Anatomical Insights on the Cervical Nerve for Contemporary Face and Neck Lifting: A Cadaveric Study.

BACKGROUND: Despite the significant roles it plays in the functions of the platysma and lower lip, the cervical branch of the facial nerve is often overlooked compared to other branches, but its consideration is critical for ensuring the safety of neck surgeries. OBJECTIVES: The aim of this study was to clarify the anatomical discrepancies associated with the cervical branch of the facial nerve to enhance surgical safety. METHODS: The study utilized 20 fresh-frozen hemiheads. A 2-stage surgical procedure was employed, beginning with an initial deep-plane facelift including extensive neck dissection, followed by a superficial parotidectomy on fresh-frozen cadavers. This approach allowed for a thorough exploration and mapping of the cervical nerve in relation to its surrounding anatomical structures. RESULTS: Upon exiting the parotid gland, the cervical nerve consistently traveled beneath the investing layer of the deep cervical fascia for a brief distance, traversing the deep fascia to travel within the areolar connective tissue before terminating anteriorly in the platysma muscle. A single branch was observed in 2 cases, while 2 branches were noted in 18 cases. CONCLUSIONS: The cervical nerve's relatively deeper position below the mandible's angle facilitates a safer subplatysmal dissection via a lateral approach for the release of the cervical retaining ligaments. Due to the absence of a protective barrier, the nerve is more susceptible to injuries from direct trauma or thermal damage caused by electrocautery, especially during median approaches.

Anatomical insights of the mylohyoid for clinical procedures in dentistry.

INTRODUCTION: The purpose of this study is to provide useful data by conducting a comprehensive study of the mylohyoid muscle and its related structures. MATERIALS AND METHODS: Fifty-eight mandibles and 30 mylohyoid muscles from Korean adult cadavers were used. The shape and location of the mylohyoid line were analyzed by using digital calipers. The mylohyoid muscle and its herniation were observed using ultrasonography. After dissection, morphometric measurements of the muscle and herniation were conducted. The distribution pattern of the nerve to mylohyoid muscle was confirmed. RESULTS: The proportion of the distance between the cementoenamel junction and the mylohyoid line decreased from the mesiolingual cusp of the mandibular first molar (1:0.57) to the distolingual cusp of the mandibular second molar (1:0.41). The mylohyoid muscle was large, thick, and deep in men. Herniation was observed in 16 (53.3%) cases, and it was concentrated in the anterior one-third (52.2%) of the muscle. The richest arborization of the nerve to mylohyoid muscle was in the middle one-third (52.9%) of the muscle. CONCLUSIONS: The results of the mylohyoid line can be applied in the reconstruction of the occlusal plane in edentulous patients. Differences between the sexes should be considered in the morphological characteristics of the mylohyoid muscle. Differential diagnosis of herniation is particularly important in the anterior one-third of the muscle. In the case of treatment with botulinum toxin in the mylohyoid muscle, it is recommended to inject into the middle one-third area considering the depth and thickness of the muscle in that area.

Revisiting the relationship between the submandibular duct, lingual nerve and hypoglossal nerve.

BACKGROUND: The aim of the study was to evaluate the relations between submandibular duct, lingual nerve and hypoglossal nerve for making a reassessment of this area in fresh frozen specimens. Also, the distance between the angle of the mandible and the vertical line drawn from the point where submandibular duct crossed lingual nerve to the base of the mandible was measured to determine a new landmark for neck surgeons. MATERIALS AND METHODS: Fourteen fresh frozen head and neck specimens were dissected and evaluated. A marginal mandibular incision was made from the mastoid process to the chin. RESULTS: In 8 cases, lingual nerve was crossing the submandibular duct superiorly; in 5 cases, lingual nerve was crossing the duct infero-medially and in 1 case it was parallel to the duct. In 1 case, lingual nerve subdivided into anterior and posterior branches. In 2 cases, 2 parallel submandibular ducts were found and the lingual nerve was crossing the upper duct from superior. In 1 case, lingual nerve was crossing the duct infero-medially and then it was subdividing into branches superior to mylohyoid. In 12 cases, the course of hypoglossal nerve was classical. In 1 case, hypoglossal nerve crossed the submandibular duct medially and coursed parallel to the tendon of posterior belly of digastric. And in another case, hypoglossal nerve crossed the inferior branch of submandibular duct medially. The other structures in this area were as usual. CONCLUSIONS: The main factor for reducing nerve damage during surgery is the understanding of the anatomy of this area.

