See discussions, stats, and author profiles for this publication at: https://www.researchgate.

net/publication/381478111

Morphological Characteristics of the Double Mental Foramen and Its

Relevance in Clinical Practice: An Observational Study

Article in Diagnostics · June 2024

DOI: 10.3390/diagnostics14121277

CITATIONS READS

0 20

6 authors, including:

Alejandro Bruna Pablo Nova-Baeza

Playa Ancha University University of Santiago, Chile
13 PUBLICATIONS 3 CITATIONS 22 PUBLICATIONS 21 CITATIONS

SEE PROFILE SEE PROFILE

Mathias Orellana Walter Aquiles Sepúlveda-Loyola

Universidad Andrés Bello Universidade Estadual de Londrina
44 PUBLICATIONS 51 CITATIONS 71 PUBLICATIONS 1,508 CITATIONS

SEE PROFILE SEE PROFILE

All content following this page was uploaded by Pablo Nova-Baeza on 17 June 2024.

The user has requested enhancement of the downloaded file.

 diagnostics

Article
Morphological Characteristics of the Double Mental Foramen
and Its Relevance in Clinical Practice: An Observational Study
Alejandro Bruna-Mejias 1 , Pablo Nova-Baeza 2,3, * , Florencia Torres-Riquelme 4 , Maria Fernanda Delgado-Retamal 4 ,
Mathias Orellana-Donoso 5,6 , Alejandra Suazo-Santibañez 7 , Walter Sepulveda-Loyola 7 , Iván Valdés-Orrego 8 ,
Juan Sanchis-Gimeno 9 and Juan José Valenzuela-Fuenzalida 4

1 Departamento de Ciencias y Geografia, Facultad de Ciencias Naturales y Exactas, Universidad de Playa

Ancha, Valparaiso 2360072, Chile; alejandro.bruna@upla.cl
2 Unidad de Anatomía Humana Normal, Escuela de Medicina, Facultad de Ciencias Médicas,
Universidad de Santiago de Chile, Santiago 9160000, Chile
3 Departamento de Ciencias Químicas y Biológicas, Facultad de Ciencias de la Salud,
Universidad Bernardo O’Higgins, Santiago 8370993, Chile
4 Departamento de Morfología, Facultad de Medicina, Universidad Andrés Bello, Santiago 8370146, Chile;
ftorresriquelme@gmail.com (F.T.-R.); fernanda.delgado1771@gmail.com (M.F.D.-R.);
juan.kine.2015@gmail.com (J.J.V.-F.)
5 Escuela de Medicina, Universidad Finis Terrae, Santiago 7501015, Chile; mathor94@gmail.com
6 Department of Morphological Sciences, Faculty of Medicine and Science, Universidad San Sebastián,
Santiago 8420524, Chile
7 Faculty of Health and Social Sciences, Universidad de Las Américas, Santiago 8370040, Chile;
alej.suazo@gmail.com (A.S.-S.); walterkine2014@gmail.com (W.S.-L.)
8 Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Santiago 8910060, Chile;
ivan.valdes@gmail.com
Citation: Bruna-Mejias, A.; 9 GIAVAL Research Group, Department of Anatomy and Human Embryology, Faculty of Medicine,
Nova-Baeza, P.; Torres-Riquelme, F.; University of Valencia, 46001 Valencia, Spain; juan.sanchis@uv.es
Delgado-Retamal, M.F.; * Correspondence: pablo.nova@usach.cl
Orellana-Donoso, M.;
Suazo-Santibañez, A.; Abstract: The mental foramen (MF) is an opening found bilaterally on the anterolateral aspect of
Sepulveda-Loyola, W.; Valdés-Orrego, the mandible; it can be round or oval and have different diameters. One of the anatomical variants
I.; Sanchis-Gimeno, J.; of the jaw is the presence of an accessory mental foramen (AMF). These are usually smaller than
Valenzuela-Fuenzalida, J.J. the MF and can be located above, below, or to the sides of the main MF. The objective of this study
Morphological Characteristics of the was to recognize the presence of AMF in dry jaws of the Chilean population and collect information
Double Mental Foramen and Its about its clinical relevance reported in the literature. In this descriptive observational study, we have
Relevance in Clinical Practice: An
collected dried jaws obtained from three higher education institutions in Santiago de Chile, from
Observational Study. Diagnostics 2024,
the Department of Morphology of the Andrés Bello University, the Normal Human Anatomy Unit
14, 1277. https://doi.org/10.3390/
of the University of Santiago, and the Human Anatomy pavilion from the Faculty of Medicine of
diagnostics14121277
the Finis Terrae University. The samples for this research were obtained by convenience, and the
Academic Editors: Mario Manto and observation of the jaws was carried out in the human anatomy laboratories of each institution by
Dongbin Ahn three evaluators independently, and a fourth evaluator was included to validate that each evaluation
Received: 25 April 2024 was correct. The sample for this research came from 260 dry jaws, showing the following findings
Revised: 25 May 2024 from the total jaws studied, and to classify as an accessory MF, it will be examined and measured
Accepted: 11 June 2024 so that it complies with what is declared in the literature as the presence of AMF, which is between
Published: 17 June 2024 0.74 mm. and 0.89 mm. There were 17 studies included with a sample that fluctuated between 1 and
4000, with a cumulative total of 7946 and an average number of jaws analyzed from the studies of
467.4, showing statistically significant differences between the means with the sample analyzed in
this study; p = 0.095. For the cumulative prevalence of the presence of AMF, this was 3.07 in this study,
Copyright: © 2024 by the authors.
and in the compared studies, the average of AMF was 8.01%, which did not present a statistically
Licensee MDPI, Basel, Switzerland.
significant difference; p = 0.158. Regarding the presence of variants of unilateral AMF, this occurred
This article is an open access article
distributed under the terms and
in five jaws, which is equivalent to 1.84% in the sample of this study, while in previous studies, it
conditions of the Creative Commons was 7.5%, being higher on the left side than on the right. The presence of AMF is a variant with high
Attribution (CC BY) license (https:// prevalence if we compare it with other variants of the jaw. Knowledge of the anatomy and position
creativecommons.org/licenses/by/ of the AMF is crucial to analyze different scenarios in the face of surgical procedures or conservative
4.0/). treatments of the lower anterior dental region.

