Root groove depth and inter-orifice canal distance as anatomical predictive factors for danger zone in the mesial root of mandibular first molars

Objectives This study evaluated the danger zone (DZ) in mesial roots of mandibular molars and the correlation between anatomical references of the DZ and some anatomical landmarks including tooth/root length, depth of mesial and distal grooves, and inter-canal orifices distance. Material and methods Twenty-eight mesial roots of mandibular molars with 2 independent canals were scanned and divided into 2 groups according to root length. The anatomical landmarks were correlated (Pearson or Spearman coefficients) with root level, thickness, and position of the DZ and also compared (independent samples t or Mann-Whitney tests) between the 2 groups at α = 5%. Results No statistical difference was observed between groups regarding DZ parameters and depth of mesial and distal grooves ( P > 0.05). Orifice distance in group 2 (4.49 ± 0.75 mm) was significantly greater than group 1 (3.76 ± 0.89 mm) ( P < 0.05). Significant correlations ( P < 0.05) were found between (i) DZ level and root/tooth length ( r = 0.54 and 0.49, respectively), (ii) DZ thickness and distal groove depth ( r = − 0.45), and orifice distance ( r = 0.38), and (iii) DZ position and depth of mesial ( r = 0.39) and distal ( r = 0.40) grooves. Other variables such as root length and distal groove depth ( r = 0.28), and orifice distance and mesial groove depth ( r = 0.36) were also correlated ( P < 0.05). Conclusions The length of tooth/root, the distance of canal orifices, and the depth of mesial/distal grooves of mesial roots of mandibular molars might be predictive factors for the root level, position, and thickness of the DZ. Clinical relevance The length, distance of mesial canal orifices, and the depth of mesial and distal grooves of the mesial roots of mandibular molars might be moderate predictive factors for the root level, position, and thickness of the DZ.