Canals in maxillary molars were prepared in vitro using ProTaper instruments without major procedural errors. These instruments may be more effective in shaping narrow canals than wider, immature ones.

Peters OA, Peters CI, Scho « nenberger K, Barbakow Aim To investigate physical parameters for ProTaper nickel^titanium (NiTi) rotary instruments whilst preparing curved canals in maxillary molars in vitro. Methodology A novel torque-testing platform was used to prepare root canals in 15 extracted human maxillary molars with ProTaper rotary instruments. Peak torque and force was registered along with numbers of rotations required to shape the canals. Canals were divided into 'wide' and 'constricted' groups depending on canal volumes assessed by micro computed tomography. Mean scores for each instrument type were calculated and statistically compared using anova and Sche¡e¤ posthoc tests. Results Mean torque varied between 0.8 AE 0.5 and 2.2 AE 1.4 N cm whilst mean force ranged from 4.6 AE 2.6 to 6.2 AE 2.7 N. Mean numbers of rotations totalled up to 21. All three variables registered were signi¢cantly correlated to preoperative canal volumes (P < 0.001) and di¡ered signi¢cantly between 'wide' and 'constricted' canals (P < 0.001). Conclusions Whilst high forces were used in some cases, no ProTaper instrument fractured when a patent glide path was present. There were signi¢cant positive correlations between canal geometry and physical parameters during shaping.

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