Electromyographic analysis of the buccinator muscle

New method of recording the functional activity pattern of the buccinator from the mucosal surface

OBJECTIVES

The buccinator (BUC) is an important muscle for oral function. Since it lies deep in the facial skin, recording its activity is difficult; thus, studies on its function are limited. We developed a method to access the deep facial muscles from the mucosal side. The aim of this study was to test the reliability of the new recording method for the BUC and to investigate the BUC behavior in typical facial functions.

METHODS

To evaluate the new method, BUC activities were recorded simultaneously with a gel-type electrode on the skin and the newly developed surface electrode on the buccal mucosa. Electromyographic (EMG) activities in function, such as chewing and swallowing, along with the activities of the lower orbicularis oris (OO), zygomaticus major, masseter, and digastric muscles, were compared using the two recording methods. EMG activities among various tasks were compared using normalized values based on those obtained during maximum lip closure (MaxLC).

RESULTS

The new surface electrode was made of gold plates on a thin plastic fixed to a stainless-steel wire frame and weighed less than 1 g. The BUC activity recorded from the mucosa was the highest during a corner-pulling task and was low during clenching. The BUC was active during MaxLC, similar to the OO, and the BUC activity pattern among tasks recorded from the mucosa was identical to that reported by previous studies using intramuscular electrodes. The new electrode evaluated the BUC activities quantitatively, and the recordings by the new electrode were free from contamination.

CONCLUSIONS

The findings of this study confirmed the reliability of the new BUC recording method. It could be easily placed correctly within seconds, without the need for cleansing or sterilizing the skin. The BUC and OO were active during a MaxLC task, indicating that the BUC assists lip closure by pulling the corners of the mouth. The basic facial functions evaluated, including chewing, were similar to those studied by intramuscular electrodes.

Ptosis With Aberrant Facial Nerve Regeneration Following Bell Palsy

ABSTRACT

Bell palsy is the most common lesion affecting the facial nerve. Aberrant facial nerve regeneration following facial nerve palsy may cause facial nerve synkinesis and ptosis. The authors present a 65-year-old male who suffered from left peripheral facial nerve palsy in 2017. During the recovery period, he had moderate ptosis in primary gaze, and he also noted left upper eyelid closure when he tried to blow something or puff his cheeks. Neurologic examination was normal except for the synkinetic movements as described above. Surgery was planned with an attempt to resect a part of the orbicularis oculi muscle (OOM) to decrease the synkinetic eyelid closure. In addition, the levator muscle was advanced for treatment of the ptosis. Before surgery, an electromyography study by a neurologist showed normal activity of the OOM but failed to demonstrate the relationship between this muscle and other muscles due to technique failure. However, after surgery electromyography studies of the facial and orbicularis oris muscle suggested that cheek puffing produced contraction in the OOM. During follow-up time, the patient was satisfied with the surgical results. To the best of our knowledge, this is the first report to describe ptosis with aberrant facial synkinesis during cheek puffing was treated with surgery.

Anatomical connections between the buccinator and the tendons of the temporalis

The aim of this study was to clarify the anatomical relationship between the buccinator and the temporalis in order to improve understanding of the precise and coordinated movements of the mouth and the mandible. The buccinator and the temporalis were investigated in 72 hemifaces from Korean cadavers. Removing the buccal fat pad from the buccinator revealed that the fascia encircled the space between the superficial and deep tendons of the temporalis laterally, and the external surface of the buccinator medially in all specimens (100%). The fascia was located between the buccinator and the tendons of the temporalis, thereby connecting these two muscles. The fascial space was filled with connective tissue, and the buccal nerve and artery passed through this space. The inferior fibers of the buccinator arose from the anterior portion of the deep tendon of the temporalis in all specimens (100%). The anterior portion of the deep tendon of the temporalis extended forward obliquely between the ramus and body of the mandible. Thus, both the anterior portion of the deep tendon of the temporalis and its attaching inferior muscle fibers of the buccinator coursed obliquely. The above observations indicate that the connecting fascia between the buccinator and tendons of the temporalis and the inferior fibers of the buccinator that were attached to the deep tendon of the temporalis could assist in coordinatation of the movements of the mandibular region and the mouth angle in the timing and strength of contraction of the muscles during mastication, facial expression, and speech.

