Anterior Belly Research Articles

Adipocyte Apoptosis Following a Novel Method for Double Chin Reduction: A Pilot Human Histology Study.

Submental fullness is perceived as unattractive by both men and women. The noninvasive simultaneous delivery of HIFES and synchronized radiofrequency+ (Sync RF+) technologies aims to address the submental fullness by concurrently targeting the skin, adipose tissue, and weakened anterior belly of the digastric muscle, the three contributing layers to the double chin appearance. This study aims to investigate the histological changes to adipose tissue related to cell morphology, caspase-7, and Bcl-2 levels to detect adipocyte apoptosis following the HIFES and Sync RF+ treatment on human subjects. The active group (n = 6) received single 20-min treatment on the submental area, while the control group (n = 2) did not receive any treatment. Biopsies of subcutaneous fat tissue were obtained at baseline, and 24 h and 7 days posttreatment. The specimens were histologically and immunohistochemically analyzed for changes in morphology, caspase-7, and Bcl-2 levels. Observed caspase-7 levels increased by 511% at 24-h posttreatment, and 101% at 7 days (p < 0.0001), while the Bcl-2 levels decreased by 89% at 24 h and 24% at 7 days posttreatment (p < 0.0001). The control group had no statistically significant relative changes in the activity of caspase-7. Posttreatment adipocytes were shrunken in size, and shapes lost their uniformity compared to baseline. Five of six subjects reported the treatment as being comfortable. No adverse events were observed during the study. The results of this human histology study indicate that noninvasive HIFES and Sync RF+ technologies have a favorable safety profile for submental fat reduction through the induction of adipocyte apoptosis. ClinicalTrials.gov identifier: NCT06282172.

Variation and Arrangement of the Digastric Muscle in a Chinese Population.

The digastric, a prominent anatomic feature of the head and neck, exhibits clear ethnographic differences in the incidence of variation in its anterior belly (AB) and the relationship of its intermediate tendon (IT) to the stylohyoid (SH). There is a limited amount of information available regarding the digastric in the Chinese population, with most descriptions being individual cases. The present study aims to investigate the variability of AB, elucidate the relationship between IT and SH, and further address the arrangement of individual digastric muscles according to the type of AB and posterior belly (PB) of the digastric, as well as IT, in a Chinese population. Anatomic dissections of the head and neck were carried out bilaterally after student-performed neck dissections during a topographic anatomy course. The types of AB, PB, and IT were recorded to characterize and classify each digastric muscle. The incidence of AB variation was 21.05%. IT type Ⅰ and IT type Ⅱ accounted for 31.25% and 68.75%, respectively. The gross anatomy of the digastric was dominated by the arrangement of AB type I, IT type Ⅱ, and PB type I (63.16%). In addition, 2 rare AB variations were identified. To the best of our knowledge, this is the first report describing individual digastric arrangements and anatomically defining the normal digastric arrangement in the Chinese population. Careful consideration of the variant and anomaly of the digastric is critical for both surgeons and radiologists to provide accurate diagnostic and therapeutic procedures.

Incidental Finding of Double Posterior Belly of Digastric Muscle in Head and Neck Cancer Patient.

The digastric muscles have important roles in swallowing, chewing, speech, and landmark identification during neck dissection. The posterior belly of the digastric muscle (PBDM) is often useful for defining boundaries in surgical neck dissection as it contributes to the carotid, submandibular, and submental triangles. The cadaveric prevalence rate of anatomic variations in the digastrics has been reported to be 31.4% of the population with most occurring in relation to the anterior belly of the digastric muscle (ABDM). Few reports describe variations in the PBDM. While anatomic variants of the digastric muscles do not present with clinical manifestations, they can be mistaken as neck masses and contribute to intraoperative complications. We present a case report of a 73-year-old male with a past medical history significant for Parkinson's Disease, who was incidentally found to have a duplicate PBDM intraoperatively while receiving surgical management of a left buccal squamous cell cancer. Nine months prior to surgery, the patient began experiencing trismus and some mild dysphagia that were eventually worked up to reveal left buccal squamous cell carcinoma (SCC). Prior to this, the patient did not have clinical symptoms demonstrating dysfunction that could be related to or indicative of this anatomical abnormality preceding symptoms related to left buccal SCC growth. The procedure included a wide local excision, left modified radical neck dissection and left submental artery island flap with suprahyoid neck dissection. The superior duplicate PBDM was found to be overlying the stylohyoid muscle. It is important for surgeons operating in the head and neck to be aware of the possibility of this rare variation, and to be conscientious when it is identified so that it does not prohibit or limit a thorough dissection of the neck structures where oncologic clearance is paramount.

