Age-related decrease of cholinergic parasympathetic reflex vasodilation in the rat masseter muscle.

Skeletal muscle hemodynamics, including that in jaw muscles, is an important in their functions and is modulated by aging. Marked blood flow increases mediated by parasympathetic vasodilation may be important for blood flow in the masseter muscle (MBF); however, the relationship between parasympathetic vasodilation and aging is unclear. We examined the effect of aging on parasympathetic vasodilation evoked by trigeminal afferent inputs and their mechanisms by investigating the MBF during stimulation of the lingual nerve (LN) in young and old urethane-anesthetized and vago-sympathectomized rats. Electrical stimulation of the central cut end of the LN elicited intensity- and frequency-dependent increases in MBF in young rats, while these increases were significantly reduced in old rats. Increases in the MBF evoked by LN stimulation in the young rats were greatly reduced by hexamethonium and atropine administration. Increases in MBF in young rats were produced by exogenous acetylcholine in a dose-dependent manner, whereas acetylcholine did not influence the MBF in old rats. Significant levels of muscarinic acetylcholine receptor type 1 (MR1) and type 3 (MR3) mRNA were observed in the masseter muscle in young rats, but not in old rats. Our results indicate that cholinergic parasympathetic reflex vasodilation evoked by trigeminal afferent inputs to the masseter muscle is reduced by aging and that this reduction may be mediated by suppression of the expression of MR1 and MR3 in the masseter muscle with age.

Transverse facial artery: Its role in blindness after cosmetic filler and botulinum toxin injections.

Masseter injections for cosmetic or pathological reasons are increasingly common, as are filler injections using dual or multiplane techniques in the lateral facial regions or for jawline contouring. The occurrence of blindness following these procedures often remains unexplained. This study aimed to determine the anatomical explanation for this debilitating complication by investigating the transverse facial artery and its relation to the masseter. For this purpose, we dissected 35 cheek specimens with latex injections and 10 specimens without latex. The external carotid artery was dissected up to its bifurcation into the maxillary and superficial temporal arteries. Results showed that the transverse facial artery arose from the superficial temporal or external carotid artery that runs between the zygomatic arch and the parotid duct. Three types of transverse facial arteries were observed: type I: a short artery that did not extend beyond the masseter muscle; type II: a transverse artery that ran to the nasolabial fold and anastomosed to the facial artery; and type III: a sizable transverse artery that substituted the hypoplastic facial artery, continued as the angular artery, and then anastomosed to the dorsal nasal artery. Knowledge of these three types of transverse facial arteries is a prerequisite to study the vascular territory. Type III provides an explanation for the occurrence of blindness after lateral face injections. We consequently define a line that runs from the tragus to the outer quarter of the upper lip as the risk area, while the safe zone is located on either side of this line.

Image Guided Sclerotherapy of Masseteric Venous Malformations.

OBJECTIVE: To describe results of image guided sclerotherapy of venous malformations (VM) localized in the masseter muscle. METHODS: Retrospective review of prospectively maintained data was done to include consecutive cases treated over 5-year period, with minimum 6 months follow-up. Sclerotherapy was done using ultrasound (US) guided needle puncture(s) of the lesions percutaneously, and 3% polidocanol foam injected under image guidance. RESULTS: Seventeen cases (10 male, 7 female) with mean age 15.6 years (range 6-28 years) were identified. Clinical presentation was with facial asymmetry, becoming pronounced on jaw clenching, and three cases had mild local pain. On US, the lesions appeared as partially compressible masses with anechoic spaces, showing color filling on releasing probe pressure. Fourteen had phleboliths. Eight patients had undergone magnetic resonance imaging, lesions appearing as oval, homogenous, lobulated, T2 hyperintense masses, with heterogeneous contrast enhancement. Number of sclerotherapy sessions were-single in four cases, two in eight cases and three in five cases, for total of 35 sessions (average 2.05 session per patient). The mean dose of drug injected per session was 1.85 mL and total mean dose per patient was 2.79 mL. Post-procedure vomiting occurred in one patient while all had local swelling and mild pain, lasting between 3 to 7 days. No facial nerve palsy or sloughing/ulceration/skin necrosis was noted. On US follow-up (6-26 months, mean 15.9 months), 12 patients had small echogenic masses without any vascularity, and five had small anechoic areas <25%. All patients had complete resolution of swelling and pain. CONCLUSIONS: For VMs localized to the masseter muscle, image guided sclerotherapy is highly effective and safe, and recommended as first line treatment.

