A survey of interfacial forces used during filing of root canals

The pattern of dentine removal during endodontic instrumentation is influen ced by many factors including the interfacial forces applied by the operato r. The aim of this study was to investigate the influence of operators and different sizes and types of instruments on the magnitude of these interfac ial forces. Single-rooted teeth were mounted on a cantilevered aluminium be am to which two pairs of single element strain gauges were joined in a half -bridge configuration and mounted at right angles to each other. The strain gauges were connected to an analogue-to-digital converter fitted in a micr o-computer via conditioning amplifiers. This enabled strains to be recorded over a period of time. Twenty operators instrumented root canals using a s eries of hand instruments for 1 min each. The mean interfacial forces used by operators demonstrated a wide variation ranging from 9.06 g to 149.42 g (range of forces from 0-331 g) but there was a consistency in the relative magnitude for each operator. The 20 operators could be divided into 13 grou ps which were significantly different (alpha = 0.05) from each other. There were significant differences (alpha = 0.05) between the forces used for ea ch of the K-Flex files (15, 25, 35, 45, and 70), the force increasing with the file size. There was also a significant difference (alpha = 0.05) in th e forces used between the Flexofile (#25) and the #25 K-Flex and Hedstrom f iles. However, there was no significant difference between the K-Flex and H edstrom files.