538© IJMDC. https://www.ijmdc.com

International Journal of Medicine in Developing Countries

Evaluation of the location of mental foramen by cone-beam computed tomography for patients visiting dental clinics at Qassim UniversityAbdulsalam Saleh Alharbi1*, Hatim Saeed Almutairi1, Abdulmajeed Fahad Albishri1, Shaul Hameed Kolarkodi2

ABSTRACT

Background: The mental foramen (MF) is located bilaterally on the anterior surface of the mandible. It is usu-ally seen between the roots of the first and second mandibular premolars. It is challenging to locate the MF clinically; the knowledge of the exact location of the MF is vital before placing implants to achieve effective mental nerve block anesthesia. Hence the current study was aimed at evaluating the location of MF by Cone-Beam computed tomography (CBCT) for patients visiting dental clinics at Qassim University.

Methodology: The study sample of 43 CBCT images, with MF visible on both sides of the mandible, was selected from achieves, with age groups ranged 20-60 years. After determining the horizontal and vertical diameter of each MF, a ratio of both diameters (H:V) was calculated and used to classify the form of MF into one of three types: Type I (oval horizontal form), Type II (oval vertical form), and Type III (round form). The location of the MF was noted. The variables were statistically analyzed using Statistica 12.5 PL software (StatSoft, Poland).

Results: The current study revealed that the most frequent anterior-posterior position of the MF on both the right and left sides in female and male subgroups was a location between the first and second premolar. While the most frequent superior-inferior position of the MF was below the apices of the first and second mandibular premolar teeth roots. Type II MF was the most rarely observed type in a whole studied population.

Conclusion: The current study showed that CBCT analysis for the type and location of MF could contribute to the success of implant planning and to avoid future complications.

Keywords: Cone beam computed tomography, mental foramen, implant dentistry.

Introduction

The mental foramen (MF) is a bilateral opening localized

on the anterior surface of the mandible. Most often,

it is situated between the first and second inferior

premolars. It is crucial and challenging to locate MF

by clinical procedures. Knowing the exact location

of the MF is vital for placing implants and effective

mental nerve block anesthesia. One of the complications

during implant placement in the anterior mandible is a

neurosensory alteration in the chin and lower lip due to

improper identification and protection of the MF and

anterior mental loop. In this method, using a cone-shaped

ionizing radiation beam, the high-resolution cross-

sectional three-dimensional (3D) images in the frontal,

sagittal, and transverse planes are provided by CBCT. It

can help to obtain detailed information on structures of

the maxillofacial complex and enables identification and

precise evaluation of the anatomical variations.

Knowledge of the precise location and well-defined

shape, size, and number of MF are crucial for different

clinical dental procedures. Successful and complication-

free dental procedures such as curettage, root canal

Correspondence to: Abdulsalam Saleh Alharbi*College of Dentistry, Qassim University, Al-Qassim, Saudia Arabia.Email: Abdussalam1415@gmail.comFull list of author information is available at the end of the article.Received: 16 December 2020 | Accepted: 29 December 2020

Abdulsalam Saleh Alharbi et al, 2021;5(2):538–544.https://doi.org/10.24911/IJMDC.51-1608148826

ORIGINAL ARTICLE

Evaluation of the location of mental foramen by cone-beam computed tomography

539

treatment, periapical surgery, orthognathic surgery, and

effective anesthesia during nerve blocks depend on an

operator's knowledge about MF [1]. Implant placement

in the inter-foramina area is strictly related to the MF

location because it determines the position of the most

distal implants. Many studies indicate that a minimum

distance between MF and an implant should amount to

6 mm [2,3]. Any invasive procedure performed in this

region may damage the neurovascular bundles and cause

serious complications such as paresthesia [4].

So far, it is known that the MF position depends on the

ethnic origin of the patients [5]. A location and number

of MF can be evaluated with different methods such as

macroscopic investigations on dry skulls [6,7], plane

radiographs [8,9], and computed tomography (CT)

images [10]. Among several methods, the most accurate

and safest method for patients is currently considered to

be the cone-beam computed tomography (CBCT) study.

In this method, a cone-shaped ionizing radiation beam

is used to obtain the high-resolution cross-sectional

images in the front, sagittal, and transverse planes

[11,12]. Moreover, CBCT is a cheaper test than classical

CT and requires a significantly lower ionizing radiation

dose [13,14]. CBCT provides three-dimensional (3D)

images, which can help to obtain detailed information

on structures of the maxillofacial complex, and enables

identification and precise evaluation of the anatomical

variations [15,16]. Hence, this study aimed to determine

the size and location of MF in relation to the lower teeth

using CBCT.

Material and Methods

Following ethical approval, 43 CBCT images were

selected from the Qassim University Dental Clinics.