Effect of passive jaw opening on the electromyographic activity of the temporalis, masseter, digastric, and infrahyoid muscles in healthy adults

ABSTRACT Objective To investigate the surface electromyography (EMG) activity of the temporalis, masseter, digastric, and infrahyoid muscles during passive jaw opening in healthy adults. Methods The EMG activity of the masseter, temporalis, digastric anterior belly, and infrahyoid muscles on the right side was recorded during the four jaw-opening tasks: active opening to 20 mm (AO20); active opening to 40 mm (AO40); passive opening to 40 mm with a rubber mouth prop on the right posterior teeth (POR40); and passive opening to 40 mm with a mouth prop on the left posterior teeth (POL40). Results The EMG amplitude of the digastric anterior belly and infrahyoid muscles in either POL40 or POR40 was significantly less than that in AO20 or AO40, respectively. Conclusion Passive jaw opening reduces the EMG activity of the digastric and infrahyoid muscles significantly and could help reduce the load on these muscles during prolonged mouth-opening conditions.

Comparison between botulinum toxin type A injection on masseter muscle only and additional injection on anterior belly of digastric muscle in sleep bruxism patients: A clinical trial.

This study aims to evaluate the effects on bite force and muscle thickness of the botulinum toxin (BoNT) injection for patients with sleep bruxism (SB) by comparing injections into the masseter muscle only and both the masseter and the anterior belly of the digastric muscle (ABDM) in a clinical trial. Twelve SB patients received BoNT-A injections using US-guided techniques into the masseter muscle only (Group A), while the remaining 12 SB patients received injections into both the masseter and ABDM (Group B). Bite force and muscle thickness were measured before injection, as well as 1 and 2 months after injection. The bite force and masseter muscle thickness decreased in both Group A and Group B before injection, and at 1 and 2 months after injection. However, there was no significant difference (p > .05, repeated measures analysis of variance) between the two groups, and there was also no significant difference in ABDM thickness (p > .05, repeated measures analysis of variance). This study is the first to assess the short-term effects of BoNT injected into ABDM for SB control. Results show no influence on SB reduction, suggesting the need for further research on BoNT's effectiveness in controlling intense ABDM contractions during sleep and assessing suprahyoid muscle potential impact on rhythmic masticatory muscle activity occurrence.

Navigating the void: outcomes and adaptations during parotid surgery in the absence of posterior belly of digastric muscle.

It is well known that the digastric posterior belly is one of the essential landmarks for facial nerve identification during parotid surgery. While there were multiple reports about variations of the digastric anterior belly, only a few anatomical variations of the posterior belly of the digastric muscle have been described.In this article, we describe an anatomical variation of the posterior belly of digastric muscle found during superficial parotidectomy of a patient with pleomorphic adenoma. This anatomical variation also led to an anatomical variation in the position of the facial nerve.To our knowledge, this is the first report of an absent posterior belly of digastric muscle found during live parotid surgery. The knowledge of current anatomical variation may help to avoid facial nerve injury during parotid surgery and preserve the function of muscles of facial expression.

Sihler's staining of the anterior belly of digastric muscle for botulinum toxin injection.

The anterior belly of the digastric muscle (ABDM) is the target of botulinum toxin injection; however, anatomical considerations related to the injection point are absent. This study used Sihler's staining to analyze the intramuscular nerve distribution of ABDM to identify the most effective botulinum toxin injection points. We used 12 specimens from 6 embalmed cadavers in this study. The specimens were manually dissected to preserve the mylohyoid nerve and subjected to Sihler's staining. From the gnathion to and hyoid bone, the ABDM was divided into three equal parts, distinguishing the anterior, middle, and posterior thirds. Only a branch of the mylohyoid nerve entered the ABDM, and its entry point was located in the middle-third region in all cases. The nerve endings were concentrated in the middle third (100%), followed by the anterior third (58.3%) and were not observed in the posterior third. The landmarks used in this study (gnathion and hyoid bone) are easily palpable on the skin surface, allowing clinicians to target the most effective injection site (middle third of ABDM). These results provide scientific and anatomic evidence for injection points, and will aid in the management of ABDM injection procedures in clinical practice.

