Table 2 Mean minimum dentin thickness (mm) in the MB roots of the maxillary first molars and M roots of the mandibular first molars. For each parameter, different letters indicate a significant difference (P < 0.05).

MB root of maxillary first molar

1 mm

24

1.00 ± 0.55^a

0.96 ± 0.53^a

0.76 ± 0.25^a

0.69 ± 0.61^a

0.74 ± 0.28^a

0.63 ± 0.61^a

0.78 ± 0.23^a

0.69 ± 0.58^a

2 mm

28

1.37 ± 0.26^b

0.95 ± 0.52^a

1.01 ± 0.28^b

0.91 ± 0.23^a,b

0.84 ± 0.36^a,b

0.65 ± 0.24^a

0.89 ± 0.30^a,b

0.80 ± 0.23^a,b

3 mm

28

1.69 ± 0.28^c

1.53 ± 0.57^b

1.13 ± 0.25^b,c

1.01 ± 0.27^b

0.96 ± 0.22^b,c

0.78 ± 0.20^a,b

1.03 ± 0.23^b,c

0.87 ± 0.21^a,b

4 mm

28

1.90 ± 0.32^c,d

1.95 ± 0.55^b,c

1.21 ± 0.22^b,c

1.05 ± 0.25^b

1.08 ± 0.21^c

0.85 ± 0.20^a,b

1.10 ± 0.25^b,c

0.95 ± 0.24^a,b

5 mm

28

2.03 ± 0.29^d

2.17 ± 0.47^c

1.32 ± 0.20^c

1.13 ± 0.20^b

1.15 ± 0.17^c

0.93 ± 0.18^b

1.22 ± 0.18^c

1.03 ± 0.22^b

M root of mandibular first molar

1 mm

24

1.06 ± 0.66^a

0.85 ± 0.35^a

0.78 ± 0.52^a

0.48 ± 0.32^a

0.77 ± 0.68^a

0.47 ± 0.33^a

0.72 ± 0.62^a

0.51 ± 0.29^a

2 mm

31

1.45 ± 0.38^b

1.54 ± 0.50^b

0.89 ± 0.25^a,b

0.80 ± 0.30^b

0.94 ± 0.29^a,b

0.77 ± 0.24^b

0.89 ± 0.24^a,b

0.76 ± 0.22^b

3 mm

31

1.73 ± 0.32^b,c

1.80 ± 0.44^b,c

1.04 ± 0.20^b,c

0.92 ± 0.22^b

1.06 ± 0.29^b

0.86 ± 0.25^b

0.96 ± 0.25^a,b

0.88 ± 0.23^b

4 mm

31

1.87 ± 0.33^c

1.98 ± 0.40^c

1.12 ± 0.17^c

1.00 ± 0.24^b

1.15 ± 0.22^b

0.94 ± 0.26^b

1.07 ± 0.22^b

0.86 ± 0.27^b

5 mm

31

1.96 ± 0.31^c

2.02 ± 0.39^c

1.17 ± 0.17^c

0.97 ± 0.23^b

1.22 ± 0.18^b

0.94 ± 0.25^b

1.10 ± 0.19^b

0.91 ± 0.25^b