Electromyographic Analysis of the Circumoral Muscles of Facial Expression

Electromyography of the circumoral muscles was undertaken with the use of fine-wire electrodes that were inserted into of hair follicles of ten patients with full dentitions and normal occlusion. The inferior circumoral muscles, which initiated many oral activities, had a higher degree of activity than did the superior circumoral muscles. Tonic discharge during mandibular rest was infrequent.

Electromyographic Analysis of the Masseter and Buccinator Muscles with the Pro-Fono Facial Exerciser Use in Bruxers

The aim of this study was to evaluate the efficiency of the Pró-Fono Facial Exerciser (Pró-Fono Productos Especializados para Fonoaudiologia Ltda., Barueri/SP, Brazil) to decrease bruxism, as well as the correlation between the masseter and the buccinator muscles using electromyography (EMG). In this study, 39 individuals ranging from 23 to 48 years of age were selected from a dental school and then underwent surface EMG at three different periods of time: 0, 10, and 70 days. They were divided into a normal control group, a bruxer control group (without device), and an experimental bruxer group who used the device. The bruxer group showed a greater masseter EMG amplitude when compared to the normal group, while the experimental group had deceased activity with a reduction in symptoms. The buccinator EMG spectral analysis of the experimental bruxist group showed asynchronous contractions of the masseter muscle (during jaw opening) after using the Pró-Fono Facial Exerciser. The normal group also showed asynchronous contractions. Upon correlation of the data between these muscles, the inference is that there is a reduction in bruxism when activating the buccinator muscle.

An electromyographic analysis of orbicularis oris and buccinator muscle activity in patients with complete dentures fabricated using two neutral zone techniques--a pilot study

PURPOSE

Several studies have evaluated electromyographic (EMG) activity of perioral muscles in patients using unsatisfactory old complete dentures and after the insertion of new clinically acceptable dentures; however, studies evaluating EMG activity of orbicularis oris (OO) and buccinator (BUC) muscles in patients wearing complete dentures fabricated using swallowing (SNZ) and phonetic neutral zone (PNZ) techniques are lacking in the literature. The purpose of this study was to evaluate differences in muscle activity of the superior orbicularis oris (SOO), inferior orbicularis oris (IOO) and BUC muscle during the use of unsatisfactory old complete dentures, in comparison with the satisfactory dentures fabricated using the two neutral zone techniques.

MATERIALS AND METHODS

Ten completely edentulous participants dissatisfied with their existing mandibular complete dentures participated in the study. Each patient received two sets of new dentures fabricated using the SNZ and PNZ techniques. Surface EMG activity of the OO and BUC muscles was recorded using a 4-channel Medelec premier plus electromyography machine while the patients still used their old dentures (group A) and with the SNZ (group B) and PNZ (group C) dentures. On the basis of participation in the study, five participants first received the SNZ dentures and five the PNZ type. After having worn the prosthesis for a minimum of 2 months, EMG recordings were repeated for the first set of dentures. The prostheses were then changed and the procedures repeated. The activity of OO and BUC muscles was recorded at rest, while pursing and laughing, and during pronunciation of various syllables. Results are expressed as mean ± SD and as absolute numbers and percentage. ANOVA with appropriate correction (Bonferroni or Tamhane) and Student's t-test were used for statistical analysis. A p-value < 0.05 was taken to indicate a significant difference.

RESULTS

There was no statistically significant difference in the mean EMG activity of SOO, IOO, and BUC muscles at rest, or during pursing or laughing among the three groups. No significant difference was observed in the mean EMG activity of SOO and BUC muscle among the groups for all the syllables pronounced. For IOO, a statistically significant difference was observed among the groups for the words "baby" and "cheese." Within-group comparisons of the mean EMG activities of SOO and IOO during pronunciation and pursing showed no significant difference; however, at rest a statistically significant difference was observed in group B.

