Dentine-removing characteristics of an ultrasonically energized K-file

This in vitro study evaluated the pattern of dentine removal when an ultrasonically energized file (Cavi-Endo-size 25 file) was applied to flat surfaces of dentine under standardized conditions. The influences of power setting, interfacial force between file and dentine, direction of file oscillation and operator-assisted movement were examined. Impressions of the instrumented surfaces revealed characteristic patterns consisting of a series of oblique crests, each one parallel to the next and separated by a constant distance along the line of contact with the file. Determination of height, width and separation of these crests with a Reflex microscope aided objective assessment. The simplest pattern was formed when the energized file was held against the dentine (power setting = 1; interfacial force = 30 g). Increasing the power setting to 8 caused deeper troughs over the apical 5 mm. The width of the crests corresponded to the taper of the file except at the apical tip where the crests were relatively wider. However, increasing the interfacial force to 60 g reduced the efficiency of the apical part of the file. The superimposition of operator-induced movement greatly increased the extent of dentine removal, resulting in a tapering groove with a persistent crestal pattern. Oscillation of the file perpendicular to the dentine surface had a significantly greater influence on dentine removal, producing a deeper groove than was obtained with oscillation parallel to the surface. These findings may be of relevance in aiding controlled root canal preparation when using the Cavi-Endo instrument.