FACTORS AFFECTING THE CUTTING ABILITY OF SONIC FILES

The aim of this study was to investigate the cutting ability of sonic files, A model system was developed and the following variables evalua ted: file type, Heliosonic or Shaper; file length, 21 or 29 mm; power, air inlet ring opening of half or fully open; stroke length, 2 or 4 m m; stroke rate, one or two cycles per second; and load 50 or 100 g. A 2(6) full-factorial analysis with two replications into the effect of the above variables on the cutting ability of the MM1500 sonic instrum ent was performed, A new size 25 file was used for each cut, together with water irrigation, and the substrate used was l-mm thick sections of bovine bone, The differences between the variables were significant (ANOVA, P < 0.001), However, examination of the F-values showed that the most significant variable to affect cutting was load, followed by power, file type, stroke length and stroke rate, with the least signif icant variable being file length, The most significant interaction was between rate and length of stroke. An increase in stroke rate from on e to two cycles per second at a stroke length of 2 mm produced an incr ease in cutting for both the Heliosonic and Shaper files, However, at the longer stroke length of 4 mm, the same increase in rate resulted i n a decrease in cutting for the Shaper files, Therefore, it is suggest ed that operators should press the file against the canal wall and mov e it slowly to maximize cutting.