Comparative Evaluation of Digital Cephalometric Tracing Applications on Mobile Devices and Manual Tracing

Introduction

Effective orthodiagnosis and treatment planning is based on a thorough understanding of the underlying skeletal, dental, and soft tissue anatomical and functional interaction of a particular patient. Important diagnostic records needed before initiating orthodontic treatment include medical and dental history (past to present), mounted diagnostic casts, and cranial radiographs (panoramic and cephalometric) [1]. To ensure a proper diagnosis and treatment plan, various methods are employed to analyze all of these records [2]. In 1931, Broadbent introduced cephalometric radiography as a means to diagnose and plan orthodontic cases [3], and it remains one of the most economic and effective tools in orthodontic treatments.

The skeletal growth pattern can be predicted by sequential cephalometric analyses, which can also help estimate orthognathic treatment outcomes [4]. This predictive capacity of cephalograms is a crucial part of treating dentofacial abnormalities, especially those that are skeletal. The process of cephalometric tracing is traditionally done by hand on acetate paper placed over a lateral radiographic film [5]. Identifying specific anatomic landmarks requires a cephalometric protractor and a mechanical pencil. The use of a reference landmark on the acetate paper helps in repositioning and fixing it over the film. Measuring the anatomical planes that run from one landmark to another is done for linear measurements, whereas angular measurements are taken when 2 planes come together [6]. The values measured (linear and angular) can be then compared to normal values to determine specific readings for skeletal, dental, or soft tissue parameters [7]. The manual tracing method has been the only method available for cephalometric tracings for many years. The proper interpretation requires angular and linear measurements. The manual method has its drawbacks, such as the time it takes to perform and the difficulty in identifying landmarks [8]. Technological advances in the 1960s, like digital radiographs with advantages of speedy processing, enhanced image quality, and storage in digital format, paved the way for computer analysis in cephalometric radiographs. Computer-assisted measurements involve using a simple basic digitizer that gives the cephalometric landmarks an X and Y coordinate axis, which were later automated using an image processing system (CLIP4) [9], but provided identification of only 2 landmarks (sella and menton). Further parallel advances in radiography and computers led to development of sophisticated orthodontic software packages [10], among which Dolphin Imaging software has become very popular since its introduction in 1994 (at the 9th Brazilian SPO Orthodontic Conference), for orthodontic diagnosis [5]. This software facilitated digital cephalometric tracing with the ability to store the radiographic soft copy on a computer storage space in the hard drive [11].

The widespread use of smartphones and tablets among healthcare providers has been influenced by the advent of portable technology [12]. Tasks that used to be cumbersome and required a lot of bigger machines and/or equipment are now easier and more convenient to do. Dentistry, including orthodontic practices, has found the value of newly developed applications in smartphones and tablets as a means to facilitate and aid diagnosis and treatment planning protocols [13]. A few free versions of smartphone and tablet applications (CephNinja and OneCeph, Google, Inc, CA) were developed specifically for cephalometric tracings using the certified analytical computerized cephalometric program (Viewbox) [14]. It became possible for the developers to create the applications on these platforms since these devices have central processing and graphic units capable of computing and analyzing different tasks, comparable to mid-range personal computers (PC). This in turn made it easier for developers to efficiently code these applications on portable devices. However, their availability depends on the operating system of the devices (iOS operating system for Apple devices; OS for Mac) [15,16]. In April 2016, NSX (Networking and Security Virtualization VMware NSX) technology in India introduced OneCeph as a smartphone-based application to perform digital cephalometric tracing [17]. Soft copy (digital) uploading to the platform allowed cephalometric analysis, including tracing parameters for skeletal, dental and soft tissue landmarks. Further updates enhanced additional analytical methods with additional parameters. Shettigar et al [18] compared OneCeph with Dolphin Imaging software using a PC, and observed 4 parameters from a total of 15 to have a significant difference. Before introduction of OneCeph, another application-based cephalometric analyzer called CephNinja (Cyncronus LLC technology) was introduced, which could perform digital cephalometric tracing on a wireless, portable tablet-based platform [19]. It provides various analyses that include the parameters of skeletal, dental, and soft tissue. Subsequent updates also allowed one to draw teeth and adjust soft tissue contour outlines. Livas et al [20] assessed its diagnostic accuracy for software Viewbox and concluded that CephNinja was the best alternative in terms of reliability with Viewbox. On the contrary, Aksakallı et al [21] reported differences in measurement for cephalometric landmarks (orbitale, porion, gonion, and apex regions).

