Orthodontic application of color image addition to visualize differences between sequential radiographs

A new technique was developed making it possible to visualize changes that take place after premolar transplantation. Three sequential radiographs fro m a series of standardized control examinations were digitized and register ed to the first radiograph in the series using subtraction technique. The d igitized radiographs were then transformed into monochromatic images: red, blue, and green, After correction of gray level and contrast, the three rad iographs were superimposed. All details that were common in the radiographs were then displayed in black-and-white. Details that were different appear ed in color. Red and blue combines into magenta, blue and green into cyan, and green and red into yellow. A procedure was developed to create color-co ded radiographs according to the above. The procedure was applied to cases that had been treated by premolar transplantation. The color coding offers the possibility to identify any radiographic changes that take place over t ime, eg, growth, apposition or resorption of bone, and progression or regre ssion of pathological processes.