|DENTAL SCIENCE - ORIGINAL ARTICLE
|Year : 2015 | Volume
| Issue : 6 | Page : 465-469
Digital model as an alternative to plaster model in assessment of space analysis
A Anand Kumar, Abraham Phillip, Sathesh Kumar, Anuradha Rawat, Sakthi Priya, V Kumaran
Department of Orthodontics, JKK Nattraja Dental College, Komarapalayam, Namakkal, Tamil Nadu, India
|Date of Submission||28-Apr-2015|
|Date of Decision||28-Apr-2015|
|Date of Acceptance||22-May-2015|
|Date of Web Publication||1-Sep-2015|
Dr. A Anand Kumar
Department of Orthodontics, JKK Nattraja Dental College, Komarapalayam, Namakkal, Tamil Nadu
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Introduction: Digital three-dimensional models are widely used for orthodontic diagnosis. The purpose of this study was to appraise the accuracy of digital models obtained from computer-aided design/computer-aided manufacturing (CAD/CAM) and cone-beam computed tomography (CBCT) for tooth-width measurements and the Bolton analysis. Materials and Methods: Digital models (CAD/CAM, CBCT) and plaster model were made for each of 50 subjects. Tooth-width measurements on the digital models (CAD/CAM, CBCT) were compared with those on the corresponding plaster models. The anterior and overall Bolton ratios were calculated for each participant and for each method. The paired t-test was applied to determine the validity. Results: Tooth-width measurements, anterior, and overall Bolton ratio of digital models of CAD/CAM and CBCT did not differ significantly from those on the plaster models. Conclusion: Hence, both CBCT and CAD/CAM are trustable and promising technique that can replace plaster models due to its overwhelming advantages.
Keywords: Computer-aided design/computer-aided manufacturing, cone-beam computed tomography, Bolton′s ratio, digital models
|How to cite this article:|
Kumar A A, Phillip A, Kumar S, Rawat A, Priya S, Kumaran V. Digital model as an alternative to plaster model in assessment of space analysis. J Pharm Bioall Sci 2015;7, Suppl S2:465-9
|How to cite this URL:|
Kumar A A, Phillip A, Kumar S, Rawat A, Priya S, Kumaran V. Digital model as an alternative to plaster model in assessment of space analysis. J Pharm Bioall Sci [serial online] 2015 [cited 2020 Jan 17];7, Suppl S2:465-9. Available from: http://www.jpbsonline.org/text.asp?2015/7/6/465/163506
The classical orthodontic patient documentation is composed of a lateral head film, orthopantomogram, facial and dental photography, and plaster cast. Orthodontic models document the initial conditions, treatment progress, and the final treatment result, and also use these models to present their treatment results to fellow workers and patients for the purposes of education, evaluation, and systematic investigation.
Study models are a reliable and popular form of diagnostic record. Since they are a dimensionally accurate representation of the dentition, a number of measurements and analysis such as tooth size-arch length discrepancy and prediction of permanent tooth size can be obtained from plaster study models.
Digital models, on the other hand, alleviate many of the obstacles encountered with plaster models. They are not subjected to physical impairment and do not produce any dust. They also require comparatively negligible storage space. Retrieval was quick and efficient, it also an excellent tool for patient education.
Digital models can be created by two methods, direct and indirect methods.  The direct method for the creation of virtual models are either the direct scan of the dentition with an intraoral scanner using structured light or radiographic data such as cone-beam computed tomography (CBCT), magnetic resonance for imaging, computed tomography. The virtual dental models derived from CBCT have radiographic data. An indirect method as the name implies, requires additional steps, such as impression and pouring of the models in plaster, before it is captured into a digital format. The scanning of an impression or plaster cast can be done by a laser, structured light or even radiographic methods such as OrthoCAD, computer-aided design/computer-aided manufacturing (CAD/CAM).
The Cone-Beam Computed Tomography (CBCT) scanners were introduced in the late 1990s.  Since then, there has been an enormous interest in this new imaging acquisition technique that utilizes a volumetric scanning machine. This technology was based on a cone-shaped X-ray beam directed at a flat two-dimensional (2D) detector. As both rotate around the patient's head, a series of 2D images were generated. The software then reconstructs the images into Three-dimensional (3D) data set using a specialized algorithm.  As the digital models are becoming common, research needs to be done to evaluate its accuracy in measuring the tooth size analysis. , The purpose of this study was to compare the linear measurements of the digital model obtained from cone beam computerized images and CAD/CAM with plaster models measurements.
| Materials and Methods|| |
The present study comprised of a sample of 50 adults all aged above 18 years. This study was performed after ethical committee clearance.
