Validation of Cone Beam CT Scan for Measurement of Palatal Depth in Study Casts Z. Radzi1, N.A. Yahya1, N.H. Abu Kasim1, N.A. Abu Osman2, Z.Y.M. Yusof1, F.N. Mohd.1, N.H.M. Noor1, M. Jamaludin1, S.A. Othman1, U.H. Obaidellah3, N.H. Mohamed1, R. Kadir1, P. Nambiar1 1
University of Malaya, Faculty of Dentistry, Kuala Lumpur, Malaysia. University of Malaya, Faculty of Engineering, Kuala Lumpur, Malaysia 3 University of Malaya, Faculty of Computer Science and Information Technology, Kuala Lumpur, Malaysia 2
Abstract — The purpose of this study was to validate the use of digital dental study casts obtained from Cone beam CT Scan (CBCT) against gold standard; that is traditional dental study cast measured with digital caliper. Thirty-four study casts of Malaysian Aborigines were selected from Centre of Malaysian Pribumi Studies Databank. Palatal depth of each study casts were measured using Mitutoyo digital caliper. Subsequently, all the study models were scanned using i-CAT CBCT and the palatal depth were measured using i-CAT software. Data were analysed using SPSS version 12.0 where Intraclass correlation and paired T-test were employed. There was no significant difference in palatal depth between CBCT and Mitutoyo digital caliper (p>0.05). Average measures for Intraclass Correlation is 0.753 indicate that it is consistently good. Within the limitation of this study palatal depth measurement produced by CBCT was as accurate as the digital caliper. However, more samples and parameters should be added to further substantiate the result of this study. Keywords — validation, dental study casts, palatal depth, CBCT & Digital Caliper.
I. INTRODUCTION One of the key successes in orthodontic treatment is the appropriate treatment plan that is based on complete dental records. In clinical orthodontics, the four main dental records are clinical case notes, radiographs, clinical photographs and dental casts [1]. Beside to aid clinical diagnosis, dental casts are usually collected by clinicians to monitor the progress of the treatment and to compliment the written record [2]. It is made by taking the impression of upper and lower dentition using impression materials and subsequently the impressions are poured with dental stone. The upper and lower dental stone will then be trimmed, labeled and kept in the box [3]. The medico-legal requirement in some countries is that all clinical records including study casts should be retained for a period of 11 years, or 11 years after a patient reaches the age of 18 years [4]. The need to retain dental casts for
future reference has created storage problem for dental hospital and orthodontists [5]. Therefore a more convenient and cost effective means of recording, maintaining and retrieving this information is needed. With the advancement in information technology, most of the dental hospitals have started to store all clinical case notes, radiographs and clinical photographs in digital format. Many hospitals have also scanned all the previous records and stored it in digital forms. However, the dental cast still remained in its original forms. Various attempts have been made to convert the traditional dental casts to digital forms. Some of the dental casts have been reproduced in two-dimensions by taking its photocopies [6] and photographs [7]. There-dimensional reproduction of dental casts has been attempted using holography [8, 9, 10] and stereophotogrammetry [11, 12]. However, these methods suffered from various shortcomings that leave the conventional dental casts have still not been replaced [2]. These drawbacks have lead to another phase of development where the computer-based digital orthodontic models have been developed. In 1991, OrthoCAD has introduced a digital model service to Orthodontists throughout USA and Canada. Since then, digital model has received a good response from the orthodontists. According to Joffe [13] the data indicated that 10 per cent of orthodontists in Canada and the USA use digital models [13]. Recently, a new type of CT scan is introduced in clinical dentistry; that is cone beam CT scan (CBCT). It has the potential to reduce the size and costs of CT Scanners. This scanner is capable of producing the images with isotropic submilimeter spatial resolution that is suitable for dentomaxillofacial CT scanning. Furthermore, when combine with application-specific software tools, CBCT can provide the clinician with a complete solutions for performing specific diagnosis [14]. However, not much is known of whether the CBCT is able to scan the dental cast that is made of dental stone with a typical density of 2.3 gm/cm3 [15] . If it is possible, this method could be useful in scanning the specific dental casts if not all for specific reason. This will allow the dental cast
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Validation of Cone Beam CT Scan for Measurement of Palatal Depth in Study Casts
to be stored in digital format and to be analyzed with various softwares. To date, there is no reported study on scanning the study cast that is made of dental stone with CBCT. On the other hand, it is important for any institution or dental hospital to ensure that what ever the conversion of study cast into digital format will not cause loss to all the details and precious information as it may be needed for future references. In clinical dentistry, various linear measurements can be assessed using study casts such as palatal depth. Caliper measurements are regarded as the ‘gold standard’ against other measurement techniques are compared [2]. Therefore, the objective of this study was to compare one of the linear measurements that is ‘palatal depth’ on study casts using calipers against with those on digital models scanned with cone beam CT scan.
