Table 9.

Summary of inter-orifices distances results of the mandibular first molar

Studies	Whole tooth/ root (N)	IOD Definition	Level	Values (mm) MEAN ± SD (Range)
Gu et al. [12]	Whole tooth/ (25)	length of a line between centre points of two orifices	Pulp chamber floor	MBO-MLO = 2.35
Harris et al. [52]	Whole tooth (22)	1. The shortest linear distance between canals' orifices 2. The longest linear distance between canals' orifices	1.5 mm coronal to the furcation	Longest MB-ML = 3.09 Shortest MB-ML = 1.43 Longest DB-DL = 1.98 Longest M-D = 4.35
Versiani et al. [56]	MR (258)	Distance between the mesial canals' orifices	1.5 mm coronal to the furcation	MMC-MLC 1.34 ± 0.74 (0.45–3.92), and MMC-MBC 1.35 ± 0.74 (0.35–3.38)
Moe et al. [60]	MR (75)	Distance between the centres of the MB and ML canals	at 1.5 mm coronal to the furcation	2.60 ± 0.41 (1.69–3.48 mm)
De-Deus et al. [11]	MR (28)	The linear distance between (MB) and (ML) canal orifices' centres	At the lowest level of the CEJ on the buccal aspect of the crown	MB-ML 3.76 ± 0.89 (2.36–5.58) in grp I 4.49 ± 0.75 (3.28–6.08) in grp II

IOD Inter-orifice distance, CEJ Cementoenamel junction, MR Mesial root, grp I Group 1—root length between 8 and 9.6 mm, grp II Group 2—root length between 11.5 and 13.1 mm, MBO Mesiobuccal orifice, MLO Mesiolingual orifice, MLC mesiolingual canal, MBC mesiobuccal canal