Diagnostics 2024, 14, 1277. https://doi.org/10.3390/diagnostics14121277 https://www.mdpi.com/journal/diagnostics

Diagnostics 2024, 14, 1277 2 of 11

Keywords: mental foramen; anatomical variation mental foramen; double mental foramen;
clinical anatomy

1. Introduction
The mental foramen (MF) is an opening found bilaterally on the anterolateral aspect
of the mandible; it can be round or oval and have different diameters [1]. One of the
anatomical variants of the mandible is the presence of accessory mental foramen (AMF).
These are usually smaller than the main MF and are located either above, below, or to the
sides of the main MF [2]. The presence of AMF can be both bilateral and unilateral, singular,
or multiple, which is uncommon. The characteristic of this foramen is that it is connected
to the mandibular canal; given that any other orifice that is present on the anterior face of
the mandible near the MF that is not in relation to the mandibular canal, it is considered
a nutritive foramen, which usually tends to be smaller in size than the AMF and MF [3].
This is relevant because the content of this AMF is the same as the main MF, that is, the
inferior alveolar artery, inferior alveolar nerve, mental nerve, and inferior alveolar vein.
According to the aforementioned information, we can affirm that the content of the MF
is identical to that of the AMF. Among other vessels and neurovascular structures, these
structures innervate the gums, teeth, the inner surface of the cheeks, the skin of the chin,
the skin of the corners of the mouth, the mucous membrane, and the lower lip, in addition
to irrigating the entire area surrounding these structures [4].
From the point of view of embryology, the MF does not complete its development until
the 12th week of gestation, which happens after the mental nerve branches into fascicles.
The jawbone begins its formation once it is found. The inferior alveolar nerve and its
branches are complete, so the MF and the MFA are formed in the same time range. Once
the mandible has matured, no more MFAs are formed. An example of this is Balcioglu’s
study from 2011, which describes a 30-week fetus with an MFA on the right side [5].
The range of prevalence in the population varies according to ethnicity and sex,
ranging from 1% in the Russian population to 10% in the Arabic population. The different
studies systematically reviewed confirm a lower presence of this foramen in Caucasian
populations and a greater predominance in Middle Eastern countries [3,6–8]. This takes on
special relevance when performing dental procedures since, although in some populations
it is very rare for the patient to present this anomaly as in countries like Saudi Arabia, 1 in
10 patients have it. The sex of the patient also becomes relevant since the majority of studies
reviewed agree that its presence is greater in men than in women, and its highest incidence
is on the right side of the jaw [3]; however, women are more likely to have multiple AMFs
than men, according to the Gümüşok study, in which only women had multiple AMFs [9].
This variant originates in a branch of the mental nerve before it exits through the MF, thus
resulting in the different locations, sizes, and arrangements of this AMF [1,5].
In terms of clinical complications, it usually causes problems in anesthesia procedures,
parasymphyseal fractures, or fractures that affect the jaw near the area of the first and
second premolar, genioplasty treatment, orthognathic surgeries, dental implant surgeries,
osteotomy, neurectomy, trauma, mandibular subapical surgery, periapical surgeries, open
reduction of an anterior mandibular fracture, inferior alveolar nerve transposition surgery,
and molar extraction [1,10]. In the case of local anesthesia, what is sought is the mental
nerve block; however, if the distance between the AMF and the MF is wide, a double
anesthesia must be performed to prevent the patient from feeling pain since the AMF
presents an accessory branch of the mental nerve [11,12]. In the case of implants, the
location of the AMF becomes especially important, because its arrangement limits the
length and width of the dental implant to be placed in the interforaminal area, which
is why it is important to calculate the distance between the AMF and MF [13]. In the
case of genioplasty, this variously causes an intervention in the osteotomy lines that are
drawn to perform the surgery, interfering in a similar way in mandibular subapical surgery.
Diagnostics 2024, 14, 1277 3 of 11

On the other hand, in transposition surgery of the inferior alveolar nerve, it generated
greater difficulty in performing surgery [14]. If this is not taken into consideration, various
iatrogenic injuries can be inflicted on the patient, ranging from numbness of the lower
lip, hypoesthesia of the mandibular area, cheeks, chin, corners of the mouth, and lips, to
hemorrhages or permanent damage to the accessory mental nerve [15]. Therefore, it is
important to complete an evaluation before performing any procedure on the symphysis
and mandibular body or in case the patient presents recurrent problems with anesthesia.
This should be performed using a cone beam computed tomography (CBCT), which will
provide a precise 3D image of the mandible, thus allowing identification of both the MF and
AMF and distinguishing the latter from the nutritional orifices. This procedure should not
be performed using panoramic radiography (OPG) since they give false negatives, because
their image is not so sharp, making it almost imperceptible. These AMFs are imperceptible,
having an efficiency of only 48%; in rare cases, these AMFs may be multiple [16].
The objective of this study was to recognize the presence of the double MF in the
dry jaws of the Chilean population and to compile the greatest information on the clinical
relevance reported in the literature.