Case report of unique anastomosis between facial and inferior alveolar arteries.

PURPOSE: Understanding anatomical variations of the facial artery and its branches is important for dental and medical practitioners. METHODS: Routine cadaveric dissection of the head and neck was performed to demonstrate the origin and branches of the facial artery. RESULTS: Facial artery emerged from a common linguofacial trunk off the external carotid artery. On the face, the facial artery first gave off a pre-masseteric branch. Immediately after, an aberrant artery emerged from the facial artery that coursed along the ramus of the mandible, which upon further dissection and examination was found to anastomose with inferior alveolar artery within the ramus of the mandible. CONCLUSIONS: We report a unique anastomosis between facial and inferior alveolar arteries, vessels that have not been previously shown to communicate. This case report may provide useful information for oral and maxillofacial surgeons as well as dentists performing inferior alveolar nerve blocks.

Segmental Gracilis Muscle Transplantation for Midfacial Animation in Möbius Syndrome: A 29-Year Experience.

BACKGROUND: Möbius syndrome is a complex congenital disorder of unclear cause involving multiple cranial nerves and typically presenting with bilateral facial and abducens nerves palsies. At The Hospital for Sick Children, Toronto, Ontario, Canada, microneurovascular transfer of free-muscle transplant is the procedure of choice for midfacial animation. The primary aim of this study was to investigate surgical outcomes of the procedure in terms of complications, secondary revisions, and smile excursion gains. METHODS: A retrospective 29-year review was performed using patient records from a single tertiary care center. The authors included children with Möbius syndrome who had undergone facial animation surgery with a free segmental gracilis muscle transfer and microneurovascular repair between January 1, 1985, and August 31, 2014. Smile excursion measures were obtained using the Facial Assessment by Computer Evaluation-Gram on a subset of the included patients. RESULTS: A total of 107 patients undergoing 197 reconstructive procedures met inclusion criteria. Most reconstructions relied on the motor nerve branch to the masseter for innervation [n = 174 (88 percent)]. Thirteen complications were reported, of which six required surgical interventions. Three revision procedures were performed: scar revision, muscle repositioning, and removal of infected permanent suture material. The use of the motor nerve branch to the masseter resulted in good commissure excursion gains (average, 4.61 mm for bilateral cases and 9.34 mm for unilateral reconstructions). CONCLUSION: Midfacial animation with segmental gracilis muscle transfer for patients with Möbius syndrome provides gains in the amplitude and symmetry of oral commissure excursion and carries a reasonably low complication rate. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.

Minimally Invasive Approach for Resection of Masseteric Vascular Malformations.

OBJECTIVE: Vascular malformations (VMs) in the head and neck region often cause esthetic as well as functional problems for patients. Intramuscular VMs (IVM), such as those in the masseter, can cause severe facial asymmetry and typically are excised transcutaneously to facilitate wide exposure and safe dissection from the facial nerve. This requires extensive dissection, prolonged healing, and can lead to suboptimal facial scarring. METHODS: We describe the technique of resecting large IVMs of the masseter muscle in 3 patients using an entirely intraoral approach with continuous nerve monitoring and without visible facial scarring or secondary deformity. Preoperative injection of sclerotherapy was performed to reduce intra-operative bleeding and optimize resection. RESULTS: Successful excision was performed without complication in 3 patients to date. Total average operating room time was 120 minutes (range 95-145 minutes). Estimated blood loss was 213 mL (range 180-240 mL). The patients were discharged home either post-operative day (POD) 1 or 2, with 1 returning to work POD 4. Facial nerve function was normal postoperatively and no hematomas developed. Subjective masticatory function was equivalent to preoperative levels in all patients. CONCLUSIONS: Intraoral excision of VMs of the masseter muscle can be safely performed without added risk or complication. Continuous facial nerve monitoring allows minimally invasive approaches to be considered with less risk of iatrogenic facial nerve injury. We purport that this is a safe and effective method with substantially better esthetic outcomes compared with traditional transcutaneous approaches.

