Background: Mandibular first molars appear to be the most commonly
tooth subjected to a root canal treatment, therefore a better understanding of
the anatomy critical zones for resistance of this teeth may decrease the
treatment’s failure rate. So, this study was conducted to evaluate the dentin
thickness of the danger zone in mesial roots of mandibular first molars using
cone beam computed tomography in an Iranian population. Methods: In this
cross-sectional study, 210 Cone Beam Computed Tomography acquisition of the
mandibular first molars were collected from a radiology center in Qazvin. The
dentin thickness of the mesial roots (mesiobuccal and mesiolingual canals) was
measured from the furcation to 5 mm below. The relationship between the dentin
thickness in the danger zone and parameters, like age, gender, placement side,
root length, the curvature of the canal, canal type, presence of middle mesial
canal, and distance between the orifices of the mesial canals was investigated.
Frequency, mean and standard deviation for variables were calculated, and data
analysis was done by SPSS using simple and multiple linear regression and Pearson
correlation coefficient. Also, two-sample t-test was used to compare
mesiobuccal and mesiolingual on two sides. The significant level was also
considered at (p 0.05). Results: The average minimum
thickness of danger zone dentin was found to be 0.885 0.259 mm in the
mesiobuccal canal and 0.906 0.206 mm in the mesiolingualcanal. Also, the
minimum thickness of dentin in the mesiobuccal and mesiolingual canals in the
range of 0 to 1 mm from the furcation was more than in other areas. There was no
significant relationship between the minimum dentin thickness of the danger zone
with gender, placement side, root length, canal type, and mesial canal entrance
distance. But with increasing age, the thickness of dentin in the danger zone in
the mesiolingualcanal increased significantly (p = 0.008). It was also
observed that with the increase in the curvature of the canal, the thickness of
the dentin in the danger zone in the mesiobuccal canal decreased (moderately
curved (p = 0.008), severely curved (p = 0.046)). In addition,
the thickness of the dentin in the mesiobuccal and mesiolingual canal was less in
the samples with the middle mesial canal (p = 0.047, 0.044).
Conclusions: Less dentin thickness in the danger zone in the mesial
roots of mesiolingual mandibular first molars was seen in younger patients in
mesiolingual canal, with a greater degree of canal curvature in the mesiobuccal
canal and teeth with a middle mesial canal. Therefore, it is suggested that large
taper instruments should be used with more precision to prevent complications.