Clinical anatomy of the nerve to the mylohyoid

Mylohyoid Muscle: Current Understanding for Clinical Management-Part I: Anatomy and Embryology

The mylohyoid is one of the suprahyoid muscles, along with the geniohyoid, digastric, and stylohyoid muscles. It lies between the anterior belly of the digastric muscle inferiorly and the geniohyoid superiorly. In Part I, the anatomy and embryology of the mylohyoid muscle will be reviewed in preparation for the clinical discussion in Part II.

Preservation of the Nerve to the Mylohyoid Muscle During Submental Island Flaps: An Anatomic Feasibility Study for Facial Nerve Reanimation Procedures

The submental island flap is an axial pattern pedicle flap widely used in head and neck surgery because of its ease and success. Indications of the submental island flap range from reconstruction for the malignant tumor resection to loss of temporal bone and facial skin due to trauma. Whereas, intraoperative facial nerve injury is not uncommon. We verified whether it was possible to localize the nerve to the mylohyoid muscle and reanimate the facial nerve during submental island flap procedures by preserving the mylohyoid muscle using human fresh cadaveric specimens. Six cadaveric heads were dissected and the position of the nerve to the mylohyoid muscle identified to the mylohyoid triangle documented. We identified the nerve to the mylohyoid muscle on all sides within the mylohyoid triangle and were able to separate the nerve from the submental island flap completely. Our results suggest that facial nerve reanimation using the nerve to the mylohyoid muscle can be used while reconstructing with a submental island flap in cases of intraoperative facial nerve injury.

Cutaneous branch of the nerve to the mylohyoid muscle: potential cause of postoperative sensory alteration in the submental area

BACKGROUND

Previous studies suggest that the nerve to the mylohyoid muscle could have a cutaneous branch. However, its clinical relevance has rarely been discussed because there is insufficient evidence for it. Our aim in this study was to investigate the anatomy of the cutaneous branch of the nerve to the mylohyoid muscle and extend the discussion to surgical management.

METHODS

Twenty sides from ten embalmed cadaveric heads were dissected to identify the cutaneous branch of the nerve to the mylohyoid muscle. The cutaneous branch was traced up to its termination.

RESULTS

The cutaneous branch was observed in 90% and classified into types I and II. In type I, the terminal trunk reached the anterior belly of the digastric muscle. In type II there were two types of terminal trunks, superior and inferior branches, which were identified on all sides. The number of the terminal trunk was one in 23.1% (type I; 6/26) and two in 76.9% (type II; 20/26).The terminal points of the cutaneous branch were all located within a 3cm×2cm rectangular segment in the center of the submental area.

CONCLUSIONS

We propose a new dermatome including the nerve to the mylohyoid muscle in the center. Understanding the cutaneous branch of the nerve could help surgeons to prevent iatrogenic sensory loss of the submental area.

Localizing the nerve to the mylohyoid using the mylohyoid triangle

The nerve to the mylohyoid muscle has been well studied but there are no specific anatomical landmarks for identifying it. Therefore, we aimed to identify anatomical landmarks for localizing the nerve to the mylohyoid muscle in the submandibular region. Sixteen sides from eight embalmed Caucasian cadaveric heads were used in this study. The mean age at the time of death of the specimens was 80.3 years. The anterior and posterior bellies of the digastric muscle, submental artery, and mylohyoid muscle were dissected to verify their relationships with the nerve to the mylohyoid muscle. The nerve to the mylohyoid muscle was found medial to the submental artery, lateral to the anterior belly of the digastric muscle, and anterior to the posterior border of the mylohyoid muscle on all sides. Herein, we identified what we term the mylohyoid triangle. This anatomical region can help localize the nerve to the mylohyoid muscle.

Postoperative CT findings of orthognathic surgery and its complications: A guide for radiologists

Orthognathic surgery is the standard procedure to correct congenital, developmental, or acquired dentofacial deformities. The maxillomandibular relationship corrected by orthognathic surgery can improve facial esthetics, masticatory function, articulation, and breathing. The most common types of osteotomies include the combination of Le Fort I osteotomy, bilateral sagittal split mandibular ramus osteotomy, and genioplasty. High-resolution low-dose computed tomography is useful for evaluating the facial skeleton and soft tissues after surgery as well as for depicting a variety of possible complications. This article reviews the postoperative imaging findings of the most common orthognathic surgeries and their potential complications on multidetector-row computed tomography.

Dual innervation of the submandibular gland by nerve to mylohyoid and chorda tympani

The chorda tympani typically utilises the lingual nerve and submandibular ganglion to transmit parasympathetic fibres to the submandibular gland. During a routine anatomy dissection, the submandibular gland was found to be innervated by both the lingual nerve and the nerve to mylohyoid. The clinical implications of this variant dual innervation to the submandibular gland is not clear due to its rarity: however, recognising such a variation should be borne in mind during surgical intervention near the nerve to mylohyoid.

