Shaping ability of Hero 642 rotary nickel-titanium instruments in simulated root canals: Part 1.
OBJECTIVE
To determine the general efficacy and shaping ability of Hero 642 nickel-titanium rotary instruments during the preparation of simulated canals. Part 1 of this two-part report describes the efficacy of the instruments in terms of three-dimensional canal form.


METHODS
A total of 40 simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by Hero 642 instruments using a crown-down preparation sequence. The efficacy of the instruments was assessed in terms of preparation time, instrument failure, canal blockages and loss of canal length. Intra-canal impressions were taken of the prepared canals in order to assess three-dimensional canal form.


RESULTS
The mean time for canal preparation was 8.6 min and was influenced significantly (P < 0.05) by canal shape. Two instruments fractured and eight instruments deformed; significant differences were observed between canal shapes (P < 0.05). All of the canals remained patent. Fifteen canals (39.5%) maintained the correct working distance, 15 lost distance and eight canals gained length. Examination of intracanal impressions demonstrated that the majority of canals (79%) had apical stops; canal shape had a significant influence (P < 0.001) on the quality of apical stops. With one exception all canals had smooth canal walls and all of the canals showed good flow characteristics. Taper was poor in 30 canals (79%) and good in eight canals (21%).


CONCLUSIONS
Hero 642 rotary nickel-titanium instruments prepared simulated canals rapidly but with a three-dimensional form that lacked adequate taper.
Thompson
S A
SA
Department of Adult Dental Health, Dental School, University of Wales College of Medicine, Heath Park, Cardiff CF14 4XY, UK. thompsonsa@cardiff.ac.uk
Dummer
P M
PM
D003754:Dental High-Speed Equipment; D003762:Dental Instruments; D004868:Equipment Failure; D006801:Humans; D003765:Models, Dental; D009532:Nickel; D015203:Reproducibility of Results; D018915:Root Canal Preparation / Q000295:instrumentation*; D013997:Time Factors; D014025:Titanium
C040654:titanium nickelide; D009532:Nickel; D014025:Titanium