Jaw Elevator Research Articles

Unravelling the Complexities of Bite Force Determinants in Paediatric Patients: A Literature Review.

The amount of maximum voluntary bite force (MVBF)is determined by the combined action of the jaw elevator muscles, which are altered jaw biomechanics and reflex processes. Bite force (BF) measurements can yield valuable information on the activity and function of the jaw muscles. The accuracy of biting force measurements depends on several variables, including age, gender, malocclusion, dental caries, dental prosthesesand temporomandibular joint (TMJ). This information is essential for evaluating the development and function of the masticatory system, identifying potential abnormalities or impairmentsand guiding appropriate treatment interventions for paediatric patients. The aim of this article is to review the literature on the factors affecting bite force and the importance of these factors in assessing dental development and guiding interventions for paediatric patients with bite force-related issues. Additionally, establishing normative values for bite force in different age groups can aid in monitoring growth and detecting any deviations from expected patterns. Measuring bite force in paediatric patients is significant in comprehensive oral health assessment and management.

Comparison Between Maximum Bite Force on First Molar with Prosthesis and Contralateral First Molar Without Prosthesis

Background: Bite force is an indicator of the functional state of the masticatory system that results from the action of jaw elevator muscles modified by the craniomandibular biomechanics. Bite force measurement is essential in dental treatment as an extreme bite force on tooth may affect health of periodontium and increase risk of prosthesis fracture. A patient with low biting force may be helpful for the successful long-term outcome of prosthesis. A variety of devices has been used to record human bite force. Nowadays, sensitive electronic devices are used those are both accurate and precise enough. Recently, T-scan has been more popular to record the pattern of occlusion. The T-scan system precisely and dynamically records the occlusal contact time, force, and area in percentage. T-scan identify both force and timing which are the most fundamental parameters for measuring occlusion. The present study was designed to compare maximum bite force on first molar with prosthesis and contralateral first molar without prosthesis by using T-scan. Objectives: To compare maximum bite force (MBF) on first molar with prosthesis and contralateral first molar without prosthesis. Materials and Methods: This quasi-experimental type study was conducted in the Department of Prosthodontics, BSMMU. The patients were selected by a consecutive sampling technique, requiring permanent restoration in endodontically treated first molar on one side and natural first molar on contralateral side. The selected tooth was prepared for full veneer crown following standard procedure with armamentarium. Symptomless patients up to 3 months were measured bite force on cemented prosthesis and contralateral natural tooth. Bite force was measured with T-scan for three times with 30 sec interval and highest value was recorded in a data collection sheet for each patient to compare maximum bite force on first molar with prosthesis and contralateral first molar without prosthesis in the same patient. Result: The maximum bite force at the first molar without prosthesis was 14.30 ±4.2% and first molar with prosthesis was 12.05 ±3.55%. Tooth without prosthesis maximum bite force was significantly more than the tooth with prosthesis. Conclusion: Maximum bite force was significantly higher in tooth without prosthesis than the tooth with prosthesis. The difference of maximum bite force was not statistically significant in relation to gender, age and BMI.

Physiotherapy and occlusal splint treatment in myalgia, cervi-cogenic headache, and arthralgia: a case report

Abstract: The purpose of this study was to describe a rare case of myalgia, cervicogenic headache, and arthralgia in which interaction of physiotherapy, relaxation techniques, cognitive and behavioral counseling, psychosocial support, and occlusal splint treatment resulted in a positive outcome. A 27-year-old woman presented to our clinic with myalgia of the right side of the face, right temporomandibular joint arthralgia, right and left temple pain, jaw elevator muscle pain, and head and neck muscle soreness. The right and left joints' magnetic resonance imaging revealed anterior disc displacement without reduction. The treatment strategy aimed for a non-invasive treatment approach to relieve pain and restore functions. An occlusal appliance with an anterior bite plane was selected, along with counseling, psychosocial support, physiotherapy, posture self-control, massage of the head and neck muscles, mouth opening exercises, and self-massage. A temporomandibular specialist oversaw the splint treatment's progress, a maxillofacial surgeon managed the clinical signs and symptoms of the muscles and joints, and a physiotherapist provided the physiotherapy. Muscle stability in the head and neck has been related to temporomandibular disorders and may have repercussions on craniofacial structure and function. Keywords: physiotherapy; massage; relaxation techniques; oral splint; temporomandibular dis-order

Comparison of Jaw Elevation Device vs. Conventional Airway Assist during Sedation in Chronic Kidney Diseases Undergoing Arteriovenous Fistula Surgery: A Randomized Controlled Trial.

