Morphometric Analysis of Mandibular Foramen in Saudi Children Using Cone-Beam Computed Tomography.

OBJECTIVES: This study evaluated the position of the mandibular foramen (MF) with regard to the occlusal plane (OP) and the anterior border (AB) of the mandibular ramus (AB) in a sample of 7-12-year-old Saudi children using cone-beam computed tomography (CBCT) images.
MATERIALS AND METHODS: In this descriptive, observational study, 155 CBCT scans were selected and analyzed for positional changes in the MF. Reconstructed panoramic and axial sections were used to measure the MF-OP and MF-AB distances, respectively, on both the right and left sides of the mandible. Data were analyzed using paired t-test, independent t-test, one-way analysis of variance, and Tukey's honest significant difference post hoc tests where applicable, at a significance level of P < 0.05.
RESULTS: The mean distance of MF from the AB of the ramus was 14.68 mm, with no significant differences between the genders (P > 0.05). The MF moved upward from a position below the OP to above it, according to age in both males and females, and the difference between the age groups was significant (P < 0.05). No significant differences (P < 0.05) in the mean values of distances between the right and left sides of the mandible were seen.
CONCLUSIONS: The location of the MF varies with respect to age and should be considered while administering inferior alveolar nerve block in children to achieve a more effective anesthesia. Copyright:

INTRODUCTION

Inferior alveolar nerve block (IANB) is widely used in pediatric dental clinical practice to achieve mandibular anesthesia. This technique involves deposition of the anesthetic solution right above the mandibular foramen (MF), around the inferior alveolar nerve just before it enters the foramen on the medial aspect of the ramus. The position of the MF or the lingula has been considered to be a critical anatomical reference point for the success of IANB anesthesia.[1] Hence, a precise knowledge of anatomic location of MF is essential in achieving a more effective IANB anesthesia and thereby avoiding any associated failures. Failure rates of IANB in the range of 20%–25% have been reported in the literature.[2] They are more common, especially in children, and might be due to anatomic variations or inaccurate localization of the MF and also poor operator technique.[2] MF has been reported to show remarkable variation in position among different population, racial, and ethnic groups.[34] Most studies have been conducted in adults and on dry mandibles using two-dimensional (2D) radiographic techniques such as panoramic and/or cephalometric radiographs.[4567] Cone-beam computed tomography (CBCT) is a 3D technique with advantages such as improved accuracy, higher resolution, and less image distortion compared to 2D radiographic techniques.[8]

Very few studies have been reported in the English literature regarding the use of CBCT to determine the location of MF.[91011] To our knowledge, this is the first study investigating on the location of MF in Saudi children. The purpose of the present retrospective study was to evaluate the location of MF with respect to the occlusal plane (OP) and anterior border (AB) of the mandibular ramus in 7–12 year-old children of the eastern province of Saudi Arabia using CBCT images.

MATERIALS AND METHODS

This descriptive, observational study was based on the image analysis of 155 randomly selected CBCT data of patients, retrieved from the digital archives of the Dental Clinical Complex, College of Dentistry, for the years 2018–2020. Only CBCT radiographs of patients aged 7–12 years showing an optimal viewing and diagnostic quality were included in the study. The CBCT scans used in the study were previously acquired for various diagnostic purposes. Radiographs of subjects with a previous history of craniofacial trauma, temporomandibular disorders, and orthodontic treatment were excluded from the study. All the images were acquired by an experienced oral radiology technician according to the manufacturer's instructions using an i-CAT tomography unit (Imaging Sciences International, Hatfield, PA, USA). These images were taken at 120 kVp and 2–15 mA at different resolutions, with an exposure time of 2–8 s and a voxel of 0.3 mm depending on the field of view. Written informed consent had been taken from all patients as part of routine protocol for the use of collected data solely for research and educational purposes. The study was approved by the Institutional Research and Ethics Committee (Reference: KFU/CoD/R/0023/2019) and carried out in accordance with the principles of the Declaration of Helsinki.