CBCT images were selected according to the following

inclusion criteria: age groups range 20-60 years inclusive,

MF visible on both sides of the mandible, all mandibular

premolar teeth present, and premolar region visible on

the CBCT image. The CBCT images were selected from

the CBCT archive and communications system by a

dental and maxillofacial radiology staff member so that

only radiographs of grade one quality were included. The

exclusion criteria were images with large pathological

lesions in the mandible, bone fractures in regions of

examination, inadequate picture quality caused by

osteosynthesis plates/implants, or patient movement

during exposure were rejected. According to the above

inclusion and exclusion criteria, the resulting group of

43 patients (20 males and 23 females) was used in the

retrospective analysis. The characteristics of the study

group were presented in Table 1 and Figure 1.

All CBCT images were performed using the CALILEOS

device at 120 kVp and 5.0 mA, with a voxel size 0.125-0.25

mm and an exposure time of 20 seconds. All images were

analyzed using specialized computer software (Sirona

Dental System GmbH & Co. KG, Bonn, Germany). Three

independent researchers manually evaluated the images.

Each measurement of a single image was performed twice

separately for the left and right sides. Average values from

measurements of both researchers were calculated and

used for further analysis. Measurements were performed

on axial, sagittal, and coronal CBCT slices of 0.13 mm

thickness. The vertical size of MF (V) was determined on

the cross-sectional CBCT images, and the horizontal size

of MF (H) was assessed on axial scans (Figure 1). After

determining the horizontal and vertical diameter of each

MF, a ratio of both diameters (H:V) was calculated. The

ratio was used to classify the form of MF into one of three

types: Type I (oval horizontal form) was recognized when

H:V was over 1.24, Type II (oval vertical form) at H:V

value less than 0.76, and Type III (round form) when 0.76

≤ H: V ≥ 1.24 [17,18].

Horizontal relationships between MF and roots apices of

the lower premolars and molars were classified into six

types, as shown in Figure 2. Into three types, as shown in

Figure 3 [25].

In Introduction Section, MF was located above the level

of the apices of the first and second mandibular premolar

teeth. In Material and Methods Section had MF at the

level of the apices of the first and second mandibular

premolar teeth, whereas, in Results Section MF was

located below the level of the apices of the first and

second mandibular premolar teeth.

The variables were statistically analyzed using Statistica

12.5 PL software (StatSoft, Poland). The Kruskal-Wallis

test was used to evaluate a relationship between the

vertical and horizontal size of MF and the age of patients,

and the Mann-Whitney U test was used to evaluate the

relationship between horizontal and vertical diameters of

MF and sex of the patients. The chi-square test was used

Table 1. Characteristics of the study group.

Age of patients (years)

GenderTotal NMale Female

N % N %20-27 9 45.0 12 52.2 21

28-60 11 55.0 11 47.8 22

Total 20 100.0 23 100.0 43

Figure 1. Cross sectional images of CBCT showing horizontal and vertical measurements of mental foramen.

Evaluation of the location of mental foramen by cone-beam computed tomography

540

to evaluate the relationship between the type of MF and

age and sex of the patients. The statistical significance

was established at p < 0.05.

Results

In the current study, there were no significant differences in

values of the vertical diameters and the H:V ratio on both

sides in relation to the age of participants. However, there

was a significant difference in the value of the horizontal

diameter on the right side in relation to the participant's

age. Comparison of the average values of the horizontal

diameters between male and female subgroups revealed

significant differences both on the right and left sides.

However, a comparison of the average values of the vertical

diameters between male and female subgroups revealed

significant differences on the left side, as shown in Table 2.

In males, the average values of a horizontal diameter (p = 0.049) were significantly higher on both right and left

sides than in the female subgroup, whereas on the left side,

the average value of the vertical diameter was significantly

higher in men (p = 0.031) as compared to women.

Figure 3. Schematic representation of the MF's superior-inferior position in relation to the lower premolars (PM1, first premolar; PM2, second premolar). Position (1) above the roots apices of PM1 and PM2, (2) at the level of the roots apices of PM1 and PM2, (3) below the roots apices of PM1 and PM2.

Table 2. Comparison of a MF size in the studied subjects.