CONCLUSION

OO and BUC muscle activities did not significantly differ, irrespective of the technique used for fabrication of complete dentures.

Atividade exacerbada do músculo bucinador em sujeitos com má oclusão de Angle Classe III

INTRODUÇÃO: Estudos descrevem a função do músculo bucinador como controlador do bolo alimentar durante a mastigação. Pouco se sabe, entretanto, sobre seu comportamento em sujeitos com distintos padrões dentário e esquelético, o que contribuiria para o desenvolvimento dos tratamentos ortodônticos e ortognático. OBJETIVO: Este estudo tem como objetivo investigar a atividade eletromiográfica do músculo bucinador, em sujeitos Classe III de Angle, durante a mastigação. MATERIAL E MÉTODO: A amostra foi constituída por 32 sujeitos saudáveis, sem Disfunção Temporomandibular durante a mastigação, sendo 16 sujeitos Classe I e 16 sujeitos Classe III. Para garantir a fidedignidade da captação do sinal, foram utilizados eletrodos diferenciais, além de testes de função, correlação e normalização dos dados. Na medida em que os dados revelaram uma distribuição não normal (teste de Shapiro-Wilk), realizou-se teste da mediana, sendo estabelecido o nível de significância em 5%. RESULTADO: Na comparação dos dados normalizados da variável Root Means Square (RMS) (µV), do período ativo, não foram encontradas diferenças significativas (Classe I: 0,469 ± 0,355; Classe III: 0,531 ± 0,355 - p: 0,4812). Entretanto, em relação às variáveis RMS (µV) do período inativo (Classe I: 0,359 ± 0,355; Classe III: 0,641 ± 0,355 - p: 0,0016), duração do período ativo (ON) (Classe I: 0,313 ± 0,180; Classe III: 0,687 ± 0,180 - p: 0,0368) e razão entre o RMS do período inativo e RMS do período ativo (RIA) (Classe I: 0,391 ± 0,355; Classe III: 0,609 ± 0.355 - p: 0,0137), foram observadas diferenças significativas. CONCLUSÃO: A partir dos dados obtidos, pôde-se constatar uma atividade exacerbada do músculo bucinador nos sujeitos Classe III de Angle.

The buccinator during mastication: A functional and anatomical evaluation in minipigs

OBJECTIVE

The buccinator muscle forms the lateral wall of the oral cavity. It is presumed to aid mastication by maintaining bolus position. Such a function would involve thickening the cheek, possibly compressing the alveolar bone and contributing to malocclusions. However, neither buccinator deformation nor its effect on pressure has been demonstrated. Our objective was to evaluate buccinator EMG during feeding, its changes in length and thickness, and the pressure exerted on its alveolar attachment, using miniature pigs as an animal model.

METHODS

EMG of the buccinator and other oral muscles was recorded with fine-wire electrodes. Anteroposterior length and mediolateral thickness of the buccinator were evaluated with implanted sonomicrometry crystals, and pressure was measured by flat transducers placed beneath the mandibular origin of the buccinator. Recordings were made during feeding and muscle stimulation. Tissues were collected postmortem for histology.

RESULTS

During mastication, buccinator EMG showed regular peaks that preceded those of the jaw closers. Pattern differences clearly distinguished working and balancing sides. The buccinator shortened and thickened when it contracted. Positive pressures were observed at the mandibular attachment of the buccinator, increasing when the muscle was active. Histological evaluation showed a complex interweaving of fibres closely associated with salivary tissue.

CONCLUSIONS

Buccinator contraction does thicken the cheek, and during mastication this activity takes place just as the closing stroke begins. In addition to controlling the bolus, there may be an effect on salivation. Despite the fact that the muscle pulls on its attachment, the local mechanical environment at the alveolar bone is one of positive pressure.