Criteria for selection of patients:
- Complete permanent dentition from first molar to first molar in both upper and lower arches
- Participant should not be under orthodontic treatment
- No severe crowding in the dentition.
Source of data
The study was performed on the basis of the patients study models and digital models using CAD/CAM and CBCT. The digital and manual measurements were made using Bolton's analysis. 
Materials used for plaster models and digital models.
- For plaster models:
- Impression of upper and lower arch made with alginate (topic alginate)
- The models were made using orthodontic stone class III (orthokal)
- For digital models:
- 3 Shape scanner D 800 and 3 Shape software (CAD/CAM)
- Sirona Orthophos XG machine and Galileo's viewer software (CBCT).
One set of alginate impressions of each participant were taken, and the impression were poured immediately to obtain the conventional plaster models. The alginate used for the plaster models was tropicalgin. The plaster material used was orthokal.
Digital models were obtained by CBCT (direct scanning) and CAD/CAM (indirect scanning).
Cone-beam computed tomographic technique
The Sirona Galileos Orthophos XG was the CBCT device used with voxel size between 0.15 mm and 0.30 mm. The image reconstruction time was approximately 4.5 min. Galileos viewer software was used to analyze 50 CBCT scans taken by a Galileo's cone beam scanner (Sirona, Charlotte, NC, USA) with a field of view of 15 cm 3 × 15 cm 3 × 15 cm 3 and a voxel resolving power of 0.125 mm.
Computer-aided design/computer-aided manufacturing technique
The cast was digitalized by scanning the cast in 3 Shape scanner D800, with image reconstruction time of approximately 3 min and digital models obtained were measured with 3 Shape software.
As the accuracy and consistency were essential for measuring, it was invariably carried away by the same operator. Tooth widths on the plaster models were measured with a digital calliper (aerospace). As described by Hunter and Priest in 1960, the greatest mesiodistal diameter was taken from the anatomic mesial contact point to the anatomical distal contact point of each tooth measured parallel to the occlusal plane. Measurements were recorded to nearest 0.01mm. Tooth width was measured in CBCT by Sirona Galileos software (Sirona The Dental Company, U.S.A) and in CAD/CAM by 3 Shape software.
The linear measurements (mesiodistal width), anterior Bolton and overall Bolton ratios were calculated for each set of models. Measurements made on the plaster models were considered the gold standard. The differences in tooth-width measurements, anterior Bolton ratio, and overall Bolton ratio between the digital models (CAD/CAM and CBCT) and the corresponding plaster models were calculated to assess the error of the method and to evaluate the validity. 
| Results|| |
P value was found using one-way ANOVA between CBCT and plaster model and between CAD/CAM and plaster models. The level of significance was P < 0.05. There was no statistically significant difference between CBCT and plaster model and also between CAD/CAM and plaster model [Table 1] and [Table 2], [Graphs 1 and 2].
|Table 1: The mean of the anterior Bolton ratio calculated from the measurements obtained from CBCT, CAD/CAM, and plaster models|
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|Table 2: The mean of overall Bolton ratio calculated from measurements obtained from CBCT, CAD/CAM, and plaster models|
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Values of CAD/CAM, CBCT are similar to the control group (plaster models).
| Discussion|| |
Diagnosis and treatment planning is the key to orthodontics. It is a progressive field that has embraced new technologies. Orthodontic study models are the corner stone of diagnosis and treatment planning. The need to retain dental casts for future reference has created storage problem for orthodontist. However digital models are gaining popularity due to their advantage over plaster models in storage, retrieving and sharing of information. 
Digital imaging technology in the dental field has emerged as one of the most important aspects of diagnosing and treating oral diseases, especially since the advent of three-dimensional techniques. In recent years, the use of CAD/CAM systems has become popular in dentistry. CAD/CAM is the process by which a model is scanned, and the data is then used to generate the coping pattern, which in turn is used for manufacturing digital models.  The CAD/CAM systems that are used in dental applications generally consist of two modules: (1) A scanner, which scans a solid model and converts the model into digital information, (2) a design software package which is utilized to design and modify the digital models. This study was done to find the accuracy of measurements made on digital models using CBCT and CAD/CAM and compared it with plaster model measurements made manually.
