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An Evaluation of the Errors in Cephalometric Measurements on Scanned Lateral Cephalometric Images using Computerized Cephalometric Program and Conventional Tracings1Priteshkumar Sureshchand Ganna, 2Sharath Kumar Shetty, 3Mahesh Kumar Yethadka, 4Akram Ansari

ABSTRACTAim and objective: The aim of this study was to compare the cephalometric measurements using Nemoceph software with manual tracings.

Materials and methods: The sample consisted of 60 lateral Cephalometric radiographs of patients randomly selected from the existing records of patients of Department of Orthodontics and Dentofacial Orthopedics, KVG Dental College and Hospital, Sullia, Dakshina Kannada. Nineteen angular and 11 linear measurements were analyzed on each radiograph. All the lateral cephalographs were hand-traced and the same Cephalographs were then scanned and were then digitally traced with Nemoceph software. The results were then tabulated in Microsoft excel. The level of significance (p-value) was 0.05 and was set at p < 0.05. Paired t-test was performed using SPSS software for comparison between tracing done by manual method and by Nemoceph software.

Results: Significant differences were found between the two methods for five (four angular and one linear) out of 30 measurements. Those five were saddle angle, articular angle, upper lip to E-Line, Frankfort horizontal to lower incisor axis angle and lower incisor axis to mandibular plane angle.

Conclusion: Both angular and linear measurements were accurate and reliable. Except, few measurements showing highly significant differences, the validity of the measurements with the Nemoceph software and with the conventional method were highly correlated.

Keywords: Manual tracing, Software-based tracing, Cephalo-metric measurement.

How to cite this article: Ganna PS, Shetty SK, Yethadka MK, Ansari A. An Evaluation of the Errors in Cephalometric Measurements on Scanned Lateral Cephalometric Images

ORIGINAL ARTICLE

1Tutor, 2Professor and Head, 3Professor, 4Senior Lecturer1Department of Orthodontics, Siddhpur Dental College and Hospital, Patan, Gujarat, India2,3Department of Orthodontics, KVG Dental College and Hospital, Sullia, Karnataka, India4Department of Orthodontics, Teerthanker Mahaveer College of Dental Sciences and Research, Moradabad, Uttar Pradesh, India

Corresponding Author: Priteshkumar Sureshchand Ganna Tutor, Department of Orthodontics, Siddhpur Dental College and Hospital, Patan, Gujarat, India, Phone: 9979603332, e-mail: aamir_prit@yahoo.co.in

10.5005/jp-journals-10021-1283

using Computerized Cephalometric Program and Conventional Tracings. J Ind Orthod Soc 2014;48(4):388-392.

Source of support: Nil

Conflict of interest: None

Received on: 31/1/14

Accepted after Revision: 12/2/14

INTRODUCTION

Since, the introduction of cephalometrics by Broadbent1 in 1931, its role has been vital in orthodontic diagnosis and treatment planning, and for monitoring treatment and growth changes. Precision and reproducibility in data obtained from cephalometrics is important for the orthodontist.2

With standardized radiographs, the orientation of various anatomical structures can be studied by means of angular and linear measurements.3 The use of serial cephalometric radiographs to investigate growth and development of the facial skeleton can assist in treatment planning, and changes between pre- and post-treatment measurements can help in treatment evaluation.4,5 Cephalometric analysis can also be used to predict surgical outcome, which is important in treating dentofacial deformities.6

Cephalometric errors can be divided into acquisition, identification and technical measurement errors.7,8,9

Although radiographic film is quite stable and can retain its infor mation for many years, due to its physical nature, it is not always a dependable archive medium.10 Film deterio ration has been a major source of information loss in craniofacial biology; therefore, digital archiving of lateral cephalographs is a valuable method for orthodontic clinics.11

Hand measurements are time-consuming and there is a risk of misreading the measuring instruments and registering data to the computer.12 If digitization is carried out, then the angles and distances are automatically calculated which can eliminate the errors in drawing lines between landmarks and in measurements with a protractor. Moreover, the digital image can be manipulated to process the image and alter its visual appearance which can facilitate landmark identification.13,14

An Evaluation of the Errors in Cephalometric Measurements on Scanned Lateral Cephalometric Images

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In clinical orthodontics, the efficacy of both commercially available cephalometric tracing software programs and commonly used cephalometric analyses need to be evaluated for accuracy in order to allow the clinician to select appropriate software and methods of analysis.3 Several studies have been undertaken to compare the accuracy of scanned, digitized and digitally obtained radiographs with analogue methods.2,7 However, no clear consensus has arisen as to which method is preferable because the conversion of analogue film to digital format requires several additional steps that are not only time-consuming but may also introduce magnification errors.

