Shaping ability of progressive versus constant taper instruments in simulated root canals.

AIM: To compare the shaping ability of progressive versus constant taper shaft designed instruments in simulated root canals.
METHODOLOGY: Simulated L- and S-shaped resin canals were prepared by ProTaper (progressive taper) and high elasticity in rotation 642 (Hero 642) (constant taper) instruments (n = 10 canals in each case). The pre- and post-instrumentation images were recorded and assessment of the canal shape was completed with image pro plus 5.0. The width of resin removed was measured at 9 measuring points. Incidence of canal aberrations, instrument fracture, preparation time and change of working length were recorded. In addition, the change of curvature and centring ability were also assessed. The data were analysed statistically using Student's t-test or Fisher's exact-test.
RESULTS: In both canal types, Hero 642 instruments prepared canals more rapidly (P < 0.01) and maintained working length significantly more accurately than ProTaper instruments (P < 0.05). In canals prepared with Hero 642 instruments, there was less change in curvature. Instrumentation with ProTaper results in transportation towards the outer aspect of the L-shaped curved canals in the apical part and the inner aspect of the S-shaped canals at the curve. Hero 642 instruments had a better centring ability in the apical part of the canal, but resulted in shapes with a poor taper.
CONCLUSIONS: ProTaper and Hero 642 instruments prepared curved canals rapidly, maintained working length well and were relatively safe without creating perforations and danger zones. In both canal types, Hero 642 instruments maintained the original canal curvature better, and had a better centring ability in curved canals because of its constant taper design. The taper prepared by Hero 642 instruments in the coronal part of the canal was generally poor.