Since its introduction in 1953, Steiner’s manual cephalometric analysis remains to be one of the most common analyses for orthodontic diagnosis, mainly because it is simple and less confusing. It uses sella-nasion as the primary reference plane because they are more stable structures and are easily identified on radiographs [22]. While manual tracings consume time, they are also prone to random errors due to limitations of the human eye. Manual tracings are performed on printed radiographic images, which have been reported to have substantial distortion (1.1 mm vertical, 0.4 mm horizontal), although such enlargements were found to be clinically insignificant [23]. Despite their limitations, the novel digital cephalometric tracing technologies are convenient, efficient, easy to manipulate, conservative, and environmentally friendly (paperless). The ability of these digital cephalometric radiography to transfer the two-dimensional images into a digital format has additional advantages like availability of popular devices, multiple analysis using a single application, minimum storage space, and modifies image properties (eg, contrast, brightness, color saturation) [24]. Finally, the cephalometric radiographs that would otherwise deteriorate with time can now be accessed and archived with better capabilities [15]. Navarro et al [25] found lateral cephalometric radiographs were very stable but predicted that they are still liable to deteriorate, which can lead to lower quality than the original radiograph. Barbhuiya et al evaluated the accuracy and reliability of software that was on a mobile phone on 30 patients, and found angular and linear measurement accuracy to be comparable with conventional methods [26]. In an earlier study [18] too, the differences in some of the parameters relative to personal computer-based tracing software’s were reported, which formed the bases of conducting this study. Therefore, the present study aimed to evaluate the reliability of 2 different digital cephalometric tracing applications (mobile and tablet) as compared to conventional manual tracing. The study also aimed to measure various parameters of Steiner’s radiographic analysis using smart phone- and tablet-based application software. We also sought to identify those parameters of applicated based tracings which differed from manual tracing. We hypothesized that there would be no differences in the parameters of Steiner analysis between smartphone and tablet applications relative to manual cephalometric tracings, and that variations between the 3 methods will be homogenous. Alternately, the null hypothesis was that there would be no significant differences between the methods.

Material and Methods

ETHICS:

This study required ethics approval from the office of research coordination since it utilized digital archives of previously treated patients at the Department of Orthodontics, College of Dentistry of the University of the East, Manila. The study was duly approved by the committee (approval number G-2021-1-02), with particular emphasis on taking all measures to protect patient confidentiality, which was achieved through anonymization of patients’ identity and personal information. All patients whose records were taken for the study had provided a signed written informed consent before their treatment was initiated.

STUDY DESIGN:

This study had a quasi-experimental post-test research design comparing lateral cephalometric landmarks and linear and angular values of Steiner analysis between 2 digital-based tracing applications versus manual tracing. We sought to determine whether there were any differences between manual tracing and the 2 digital tracing methods for cephalometric analysis in orthodontic diagnosis and treatment planning for performing Steiner analysis. A quasi-post-test study was designed, since the study used a random assignment of samples (cephalometric tracings of previously treated patients) in which there was assignment of a control group (manual tracing) and 2 experimental groups (smartphone/tablet applications), without using a pre-test. The independent variables were lateral cephalometric radiographs and the dependent variables were the cephalometric values of Steiner analysis obtained from manual, smart phone, and tablet cephalometric tracings.

SAMPLE SIZE ESTIMATION:

The sample size for the study was guided by samples taken from previous similar studies [5,7] and verified statistically using software (Nquery, V7, Informer Technologies, USA) that calculates sample size based on the formula [N= 2 σ2×(Z α + Z β)2/D2] [27]. Using test power (0.8) with error buffer (15%) for calculating effect size at an α′ level of 0.05 and 95% confidence interval, the sample size was estimated to be 30 similar radiographic analyses for each group.

OPERATIONAL DEFINITIONS:

Pixels per inch (PPI) is a measurement that defines the number of pixels in 1 inch of radiographs when displayed on a monitor. Dots per inch (DPI) is a printer resolution measure defined as the number of ink dots in a particular area (1 square inch). With higher DPI, the image becomes sharper. The platform (computing or digital) is the environment in which software was used. Standardization for cephalometric radiography has been defined as adjusting the cephalometric radiograph size and resolution to match the image in the real-world on a scale of 1: 1.