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Fig. 2 Measurement of palatal depth using digital caliper 0.01 mm. The measurements were repeated twice after an interval of two weeks and the average value was taken for each study cast. Measurement with CBCT
Palatal depths of the dental casts were first measured with digital caliper (Mitutoyo, Japan) to the nearest 0.01mm. The landmarks used were the mesio-buccal cusp tips of both maxillary first permanent molars. A metal ruler was used to link the two cusp tips in order to construct a reference plane. A digital caliper was set to zero and the distal part was placed perpendicular against the metal ruler. As the caliper opened the graduated middle component slide out and was allowed to touch the deepest concavity of the palate (Fig. 2) and measurement was taken to the nearest
The i-cat Cone beam CT scan was used to scan the study cast. The study cast was positioned in a standardized manner on the CBCT using a specially designed platform (Fig3). The platform is designed and fabricated by The Department of CAD CAM, Faculty of Engineering, University of Malaya. Calibration of the CBCT machine was carried out prior to the scanning of the dental casts by a team of experienced technicians and radiographers. Each study cast was scanned for 10 seconds and was reconstructed into three dimensional views (Fig. 4). The duty cycle for CBCT is 3 per cent for the total exposure time and 97 per cent for the reconstruction of the images. In general it takes 9.7 second of the total exposure time to construct a 3D image. i-CAT software was used to determine the first reference plane that link right and left mesio-buccal cusp tips of the maxillary first permanent molars. The second reference plane was drawn to determine the deepest concavity of the palate that was perpendicular to the first reference plane. Palatal depth measurement was taken by measuring the distance between the deepest point of the palate perpendicular to the plane connecting right and left mesio-buccal cusp tips of the maxillary first permanent molars. The measurement was taken twice with the interval of two weeks and an average was taken for each study cast.
Fig. 1 One of the study cast that fulfilled the inclusion criteria
Fig. 3 Study casts on a specially designed platform
II. MATERIALS & METHOD Two-hundred and sixty-one dental casts of Malaysian Aborigines were taken from Centre of Malaysian Pribumi Studies Databank. Inclusion criteria for selecting study casts were: all teeth are present up to second permanent molars, no signs of caries on the study casts and intact mesio-buccal cusps of the maxillary first molars in upright position. Out of 262, only 34 study casts fulfilled the inclusion criterion and were included in this study (Fig. 1). Measurement with digital caliper
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760 Z. Radzi, N.A. Yahya, N.H. Abu Kasim, N.A. Abu Osman, Z.Y.M. Yusof, F.N. Mohd, N.H.M. Noor, M. Jamaludin, S.A. Othman, …
Fig. 4 Three-dimensional views of the study cast Data were computed and analyzed using SPSS version 12.0. Intraclass correlation and Paired T-test were employed. III. RESULTS & DISCUSSION The mean palatal depth of Malaysian Aborigines using CBCT and digital caliper were 18.97mm ± 3.32 and 18.56mm ± 2.76 respectively. In order to compare the agreement between two different methods in the measurement of palatal depth, the Intraclass Correlation Coefficient was employed. The Intraclass Correlation Coefficient (ICC) is a measure of reliability or agreement for quantitative measurements. In this study, the Intraclass Correlation Coefficient for average measures was 0.753, which indicated that there was a good correlation between both methods in measuring palatal depths (Table 1). There was no significant difference between CBCT and digital caliper in using paired t-Test. P=0.401 (p> 0.05). Paired T-test was used in coupled with ICC because it was more sensitive in comparing between both methods using the same samples. The palatal depth of the Malaysian Aborigines, were in the normal distribution for both methods CBCT and digital caliper. There was no significant difference between CBCT and digital caliper with p= 0.634. Traditional study casts have been used in clinical dentistry for many years. However, these study casts have many limitations such as easy to break during transportation. Continued use for measurement and display can wear away plaster, decreasing accuracy and increasing the likelihood of fracture. Models are usually kept in boxes to protect it from physical and chemical damage. Therefore it requires huge storage facilities. Retrieval of this study casts may not be easy as the study casts accumulates [16]. Table 1 Intraclass Correlation Coeeficient Average measures
ICC 0.753
Lower Bound 0.508
95% CI Upper Bound 0.405
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Sig 0.000