Anatomy of the Platysma Muscle.

The aim of this paper was to review the anatomy the platysma systematically.The term "platysma AND anatomy" was used to search PubMed and Scopus, producing 394 and 214 papers, respectively. After excluding 95 duplicate titles, 513 abstracts and 98 full papers were reviewed. Among these 98 papers, 83 were excluded and 5 were added. Ultimately, 20 papers were analyzed.The most common aging-related change of the platysma was shortening (70.7%), followed by thinning (25.2%). The platysma most commonly originated from the upper portion of thorax anterior to clavicle (67.7%), followed by the subcutaneous tissue of the subclavicular and acromial regions (22.6%) and pectoralis (9.7%). The platysma ascended upward and medially (68.5%) or ascended from the clavicle to the face (31.5%). The platysma most commonly inserted on the cheek skin (57.5%), followed by the cutaneous muscles around the mouth (18.6%), the mandibulocutaneous ligament or zygoma (18.6%), and the parotid fascia or periosteum of the mandible (5.3%). The platysma was most commonly innervated by the cervical branch of the facial nerve (38.2%) or the cervical branch and mandibular branch of the facial nerve (60.5%), followed by the cervical plexus (0.6%), the cervical motor nucleus (0.6%), and the glossopharyngeal nerve (0.1%). The most common action of the platysma was drawing the lips inferiorly (83.3%) or posteriorly (12.9%). Four papers classified the platysma into subtypes; however, these classification strategies used arbitrary standards.Further studies will be necessary to establish the thickness of the platysma and to characterize age-related changes of the platysma.

Characterization of the Cervical Retaining Ligaments During Subplatysmal Facelift Dissection and its Implications.

Background: The cervical retaining ligaments anchor the platysma and soft tissues of the neck to the deep cervical fascia and deeper skeletal structures. The cervical retaining ligaments tether the platysma and prohibit free mobilization and redraping of the platysma muscle in rhytidectomy. This ligament system has previously been described in the literature only qualitatively. Objectives: To define the anatomic dimensions of the cervical retaining ligaments and their relation to the platysma muscle in order to better understand the cervical retaining ligament system and how it limits motion of the platysma during rhytidectomy. Methods: Extended deep plane rhytidectomy was performed on 20 fresh cadaveric hemifaces. The extent cervical retaining ligaments were dissected and measured. The anterior extent (width) of the cervical ligament were recorded at three anatomic points on each hemiface: (1) at the level of the inferior border of the mandible; (2) at the top of the thyroid cartilage at the thyroid notch; and (3) at the level of the cricoid. Results: The average width of the cervical retaining ligaments in the neck was 15.3 mm. The width significantly decreased as they became more inferiorly positioned from the top of the neck at the anatomic measurement points, measuring 17.1 mm, 16.1 mm, and 12.6 mm (P < 0.05). Conclusions: The cervical retaining ligaments are the support mechanisms of the platysma muscle in the neck. While previously described in only a qualitative manner, this study quantifies the anterior extent of these ligaments and how they invest the lateral platysma muscle. As these ligaments tether the platysma for an average of 1.5 cm, lateral platysma elevation of this distance during rhytidectomy surgery can improve platysmal redraping during rhytidectomy and potentially improve neck rejuvenation.

Bilateral Continuous Automated Distraction Osteogenesis: Proof of Principle.