Considering the importance of cephalometric analyses for orthodontic diagnosis, the accuracy of computer-based tracing software must be established by comparing them to hand tracing on acetate paper, the current gold standard.15

Hence, this study was conducted to assess the cephalo-metric measurements by manual tracings and computerized tracings using Nemoceph software and to analyze and compare the measurements of manual tracings with digitized tracings of Nemoceph software.

MATERIALS AND METHODS

The sample consisted of 60 good quality lateral cephalographs (Gendex Orthoralix 9200 machine, Gendex Dental Systems, Hatfield, PA, 19440) without any artifacts that could interfere with locating cephalometric landmarks, selected randomly from the existing records of patients of the Department of Orthodontics and Dentofacial Orthopedics, KVG Dental College and Hospital, Sullia, DK Lateral cephalograph with distorted images were excluded.

All the lateral cephalographs obtained from the selected record were carefully hand-traced by the same observer under the same illumination and magnification on single matte lacquered polyester acetate tracing paper of thickness 35µ, using 3H lead pencil. Structures appearing as bilateral images were identified by bisecting the outlines of the images.

Nemoceph software (Nemoceph 6—Dental Studio NX, version 6.0, Spain) recommends 150 dpi resolution for scanning. In the present study, however, the cephalographs were scanned at 200 dpi using scanner with transparency adapter (Epson perfection 4180 scanner). At the time of scanning, a transparent ruler was placed adjacent to the cephalograph. The ruler was kept to assess the magnification errors during the process of scanning. Image thus acquired was stored in joint photographic experts group (JPEG) format.

Nineteen angular and eleven linear parameters were measured as shown in Figures 1 and 2 respectively.

The cephalometric analysis in the traditional method was performed using the selected lateral cephalograph. The

manual tracing was performed using lead acetate sheets and 0.3 mm pencil. Scale and protractor were used to analyze the linear and angular measurements. All the 60 samples were analyzed in a similar manner and the results were tabulated.

Then cephalometric analysis using Nemoceph software was performed. The digital cephalograph file was opened and the cephalograph was calibrated on the transparent ruler, which was kept along with the lateral cephalograph while scanning. The landmarks were then digitized. The analysis occurred automatically once the landmarks were identified. The results were then saved.

Statistical Analysis

The results were tabulated in Microsoft excel sheet. The level of significance (p-value) was set to be 0.05. Paired t-test was performed using SPSS software for comparison between tracing done by manual method and by Nemoceph software.

Fig. 1: Lateral cephalometric tracing with angular measurements

Fig. 2: Lateral cephalometric tracing with linear measurements

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RESULTS

The means of all angular and linear measurements were assessed and tabulated as shown in Table 1. Graph 1 shows comparison of the parameters used in the study between the two groups.

Out of 30 paramaters, five showed highly statistically significant differences. They are as follows:• Saddle angle• Articular angle • Upper lip to E-line • IMPA and • FMIA

DISCUSSION

Until recently, manual tracings have been considered to be the best method for accurate cephalometric analysis but advances in computer-assisted cephalometric analyzing systems have resulted in their widespread use in orthodontic practice.16

The major errors in conventional cephalometry may include projection errors and tracing errors. The most important source of tracing errors is uncertainty in landmark identification, and intra-observer error is generally less than inter-observer error.17 When we take advantage of digital cephalometry, it is important to question whether the digital image yields the same level of performance in terms of landmark identification as conventional radiographic film.

The results of the present study are in agreement with the findings of Macri and Wenzel.18 They reported that it was possible to achieve reliability in digital images comparable to that obtained with conventional equipment for radiographs with good quality. In contrast, Geelen et al reported that the precision of landmark recording was lower for enhanced monitor-displayed images than for both film and digitally enhanced hard copies in 11 of 21 landmarks.10 Also Chen et al reported significant differences in landmark identification for manually traced films and their digital counterparts.19

Table 1: Mean values and p-values of parameters used in the study

Parameters Actual figures Mean values p-valueManual Nemoceph

WITS (mm) 0-1 mm 0.3167 1.0433 0.322ULE (mm) –1 mm –0.2767 –1.2200 0.026 SLLE (mm) –2 ± 2 mm 2.8067 2.6367 0.737

CoA (mm) 93.1 ± 3.2 89.6233 87.9267 0.166CoG (mm) 121.6 ± 4.5 113.5733 112.9633 0.685ANS-Me (mm) 67.2 ± 4.7 66.2300 67.3733 0.316Nper-A (mm) 1.8 ± 2.2 –2.9533 –3.0267 0.929PogNB (mm) –3.5 ± 5.3 –9.9567 –10.3767 0.793