2. Materials and Methods

In this descriptive observational study, we have collected fresh mandibles obtained
from 3 private education institutions in Santiago, Chile, the morphology department at
Andrés Bello University, the Normal Human Anatomy Unit of the University of Santiago,
and the anatomy pavilion at the Faculty of Medicine of the Finis Terrae University. This
study met the STROBE verification standards.
The samples for this research were obtained by convenience, and the observation of
the jaws was carried out in the human anatomy laboratories of each institution by three
evaluators independently (MO-JJV and PN) and a fourth evaluator who participated in
the evaluation of the jaws to validate that each evaluation was carried out in the presence
of an accessory MF. The jaws were all evaluated on the same day at each institution, since
each evaluation did not present visual or cognitive alterations for each evaluator, as it is
simple and quick. The data collected from the images were tabulated in an Excel software
spreadsheet V. 2021 1.2.12 (Microsoft, 2020) by the same operator without the personal
identification of each individual.
Data analysis was carried out through descriptive statistics using tables that described
the number of jaws analyzed, the number of jaws with the presence of AMF, and the
laterality of the variant. To establish if there was a relationship between the variable
presence of the AMF in the sample studied in this research and with previous research, we
have added the same data as in this research to make a comparison with previous data
reported in other studies that were compared with the present study through a statistical
analysis of Student’s t-test for means of two paired samples, with statistically significant
values less than 0.05% (p = 0.05). For the analysis of the data reported by the previous
studies, we have taken the mean and prevalence of each study, and we have made an
average between all of them to then compare the mean difference with our study. Finally,
for comparison with previous studies, 4 databases were reviewed, Medline, Scopus, WOS,
and Google Scholar, and the following keywords were used: accessory MF, additional MF,
double MF, anatomical variant, clinical considerations, and clinical anatomy.

3. Results
The study was designed using a descriptive approach to evaluate the presence of
AMFs. This analysis was performed from an external view and by laterality in the mandible.
Therefore, the prevalence of AMFs in the samples were reported, taking into account
bilateral or unilateral presence, the proportion of occurrence on each side in unilateral cases,
and the duplication of the foramen on each side. The samples for this research came from
260 dry jaws, which were obtained from three institutions in Santiago, Chile, showing the
following findings of the total jaws studied, and in order to classify as an accessory MF, it
 mandible. Therefore, the prevalence of AMFs in the samples were reported, taking into
account bilateral or unilateral presence, the proportion of occurrence on each side in uni-
lateral cases, and the duplication of the foramen on each side. The samples for this re-
Diagnostics 2024, 14, 1277 search came from 260 dry jaws, which were obtained from three institutions in Santiago, 4 of 11
Chile, showing the following findings of the total jaws studied, and in order to classify as
an accessory MF, it was observed and measured so that it complied with what was de-
was observed
clared and measured
in the literature as theso that it complied
presence of an AMF. withInwhat was declared
addition, we haveinadded the literature
to each
as the presence
photograph of an AMF.
an image In addition,
that represents we have
where added to eachbundle
the neurovascular photograph
should angoimage
basedthat
on
represents
imaging wherethat
studies the neurovascular
have reported bundle should
this, which is go based 0.74
between on imaging
mm and studies
0.89 mm,that have
with
reported
which this, of
a total which is between
8 (3.07%) 0.74 mm
jaws were foundandthat
0.89presented
mm, withwith
whichanaAMF,
total of
of 8which
(3.07%) jaws
5 were
unilateral, 3 right (Figure 1), and 2 left (Figure 2), while 3 mandibles presented withand
were found that presented with an AMF, of which 5 were unilateral, 3 right (Figure 1), an
2 left (Figure
AMF 2), while
bilaterally (Figure3 mandibles
3). presented with an AMF bilaterally (Figure 3).

Figure
Figure 1.
1. Bilateral
Bilateral accessory
accessory mental
mental foramen.
foramen. The
The superior
superior AMF
AMF ofof both
both MFs;
MFs; inside
inside they
they pass
pass the
the
neurovascular bundle of the inferior alveolar vein, inferior alveolar artery, inferior alveolar nerve,
neurovascular bundle of the inferior alveolar vein, inferior alveolar artery, inferior alveolar nerve,
and to the outside of the formants the mental nerve with its accessory branches that are directed
and to the outside of the formants the mental nerve with its accessory branches that are directed
towards the AMF (Figures made by the authors.).
towards the AMF (Figures made by the authors.).

This information was compared with 19 similar studies using the same exclusion
criteria presented in Table 1 [2,3,7,9,17–31] in order to compare the results and determine
whether there was similarity with the data presented in Table 1, Chilean sample. Regarding
the prevalence of AMFs, the studies were compared with the current study. First, the
17 included studies had samples that fluctuated between 1 and 4000, a cumulative total of
7946, and an average number of jaws analyzed in all of the studies of 467.4, which did not
show statistically significant differences between the means with the sample analyzed in
this study; p = 0.095. For the cumulative prevalence of the presence of AMFs, this was 3.07
in this study, and in the compared studies, the average of AMFs was 8.01%, which did not
present a statistically significant difference; p = 0.158. Regarding the presence of variants
of unilateral AMFs, this occurred in 5 jaws, which is equivalent to 1.84% in the samples
of this study, while in previous studies, it was 7.5%, being higher on the left side than on
the right side. In previous studies, it was greater on the left side. The presence of AMFs
in this study occurred bilaterally in 1.24% compared to the average of previous studies,
which was 0.51. In the present study, it was relatively higher but not statistically significant;
p = 0.231. Finally, in the present study, the sex of the sample was not identified since the
jaws were dry, and it would have been too complicated to identify the sex. On the other
hand, previous studies that did report the sex of the sample showed that this particular
variant occurred in 127 women, which is equivalent to 21.27% of the samples with the AMF
variant, while 125 men presented the AMF variant, which is equivalent to 20.93% (Table 2).
Diagnostics 2024, 14, x FOR PEER REVIEW 5 of 12
Diagnostics 2024, 14, 1277 55ofof11
Diagnostics 2024, 14, x FOR PEER REVIEW 12

