Image processing and analysis program for measurement of bone density changes in reference and follow-up standardized extraoral oblique lateral cephalometric radiographs of the mandible

The aim of this study was to develop an image processing and analysis program for peri-implant bone density measurements of the mandible using extraoral radiographs, which includes a correction for the variable projection of the soft tissues of the face. The measurement procedure is based on pairs of reference and follow-up extraoral oblique lateral cephalometric radiographs (OLCRs) of patients with endosseous implants in the anterior part of the atrophic edentulous mandible. The procedure consists of image acquisition, correction for radiographic variation using an aluminium wedge (i.e. film exposure and development) and transformation of the grey values into aluminium-equivalent values. After correction for variation in the projection of the soft tissues of the face using internal calibration fields, the actual peri-implant bone density measurements are performed. The soft tissue projection correction significantly reduces the variation between radiographs owing to the position of the soft tissues. It is concluded that the described image processing and analysis program, in combination with extraorally made OLCRs, is a valuable technique for measurement of peri-implant bone density changes of the mandible. With minor adaptations, the program can be used for other semi-edentulous patients