Blood oxygenation of masseter muscle during sustained elevated muscle activity in healthy participants.

Myofascial pain associated with temporomandibular disorders has often been linked to pathological muscle hyperactivity. As a result, localised disturbances of intramuscular blood flow could lead to a lower level of oxygen distribution, hypoxia and microcirculatory changes. To assess haemodynamic changes in the masseter muscle during sustained elevated muscle activity (SEMA). Sixteen healthy participants performed thirty 1-min bouts of SEMA with intervals of 1-min 'rest' periods between the bouts on a bite force transducer device. The participants completed three sessions with different percentage of their maximal voluntary occlusal bite force (MVOBF): 0% (no task), 10% or 40% MVOBF tasks. The order of the sessions was randomised with 1- to 2-week intervals. Haemodynamic characteristics of the masseter muscle were estimated with use of a laser blood oxygenation monitor. Tissue blood oxygen saturation (StO2 ) during SEMA was lower than during rest (P < 0·001). The relative changes in total haemoglobin (Total-Hb) and StO2 were influenced by condition (SEMA and rest) and with interactions between condition and session (0%, 10% and 40% MVOBF tasks). These results suggest that SEMA may lead to hypoxia in the masseter muscle and that the haemodynamic characteristics and muscle symptoms depend on the magnitude of muscle contractions. Overall, the present findings may help to provide better insights into relationships between jaw muscle activity, haemodynamic changes and symptom developments with implications for clinical conditions such as bruxism characterised by different levels of tooth-grinding and tooth-clenching muscle activity.

Mastication induces long-term increases in blood perfusion of the trigeminal principal nucleus.

Understanding mechanisms for vessel tone regulation within the trigeminal nuclei is of great interest because some headache syndromes are due to dysregulation of such mechanisms. Previous experiments on animal models suggest that mastication may alter neuron metabolism and blood supply in these nuclei. To investigate this hypothesis in humans, arterial spin-labeling magnetic resonance imaging (MRI) was used to measure blood perfusion within the principal trigeminal nucleus (Vp) and in the dorsolateral-midbrain (DM, including the mesencephalic trigeminal nucleus) in healthy volunteers, before and immediately after a mastication exercise consisting of chewing a gum on one side of the mouth for 1 h at 1 bite/s. The side preference for masticating was evaluated with a chewing test and the volume of the masseter muscle was measured on T1-weighted MRI scans. The results demonstrated that the mastication exercise caused a perfusion increase within the Vp, but not in the DM. This change was correlated to the preference score for the side where the exercise took place. Moreover, the basal Vp perfusion was correlated to the masseter volume. These results indicate that the local vascular tone of the trigeminal nuclei can be constitutively altered by the chewing practice and by strong or sustained chewing.

Tissue Blood Flow During Remifentanil Infusion With Carbon Dioxide Loading.

The aim of this study was to investigate the effect of changes in end-tidal carbon dioxide tension (ETCO2) during remifentanil (Remi) infusion on oral tissue blood flow in rabbits. Eight male tracheotomized Japan White rabbits were anesthetized with sevoflurane under mechanical ventilation. The infusion rate of Remi was 0.4 µg/kg/min. Carbon dioxide was added to the inspired gas to change the inspired CO2 tension to prevent changes in the ventilating condition. Observed variables were systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), heart rate (HR), common carotid artery blood flow (CCBF), tongue mucosal blood flow (TBF), mandibular bone marrow tissue blood flow (BBF), masseter muscle tissue blood flow (MBF), upper alveolar tissue blood flow (UBF), and lower alveolar tissue blood flow (LBF). The CCBF, TBF, BBF, UBF, and LBF values were increased, while MBF was decreased, under hypercapnia, and vice versa. The BBF, UBF, and LBF values were increased, while the MBF value was decreased, under hypercapnia during Remi infusion, and vice versa. The BBF, MBF, UBF, and LBF values, but not the CCBF and TBF values, changed along with ETCO2 changes during Remi infusion.

