Table 3. Mean and standard deviations of the centering ratio of the three systems.

Centering	Protaper Revo-S (n = 27)	Revo-S (n = 27)	Hero shaper (n = 27)	P-value
Bucco-lingual centering rate
Cervical	0.09 ± 0.24	0.19 ± 0.34	0.15 ± 0.27	0.760
Middle	0.48 ± 0.41	0.28 ± 0.38	0.38 ± 0.38	0.175
Apical	0.42 ± 0.36	0.51 ± 0.54	0.47 ± 0.35	0.804
Mesio-distal centering rate
Cervical	0.24 ± 0.37	0.33 ± 0.38	0.18 ± 0.31	0.317
Middle	0.34 ± 0.40	0.49 ± 0.43	0.44 ± 0.43	0.313
Apical	0.52 ± 0.43	0.32 ± 0.41	0.43 ± 0.41	0.213