Bilateral, symmetrical, tripartite variation of the anterior belly of digastric muscle

BackgroundThe anterior and posterior bellies of digastric muscle act to facilitate components of phonation, jaw opening, and hyoid bone stabilization during swallowing. Variations in the digastric muscle within the submental triangle are well-documented in the literature. Ongoing and up-to-date reporting and knowledge of these variations is important from a clinical perspective. MethodRoutine human anatomical dissection of the anterior neck in a male donor revealed bilateral pairs of accessory muscles (n = 4) attached to and within the depth plane of right and left anterior bellies of digastric muscles. ResultsThe case presented here is of a bilateral, tripartite digastric muscle variation within the submental triangle of an anatomical donor. Attachments and relationships were noted. Variant digastric muscles were found to be innervated by the nerve to the mylohyoid muscle and supplied by the submental artery, consistent with supply to the anterior belly of the digastric muscle. ConclusionThe clinical relevance of these additional muscles primarily pertains to radiological evaluation and reconstructive surgical procedures in the submental region, as digastric muscle bellies serve as essential landmarks and potential targets. Describing anatomical variations is crucial for appropriate planning of interventions in this region.

Assessing the oral and suprahyoid muscles in healthy adults using muscle ultrasound to inform the swallowing process: a proof-of-concept study

The oral and suprahyoid muscles are responsible for movements of swallowing. Our study aimed to determine the reproducibility of static and dynamic measurements of these muscles using bedside ultrasound equipment. Forty healthy participants were recruited prospectively. Primary outcomes were evaluation of mass measurements of the anterior bellies of the digastric, mylohyoid, geniohyoid and tongue in B-mode ultrasound. Secondary outcomes were evaluation of geniohyoid muscle layer thickness and function using M-mode. Muscle mass measurements demonstrated little within-participant variability. Coefficient of Variance (CoV) across muscles were: anterior belly digastric (5.0%), mylohyoid (8.7%), geniohyoid (5.0%) and tongue (3.2%). A relationship between sex (r2 = 0.131 p = 0.022) was demonstrated for the geniohyoid muscle, with males having higher transverse Cross Sectional Area (CSA) (14.3 ± 3.6 mm vs. 11.9 ± 2.5 mm, p = 0.002). Tongue size was correlated with weight (r2 = 0.356, p = 0.001), height (r2 = 0.156, p = 0.012) and sex (r2 = 0.196, p = 0.004). Resting thickness of the geniohyoid muscle layer changed with increasing bolus sizes (f = 3.898, p = 0.026). Velocity increased with bolus size (p = < 0.001, F = 8.974). However swallow time and slope distance did not, potentially influenced by higher coefficients of variation. Oral and suprahyoid muscle mass are easily assessed using bedside ultrasound. Ultrasound may provide new information about muscle mass and function during swallowing.

Tree frogs Polypedates Dennysi landing on horizontal perches: the effects of perch diameters.

Secure landing is indispensable for both leaping animals and robotics. Tree frogs, renowned for their adhesive capabilities, can effectively jump across intricate 3D terrain and land safely. Compared to jumping, the mechanisms underlying their landing technique, particularly in arboreal environments, have remained largely unknown. In this study, we focused on the landing patterns of the tree frogs Polypedates Dennysi on horizontally placed perches, explicitly emphasizing the impact of perch diameters. Tree frogs demonstrated diverse landing postures, including the utilization of (1) single front foot, (2) double front feet, (3) anterior bellies, (4) middle bellies, (5) posterior bellies, (6) single hind foot, or (5) double hind feet. Generally, tree frogs favour bellies on slimmer targets but double front feet on large perches. Analysis of limb-trunk relationships revealed their adaptability to modifying postures, including body positions and limb orientations, for successful landing. The variations in the initial landing postures affect the succeeding landing procedures and, consequently, the dynamics. As the initial contact position was switched from front foot to hind foot, the stabilization time decreased first, reaching the minimum in middle belly landings, and then increased. The maximum vertical forces changed in an inverse trend, whereas the maximum fore-aft forces continuously increased as the initial contact position switched. As the perch diameter rose, the time expenses dropped, whereas the maximum impact increased. These findings not only added to our understanding of frog landings but also highlighted the necessity of considering perch diameters and landing styles when studying the biomechanics of arboreal locomotion.

Nerve to Anterior Belly of Digastric Muscle as a Donor for Facial Re-innervation: A Cadaveric Feasibility Study

Nerve to Anterior Belly of Digastric Muscle as a Donor for Facial Re-innervation: A Cadaveric Feasibility Study

Double Chin Concerns afterEn Bloc Mandibular U-ShapedOsteotomy: Submental-Cervical Soft Tissue Changes and Anterior Belly of Digastric Muscle Assessment.

