Detection of three-walled infrabony defects by subtraction radiography

An in vitro investigation was undertaken to establish the sensitivity of subtraction radiography for three-walled infrabony defect detection. After the creation of defects of controlled sizes in the interproximal regions of a dried mandible, subsequent radiographs were taken with the help of an occlusal stent. The radiographs were then digitized, and the images were enhanced by frame summation and averaging to reduce electronic noise. Further standardization was facilitated by the use of a step wedge on each radiograph and a computer program to correct variations in processing and exposure. The results show that defect resolution depended not only on the diameter of the defect but also on the mass of the adjacent bone. The smallest detectable lesion was 0.5 mm in diameter in the interproximal region of the premolars. In addition, a change in depth of 1 mm could be detected at the base of three-walled infrabony defects.