Morphological variations of lingula and prevalence of accessory mandibular foramina in mandibles: A study.

INTRODUCTION: The lingula is used for identifying the site for injection of local anesthetics and for excision of nerve in facial neuralgia. The relationship between lingula and lingual nerves may aid in risk associated with an impacted third molar. Due to its connection to nerve and vascular structures, the study of the lingula provides important information related to oral and maxillofacial surgical procedures, such as the sagittal split ramus osteotomy and the intraoral vertico-sagittal ramus osteotomy carried out to correct dento facial deformities. Intra-operative complications such as hemorrhage, fracture, and nerve injury may occur if lingula is not correctly identified.
MATERIALS AND METHODS: This study was conducted in the Department of Oral Medicine and Radiology, Career Post Graduate Institute of Dental Sciences and Hospital, Lucknow, U. P (India) on fifty (100 sides) dry adult human mandibles to determine the different shapes of lingula. The shapes of the lingula were classified as triangular, truncated, nodular, and assimilated types.
RESULTS: The most common shape found in the study was the triangular (61.6%) while the least common shape was the assimilated (11.6%). All types of lingule were more prevalent unilaterally. The prevalence of accessory mandibular foramina (AMF) was 12% on the right side and 4% on the left side of the mandible.
CONCLUSION: The present study provides information regarding different shapes of lingule and incidence of AMF in the populations of Lucknow and its surrounding areas (Uttar Pradesh) North India. The findings of the present study are very helpful to oro-dental surgeons, anthropologists, and forensic practice experts.

INTRODUCTION

Lingula has been described as a small tongue shaped, sharp bony projection located on the medial aspect of mandibular ramus close to the posterior margin of the mandibular foramen.[1] It is an important landmark as it lies in proximity to the mandibular foramen.[2] The inferior alveolar nerve and vessels pass laterally to the lingula through the mandibular foramen into the mandibular canal. The foramen and the lingula, because of their relations to the inferior alveolar nerve are of great clinical significance for the oro-dental surgeon. The lingula is used for identifying the site for injection of local anesthetics and for excision of nerve in case of facial neuralgia.[3] The relationship between lingula and lingual nerve may aid in risk associated with an impacted third molar.[4] Due to its connection to the nerve and vascular structures, the study of the lingula provides important information related to the oral and maxillofacial surgical procedures, such as sagittal split ramus osteotomy and intraoral vertical-sagittal ramus osteotomy carried out to correct dentofacial deformities.[5] Intraoperative complications such as hemorrhage, fracture, and nerve injury may occur if lingula is not correctly identified.[6] Variation in shapes of lingula have been reported by many authors. Truncated type of lingula was described by Hollinshead.[7] Nodular and assimilated were described by Berkovitz et al.[8] and Margon et al.,[9] respectively. Tuli et al.[3] classified lingula into four different types based on its shape, namely triangular, truncated, nodular, and assimilated.

All unnamed openings in the mandible are called Accessory foramina.[10] Although these foramina are described in the literature[1112131415] their distributions are variable. They may contain nerve fibers or blood vessels. When they transmit nerve fibers, the local anesthesia given during dental extractions may fail as branches of the nerves passing through them escape the drug. The accessory vessels contained in them may result in difficulty in controlling intra-osseous hemorrhage.

The incidence of accessory mandibular foramina (AMF) has been found greater on the medial surface than on the lateral surface and found in the vicinity of the main mandibular foramen.[16] Position and incidence of accessory foramina in mandible are important for dental surgeons and anesthetists in achieving complete nerve blocks and for avoiding injury to neurovascular structures passing through it.[17] An accessory mandibular foramen is known to provide an easy route for the spread of tumor cells following radiotherapy.[18]

The present study was undertaken to determine the different shapes of lingule and prevalence of AMF in dry mandibles of Lucknow and its surrounding areas.

MATERIALS AND METHODS

This study was conducted in the Department of Oral Medicine and Radiology, Career Post Graduate Institute of Dental Sciences and Hospital, Lucknowon fifty dry adult human mandibles (25 male dry mandibles and twenty-five female dry mandibles) to determine the different shapes of lingula. The analysis of the lingual characteristics was conducted mainly through observation, without measurement tools.

The shapes of the lingule were classified as triangular, truncated, nodular, and assimilated as per Tuli et al. classification. Lingula with a wide base and narrow rounded or pointed apex were classified as triangular [Figure 1] and the lingula with the quadrangular top as truncated [Figure 1]. The entire lingula except for its apex merged into the ramus is nodular [Figure 1] and in assimilated type [Figure 1] the lingula becomes completely incorporated into the ramus. Presence or absence of accessory mandibular foramen was also recorded [Figure 2].

Figure 1

Different shape of lingule

Figure 2

Accessory mandibular foramen

RESULTS

The distribution of different shape of lingule and AMF in male and female dry mandibles is shown in Table 1 and Chart 1.