To assess submental-cervical soft tissue changes afteren bloc mandibularU-shapedosteotomy and examine alterations in the anterior belly of digastric muscle (ABDM). A retrospective study analyzed 20 patients who underwent en bloc mandibularU-shaped osteotomy from 2018 to 2023. Preoperative (Tp) and long-term follow-up (Tf) CT data were collected for analysis, measuring mandibular volume, soft tissue thickness at menton (Mes) and cervicale (C), and ABDM parameters (length, cross-sectional area (CSA), volume, distance from centroid point to the mandibular margin). Correlation analyses were performed to investigate the connection between soft tissue thicknesschanges, ABDM changes, and mandibular osteotomy volume. Long-term follow-up revealed a significant increase in soft tissue thickness at the Mes and C points after U-shaped mandibular osteotomy, especially at the C point. The adaptive length of ABDM decreased, CSA increased, and volume decreased, but the ABDM centroid point shifted downward relative to the mandibular margin, indicating drooping protrusion. The increment of soft tissue thicknesswas moderately positively correlated with the amount of osteotomy, and the decrement of ABDMlength and volume were slightly positively correlated with the amount of osteotomy. The degree of soft tissue relaxation afterU-shaped osteotomy is related to the extent of osteotomy. Notably, the protrusion of ABDM relative to the mandibular margin affects submental-cervical contour aesthetics. Prior to U-shaped osteotomy, it is crucial to assess the soft tissue condition of the patient's lower face, and the individualized design of the osteotomy volume should be carried out cautiously and safely. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Deep Neck Contouring through the Ages.

Deep neck contouring can achieve dramatic results in young and old patients. Both genetic predisposition and aging contribute to the malposition of deep neck structures and a poorly contoured neckline. Depending on the patient's anatomy, deep neck contouring should involve a combination of submental liposuction, platysmaplasty, subplatysmal fat lipectomy, resection of the anterior belly of the digastric muscle, and either cautery or resection of the submandibular glands. Resorption of the facial bony skeleton that occurs with aging affects the ultimate postoperative mandibular contour, and postoperative results thus differ in the young versus old patient. In patients in which there is concern for excess skin laxity, a concurrent facelift is necessary to excise excess neck skin. This article includes a discussion on how a combination of aging and genetics influence a patient's neck anatomy, critical preoperative considerations prior to performing deep neck contouring, intraoperative technique, and adjunct procedures that can further improve a patient's neckline.

Comparative three-dimensional jaw muscle anatomy of marsupial carnivores (Dasyurus spp.) and the termite-eating numbat (Myrmecobius fasciatus).

Among marsupials, the endangered numbat (Myrmecobius fasciatus) is the only obligate myrmecophage with a diet comprised strictly of termites. Like many other specialised myrmecophagous mammals, numbats have a gracile and highly specialised skull morphology with an elongated rostrum and small braincase. Myrmecobiidae is one of four taxonomic families within the Australasian marsupial order Dasyuromorphia, and to date, the muscular anatomy of any member of this group is relatively poorly known. We utilised microdissection and contrast-enhanced microcomputed tomography scanning to provide the first comprehensive qualitative and quantitative descriptions of jaw muscle anatomy in numbats and quolls (Dasuyrus species). The arrangement of the jaw muscles across these species was conservative, both in gross anatomy and muscle proportions, corresponding to a 'generalised' mammalian pattern. In contrast to Dasyurus, the jaw muscles of the numbat were greatly reduced. Many aspects of the muscle anatomy of the numbat were similar to patterns reported in other myrmecophagous species, particularly a greatly reduced temporalis muscle. Unusually, the digastric muscle in the numbat was comprised of a single, large anterior belly while the posterior belly was absent. We propose that the enlarged anterior belly of the digastric may be linked to jaw stabilisation and coordination of tongue movements during feeding. The lateral insertion and fascial connection of the digastric to the tongue in numbats may also aid in distributing stress evenly across the jaw and minimise muscle fatigue. The muscle descriptions and three-dimensional models provided in this study will facilitate further analysis of musculoskeletal adaptation and evolution within the Dasyuromorphia.

Reanimation of the Lower Lip with the Anterior Belly of Digastric Transfer: A Systematic Review.

