Accessory neurovascular foramina on the lingual ...

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Original Research Accessory neurovascular foramina on the lingual surface of mandible: Incidence, topography, and clinical implications BV Murlimanju, KG Prakash1, D Samiullah, Latha V Prabhu, Mangala M Pai, Rajanigandha Vadgaonkar, Rajalakshmi Rai Department of Anatomy, Manipal University, Centre for Basic Sciences, Kasturba Medical College, Mangalore, 1 Department of Anatomy, Azeezia Medical College, Meeyyannoor, Kollam District, Kerala, India

ABSTRACT

Received : 07-07-10 Review completed : 05-10-11 Accepted : 22-02-12

Context: It was suggested that the accessory neurovascular foramina of the mandible might be of significance in relation to the effectiveness of local anesthesia following the routine inferior alveolar nerve block. Aims: To investigate the incidence of neurovascular foramina over the lingual surface of the mandible in South Indian population. Settings and Design: The study was conducted at the department of anatomy. Materials and Methods: The study included 67 human adult dry mandibles, the exact ages and sexes of which were not known. The location and number of neurovascular foramina were topographically analyzed. Statistical Analysis Used: Descriptive statistics. Results: The foramina were observed in 64 mandibles (95.5%) and were often multiple in most of the cases. They were located between the two medial incisors in 8 mandibles (1.9%), between the medial and lateral incisor in 34 mandibles (50.7%; 25-bilateral; 7-right; 2-left), between the lateral incisor and canine in 7 mandibles (10.4%; 2-bilateral; 3-right; 2-left), between the canine and first premolar in 6 cases (8.9%; 3 on each side). Foramina were also present around the genial tubercle in 56 mandibles (83.6%). Among them, 52 mandibles showed a single foramen just above the genial tubercle, 34 mandibles had foramina below the tubercles, 13 mandibles had foramina on the right side of genial tubercle and 17 were having on the left side. Conclusion: Since the anatomical details of these foramina are important to various fields of dentistry and oncology, the present investigation was undertaken. The clinical significance and implications are emphasized. Key words: Accessory foramina, anesthesia, inferior alveolar nerve, mandible, neurovascular

The demands for operative procedures such as orthognatic surgeries and implant placement, as well as introduction of new imaging techniques, have increased the interest in anatomical features and their normal variation in the human mandible.[1] The mandible contains many unnamed accessory foramina,[2] which are most commonly seen on the lingual side.[3] Many authors observed that, these foramina are variable in their distribution and are found Address for correspondence: Dr. BV Murlimanju E-mail: [email protected] Access this article online Quick Response Code:

Website: www.ijdr.in PMID: *** DOI: 10.4103/0970-9290.102252

often on the internal surface of the mandible.[2,4-6] It was suggested that, a single midline foramen just above the genial tubercle is a constant finding on the lingual surface and is observed in over 72% of specimens.[7] The foramina are generally localized at symphysis of the mandibular body[2,4] and are related either superior or inferior to the genial tubercle.[2,3,8,9] Some foramina are also found positioned lateral to the genial tubercle.[8,10] Some authors divided these foramina on the lingual surface of the mandible as medial and lateral foramina.[11,12] Sutton[2] described that these accessory foramina have a neurovascular bundle, which implies an artery, vein, and a nerve. The nerve fibres, which are present in these foramina are observed to provide accessory innervation of anterior mandibular teeth.[2,8,10,12] The foramina are significant in relation to the effectiveness of the inferior alveolar nerve block.[8,10] These foramina are known to transmit the blood vessels,[3,7,10-12] which might cause complications during the dental procedures. The role of these neurovascular foramina, in the metastasis of tumours of this region has also been established.[4,13-16] It was Indian Journal of Dental Research, 23(3), 2012


Accessory foramina of the mandible

reported that, before carrying out a surgical procedure at the anterior aspect of lower jaw, it is of utmost importance to consider and precisely locate the presence of neurovascular bundles.[17] The anatomical knowledge of neurovascular foramina is essential to the various fields of dentistry and medicine. However, the detailed studies about this subject are scarce. Even in both medical and dental anatomy textbooks, a clear description of the mandibular lingual foramina is not given.[18] Hence, this investigation was undertaken; objectives of the present study were to report the incidence of accessory neurovascular foramina of mandible in South Indian population and to analyze the foramina topographically.