The purpose of this study was to demonstrate that automated, continuous, curvilinear distraction osteogenesis (DO) in a minipig model is effective when performed bilaterally, at rates up to 3 mm/day, to achieve clinically relevant lengthening. A Yucatan minipig in the mixed dentition phase underwent bilaterally, at a continuous DO at a rate of 2 mm/day at the center of rotation; 1.0 and 3.0 mm/day at the superior and inferior regions, respectively. The distraction period was 13 days with no latency period. Vector and rate of distraction were remotely monitored without radiographs, using the device sensor. After fixation and euthanasia, the mandible and digastric muscles were harvested. The ex vivo appearance, stability, and radiodensity of the regenerate were evaluated using a semiquantitative scale. Percent surface area (PSA) occupied by bone, fibrous tissue, cartilage, and hematoma were calculated using histomorphometrics. The effects of DO on the digastric muscles and mandibular condyles were assessed via microscopy, and degenerative changes were quantified. The animal was distracted to 21 mm and 24 mm on the right and left sides, respectively. Clinical appearance, stability, and radiodensity were scored as "3" bilaterally indicating osseous union. The total PSA occupied by bone (right = 75.53 ±â€Š2.19%; left PSA = 73.11 ±â€Š2.18%) approached that of an unoperated mandible (84.67 ±â€Š0.86%). Digastric muscles and condyles showed negligible degenerative or abnormal histologic changes. This proof of principle study is the first report of osseous healing with no ill-effect on associated soft tissue and the mandibular condyle using bilateral, automated, continuous, and curvilinear DO at rates up to 3 mm/day. The model approximates potential human application of continuous automated distraction with a semiburied device.

Defining the Shape of the Mylohyoid Muscle: A Morphometric Imaging Study.

OBJECTIVES: Implantable hypoglossal nerve stimulation (HNS) therapy is an evolving therapeutic alternative for patients with refractory obstructive sleep apnea (OSA). The muscular anatomy of this region has implications for surgical access through this zone as well as positioning and anchoring of hardware in this area. The purpose of this study was to radiologically describe the topography of the mylohyoid muscle and adjacent structures across a wide age spectrum. METHODS: We retrospectively evaluated computed tomography scans of the neck in 102 patients who were imaged for reasons unrelated to the floor of mouth or submental space. Patients with prior surgery or pathology in the area of interest were excluded. Fourteen relevant muscle measurements were made on a midline sagittal image and a coronal image positioned at the midpoint between the hyoid bone and the mandible. RESULTS: We included 49 men and 53 women with an average age of 44 years (range 19-70). The average mylohyoid length was 42 mm; the average distance between the anterior digastric bellies was 17 mm. The average angle of the central mylohyoid was 174° in the sagittal plane and 164° in the coronal plane. Several measurements were significantly correlated with patient age, including the angle measurements and the distance between the digastric muscles. Aberrant digastric anatomy was common. CONCLUSIONS: The mylohyoid muscle has multiple radiologically distinct segments with predictable curvatures. An understanding of submental muscular anatomy, along with its variability between patients, may be beneficial to the development of bilateral implantable neurostimulation technology for the treatment of refractory OSA. LEVEL OF EVIDENCE: N/A Laryngoscope, 134:2970-2975, 2024.

Selective lateral compartment neck dissection for thyroid cancer.

BACKGROUND: Compartment-oriented lymph node dissection in patients with thyroid cancer and macroscopic lymph node metastases reduces recurrence and improves survival. However, the extent of lymph node dissection remains controversial. The purpose of this study was to examine the results of selective lateral compartment neck dissection (LCND) for thyroid cancer. METHODS: We completed a retrospective review of patients with thyroid cancer who underwent selective LCND from 1992-2012 to determine the extent of lymph node resection, morbidity, recurrence, subsequent operations, mortality, and duration of follow-up. RESULTS: A total of 45 LCNDs (five bilateral) were performed in 40 patients, 35 with differentiated thyroid cancer (DTC) and five with medullary carcinoma. Nineteen LCNDs (42%) were completed at the time of thyroidectomy. Levels IIA, III, IV, and VB were included in 43 LCNDs (96%) and levels IIA, III, and IV in two LCNDs (4%). Morbidity included neck or ear numbness in 19 patients (48%), neuropathic symptoms in 14 (35%), Horner syndrome in two (5%), marginal mandibular nerve paresis in two (5%), and wound infection in one (3%). Recurrence rate was 25% (10 patients) and one or more reoperations were performed in seven patients (18%) with a mean follow-up of 58 ± 60 mo (range, 1-244 mo). There were 3 ipsilateral recurrences (8%) after 40 LCNDs for DTC. Four patients died from systemic disease: three with medullary carcinoma and one with PTC. CONCLUSIONS: Selective LCND is an effective therapeutic strategy for macroscopic lymph node metastases, with an 8% recurrence rate in the ipsilateral neck in patients with DTC. Neuropathic symptoms, however, remain an important source of morbidity.