1APog (mm) 1.2 ± 1.4 6.0000 5.3533 0.173U1NA (mm) 4 mm 9.7600 10.3867 0.347L1NB (mm) 4 mm 8.5667 8.0300 0.267Saddle (°) 123° ± 5° 125.5133 122.7833 0.003 HSAr (°) 143 ± 6° 139.8233 144.2533 0.006 HSGo (°) 130 ± 7° 123.2433 122.2100 0.489 UGo (°) 52°-55° 52.6200 51.2833 0.168LGo (°) 70°-75° 70.6200 70.9500 0.706U1SN (°) 102° 117.4300 116.8370 0.665Nasolabial (°) 102 ± 8° 90.8367 90.5967 0.937MPA (°) 22° 27.5267 26.3733 0.310FA (°) 161° 162.4867 162.7733 0.788OSN (°) 11° 15.7333 14.2833 0.145U1L1 (°) 130° 109.4900 110.4200 0.542U1NA (°) 22° 34.2833 34.3533 0.96L1NB (°) 25° 32.1200 31.9033 0.852FMA (°) 25° 26.9600 26.5400 0.738FMIA (°) 90° 55.0000 50.3200 0.007 HSIMPA (°) 65° 97.7067 103.1400 0.004 HSSNA (°) 82° 82.1633 82.7500 0.503SNB (°) 80° 78.6600 79.1633 0.580ANB (°) 2° 3.2533 3.3667 0.807S: Significant; HS: highly significant

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In the present study, five (four angular and one linear) out of 30 parameters showed statistically significant differences. These five parameters were saddle angle, articular angle, FMIA, IMPA and upper lip to E-line. Upper Lip to E-line also showed statistically significant differences. However, in another study conducted by Sayinsu et al,2 upper lip to E-line did not show statistically significant difference. Chen et al19 showed significant differences in landmark location for lower incisor apex. The present study showed statistically significant differences for IMPA and FMIA. This might be because of difficulty in identifying lower incisor apex from blurred images due to superimposed structures. The statistically significant differences for FMIA might be because of FH plane. Bruntz et al20 conducted a study and concluded that FH plane is unreliable in identification with digital media. Chen et al19 showed discrepancies in the vertical component when identifying the landmarks porion, orbitale and gnathion on digital media. Thus, porion and orbitale showed significant unreliability in landmark identification; this might have affected results in this study. Previous studies showed significant errors for landmark identification of articular.5,21 This is in agreement with the results of the present study as saddle angle and articular angle, both showed significant differences.

If the films are scanned and transferred to digital format, as in this study, the quality of the original film is one of the most important criteria in the validity of the result.2

Nemoceph software recommends 150 dpi resolution for scanning. In the current study, films were scanned at a resolution of 200 dpi. For scanning lateral cephalograms, it is suggested that 75 dpi is sufficient.19 Chen et al19 stated that digital cephalometrics could produce better results if digital images of 150 dpi, 8 bits were used. During landmark digitization, magnification was often used to

more accurately identify certain structures. In several instances, the magnification caused significant pixilation and blurriness of the image, increasing the difficulty of accurate identification. Selecting a higher scanning dpi might assist in circumventing this problem.

Polat-Ozsoy et al22 showed that with the exception of a few measurements, cephalometric analysis was highly reproducible for manual method and computerized tracing using Vistadent imaging software. Naoumova et al6 showed statistically significant between-method differences for four of the 25 cephalometric variables and concluded that Digital tracing with FACAD® was sufficient for clinical purposes and comparable with manual cephalometric tracings. Kazandjian et al23 evaluated the validity and reliability of a new edge-based computerized method (Software Viewbox, with Auto Edge LockingTM) of cephalometric landmark identification and digitization. Their results showed that measurements performed using this feature were not found to agree in some of the cases with those performed after manual on screen digitization. These differences were very small, but it may need improvement. The study done by Sayinsu et al2 concluded that the validity and reproducibility of the measurements with the Dolphin imaging software and with the conventional method were highly correlated. Uysal et al16 showed that compared with the manual method, computerized measurements using Dolphin imaging software provide a significant time advantage and do not increase intra- and inter-examiner error.

The direct digital cephalogram can totally eliminate the need for scanning the traditional radiographic film which not only requires an additional time-consuming step but also can introduce magnification errors.19 Recently, the digital storage phosphor plate has been developed which has demonstrated improved subjective image quality than

Graph 1: Comparison of parameters between the two groups

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traditional cephalometric images.23,24 Three-dimensional imaging techniques are becoming increasingly popular and have opened new possibilities for orthodontic diagnosis and treatment assessment.25

The statistically significant difference between the values of five parameters of Nemoceph software compared with conventional tracings requires further investigation as these differences could be clinically relevant.

CONCLUSION

Although small discrepancies were found between the hand-tracing and computerized measurements, the differences were minimal and clinically acceptable. The user-friendly and time-saving characteristics of computerized tracing make this method inherently preferable to hand-tracing for cephalometric analysis of radiographs used in diagnosis, treatment planning, and the evaluation of treatment outcome.

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