andresearch. Med J Islam Repub Iran 2016 (24 December). Vol. 30:461.
IntroductionNowadays, the status of the oral health is
one of the great challenges in the field ofhealth, treatment and medical education. Inthis context, specialized training of the staffand students is of prime importance. One ofthe most important educational needs of thedental students is evaluation of patients'teeth and oral cavity. In this study, theteaching principles of prevention, diagnosisand treatment of the oral cavity disorderswere the learning priorities. During dentis-try education, students practice many dentalprocedures. The traditional approach indentistry education is based on the treat-
ment of those patients who are referred todental schools or based on practicing on thestandard plastic teeth. Difficulty of regularaccess to human samples and deficiency ofexpert observers are the limitations of tradi-tional methods. This study found that usingthe virtual three-dimensional tooth modelappeared to be more efficient than plasticmodels (1).
Using the virtual three-dimensional mod-el of the teeth and gums, as well as enhanc-ing the quality of dental education will re-duce learning time. Dentists need modelsfor frequent modifications to reach the bestprosthesis and to have a more accurate ex-
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amination, and appropriate design. Dentalmodeling and simulation to verify the accu-racy of the prostheses and to meet dentalstudents’ training needs seems irrefutable(2,3). Three-dimensional models in variousaspects of dental treatment, including oralsurgery, implants and orthodontics can bevery useful (4). Most common problems inthe field of dentistry are dental decays andperiodontal diseases (5).Providing a high-resolution three-dimensional model thatconsists of all the aspect of oral cavitycould be very effective (6).
Using a three-dimensional model can bean alternative method for the conventionalnon-imaging method, which reduces costs,time and increases the compliance of a finalprosthesis. The purpose of this study was topresent a three-dimensional model of theteeth to be used in the field of education,research and treatment. Furthermore, thismethod could be effective in reducing theeducational cost and time, and decreasingthe experimental test for the researchers(3). Reverse engineering is an importanttechnique to manufacture the industrialproducts, and may be used in dental model-ing (7-11). Accuracy and precision are thechallenges of reverse engineering of dentalmodeling. One of the applications of mod-eling is using the model in the finite ele-ment analysis (2,7-10). A more precise-model will be more applicable in the finiteelement analysis.
The sectioning images are used for re-verse engineering, but this method is ex-pensive, and time consuming (12,13). Re-cently, the use of Cone Beam ComputedTomography (CBCT) and Multi-Slice CT(MSCT) has reduced problems related toteeth modeling (14). One of the most im-portant challenges in three-dimensionalmodelingis the relationship between CT-Scan images and the modeling software(6,15). Because of the complex features ofthe tooth structure, different methods havebeen used for dental modeling (16). One ofthese methods is based on the mesh genera-tion algorithm, the graphic effects of whichwould be relatively acceptable. Although
this method is cost-effective, it appears tohave major weaknesses when it comes todifferent structures of the teeth (enamel anddentine), and material properties definition(2).
Another approach is based on the Voxelmethod in which material properties anddifferent teeth structures are defined. Alt-hough the apparent looks of the mesh mod-el are better, the Voxel model is more suit-able for the dental finite element analysisdue to the definition of the properties of theteeth (17). Wang et al. found a methodbased on the triangular mesh for the dentalmodeling and simulation. They used laserscanner to measure the teeth and the dia-metric shortest distance for triangular meshgeneration (1). In this study, a new methodwas used based on measuring the teethcurves by image processing. This method isbased on the surface automatic mesh gener-ation, and is a combination of the twomethods of Voxel and mesh generation.
A comprehensive knowledge of the teethleads to the more accurate virtual three-dimensional modeling. A database that con-tains geometry and properties of humanteeth are needed for dentistry education anddental researchers. A three-dimensionalmodel of dental teeth can improve dentalresearch and specialized training (18,19) aswell as develop simulation software of oralsurgery, orthodontics, and endodontic im-plants (20,21). The aim of this study was tocreate a three-dimensional model of the vir-tual teeth, used in dental education and thefinite element analysis for dental research.
MethodsIn this study, a cross-sectional picture of a
tooth for three-dimensional modeling wasused. In CT-scanning (the first method),whenever the space between the cuts isless, the resulting model would be moreaccurate. To create a three- dimensionalmodel of a tooth, another method, otherthan CT-scanning, was used. Using thismethod would help compare the accuracyof the two methods. In the second method,we cut the tooth from the top of the crown
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to the root, with a space of 0.5 millimetersbetween the cuts. Then the cross-sectional
images of the tooth preparation were taken.The teeth were mounted to examine thecross-section of the tooth images as shownin Figure1.
An example of the cutting lines on thecrown of the maxillary third molar isshown in Figure 2. Pictures, taken in eachlevel, were used in the teeth simulation.