Nonsurgical management of vascular malformation of masseter.

Intramuscular vascular anomalies are rare congenital hamartomatous lesions. Less than 1% of these occur in skeletal muscle out of which 15% arise in head and neck musculature. In the head and neck region, masseter muscle is the most common site. It accounts for about 5% of intramuscular vascular malformations. They are present from birth but are clinically apparent during infancy and childhood and occasionally during adulthood. Due to its location it is often mistaken for a parotid swelling. The usual treatment of choice is surgical excision with a margin. This is associated with loss of motor function, hemorrhage, nerve damage. Intralesional sclerotherapy, embolization are nonsurgical alternatives for treatment of slow flow venous malformations. Sclerotherapy can be used solely in multiple sittings or as an adjunct to surgery. This article presents a case report of a 28-year-old male with recurrent intramuscular vascular malformation in the masseter muscle, which was successfully treated by ethanol sclerotherapy.

Effects of experimental tooth clenching on pain and intramuscular release of 5-HT and glutamate in patients with myofascial TMD.

OBJECTIVES: It has been suggested that tooth clenching may be associated with local metabolic changes, and is a risk factor for myofascial temporomandibular disorders (M-TMD). This study investigated the effects of experimental tooth clenching on the levels of 5-HT, glutamate, pyruvate, and lactate, as well as on blood flow and pain intensity, in the masseter muscles of M-TMD patients. METHODS: Fifteen patients with M-TMD and 15 pain-free controls participated. Intramuscular microdialysis was performed to collect 5-HT, glutamate, pyruvate, and lactate and to assess blood flow. Two hours after the insertion of a microdialysis catheter, participants performed a 20-minute repetitive tooth clenching task (50% of maximal voluntary contraction). Pain intensity was measured throughout. RESULTS: A significant effect of group (P<0.01), but not of time, was observed on 5-HT levels and blood flow. No significant effects of time or group occurred on glutamate, pyruvate, or lactate levels. Time and group had significant main effects on pain intensity (P<0.05 and <0.001). No significant correlations were identified between: (1) 5-HT, glutamate, and pain intensity; or between (2) pyruvate, lactate, and blood flow. DISCUSSION: This experimental tooth clenching model increased jaw muscle pain levels in M-TMD patients and evoked low levels of jaw muscle pain in controls. M-TMD patients had significantly higher levels of 5-HT than controls and significantly lower blood flow. These 2 factors may facilitate the release of other algesic substances that may cause pain.

Effect of changes in end-tidal carbon dioxide tension on oral tissue blood flow during dexmedetomidine infusion in rabbits.

A decrease in arterial carbon dioxide tension induces an increase in masseter muscle blood flow and a decrease in mandibular bone marrow blood flow during general anesthesia. In addition, dexmedetomidine infusion reduces oral tissue blood flow. In this study we investigated how end-tidal carbon dioxide tension (ET-CO2 ) changes influence on oral tissue blood flow during continuous dexmedetomidine infusion in rabbits. Eleven male Japan White rabbits were anesthetized with sevoflurane. Then, ET-CO2 was set at 30 mmHg and adjusted to 40 and 60 mmHg, and heart rate, systolic blood pressure, diastolic blood pressure, mean arterial pressure, common carotid artery blood flow, mandibular bone marrow blood flow, masseter muscle blood flow, and blood flow in other oral tissues were measured. Following this, the ET-CO2 was returned to 30 mmHg and dexmedetomidine was infused over 60 min. The measurements were repeated. Most parameters increased, regardless of whether or not dexmedetomidine was present, and heart rate and masseter muscle blood flow decreased in an ET-CO2 -dependent manner. Dexmedetomidine infusion suppressed ET-CO2 -dependent masseter muscle blood flow change. Masseter muscle blood flow during ET-CO2 at 30 mmHg with dexmedetomidine was the same as that during ET-CO2 at 40 mmHg without dexmedetomidine. Our findings suggest that dexmedetomidine infusion and slight hypocapnia under general anesthesia suppress an increase in masseter muscle blood flow as well as reducing mandibular bone marrow blood flow. These results may be of significance for decreasing bleeding during oral and maxillofacial surgery.