MATERIALS AND METHODS The present study included 67 human adult dry mandibles, which were obtained from the departments of anatomy of our institution. The investigation has the approval of institutional review board and local ethics committee. All the specimens were adult mandibles, the exact ages and sexes of which were not known. Bones which had external pathological changes were excluded from the present study. The incidence and topography of accessory neurovascular foramina were analyzed. Only those foramina with the diameter greater than 1 mm were considered. The smaller foramina, which were less than 1mm were considered as vascular foramina and since they are present in all the mandibles, are not included in the present study.

RESULTS The topographical distribution of the accessory foramina are summarized in Figure 1. The foramina were observed [Figures 2-4] in 64 mandibles (95.5%) between the alveolar ridge of anterior mandibular teeth. They were found multiple in most of the mandibles. The topographical distribution was observed to be between the two medial incisors in 8 mandibles (1.9%), between the medial and lateral incisor in 34 mandibles (50.7%; 25-bilateral; 7-right; 2-left), between the lateral incisor and canine in 7 mandibles (10.4%; 2-bilateral; 3-right; 2-left), between the canine and first premolar in 6 cases (8.9%; 3 on each side). The foramina were also observed around the genial tubercle in 56 cases (83.6%). Among them, 52 mandibles (77.6%) had the single foramen just above the genial tubercle, 34 mandibles (50.7%) had the foramen below the tubercles, 13 mandibles (19.4%) showed the foramina on the right side of genial tubercle, and 17 on the left side (25.4%). The foramina were absent [Figure 5] in 4.5% of cases (3 mandibles).

DISCUSSION The presence of accessory foramina in mandible is frequently overlooked in clinical procedures. It is important Indian Journal of Dental Research, 23(3), 2012

Murlimanju, et al.

to note that these anatomical variations might only be preoperatively assessed radiologically and such observation might have influence on the therapeutic success.[19] It was reported that there may be two or more foramina at the mandibular midline and their location and dimensions are variable.[18] Hofschneider et al. [20] observed that the anterior region of mandible on its lingual side, has both midline as well as laterally placed foramina. Though there are few reports available on accessory foramina over the mandibular symphysis,[2,3,7,9-12,21,22] the literature investigating the accessory foramina on the internal surface of alveolar part (lingual surface) are very scarce. Some authors reported about foramina over the alveolar part between lower medial and lateral incisors as well as between lateral incisors and canines.[4,12] It was suggested that these foramina are functionally important in supplying the neurovascular components to the mandible.[5] One previous study had observed these foramina in 76.4% of the cases.[4] In their study, the foramina were located most often between the lower medial and lateral incisors. Foramina were also observed in the midline between the lower medial incisors and between lateral incisors and canines. Liang et al. [18] observed the midline lingual foramen in 98% of cases. Among them 72% were single foramen, 22% were double, and 4% were triple foramina. They also reported that 62% of the foramina were located above the genial tubercle and 38% were below it. In their study, in addition to the midline foramina, lateral foramina, which were located between midline and respective canine teeth were also observed in 62% of the cases. Among the lateral foramina, 63% were located on the right and 37% on left side. Przystanska and Bruska[23] conducted a study with 93 mandibles and observed the neurovascular foramina over the inner surface of alveolar part in 32% of their cases. The foramina were observed between the medial and lateral incisors in 98% of cases. In their study,[23] foramina were also observed at the midline and between lower lateral incisors and canines. Their histological study confirmed the presence of neurovascular bundle in these accessory foramina. The neurovascular bundle was formed by branches of mylohyoid nerve, sublingual artery and accompanying veins.[23] A study by Liang et al. [24] confirmed the presence of a well-defined neurovascular bundle, with branches of the lingual nerve and lingual artery at the superior genial foramen of the mandible. They also observed that the branches of nerve to mylohyoid and submental or sublingual artery as well as veins entering the inferior genial spinal foramina. The findings of the present study are similar to the previous reports[4,23] as these accessory neurovascular foramina were observed in 95.5% of the cases and were observed between the medial and lateral incisor in 50.7% of cases. They were also present between the two medial incisors, between lateral incisor and canine, between canine and first premolar and around the genial tubercle. The foramina are reported to transmit fibres from the nerve to mylohyoid, to supply



Murlimanju, et al.