Figure
Figure2.2. Left
Leftaccessory
accessorymental
mentalforamen.
foramen.The TheAMF
AMFatatthe
thetoptopofofthe
theMF,
MF, inside
inside the
the neurovascular
neurovascular
Figureof
bundle
bundle 2.the
of Left
the accessory
inferior
inferior mental
alveolar
alveolar foramen.
vein,
vein,inferior The AMF
inferioralveolar
alveolar at theinferior
artery,
artery, top of alveolar
inferior the MF, nerve
alveolar inside
nerveand the to
and neurovascular
tothe
theoutside
outside
ofbundle
the of the
formants inferior
the alveolar
mental vein,
nerve inferior
with its alveolar
accessory artery,
branches inferior
that alveolar
are nerve
directed
of the formants the mental nerve with its accessory branches that are directed towards and
towards to the
theoutside
the AMF
AMF
of the formants
(Figures made by the mental nerve with its accessory branches that are directed towards the AMF
authors.).
(Figures made by the authors.).
(Figures made by the authors.).

Figure 3. Right accessory mental foramen. The AMF at the bottom of the MF; inside the neurovas-
Figure
cular
Figure 3.3.Right
bundle Right accessory
of accessory
the inferior mental
alveolar
mental foramen. The
vein, inferior
foramen. The AMFAMF at the
alveolar
at the bottom
artery,
bottom of MF;
inferior
of the the MF;
alveolarinside
inside nerve,
the theand
neurovas-
to the
neurovascular
cular bundle
outside
bundle of the
of of the inferior
the inferior
formants alveolar
the mental
alveolar vein,with
vein, nerve
inferior inferior alveolar
its accessory
alveolar artery,
branches
artery, inferior inferior alveolar
that are
alveolar nerve,
directed
nerve, and and
totowards
the tothe
outsidethe
outside
AMF. The of theofformants
rest the the mental
foramina seen in nerve
the drywith its accessory
mandibles branches
correspond to that are directed
nutritional foramina towards
(Figures the
of the formants the mental nerve with its accessory branches that are directed towards the AMF. The
AMF.byThe
made therest of the foramina seen in the dry mandibles correspond to nutritional foramina (Figures
authors).
rest of the foramina seen in the dry mandibles correspond to nutritional foramina (Figures made by
made by the authors).
the authors).
This information was compared with 19 similar studies using the same exclusion cri-
This information
teria presented in Tablewas compared with
1 [2,3,7,9,17–31] in 19 similar
order studies using
to compare the same
the results andexclusion
determinecri-
teria presented
whether there was insimilarity
Table 1 [2,3,7,9,17–31]
with the data in order toincompare
presented Table 1, the results
Chilean and determine
sample. Regard-
whether
ing there wasofsimilarity
the prevalence AMFs, the with the data
studies werepresented
comparedinwith
Tablethe
1, current
Chileanstudy.
sample. Regard-
First, the
ing the prevalence of AMFs, the studies were compared with the current study. First, the
Diagnostics 2024, 14, 1277 6 of 11

Table 1. Characteristics of the studies analyzed.

Presence Foramen
Total N and Unilateral (Left and
Author and Year Country Mentoniano Bilateral
Example Right)
Accesory
Saudi
Aljarbou, 2021 [3] 603 via CBT 60/603 9.95% 27 left and 33 right They did not report
Arabia
5 via CBT and
Rahpeyma, 2018 [19] Iran 5/5 100% 1 left and 2 right 2
OPG
Zmysłowska-
Poland 200 via CBCT 28/200 10% 13 left and 15 right They did not report
polakowska, 2017 [20]
Torres, 2015 [21] Brazil 1 via CBCT 1/1 100% 1 right They did not report
23 side is not
Naitoh, 2011 [22] Japan 365 via CBCT 28/365 7.67% 7
specified
69 side is not
Gümüşok, 2017 [9] Turkey 645 via CBCT 75/645 11.62% 6
specified
21 through
Guo, 2009 [23] China embalmed adult 2/21 9.52% 2 side is not specified They did not report
corpses
Iwanaga, 2016 [24] Japan 63 via CBCT 9/63 14.28% 3 left and 1 right 5
15 side is not
Katakami, 2008 [32] Japan 150 via CBCT 16/150 10.66% 1
specified
Lam, 2019 [26] Australia 4000 via CBCT 254/4000 6.35% 122 left and 110 right 12
Li, 2018 [27] China 787 via CBCT 57/787 7.24% 16 left and 37 right 4
Muinelo Lorenzo, 357 via CBCT and
Spain 48/357 13.44% 20 left and 28 right They did not report
2021 [31] PAN
Naitoh, 2009 [28] Japan 157 via CBCT 15/157 9.55% 6 left and 9 right They did not report
96 through dry
Paraskevás, 2015 [29] Germany 4/96 4.16% 4 side is not specified They did not report
jaws
Sun, 2013 [30] South Korea 446 via CBCT 39/446 8.74% 13 left and 20 right 6
Tiwari, 2022 [2] Nepal 47 dry jaws 4/47 8.51% 4 left and 0 right They did not report
Toh, 1992 [33] Japan 3 corpses 3/3 100% 1 left and 2 right They did not report
Current study, 2024 Chile 260 dry jaws 8/260 3.07% 3 left and 2 right 3

Table 2. Summary of articles included and compared with the current study.

