Age-related variations in the location of the mental foramen: a retrospective panoramic radiographic study in children

Introduction

The mental foramen (MF) serves as a significant anatomical landmark located bilaterally in the anteriorlateral region of the mandible, near the apices of the first and second premolar teeth (1, 2). This funnel-shaped structure typically remains equidistant from the superior and inferior borders of the mandible, with approximate dimensions of 4–6 mm in width and 3–4 mm in length. Its morphology and position may be influenced by factors such as gender, race, and ethnicity (3).

Precise identification of the mandibular foramen (MF) is crucial for numerous dental and medical procedures, such as implant placement, surgical interventions, endodontic treatments, osteotomies, and anesthetic injections (1, 2). Damage to the nerves and arteries passing through this region may lead to partial or complete sensory loss in the affected area (4).

Furthermore, the position of the mental foramen (MF) can be employed to evaluate the morphometric symmetry of the mental triangle, as well as the microscopic and macroscopic morphology of the mandible, bone regeneration activity, and even paleoanthropological features of the facial skeleton across various demographic groups (2). Various imaging modalities, including computed tomography (CT), cone beam computed tomography (CBCT), periapical radiography, panoramic radiography, magnetic resonance imaging (MRI), and palpation, are used to locate the MF (3) precisely.

In clinical practice, panoramic radiography is frequently recommended because it offers a comprehensive view of the oral cavity, jaws, and temporomandibular joints. Although computed tomography (CT) scans provide more detailed anatomical information, panoramic radiography is often favored due to its cost-effectiveness, ease of acquisition and interpretation, and reduced radiation exposure (3). Precise identification of the mental foramen (MF) is essential for the successful administration of anesthesia, implant placement, surgical planning, and the prevention of postoperative complications in the premolar region (4, 5). This study aims to assess the horizontal and vertical positions of the MF across various age groups.

Material and methods:

Measurement of the Horizontal Location of the MF:

The horizontal positioning of the MF was established using the digital ruler tool (7), in accordance with the classification proposed by Chkoura and El-Wady (6). The position of the MF relative to the premolars was categorized as follows (see Figure 1):

• Type 1: Mesial to the apex of the first premolar.
• Type 2: In line with the apex of the first premolar.
• Type 3: Between the apices of the first and second premolars.
• Type 4: In line with the apex of the second premolar.
• Type 5: Between the apices of the second premolar and the first molar.

For measurements involving primary molars, tangential lines were delineated on the mesial surface of both the first and second primary molars, along with lines extending from the central region of the crowns through the area situated between the two roots. It is noteworthy that primary molars generally have two roots, (6). The classification for the MF associated with primary molars was subsequently articulated as follows:

• Type 1m: Mesial root of tooth D.
• Type 2m: Apex of tooth D.
• Type 3m: Distal root of tooth D.
• Type 4m: Between teeth D and E.
• Type 5m: Mesial root of tooth E.
• Type 6m: Apex of tooth E.
• Type 7m: Distal root of tooth E.

Result

Table 1 delineates the distribution of various vertical positions of the mandibular foramen (MF) among patients aged 4 to 18 years. The most prevalent position was identified in the middle third, with a frequency of 93.6%. The coefficient of agreement for the vertical positioning of the MF was determined to be 0.074 (P < 0.001).

Table 2 illustrates the distribution of various vertical positions of the mandibular fossa (MF) in males and females. No statistically significant difference in the vertical position of the MF was observed between genders (p = 0.751). While the prevalence of middle-third positions was marginally higher in males (94.1%) than in females (93.2%), this variation did not reach statistical significance.

Table 3 illustrates the prevalence of various horizontal positions of the mandibular foramen (MF) among patients aged 4 to 18 years. Type 3, located between the apices of the first and second premolars, was the most frequently observed position, accounting for 51.6% of instances. The coefficient of agreement concerning the horizontal position of the MF was 0.75 (P < 0.001).