In the first step, CT-Scan images wereused, with a CT-Scan device (GEHiSPEED NX / I Pro CT) of the space of50 microns between the sections. Timemeasured for each frame was about 20 sec-onds. For a tooth measurement, an averagetime of an hour was spent. On average, 80images of each tooth were prepared. Thespace between the cross- sectional imageswas about 200 to 500 micrometers. In thenext step, the hard tissue margin was de-tected in each image. Matlab (R2009b) wasused as an image processing software.
The detection algorithm was based on thedifference of color in the images, and ulti-mately this software defined the boundariesof the hard tissue. The boundaries werespecified in the Matlab (R2009b) for eachimage. An example of image processing forthe second premolar is shown in Figure 3.
The images were transferred to Solid-works 2015 software. Tooth border curvewas fitted on B-spline curves, using leastsquare-curve fitting algorithm with lessthan 5%error. An example of the fitted
Fig. 1. The Teeth Were Mounted to Examine theCross-section of the Tooth Images
Fig. 2. Cutting Lines for Tooth Slices
Fig. 3. An Example of the Detection of the Tooth Margin in Matlab
Fig. 4. An Example of Marginal Detection in Matlab and Its Adaptation on B-Spline Curve in Solidworks
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boundary lines is shown in Figure 4 (thered line is the example of curve fitting onthe tooth border in Solidworks 2015 soft-ware).
To create boundary curves tooth, a cross-sectional image of each tooth was preparedwith the space of 0.2mm from each other.The curves were transferred to Solidworks2015 in compliance with the order. A seriesof images produced by this method areshown in Figure 5 (mandibular molars).
After transferring all curves to Solid-works for each tooth, the surface was creat-ed based on the surface fitting technique.This surface was meshed in Meshlab-v132software, and the optimization of the sur-face was done based on the remeshingtechnique. Remeshing technique was basedon the downsizing of the model meshes,and the pyramid tetrahedral mesh was used.An example of this method and creation ofthe model is shown in Figure 6. Initialmodel is shown in part A. Part D in Figure6 displays the model after the remeshingtechnique. All apparent faults in this modelhave been corrected.
To assign the mechanical properties, wehad to create an intrinsic structure of thetooth other than its surface. Cutting the sec-tion of intrinsic structure of the tooth isshown in Figure 7. Finally, the modelswere created with the format of "STEP".
To perform the finite element analysis onthe model, the mechanical properties of theteeth should be allocated. The Young'smodulus of tooth enamel (E=88GPa) was
attributed (22,23). The three-dimensionalmodeling algorithm used in the study isshown in Figure 8.
Rendering is the final step of the simula-tions that providesthe model with real ef-fects. The virtual three-dimensional model,which was created with real teeth, was usedfor comparison (Fig. 9).
Fig. 5. A Set of B-Spline Curves Used for Molar Teeth Modeling in Solidworks 2015
Fig. 6. Steps to Prepare and Improve the Quality ofthe Model Surface (A to D)
Fig. 7. Cutting the Section Images of the Tooth inDifferent Levels
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ResultsIn this study, the cross-sectional images
were used for modeling. In this model, the
cost and time were reduced compared toother studies. This modeling can be per-formed without destroying the structure ofreal teeth, and could be used in the finiteelement analysis for designing implants,dental prosthesis. To our knowledge, therewas no reported document on the educa-tional function of the finite element analy-sis in the literature. Without precise geo-metric dimensions of the teeth, the finiteelement analysis and E-learning will not beaccurate. This study presented a methodol-ogy for communication between CT-scanimages and the finite element and trainingsoftware through which modeling and sim-ulation teeth were performed.
Measuring the tooth dimensions demon-strate that the error was in the range of 5%.It is possible to obtain detailed models withhigh accuracy and less error, but this great-ly increases the time and cost of modeling.The method described in this study hassome advantages to the laser scanningmethod. One of the problems in laser scan-ning method is the lack of adequate accessand lack of sufficient precision in the mod-el.
DiscussionThe three-dimensional models of the hu-
man body anatomy could improve medicaleducation, describe a variety of diseases,and help determine the types of injury. Inthis study, by using images obtained fromCT-scanning and the cutting sections of theteeth, three-dimensional models of teethwere created, whereas in other studiescloud points were used to create the three-dimensional model of teeth (23,24). In thisstudy, the possibility of creating a virtualthree-dimensional model of hard tissue(teeth) was provided. This model increasesthe quality of specialized training in dentis-try and significantly improves the qualityand accuracy of dental procedures.
ConclusionThe method presented in this study has
the following basic characteristics:
Fig. 8. The Three-Dimensional AlgorithmModeling of Teeth Simulation
Fig. 9. Comparison of the Virtual Three-Dimensional Model of the Teeth with RealTeeth
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The three-dimensional model was moreuseful to the dental students and dentists. The method presented in this study, in
comparison with the other methods, is moreaccurate and less expensive, and the possi-bility of creating a three-dimensional modelof the tooth with respect to CT-Scan imag-es is higher. Based on the three-dimensional model
proposed, analysis of the design and manu-facturing of implants and dental prosthesisare possible. Itis possible to create a detailed model-
with maximum error of 50 micrometers bythis model.
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