ORIGINAL ARTICLES DERIVED FROM RESEARCH

 

A COMPARISON OF ANGLE MEASURE REPRODUCIBILITY BETWEEN MANUAL AND COMPUTERIZED TRACING

 

 

Margarita María Bonilla Londoño¹, Judith Patricia Barrera Chaparro², Ángela Patricia Arroyave Godoy³, Mónica Eliana Díaz Roa⁴

 

¹ Dentist, Specialist in Orthodontics, Fundación Universitaria San Martín, Bogotá, Colombia

² Dentist, Specialist in Epidemiology. Research Professor, Graduate School of Dentistry, Fundación Universitaria San Martín, Bogotá, Colombia. Email address: barrerajudith@gmail.com

³ Dentist, Specialist in Orthodontics, Fundación Universitaria San Martín, Bogotá, Colombia

⁴ Dentist, Specialist in Orthodontics, Fundación Universitaria San Martín, Bogotá, Colombia

 

SUBMITTED: MAY 8/2012-ACCEPTED: JULY 30/2013

 

Bonilla MM, Barrera JP, Arroyave ÁP, Díaz ME. A comparison of angle measure reproducibility between manual and computerized tracing. Rev Fac Odontol Univ Antioq 2014; 25 (2):.

 

 

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ABSTRACT

INTRODUCTION: digital cephalometry allows handling errors produced during manual tracing; the purpose of this study was therefore to evaluate the reproducibility and precision of angle measures between manual tracing and that obtained with Cephapoint in digital radiography. METHODS: 11 direct digital radiographs taken to orthodontics students were introduced in the Cephapoint computer program. 9 angles were measured in both hand-tracing digital radiography and Cephapoint. All measurements were made by 3 operators with 1-week interval. We calculated the average interobserver error to find the reproducibility of each angle measure, and the average intra-observer error to determine the accuracy of each observer. RESULTS: : the FH/N/Pg angle showed the smallest interobserver error difference (0.10°) in both methods, favoring manual tracing. On the other hand, the angles with the smallest inter-observer error difference in computerized tracing were LI-NB (0.11°) and N-A/Pg (0.11°). Intraobserver reproducibility showed excellent Intraclass Correlation Coefficient (ICC) in both methods. CONCLUSIONS: reproducibility of angular measurements did not show significant differences between manual and computerized tracing. According to the findings of this study, the methods under evaluation offer equal diagnostic validity.

Key words: cephalometry, reproducibility of results, radiography, radiographic imaging by dual photon emission.

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INTRODUCTION

In orthodontics, a great deal of treatment success and patient satisfaction depend on aspects such as diagnosis, treatment options, and the operator's skills. Timely and appropriate diagnosis is essential to establish treatment goals, with various means and tools available, including cephalometric tracing, which has been used since 1930 to evaluate anthropometric data.¹ This technique consists of taking measurements on a radiograph of the patient's skull, where points are located, planes are traced, and angles are measured. The results are compared with measures previously established by several studies.^2-6 These studies have achieved the standardization of methods of analysis so that cephalometric tracing is now considered a reliable diagnosis technique⁷

Tracings can be made manually or digitally, with computer programs such as Quick Ceph,⁸ Dolphin Imaging,^9-12 or VistaDent,¹³ which provide accurate diagnosis besides offering ways to storage patients' images.¹⁴

Proper manual tracing provides results comparable to those obtained with cephalometric analysis performed with computerized methods, so it is considered a reliable method with high clinical validity.^{15, 16}

Cephalometric analysis errors can be systematic or random; the latter include errors of location and identification of reference points, as well as measurement errors.¹⁴ Digital cephalometry can eliminate the systematic errors produced during the manual method while tracing lines between points of reference and taking measurement with a protractor.¹⁴

Recently, Bonilla et al¹⁷ conducted a study to determine the reproducibility of 14 cephalometric points in hard tissue. For this study, they created and used Cephapoint, a software that allows landmark identification on a computer monitor directly with the cursor. They used a sample of 22 films, 11 digital and 11 conventional radiographs, each pair taken on the same patient and with the same equipment; they took the digital radiograph first followed by the conventional one. They found out that all the points present similar reproducibility in both types of radiograph, with the least inter-observer error in direct digital imaging. The authors recommend conducting further research to assess angular measurements in direct digital radiography and to compare it to other methods,

The objective of this study was to assess angle measure reproducibility between manual tracing and that obtained with Cephapoint on a digital image.

