Factors affecting the wear of sonic files.

The aim of this study was to investigate factors affecting the wear and cutting ability of sonic files. A model system was used and the following variables evaluated, file type; Heliosonic, Rispisonic or Shaper, load; 25, 50 or 100 grams and length of time in use; new, 30 or 60 seconds. A 3(3) full factorial analysis with two replications into the effect of the above variables on the cutting ability of the Heliosonic, Rispisonic and Shaper files powered by the MM1500 sonic instrument was performed. A new file size 25 (Heliosonic and Shaper) or No 3 (Rispisonic) was used for each cut together with water irrigation and the substrate used was 1 mm thick sections of bovine bone. All variables had a significant effect on cutting (ANOVA. p < 0.001). However examination of the F values showed that the most significant variable was load, followed by file type, and time. The most significant interaction was between file type and load followed by time and file type. The interaction between time and load was not significant (p > 0.05). The Rispisonic file was most susceptible to wear during use especially at higher loads and the Heliosonic file cut least. It is suggested that the Shaper file is the better design of the three with respect to cutting ability and wear with use.