The selected CBCT image scans were transferred from the i-CAT DICOM (Digital Image Communication in Medicine) viewer software to an image-processing tool of the software (i-CAT Vision software). The study was conducted using reconstructed images of panoramic and axial sections. All measurements were performed digitally with a distance tool on both the right and left sides of the subjects. In the reconstructed panoramic image, the MF reference point was marked, and the distance tool was enhanced to measure the distance (in millimeters to first decimal place) between the most superior–anterior point of the MF and the OP of the mandibular first molar (OP). The OP represented the straight line of the cusps of the mandibular first molar. The distance tool was used to extend this line posteriorly to measure the distance between the MF and the posterior extension of the OP. When the first molar was tilted or not present and the OP could not be identified, the patient was excluded. The location of the MF was recorded as either above (+), at or below the OP (−). Cross-sections of 1 mm thickness of axial sections were taken at the area of MF. The MF reference point marked on reconstructed panoramic image was localized and confirmed on 3D images. Using the 3D distance tool of the visual imaging software, the marked point of MF was selected on the axial sections, and the distance between MF and deepest point of AB of the ramus was measured. Two well-trained and experienced examiners, who were blind to the age and gender of the subjects, conducted all anatomic measurements. To check for the examiner's reliability, 10% of images were selected randomly, and the study variables were measured followed by repeat of measurements on the same sample after an interval of 2 weeks, without the knowledge of subject's age and gender.

The data were subjected to statistical analysis by using the Statistical Package for the Social Sciences (SPSS), version 20.0 (SPSS Inc., Chicago, IL, USA). Descriptive statistics including the mean values and respective standard deviations (SDs) were calculated for all measurements. The mean values of measurements of right and left sides were compared using a paired samples t-test. Independent t-tests were used for comparisons of mean values between the genders. Measurements were tested between the age groups, using a one-way analysis of variance (ANOVA), and Tukey's honest significant difference post hoc tests corrected for multiple comparisons. Statistical significance level was set at P < 0.05.

RESULTS

Out of the initial 169 images, 14 were excluded for reasons including distorted radiographic images causing identification of reference points difficult. The intra-examiner and inter-examiner agreements evaluated using the weighted kappa statistic were found to be 0.89 and 0.87, respectively. The final study sample included a total of 155 (310 sides) imaging studies with 73 males and 82 females, with a mean age of 10.22 ± 1.66 (mean ± SD) years. Based on age, the subjects were divided into group I (7–8 years), group II (9–10 years), and group III (11–12 years). Table 1 shows the descriptive statistics of the study groups' age and gender. The measurements were taken on both the right and left sides for each subject.

Table 1

Descriptive statistics of the study sample

Age group (years)	n	Male (n)	Female (n)	Age (mean±SD)	Median age
7–8	44	23	21	8.07±0.52	8.20
9–10	53	22	31	10.08±0.48	10.30
11–12	58	28	30	11.98±0.53	11.8
Total	155	73	82	10.22±1.66	10.40

SD: Standard deviation

Comparison of distances between the right and left sides of the mandible

The mean distances of MF from the AB of ramus and the OP measured on the right and left sides in both male and female subjects are shown in Table 2. There were no significant differences (P < 0.05) between the right- and left-sided distances from the MF to the AB of the ramus or the OP. Therefore, the data from both the sides were pooled, and an average distance of variables was calculated for each subject, which was considered in later analyses.

Table 2

Comparison of the distances between the right and left sides of the mandible

Variable	Side	Gender				Total	P
		Male (n=73)	P	Female (n=82)	P
AB–MF (mm)	Right	14.637±1.16	0.640	14.728±1.12	0.452	14.685±1.14	0.826
	Left	14.667±1.29		14.683±1.13		14.675±1.20
OP–MF (mm)	Right	0.529±2.88	0.251	0.725±2.62	0.230	0.633±2.74	0.944
	Left	0.489±2.89		0.764±2.63		0.635±2.75

P value: Paired sample t-test for comparison between the right–left sides. Data are presented as mean±SD unless otherwise indicated. SD: Standard deviation. AB: Deepest point of the anterior border of the ramus, MF: Most superior–anterior point of mandibular foramen; OP: Occlusal plane of the mandibular first molar

Comparison of distances between males and females

The male subjects exhibited slightly higher mean distance values of MF–AB and MF–OP than in females. However, independent sample t-test indicated that these gender differences were not statistically significant (P < 0.05). Table 3 shows the mean distance values of MF–AB and MF–OP in the study groups according to age and gender.

