Material and methods

The sample PA radiographs of this study, which had the same resolution and quality, were gathered randomly from the 10-year archive at the Department of Orthodontics, Faculty of Dentistry, of Yeditepe University, Istanbul, Turkey. The radiographs belonged to 39 asymmetric patients (20 women, 19 men) ranging in age from 18 to 45 years (mean ± SD, 31.3 ± 12.2 years). The following were the inclusion criteria: no cleft and lip, and no diagnosed systemic diseases or craniofacial syndromes. Patient data were handled according to the requirements and recommendations of the Declaration of Helsinki. Ethical approval was obtained from the institutional review board of Yeditepe University. The cephalometric radiographs used in this study were created using a Promax x-ray device (Planmeca, Helsinki, Finland) with the patients were in natural head position. Source to ear rod distance was 160 cm, and ear rod to film distance was 17.5 mm. All radiographs were covered with tracing paper. For each radiograph, an individual coordinate system was formed. On each corner of the paper, a large plus sign was drawn to trace the papers identically, and the sign on the upper right corner was used used as the x and y coordinates ( Fig 1 ). The tracings were made by 2 operators (F.U. and D.G.C.), who are experienced orthodontists, after a calibration session with the written definitions of the points and practical trials were carried out together. A total of 29 landmarks were marked on tracing paper manually using a 0.1-mm pen (Ecco pigment; Faber-Castell, Stein, Germany): 22 landmarks were bilateral, and 7 were on the midline. The list and the definitions of landmarks marked on each PA cephalometric radiograph are given in Table I . The operators repeated the tracings 1 month later.

PA cephalometric landmarks and coordinate system used in the study.

The tracing papers were scanned into digital format at 300 dpi using a scanner (1680 Pro; Epson, Nagano, Japan) with 1600 dpi imaging, 40 × 800 pixels per line, and 48-bit color depth for both film and reflective scanning, and displayed on a 15-in, 1024 × 768 high-pixel resolution monitor (model FP581, Benq, Taipei, Taiwan) with a pixel pitch of 0.297 mm, a contrast ratio of 450:1, and brightness of 250 candela per square meter. Each scanned paper was saved as a portable document file (PDF). The coordinate system was established with software (AutoCAD, 2004 version; Autodesk, San Rafael, Calif).

Statistical calculations were carried out with software (NCSS, Kaysville, Utah) for Windows. In addition to descriptive statistics (means, standard deviations), intraclass correlation coefficients (ICCs) were used for determining interexaminer and intraexaminer agreement for each cephalometric variable. ICC, derived from analysis of variance, assesses rating reliability by comparing the variability of the different ratings of the same subject to the total variation across all ratings and all subjects. It is a measure of the homogeneity of elements within clusters and has a maximum value of 1 when there is complete homogeneity within clusters. For the detection of interexaminer error, the mean of the 2 measurements done by each examiner was used. To better understand the disagreement seen for controversial points, Bland-Altman plots were used to explore the results in a graphic approach.

Results

The results showed that each operator was consistent in the repeated measurements (intraexaminer agreement) in most landmarks marked ( Table II ). ICC values of 0.75 or above are considered good, and those above 0.90 are excellent. In this section, landmarks with an ICC less than 0.90 are reported along with the millimeter difference between measurements for ease of comparison with previous studies.

One examiner (F.U.) had ICC values of 0.88 and 0.99 for the x and y coordinates of the left gonion. The mean difference of the 2 markings for this landmark was 0.37 ± 1.28 mm for the x coordinate ( Table III ). The x coordinate of the right mastoid process showed an ICC of 0.88 by 1 examiner (F.U.). The mean difference of the 2 markings for this landmark was 0.47 ± 0.35 mm for the x coordinate. The rest of the intraexaminer ICC values were mostly higher than 0.90 or 0.95, showing excellent agreement ( Table II ).

Table III

Mean difference and standard deviations of the landmarks, which have a confidence interval for intra- and interexaminer agreement between 75% and 90%

Landmark	Intraexaminer (F.U.)		Intraexaminer (D.G.C.)		Interexaminer marking 1		Interexaminer marking 2
	x-axis, mean difference ± SD	y-axis, mean difference ± SD	x-axis, mean difference ± SD	y-axis, mean difference ± SD	x-axis, mean difference ± SD	y-axis, mean difference ± SD	x-axis, mean difference ± SD	y-axis, mean difference ± SD
Gonion, left	0.37 ± 1.28	0.84 ± 0.09	0.29 ± 0.52	0.40 ± 1.11	0.73 ± 1.94	0.84 ± 0.31	0.84 ± 0.40	0.33 ± 1.02
Mastoid process, right	0.00 ± 0.69	0.65 ± 0.36	0.47 ± 0.35	0.35 ± 1.03	0.90 ± 0.12	0.93 ± 0.12	0.74 ± 036	0.90 ± 0.16
Zygomatic, right	0.20 ± 0.79	0.20 ± 0.58	0.27 ± 0.54	0.70 ± 0.61	0.41 ± 0.93	0.50 ± 0.58	0.34 ± 0.92	0.72 ± 0.32
Condyle superior, right	0.03 ± 0.60	0.29 ± 1.21	0.16 ± 1.35	0.02 ± 1.08	0.75 ± 0.97	0.71 ± 1.04	0.55 ± 0.97	0.40 ± 1.04
Crista galli	1.04 ± 0.68	0.31 ± 1.23	0.76 ± 0.85	0.24 ± 1.26	0.34 ± 0.73	0.60 ± 0.54	0.17 ± 0.86	0.52 ± 0.60

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