Managing the neck in the era of the short scar face-lift.

A recent trend in rhytidectomy has included the introduction of various short incision techniques, particularly the S-lift, the minimal access cranial suspension lift, and other short scar methods. However, this trend has not been without a criticism that these minimally invasive techniques might be limited in what might be achievable by such surgery. As with more traditional face-lift surgery, the management of the neck often presents as the most challenging aspect of the procedure when using short scar techniques. This article will present a brief history of cervical rhytidectomy and relevant surgical anatomy, as well as the authors' algorithmic approach to surgical assessment and management of the neck, the short incision operative techniques, and potential complications. In the authors' experience, attention to both the selection criteria and operative modifications in the execution of short scar techniques are critical to optimizing outcomes in cervical rejuvenation.

Neuromodulators: available agents, physiology, and anatomy.

Neuromodulators have risen to the forefront of aesthetic medicine. By reversibly relaxing target muscles, neuromodulators exhibit their effect by softening hyperfunctional lines. An understanding of their physiology, relevant facial anatomy, and current agents is imperative for a successful aesthetic practice.

The masticatory system under varying functional load. Part 2: Effect of reduced masticatory load on the degree and distribution of mineralization in the rabbit mandible.

A reduction in mechanical loading of the mandible brought about by mastication of soft food is assumed to decrease the remodelling rate of bone, which, in turn, might increase the degree of bone mineralization. The effect of a reduction in masticatory functional load on the degree and distribution of mineralization of mandibular bone was investigated in male juvenile New Zealand White rabbits. The experimental animals (n=8) had been raised on a diet of soft pellets from 8 to 20 weeks of age, while the controls (n=8) had been fed pellets of normal hardness. The degree of mineralization of bone (DMB) was assessed at the attachment sites of various jaw muscles, the condylar head, and the alveolar process. Differences between groups and among sites were tested for statistical significance using a Student's t-test and one-way analysis of variance, respectively. The DMB did not differ significantly between the experimental and control animals at any of the sites assessed. However, in the rabbits that had been fed soft pellets, both cortical bone at the attachment sites of the temporalis and digastric muscles and cortical bone in the alveolar process had a significantly higher DMB than cortical bone at the attachment site of the masseter muscle, while there were no significant differences among these sites in the control animals. The results suggest that a moderate reduction in masticatory functional load does not significantly affect the remodelling rate and the DMB in areas of the mandible that are loaded during mastication but might induce a more heterogeneous mineral distribution.

The association between jaw-opening strength, geniohyoid muscle thickness and echo intensity measured by ultrasound.

AIM: Jaw-opening strength is an indicator of swallowing function including hyoid bone elevation. Geniohyoid muscles play an important role during hyoid bone elevation. This study aimed to investigate whether geniohyoid muscle thickness and echo intensity measured by ultrasonography were related to jaw-opening strength. MATERIAL AND METHODS: Sixty-eight participants (39 men) with an average age of 77±7.7 years were recruited from a functional training health care facility. We measured muscle thickness and echo intensity of the geniohyoid muscle on transverse ultrasound images. RESULTS: Age, calf circumference, grip strength, muscle thickness and echo intensity were significantly associated with jaw-opening strength in univariate analyses. After adjusting for grip strength in multiple regression analysis, geniohyoid muscle thickness and echo intensity were significantly associated with jaw-opening strength (ß=0.29 for muscle thickness, ß=-0.26 for echo intensity). CONCLUSIONS: There was a positive correlation between geniohyoid muscle thickness and jaw-opening strength; echo intensity negatively correlated with jaw-opening strength. Ultrasound evaluation of geniohyoid muscle status provides important information about maintaining jaw-opening strength.

Suboccipital muscle of sharpnose sevengill shark Heptranchias perlo and its possible role in prey dissection.