Simulation of dynamic orofacial movements using a constitutive law varying with muscle activation

This paper presents a biomechanical model of the face to simulate orofacial movements in speech and non-verbal communication. A 3D finite element model, based on medical images of a subject, is presented. A hyperelastic Mooney-Rivlin constitutive law accounts for the non-linear behaviour of facial tissue. Muscle fibres are represented by piece-wise uniaxial tensile element that generate force. The stress stiffening effect, an increase in the stiffness of the muscles when activated, is modelled by varying the constitutive law of the tissue with the level of activation of the muscle. A large number of facial movements occurring during speech and facial mimics are simulated. Results show that our modelling approach provides a realistic account of facial mimics. The differences between dynamic vs. quasi-static simulations are also discussed, proving that dynamic trajectories better fit experimental data.

An anatomical study of the buccinator muscle fibres that extend to the terminal portion of the parotid duct, and their functional roles in salivary secretion

Until now there has been no definitive anatomical study describing the area where the parotid duct enters the buccinator muscle. In this study, we performed anatomical and histological examinations to investigate the relationship between the parotid duct and the buccinator muscle. Thirty specimens (including the buccinator and the terminal portion of the parotid duct) were obtained from embalmed Korean cadavers. Dissection was performed on 22 of these specimens, and the remaining eight specimens were prepared for histological examination and stained with haematoxylin-eosin or Gomori trichrome. In all specimens, small, distinct muscle fibres originating from the buccinator muscle extended to and inserted into the terminal portion of the parotid duct. The topography of these fibres varied, and we classified them into three categories according to where they originated. Type I buccinator muscle fibres, which inserted into the terminal portion of the parotid duct, originated simultaneously from the anterior and posterior aspects of the duct (ten cases, 45.5%). Type II fibres originated from the anterior aspect of the duct and inserted into the anterior side of the duct (seven cases, 31.8%). Type III fibres originated from the posterior aspect of the parotid duct and ran anteriorly toward the duct (five cases, 22.7%). These results were confirmed in the histological examination of all eight specimens. Based on these findings, we have proposed a tentative description of the physiological role of the buccinator muscle fibres in salivary secretion and in the formation of the sialoliths.

Coordination of cranial motoneurons during mastication

Mastication is the first stage of digestion and involves several motor processes such as food intake, intra-oral food transport, bolus formation and chewing in its broad sense. These complicated motor functions can be accomplished by the well-coordinated activities in various cranial motoneurons innervating the jaw, hyoid, tongue and facial muscles. The brainstem masticatory central pattern generator (CPG) plays a crucial role in generating basic activity patterns of these cranial motoneuron groups. However, descending inputs from higher brain (e.g., cerebral cortex) and mastication-generated peripheral sensory inputs also play important roles in modulating the activity pattern of each motoneuron so that the final motor outputs fit the environmental demand. In this review, we focus on the coordination of the trigeminal, facial and hypoglossal motoneurons during mastication. We first summarize findings showing the activity patterns of muscles innervated by these motoneurons during natural mastication, and then discuss the possible neural mechanisms underlying their coordinated activities during mastication.

Activity of peri-oral facial muscles and its coordination with jaw muscles during ingestive behavior in awake rabbits

To study peri-oral facial muscle activity patterns and coordination with jaw muscles during ingestive behavior, electromyographic (EMG) activities in the peri-oral facial (buccinator: BUC, orbicularis oris: ORB) and jaw (masseter, digastric) muscles along with jaw movement trajectories were recorded in awake rabbits. A standardized amount of apple in a cylindrical shape was used as the test food. The period from food intake to just before swallowing (the masticatory sequence) was divided into three masticatory periods (preparatory period, rhythmic chewing period and preswallow period) based on the activity pattern of jaw muscles and jaw movement trajectories, and jaw movements and EMG activities in both the jaw and facial muscles during each masticatory period were assessed. Both the jaw and facial muscles were active throughout the masticatory sequence, and the activity patterns of facial muscles and the pattern of coordination between the facial and jaw muscles varied for each masticatory period. No consistent pattern was noted for the BUC activity during the preparatory period, whereas the ORB showed tonic activity throughout this period. During the rhythmic chewing and preswallow periods, both the ORB and BUC showed jaw-movement-related rhythmic bursts. However, significant differences were noted in the burst properties in both facial muscles and their temporal correlations with the jaw muscle activities between these two periods. Results suggest that the neural mechanisms regulating facial muscle activities may differ between the masticatory periods, and such mechanisms may contribute to the well-coordinated orofacial movements required for smooth masticatory sequence.