SAMPLE SELECTION:

This cross-sectional study used a randomly selected (from digital archives) sample of 30 lateral cephalograms (of previously treated orthodontic patients) that constituted 17 male and 13 female subjects with a set of permanent natural dentition and a mean age of 22 years 9 months. These radiographs were part of the investigation process prior to diagnosis and treatment of these subjects. The selection of lateral cephalometric pretreatment radiographs was based on certain inclusion and exclusion criteria. These included an age range (18 to 35 years), regardless of sex and malocclusion type, had a complete set of natural permanent dentition, good-quality radiograph that permitted identification of desired landmarks, and radiographs were taken from the same machine and technique with similar calibration and display calibration ruler. Pixelated radiographs, which contain a low number of pixels, and those radiographs with gross dimensional discrepancies were excluded from the study. These inclusion criteria ensured that patient records had minimal variations and met the requirements of the study. The age range recruited ensured patients had minimal variations in teeth as a result of decay, since decay can change tooth positions. It also ensured that all radiographs used similar exposure techniques (head immobilized with cephalostat, guided by Frankfort horizontal plane parallel to the ground/perpendicular to mid-sagittal plane) [28]. Radiographs were randomly selected from digital archives by 2 independent reviewers experienced in the field of orthodontics, both of whom were blinded to the objectives and outcome of the study. The same radiographs were used for 3 independent groups [manual tracing – Gp M, smartphone tracing application (OneCeph) – Gp S and tablet tracing application (CephNinja) – Gp T].

DIGITAL CALIBRATION:

All radiographs were digitally calibrated by using dots/pixels per inch (DPI/PPI) [29], which was obtained from the scanner device. The method does not require a high-quality printer and provides up to 300 DPI for all printers. Once the DPI settings were known, the image was calibrated to real-world size. DPI was acquired by uploading a digital cephalometric radiograph to a Photoshop file (Adobe Systems, Inc., San Jose, CA) that could be calibrated and resized to a real-world scale of 1: 1 printing to hard-copy using the same interface. Hard-copy printing was done with the same software to keep the standardized settings for image size and to prevent image printing distortion if printed using other software. All radiographic images were printed from a JPEG (Joint Photographic Experts Group) file extension.

For calibration of radiographic images in Gp S and Gp T, a calibrating ruler provided with the application was used to measure 2 points on each image to reflect a real-world size on the monitor of the screen used [30]. All machines used can be accurately measured and corrected for magnification using the millimeter calibration ruler.

RADIOGRAPHIC TRACING:

All tracings were performed by 1 blinded operator to minimize inter-examiner variations, blinded to study outcome and objectives. The operator was an experienced specialist and consultant (orthodontist) who has been working as an academician and clinician for more than 10 years. Pertaining to the study objectives, he was trained in terms of the number of radiographs to be completed in a single day and limited analysis to be performed on each radiograph. Accurate landmark identification was supervised by an experienced staff member, who also has been working as an academician/clinician for 9 years in the same specialty with the same position. Only 5 tracings were performed in a working day so as to avoid inaccuracies due to eye fatigue and strain. To prevent the measurement error and to test the magnitude of intra-examiner error, 5 randomly selected samples were retraced and re-measured by the same researcher 1 week after the initial measurements. The calculated random error was measured using Dahlberg’s test.

IDENTIFYING ANATOMICAL LANDMARKS FOR ANALYSIS:

A schematic outline of various anatomical landmarks to be identified and analyzed (Steiner analysis) for the study were organized. A digital representation of the identification of all landmarks and their coded numbers is presented in Figure 1. The description of each coded landmark, which includes the location of the particular point or the plane between 2 points, is presented in Table 1.