Number of Unilateral Bilateral Prevalence in Prevalence in Prevalence by

Total Studies
Jaws Prevalence Prevalence Women Men Region
Asia: 12
Oceania: 1
7946
17 597/7.5% 41/0.51% 127/21.27 125/20.93% Africa: 0
Mean 467.4
America: 1
Europe: 3
Current study,
260 5/1.84% 3/1.23% - - 1 South America
2024

4. Clinical Considerations
The recognition of AMFs contributes to the use of an adequate surgical technique
and prevents possible damage to the nerves and vessels of the treated regions, a situ-
ation that is described by Torres, Zmyslowk, Paraskeva, Tiwari, Sun, Rayphema, and
Munielo [2,15,20,21,29,31]. According to Savoldi [32,34], it is important to consider the use
Diagnostics 2024, 14, 1277 7 of 11

of three-dimensional CBCT images before surgical procedures in the area of the mandibular
premolars and molars in order to evaluate the course of the AMF and the neurovascular
structures in the area, preventing erroneous diagnoses and periosteal detachment dur-
ing implant, periodontal, and periapical surgery, as described by Sun, Lam, Katamaki,
Iwanaga, Gumusok, and Aljarbou [3,24–26,30]. Relating to the above, Naitoh [26] adds
that more studies are needed on the interpretation of various fine neurovascular struc-
tures of the jaw, such as the mandibular bifid and mandibular lingual bone canals, using
rotational panoramic radiographs where the information obtained from the CBCT is fed
back. Savoldi and Guo [23,34] proposed that it could be useful to predict MFs in pa-
tients with missing teeth by looking at combined soft and hard tissue reference points.
Furthermore, Iwanaga [24] suggests that the recognition of AMFs is useful for avoiding
neurovascular complications during implant surgery, nerve blocks, and other oral surgery
procedures. However, further general anatomical studies of AMNs and AMFs should be
performed to clarify the courses of AMN function and allow for predictions about them.
Iwanaga et al. [4] reported that, when the periosteum around the AMF is elevated, the
small number of risk assessments should be taken into account to predict intraoperative
and postoperative complications caused by damaging the foramen and accessory holes in
the jaw that compromise the arteries and nerves in the area. During dental procedures,
such as cleaning and modeling, doctors must respect the precise working length; otherwise,
it could cause damage and/or side effects in the patient. This is mentioned in the study
by Hester et al. [35], which states that excessive preparation of the canal and violation of
the apical foramen, an opening where blood vessels and nerve endings pass that nourish
the dental pulp (soft tissue found inside the tooth), can cause direct physical injury to the
mental nerve and paresthesia therein. Consequently, if the doctor does not corroborate
the presence of this anatomical variant, and if the patient presents with it, it could cause
the damage mentioned above and also cause damage to an accessory branch of the nerve,
overestimating the symptoms and complications of the treatment.
The situation mentioned above was evidenced in a study by Kqiku [36], which de-
scribes a patient who presents with paresthesia and anesthesia with swelling. Radiographi-
cally, the periapical lesion, which corresponds to a pathology at the level of the alveolar
bone and represents an inflammatory response due to bacterial infection of the root canals,
was very close to the mental nerve but without direct anatomical contact. They discussed
various options as to what could have caused this; one possibility was local pressure on the
mental nerve as a consequence of the accumulation of purulent exudate in the mandibular
bone. It should be noted that, although the involvement is close to the dental alveolus joint,
mostly the accessory MF is inferior. Studies have shown that, in the presence of an AMF,
the normal MF could have a rise, which would cause this foramen and the neurovascular
content to approach the treatment region, potentially causing alterations and vascular or
nervous disorders associated with the procedure or treatment to be performed [36].

5. Discussion
In this observational study, we have verified the presence of MFs in dry jaws and
shown that this structure in the Chilean population appears as a variant. We have also
determined, through an analysis of the literature, that the MF presents important clinical
considerations for surgeons.
Although we found no small number of studies that discuss AMFs, not all of them
found their samples with the variant randomly; some studies evaluated only jaws with
AMFs. The AMF is usually smaller than MF, ranging from 0.74 mm. to 0.89 mm. There is a
distance between the AMF and MF of 0.67 mm to 6.3 mm; therefore, they can be located in
different areas around the MF. Most commonly, the AMF is found inferior to the MF, either
anterior or posterior. However, there have been cases where the AMF is located toward the
superior between the first premolars and the second molar, but this location also depends
on the study population, thus there are discrepancies among some studies. Naitoh [28]
notes that AMFs occur mainly in the posteroinferior region of the MF. Balcioglu [5], on
Diagnostics 2024, 14, 1277 8 of 11

