For all groups, the mean maximum penetration depths and standard deviations are given in Table 1. The nonsterilized TiN-coated (group B.C)fifiles reached significantly greater maximum penetration depths than the nonsterilized uncoated instruments (group A.C; P < 0.001).
The sterilized uncoated files (groups A.1-A.3) displayed lower maximum penetration depths than the never-sterilized control instruments (group A.C). Out of 12 NaOCl-treated uncoated instruments (group A.3), two files fractured during the determination of cutting efficiency; no other instrument separations were recorded.
Anova revealed no significant difference amongst the four groups of the TiN-coated instruments (P = 0.110). Independent of the number of sterilization cycles or the immersion in NaOCl prior to sterilization, the maximum penetration depths of the coated instruments (Fig.1) showed no statistically significant difference in comparison with the penetration depths of the control instruments (P > 0.05).

Table 1. Mean maximum penetration depths (mm) and SD achieved by the instruments of the different groups (for each group n=12 instruments).



Figure 1. Notched boxplots of the maximum penetration depths (mm) achieved by the TiN-coated instruments of the different groups.
Group B.1: Five cycles of sterilization; B.2:10 cycles of sterilization; B.3: NaOCl treatment prior to five cycles of sterilization; B.C: Nonsterilized controls.