Skull and head muscles of Heptranchias perlo were studied. Its distinctive features include the suboccipital muscles, described for the first time, the absence of the palatoquadrate symphysis, a longitudinally extended mouth, and teeth unsuited for dissecting prey in typical method of modern sharks, which is cutting motions powered by head shaking from side to side. The palatoquadrate cartilages of H. perlo and closely related Hexanchidae articulate with the neurocranium via orbital and postorbital articulations, which together allow for lateral expansion of the jaws, but restrict retraction and protraction. We interpret these features as an adaptation to a different method of prey dissection, that is, ripping in a backward pull. It employs the specific postorbital articulation together with the suboccipital muscles as force-transmitting devices, and is powered by swimming muscles which produce a rearward thrust of the tail. During this type of dissection, the anterior part of the vertebral column should experience a tensile stress which explains the replacement of rigid vertebral bodies by a collagenous sheath around the notochord in H. perlo. The backward-ripping dissection could have been common among ancient Elasmobranchii based on the similarly developed postorbital articulation, a longitudinally extended mouth, and the absence of the palatoquadrate symphysis. A biomechanical comparison with the extinct Pucapampella indicates that ancient elasmobranchs could be also specialized in the backward-ripping prey dissection, but their mechanism was different from that inferred for H. perlo. We suggest that in the early evolution of sharks this mechanism was replaced by head-shaking dissection and then later was restored in H. perlo on a new morphological basis. A new position of the postorbital articulation below the vertebral axis is fraught with the braincase elevation when backward ripping the prey, and as a counter-mean, requires formation of suboccipital portions of the axial musculature unknown in other sharks. Homology and origin of these portions is considered.

Simple identification of the third segment of the extracranial vertebral artery by extreme lateral inferior transcondylar-transtubercular exposure (ELITE).

PURPOSE: The exposure of the third segment of the extracranial vertebral artery (V3) is an important step in the extreme lateral inferior transcondylar-transtubercular exposure (ELITE) approach. The muscular suboccipital triangle provides one of the landmarks to identify the V3 segment; however, identification of this triangle and dissection of the V3 segment is not always straightforward in the actual surgery. Blind dissection below the level of the foramen magnum can lead to vertebral artery injury. While the surgeon may be able to readily define the V3 segment of the vertebral artery by feeling its pulse, it is important to have a safe systematic approach to finding the V3 segment when the vessel is illusive. We propose a simple method to identify the V3 segment avoiding accidental injury of the vertebral artery. METHODS: Sixteen cadaver heads (using both sides) were prepared by injecting red- or blue-coloured silicone into their arteries and veins, respectively. We performed an ELITE bilaterally on each cadaver head following four key bony landmarks. A postauricular lazy S-shaped skin incision was made centered just behind the mastoid tip. The posterior neck muscles were cut along the line of the skin incision behind the attachment of the sternocleidomastoid muscle to expose the occipital bone. All the incised muscles were reflected anteriorly as the ELITE is a dorsolateral approach. A suboccipital craniotomy was made exposing the posterior half of the sigmoid sinus up to the inferior retrosigmoid point (point A). The foramen magnum was opened after the craniotomy was completed. The dura on the foramen magnum was followed posteriorly in order to identify the occipital midline dural point (point B) that is identified by the bony ridge at the junction of the posterior fossa dura on the foramen magnum and the posterior most aspect of the spinal dura. The posterior tubercle of C1 (point C) was identified directly inferior to Point B. The posterior arch of C1 was followed anteriorly from the tubercle to find the "J-groove", which cradles the vertebral artery (point D). The V3 segment lies above this groove, covering the paravertebral venous plexus. We measured the distances between the landmarks introduced above after completion of the exposure. RESULTS: The distance between points A and B was 30.5 +/- 5.6 mm, points B-C was 10.4 +/- 2.3 mm, points C-D was 19.1 +/- 3.8 mm. The V3 segment was identified using the anatomical relationships described above in all heads. In no cadaver specimen was the artery injured. CONCLUSIONS: Identification of the V3 segment of the vertebral artery by systematically detecting the four anatomical points defined above is simple and much safer than a direct dissection below the foramen magnum.

Anatomic landmarks for localization of the spinal accessory nerve.

