Influence of the rotation centre in panoramic radiography.

The aim is to present the curve of the rotation centre in dental panoramic radiography and to examine its influence on organ doses. A screenless film was fixed between the layers of an Alderson Rando phantom in the centre of the mandible. The phantom was positioned in two different X-ray units [Scanora (Soredex, Helsinki, Finland) and Orthophos (Sirona, Bensheim, Germany)] and exposed. Organ doses and effective doses were determined. The curves of the rotation centre showed clear differences especially in the area of the parotid gland. These differences corresponded to the differences in organ doses and in effective doses (Scanora: 29.9 microGy; Orthophos Plus: 14 microGy). Artefacts might be shown (Orthophos, result of a plate osteosynthesis) or not (Scanora) due to the different rotation centres. Differences in organ doses and in image quality, e.g. artefacts, were explained with the curve of the rotation centre and beam geometry.