Patients with chronic renal failure (CRF) are likely to have obstructive sleep apnea (OSA) underdiagnosed, and maintaining airway patency is important during sedation. This study compared Jaw elevation device (JED) with conventional airway interventions (head lateral rotation, neck extension, oral or nasal airway insertion, and jaw thrust maneuver) during sedation and hypothesized that JED may be effective to open the airway. A total of 73 patients were allocated to a conventional group (n = 39) and a JED group (n = 34). The number of additional airway interventions was the primary outcome. Percentage of patients with no need of additional interventions and apnea-hypopnea index (AHI) were secondary outcomes. The number of additional interventions was significantly less in the JED group compared to the conventional group (0 (0–0) vs. 1 (0–2); p = 0.002). The percentage of patients with no requirement for additional interventions was significantly higher in the JED group compared to the conventional group (76.5% vs. 43.6%; p = 0.004). AHI was significantly lower in the JED group compared to the conventional group (4.5 (1.5–11.9) vs. 9.3 (3.8–21.9), p = 0.015). In conclusion, JED seems to be effective in opening the airway patency during sedation in CRF patients.

The Effect of Tooth Loss on Craniofacial Morphology

The morphology of the craniofacial skeleton is known to be responsive to changing biomechanical loads produced by feeding. Edentulism, or tooth loss, has previously been shown to have an impact on the structure of the craniofacial bones, particularly the alveolar bone and palate, as well as on the material properties of the cortical bone. However, it is less clear what effect tooth loss has on the masticatory muscles and their bony attachment sites. In this study, we use geometric morphometrics on human skulls to compare the shape of the mandible and facial skeleton in edentulous and dentate individuals. Following from previous work, we expect that edentulous individuals will exhibit decreased alveolar bone height in both the mandible and maxilla. We further hypothesize that edentulous individuals will display a recession of bone at the insertion sites of the masticatory muscles, namely the zygomatic arch and the mandibular ramus. CT scans of individuals greater than 50 years of age (n=40) were obtained from the New Mexico Decedent Imaging Database (NMDID). Individuals with no teeth were sorted into the edentulous group, while individuals with more than 22 of 36 teeth were sorted into the functionally dentate. 3D Slicer software was used to generate 3D models, and 3D fixed and sliding landmarks were placed along the mandible, maxilla, zygomatic arch, palate, and orbit. Principal component analysis (PCA) and Procrustes ANOVAs were performed separately on the Procrustes-aligned coordinate data for the crania and mandibles. We identified significant differences in facial and mandibular shape between groups. In both cases, differences were largely driven by resorption along the alveolus. Variation in the morphology of edentulous individuals suggests that the time since tooth loss and behavioral factors, such as denture wearing, may impact the degree of alveolar resorption. Interestingly, edentulous individuals tended to have relatively smaller coronoid processes and posteriorly extended mandibular angles. This suggests that tooth loss may result in greater relative atrophy of the temporalis muscle, a jaw elevator/retractor, compared to the masseter muscle, another jaw elevator which is involved in resisting gravity and positional jaw closure. Further studies are needed to investigate the impact of tooth loss on muscle morphology to confirm this. These additive effects between bone resorption and muscle atrophy likely explain the altered facial morphology demonstrated by edentulous populations.

Differences in muscle mechanics underlie divergent optimality criteria between feeding and locomotor systems.