The soft tissue landmarks to avoid injury to the facial artery during filler and neurotoxin injection at the nasolabial region.

The aim of this study was to locate the course of the facial artery and to propose "the danger line" vulnerable to vascular complications following filler injection. The entire facial soft tissues were harvested from 14 Thai soft embalmed cadavers as a facial flap specimen. Measurements of the distance, the depth, and the diameter of the facial artery were done at level of the oral commissure and the nasal ala. The distance between the facial artery and the oral commissure was 15.3 ± 3.7 mm and the depth from the skin was 11.1 ± 3.1 mm. The distance between the facial artery and the nasal ala was 6.7 ± 4.4 mm and the depth was 11.6 ± 3.7 mm. The diameters of the facial artery at level of the oral commissure and the nasal ala were 2.6 ± 0.8 and 1.9 ± 0.5 mm, respectively. Maximum risk of arterial complication from dermal filler injection lateral to the oral commissure is located approximately 15 mm at the depth of 11 mm. High risk of arterial injury at the lateral nasal ala is located at 7 mm with the depth of 12 mm.

Management of intramuscular venous malformations of the masseter muscle.

Less than 1% of vasoformative tumours throughout the body occur in skeletal muscle and 15% of them arise in head and neck musculature. The masseter muscle is the most frequent site and accounts for approximately 5% of all intramuscular vascular malformations in the head and neck region. Masseteric venous malformations have a typical clinical presentation and imaging characteristics that should allow clinicians to distinguish them from other abnormalities presenting in this area. We present seven cases of these unusual intramasseteric venous malformations and the diagnosis and management of these lesions is discussed. The diagnosis was made on clinical grounds and was confirmed on MRI. All underwent surgical excision through a facelift approach and were successfully removed from within the substance of the masseter muscle with preservation of the facial nerve. Venous malformations within the masseter are rare but are easy to diagnose and can be reliably surgically excised without complications.

Segmental masseteric flap for dynamic reanimation of facial palsy.

The masseter muscle is one of the major chewing muscles and contributes to define facial contour. It is an important landmark for aesthetic and functional surgery and has been used for facial palsy reanimation or as source of donor motor nerve. We present an anatomic study to evaluate the possibility of using a muscle subunit for dynamic eye reanimation. Sixteen head halves were dissected under magnification to study the neurovascular distribution and determine safe muscle subunits; areas of safe/dangerous dissection were investigated. Once isolated, the arc of rotation of the muscular subunit was measured on fresh body to verify the reach to the lateral canthus. The patterns of neurovascular distribution and areas of safe dissection were identified; the anterior third of the muscle represents an ideal subunit with constant nerve and artery distribution. The muscle is too short to reach the lateral canthus; a fascia graft extension is needed. The information provided identified the main neurovascular branches and confirms the feasibility of a dynamic segmental flap. The need of efficient motor units for facial reanimation demands for different surgical options. A detailed anatomic description of the neurovascular bundle is mandatory to safely raise a functional motor subunit.

Surgical treatment of masseteric venous malformations and outcomes.