This anatomical study examines the anatomic topography and landmarks for localization of the spinal accessory nerve (SAN) during surgical dissections in 40 fresh human cadavers (2 females and 38 males; ages from 22 to 89 years with a mean of 60 years). In the submandibular region, the SAN was found anteriorly to the transverse process of the atlas in 77.5% of the dissections. When the SAN crossed the posterior belly of the digastric muscle, the mean distance from the point of crossing to the tendon of the muscle was 1.75 +/- 0.54 cm. Distally, the SAN crossed between the two heads of the SCM muscle in 45% of the dissections and deep to the muscle in 55%. The SAN exited the posterior border of the sternocleidomastoid muscle in a point superior to the nerve point with a mean distance between these two anatomic parameters of 0.97 +/- 0.46 cm. The mean overall extracranial length of the SAN was 12.02 +/- 2.32 cm, whereas the mean length of the SAN in the posterior triangle was 5.27 +/- 1.52 cm. There were 2-10 lymph nodes in the SAN chain. In conclusion, the nerve point is one of the most reliable anatomic landmarks for localization of the SAN in surgical neck dissections. Although other anatomic parameters including the transverse process of the atlas and the digastric muscle can also be used to localize the SAN, the surgeon should be aware of the possibility of anatomic variations of those parameters. Similar to previous investigations, our results suggest that the number of lymph nodes of the SAN chain greatly varies.

Levator submandibuli muscle (Banjo muscle) a rare muscle in human beings; anatomy, morphogenesis, function and incidence.

A rare muscle named Levator Submandibuli (LS) or Banjo muscle (after the author) is present in few persons. It is situated in the submandibular region superficial to the mylohyoid muscle. It consists of two triangular right and left halves whose fibres originate by interdigitating with each other from a median intermuscular septum attached above to the mandible, below to the hyoid bone, parallel and continuous with the intermuscular septum of the mylohyoid muscle. Levator Submandibuli muscle fibres of each side insert into a tendon which is continuous at each side with the central tendon of the digastric muscles. Contraction of the muscle would elevate and support the submandibular region particularly during swallowing and during any activity which increases the oro-pharyngeal pressure such as blowing a trumpet. The muscle is not an accessory/anomaly of the digastric nor of mylohyoid muscle. Its anatomy indicated that, it is a separate muscle innervated by a branch from the mylohyoid nerve. It is suggested that, there is predilection for the appearance of a separate muscle in the submandiblar region distinct from mylohyoid and digastric muscles. It is further suggested that during myogenesis when the migrating myogenic (myoblasts) cells destined to form levator submandibuli are halted at the proximity of the site of formation of anterior belly of the digastric muscle, an anomalous/accessory muscle of the digastric is formed. But when the myoblasts reach their predestined position in the submandibular region, an independent muscle, levator submandibuli (Banjo muscle) is formed. The muscle has an incidence of about 0.3% in Caucasian and 0.4% in black Africans.

Superficial, suprahyoid, and infrahyoid neck musculature in naked mole-rats (Heterocephalus glaber): Relative size and potential contributions to independent movement of the lower incisors.

Naked mole-rats (Heterocephalus glaber) are fossorial, eusocial rodents that exhibit the unusual capability of moving their lower incisors independently in lateral and rostroventral directions. The evolution of this trait would presumably also involve concurrent alterations in neck musculature to support and control movements of the lower incisors. In order to assess morphological adaptations that might facilitate these movements, we performed detailed dissections of the neck musculature of adult naked mole-rats. In addition to characterizing attachment sites of superficial, suprahyoid, and infrahyoid musculature, we also quantified muscle mass and mandibular features thought to be associated with gape (condyle height, condyle length, and jaw length). Based on muscle attachment sites, the platysma myoides may contribute to lateral movement of the lower incisor and hemi-mandible in naked mole-rats. The large digastric muscle is likely to be a main contributor to rostroventral movement of each lower incisor. The geniohyoid and mylohyoid muscles also likely contribute to rostroventral movements of the lower incisors, and the mylohyoid may also produce lateral spreading of the hemi-mandibles. The transverse mandibular (intermandibularis) muscle likely serves to reposition the lower incisors back to a midline orientation following a movement.

Tooth extraction and subsequent dental implant placement in Sprague-Dawley rats induce differential changes in anterior digastric myofibre size and myosin heavy chain isoform expression.

