PRECURVING OF NICKEL-TITANIUM FILES AFFECTS TRANSPORTATION IN SIMULATED CANALS

Instrumentation studies comparing nickel-titanium with stainless-steel files have been performed without precurving the nickel-titanium file s. It is unknown what influence the precurving of nickel-titanium file s would have on transportation in small curved canals of varying curva tures. 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, 3 0, 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, an d size 30 nickel-titanium files were; used to instrument the canals. A transportation ''t'' index was determined at two levels: T1 (1 mm fro m the apex) and TB (a line bisecting the curve of the canal). For GC a t T1 and TB, 45- and 25-degree curved instruments, respectively, produ ced significantly less transportation (p < 0.0001). For AC at T1 and T B, 35- and 0-degree curved instruments, respectively, produced signifi cantly less transportation (p 0.0001). Comparing GC and AC, the transp ortation for GC was significantly less (p < 0.0015).