From Jay Matani and Mohit Kheur
The anatomic inter
relationship of the neurovascular structures within the inferior alveolar
canal: A Cadaveric and Histological study.
Abstract
Objective:
The location and inter relationship of the structures of the inferior alveolar
neurovascular bundle within the mandibular canal has not been clearly defined. The
knowledge of the same is important while planning surgeries in the posterior
mandible
Methods:
8 cadaveric mandibles were dissected and sections were made at the distal
aspect of every tooth. The inferior alveolar neurovascular bundle was identified
and examined for the location of the inferior alveolar artery, vein and nerve. Hematoxylin
and Eosin sections were made for each specimen to confirm the position of these
structures.
Results:
All the sections in all the specimens confirmed that a blood vessel lies
superior to the nerve. This position appeared consistent in all the positions
relative to all the posterior teeth. There was a variation in the bucco-lingual
positioning of these structures relative to each other for the various
mandibles.
Conclusion:
A blood vessel is found to always lie superior to the inferior alveolar nerve
within the mandibular canal. Variations in the inter relationship of the
structures is present.
Significance:
This cadaveric study proves that all along the course of the neurovascular bundle,
at various cross sections studied, the inferior nerve is always inferior to a
blood vessel. There can be great variations to the positioning of the
structures within the neurovascular in the bucco-lingual dimension and also in
the exit of the nerve in various mandibles. Knowledge of the location of the
structures is of importance during surgical procedures carried out in the
vicinity of these structures.
Keywords:
mandible; alveolar nerve, inferior; anatomy; dental implants.
Introduction:
The
knowledge of the anatomical position of the structures within the inferior
alveolar canal is important for any surgical procedure in the posterior
mandible. The inferior alveolar neurovascular bundle enters the mandible at the
mandibular foramen and runs downward and medial within the mandibular canal
(MC) to exist from the mental foramen. The neurovascular bundle that occupies
the inferior alveolar canal contains the inferior alveolar nerve, the inferior
alveolar artery and the inferior alveolar vein.
Osteotomies
for endosseous implants should not be made until the position of the mandibular
canal is established. Prior to any surgical procedure, radiographic examination
is carried out either using panoramic radiographs or conventional or
computerized tomographies. Peker reported that the mandibular canal could not
be located in 19.4 % of the panoramic radiographs and 13.9% of the conventional
tomographs [1]. During various surgical procedures of the posterior mandible
there is a risk of complications involving the inferior alveolar neurovascular
bundle. These could include altered sensation, numbness and pain, complete loss
of sensation or excessive bleeding. Inferior alveolar nerve (IAN) injury occurs
as a complication of mandibular third molar surgery with a frequency varying
from 0.5% to 8% [2, 3].
Encountering
anatomic variations is possible during surgical procedures and such incidences
can manifest from ineffective mandibular blocks to major complications after surgery.
Kilic examined the mandibular canal in hemimandibles of cadavers and reported
the presence of several branches of the inferior alveolar nerve at different
sections [4]. Pogrel examined cadaveric mandibles for understanding the
relationship of the neurovascular bundle in the 3rd molar region [5].
He reported that there was a consistent presence of the vein along with the
nerve. The artery was solitarily present. The precise location of these
structures in relation to each other at different location in the mandibular
canal has not been reported. This knowledge may be of some importance in procedures
involving third molars and implant-related procedures.
The
aim of this study is to understand the intracanal relationship of these
structures during the course traversed by the neurovascular bundle from the 3rd
molar up to its exit from the body of the mandible.
Materials
and methods:
Eight
fully dentate hemi mandibles were selected from preserved human cadavers. Following
gross dissection, the mandibles were carefully separated from all muscle
attachments keeping the inferior alveolar neurovascular bundle intact at the
mandibular and mental foramen region. A water cooled carborundum disc was used
to make vertical sections distal to each tooth. The neurovascular bundle was
exposed and the vein, artery, and nerve were visually identified to determine their
exact orientation within the canal and in the mandible (Figure 1a to 1f). The gross
identification of the structures was done under 6x magnification.
A
histological evaluation was done for all the sections to identify and confirm
the location of the artery, vein and nerve to each other (Figure 2). The
sectioned specimens were fixed for 24 hours in 10% neutral buffered formalin
and then kept in decalcifying agent (20% EDTA) for 15 days. The specimens were
then immersed in a combination of 5 % formic and 10 % nitric acid for a period
of 15 days. After decalcification was complete, the mandibles
were processed and embedded in paraffin and sectioned into 5-µm slices. The
sections were stained with routine Hematoxylin and Eosin stain and then studied
under a compound microscope for further evaluation. The sections were taken at
4x (objective) magnification scanner view.
Results:
The
mandibular canal and neurovascular bundle of the mandibular canal were visible
in all hemimandibles. The relationship of the artery, vein and nerve to each was
examined from the external cortices of the mandible, from distal of the 3rd
molar until its exit from the mental foramen. A schematic representation of the
structures was made to understand their relationship to each other (Figure 3). In
all the cross sections studied a blood vessel was evident superior to the
position of the nerve. Out of the 25 cross sections studied, a vein was present
superior to the nerve in 19 (76%) of the sections. Both the blood vessels were
present superior to the nerve in 16 (64%) out of the 25 cross sections. The
bucco-lingual relationship of the structures had variation. In only 12 out of
25 sections (48%) one blood vessel was present buccal to the inferior alveolar
nerve.