Table 4 illustrates the distribution of various horizontal positions of the mandibular foramen (MF) among males and females. Type 3 was present in 56.1% of females and 46.7% of males. The occurrence of Type 2 positions was more prevalent in males than in females. Nevertheless, no statistically significant correlation was identified between the horizontal position of the MF and gender, as determined by the Monte Carlo chi-square test.

Table 5 illustrates the frequency of different horizontal positions of the MF with deciduous teeth. Type 3 was the most common horizontal position between the ages of 4 and 12, accounting for 35.1%. The coefficient of agreement for the horizontal position of the MF in this age group was 0.75 (P < 0.001).

Table 6 presents the distribution of various horizontal positions of the mandibular foramen (MF) in males and females relative to deciduous teeth. Type 3 was identified in 35.6% of females and 34.5% of males.

The prevalence of Type 2 positions was greater in males compared to females. No statistically significant association was observed between the horizontal position of the MF and gender, as determined by the Monte Carlo chi-square test.

Discussion

The Mental Foramen (MF) constitutes a significant anatomical feature located in the anterior-lateral region of the mandibular bone. In the vicinity of the MF, critical neural structures exist that are instrumental in the pulpal anesthesia of the teeth and lips. Consequently, understanding the anatomical position of the MF can facilitate the investigation of infiltration injection techniques in the mandible. Additionally, knowledge of the MF’s location helps reduce iatrogenic injuries during dental procedures. The position of the MF is affected by various factors, including gender, age, race, and growth patterns, (8, 9). Panoramic radiography is among the most widely used radiographic modalities for imaging oral and facial structures. Multiple studies have reported that panoramic radiography provides adequate accuracy for angular and linear measurements of the mandible (10, 11). Furthermore, this imaging technique is particularly well tolerated by pediatric patients (12, 13). Therefore, the present study aimed to determine the vertical position of the MF across different age groups ranging from 4 to 18 years, utilizing panoramic radiographic schemas.

In the present study, the most common anteroposterior position of the MF compared to permanent teeth is between the roots of the first and second premolar teeth, and after that, along the first premolar tooth.

In the study conducted by BULUT et al., which bears significant similarity to the present study regarding the age group, it was demonstrated that in the age range of 7 to 17 years, the most frequent horizontal position of the mandibular foramen (MF) is located between the first and second premolars, with the second most common position along the premolar teeth (9). One possible explanation for this observation is the higher prevalence of the 6- to 12-year age group in our study sample, which accounts for the difference in the secondary rank of frequency noted between the two studies. In our investigation, the distribution of the horizontal position of the MF by age group indicated that within the 6 to 12-year cohort, the most common position was between the first and second premolars, followed by the first premolar. Conversely, in the 6- to 12-year age group, the highest frequency was observed in the premolars, with the second most common position in the second premolar, as identified in previous research (14–16). According to BULUT et al., multiple studies involving individuals aged 18 years or older have reported that the most frequent position of the MF is between the first and second premolars.

Numerous studies have been conducted by researchers in Iran on this issue, each involving diverse populations and ethnic groups and in a study focusing on a selected population of Rafsanjan city, comprising individuals aged 25 to 45 years, Tahakheri and Karimi concluded that the region between the first and second premolars was the most frequently observed location for a mandibular foramen (MF) in panoramic radiographs, with a prevalence of 44%. Subsequently, the area beneath the second premolar was identified as the most common site, accounting for 36%. In the studies by Niknami and Ekran et al., the most prevalent site of MF was between the fourth and fifth mandibular teeth. However, certain studies have reported the MF located along the longitudinal axis of the second premolar, findings inconsistent with our study. Among these is the research by Al-Mahlawi et al., which concluded that the most common position of the MF is beneath the apex of the second premolar in a Saudi population aged 16 to 68 years, based on CBCT radiographs. The results of Rathod et al.’s study on a population in Vijayapur, involving patients aged 15 to 40 years and employing panoramic radiography, indicated that the most frequent location for the MF was along the second premolar, accounting for 54.2%, followed by between the first and second premolars at 37.5%. Additionally, the study by Zamani et al., conducted in Isfahan and involving subjects aged 10 to 35 years, demonstrated that the most common site for MF in the Iranian population, as observed on panoramic radiographs, is beneath the apex of the second premolar, with a prevalence of approximately 56. The disparities among these studies may be attributed to variations in radiographic evaluation techniques, sample sizes, racial backgrounds, and age groups.