 

METHODS

This was a concordance study on 11 profile direct digital radiographs taken by orthodontic students and used in a previous study by Bonilla et al.¹⁷

The radiographs were taken in the natural position of the head by a trained operator. Each participant was taken one direct phosphoactivated digital radiographic image with an FCR CAPSULA X® equipment, which immediately transfers the image to the computer monitor. Each participant's radiographic image was exported to Cephapoint, a computer program designed in a previous study.¹⁷

A selection of angle measures was performed, and three observers clearly determined their locations, as follows: position of the maxilla with respect to the base of the skull, which is measured by the angle formed by the planes going from the Sella Turcica to Nasion and from Nasion to point A (SNA); position of the mandible with respect to the base of the skull, an angle taken at the intersection of the Sella Turcica to Nasion and from Nasion to point B (SNB); upper incisor inclination, an angle formed by the longitudinal axis of the most vestibular upper incisor and the palatal plane (U1-PP); Lande's angle, formed by the intersection of the Frankfort plane and the line that goes from Nasion to point A (FH/NA); facial depth, an angle formed by the Frankfort plane and the line from point A to Pogonion (FH/N/Pg); angle of hard tissue convexity, formed by the intersection of the planes going from Nasion to point A and from point A to Pogonion (N-A/Pg); inclination of the lower incisor with the NB angle formed by the longitudinal axis of the most vestibular lower incisor and the plane going from Nasion to point B (LI/NB); nasolabial angle, formed by the intersection of the planes going from Columella to Subnasale and from Subnasale to Labrale superius (Cm/Sn/Ls); and the soft tissue convexity angle taken at the intersection of the plane between the Glabella of soft tissue and Subnasale, and the plane that goes from Subnasale to the Pogonion of soft tissue (G'/Sn-Pg').

All these manual tracings were made using digital radiography printing on radiographic paper, with a DRY PIX 2000 printer (FUJI FILM USA®), a corrected 1:1 scale, and a negatoscope under artificial light. A same operator made the profilograph for each digital radiograph, which was made 3 times in order to avoid differences greater than 1 mm among the traced anatomical structures. We also used cephalometric paper (Ortho Organizers®) 0.76 mm thick (0.03 inches), and a HB 0.5 mm lead (Faber Castell®). A millimeter ruler (Faber Castell®) was used for plane tracing, and a Bimler appliance was used for measurements. The three observers made the manual tracing of angles for each digital radiograph.

In this study, the average position for each angle measure identified by the three observers was defined as the "benchmark". This benchmark was used to determine interobserver errors in manual and digital tracing. The average differences in degrees between the benchmark and the measurements made by the observers were defined as interobserver error, and this in turn was used as the variable that determines reproducibility for each angle measure. As a result, reproducibility in the identification of angle measures for each method (manual and digital) could be defined as the differences in magnitude of these distances from the average between the two types of tracing.

According to each observer's measurements, intra-observer precision or error is defined as the level that indicates how close are the angular measurements obtained during the first and second observations with weekly intervals. It is obtained by comparing the measures of each operator and is calculated by means of intraclass correlation coefficient (ICC). Figure 1 shows the study design.

 

STATISTICAL ANALYSIS

The data were collected in Microsoft Excel 2007, and analyzed in the statistical program for Social Sciences SPSS, version 15.0. The quantitative variables were analyzed through averages and standard deviations. To compare manual and computerized tracing, we used Student's- t test for independent groups and the Levene test for equality of variances. We used a significance level of α = 0.05 for all the tests, and confidence intervals with 95% reliability.

 

RESULTS

In the measures taken in both the manual digital radiograph tracing and the digital radiograph image imported to Cephapoint, the interobserver error and standard deviation displayed in table 1 shows levels above 7.9° in these two angles: Cm/Sn/Ls and U1-PP in both methods (manual and digital tracing).

table 1

En el trazado manual, los ángulos que presentaron mayor diferencia en el promedio de error interobservador, comparado con el trazo digital, fueron: G'/Sn-Pg' (0,32°), II-NB (0,11°) y N-A/Pg (0,11°). En el trazado computarizado, los ángulos que presentaron mayor diferencia en el error interobservador, fueron SNA (0,52°), U1-PP (0,52°), Cm/Sn/Ls (0,47°), SNB (0,21°), FH/NA (0,20°) y FH/N/Pg (0,10°). Al comparar el promedio del error interobservador entre el trazo manual y el computarizado, no se encontraron diferencias significativas. (p ≥ 0,05).

In most of the angles, the level of inter-observer error dispersion was lower in manual tracing, as the standard deviation data indicate (table 1).

When comparing both tracing methods in terms of their standard deviations, the greatest differences were found in the manual method for these angles: FH/NA, G'/Sn-Pg', N-A/Pg, and SNA, and for the computerized method in Cm/Sn/Ls, FH/N/Pg, LI-NB, SNB, and U1-PP, with no significant statistical differences.

The FH/N/Pg angle had the smallest interobserver error difference (0.10°) in both methods, favoring the manual tracing; also, the angles with the smallest inter-observer error difference in computerized tracing were LI-NB (0.11°) and N-A/Pg (0.11°). While SNA (0.52°) and U1-PP (0.52°) were the angles with the greatest inter-observer error difference for the manual method, and G'/Sn-Pg' (0.32°) was the angle with the greatest inter-observer error difference for the computerized method.

