Factors affecting the cutting ability of sonic files

An in vitro comparative study of intracanal fluid motion and wall shear stress induced by ultrasonic and polymer rotary finishing files in a simulated root canal model

Objective. This in vitro study compared the flow pattern and shear stress of an irrigant induced by ultrasonic and polymer rotary finishing file activation in an acrylic root canal model. Flow visualization analysis was performed using an acrylic canal filled with a mixture of distilled water and rheoscopic fluid. The ultrasonic and polymer rotary finishing file were separately tested in the canal and activated in a static position and in a cyclical axial motion (up and down). Particle movement in the fluid was captured using a high-speed digital camera and DaVis 7.1 software. The fluid shear stress analysis was performed using hot film anemometry. A hot-wire was placed in an acrylic root canal and the canal was filled with distilled water. The ultrasonic and polymer rotary finishing files were separately tested in a static position and in a cyclical axial motion. Positive needle irrigation was also tested separately for fluid shear stress. The induced wall shear stress was measured using LabVIEW 8.0 software.

Comparison of two endodontic handpieces during the preparation of simulated root canals

The objective of this in vitro study was to compare and assess two endodontic handpieces during the preparation of simulated root canals. One hundred and sixty simulated root canals in clear resin blocks, of two angles and positions of curvature, were prepared using either Shaper files activated by the MM1500 Sonic Air handpiece (Micro-Mega, Besançon, France) or Excalibur files activated by the W & H Excalibur 969 handpiece (W & H, Bürmoos, Austria). Files of 21-mm or 25-mm length were used. When preparing the canals, the files were used either in line with or perpendicular to the canal curvature. Preparation of the canals was carried out using a technique described in the manufacturers' literature. A variety of parameters were used to compare the handpieces, including an assessment of the canal preparation time, the deformation or fracture of instruments, loss of canal length, weight loss from the resin blocks and the overall postpreparation canal shape. Both handpieces provided an efficient and easy method of preparing and shaping the root canal with little operator fatigue. The MM1500 Sonic Air handpiece took significantly more time (P < 0.001) to prepare the canals and was associated with both more loss of working length (P < 0.05) and more loss of weight (P < 0.001). Both handpieces created a high percentage of aberrations in the shapes of prepared canals. The MM1500 Sonic Air handpiece created significantly more aberrations than the Excalibur handpiece (P < 0.05 for zip and elbow, P < 0.05 for danger zone and coronal narrow). The effects of the variables, canal curvature, file length and the plane of use of the file, on the performance of the handpieces, were also assessed.

Intra-canal cutting ability of MM1500 files

The aims of this study were to develop a model system capable of monitoring lateral forces during root canal preparation and to measure the cutting ability of files activated by the MM1500 sonic handpiece. Forces were monitored by a calibrated model system which utilized a combination of spring steel beams fitted with strain gauges, these were interfaced through two strain gauge amplifiers to an x-y recorder. Single rooted canine teeth (n = 36; 32 experimental, four control) were mounted in a two-part acrylic mould (which was an integral part of the model system) prior to sectioning horizontally 11 mm from the tooth apex. A 2(4) full factorial experiment with two replications was performed. Four 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 used for 1 min in each canal with water irrigation. The control group was 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 significant increase in cutting ability (ANOVA, P < 0.001). However, stroke rate was not found to have a significant effect (P > 0.05). None of the interactions between the variables were significant and there was no significant difference in the control group (P > 0.05). In conclusion, this work has developed a model system to monitor lateral forces and has shown that instrument design and operator usage affect dentine removal from a root canal wall.