OBJECTIVE: to determine if tooth loss and dental implant placement in rats induce changes in the morphological and histochemical features of the Anterior Digastric muscle. DESIGN: Adult male Sprague-Dawley rats had their right maxillary molar teeth extracted. 'Extraction-1' and 'Extraction-2 groups were sacrificed, respectively, 4 or 8 weeks later, and an Implant group had an implant placement 2 weeks after the molar extraction, and rats were sacrificed 3 weeks later (n = 4/group). Naive rats (n = 3) had no treatment. Morphometric and immunohistochemical techniques quantified Anterior Digastric muscle myofibres' cross-sectional area (CSA) and myosin heavy chain (MyHC) isoform proportions. Significant ANOVAs were followed by post-hoc tests; p < 0.05 and 0.1 were considered to reflect levels of statistical significance. RESULTS: In naïve rats, the peripheral regions of the Anterior Digastric muscle was dominated by MyHC-IIx/b isoform and there were no MyHC-I isoforms; the central regions dominated by MyHC-IIx/b and MyHC-IIa isoforms. Compared with naive rats, tooth extraction produced, 8 (but not 4) weeks later, a decreased proportion of fast-contracting fatigue-resistant MyHC-IIa isoform (p = 0.08), and increased proportion of fast and intermediate fatigue-resistance MyHC-IIa/x/b isoform (p = 0.03). Dental implant placement following tooth extraction attenuated the extraction effects but produced a decreased proportion of fast-contracting fatiguable MyHC-llx/b isoform (p = 0.03) in the peripheral region, and increased inter-animal variability in myofibre-CSAs. CONCLUSIONS: Given the crucial role that the Anterior Digastric muscle plays in many vital oral functions (e.g., chewing, swallowing), these changes may contribute to the changes in oral sensorimotor functions that occur in humans following such treatments.

From fish to modern humans--comparative anatomy, homologies and evolution of the head and neck musculature.

In a recent paper Diogo (2008) reported the results of the first part of an investigation of the comparative anatomy, homologies and evolution of the head and neck muscles of osteichthyans (bony fish + tetrapods). That report mainly focused on actinopterygian fish, but also compared these fish with certain non-mammalian sarcopterygians. The present paper focuses mainly on sarcopterygians, and particularly on how the head and neck muscles have evolved during the transitions from sarcopterygian fish and non-mammalian tetrapods to monotreme and therian mammals, including modern humans. The data obtained from our dissections of the head and neck muscles of representative members of sarcopterygian fish, amphibians, reptiles, monotremes and therian mammals, such as rodents, tree-shrews, colugos and primates, including modern humans, are compared with the information available in the literature. Our observations and comparisons indicate that the number of mandibular and true branchial muscles (sensu this work) present in modern humans is smaller than that found in mammals such as tree-shrews, rats and monotremes, as well as in reptiles such as lizards. Regarding the pharyngeal musculature, there is an increase in the number of muscles at the time of the evolutionary transition leading to therian mammals, but there was no significant increase during the transition leading to the emergence of higher primates and modern humans. The number of hypobranchial muscles is relatively constant within the therian mammals we examined, although in this case modern humans have more muscles than other mammals. The number of laryngeal and facial muscles in modern humans is greater than that found in most other therian taxa. Interestingly, modern humans possess peculiar laryngeal and facial muscles that are not present in the majority of the other mammalian taxa; this seems to corroborate the crucial role played by vocal communication and by facial expressions in primate and especially in human evolution. It is hoped that by compiling, in one paper, data about the head and neck muscles of a wide range of sarcopterygians, the present work could be useful to comparative anatomists, evolutionary biologists and functional morphologists and to researchers working in other fields such as developmental biology, genetics and/or evolutionary developmental biology.

Practical application of anatomy for the dental implant surgeon.

A proficient knowledge of oral anatomy is needed to provide effective implant dentistry. This article addresses basic anatomic structures relevant to the dental implantologist. Pertinent muscles, blood supply, foramen, and nerve innervations that may be encountered during implant procedures are reviewed. Caution must be exercised when performing surgery in certain regions of the mouth. Furthermore, numerous suggestions are provided regarding the practical application of anatomy to facilitate successful implant therapy.