Figure 1: Topographical distribution of the neurovascular accessory foramina of the mandible. Figure 2: Accessory foramina over the lingual surface of the mandible; (a, b) foramina between the medial and lateral incisors; (c) foramen above the genial tubercle; (d, e) foramina on right and left side of the genial tubercle; (g) genial tubercle.

Figure 3: Accessory foramina over the lingual surface of the mandible; (a) foramen between the medial and lateral incisors; (b) foramen between lateral incisor and canine; (c) foramen between canine and first bicuspid; (d) foramen above the genial tubercle; (e) foramen below the genial tubercle; (h, i) foramina on right and left side of the genial tubercle; (g) genial tubercle.

Figure 4: Accessory foramina over the lingual surface of the mandible; (a) foramen between the two medial incisors; (b) foramen between lateral incisor and canine; (g) genial tubercle.

the mandibular teeth, thereby providing escape of pain fibres to these teeth after the inferior dental nerve block at the mandibular foramen.[10] In a radiological study[25] on spiral CT scans, the superior and inferior genial foramina were observed in 81% cases (53% above the genial tubercle and 47% below). In 29% of cases, the double foramina were observed. In the present study, foramina were observed around the genial tubercle in 83.6% of cases, which is almost similar to the findings of radiological study.[25] But in the present study, foramina on either side of the genial tubercle were also observed.

Figure 5: Mandible with absence of accessory foramina on the lingual surface of the mandible; (g) genial tubercle.

The oral implants are routinely used for rehabilitation of edentulous mandible and this procedure is often considered as uncomplicated especially in an implant placement to the symphyseal area. However, some nerve disturbance in the anterior mandible after the implant placement has been Indian Journal of Dental Research, 23(3), 2012


Murlimanju, et al.


reported. It was suggested that the preoperative radiographic planning of the implants at the anterior mandible should pay attention to the mandibular incisive and lingual canals along with the mental foramen in order to avoid neurovascular complications.[26] Liang et al.[24,25] proposed that the surgical procedures should consider a proper preoperative assessment of the genial tubercle foramina. The anterior mandibular region is also used as a donor site for grafting procedures. The increased use of such surgical procedures might explain the growing interest in the basic anatomical aspects of the mandibular symphysis.[24] Because of extreme bone resorption, some preprosthetic procedures such as vestibuloplasty might present a risk for damage to the lingual foramina and their content.[18] The morphology and topography of these foramina are important during the anterior dental surgeries like implant placement, lowering genial spines in edentulous patients, genioplasty, and grafting procedures.[18] It was also suggested that the neurovascular foramina might be of significance in relation to local anesthesia following the inferior alveolar nerve block. Also, they could cause bleeding during dental surgeries because of vascular trauma. The injury could be of sufficient to provoke a hemorrhage intraosseously or in the connective soft tissue, which might be difficult to control. Mason et al. [27] reports the major hemorrhage at floor of mouth caused by surgery in the mental interforaminal region. The precise preoperative planning procedures and careful preoperative lingual probing form essential parts of surgery in the midline region, in order to avoid surgical complications such as haemorrhage or neurosensory disturbances.[24] In clinical practice, each patient must be assessed thoroughly to identify the neurovascular structures, considering large variability in neurovascularisation of the human mandible. Low dose cone beam computed tomography is a valuable tool in evaluating the anatomical variations in mandible neurovascularisation. [1] The high resolution magnetic resonance imaging has also been found to be a very useful alternative for microanatomical identification of vessels and nerve bundles in the mandible.[17] Lustig et al.[28] proposed that an ultrasound/doppler evaluation should be included in the preoperative plan, which might assess flow of blood to the chin through the lingual foramina and give some idea about their location.

ACKNOWLEDGEMENTS The authors thank Mr. Mohammed Ashraf C. and Ms. Mary Titty Paul for their valuable help while conducting this study.

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Since the anatomical details of these foramina are important to various fields of dentistry and oncology, the clinical interest is extensive and anatomical references about this subject are scarce, we aimed to submit this investigation to the medical and dental literature. We suggest that surgeons performing the extraction procedures at mandible should be aware of these accessory foramina and thus plan the anesthesia at an appropriate anatomical site. Indian Journal of Dental Research, 23(3), 2012

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Indian Journal of Dental Research, 23(3), 2012