Isthmuses, accessory canals, and the direction of root curvature in permanent mandibular first molars: an in vivo computed tomography study

Aria Chuppani Dastgerdi; Manizheh Navabi; Vahid Rakhshan

doi:10.5395/rde.2018.45.e7

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Dastgerdi, Navabi, and Rakhshan: Isthmuses, accessory canals, and the direction of root curvature in permanent mandibular first molars: an in vivo computed tomography study

Research Article

Restor Dent Endod 2020;45(1):e7.

Published online: 4 February 2020

DOI: https://doi.org/10.5395/rde.2018.45.e7

Isthmuses, accessory canals, and the direction of root curvature in permanent mandibular first molars: an in vivo computed tomography study

Aria Chuppani Dastgerdi¹, Manizheh Navabi^2,^*, Vahid Rakhshan¹

¹Department of Dental Morphology, Dental Branch, Islamic Azad University, Tehran, Iran

²Department of Removable Prosthodontics, Dental Faculty, Tehran Medical Sciences, Islamic Azad University, Tehran, Iran

^*Correspondence to Manizheh Navabi, DDS Academic Faculty Member, Department of Removable Prosthodontics, Dental Faculty, Tehran Medical Sciences, Islamic Azad University, Pasdaran Ave., No. 9, Tehran 1946853314, Iran. E-mail: dr.ma.navabi@gmail.com

Received 26 April 2019 Revised 22 July 2019 Accepted 17 September 2019

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Objectives

This study was performed to assess the anatomy of mandibular first molars.

Materials and Methods

In this in vivo study, cone-beam computed tomography (CBCT) volumes of 312 bilateral intact first mandibular molars from 156 patients (79 men and 77 women; average age, 35.6 ± 11.2 years) were investigated in terms of the direction of each canal's curvature in the buccolingual and mesiodistal dimensions (direction of the position of the apex in relation to the longitudinal axis of the root), the presence of an isthmus (a narrow, ribbon-shaped communication between 2 root canals) in 3 segments (0–2, 2–4, and 4–6 mm) from the apex), and the presence and number of accessory canals (smaller canals besides the main root canals, connecting the pulp to the periodontium). Data were analyzed statistically (α = 0.05).

Results

Mesiolingual canals were mostly buccally and distally inclined, while mesiobuccal and distolingual canals were mostly distally curved. Isthmuses were more common in younger patients (χ² test, p < 0.05). The average numbers of accessory canals in the apical, middle, and coronal segments were 9.9 ± 4.2, 6.9 ± 2.9, and 9.3 ± 3.0 canals per segment, respectively (analysis of variance, p < 0.001). Age and sex were not associated with the number of accessory canals (p > 0.05).

Conclusions

The complex anatomy of these teeth deserves attention during non-surgical or surgical endodontic treatment. Around the apex, isthmuses might be more prevalent in younger and female individuals.

Keywords: Anatomy, Endodontics, Cone beam computed tomography

References

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Figure 1.

An example of accessory canals. In the bottom image, the main (yellow) and accessory (red) canals are marked.

Table 1.

Distribution of apical foramen locations in mesiobuccal, mesiolingual, distobuccal, and distolingual canals

Canal	Buccolingual dimension			Mesiodistal dimension
Canal	Straight	Buccal	Lingual	Straight	Mesial	Distal
Mesiobuccal	218 (69.8)	38 (12.2)	56 (17.9)	27 (8.6)	3 (0.9)	282 (90.4)
Mesiolingual	83 (26.6)	226 (72.4)	3 (0.9)	20 (6.4)	7 (2.2)	285 (91.3)
Distobuccal	249 (79.8)	49 (15.7)	14 (4.5)	8 (2.6)	0 (0)	304 (97.4)
Distolingual	137 (77.8)	29 (16.5)	10 (5.7)	0 (0)	0 (0)	176 (100)

Values are presented as number (%).

Table 2.

Distribution of isthmuses in each root segment

Age (yr)	Root	Root segment (mm)
Age (yr)	Root	0–2	2–4	4–6
20–39	Mesial	53 (17.0)	100 (32.0)	116 (37.1)
	Distal	34 (10.9)	64 (20.5)	71 (22.7)
40–60	Mesial	41 (13.1)	59 (18.9)	78 (25)
	Distal	26 (8.3)	28 (8.9)	45 (14.4)

Values are presented as number (%).

Table 3.

