Instrumentation studies comparing nickel-titanium with stainless-steel files have been performed without precurving the nickel-titanium files. It is unknown what influence the precurving of nickel-titanium files would have on transportation in small curved canals of varying curvatures. One hundred-sixty resin blocks with simulated canals were used. Eighty blocks had gradual (gradual curve (GC)) 30-degree curves; the remainder had abrupt (abrupt curve (AC)) 30-degree curves. Ten blocks for each curvature and for each degree of precurving (0,15, 20, 25,30, 35,40, and 45) were instrumented with a machine that imparted only an in and out motion. Simulated canals were a size 30 at the apex, and size 30 nickel-titanium 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, 45- and 25-degree curved instruments, respectively, produced significantly less transportation (p < 0.0001). For AC at T1 and TB, 35- and 0-degree curved instruments, respectively, produced significantly less transportation (p < 0.0001). Comparing GC and AC, the transportation for GC was significantly less (p < 0.0015).
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