2020, Number 3
Comparative study of natural teeth and 3D printed teeth using a cone-beam computed tomography
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Language: English/Spanish [Versión en español]
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Page: 190-197
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ABSTRACT
Aim: To determine the accuracy of measurements of both in vivo teeth and teeth printed with data obtained using a computed tomography (CBCT) cone-beam computed tomography (CBCT). Material and methods: For orthodontic purposes, linear measurements of 15 extracted teeth were made using a CBCT. The information obtained was recorded in the Invesalius 3 software for segmentation; then they were printed with an Envision Tech 3D printer with a polymer. All data were collected in SPSS version 22 software. To determine the statistical difference between variables, the Student t test was used. Results: median in vestibular-lingual in teeth in vivo was 8.07 mm and for 3D printed teeth was 7.90 mm. The mesio-distal median was 8.03 mm for teeth in vivo and for 3D printed teeth was 7.78 mm and for incisal-apical median was 18.95 mm to in vivo teeth and 18.47 mm to 3D printed teeth. Conclusions: there were no statistical differences between the measurements of the in vivo teeth and those of the 3D printed teeth, which could affect the treatment plans. However, these minor differences may have clinical implications.INTRODUCTION
The success of orthodontic treatments is based on both a detailed diagnosis and a detailed treatment plan. An essential factor in the orthodontic diagnosis and treatment plan is the ability to predict the real size of the teeth, which are sometimes found within the jaws due to natural or pathological situations. An accurate prediction of the dimensions of these teeth helps determine if there is enough room for their eruption or traction for proper alignment within their arches.
For many years, only two-dimensional radiographic (orthopantomography and periapical radiographic) were available to evaluate the size and shape of the dental organs, both those that had already erupted and those that were about to do so.
With the appearance of computerized axial tomography (CT) in the 1970s, the diagnosis and prediction of the size and shape of dental organs evolved and thus it was possible to obtain information more precise on their shape and location.
In the dental area, the use of CT was limited by its high cost. With the development of cone-beam computed tomography (CBCT), its cost decreased considerably, making it more accessible. A CBCT scan consists of several exportable DICOM files (digital imaging and communications in medicine) a term adopted in the early 1980s. From a CBCT it was possible to observe all the structures of the oral cavity in three dimensions; to isolate each of the desired elements, the image segmentation process was developed. This process generates multiple regions of a digitized image to simplify the image and turn it into an easy-to-analyze object of relevance.1,2
The segmentation of teeth from a CBCT allows virtual modeling of the entire dentition, showing the anatomy of the dental root and the supporting bone in a more complete model, compared to traditional plaster models. This makes it possible to observe all the anatomical structures that surround a dental organ in isolation or as a whole and in the matter of orthodontics to assess the anchorage of the teeth, according to the volume of the dental roots.3,4
An additive manufacturing process, known as 3D (third dimension) printing, must be done to convert a digital image into a physical model. Several 3D printing techniques have been described in the orthodontic literature.5,6
Some studies have shown that certain 3D printers may be accurate to reproduce models that can replace traditional dental models for diagnosis and treatment planning. This is because it will be possible to determine the shape, size, and exact location of each structure that makes up the oral cavity. It will also allow isolating and modeling each of these structures. This, in turn, gives rise to a wide range of treatments that range from predicting the size of teeth in mixed dentition, to get an exact replica of an organ to be implanted6-9 and even elaborating a setup to create custom parts10 so we can accurately determine the position of the dental roots.
Liu et al.11 used the water displacement system to measure the volumes obtained from natural teeth compared to those of teeth printed from a CBCT and concluded that the printed teeth showed small differences.
This paper aims to determine if the 3D printing files obtained from the segmentation of the dental organs in a CBCT are similar in shape and size to those of natural teeth, using linear measurements with a digital caliper.
MATERIAL AND METHODS
Fifteen unerupted dental organs, from any jaws, belonged to patients who attended the Graduate program of Orthodontics, Technologic University of México (Postgrado de Ortodoncia, Universidad Tecnológica de México), México.
Whose extraction was indicated in the treatment and that their extraction was diagnosed using a CBCT, were selected. Subsequently, the unerupted dental organs were surgically removed. In parallel, these teeth were segmented in the DICOM operating system and printed from the CBCT.
CONE BEAM COMPUTED TOMOGRAPHY
All patients underwent a CBCT using an I CAT scanner with a field of view of 25 cm. The scan was carried out according to the manufacturers' specifications; the voxel size was 0.292 mm (120 Kv, 10 A) and the data was exported using DICOM files that had the same cutting distance of the size of each voxel.
