INTRA-CANAL CUTTING ABILITY OF MM1500 FILES

The aims of this study were to develop a model system capable of monit oring lateral forces during root canal preparation and to measure the cutting ability of files activated by the MM1500 sonic handpiece. Forc es were monitored by a calibrated model system which utilized a combin ation of spring steel beams fitted with strain gauges, these were inte rfaced through two strain gauge amplifiers to an x-y recorder. Single rooted canine teeth (n = 36; 32 experimental, four control) were mount ed in a two-part acrylic mould (which was an integral part of the mode l system) prior to sectioning horizontally 11 mm from the tooth apex. A 24 full factorial experiment with two replications was performed. Fo ur variables were selected for evaluation, load (50 and 100 g), power (air inlet ring half or fully open), file type (Heliosonic or Shaper) and stroke rate (1 or 2 cycles per second). A new file (size 25) was u sed for 1 min in each canal with water irrigation. The control group w as not instrumented. The cross-sectional root canal area was measured before and after instrumentation using image analysis and increase in area was used as an indication of cutting ability. The results showed that the increase in load, power and the Shaper file all produced a si gnificant increase in cutting ability (ANOVA, P < 0.001). However, str oke rate was not found to have a significant effect (P > 0.05). None o f the interactions between the variables were significant and there wa s no significant difference in the control group (P > 0.05). In conclu sion, this work has developed a model system to monitor lateral forces and has shown that instrument design and operator usage affect dentin e removal from a root canal wall.