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 Scheffe post hoc tests. Results Mean torque varied between 0.1 +/- 0.1 and 0.8 +/- 0.5 N cm while mean force ranged from 4.2 +/- 2.0 to 7.3 +/- 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 significantly 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 were highly 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.

Aim To investigate clinical results of root canal treatment performed with the aid of nickel-titanium (NiTi) rotary instruments. Summary A total of 179 patients underwent root canal treatment with either (A) Lightspeed, or (B) ProFile .04 or (C) ProFile .04 and .06 or GT rotary instruments to create tapered preparations. In groups A and B, laterally condensed gutta-percha and AH Plus were used. Canals in group C were obturated with System B, Obtura II and Roth's 801 sealer. Initial and recall radiographs were assessed using the periapical index (PAI). Outcomes were analysed using chi-square tests, event-time analyses and logistic regression models. Two hundred and thirty-three teeth were radiographically assessed after a mean interval of 25.4+/-11.8 months. Favourable outcome of treatment, defined as PAI86.7%. Logistic regression analysis and univariate analyses indicated that teeth with preoperative PAI scores >2 and retreated teeth had a significantly lower chance of healing compared with periapically healthy teeth and primary treatments, respectively. Preparation technique, length of fill and the type of sealer did not significantly affect healing rates. Key learning points Root canal treatment with NiTi root canal instrumentation systems renders favourable outcomes in more than 86% of the cases. Outcome is significantly affected by preoperative diagnoses but not by the specific choice of instrumentation system.

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 (muCT) at a resolution of 36 mum. 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 Scheffe post-hoc tests. Results Volume and surface area increased significantly 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 significant shaping errors. Canal anatomy had an insignificant impact on preparation, indicating that FlexMaster instruments were able to shape 'constricted' canals as well as 'wide' ones.

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 Scheffe posthoc tests. Results Mean torque varied between 0.8 +/- 0.5 and 2.2 +/- 1.4 N cm whilst mean force ranged from 4.6 +/- 2.6 to 6.2 +/- 2.7 N. Mean numbers of rotations totalled up to 21. All three variables registered were significantly correlated to preoperative canal volumes (P < 0.001) and differed significantly 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 significant positive correlations between canal geometry and physical parameters during shaping.

Aim This paper describes the initial experiences following the introduction of a rotary engine-driven preparation technique into the undergraduate endodontic programme at the Zurich University Dental Centre. Methods Forty third-year students practised the ProFile .04 (PF .04) technique between January and July 2001 in a preclinical course. Between November 2001 and February 2002, 20 of these students (Group A) root-treated 51 teeth in their clinical course using either PF .04, the balanced force technique (BFT) or a combination of both. The second group of 20 students (Group B) similarly treated another 36 randomly selected teeth between April and July 2002. Types of teeth treated by the students and the canal preparation techniques were recorded. The students also completed a short questionnaire, evaluating their opinions of the new course. Results Of the 87 teeth endodontically treated during the clinical course, 34, 14 and 39 were shaped using PF .04 alone, a combination of PF .04 and BFT and BFT alone, respectively. No rotary instruments were fractured during the 1-year clinical course, although some instruments were fractured during the preclinical laboratory course. Overall, the students rated the rotary technique as positive. Conclusion A rotary technique was successfully introduced into an undergraduate endodontic programme (this will be continued in the foreseeable future). However, the continuity between the preclinical and the clinical courses was poor as a result of the constraints of the general teaching programme.

Aim To evaluate the relative performance of ProTaper nickel-titanium (Ni-Ti) instruments shaping root canals of varying preoperative canal geometry. Methodology Extracted human maxillary molars were scanned, before and after shaping with ProTaper, employing micro computed tomography (muCT) at a resolution of 36 mum. Canals were three-dimensionally reconstructed and evaluated for volume, surface area, 'thickness' (diameter), canal transportation and prepared surface. Based on median canal volume, 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 repeated-measures anova and Scheffe posthoc tests. Results Volume and surface area increased significantly and similarly in mb, db and p canals, and gross preparation errors were found infrequently. Root canal diameters, 5-mm coronal to the apex, increased from 0.38 to 0.65 mm, 0.42 to 0.66 mm and 0.57 to 0.79 mm for mb, db and p canals, respectively. Apical canal transportation ranged from 0.02 to 0.40 mm and was independent of canal type; 'wide' canals had a significantly higher (P < 0.05) proportion of unprepared surfaces than 'constricted' canals. Conclusions 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.

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