The anatomy of buccinator—insights from functional casts of the oral vestibule

OBJECTIVE

When a dental elastomer is placed in the oral vestibule and the facial muscles contracted while it sets, the functional cast produced frequently shows a deep anteroposterior groove, and marked posterosuperior and smaller anteroinferior bulges. This study investigates whether these features have a structural or a physiological basis.

DESIGN

Casts of the right side of the oral vestibule of dissecting room cadavers and living volunteers were made using a polyvinylsiloxane dental elastomer. The volunteers each produced two functional casts in each of the following situations: while the teeth were clenched but the facial muscles inactive, while grimacing, and while swallowing.

RESULTS

Grooves and bulges were largely absent in casts from the dissecting room cadavers and of living volunteers with the teeth clenched but the facial muscles inactive. They were present when the elastomer set while the subjects grimaced but most marked when they had been swallowing their saliva. The depth of the grooves varied between individuals and generally was greatest alongside the second molar teeth. We found that the posterosuperior bulge did not coincide with the position of the parotid duct.

CONCLUSIONS

The anteroposterior groove represents a well developed horizontal part of buccinator. The regions of the casts bulging superior and inferior to the groove probably represent weaker regions of buccinator towards its maxillary and mandibular attachments. The bulge superior to the groove was not explained by a weakness in buccinator where it is pierced by the parotid duct.

Investigation of the factors related to the formation of the buccal mucosa ridging

The aim of this study was to clarify the factors related to the formation of the buccal mucosa ridging, which has been mentioned to be a clinical sign of clenching. Twenty-one individuals were investigated and divided into three groups: (i) those without buccal mucosa ridging, (ii) the buccal mucosa ridging located in all the posterior teeth region, and (iii) the buccal mucosa ridging corresponding only to the molar teeth region. A pressure sensor was used and placed at two points: first upper premolar and second upper molar. The recording tasks were: (i) silent reading at rest, (ii) light voluntary clenching, (iii) maximum voluntary clenching, (iv) holding the cheeks tightly against the teeth while light voluntary clenching, (v) holding the cheeks tightly against the teeth without tooth contact, (vi) pulling angle of mouth laterally while light voluntary clenching, (vii) pulling angle of mouth laterally without tooth contact and (viii) swallowing. No significant differences were found between groups in all the recording tasks except for the swallowing, at which significant difference (P < 0.05) was found between the groups of individuals having buccal mucosa ridging and without it. Based on these results it became clear that the buccal mucosa pressure exerted on the buccal aspect of teeth during swallowing plays an important role in the formation of buccal mucosa ridging.

Non-invasive monitoring of functionally distinct muscle activations during swallowing

OBJECTIVES

Dysphagia is an important consequence of many diseases. As some of the muscles of deglutition tend to be deep to the surface, needle electrodes are typically used, but this limits the number of muscles that can be simultaneously recorded. Since control of swallowing involves central pattern generators (CPGs) which distribute commands to several muscles, monitoring several muscles simultaneously is desirable. Here we describe a novel method, based on computing the independent components (ICs) of the simultaneous sEMG recordings (Muscle Nerve Suppl 9 (2000) 9) to detect the underlying functional muscle activations during swallowing using only surface EMG (sEMG) electrodes.

