DENSITOMETRIC MEASUREMENTS OF THE MANDIBLE - ACCURACY AND VALIDITY OFINTRAORAL VERSUS EXTRAORAL RADIOGRAPHICAL TECHNIQUES IN AN IN-VITRO STUDY

In this study a comparison is made between intraoral and extraoral rad iographical techniques for quantitative measurements of bone density i n the edentulous mandible. A phantom model, composed of a dry mandible surrounded by a soft tissue substitute was used. Radiographs were mad e of aluminium implants of known volumes. Intra- and extraorally place d reference wedges of aluminium or a combination of aluminium and plex iglas were used for the measurement of the aluminium volume of the abo ve-mentioned implants and compared with the real volume. The IBAS imag e analysis system was used for image processing and measurements. A sy stematic deficit in the measured volume of 15 to 29% was found. This e rror was irrespective of the radiographical technique and indicates a constant underestimation of the aluminium volumes. The differential in fluence of the secondary radiation on the images of the jaw and the we dge is proposed to be a possible cause of this constant underestimatio n. The intraoral and extraoral techniques do not display significant s tatistical differences in the levels of validity or accuracy. Obtainin g serial intraoral radiographs of adequate quality in the atrophic ede ntulous mandible can be problematic. It is concluded from this in vitr o study that in these cases Oblique Lateral Cephalometric Radiographs may provide a valuable alternative for quantitative image analysis.