Afterward, the unerupted teeth were extracted and cleaned to remove the remains of soft tissue, bone, blood, and dental calculus.
SEGMENTATION AND PRINTING
Dental organs to be extracted were segmented using the DICOM files to print them and perform the comparative study.
Segmentation
Dental segmentation was performed in the open program designed for segmentation InVesalius 3; this program has several densities available, which means having more voxel possibilities with gray values to perform segmentation. Values can be defined to determine absolute or relative gray values. Segmentation is semi-automatic with manual adjustments to define sections (Figure 1).
After calculating the segmentation, the smoothing function was used, the density threshold to be worked on was selected, and both the version without smoothing (2A) and with smoothing were saved for comparison. To differentiate each of these versions, each tooth was stained to be able to identify them, and they were saved in STL format for printing (Figure 2).
3D printing
The files of the smoothed teeth were printed using the EnvisionTEC VIDA printer with a photopolymer OP 13, E-Model 3SP, same brand.
Linear measurements in the extracted teeth were made using a digital caliper of both mesiodistal and buccolingual diameters and total height. All measurements were performed and recorded by a single examiner. Likewise, the same measurements were made in the digitally printed dental organs, calculating the diameters and the total height, and were also recorded by a single examiner.
STATISTICAL ANALYSIS
All of the data were entered into a spreadsheet of the Excel 2003 program (Microsoft, Redmond, Wash). Statistical analysis was carried out using PSS (Version 12.0, SPSS, Chicago, Ill). The database was prepared in the SPSS version 22 program. Descriptive statistics were used. For the quantitative variables, measures of central tendency and dispersion were used. A homogeneity analysis of the variables was performed using the Levence statistic, so parametric statistics were used. The statistical analysis was carried out in the same program, applying the t Student test to determine if there were statistically significant differences between the variables studied.
RESULTS
The sample has a free distribution, probably due to the size of the sample, so it was decided to do the Mann-Whitney U analysis, which is based on the difference in rank and is a counterpart of the Student t test which is used in quantitative variables with a normal distribution (Table 1).
In this study, linear measurements were made using a digital vernier (Figures 3, 4 and 5).
When comparing all medians, it was found that the real teeth were always the largest. Although, from a statistical point of view this difference was not significant.
DISCUSSION
The development of technology has made orthodontists increasingly involved in the use of CBCT and its applications, such as digital printing.12-14 The segmentation process is not easy, and it depends on many factors, such as operator differences in location, correctly differentiating tissues, operator experience, ability to enlarge the image, manipulation of contrasts and colors, as well as the operator's criteria. All of this implies a significant learning curve.
In this study, CBCTs with a large field of view were used, which caused some problems with proper segmentation.3 A large field of view (such as that regularly used by orthodontists) is considered to have little contrast, creating difficulties in performing segmentation more accurately.
The results obtained in general in this study show that the segmented and smoothed teeth, and subsequently printed when measured linearly with a digital vernier, compared to the real teeth, the mesiodistal, vestibular-lingual, and apical-incisal measurements showed little significant difference, in statistical terms.
These results contrast with those of other studies that report that only smoothing the teeth and performing a volumetric measurement can produce differences of 4-7% when measuring smoothed and non-smoothed teeth.11 Likewise, Nylbankar15 points out that the program used for segmentation can lead to statistically significant differences in volumetric measurements.
Nowadays, new technologies have emerged that allow improving the images generated by CBCTs. They mainly consist of modifying the size and making the voxels more uniform16 which makes a more effective segmentation process that can generate a 3D model more like the size of the original model.
In this study, the linear measurements obtained from the printed teeth compared to the measurements from the real teeth were similar. However, it is necessary to perform volumetric measurements and improve the quality of the images obtained using the CBCT. The results would show its effectiveness in obtaining 3D models that could be used clinically with success. In this way, the CBCT could be more useful since it would not only be possible to use it to measure hard structures but also soft ones, such as the tongue.17
CONCLUSIONS
- 1. In the linear measurements performed there was no statistically significant difference between the real teeth and those printed from the data of a CBCT.
- 2. CBCT is a valuable tool not only for diagnosis but also for obtaining printed replicas that open the possibility of using it in other dental procedures, such as autotransplantation cases.
- 3. Volumetric measurements are suggested to verify the similarity between real teeth and 3D printed replicas.
REFERENCES
AFFILIATIONS
1 Departamento de Ortodoncia de la Universidad Tecnológica de México.
CORRESPONDENCE
Alberto Teramoto Ohara. E-mail: ateramot@gmail.comReceived: Noviembre 2019. Accepted: Febrero 2020.