METHODS

Seven normal subjects repeatedly swallowed liquids of varying consistency while sEMG was recorded from 15 electrodes from the face and throat. Active areas of EMG were excised from the recordings and the ICs of the sEMG were calculated.

RESULTS

The ICs demonstrated less swallow-to-swallow variability than the raw sEMG. The ICs, each consisting of a unique temporal waveform and a spatial distribution, provided a means to segregate the complex sequence of muscle activation into rigorously defined separate functional units. The temporal profiles of the ICs and their spatial distribution were consistent with prior needle EMG studies of the cricopharyngeal, superior pharyngeal constrictor, submental and possibly arytenoid muscles. Other components appeared to correspond to EKG artifact contaminating the EMG recordings, laryngeal excursion, tongue movement and activation of the buccal and/or masseter musculature At least two of the components were affected by the consistency of the liquids swallowed. Re-testing one subject a week later demonstrated good intertrial reliability.

CONCLUSIONS

We propose that the ICs of the sEMG provide a non-invasive means to assess the complex muscle sequence activation of deglutition.

Cortico-bulbar fibers to orofacial muscles: recordings with enoral surface electrodes

A new recording technique was developed to eliminate current problems on recording transcranial evoked facial muscle responses. A fork-shaped device equipped with 2 pairs of Ag/AgCl-electrodes was inserted enorally at the buccinator muscle level. Advantages offered by this method comprise clearly defined negative deflection of the compound muscle action potential, lack of relevant volume conduction from adjacent muscles, reliability of amplitude criteria, absence of interfering stimulus artifacts, easy achievement of preactivation, and noninvasive recording by surface electrodes. In 43 healthy subjects transcranial magnetic stimulation evoked contralateral responses at a mean latency and mean amplitude of 10.3 +/- 1.1 ms and 1.6 +/- 1.1 mV, respectively on the right side of the face and of 9.9 +/- 1.0 ms and 1.6 +/- 1.1 mV, on the left side of the face. Ipsilateral cortical evoked responses were observed in 29 and 25 subjects (left and right side of the face) at a mean latency and amplitude of 10.7 +/- 2.5 ms and 0.8 +/- 0.5 mV, respectively on the left side of face and of 11.9 +/- 3.2 ms and 1.1 +/- 1.2 mV, on the right side of face. No responses were obtained in 2 and 4 subjects (left and right side of the face), and could not be assessed due to simultaneous facial nerve stimulation in 12 and 14 subjects (left and right side of the face).

The effects of food consistency on jaw movement and posterior temporalis and inferior orbicularis oris muscle activities during chewing in children

The possible effects of food consistency on the number of chews and the lapse of time in a chewing sequence, the jaw-movement pattern and velocity, and jaw and lip muscle activity during chewing were investigated. Fifteen healthy children with good occlusion were selected. First, each subject freely chewed hard (HJ) and soft (SJ) types of jelly without specifying the chewing side. The number of chews and elapsed time in a masticatory sequence (from the start of chewing to the completion of the final swallow) were measured. Second, the subjects performed right- and left-sided chewing of the same food. The electromyograms (EMG) of posterior temporalis (PT) and inferior orbicularis oris (OI) muscles on the right and left sides and associated jaw movement records were sampled. The HJ was chewed more times and with a longer time until finally swallowed (p < or = 0.0007) than the SJ. The HJ chewing also showed broader masticatory loops (p < or = 0.0199) in the frontal view and higher peak activities (p < or = 0.0007) for the PT muscle. The closing phase was longer when chewing the HJ than SJ, but the opening and intercuspal phases remained stable. More lateral excursion of the jaw was seen when chewing the HJ, but the jaw-movement trajectories in the sagittal and vertical directions were not affected by the change in consistency of the food. The jaw-closing velocities for the HJ chews were significantly slower (p < or = 0.0351) than those for the SJ chews in three directions. The HJ chews also revealed a longer duration between the onset of EMG burst for the PT muscle and the beginning of the centric occlusion (p < or = 0.0146). The OI muscle showed increased activity in accord with jaw opening, and consistent reciprocal cyclic activity with the PT muscle in terms of temporal associations (r > or = 0.5250; p < or = 0.0495). The OI muscle started to burst at a later part of the intercuspal phase, and frequently showed secondary activity in the jaw-closing and intercuspal phases. The peak activity for the ipsilateral OI muscle was significantly higher (p < or = 0.0106) than that for the contralateral OI muscle for both the HJ and SJ. The OI muscle activity, however, did not differ between the hard and soft jellies.(ABSTRACT TRUNCATED AT 400 WORDS)