the other hand, presented a case of the AMF anterior to the MF in a 6-year- old child, and
Han [37] reports that the AMF is located toward the anteroinferior of the MF. This could
indicate that, depending on the ethnicity and population, different locations of the AMF
could be associated, but there is no study with an adequate methodology that categorically
confirms that the location is different according to ethnicity or race. Regarding anatomy and
presence, this foramen tends to be confused with nutritional foramen, which can be multiple
and are not connected to the mandibular canal, which is a substantial difference with the
AMF, which has a close relationship with the mandibular canal and its neurovascular
content. This confusion usually occurs when performing an orthopantomography, which
can result in false negatives of the AMF due to the poor quality of the image, having more
than 50% error when it is dictated as a nutritional foramen instead of the AMF. For this
fact, a CBCT is the most appropriate way to search for this anatomical variation, because it
provides a clear 3D image that will allow the doctor to see the differences that exist between
the nutritional foramen concerning the AMF and MF.
On the other hand, the AMF has its origins in the branching of the mental nerve before
it exits through the MF; embryologically, they complete their development in the 12th week
of gestation after the branching of the inferior alveolar nerve. This means that both the
AMF and MF become formed during similar time frames. Once the mandible matures, this
foramen cannot form; therefore, an adult or pediatric patient who was born without one
or more AMFs would not develop this anatomical variation in the future; that is, a single
diagnosis would suffice. An example of this is described by Balcioglu [5], who presented
the case of a 30-week fetus with an AMF on the right side. This could indicate the possibility
of diagnosing this variation, either in a neonate or in an adult, thus decreasing possible
risks in dental care across the entire age range.
Regarding the content, we have the inferior alveolar artery, inferior alveolar nerve,
inferior alveolar vein, and other neurovascular structures. These structures innervate the
gums, the teeth, the inner surface of the cheeks, the skin of the chin, the skin at the corners
of the mouth, the mucous membrane, and the lower lip, in addition to irrigating the entire
area surrounding these structures. Since they are all related to both the MF and AMF, it
is important at a clinical level. An example of this is with anesthesia. To correctly carry
out this process in a patient with an AMF, a double anesthesia must be performed, not
only in the mental nerve of the MF but also in the AMF, through which this nerve will
also pass. In turn, the accessory mental nerve (AMN) that passes through the AMF has
branching patterns. Iwanaga [24] defines this distribution as being mainly directed toward
the right angular region; however, Toh [33] defines three different patterns. The first being
an AMF in the left zone to the MF; in this pattern, the AMN is a branch from the corner of
the skin of the mouth that subsequently communicates with a branch of the facial nerve.
The second pattern is a right AMF with a location superior to the MF; in this case, the AMN
is a branch of the mucous membrane and skin belonging to the corner of the mouth that
will subsequently generate communication with the oral nerve and innervate the gum of
the molars. The third pattern is an AMF on the right side above the MF, whereby the AMN
emerges from the AMF as a mucosal branch belonging to the medial area of the lower lip
that will later communicate with branches of the inferior alveolar nerve. The branches vary
by location—anterior, superior, posterior, and inferior—and by the distance between the
AMF and MF, the latter being a determining factor. The second and third cases have the
same location of the AMF but different distances between the MF and AMF; therefore, it is
this distance added to the location that indicates how the AMN will be distributed since
it complements and completes the innervation in areas where the MN (mental nerve) is
not distributed.
In terms of its distribution, this varies according to ethnicity, population, and sex.
There is a lower presence of these AMFs in the Caucasian population; for example, Russia
has only a 1% prevalence, whereas there is a significant incidence in countries in Asia
and the Middle East, including Japan, Sri Lanka, India, Iran, and Saudi Arabia, where
the presence of AMFs is around 10% or more. Although authors such as Naitoh [22]
Diagnostics 2024, 14, 1277 9 of 11

indicate that there is no significant difference in prevalence according to gender, Toh [33]
proposes that AMFs are more frequent in male patients of African or American ethnicity,
and Gumusok [9] determined that the prevalence in Turkey was higher in men than in
women. In that study, however, all multiple AMFs were in women, which indicates a
possible tendency for women to have more than one AMF. These data show that this
anatomical variant is common in many countries and populations, so it is important to
consider it for the safety of patients and for a procedure that is both adequate and successful.
Regarding the symptoms in the studies presented, no sign has been described that
causes any associated pathology; only the effects generated after a surgical procedure or
through pathologies that affect surrounding structures are mentioned. Given the above,
it could be deduced that patients could present this variant throughout their lives and be
unaware of its presence since it does not produce symptoms by itself. In relation to clinical
considerations, we have already mentioned that identifying this variant is of utmost impor-
tance, specifically to prevent damage to nerves and blood vessels associated with the MF
and to avoid detachment of the periosteum during dental, periodontal, and periapical im-
plant surgery, as it can present a different distribution from the established one. According
to the above, the use of three-dimensional CBCT images before surgical procedures on the
jaw is crucial to evaluate the course of nerves and blood vessels, preventing misdiagnosis
and complications. Furthermore, neurovascular complications during dental procedures,
such as implant surgery and nerve blocks, could be avoided by recognizing this anatomical
variant. Also, in dental procedures such as cleaning and modeling, it is essential to respect
the precise working length in cases where excessive preparation of the canal and violation
of the apical foramen is performed on a person with this variant. Neglecting to check for
the presence of this anatomical variant could cause direct physical injury to the mental
nerve and paresthesia and could damage the accessory branch of the nerve, overestimating
the symptoms and complications of the treatment. Paresthesia and anesthesia are some of
the effects that are deduced according to the research that is generated by not carrying out
an adequate review of the presence of this variant since these symptoms are exhibited by
the presence of an infection or damage close to the mental nerve.
Finally, the data presented in this study show the similarities to previous studies in
terms of the presence of AMFs in the laterality and the region where this variant occurs.
We believe that identifying the anatomical variants is essential and useful in several fields,
including medical practice. By identifying anatomical variants, doctors can recognize and
diagnose diseases or medical conditions in a more specific and efficient way, avoiding
errors and inadvertent injuries to important structures in surgical procedures.

6. Conclusions
The presence of AMFs is a variant with a high prevalence if we compare it with other
variants of the jaw. Knowledge of the anatomy and position of the AMF is crucial to
analyzing different scenarios in the face of surgical procedures or conservative treatments
of the lower anterior dental region. When the presence of this variant is recognized,
all precautions can be taken to avoid excessive bleeding or paresthesia or paresis of the
mental nerve and its territory of innervation. Finally, we believe that the development of
new clinical anatomical studies that associate the presence of the AMF will improve the
management and treatment of these patients.

Author Contributions: Methodology, A.B.-M., M.F.D.-R., A.S.-S., I.V.-O. and J.J.V.-F.; Software, F.T.-R.,
M.O.-D., W.S.-L. and J.S.-G.; Validation, A.B.-M. and J.J.V.-F.; Formal analysis, P.N.-B., F.T.-R. and
M.F.D.-R.; Investigation, P.N.-B., M.O.-D., W.S.-L. and I.V.-O.; Resources, F.T.-R. and J.S.-G.; Data
curation, P.N.-B., M.O.-D., A.S.-S. and W.S.-L.; Writing—original draft, A.S.-S., J.S.-G. and J.J.V.-F.;
Supervision, J.S.-G. and J.J.V.-F.; Project administration, M.F.D.-R.; Funding acquisition, J.S.-G. All
authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Diagnostics 2024, 14, 1277 10 of 11

Institutional Review Board Statement: The samples are donations of common graves from different
cemeteries in the metropolitan region of Santiago de Chile, these are used for teaching. Which has the
permission of the aforementioned study houses to carry out teaching and research without having to
go through ethics or approval committees, since these are met when the samples enter the normal
anatomy laboratories with resolution S:64-2022-1042, we also clarify that this study did not involve
people or live animals.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data presented in this study are available on request from the
corresponding author. The data are not publicly available due to privacy.
Acknowledgments: Universidad de Playa Ancha, plan de Fortalecimiento Universidades Estatales-
Ministerio de Educación, convenio UPA 1999.
Conflicts of Interest: The authors declare no conflict of interest.

