Table 2. Mean and standard deviation of the volume of filling material at baseline, after filling removal with rotary instruments, and after re-preparation taking into consideration the presence or absence of an isthmus in the mesial root of mandibular molar.

	Baseline (Micro-CT #1)
	1-3 mm	3-5 mm	5-7 mm	TOTAL
Presence of an isthmus	0.83Aa	1.45Aa	1.91Aa	3.77Aa
	(±0.25)	(±0.40)	(±0.49)	(±1.39)
Absence of an isthmus	0.57Ab	1.07Ab	1.51Ab	2.62Ab
	(±0.12)	(±0.28)	(±0.28)	(±0.76)
	Filling removal with rotary instruments (Micro-CT #2)
	1-3 mm	3-5 mm	5-7 mm	TOTAL
Presence of an isthmus	0.43Ba	0.57Ba	0.61Ba	1.63Ba
	(±0.26)	(±0.29)	(±0.35)	(±0.78)
Absence of an isthmus	0.13Bb	0.13Bb	0.13Bb	0.40Bb
	(±0.12)	(±0.19)	(±0.17)	(±0.43)
	Re-preparation with ProTaper Next (Micro-CT #3)
	1-3 mm	3-5 mm	5-7 mm	TOTAL
Presence of an isthmus	0.34Ba	0.52Ba	0.57Ba	1.42Ba
	(±0.22)	(±0.32)	(±0.33)	(±0.73)
Absence of an isthmus	0.12Bb	0.10Bb	0.10Bb	0.32Bb
	(±0.12)	(±0.17)	(±0.17)	(±0.42)

Different uppercase letters in rows compare the presence or the absence of an isthmus in the same root level after each stage of retreatment using ANOVA and Tukey’s tests (P<0.05). Different lowercase letters in the columns compare the presence and the absence of an isthmus in each root level and stage of retreatment using Student’s t-test (P<0.05)