Aim To evaluate the relative performance of FlexMaster nickel^titanium instruments shaping maxillary molar root canals in vitro. Methodology Extracted human maxillary molars were scanned, before and after root-canal shaping, with FlexMaster, employing micro-computed tomography (mCT) at a resolution of 36 mm. Canals were three-dimensionally reconstructed and evaluated for volume, surface area,`thickness' (diameter), canal transportation and prepared surface. Based on median canal volume, the canals were divided into`wide' and`constricted' groups. Comparisons were made between mesiobuccal (mb), distobuccal (db) and palatal (p), as well as`wide' and`constricted' canals, using ANOVA and Sche¡e¨post-hoc tests.Results Volume and surface area increased signi¢-cantly and similarly in mb, db and p canals, and no gross preparation errors were found. Mean root-canal diameters, 5 mm coronal to the apex, increased from 0.45 to 0.65 mm, from 0.41 to 0.56 mm and from 0.79 to 0.85 mm for mb, db and p canals, respectively. Apical canal transportation ranged from 0.01 to 0.29 mm and was independent of canal type;`wide'canals had a significantly higher (P < 0.05) proportion of unprepared surfaces than`constricted'canals had. Conclusions FlexMaster instruments shaped curved and narrow root canals in maxillary molars to sizes 40 and 45 without signi¢cant shaping errors. Canal anatomy had an insigni¢cant impact on preparation, indicating that FlexMaster instruments were able to shapè constricted'canals as well as`wide'ones.

Hu « bscher W, Barbakow F, Peters OA. Root-canal preparation with FlexMaster: assessment of torque and force in relation to canal anatomy. International Endodontic Journal, 36, 000^000, 2003.Aim To investigate physical parameters of FlexMaster nickel-titanium instruments while preparing curved canals in maxillary molars in vitro. Methodology A torque-testing platform was used to prepare root canals in 11 extracted human maxillary molars with FlexMaster 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 microcomputed tomography. Resistance to cyclic fatigue was also tested. Mean scores for each instrument type were calculated and statistically compared using ANOVA and Sche¡ep ost hoc tests. Results Mean torque varied between 0.1 AE0.1 and 0.8 AE 0.5 N cm while mean force ranged from 4.2 AE 2.0 to 7.3 AE 3.5 N. Mean numbers of rotations totalled up to 18. All three variables registered showed weak correlations to preoperative canal volumes (P < 0.01) and differed signi¢cantly between`wide' and`constricted' canals (P < 0.001). Numbers of rotations to fracture in a cyclic fatigue test were between 348 and 1362. Conclusion FlexMaster instruments generated low torque scores and werehighly resistant to cyclic fatigue,whilst three instruments fractured in extremely narrow canals. Consequently, more research is required to limit fracture incidence and to optimize instrumentation guidelines.

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