Enzyme-histochemical and morphological characteristics of muscle fibre types in the human buccinator and orbicularis oris

Human masticatory muscles, originating from the first branchial arch and innervated by the trigeminal nerve, have a fibre composition distinct from that of limb and trunk muscles. The zygomatic muscles, originating from the second branchial arch and innervated by the facial nerve, differ in fibre composition from either the masticatory or the limb and trunk muscles. To elucidate further the structural basis for function, and the influence of embryological origin and innervation on oro-facial muscles, the buccinator and orbicularis oris muscles, which originate from the second branchial arch and are innervated by the facial nerve, were investigated. Like the masticatory and zygomatic muscles, they have a large representation in the cerebral cortex. Both muscles were composed of type I, type IIA and a few type IIC fibres of about equal diameter. However, the type I fibres had a different myofibrillar ATPase reaction from those in masticatory, zygomatic, limb and trunk muscles; this was a moderate to strong staining at pH 9.4, indicating a special isomyosin composition. Whereas the buccinator was composed of 53% type I fibres, the orbicularis oris had a 71% predominance of type II fibres. In both muscles, the mean fibre diameter and its marked intramuscular variability were similar to earlier findings in the zygomatic muscles. No muscle spindles were found. The large number of type I fibres in the buccinator implies a capacity for endurance during continuous work at relatively low levels of force. The predominance of type II fibres in the orbicularis oris indicates that it is built up of fast-twitch motor units, related to properties such as rapid acceleration and high speed during intermittent oro-facial movements. The similarities and differences in fibre-type composition between the facial, masticatory and limb muscles imply that specific functional demands are of greater importance for muscle differentiation than embryological origin and nerve supply.

Patterns of activity of perioral facial muscles during mastication in man

The activity of buccinator, orbicularis oris superior and inferior, quadratus and triangularis muscles was recorded by surface and needle electrodes during spontaneous unilateral mastication of small or large boluses. Their activity was compared with that of the masticatory muscles masseter and digastric, and with the vertical movement of the jaw. The facial muscles were active during mastication, displaying both tonic and phasic activity. Although the cyclic activity was broadly linked to lowering of the jaw, there was no strict time correspondence between the activity of the various facial muscles themselves, or between the activity of the facial muscles and the digastric. The timing and amplitude of facial muscle activity were affected by the duration of the masticatory cycle, the side on which chewing took place, the size of the bolus, and whether or not lip to lip contact was made.

Electromyographic analysis of the "baccinator mechanism" in human beings

Electromyography of the muscles of the "buccinator mechanism" was undertaken, utilizing indwelling fine-wire electrodes. Electromyograms were made of 14 subjects with normal occlusion during various oral activities. Several activities elicited simultaneous contraction of all muscles. Simultaneous activity represents a potential restraining force of this muscular band on the dentition.

Electromyographic investigations of the tongue and circumoral muscular sling with fine-wire electrodes

The electromyographic (EMG) examination of 11 normal individuals in whom bipolar fine-wire indwelling electrodes were placed showed no EMG activity during rest periods and only very slight to slight activity during normal oral functionsmduring aberrant oral activity, such as thumb-sucking, the orbicularis oris and genioglossus muscles gave a marked EMG response and the buccinator muscles were slightly active. These findings may help explain the classical malocclusions seen in tongue-thrusters and thumb-suckers.