A comparison of the reproducibility of manual tracing and on-screen digitization for cephalometric profile variables.

The aim of this investigation was to analyse and compare the reproducibility of manual cephalometric tracings with on-screen digitization using a soft tissue analysis. A random sample of 20 lateral cephalometric radiographs, in the natural head posture, was selected. On-screen digitization using Viewbox 3.1.1.9 cephalometric software and manual tracing on a 1:1 printout of the image was carried out twice in different sessions 1 week apart. Differences were analysed using a repeated measurement analysis of variance with method, session, and method-session interaction as explaining variables. The differences were expressed as an absolute percentage of the overall mean. The findings of the present study indicate that the two measurement methods differ significantly for 11 variables (P = 0.001 to P = 0.042). The area around stomion was the least reproducible. Except for s-n(s)-unt, nasal protrusion, with the manual technique, all mean differences between sessions and between methods were less than 1 degree or 1 mm and were, on-screen, smaller for 13 variables compared with those traced manually. Absolute percentage differences of the overall mean were smaller for seven variables with the digital technique and three variables in the manual technique, while four manual variables and one on-screen variable exceeded 2 per cent of the overall mean. Although small significant differences were found, the clinical relevance remains questionable.