A survey of interfacial forces used during endosonic instrumentation of root canals

Aim The aim of this in-vitro study was to measure interfacial forces acting between root canal dentine and ultrasonic files during endosonic instrumen tation. Methodology 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 mounted at right angles to each other. The strain gau ges were connected to an analogue-to-digital converter fitted in a microcom puter via a conditioning amplifier. This enabled strains to be recorded as a function of interfacial forces over a period of time. Twenty operators in strumented root canals using sizes 15, 20 and 25 ultrasonically energized K -type files. The lateral forces generated were calculated. Results The mean interfacial forces used varied widely between operators an d files, ranging from 18 g to 149 g, but there was a consistency In the rel ative magnitude for each operator. The average force used by the operators increased with file size; the differences between file sizes were significa nt (P < 0.05). Conclusions The range of forces measured is broader than previously reporte d and may have a bearing on possible uncontrolled dentine removal, even dur ing ultrasonically activated irrigation.