Measurement of endodontic file lengths: Calibrated versus uncalibrated digital images

This in vitro study compared the accuracy of file length measurements made on calibrated and uncalibrated direct digital images. Endodontic files of k nown lengths and ISO sizes were used in 10 single-rooted, relatively straig ht teeth within cadaver specimens. The crowns of the teeth were ground flat and an orthodontic wire of known length was secured to the coronal surface . This wire was placed mesiodistally and perpendicular to the root and serv ed as the reference point for the file measurement and as a calibration ref erence length. A #20 file was hand-measured to a length that reached the ap ical third of each tooth. It was inserted and a radiographic image was secu red. The instrument was remeasured three additional times at different leng ths on the same tooth and reinserted before each image acquisition. Thus 40 digital images were acquired using a GE X-ray unit and a Schick Computed D ental Radiography (CDR) #2 sensor. These images were placed in random order , and an independent, blinded investigator determined the file lengths usin g on-screen calibrated and uncalibrated measurement of the CDR image with a straight-line and multiple-line measuring technique. The experimental meas urements were compared with each other and with the known clinical measurem ents. A two-way analysis of variance indicated that there was a statistical ly significant difference showing that the calibrated measurements were mor e accurate than the uncalibrated measurements (p = 0.0001), and there was n o significant difference between the straight-line and multiple-line measur ing techniques (p = 0.14).