Table 3

Comparison of the distances between the age groups and the gender

Variable	Age group (years)	Gender
		Male	P*	Female	n*	P †	Total	P*
AB–MF (mm)	7–8	13.27±0.65	0.000	13.19±0.72	0.000	0.729	13.23±0.68	0.000
	9–10	14.99±0.75		14.95±0.57		0.815	14.97±0.65
	11–12	15.51±0.72		15.50±0.50		0.950	15.50±0.61
	Total	14.65±1.19		14.70±1.09			14.68±1.1
OP–MF (mm)	7–8	−3.13±0.85	0.000	−2.76±1.10	0.000	0.231	−2.95±0.99	0.000
	9–10	0.49±0.63		0.43±0.60		0.730	0.46±0.61
	11–12	3.51±0.81		3.52±1.01		0.962	3.51±0.91
	Total	0.509±2.88		0.74±2.62			0.63±2.74

*P: P value of one-way ANOVA test (significance among age groups), †P: P value of independent sample t-test (significance of male to female). Data are presented as mean±SD unless otherwise indicated. SD: Standard deviation. AB: Deepest point of the anterior border of the ramus, MF: Most superior–anterior point of mandibular foramen; OP: Occlusal plane of the mandibular first molar, ANOVA: Analysis of variance

Comparison of distances among age groups

In the entire study sample and within the same gender, one-way ANOVA test indicated that the mean values of distances of MF–AB and MF–OP differed significantly (P = 0.000) among age groups [Table 3]. Post hoc analysis revealed that the significance was between each pair of age groups. The distance of MF from the AB of the ramus in the study sample was 14.68 ± 1.13 (mean ± SD) with a maximum of 16.58 mm and a minimum of 12.35 mm. The mean values of distances from the MF to the AB of the ramus tended to increase with age in both males and females with no statistically significant difference (P > 0.05) between the genders. The mean MF–OP distance for each age group in both males and females is shown in Table 3. The MF was found to be higher, based on OP, in males than in females in 7–8 years' and 9–10 years' age groups. However, it was found to be at the same level in 11–12 years' age group in both the genders. The MF moved vertically from a position below the OP to above it, according to age in both males and females, and the difference between age groups was statistically significant (P < 0.05).

DISCUSSION

The position of MF depends on the mandibular growth including the associated dimensional changes of ascending ramus and as such is one of the most variable anatomical landmarks.[12] Several studies investigated the location of MF using different methods. Although most studies were conducted on panoramic radiographs, literature reported that these radiographs pose difficulties in evaluating the exact size and position caused by image magnification and/or distortions due to change in head position or overlapping of virtual images of structures. Hence, horizontal distances are known to be particularly unreliable compared to relatively reliable vertical distances with panoramic radiographs.[13] Studies comparing the location of the MF using both dry mandible and radiographic methods had shown no significant differences between the two methods.[14] Contrary to this, Afsar et al.[4] and Patil et al.[3] had reported conflicting results. While dry mandible method could locate anatomical landmarks accurately, obscure details regarding the age and gender and the difficulty in location of OP have been reported to affect the validity of resulting measurements.[15] CBCT has the ability to produce highly accurate images and determine precise location of anatomical structures. Moreover, the distance and angles measured on CBCT correspond very closely to the actual size of the object.[16] In this study, CBCT was chosen to determine the distance between MF and specific landmarks as it provides better viewing of anatomical structures and images can be reformatted to all the three planes.

