Table 2 Publications concerning landmark identification

Baumrind and Frantz [21]

Quantification of errors in landmark identification

5 observers

20 lateral skull radiographs

Observer identified 16 cephalometric landmarks on a transparent plastic template

Mean, standard deviation and standard errors

Least reliable landmarks: gonion and lower incisor apex

Moderate

Effects of errors on angular and linear measurements

Kvam and Krogstad [27]

Evaluation of measurements in lateral cephalograms.

18 observers

3 lateral skull radiographs

Hand cephalometric analysis made by each participant, 8 angles measured

Mean and standard deviation

16 out of 24 angular measurements: less variability in post-graduates than students

Low

Assess influence of knowledge and impact of angular errors

In 7 measurements, no difference was observed

Post-graduates' tracings used for diagnostic purposes

Standard deviation of students greater than post-graduates

Haynes and Chau [22]

Evaluation of landmark identification on Delaire analysis

2 observers

28 lateral skull radiographs

Establish a co-ordinate system for measurement on tracings

Mean deviation

Intra-observer: NS differences between values of T1 and T2 tracings

Moderate

Comparison with data of conventional cephalometry

Radiographs were traced twice by each observer (3 to 4 weeks)

Inter-observer: differences between the averaged mean values on tracings were NS for either x or y co-ordinates

Ahlqvist et al. [26]

Study the magnitude of projection errors on measurements in cephalometry

1 observer

A patient was modelled

Computer software designed to allow movement of model on the 3 axes. The magnitude of errors was studied by a diagram

Measurement errors studied by a diagram with the relative length of distances between modelled landmarks

Less than 1% error on length measurements if head is rotated up to 5°

Low

Study the effects of incorrect patient position on linear measurements

Head rotated more than 5° the error is increased

Houston et al. [23]

Evaluate errors at various stages of measurements in cephalometric radiograph

4 observers

24 lateral cephalograms

2 radiographs of the same patient

Analysis of variance

Error variance is small (radiograph and tracing) when compared with the variance among groups

Moderate

Radiographs traced on acetate sheet by each observer at T1/T2 (1-week interval)

SNA has a higher tracing variance than SNB due to the difficulty to identify point A

Kamoen et al. [24]

Determine errors involved in landmark identification and its consequence to treatment results

4 observers

50 lateral cephalograms

Items studied: (1) accuracy of digitiser, (2) intra- and inter-observer digitising errors and (3) intra- and inter-observer tracing errors

(1) Levene's test for homogeneity of variances, (2) one-way ANOVA and (3) Levene's test for homogeneity

(1) NS variances of co-ordinates for landmark at different positions on the digitiser. (2) NS intra- and inter-observer differences in digitisation. (3) S differences in landmarks and in the same landmark on different cephalograms and between observers

Moderate

Tng et al. [25]

Evaluate the validity of dental and skeletal landmarks. Effect on angles and distances.

1 observer

2 lateral cephalograms of 30 dry skulls

Steel balls placed in 15 dental and skeletal landmarks

Mean and standard deviation

7 out of 10 skeletal and 5 dental landmarks were NS (p < 0.05)

Moderate

Two radiographs taken with and without the markers and digitised. Measurements compared

4 angles (SNA-SN/MnP, MxP/MnP and LI/MnP) and 3 distances (N-Me, MxP-Me and Lie to APg) were invalid (p < 0.05)

Major errors in angles with dental landmarks

Bourriau et al. [5]

Analyse the influence of film-object distance and type of receptor on landmark identification

53 orthodontists

4 lateral cephalograms of the same patient

19 cephalometric landmarks on each film

Mean

NS difference between 2 imaging receptors neither between 2 cephalograms achieved by 2 equipments (p > 0.99)

Low

2 radiographs performed at an equipment with a 4-m arm and 2 in a 1.50-m arm equipment with 2 different imaging receptors (digital and indirect digital)

Results obtained by cephalometric analysis was judged: ‘very important’ for 20.5%, ‘important’ for 70%, ‘less important’ for 8% and ‘accessory’ for 1 participant