Furthermore, in this cross-sectional, analytical investigation, the horizontal position of the mandibular canal (MF) relative to the milk teeth was examined, as limited research exists on this topic. Lim et al., by analyzing spatial changes in the MF during childhood, concluded that such variations are common. The most frequent horizontal position of the MF concerning the primary teeth was along the mesial root of the second primary molar. In the present study, the predominant horizontal positioning of the MF relative to milk teeth generally correlated with the extension of the distal root of the first deciduous molar, followed by the extension of the mesial root of the second deciduous molar. However, regarding age stratification within the 4 to 6-year age group, the most frequent horizontal position of the MF was along the distal root of the first deciduous molar. Conversely, in the older age cohort, the predominant position was associated with the extension of the mesial root of the second molar. These findings are consistent with Lim’s study, given that Lim’s age range was 5 to 16 years.

In the study conducted by Eunjeong Jo et al., the highest frequency of the MF position in the age group of 6 to 13 years was observed along the mesial root of the second molar, which is consistent with the findings for the age group of 6 to 12 years in the current study (24). In the 2022 research by Vathariparambath et al., which closely parallels the age group examined (8 to 18 years) in the present study, it was reported that, in most cases, the MF is located between the first and second molars. This variation may be attributable to differences in age ranges and sample sizes within each age group (25).

The study by Gershenson et al. also demonstrated that, in most instances, the position of the mandibular fossa (MF) was aligned with the root of the first molar. This correlation may be attributed to the younger age of the skulls examined in Gershenson’s research; indeed, the study included samples before tooth eruption (26).

In the present study, the mental foramen (MF) was observed to displace distally with increasing age. The study by Vathariparambath et al. (2022) is comparable to the current investigation in terms of age group, as it examined the position of the MF in individuals aged 8 to 18 years using radiography. Cone-beam computed tomography (CBCT) concluded that the position of the MF shifts upward and posteriorly with age within this demographic (25). The findings of Azab et al.’s study on pediatric subjects also indicated that the MF in the 6- to 10-year age group is smaller than that in older children, with the younger cohort exhibiting a more posterior position (27). Furthermore, in 2011, Balcioglu et al. conducted research on fetuses and examined changes in the horizontal position of the MF before and after birth. Their results demonstrated that the MF tends to move posteriorly with human growth. Additionally, the radiographic examination in this study involved children aged 4 to 12 years, where similar results were observed (28).

In the present study, the highest frequency of the vertical position of the mandibular foramen (MF) was observed in the middle third, and with increasing age, the likelihood of the MF being situated in the middle third increased. However, these findings were not statistically significant. The findings of Vathariparambath et al., using CBCT imaging in the age range of 8 to 18 years, demonstrated that the MF shifts position with advancing age(Campo, 25). Furthermore, Dotto and colleagues examined the position of the MF in children aged 10 to 12 years in 2006. Their results indicated that the MF was located in the lower third in children aged 10 to 11 years and in the middle third in 12-yearold children. These studies suggest that the position of the MF during the mixed dentition period varies with individual growth (29). These findings are consistent with the results of our research. As age increases and the horizontal and vertical dimensions of the mandible grow, the position of the MF tends to be located in the middle third (superiorly) and between the first and second premolars. However, Lim et al.’s study indicated that the MF shifts downward with increasing age. The discrepancies between these results may be attributed to racial differences and sample size (23).