References
1. Lipski, M.; Tomaszewska, I.M.; Lipska, W.; Lis, G.J.; Tomaszewski, K.A. The mandible and its foramen: Anatomy, anthropology,
embryology and resulting clinical implications. Folia Morphol. 2013, 72, 285–292. [CrossRef] [PubMed]
2. Tiwari, N. Left Accessory Mental Foramen in Dry Mandibles in Department of Anatomy in a Medical College: A Descriptive
Cross-sectional Study. J. Nepal Med. Assoc. 2022, 60, 805–807. [CrossRef] [PubMed]
3. Aljarbou, F.; Riyahi, A.M.; Altamimi, A.; Alabdulsalam, A.; Jabhan, N.; Aldosimani, M.; Alamri, H.M. Anatomy of the accessory
mental foramen in a Saudi subpopulation: A multicenter CBCT study. Saudi Dent. J. 2021, 33, 1012–1017. [CrossRef] [PubMed]
4. Iwanaga, J.; Saga, T.; Tabira, Y.; Nakamura, M.; Kitashima, S.; Watanabe, K.; Kusukawa, J.; Yamaki, K.-I. The clinical anatomy of
accessory mental nerves and foramina. Clin. Anat. 2015, 28, 848–856. [CrossRef] [PubMed]
5. Balcioglu, H.A.; Kilic, C.; Akyol, M.; Ulusoy, A.T. Horizontal migration of pre- and postnatal mental foramen: An anatomic study.
Int. J. Pediatr. Otorhinolaryngol. 2011, 75, 1436–1441. [CrossRef]
6. Yoon, T.Y.; Ahmadi, A.G.; Saed, N.A.; Estrin, N.; Miller, D.E.; Dinh, T.N. Prevalence and anatomical characteristics of the accessory
mental foramen: A study using cone beam computed tomography. Gen. Dent. 2019, 67, 62–67. [PubMed]
7. Valenzuela-Fuenzalida, J.J.; Cariseo, C.; Gold, M.; Díaz, D.; Orellana, M.; Iwanaga, J. Anatomical variations of the mandibular
canal and their clinical implications in dental practice: A literature review. Surg. Radiol. Anat. 2021, 43, 1259–1272. [CrossRef]
[PubMed]
8. Daniel, P.; Rajkohila, J.; Ambikaipakan, S.; Rabi, S. Morphological and morphometric analysis of accessory mental foramen in dry
human mandibles of south indian population. Indian J. Dent. Res. 2018, 29, 56–60. [CrossRef]
9. Gümüşok, M.; Akarslan, Z.Z.; Başman, A.; Üçok, Ö. Evaluation of accessory mental foramina morphology with cone-beam
computed tomography. Niger. J. Clin. Pract. 2017, 20, 1550–1554. [CrossRef]
10. Nagarajappa, A.K.; Alam, M.K.; Alanazi, A.A.; Bandela, V.; Faruqi, S. Implications of impacted mandibular cuspids on mental
foramen position. Saudi Dent. J. 2020, 33, 713–717. [CrossRef]
11. Filo, K.; Schneider, T.; Locher, M.C.; Kruse, A.L.; Lübbers, H.T. The inferior alveolar nerve’s loop at the mental foramen and its
implications for surgery. J. Am. Dent. Assoc. 2014, 145, 260–269. [CrossRef] [PubMed]
12. Dalga, S. Topographic and morphometric study of the mental foramina of Abaza goats with its clinical implication for regional
anesthesia. Folia Morphol. 2020, 79, 576–579. [CrossRef] [PubMed]
13. Greenstein, G.; Tarnow, D. The mental foramen and nerve: Clinical and anatomical factors related to dental implant placement:
A literature review. J. Periodontol. 2006, 77, 1933–1943. [CrossRef] [PubMed]
14. Hwang, K.; Lee, W.J.; Song, Y.B.; Chung, I.H. Vulnerability of the inferior alveolar nerve and mental nerve during genioplasty:
An anatomic study. J. Craniofacial Surg. 2005, 16, 10–14, discussion 14. [CrossRef]
15. Laher, A.E.; Wells, M.; Motara, F.; Kramer, E.; Moolla, M.; Mahomed, Z. Finding the mental foramen. Surg. Radiol. Anat. 2016, 38,
469–476. [CrossRef] [PubMed]
16. Pelé, A.; Berry, P.-A.; Evanno, C.; Jordana, F. Evaluation of Mental Foramen with Cone Beam Computed Tomography: A Systematic
Review of Literature. Radiol. Res. Pract. 2021, 2021, 1–10. [CrossRef]
17. Orhan, A.I.; Orhan, K.; Aksoy, S.; Özgül, O.; Horasan, S.; Arslan, A.; Kocyigit, D. Evaluation of perimandibular neurovasculariza-
tion with accessory mental foramina using cone-beam computed tomography in children. J. Craniofacial Surg. 2013, 24, e365–e369.
[CrossRef]
18. Yalcin, T.Y.; Bektaş-Kayhan, K.; Yilmaz, A.; Ozcan, I. An Alternative Classification Scheme for Accessory Mental Foramen. Curr.
Med. Imaging 2021, 17, 410–416. [CrossRef] [PubMed]
19. Rahpeyma, A.; Khajehahmadi, S. Accessory mental foramen and maxillofacial surgery. J. Craniofacial Surg. 2018, 29, e216–e217.
[CrossRef]
20. Zmysłowska-Polakowska, E.; Radwański, M.; Ł˛eski, M.; Ledzion, S.; Łukomska-Szymańska, M.; Polguj, M. The assessment of
accessory mental foramen in a selected polish population: A CBCT study. BMC Med. Imaging 2017, 17, 17. [CrossRef]
Diagnostics 2024, 14, 1277 11 of 11