Intramuscular venous malformations are often misdiagnosed as other types of tumors with similar presentations. We describe here the typical presentation of a venous malformation within the masseter muscle, including the physical findings and imaging, and present our experience with the surgical excision of these lesions. This is a review of 10 patients with venous malformations localized to the masseter muscle who presented to our institution between 2008 and 2011. The patients included 6 females and 4 males. Of these venous malformations, 80% were noted in childhood, and the remainder manifested later in adolescence. Pain, swelling, and facial asymmetry were the presenting complaints. Magnetic resonance imaging, Doppler ultrasonography, and whole-body blood scintigraphy were used to characterize the lesions. All patients were treated by total resection of the lesion while preserving the marginal mandibular branch of the facial nerve. Magnetic resonance imaging showed the lesions to be isointense with surrounding muscle on T1-weighted images and hyperintense on T2-weighted images. Gross examination of the resected specimens revealed multicolored tissue with dilated vascular channels, frequently containing phleboliths. After the operation, all patients showed improvement in both symptoms and appearance. This improvement was sustained at a mean follow-up of 21 months. Masseteric venous malformations typically present with a pattern of clinical and imaging findings that should allow surgeons to distinguish them from other diseases in the cheek area. Complete surgical excision is a treatment option for these patients and can be performed without facial nerve injury or excessive bleeding. This procedure can result in excellent outcomes for localized intramasseteric venous malformation.

Roles played by histamine in strenuous or prolonged masseter muscle activity in mice.

Bruxism and/or clenching, resulting in fatigue or dysfunction of masseter muscles (MM), may cause temporomandibular disorders. Functional support of the microcirculation is critical for prolonged muscle activity. Histamine is a regulator of the microcirculation and is supplied by release from its stores and/or by de novo production via the induction of histidine decarboxylase (HDC). Interleukin (IL)-1, a cytokine involved in temporomandibular disorders, is an inducer of HDC. In the present study, we examined the roles of histamine, HDC and IL-1 in MM activity. Experiments were conducted using our R+G+ model. A mouse restrained (R+) inside a narrow cylinder (front end blocked with a thin plastic strip) gnaws away (G+) the strip to escape, with the weight reduction in the strip serving as an index of MM activity. Fexofenadine (a peripherally acting histamine H1 receptor antagonist) reduced MM activity in normal mice. Both H1 receptor-deficient and HDC-deficient mice exhibited low MM activity. Prolonged R+G+ induced HDC activity in MM. Mast cell-deficient mice exhibited strikingly low HDC induction in MM (and also in the quadriceps femoris muscle) in response to muscle activity or IL-1ß. Mast cells were present around blood vessels and nerves in the epimysium and perimysium of MM. These results, together with others reported previously, suggest that: (i) peripheral histamine supports strenuous MM activity; (ii) strenuous MM activity stimulates mast cells to release histamine and to induce HDC (which replenishes the histamine pool in mast cells, possibly mediated by IL-1); and (iii) peripheral histamine H1 receptor antagonists may be effective in treating temporomandibular disorders or preventing prolonged clenching and/or bruxism.

Inactivation of mechano-sensitive dilatation upon repetitive mechanical stimulation of the musculo-vascular network in the rabbit.

Mechano-sensitivity of the vascular network is known to be implicated in the rapid dilatation at the onset of exercise, however, it is not known how this mechanism responds to repetitive mechanical stimulation. This study tests the hypothesis that the mechanically-induced hyperaemia undergoes some attenuation upon repetitive stimulation. Muscle blood flow was recorded from 9 masseteric arteries (5 right, 4 left) in 6 anesthetized rabbits. Two mechanical stimuli, masseter muscle compression (MC) and occlusion of the masseteric artery (AO), were provided in different combinations: A) repeated stimulation (0.5 Hz, for 40 s); B) single stimuli delivered at decreasing inter-stimulus interval (ISI) from 4 min to 2 s, C) single AO delivered before and immediately after a series of 20 MCs at 0.5 Hz, and vice-versa. Repetitive AO stimulation at 0.5 Hz produced a transient hyperaemia (378 ±189%) peaking at 4.5 ±1.4 s and then decaying before the end of stimulation. The hyperaemic response to individual AOs progressively decreased by 74 ±39% with decreasing ISI from 4 min to 2 s (p<0.01). Non significant differences were observed between AO and MC stimulation. Decreased response to AO was also provoked by previous repetitive MC stimulation, and vice-versa. The results provide evidence that the mechano-sensitivity of the vascular network is attenuated by previous mechanical stimulation. It is suggested that the mechano-sensitive dilatory mechanisms undergoes some inactivation whose recovery time is in the order of a few minutes.