SHAPING ABILITY OF THE M4 HANDPIECE AND SAFETY HEDSTROM FILES IN SIMULATED ROOT CANALS

The aim of this study was to assess the shaping ability of the M4 reci procating handpiece and Safety Hedstrom files in simulated canals, A t otal of 40 simulated canals of various angles and positions of curvatu re were prepared with an M4 handpiece using Safety Hedstrom files orie nted with the ground, flattened surface towards the inner aspect of th e curve, A standard regimen was adopted throughout, Pre- and post-oper ative longitudinal images of the canals were taken with a video camera and stored and manipulated in a computer with image analysis software . The presence of canal aberrations and the amount and location of res in material removed as a result of preparation were determined from co mposite images of superimposed pre- and post-operative views. Preparat ion time varied significantly (P < 0.001) between the canal types; ove rall, 20 degrees canals were prepared more quickly than 40 degrees can als, Zips and elbows were observed in 16 out of the 40 canals with mos t (11) being created in 40 degrees specimens. Ledges were found in 19 canals and perforations in only 1. There were no significant differenc es between canal shapes for these aberrations. Excessive removal of ma terial from the inner aspect of the canal at the curve to create a dan ger zone was found in 20 canals, but only in those with 40 degrees cur ves, Significant differences in total canal width between the canal ty pes were seen at the zips (P < 0.05), elbows (P < 0,05) and danger zon es (P < 0.001). Transportation at the danger zones varied significantl y (P < 0,001) between canal types, Under the conditions of this study, the M4 handpiece and Safety Hedstrom files created hour-glass prepara tions in a substantial proportion of canals, In reality, the Safety He dstrom file with its one flattened surface was ineffective at reducing removal of material along the inner aspect of canal curves in severel y curved specimens and clearly has the potential to create strip perfo rations in teeth.