Subgroup

Right side Left sideHorizontal

diameter (mm)Vertical

diameter (mm) H:V Horizontal diameter (mm)

Vertical diameter (mm) H:V

Mean ± SD (min-max)

Mean ± SD (min-max)

Mean ± SD (min-max)

Mean ± SD (min-max)

Mean ± SD (min-max)

Mean ± SD (min-max)

Age (years)

20-274.07 ± 0.99 3.50 ± 0.67 1.18 ± 0.29 4.38 ± 0.93 3.56 ± 0.77 1.25 ± 0.22

(2.86-6.16) (2.28-5.33) (0.70-1.73) (2.46-6.44) (2.16-5.46) (0.75-1.65)

28-603.57 ± 0.71 3.47 ± 0.67 1.07 ± 0.29 3.76 ± 0.74 3.66 ± 0.79 1.06 ± 0.24

(2.34-4.86) (2.01-5.33) (0.67-1.67) (2.75-4.95) (2.81-6.15) (0.47-1.72)

p value .048 .815 .982 .524 .966 .871

Gender

Male 3.84 ± 1.06 3.53 ± 0.81 1.12 ± 0.31 4.14 ± 1.07 3.89 ± 0.92 1.09 ± 0.25

(2.34-6.16) (2.01-5.33) (0.67-1.67) (2.75-6.44) (2.53-6.15) (0.47-1.65)

Female3.78 ± 0.72 3.44 ± 0.51 1.13 ± 0.28 3.99 ± 0.70 3.38 ± 0.54 1.20 ± 0.24

(2.84-5.25) (2.28-4.45) (0.70-1.73) (2.46-5.19) (2.16-4.71) (0.75-1.72)

p value 0.049 0.183 0.588 0.041 0.031 0.819

Figure 2. Schematic representation of the MF's anterior-posterior position in relation to the lower teeth (I1, central incisor; I2, lateral incisor; C, canine; PM1, first premolar; PM2, second premolar; M1, first molar). Position (1) between the C and PM1, (2) in line with the long axis of the PM1, (3) between the long axes of the PM1 and PM2, (4) in line with the long axis of the PM2, (5) between the long axes of the PM2 and M1 and, (6) in line with the long axis of the mesial root of the first lower molar.

Evaluation of the location of mental foramen by cone-beam computed tomography

541

There were no significant relationships between age

and gender of the patients (p > 0.05) and type of MF on

the right and left sides, as shown in Table 3. However,

it is worth noting that Type II MF was the most rarely

observed type among the whole studied population.

The most frequent anterior-posterior position of the

MF on both the right and left sides in female and male

subgroups was between the first and second premolar, as

shown in Table 4.

The most frequent superior-inferior position of the MF

on both the right and left sides was below the level of the

apices of the first and second mandibular premolar teeth

roots, as shown in Table 5.

Discussion

In the current study, the shape, size, and position of the

MF were evaluated in the patients who visited dental

clinics of Qassim University to take CBCT. According

to the size of MF, no differences with relation to the age

of the subjects were observed except for the horizontal

diameter on the right side. On the other hand, statistically

significant differences were observed in the size of MF in

relation to the sex of the patients. In men, the horizontal

diameter on both sides of the mandible and vertical

diameter on the left side was higher than those observed

in women. The results were consistent with those found

by Ewa et al. [19], Gungor et al. [20], Zhang et al. [18],

and Kalender et al. [21], in which the horizontal and

vertical diameters also evaluated in the CBCT study were

higher in men in comparison to women. In our research,

the values of the horizontal and vertical diameters seem

to be higher than in Turkey assessed using the CBCT

method [20] as well as in Bosnia [7] and Sri Lanka [22],

where the studies on human mandibles were performed.

In contrast, the values were lower than those observed

in the Chinese population in CBCT studies [18]. It can

confirm the thesis about differences in the size of MF

between different ethnic groups.

Table 3. Comparison of a MF type in the studied subjects.

SubgroupMF type - right side MF type - left side

I II III I II IIIN (%) N (%) N (%) N (%) N (%) N (%)

Age (years)

20-27 8 (38.1) 1 (4.7) 12 (57.1) 9 (42.9) 1 (4.7) 11 (52.4)

28-60 7 (31.8) 4 (18.2) 11 (50.0) 3 (13.6) 1 (4.5) 18 (81.8)

p value 0.389 0.097

Gender

Male 8 (40.0) 3 (15.0) 9 (45.0) 3 (15.0) 1 (5.0) 16 (80.0)

Female 7 (30.4) 2 (8.7) 14 (60.9) 9 (39.1) 1 (4.3) 13 (56.5)

p value 0.563 0.211

Table 4. Comparison of the horizontal location of the MF in relation to the gender of the patients.

Right side Left side2 N (%) 3 N (%) 4 N (%) 1 N (%) 2 N (%) 3 N (%) 4 N (%) 5 N (%)

M 3 (15.0) 15 (75.0) 2 (10.0) 0 (0.0) 1 (5.0) 17 (85.0) 2 (10.0) 0 (0.0)

F 4 (17.4) 12 (52.2) 7(30.4) 1 (4.3) 7 (30.4) 9 (39.1) 5 (21.7) 1 (4.3)

Evaluation of the location of mental foramen by cone-beam computed tomography

542

Evaluation of the ratio of the two diameters was helpful in

the assessment of the shape of MF. In our study, the most

frequent shape was the round shape (Type III), whereas

the next most frequent was the oval horizontal shape

(Type I). Our observations correspond to those obtained

by Sankar et al [23]. in the Indian population in the studies

on human mandibles, similarly to findings noticed by

Sekerci et al. [24] in the Turkish population and Alam et

al. in the Arabic population in CBCT studies [25].