Anomalies and Clinical Significance of Mylohyoid Nerve: A Review

Background

The mylohyoid nerve is a branch of the inferior alveolar nerve (IAN), which is a branch of the posterior division of the mandibular nerve (MN). It is the source of motor nerve supply to the mylohyoid and anterior belly of the digastric muscle. At times, it provides sensory innervation to the mandibular teeth and skin below the chin. Since the location, anatomical variation and communications of the mylohyoid nerve are varied, it becomes clinically important to have an in-depth knowledge when treating patients for dental and maxillofacial procedures. Such anatomical variations of the mylohyoid nerve innervations may account for failure of the nerve blocks and hence, knowledge is very important for the practitioner.

Materials and Methods

A thorough literature search was done using the key words mandibular nerve, communications of the mylohyoid nerve, inferior alveolar nerve, lingual nerve, failure of dental anaesthesia, mylohyoid nerve and dental implants "from the Databases - PubMed, Scopus Embase and Web of Science (years 1952-2020)".

Results

The mylohyoid nerve may contain motor and sensory fibres, it may pass through the mylohyoid groove or canal and communicate with other nerves, which is clinically significant. Such anatomical variations may be one of the reasons for the failure of the inferior alveolar nerve block.

Conclusion

Awareness of these variations is very significant in planning treatment and avoiding any unnecessary steps. The most frequently encountered anatomic variation of the mylohyoid nerve was innervation of the submental skin and the anterior teeth.

Disuse atrophy of masticatory muscles after intracranial trigeminal schwannoma resection: A case report and review of literature

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Temporomandibular disorders (TMD) are diseases of the temporomandibular joint and masticatory muscles, and are often difficult to be diagnosed.

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Determining the cause of facial asymmetry and jaw deviation are quite challenging.

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The morphologic and functional characteristics of masticatory muscles are maintained by sensory and motor innervation from the trigeminal nerve.

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Trigeminal schwannoma is a rare benign tumor originating from the Schwann cells.

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We experienced a case of masticatory muscle disuse atrophy during long-term follow-up after resection of intracranial trigeminal schwannoma.

Introduction

Temporomandibular disorders (TMD) are diseases of the temporomandibular joint and masticatory muscles, and are often difficult to be diagnosed because they have various symptoms, pathological conditions and causes.

Presentation of case

Herein, we report a 78-year-old male referred to our hospital with a diagnosis of TMD and presenting with facial asymmetry, marked deviation to the right side on vertical mandibular movement and complaints of abnormal perception at the right oral and buccal region. Past medical history revealed that he had undergone a right intracranial trigeminal schwannoma resection 9 years prior. Computed tomography (CT) showed disuse atrophy of the right side of 4 masticatory muscles and 2 suprahyoid muscles controlled by the motor component of the mandibular division (V3) of the trigeminal nerve (TGN). Together with the neurosurgeon, we confirmed that there was no recurrence of the tumor and explained to the patient that the oral and maxillofacial symptoms are after-effects of the operation, and we provided oral hygiene instructions and coordinated cleaning of the inside of the oral cavity.

Discussion

Although it is difficult to compare treatment methods from case to case, we believe that in our case, the patient's understanding of the cause of his discomfort contributed significantly to the improvement of his quality of life.

Conclusion

We experienced a case of masticatory muscle disuse atrophy during long-term follow-up after resection of intracranial trigeminal schwannoma. Further studies are needed to develop the diagnostic and therapeutic protocols for disuse atrophy.

[Root dislocation into the mouth floor as a complication of lower impacted third molar extraction]

Root dislocation into soft tissues during lower jaw third molar extraction belongs to clinically rare complications. The thickness of the cortical plate on the third molar lingual side does not exceed 1.5 mm. Working with an elevator, or headpiece, it is possible to push the roots into the adjacent soft tissue. It is not possible to remove displaced tooth fragment through the socket, it requires additional surgical access from the lingual side. The authors described three clinical cases of root dislocation during third molar removing. Successful surgical treatment was done.

Mylohyoid foramen of mandible: a rare exit point of intra-mandibular origin of nerve to mylohyoid

Nerve to mylohyoid is a branch of inferior alveolar nerve. It arises in the infratemporal fossa and runs in the mylohyoid groove of mandible to reach the submandibular region, where it supplies the anterior belly of digastric and mylohyoid muscles. Though sensory distribution of this nerve have been described, it is predominantly a motor nerve. Here, a rare intra-mandibular origin of nerve to mylohyoid has been presented. This nerve arose from the inferior alveolar nerve inside the mandible and came out to the submandibular region by passing through a small foramen present on the medial surface of the body of the mandible. It ended by supplying the anterior belly of digastric and mylohyoid muscles. The knowledge of this variation could be of importance to maxillofacial surgeons and radiologists.