__Results.__

**Rotational speed.**

The mean and standard deviation of the angle and radius of curvature within the three subgroups are listed in Table 1. The mean angle of curvature and the mean radius of curvature were 44.5 ï‚°ï€ and 4.9 mm for subgroup 1, 45.2 ï‚°ï€ and 4.7 mm for subgroup 2 and 43.9 ï‚°ï€ and 5.1 mm for subgroup 3.

Instrument deformation and separation did not occur in any of the three subgroups. Instruments locked only in subgroup 3 (350 r.p.m.) with a significant difference between subgroups 1 and 3, and 2 and 3 (Table 2).

**Torque.**

The mean and standard deviation of the angle and radius of curvature within subgroups 4, 5 and 6 are listed in Table 1. The mean angle of curvature and the mean radius of curvature were 54.7 ï‚°ï€ and 6.6 mm for subgroup 4, 54.2 ï‚°ï€ and 7.1 mm for subgroup 5 and 54.9 ï‚°ï€ and 6.9 mm for subgroup 6. Instrument locking, deformation, and separation did not occur in any of the three subgroups.

**Operator proficiency.**

The mean and standard deviation of the curvature angle and the curvature radius of subgroups 7, 8 and 9 are listed in Table 1.

**Table 1.** Mean and standard deviation of the angle and radius of curvature of the three subgroups in the three parts of the study.

**Table 2.** Rotational speed: incidence of instrument locking, deformation, and separation.

**Table 3.** Operator proficiency: incidence of instrument locking, deformation, and separation.

The mean incidence of instrument locking, deformation, and separation is reported in Table 3. In subgroup 7, neither locking, deformation or separation occurred. In subgroup 8, only a small number of instruments locked and deformed; separation did not occur in this subgroup. Forty-three instruments were required to complete the cleaning and shaping of the 100 canals included in this subgroup. In subgroup 9, 11 out of 60, nine out of 60, and two out of 60 instruments were locked, deformed, and separated, respectively. Fifty-one instruments were required to complete the cleaning and shaping of the 100 canals included in this subgroup. Statistical analysis did not demonstrate any significant difference between groups 7 and 8 with respect to instrument locking, deformation, and separation. Instruments in subgroup 9 locked significantly more than the instruments in subgroups 7 and 8. The incidence of instrument deformation was statistically different between subgroups 7 and 9. There was no significant difference in the incidence of instrument separation between the three subgroups (Table 3).

A trend toward a higher incidence of instrument failure in smaller tapers was noted when the operators were evaluated. Nine out of 12 separated instruments and two out of two deformed instruments were 0.06 taper GT rotary instruments.