In the current study, there was no statistically significant difference between females and males concerning the vertical position of the mandibular foramen (p=0.751). Conversely, in the research conducted by Bulut and Vathariparambath, gender was identified as a factor influencing the distance between the mandibular foramen and the inferior border of the mandible, which directly reflects the vertical positioning of this foramen and was found to be significantly influential (9, 25). The disparate findings across these studies may be attributable to racial and demographic variations, as different racial groups can exhibit distinct skeletal structures. Furthermore, in the present investigation, no significant difference was observed between females and males regarding the horizontal position of the mandibular foramen relative to the milk teeth (p=0.324). In contrast, the study by Azab et al., which analyzed 19 CBCT radiographs, reported a statistically significant difference in the horizontal positioning of the mandibular foramen relative to the milk teeth among children under 10 years of age, differentiated by gender (27). The inconsistency in findings may stem from differences in sample size, racial background, and growth patterns. Additionally, this study identified a significant difference between females and males regarding the horizontal position of the mandibular foramen relative to permanent teeth (p=0.044). This variation in significance between primary and permanent teeth is a novel observation in this study, potentially indicating instability in dental and skeletal growth over time and the differing effects of puberty and growth spurts on males and females.

The conclusions of this study indicate that there are significant variations in the positioning of the mandibular foramen (MF) by age and gender in pediatric and adolescent populations. The location of the MF undergoes positional shifts concomitant with mandibular growth, transitioning during the period of mixed dentition—comprising both deciduous and permanent teeth—as well as during growth spurts and puberty, which similarly impact its position across sexes. Consequently, knowledge of the MF’s location is essential for treatment planning, particularly before administering local anesthesia. The most prevalent position of the MF was identified at the distal root of the deciduous first molar and within the mixed dentition, along the mesial root of the second molar in deciduous teeth. Given that infiltration injections are administered in these regions during both childhood and mixed dentition stages, it can be hypothesized that the success of infiltration anesthesia in the treatment of mandibular deciduous teeth may be attributable, in addition to bone penetration by the anesthetic, to access through the MF and the subsequent blockade of the mental nerve and other sensory nerves supplying the deciduous teeth in this region. This hypothesis is corroborated by observations of lip numbness following numerous mandibular infiltration injections. As such, further research is warranted to compare the efficacy of infiltration anesthesia with that of the inferior alveolar nerve block. Future clinical investigations should document post-infiltration lip numbness, including its duration. Moreover, the caudal displacement of the MF with advancing age may be explained by the hypothesis that the horizontal growth rate of the mandibular bone anterior to the chin foramen exceeds that posterior to the chin, necessitating further research to validate or refute this supposition.

Conclusion

Based on the findings of this study, several important conclusions can be drawn regarding the position of the mental foramen in children and adolescents. Firstly, the position of the mental foramen exhibits significant variation with age, reflecting mandibular growth and the transition from mixed dentition to permanent dentition. The most prevalent horizontal position of the mental foramen has been identified to be between the first and second premolars, with a distal shift observed as age increases. Vertically, the mental foramen is most commonly situated in the middle third of the mandible, with this likelihood increasing with age; however, these changes were not statistically significant. These findings are in agreement with several prior studies, although some variation may be attributable to racial and demographic differences.

Regarding gender differences, no significant variations were observed in the vertical or horizontal positions of the mandibular foramen (MF) concerning deciduous teeth. However, a notable discrepancy in the horizontal positioning of the MF was identified between male and female subjects regarding permanent teeth, suggesting that mandibular growth spurts and puberty may influence MF positioning differently across sexes.

From a clinical perspective, these findings underscore the significance of comprehending the position of the mandibular foramen (MF) during the administration of local anesthesia in pediatric and adolescent populations. The placement of the MF, especially in relation to deciduous teeth, may be instrumental in the success of infiltration anesthesia for mandibular procedures. The study advocates additional clinical research to examine the potential benefits of infiltration anesthesia compared with traditional inferior alveolar nerve block techniques, particularly among younger patients. Moreover, the posterior displacement of the MF with increasing age may offer valuable insights into mandibular growth rate variability, a hypothesis warranting further exploration.

Ethical approval and consent to participate

The research Ethics committee of Qazvin University of Medical Sciences approved this study (IR.QUMS. REC.1400.245).

Data availability statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

The authors extend their gratitude to Qazvin University of Medical Science, Iran, for their generous support.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal associations that could have influenced the work reported in this paper.

Supplementary material

Supplementary Materials are available upon genuine request to the Corresponding Author.

Funding

None