The distance between MF and OP has major importance as the latter has been considered to be the key reference while administering IANB.[1117] Various studies had defined OP in different ways, and the location of the MF was recorded as above, at, or below the OP. Lim et al.[5] in a study determined the OP by connecting the height of the cusps of the mandibular primary molars to the first permanent molar or from the fully erupted permanent premolars to the first permanent molar. Other authors considered OP as the reference line passing through the canine tip and the most prominent point on the end-most fully erupted tooth[18] or as passing only through the second mandibular molar and the MF.[19] In our study, the OP was represented by the straight line of the cusps of the mandibular first molar, extended posteriorly by the software ruler. Similar definition of OP was used by other authors.[1517] Russa and Fabian[20] had suggested the mandibular first molar to be the best reference point aiding in the intraoral approach of the inferior alveolar nerve, which eliminates the error reported when adjacent teeth was used as OP. In cases with difficulty in establishing the OP due to the unstable occlusion of the mixed dentition, an analysis related to the Hellman stage based on the clinical stage of mandibular growth rather than the chronological age has been considered to be appropriate.[15]

Because no significant differences were observed between the measurements on the right and left sides, it can be considered that the subjects were anatomically normal without mandibular growth deviations. This observation corroborates with that of a previous study by Feuerstein et al.[15] The results of our study are in agreement with those of the literature where no significant differences in MF location between the gender,[421] and also between the right and left sides of the mandible, were noted.[1822]

Regarding the vertical distance between MF and OP, the results of our study varied when compared to those from other studies of similar age groups.[715] This may be attributed to the method used in our study wherein the most superior–anterior point of MF was chosen as the reference point, whereas others had used different reference points including either the highest point on the lingula or the center of the MF.[715] The results of the present study implied that the vertical position of the MF showed significant increase with age. This finding was similar to that seen in previous studies,[71823] whereas few other authors have reported contradictory results.[4102224] Ezoddini Ardakani et al. in a study on Iranian children reported that the MF was located below the OP at age 9 years and was slightly below or above the OP in those aged above 9 years.[23] The present study showed that there was a significant shift in the MF position from below the OP in younger children, to the level of OP at age 9 years and then moved above the OP with age. A similar trend was noted by other investigators and had attributed pubertal growth spurts to the positional changes in the vertical dimension between MF and OP.[51723]

The distance between the MF and AB may be used as reference for the length of the needle to be inserted into the soft tissue. Most studies in the literature had reported that the growth in the AB of ramus was almost constant[592325] and no statistical differences were found in horizontal distance between MF and AB.[7] In our study, the MF to AB distance tended to increase with age in both males and females with no statistically significant difference (P > 0.05) between the genders. However, the difference was found to be significant when compared between the study age groups (P = 0.000). The MF was located at a mean distance of 14.68 mm from the AB of the ramus in the present study. Based on the findings, the authors suggested the use of a short needle to perform IANB in children, as the estimation of depth of penetration with a short needle is easier than that with a long needle.

Moreover, studies investigating the location of MF on radiographs have used either the lingula or the MF as landmarks, and also different reference points were used for measurements. These variations in normal anatomical landmarks and the varying definitions of MF when used as a reference point for horizontal or vertical measurements might lead to discrepancies and could have implications for administering an IANB in children.[25] Furthermore, other factors such as the study population group, methodology used, age, and ethnicity may also be related to these variations. In our study, the chosen reference point of the MF to measure the study variables could be related to the technique used wherein the needle had to deposit the anesthetic solution above the MF, prior to the entry of IAN into the mandibular canal.

With respect to limitations, the mean distance of the MF from the AB was solely based on bony anatomical landmarks, and the soft tissue thickness of the insertion point of the needle was not measured in the present study. Further studies are needed to determine the actual needle insertion depth followed by a clinical trial to evaluate the efficacy of IANB.

CONCLUSIONS

The current study provides additional information to the literature regarding the location of the MF in relation to the AB of the ramus and the OP in 7–12-year-old Saudi children. The use of CBCT images was beneficial in determining the position of MF based on landmarks used in the IANB. The measurements obtained in the present study could be used as reference to increase the clinical success when performing IANB in Saudi children. Moreover, as significant age-related changes to the MF position were noted in children, further longitudinal studies to confirm these differences are needed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.