MANUAL TRACING (GP M):

Printed copies of pretreatment lateral cephalometric radiographs were used for manual tracing. Digitally standardized radiographs were printed on glossy photo paper. Manual tracings were made on acetate paper, which was attached to the printed radiograph using clear tape. The tracing sheet was attached to the printed radiograph paper with the glossy side facing away from operator and the rough surface on top, to allow marking with a pencil. Three reference crosses were marked on each printed radiograph at wide distances, but within reach of the overlying tracing paper. This was to allow the overlying tracing paper to be oriented in case the tape came loose or there was movement while recording. The outline of the bony landmarks was then traced on the acetate paper to yield surface characteristic of the cranial cephalogram. Similarly, the soft tissue outline was also traced from the printed radiograph. A 0.5-mm mechanical pencil was used for marking and drawing landmarks. For linear measurement, a line drawn from one point to another was carried by using a transparent ruler, the outer margins of which were kept on the outline of the particular landmarks, and then a line was drawn from one point to another. For angular measurements, a protractor was used, which was aligned on 2 lines at right angle to each other, while at the same time demonstrating the angle of the landmark in the area of interest. The angle was thus recorded by observing the line denoting the angle on the transparent protractor and underlying landmark.

Steiner analysis landmarks were placed over the prospective anatomical structures (Figure 2). The goal of landmark placement was to identify only those landmarks involved directly in Steiner analysis. This provided the maximum diagnostic information with the minimum number of measurements. The linear and angular values were identified and measured using a pencil and a cephalometric protractor to achieve Steiner parameters, and the values of each parameter were written on the back of the cephalometric radiograph printout.

SMARTPHONE APPLICATION TRACING (GP S):

Digital pretreatment lateral cephalometric radiographs were used for this application (Oneceph on Samsung S20, Beta 13, (NXS technology, Hyderabad, India) and installed on an Android (OS9) smartphone. The radiographs were uploaded into the application using a USB-C transfer port in JPEG format. The radiographs were transferred and standardized (calibrated) inside the application. Standardization was done by placing a start and end point of a known distance on the standardized ruler. The measurement was then written inside the box. Steiner analysis is an inbuilt feature that appears on analysis. All landmarks desired are placed using arrows at the bottom of the screen. All anatomic landmarks are identified and marked using a stylus pen. A guide that aids in correct positioning of the desired landmark over the structure of the digital radiographic image is also present. The result of Steiner’s analysis was displayed in a PDF format.

TABLET APPLICATION TRACING (GP T):

Digital pretreatment lateral cephalometric radiographs were uploaded into the application CephNinja on iPad 9^th generation, Version 4.11 (Cyncronus LLC, WA, USA) in JPEG format using a manufacturer-provided cable. The photographs were then transferred to the application installed on an Apple tablet (IOS13). The radiographs were standardized (calibrated) inside the application by choosing an image from the gallery, and then moving the ruler (red-colored) and enlarging it to fit over the standardized (calibrated) ruler. Tracing was done by placing the correctly labeled landmark placed over the anatomic structures. All anatomical landmarks were identified using a stylus pen. At the end of the tracing, the examiner clicked on “Analysis” and the results of the measurements of the parameters were exported in a PDF format.

: Once the respective cephalogram was uploaded, the cephalometric landmarks and their respective description were traced for Steiner analysis (Table 1). Each cephalometric landmark was identified, located, and marked, followed by their verification based on anatomical positions. Once a landmark was identified, the lines and planes that are depicted in Table 1 and Figure 1 were traced. Following tracing of the landmarks, the planes and lines that represent Steiner analysis were obtained on each individual radiograph (Figure 2). Steiner analysis was undertaken in a sequence. Landmarks for linear measurements were identified followed by their respective measurements. Then, the landmarks for angular measurements were identified followed by their respective measurements. Any deficiency during angular measurement was identified and the desired plane was drawn. The analysis was done for 5 skeletal, 3 dental, and 1 soft tissue cephalometric relations. Measurements included 5 angular (SNA, SNB, ANB, SNMPA, SNOP), 3 linear U1NA (mm and degrees), L1NB (mm and degrees), U1L1 (U=upper, L=lower), and 1 soft tissue (S line). The measurements on the manual tracings were done using a protractor (3M Unitek, Campinas, São Paulo, Brazil), while in the other groups the measurements were displayed on the respective screen.

