The effect of instrument precurving on transportation in simulated curved canals

The results of instrumentation studies in small curved canals using various instruments and techniques are not consistent. The amount of instrument precurving and a gradual or abrupt curve of the canal may have influenced the results of these studies. One hundred sixty resin blocks with simulated canals were used. Eighty blocks had gradual (GC) 30 degree curves, the remainder had abrupt (AC) 30 degree curves. Ten blocks for each curvature and for each degree of precurving amount (0, 15, 20, 25, 30, 35, 40, or 45 degrees) were instrumented with a machine that imparted only an in and out motion. The simulated canals were size 30 at the apex, and size 30 stainless steel K-files were used to instrument the canals. A transportation ("t") index was determined at two levels: T1 (1 mm from the apex) and TB (a line bisecting the curve of the canal). For GC at T1 and TB, 40- and 20-degree curved instruments respectively produced significantly less transportation than all other curvatures (p < 0.0001). For AC at T1 and TB, 35 and 25 degree instruments respectively produced significantly less transportation than all other curvatures (p < 0.0001). Comparing GC and AC, the transportation for AC was significantly less (p < 0.0015).