Discussion:
The
anatomy of inferior alveolar canal has been documented in various textbooks and
previous cadaveric studies. However the relationship of the structures within
the canal is still unclear. The relative location of the inferior alveolar
canal and associated foramina in adults remain fairly constant without regard
to age and sex [6]. Levine reported that the bucco-lingual IAN canal position varied
with the age and race of the patient [7]. Many variations have been reported in
the literature with regards to the inferior alveolar nerve and it course. Lui
classified the course of the IAN as linear curve, spoon-shape curve,
elliptic-arc curve and turning curve [8]. These variations were seen on the
pantomographs. Juodzbalys reported that the mandibular canal bifurcates in the
inferior superior or medial lateral plane [9]. Observation of the MC shape from
the mandibular foramen towards the anterior part of the mandible showed several
characteristic variations in the form of round/oval, tear-drop and dumbbell
shape [10]. The identification of these variations may not be possible without
conventional or computerized tomography. Therefore there is a need to
understand the relationship of the structures within the canal.
Pogrel
reported the relationship of these structures in the third molar region and
concluded the presence of the vein superior to the nerve [5]. The artery was
found to be lingual to the nerve. This concurs with the results obtained from
this cadaveric study. However his study reports the locations in the 3rdmolar
regions only, which are not significant for dental implant surgery. When the
roof of the inferior alveolar canal is breached bleeding may occur and this may
be due to the damage to the vein. However if the insertion of the implant is halted
at this point, damage to the nerve can be avoided.
Conclusion:
1. Variations were seen in the intra canal
position of the inferior alveolar nerve, artery and vein in different regions
of the same mandible and in different mandibles.
2. A blood vessel was found to always lie
superior to the inferior alveolar nerve within the mandibular canal.
3. Variations are seen in the bucco-lingual
positions of the structures within the mandibular canal in different regions of
the same mandible and in different mandibles.
References:
1. Peker I, Alkurt MT, Mihcioglu T. The use of 3
different imaging methods for the localization of the mandibular canal in
dental implant planning. The
International Journal of Oral & Maxillofacial Implants 2008; 23: 463-70.
2. Blaeser BF, August MA, Donoff RB, et al:
Panoramic radiographic risk factors for inferior alveolar nerve injury after
third molar extraction. Journal of Oral
and Maxillofacial Surgery 2003; 61:417-
21.
3. Nakagawa Y, Ishii H, Nomura Y, et al: Third
molar position: Reliability of panoramic radiography. Journal of Oral and Maxillofacial Surgery 2007; 65:1303- 8.
4. Kilic C, Kamburoglu K, Ozen T, Balcioglu HA,
Kurt B, Kutoglu T, et al. The Position of the Mandibular Canal and Histologic
Feature of the Inferior Alveolar Nerve.
Clinical Anatomy. 2010; 23:34–42.
5. Pogrel MA, Dorfman D and Fallah H. The
Anatomic Structure of the Inferior Alveolar Neurovascular Bundle in the Third
Molar Region. Journal of Oral and
Maxillofacial Surgery 2009; 67:2452-2454.
6. Angel JS, Mincer HH, Chaudhry J and Scarbecz
M. Cone-beam Computed Tomography for Analyzing Variations in Inferior Alveolar
Canal Location in Adults in Relation to Age and Sex. Journal of Forensic Sciences, 2011; 56: 216-19.
7. Levine MH, Goddard AL and Dodson TB. Inferior
Alveolar Nerve Canal Position: A Clinical and Radiographic Study. Journal of Oral and Maxillofacial Surgery 2007;
65:470-474.
8. Liu T, Xia B, Gu Z. Inferior alveolar canal
course: a radiographic study. Clinical
Oral Implants Research. 2009; 20:
1212–1218.
9. Juodzbalys G, Wang HL, Sabalys G. Anatomy of
Mandibular Vital Structures. Part I: Mandibular Canal and Inferior Alveolar
Neurovascular Bundle in relation with Dental Implantology. Journal of Oral & Maxillofacial Research 2010 1(1):e2.
10. Megumi Ueda, Kenji Nakamori, Kaori Shiratori,
Tomohiro Igarashi, Takanori Sasaki, Naoki Anbo, et al. Clinical Significance of
Computed Tomographic Assessment and Anatomic Features of the Inferior Alveolar
Canal as Risk Factors for Injury of the Inferior Alveolar Nerve at Third Molar
Surgery. Journal of Oral and
Maxillofacial Surgery 2012; 70:514-520.
Legends:
Figure 1a to 1f:
Cross-sections of cadaveric mandibles
Figure 2: Histologic
examination of the specimen showing Inferior alveolar nerve, artery and vein
Figure 3: Schematic
representation of the neurovascular bundle
No comments:
Post a Comment