STATISTICAL ANALYSIS:

Data obtained were entered into 3 different Microsoft Excel spreadsheets that were named according to the respective groups. The data were corrected and refined for any errors, and then coded, followed by entry into SPSS version 24.0 (SPSS 24.0; SPSS, Inc., Chicago, Illinois, USA) for statistical analysis and testing. Descriptive statistics derived were means and standard deviations for each measured parameter of Steiner analysis. Results were then tested for distribution of data (normality) using Shapiro-Wilk test and Lilliefors significance correction. The null hypothesis was tested using Levene’s test to assess the equality of error variance. All Steiner analysis parameters in the 3 different groups were tested using ANOVA to look for differences among groups. For all tests, the probability ‘p’ value was considered to be significant if it was less or equal to 0.05 (p≤0.05).

Results

Steiner Analysis: The mean and standard deviations of 11 parameters of Steiner analysis of Gp M, Gp S and Gp T, measured in degrees and millimeters, are presented in Table 2. Angular measurement SNA between the 3 groups fell in the range of 80.73±2.95 to 80.86±2.88, SNB (79.34±4.26 to 79.39±4.32), ANB (1.64±2.37 to 1.79±2.41), SNMP (31.89 to 31.93) and SNOP (16.53 to 16.59), indicating there were negligible differences between the 3 tracing methods. Similarly, linear measurements were well within the same range, with little differences in mean values [U1NA (range 9.09 to 9.27), L1NB (range 7.39 to 7.50)] or deviations.

Comparison of Subgroups: To assess the equality of variances for each parameter calculated in the 3 groups, Levene test results are presented in Table 3. The Levene test shows that the p values exceeded the significance level of 0.05, indicating that the variances observed among groups were not significantly different from each other. For angular measurements, the p value was in the range of 0.90 to 1.00, which was considered to be non-significant (p≤0.05). For linear measurement, the p values fell in the range of 0.86 to 0.99, which was again higher than the predetermined value for considering statistical significance (p≤0.05). The interpretation of these values therefore establishes that the variances observed among groups were not significantly different from each other and the homogeneity assumption of the variance was met. Therefore, the 3 methods of tracing showed no significant differences for any of the parameters of Steiner analysis. The Levene test also tests the null hypothesis that the error variance of the dependent variable is equal across groups. Table 4 presents the one-way ANOVA test results from differences among and within groups for all parameters of Steiner analysis. ANOVA indicated no significant difference existed between the 3 methods for any of the parameters of Steiner analysis. All parameters analyzed showed p values greater than the threshold of 0.05, suggesting that the 3 methods did not differ significantly for any parameter.

Discussion

STRENGTH AND LIMITATIONS OF THE STUDY:

The results of this study further substantiate the already existing evidence of digital cephalometric applications being reliable in terms of cephalometric tracings for orthodontic patients. Digital photographs that are uploaded in applications have a very significant advantage of image enhancement and enlargement (zoom) that allows less errors while tracing. The study has its own limitations, which include lack of screen size difference determination between smartphone and tablet, only 1 analysis (Steiner analysis) was performed due to the availability of common analysis in smartphones and tablets, the small sample size, and the standardization for each group was different because there is no common standardization that can be applied to all. Further limitations of using digital applications generally are that they receive updates for various purposes, which might influence the results before and after updates. Manual tracing has its own limitations, which include modifications in the printout based on printer settings, and printer vibrations inducing errors in printing. The assumptions made during the research included that the new updates for both the applications (smartphone-based and tablet-based), and fixes (including performance issues, some improvements in soft tissue analysis) for previous issues.

CLINICAL IMPLICATIONS:

For many years, manual tracing has been the only available method for cephalometric tracing, despite having many drawbacks. With the advancement of technology and the availability of digitizing X-rays, it has overcome some of the issues related to manual tracing. Smartphone-based and tablet-based digital cephalometric tracing applications provide a new alternative for clinicians, combining faster tracing time with more contrast of colors and the ability to zoom in/out. As a result, it reduces or prevents eyestrain when using these devices.

Conclusions

Within the scope and limitation of this study, it can be concluded that digital tracing using smartphones and tablets is equally good at performing a reliable cephalometric analysis for orthodontic diagnosis and treatment planning. The study also found that calibration and standardization are important for proper results. The study also concludes that, irrespective of techniques used, standardization and calibration procedures play significant roles in the final outcome of such comparisons. The manual method for cephalometric tracing can be replaced by any digital method described in this study. Also, it is important to note that when digital modes are not available, the manual method should be performed; it should not be discarded completely until proven otherwise, for it is still as reliable as digital methods.