Number of accessory canals per root segment

Age (yr)	Root	Root segment
Age (yr)	Root	Cervical	Middle	Apical
20–39	Mesial	4.98 ± 1.70	3.72 ± 1.71	5.30 ± 2.49
	Distal	4.25 ± 1.55	3.05 ± 1.92	4.41 ± 2.22
40–60	Mesial	4.92 ± 1.93	3.92 ± 1.92	5.41 ± 2.41
	Distal	4.48 ± 1.60	3.11 ± 1.70	4.68 ± 2.26

Data are presented as mean ± standard deviation.

Table 4.

Summary of reports on root and canal curvature

Author	Year	Country	Ref.	Method	Sample size	Root/canal curvature
Rocha et al.	1996	Brazil	[19]	In vitro (clearing technique) assessment of root curvature	232	Mesial root: 73% distal, 17% straight Distal root: 8% distal, 12% mesial, 78% straight
Estrela et al.	2015	Brazil	[17]	CBCT (in vivo) assessment of canal curvature	200	92.7% curvature in the apical third, 73.2% curvature in the cervical third
Schäfer et al.	2002	Germany	[18]	CBCT (in vitro) assessment of canal curvature	50	58% to 76% of curved canals with 33° to 48° angles

CBCT, cone-beam computed tomography.

Table 5.

Summary of reports on isthmus prevalence and locations (all reported values are percentages)

Author	Year	Country	Ref.	Method	Sample size	Mesial root	Most common location	Distal root	Most common location
de Pablo et al.	2010	Spain	[20]	Review of literature of 41 articles	18,781	54.8% (range 23%–77%)	Middle third	20.2% (range, 8%–55%)
Demirbuga et al.	2013	Turkey	[27]	Micro-CT (in vitro)	1,748	30%	–	12%	–
Chourasia et al.	2012	India	[29]	In vitro (clearing technique)	150	30%	–	10%	–
Al-Qudah and Awawdeh	2009	Jordan	[7]	In vitro (clearing technique)	330	37.3%	Middle and apical thirds	13%	Middle third
Ahmed et al.	2007	Sudan	[8]	In vitro (clearing technique)	100	62%	–	8%	–
Villas-Bôas et al.	2011	Brazil	[25]	In vitro (micro-CT)	60 first/second molars	61%	3–4 mm from apex	–	–
Gulabivala et al.	2001	Myanmar	[9]	In vitro (clearing technique)	139	69.2%	–	9.2%	–
Mohammadzadeh Akhlaghi et al.	2017	Iran	[2]	In vitro (clearing technique)	150	44.6%	22.5% (2 mm from apex), 41.7% (4 mm), 35.8% (6 mm)	27.3%	34.3% (2 mm), 36.5% (4 mm), 29.3% (6 mm)
Faraz et al.	2015	–	[28]	In vitro (clearing technique)	123	10%	–	5%	–
Peiris et al.	2008	Japan	[10]	In vitro (clearing technique)	177 first/second molars	d 77.4%	Middle third	11.3%	Middle third
Mehrvarzfar et al.	2012	Iran	[4]	In vitro (clearing technique)	60	83%	92%, 88%, and 70% respectively in ranges 6, 4, and 2 mm from apex	–	–
Gu et al.	2009	China	[24]	Micro-CT (in vivo)	120	81%	At 6 mm from apex of mesial root: 20–40 years old (80%), 40–60 (67%), and over 60% (30%)
von Arx et al.	2005	–	[6]	Endoscope (in vivo)	56	88.5%	3–4 mm from apex	–	–
Fan et al.	2010	–	[26]	Micro-CT (in vivo)	126	85%	5 mm from apex	–	–

CT, computed tomography.

Table 6.

Summary of reports on the prevalence and location of accessory canals (all reported values are percentages)

Author	Year	Country	Ref.	Method	Sample size	No. of accessory canals
Author	Year	Country	Ref.	Method	Sample size	Mesial root	Distal root
Al-Qudah and Awawdeh	2009	Jordan	[7]	In vitro (clearing technique)	330	1% (0.6% in the middle third, 0.3% in the apical third)	3% (all in the apical third)
Ahmed et al.	2007	Sudan	[8]	In vitro (clearing technique)	100	52%	–
Gulabivala et al.	2001	Myanmar	[9]	In vitro (clearing technique)	139	11% in the apical third (highest percentage)	–
Peiris et al.	2008	Japan	[10]	In vitro (clearing technique)	177 first/second molars	45.2% in the apical third	29.4% in the apical third

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