Radiographic measurement of residual root thickness in premolars with postpreparation

A minimum thickness of 1 mm has been suggested for the residual root wall i n post preparation. The objective of this paper is to evaluate the reliabil ity of radiography when used to measure root thickness. In 106 upper first premolars with one and two root canals, post preparations were made with Pe eso reamers to a depth in the root equal to the crown length. Bucco-palatal radiographs were taken of each tooth. The films were processed and project ed with a magnification of x20. The smallest thickness of the mesial and di stal walls of each root at the apical end of the preparation was measured a nd recorded. The teeth were then cut at the level of the measurement, and t he smallest thickness of the proximal wails was measured using a microscope with a micrometric eyepiece. Fourteen percent of the teeth with one root c anal and 27% of the teeth with two root canals could not be measured due to blurred radiographic contours. Variance analysis showed a highly significa nt difference (p < 0.001) when radiographic and anatomical measurements wer e compared. The radiograph showed greater thicknesses than were actually pr esent and should not therefore be considered to be a reliable method for me asuring residual thickness of tooth wails after post preparation.