However, the oval horizontal shape was the most

frequent form in the Chinese population during the

CBCT studies found by Zhang et al. [18] and Ewa et

al. in the Polish population [14]. The same results were

found by Ilayperuma et al. in the Sri Lanka population in

studies on human mandibles [22] as well as Voljewica et

al. in the Bosnian population in human mandibles [7]. It

seems, therefore, that not only the size but also the shape

of the MF is heterogeneous among different populations.

In our study, the superior-inferior position of the MF

below the level of the apices of the first and second

mandibular premolar teeth roots was the most frequent

location, regardless of gender and age on both the left

and right sides. The second most frequent position of the

MF found in our patients was a location at the level of

the apices of the first and second mandibular premolar

teeth roots. The results were similar to those obtained by

Sekerci et al [24]. in CT studies and other researchers

[25,26,19] using both CBCT and panoramic radiographs

methods.

In the anterior-posterior position, the most frequent MF

location regardless of the gender of the subjects was a

position between the first and second premolars of the

mandible characteristic for older patients and, next, a

location in the long axis of the second premolars of a

mandible, typical for the youngest patients on the right

side. Our studies correspond with the results of the

research carried out in every case using CT methods

by Ewa et al. [14], Sekerci et al. [24], and Kalender et

al. [21] in the Turkish population. In Gungor et al. [20]

an MF position between the first and second premolars

was found to be the most typical location in women.

However, Voljevica et al. [7] observed in the patients in

Bosnia, the most frequent MF position on the right side

were in the long axis of the second premolar and on the

left side between the first and the second premolars of

the mandible.

In the studies performed by Igbigbi and Lebona

in Malawians [27], and Mbajiorgu et al. [28] in

Zimbabweans both on human mandibles and also by

Alam et al. [25] in the Arabic population in CBCT, the

most common MF position was in the long axis of the

second premolar. The same results were obtained for the

Chinese [29], Nigerian [30], Saudi [31], Kenyan [32],

Kurdish [8], and Sri Lankan [22] populations in studies

on human mandibles and based on Orthopantomography

(OPG) and oblique lateral radiographs. However, Santini

and Land in the British population in studies on human

mandibles [33], Al-Khateeb et al. [26] in the northern

regional Jordanian population [26], and Kqiku et al.

[34] in the Kosovarian population in the studies based

on OPG radiographs found the most frequent location

of MF between the first and second premolars of the

mandible.

Table 5. Comparison of the vertical location of the MF in relation to the gender of the patients.

Right side Left side2 N (%) 3 N (%) 2 N (%) 3 N (%)

M 1 (5.0) 19 (95.0) 1 (5.0) 19 (95.0)

F 9 (39.1) 14 (60.9) 10 (43.5) 13 (56.5)

Evaluation of the location of mental foramen by cone-beam computed tomography

543

Therefore, it seems that there is no single and universal

pattern of MF location in different populations.

This makes a precise assessment of the MF location

characteristic for every population as very helpful in

clinical dental practice. The determination of the shape,

size, and position of the MF is critical, considering

numerous dental procedures carried out in the mandible.

Thus, obtained results could be beneficial for many

clinicians.

However, this study's limitation seems to be a lack of

assessment of a distance of an upper limit MF from the

alveolar crest edge and the distance of an MF lower limit

from the lower edge of a mandible.

Conclusion

The current study showed that CBCT analysis for the

type and location of MF could contribute to the success of

implant planning and avoidance of future complications. Since the sample size taken in our research was small,

we recommend research in this area with a larger study

group in the future.

List of Abbreviations

MF Mental ForamenCBCT Cone-Beam Computed tomographyOPG Orthopantomography

Conflict of interestThe authors declare that there is no conflict of interest regarding the publication of this article.

FundingNone.

Consent to participateInformed consent was obtained from all the participants.

Ethical approvalEthical approval was granted by the Ethics Committee of College of Dentistry, Qassim University via reference/letter number #: EA/6046/2019 dated.

Author details Abdulsalam Saleh Alharbi1, Hatim Saeed Almutairi1, Abdulmajeed Fahad Albishri1, Shaul Hameed Kolarkodi2

1. College of Dentistry, Qassim University, Al-Qassim, Saudia Arabia

2. Department of Maxillofacial Surgery and Diagnostic Science, College of Dentistry, Qassim University, Al-Qassim, Saudia Arabia.

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