21. Torres, M.G.G.; Valverde, L.d.F.; Vidal, M.T.A.; Crusoé-Rebello, I.M. Accessory mental foramen: A rare anatomical variation
detected by cone-beam computed tomography. Imaging Sci. Dent. 2015, 45, 61–65. [CrossRef]
22. Naitoh, M.; Yoshida, K.; Nakahara, K.; Gotoh, K.; Ariji, E. Demonstration of the accessory mental foramen using rotational
panoramic radiography compared with cone-beam computed tomography: Demonstration of the accessory mental foramen
using rotational panoramic radiography. Clin. Oral Implant. Res. 2011, 22, 1415–1419. [CrossRef]
23. Guo, J.L.; Su, L.; Zhao, J.L.; Yang, L.; Lv, D.L.; Li, Y.Q.; Cheng, F.B. Location of mental foramen based on soft- and hard-tissue
landmarks in a chinese population. J. Craniofacial Surg. 2009, 20, 2235–2237. [CrossRef]
24. Iwanaga, J.; Watanabe, K.; Saga, T.; Tabira, Y.; Kitashima, S.; Kusukawa, J.; Yamaki, K. Accessory mental foramina and nerves:
Application to periodontal, periapical, and implant surgery. Clin. Anat. 2016, 29, 493–501. [CrossRef] [PubMed]
25. Direk, F.; Uysal, I.I.; Kivrak, A.S.; Fazliogullari, Z.; Unver Dogan, N.; Karabulut, A.K. Mental foramen and lingual vascular canals
of mandible on MDCT images: Anatomical study and review of the literature. Anat. Sci. Int. 2018, 93, 244–253. [CrossRef]
[PubMed]
26. Lam, M.; Koong, C.; Kruger, E.; Tennant, M. Prevalence of accessory mental foramina: A study of 4000 CBCT scans. Clin. Anat.
2019, 32, 1048–1052. [CrossRef]
27. Li, Y.; Yang, X.; Zhang, B.; Wei, B.; Gong, Y. Detection and characterization of the accessory mental foramen using cone-beam
computed tomography. Acta Odontol. Scand. 2018, 76, 77–85. [CrossRef] [PubMed]
28. Naitoh, M.; Hiraiwa, Y.; Aimiya, H.; Gotoh, K.; Ariji, E. Accessory mental foramen assessment using cone-beam computed
tomography. Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endodontol. 2009, 107, 289–294. [CrossRef] [PubMed]
29. Paraskevas, G.; Mavrodi, A.; Natsis, K. Accessory mental foramen: An anatomical study on dry mandibles and review of the
literature. Oral Maxillofac. Surg. 2015, 19, 177–181. [CrossRef]
30. Sun, C.X.; Henkin, J.M.; Ririe, C.; Javadi, E. Implant failure associated with actinomycosis in a medically compromised patient. J.
Oral Implant. 2013, 39, 206–209. [CrossRef]
31. Muinelo-Lorenzo, J.; Rodríguez-Pato, R.; Martínez-Reglero, C.; Salgado-Barreira, A.; Suárez-Cunqueiro, M.M. Detection of
the Accessory Mental Foramina on Human Mandibles Using Cone-beam Computed Tomography: A Systematic Review and
Meta-analysis. J. Endod. 2021, 47, 1215–1228. [CrossRef] [PubMed]
32. Katakami, K.; Mishima, A.; Shiozaki, K.; Shimoda, S.; Hamada, Y.; Kobayashi, K. Characteristics of accessory mental foramina
observed on limited cone-beam computed tomography images. J. Endod. 2008, 34, 1441–1445. [CrossRef]
33. Toh, H.; Kodama, J.; Yanagisako, M.; Ohmori, T. Anatomical study of the accessory mental foramen and the distribution of its
nerve. Okajimas Folia Anat. Jpn. 1992, 69, 85–88. [CrossRef] [PubMed]
34. Savoldi, F.; Yon, M.J.; Kwok, V.M.; Yeung, A.W.; Tanaka, R.; Tsoi, J.K.; Matinlinna, J.P.; Bornstein, M.M. Accuracy of CBCT in the
Identification of Mental, Lingual, and Retromolar Foramina: A Comparison with Visual Inspection of Human Dry Mandibles. Int.
J. Periodontics Restor. Dent. 2021, 41, e277–e286. [CrossRef] [PubMed]
35. Hester, K.M.; Rahimi, O.B.; Fry, C.L.; Nation, H.L. The relative locations of the supraorbital, infraorbital, and mental foramina:
A cadaveric study. J. Anat. 2021, 239, 782–787. [CrossRef] [PubMed]
36. Kqiku, L.; Weiglein, A.; Kamberi, B.; Hoxha, V.; Meqa, K.; Städtler, P. Position of the mental foramen in Kosovarian population.
Coll. Antropol. 2013, 37, 545–549.
37. Han, S.-S.; Hwang, J.J.; Jeong, H.-G. Accessory mental foramina associated with neurovascular bundle in Korean population.
Surg. Radiol. Anat. 2016, 38, 1169–1174. [CrossRef]

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual
author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to
people or property resulting from any ideas, methods, instructions or products referred to in the content.

View publication stats