Background: Dynamic reanimation of the lower lip is a challenging issue for patients, with depressor asymmetry commonly addressed with chemodenervation, selective neurectomy, or myectomy. Objective: To determine whether the anterior belly of digastric transfer is an effective method of lower-lip reanimation for patients with either isolated marginal mandibular branch weakness or inadequate depressor function after hemifacial reanimation, as measured by patient satisfaction and objective symmetry evaluation. Method: Systematic review of the literature was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Abstracts and full texts were reviewed. A Risk of Bias assessment was performed. Results: Nine studies with 164 patients were included. Anterior belly of digastric transfer was successfully performed in 162 patients. Most patients (52%) underwent one-staged reanimation innervated by the native nerve to the mylohyoid. A two-staged approach after placement of a cross face nerve graft was performed in 46%. Patient satisfaction was excellent (90.6%), with minimal complications including revision (4/162), infection (4/162), and lipofilling (8/162). Conclusion: In patients seeking a permanent outcome, use of an anterior belly of digastric transfer in either a one-stage or two-stage approach appears to be a safe and effective method to restore symmetry and dynamic function.

Deep Neck Contouring: Indications and Techniques.

A deep comprehension of key anatomical issues, along with the targeted application of suitable therapies, is vital for attaining exceptional neck contours. Traditional surgical approaches often focus solely on modifying subcutaneous fat and, occasionally, the platysma muscle, neglecting subplatysmal structures. This narrow focus may yield less-than-ideal results and potentially exacerbate existing issues, leading to additional contour abnormalities that prove challenging to correct. In fact, in most cases, there are additional factors deep to the platysma-such as subplatysmal fat, the anterior bellies of the digastric muscles, perihyoid fascia, and the submandibular glands-that contribute to obtuse neck contours. For these patients, accessing the neck through a submental incision allows for precise management of these deep neck structures as required. Unfamiliarity with deep anatomical structures can deter surgeons from performing subplatysmal procedures due to unwarranted concerns about increased complication risks. However, both published clinical series and our clinical experience indicate favorable long-term outcomes with natural, refined, harmonious neck contours and a minimal rate of complications. This article serves as a comprehensive guide, describing indications, strategies, and providing a step-by-step description of the senior author's techniques for mastering deep neck contouring.

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.

Mylohyoid Muscle: Current Understanding for Clinical Management Part II: Clinical Anatomy, Radiology, and Surgical/Clinical Relevance.

The mylohyoid is one of the suprahyoid muscles along with the geniohyoid, digastric, and stylohyoid muscles that lies between the anterior belly of the digastric muscle inferiorly and the geniohyoid superiorly. In Part II, the radiology and clinical/surgical importance of the mylohyoid muscle will be discussed.

Botulinum Toxin Injection into the Digastric Muscle: Current Clinical Use and a Report of Five Cases.

The present research aimed to review the clinical applications of botulinum toxin-A (BTX-A) injection into the anterior belly of the digastric muscle (ABDM) and to highlight the potential role of the BTX-A injection into ABDM in preventing postsurgical relapse. Five Class II malocclusion patients who underwent orthognathic surgery received BTX-A injections into both ABDM for the prevention of postoperative relapse. The relapse was evaluated using lateral cephalometric radiographs by comparing the postoperative cephalometric analyses at two different time points, postoperatively at 2 weeks (T1), and long-term, at 9 months after the surgical intervention (T2). The results demonstrated no significant differences between T2 and T1 for the Selle-Nasion-point A (SNA) angle, Selle-Nasion-point B (SNB) angle, point A-Nasion-point B (ANB) angle, mandibular length, and sagittal mandibular position. The patients exhibited stable occlusion without any signs of relapse after the surgery. A single BTX-A injection into the ABDM can effectively prevent postoperative relapse in Class II malocclusion patients, following orthognathic surgery. From a clinical perspective, in case of optimal dosage and procedure, BTX-A injection could be considered as the primary option for the prevention of postsurgical relapse for Class II malocclusion patients.

A clinical perspective on the anatomical study of digastric muscle.

One of the suprahyoid muscles is the digastric muscle which comprises anterior and posterior bellies joined by an intermediate tendon. Because of its close relationship with the submandibular gland, lymph nodes, and chief vessels of the neck, detailed knowledge about the morphometry of the digastric muscle is essential. The objective of the current cross-sectional evaluative study is to record morphometry along with the digastric muscle's origin, insertion, and variability. Forty human cadavers (25 males and 15 females) were dissected, and the head and neck regions were studied in detail. The attachment of the digastric muscle anterior belly to the digastric fossa of the mandible was noted, and the distal attachment of the posterior belly to the mastoid notch was traced. The length of the anterior belly from the digastric fossa to its intermediate tendon and the length of the posterior belly from the intermediate tendon to its mastoid attachment were measured. There is a fair correlation between the length of the neck and the length of the anterior and posterior belly. The study also identified two cases of bilateral accessory bellies of the anterior belly of the digastric. Normal morphometric data is provided by this study on details of the digastric muscle. It is significant from a clinical and surgical point of view as the muscle lies in proximity to the important structures of the neck.