In contrast, the digital study casts offer a lot of advantages. The biggest advantage of this system is to allow storage of invaluable information contained in these threedimensional records, which would otherwise be lost on a moment’s carelessness due to the plaster study model breaking. Also, certain model analysis results are now available using high performance computer. Furthermore, digital study models offer advantages that include ease of storage and retrieval, ease of interoffice transferability, and possibly equal or better diagnostic capabilities. It allows the models to be digitized, measured with software tools, stored electronically, and retrieved with a computer [17]. In 2005, Rheude et al. [18], evaluated the use of digital study models in orthodontic diagnosis and treatment planning. They found that in the vast majority of situations digital models can be successfully used for orthodontic records [18]. One year later, Stevens et al. [19], carried out the study on validity, reliability, and reproducibility of plaster versus digital study model. They found that preliminary results did not indicate that digital models would cause an orthodontist to make a different diagnosis of malocclusion if compared to plaster models; digital model does not compromise choice for treatment planning or diagnosis [19]. More recently, Lundner (2007) evaluated the correlations of a comprehensive cast analysis between plaster and e-models (GeoDigm, Chanhassen, Minn) digital models. Forty-nine corresponding plaster and digital study models were selected according to the inclusion criteria, resulting in a mixture of pretreatment and posttreatment models. The Intra Class Correlation Coefficient was computed to assess reliability, and mean differences and corresponding 95% confidence intervals were computed to assess bias. They found that digital models was an appropriate alternative to plaster models for comprehensive cast analysis [20]. Mullen et al. (2007) evaluated the accuracy and speed of measuring the overall arch length and the Bolton ratio, and the time to perform a Bolton analysis for each patient by using software (emodel, version 6.0, GeoDigm Corp, Chanhassen, Minn) and compared with hand-held plaster models. They found that, when performing a Bolton analysis, the emodel can be as accurate as, and significantly faster than, the traditional method of digital calipers and plaster models [21]. Our finding is in agreement with the findings by Rheude et al., (2005), Stevens et al. (2006), Lundner (2007) and Mullen et al. (2007), that the use of digital study model is an appropriate alternative to plaster models for dental cast analysis. However, direct comparison cannot be made as the methods used are different. Our research work compared the validity of measurement using dental casts and scanned image of the dental casts, whereas other research work compared the dental casts and images taken from dental impressions [18,19, 20, 21].
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Validation of Cone Beam CT Scan for Measurement of Palatal Depth in Study Casts
In our study we have excluded the models that presented with the tilted mesio-buccal cusp tips. This exclusion was to avoid the any discrepancy in establishing the reference plane. The mesio-bucal cusp tip that was tilted can be lower that the mesio-palatal cusp tip. Therefore, it would be difficult to link the mesio-buccal cup tips on the right and left maxillary first permanent molar using traditional dental casts. However, it is possible to link the two mesio-buccal cusp tips even though they are lower that mesio-palatal cusp tips using digital study models with cone beam CT scan. Perhaps, for standardization in research the utilization of digital study casts will provide more consistent data when measuring the palatal depth. However, cost-benefit analysis need to be carried when using the cone beam CT scan in scanning the study casts. For selected cases, study cast could be scanned as this method could provide a reliable 3-D data for diagnosis 3D data analysis.
4. 5. 6. 7.
8. 9. 10. 11.
12. 13.
IV. CONCLUSIONS
14.
In light of the study to compare the agreement between two continuous measurements (validation of two different methods in measurement of palatal depth) of palatal depth using CBCT and digital caliper it was found that: 1. The Intra Class Correlation Coefficient for average measures is 0.753 indicating a good correlation between both methods in the measurements of palatal depths. 2. There was no significant difference (p> 0.05) in the measurements using CBCT and digital caliper. 3. Therefore, the use of CBCT in measurement of palatal depth could be advocated.
15. 16.
17. 18. 19.
Based on the findings and observation in this study the followings are recommended: 1. Future research should be carried out as baseline information with bigger sample size and more parameters. 2. Validation in palatal depth using other methods 3. Cost-benefit analysis to ensure that the recommended method is economical and reliable.
2. 3.
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Dr Zamri Radzi University of Malaya Lembah Pantai Kuala Lumpur Malaysia
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