As for the evaluation of intra-observer accuracy or error, the manual method showed an excellent intraclass correlation coefficient (ICC), being over 0.9 for all the measurements, except for FH/NA, which was 0,847 (Observer 2) (table 2).

table 2

In the computerized method, the ICC was above 0,844, with the exception of angle N/FH/Pg, which was 0,784 (Observer 2), and N-A/ Pg, which was 0,793 (Observer 1) (table 3).

table 3

 

DISCUSSION

The present study showed that inter-observer error averages of manual versus computerized tracing did not present significant differences between both methods; However, there were higher values for the SNA and U1-PP angles in computerized tracing, and for G'/Sn-Pg' in manual tracing.

Concerning the SNA angle, some authors1, ^12-18 maintain that the computerized method shows a decrease in cephalometric measurement differences, and is therefore a more accurate method due to different software characteristics such as pixels, contrast and brightness. These factors make it a more reliable method, especially when benchmark location must be done in a contour with bone depth, such as A, B and N. The location of these benchmarks is important when determining the magnitude of horizontal discrepancy in the maxilla, in an angular measurement like SNA, so that benchmark errors along the horizontal axis would be more significant than errors along the vertical axis.¹

In this sense, any change in the horizontal position of point A means a significant change in SNA results. Selecting a benchmark in cephalometric analysis is important for successful diagnosis and treatment planning.¹ Accordingly, Lim et al¹⁸ found out that anatomical benchmarks with low radiodensity, such as point A, tend to be less reliable to identify in computed radiography.

The results obtained for the U1-PP angle in the present study are similar to those obtained by Collins et al,¹⁹ who suggest that the maxillary and mandibular planes in a radiograph are marked between two points that are difficult to locate. In addition, they claim that the increase in measure variability occurs because it is necessary to digitize four points to measure certain angles (U1-PP), and 3 points for other angles (SNA and SNB). Other reasons for this variation are root superposition, which makes it difficult to accurately locate apices,^{12, 20} and the lack of contrast in this area,¹² which makes the measures related to the root apices of the incisors located in the benchmarks less reproducible.^{21, 22} Similarly, Bonilla et al¹⁷ found differences in the X and Y axis for ENA and ENP, both in the conventional image and the digital one; this alters the reproducibility of these points and affects the correct tracing of the palatal plane.

The G'/Sn-Pg' angle presented greater inter-observer error difference in the manual tracing, since the Subnasale point has a higher average error on the X axis; also, it is hard to locate the Pogonion on a curve, as reported by Chen.²⁰

In this study, the FH/N/Pg angle showed less inter-observer error, i.e., high reproducibility in both methods, contrasting the report by Sayinsu et al¹¹ for whom all the parameters with lower correlations were measures related to the Frankfort plane, which goes through the Porion and the Orbital. Similarly, other authors^{12, 20, 24} observed that the Porion is located in complex radiopaque structures that overlap to each other, and the Orbital point is more inexact, probably due to the narrow vertical alignment on the left and right sides of the orbits.⁹ Likewise, Bonilla et al¹⁷ found out that the Porion presented greater standard deviation on the Y axis, and the Infra-orbital point on the X axis in conventional imaging. This is consistent with Geelen et al,²¹ who found extensive error distribution dispersion in both axes, indicating an inexact point. Similarly, McClure et al⁹ reported that the Pogonion is located on the Menton contour curve, and therefore this point may be difficult to identify.

In this study, the Cm/Sn/Ls angle was within the highest inter-observer error averages in computerized tracing. Concerning this measure, some authors²⁴ report that the Nasolabial angle is a measure with great clinical relevance in soft tissue analysis, requiring the construction of two lines along the bottom contour of nose and lip. However, there are large variations among the tracing methods, as other studies indicate.^{3, 25-27} On the other hand, Hwang et al²⁴ found significant differences and low reproducibility for the Nasolabial angle when using the tangent line tracing method, a result that was attributed to the anatomical shape ("S" shape) of the lower part of the nose, and not to the lack of coherence in tangent construction. They also concluded that variability in the elaboration of a tangent on the upper lip contributes to the low reproducibility of the Nasolabial angle. In another study, Swennen et al¹² found no statistically significant differences between the methods of analysis and the image format, with the exception of the Nasolabial angle, which exceeded the clinical significance. The difficulty in constructing this angle is therefore evident.

The values seen in table 1, with respect to inter-observer error averages, correspond to the average of angles obtained for manual and computerized tracing. The malocclusion type was used as a sample inclusion criterion, and therefore the values in the table reflect this variability among the angles measured; this is why the analysis of results was based on the differences between the methods.

All the intraclass correlation coefficients (ICC) indicate high levels of precision in both methods; however, a lower correlation for the FH/NA angle was found in manual tracing, and for FH/N/Pg, N-A/Pg angles in the computerized method.

According to the results of the present study, the differences in these methods are not clinically relevant, so the application of either analysis does not affect diagnosis. Regardless of the method used, the clinician must be trained and calibrated for it.¹¹ Therefore, the choice of the method of analysis depends on the orthodontist's criterion in terms of advantages, disadvantages, cost, time, accessibility, and comfort.

 

CONCLUSIONS

Angle measure reproducibility between manual and computerized tracing methods did not show significant differences, suggesting that both methods offer equal diagnostic validity.

 

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