Table 1

Prevalence of different shapes of lingule in male and female human dry mandible

Chart 1

Disribution of shapes of lingulae

The distribution of different shapes of lingule in male and female mandibles with respect to the side is shown in in [Figures 3–6] and distribution of AMF in male and female mandibles is shown in Figure 7.

Figure 3

Distribution of triangular shape lingula in male and female dry mandible side wise

Figure 6

Distribution of assimilated shape lingula in male and female dry mandible side wise

Figure 7

Distribution of accessory mandibular foramen

Distribution of truncated shape lingula in male and female dry mandible side wise

Distribution of nodular shape lingula in male and female dry mandible side wise

From the chart 1, it was observed that triangular shape is found to be more in females than males and the nodular shape was found to be more among males than females. However, the percentage of mandibles of Truncated and Assimilated shape among male and female are found to be same. Furthermore, we have validated through applying Chi-square test for independence of attributes and assumed the hypothesis that the shapes of the mandible are of gender independent, i.e., there is no association between gender and shapes of mandibles. R-software is used to test the hypothesis as given below:

Z- read. table (“clipboard,” header = T)

Chi-squared test (z).

Pearson's Chi-squared test

X-squared = 2.6571, df = 3, P = 0.4476.

From the above-mentioned output, it is observed that P value is 0.4476 is greater than 0.05 and hence we accept the null hypothesis and hence, it is concluded that shape of the mandible is gender independent meaning that there is no association between gender and shapes of the mandible.

From the above table, it was observed that prevalence of triangular shaped lingule were more followed by truncated, nodular and assimilated shaped lingule. The prevalence of triangularly shaped lingule (left side), and truncated shaped (left and right side) were statistically significant(As P > 0.5)

DISCUSSION

The frequency of different morphological types of lingula studied by different authors varied among different populations and races.

Different morphological shapes of the lingula were first classified by Tuli et al.[3] into triangular, truncated, nodular, and assimilated types in adult human mandibles of Indian origin. Tuli et al. reported triangular shape to be the most common and assimilated as the least common in Indian population.[3] Hossain et al.[19] reported three types of lingule namely triangular, truncated, and assimilated types in Bangladeshi skulls. Fabian[20] classified lingula into five major types based on shape and size in the Tanzanian population. The frequency of different morphological types of lingula studied by different authors varied among different population and races. Whereas, Devi et al.[1] described truncated and nodular types of lingula to be more frequently observed in South Indian population. In another study on South Indian population, the triangular and nodular shapes were most prevalent.[21] According to Nirmale et al.[22] triangular shape was most common. In Thai mandibles, the truncated type was most common followed by nodular, triangular, and assimilated types. Lopes et al.[5] reported the triangular shape to be most common and assimilated type the least common variety of shape of lingula in the Southern Brazil population.

In the present study, the most prevalent shape of lingula was triangular, and the least prevalent shape was assimilated type, which is in accordance with the result of Samanta et al. and Kharb et al.[4] study (on populations of Indian origin) and results of Lopes et al.[5] study (Southern Brazil Population).

Chavez et al.[23] mentioned accessory foramina in fetus and reported that these foramina are connected with the mandibular canal. This connection implies that these accessory foramina may form an important route for the nerves and vessels. The passage of blood vessels and nerves makes the accessory mandibular foramen (AMF) clinically important. The embryological basis of the occurrence of the AMF has been described in the literature.[23] During development, initially, there are three inferior alveolar nerves, which innervate each of the three groups of the mandibular teeth. Later, there is a fusion of these nerves and a single inferior alveolar nerve is formed. The incomplete fusion of these three nerves leads to the development of double mandibular canals. It was reported that, in 60% of the cases, the mandibular canal was found to have the entire inferior alveolar nerve passing through it, whereas, in the remaining 40% cases, the nerves were found to be scattered.[24] The awareness of its alternate route through AMF and its position is important for achieving successful inferior alveolar nerve blocks. The presence of AMF makes it more vulnerable to the perineural spread of tumor cells from cortical to cancellous part of the bone.[25] The knowledge of AMF may thus be important for radiotherapist in planning radiation therapy.

In this study, out of 50 dry mandibles, 8 (16%) accessory mandibular foramen was found in the left side, whereas 6 (12%) AMF were found in the right side. This finding differs with the findings of Gupta et al.[17](2013) who found 18% prevalence of accessory mandibular foramen bilaterally.

CONCLUSION

The present study provides information regarding different shapes of lingula and incidence of the accessory mandibular foramen in the Lucknow and surrounding populations (North India). In this study, the most prevalent shape of lingula was triangular, and the least prevalent shape was assimilated type, The findings of our study are very helpful to oro-dental surgeons, anthropologists, and forensic practice experts.

The prevalence of accessory mandibular foramen found to be an average of 14%, so awareness of it is important for achieving successful inferior alveolar nerve blocks. The presence of AMF makes it more vulnerable to the perineural spread of tumor cells from cortical to cancellous part of bone. The knowledge of AMF may thus be important for radiotherapist in planning radiation therapy.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.