According to surveys done by Tarazona et al.  the analysis of Bolton index continues to be the most commonly used arch width index in orthodontic diagnosis. Hence, Bolton's index was used in this study to evaluate digital measurements taken from CBCT and CAD/CAM. These digital measurements were compared with the measurements taken from golden standard plaster models using a digital calliper. According to Jennifer Asquith et al. caliper measurements were regarded as the golden standard against which other measurement techniques were compared.Shellhart et alcalculated the Bolton's analysis values using vernier calipers and needlepoint divider. They found that vernier caliper was slightly more reliable than needle point dividers. In this study instead of vernier caliper, digital vernier caliper was used to eliminate the possibility of parallelex error. 
In the present study, 50 patients were selected all aged above 18 years. One set of alginate impressions was made for each patient, and the plaster models were poured immediately.  Digital models were obtained by both direct scanning of patients using CBCT and indirect scanning of plaster models using CAD/CAM. This study was done since no other previous literature compared CAD/CAM and CBCT with plaster models.
Linear measurements of each tooth (mesiodistal width) were calculated using CBCT, CAD/CAM, and digital caliper. As described by Hunter and Priest in 1960, the greatest mesiodistal diameter was taken from the anatomical mesial contact point to the distal contact point of each tooth measured parallel to the occlusal plane.  In plaster model digital calliper (aerospace) was applied to measure the mesiodistal width of the tooth. Aerospace digital calliper has two needle pointers which when placed at mesial, and distal contact point automatically showed the width digitally. In CBCT images, Galileo's viewer software is used to measure the mesiodistal width in which cursor is used to mark the mesial and distal contact point after which the width will be displayed automatically. CAD/CAM 3 Shape D800 scanner was used to scan the plaster model, and digitalization is done with S-Shape software. Cursor was used to mark the mesial and distal contact points after which width will be displayed automatically.
Mesiodistal width, overall and anterior ratio Bolton's analysis of all teeth from first molar to first molar in both arches were calculated for all 50 patients by all three methods CBCT, CAD/CAM, and digital caliper. Mean value and standard deviation of mesiodistal width, overall and anterior Bolton's ratio of all 50 patients were separately measured for CBCT, CAD/CAM and plaster models. The mean obtained by CBCT, was compared with the mean value of the digital calliper measurement. In the same way, mean obtained by CAD/CAM was compared with the mean value of the digital calliper measurement. It was found that there was no significant difference between CBCT and CAD/CAM values when compared with plaster model values. Aaron j white et al.  analysed intra-arch and inter-arch measurements obtained from the digital models by scanning two impression materials using Cone Beam Computerised tomography. The study concluded that orthodontic models from CBCT scan of two impression materials were accurate representation of intra-arch relationship. But inter arch relationship was not accurate. So in this study the digital model was obtained either directly from the mouth or by scanning models. 
Study done by Stevens et al.  found that there was no significant difference when comparing the reliability tooth size measurements obtained from plaster and digital model. In another survey done by Michael's F. Leifert et al.,  space analysis measurements taken were compared between plaster and digital models. The study found that there was no significant difference in measuring space analysis in digital models (OrthoCAD) and plaster models.
In the present study, the linear measurements and Bolton's analysis of CBCT digital models were similar with that of plaster model measurements. This is in agreement with the study done by Matthew G. Wiranto et al.  who reported that the tooth measurement of each tooth done on digital models (CBCT) did not differ significantly from those on the plaster models. The overall and anterior Bolton ratio from CBCT digital models differ significantly from the plaster model by P < 0.05. However, this difference never exceeded 1.5 mm, so it was viewed as clinically insignificant. There are no previous literatures to compare the linear measurements and Bolton's analysis of CAD/CAM digital models with that of plaster model measurements.  In the present study, when plaster models were compared with digital models (CAD/CAM), no significant difference were found for the linear measurements, as well as for the overall, and anterior Bolton's ratio.
Hence, both CBCT and CAD/CAM can be a viable replacement to plaster models in the upcoming years helping in easy storage, retrieval, and manipulation of models.
| Summary and Conclusion|| |
- There is no significant deviation was found in mean values of mesiodistal width of teeth measured by all these methods CAD/CAM, CBCT, and digital calliper
- No significant deviation was found in anterior Bolton's ratio calculated by all these methods CAD/CAM, CBCT, and digital models
- No significant deviation was found in overall Bolton's ratio calculated by all these methods CAD/CAM, CBCT, and digital models
- Hence, both CBCT and CAD/CAM are a reliable and promising technique that can replace plaster models due to its overwhelming advantages.
Financial support and sponsorship
Conflict of interest
There are no conflict of interest.
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[Table 1], [Table 2]