Shaping ability of progressive versus constant taper instruments in curved root canals of extracted teeth

Abstract Yang GB, Zhou XD, Zheng YL, Zhang H, Shu Y, Wu HK. Shaping ability of progressive versus constant taper instru-ments in curved root canals of extracted teeth. InternationalEndodontic Journal, 40, 707–714, 2007. Aim To compare the shaping ability of progressiveversus constant taper shaft instruments in curved rootcanals of extracted human teeth.Methodology A total of 40 root canals of mandib-ular molars with curvatures ranging between 20 and40 were divided into two groups of 20 canals each andembedded in a muffle system. The root canals sectionedhorizontally at three levels before preparation and thenremounted into the mould. All root canals wereprepared with ProTaper (progressive taper) or HeroShaper (constant taper) instruments. Pre- and post-instrumentation radiographs and cross-sectional ima-ges were obtained. The parameters evaluated were:working safety (instrument failure, apical blockage andloss of working length) and shaping ability (straight-ening, cross-sectional area, transportation and centringability). The data were analysed statistically usingStudent’s t-test.Results No instrument fractured during preparation.One Hero Shaper instrument permanently deformed.Both instrument systems maintained working lengthwell. The canals prepared with Hero Shaper instru-ments were straightened to a lesser degree (P < 0.05).ProTaper instruments removed more dentine in thecoronal and the middle sections of the canals. Canalsprepared with Hero Shaper instruments had lesstransportation (P < 0.01) and better centring ability(P < 0.05) in the apical section.Conclusions Both instrument systems were safe touse and maintained working length well. The canalsprepared with Hero Shaper had less transportation andwere better centred in the apical region, possiblybecause their smaller taper reduced instrument stiff-ness.Keywords: canal transportation, curved root canal,Hero Shaper, nickel-titanium, ProTaper, rotary instru-ments.