Tetrapod musculoskeletal diversity is usually studied separately in feeding and locomotor systems. However, direct comparisons between these systems promise important insight into how natural selection deploys the same basic musculoskeletal toolkit-connective tissues, bones, nerves, and skeletal muscle-to meet the differing performance criteria of feeding and locomotion. Recent studies using this approach have proposed that the feeding system is optimized for precise application of high forces and the locomotor system is optimized for wide and rapid joint excursions for minimal energetic expenditure. If this hypothesis is correct, then it stands to reason that other anatomical and biomechanical variables within the feeding and locomotor systems should reflect these diverging functions. To test this hypothesis, we compared muscle moment arm lengths, mechanical advantages, and force vector orientations of two jaw elevator muscles (m. temporalis and m. superficial masseter), an elbow flexor (m. brachialis) and extensor (m. triceps- lateral head), and a knee flexor (m. biceps femoris-short head) and extensor (m. vastus lateralis) across 18 species of primates. Our results show that muscles of the feeding system are more orthogonally oriented relative to the resistance arm (mandible) and operate at relatively large moment arms and mechanical advantages. Moreover, these variables show relatively little change across the range of jaw excursion. In contrast, the representative muscles of the locomotor system have much smaller mechanical advantages and, depending on joint position, smaller muscle moment arm lengths and almost parallel orientations relative to the resistance arm. These patterns are consistent regardless of phylogeny, body mass, locomotor mode, and feeding specialization. We argue that these findings reflect fundamental functional dichotomies between tetrapod locomotor and feeding systems. By organizing muscles in a manner such that moment arms and mechanical advantage are relatively small, the locomotor system can produce broad joint excursions and high angular velocities with only small muscular contraction. As such, the anatomical organization of muscles within the limbs allows striding animals to move relatively rapidly and with minimal energetic expenditure. In contrast, the anatomical configuration of muscles in the feeding system, at least m. superficial masseter and m. temporalis, favors their force-producing capacity at the expense of excursion and velocity.

Reliable measurement of incisal bite force for understanding the control of masticatory muscles

ObjectiveIn the present study, we aimed at evaluating the steadiness of incisal bite force during isometric contractions of masticatory muscles. DesignTwo separate experiments were carried out in 11 healthy young women. A first experiment was performed to test the reliability of our protocol for measurement of incisal bite force steadiness. The second experiment aimed to evaluate the steadiness of incisal bite force at four submaximal (i.e., percentage of maximum voluntary contraction, MVC) levels (5 %MVC, 10 %MVC, 15 %MVC, and 20 %MVC), along with the bilateral myoelectric activity of two masticatory muscles (temporalis and masseter). ResultsThe results from the first experiment showed that our protocol is substantially reliable (intraclass correlation coefficient, ICC > 0.80) for estimating force variability and moderate reliable (0.60 < ICC < 0.80) for estimating spectral properties of force signals. In the second experiment, we found that force standard deviation (SD) increased proportionally to the power of mean force, and coefficient of variation (CoV) was higher at low-intensity contractions and maintained at an approximately constant level for high-intensity contractions. The force-EMG relationships were linear for both muscles at the contraction intensities evaluated in the study (5 %MVC to 20 %MVC), and the median frequency did not change with contraction intensity. ConclusionTherefore, we presented a reliable method to estimate the incisal bite force, along with additional data on force control and myoelectric activity of jaw elevator muscles during isometric steady contractions.

Jaw Elevator Muscle Coordination during Rhythmic Mastication in Primates: Are Triplets Units of Motor Control?

The activity of mammal jaw elevator muscles during chewing has often been described using the concept of the triplet motor pattern, in which triplet I (balancing side superficial masseter and medial pterygoid; working side posterior temporalis) is consistently activated before triplet II (working side superficial masseter and medial pterygoid; balancing side posterior temporalis), and each triplet of muscles is recruited and modulated as a unit. Here, new measures of unison, synchrony, and coordination are used to determine whether in 5 primate species (Propithecus verreauxi, Eulemur fulvus, Papio anubis, Macaca fuscata,and Pan troglodytes)muscles in the same triplet are active more in unison, are more synchronized, and are more highly coordinated than muscles in different triplets. Results show that triplet I muscle pairs are active more in unison than other muscle pairs in Eulemur, Macaca, and Papio,buttriplet muscle pairs are mostly not more tightly synchronized than non-triplet pairs. Triplet muscles are more coordinated during triplet pattern cycles than non-triplet cycles, while non-triplet muscle pairs are more coordinated during non-triplet cycles than triplet cycles. These results suggest that the central nervous system alters patterns of coordination between cycles, recruiting triplet muscles as a coordinated unit during triplet cycles but employing a different pattern of muscle coordination during non-triplet cycles. The triplet motor pattern may simplify modulation of rhythmic mastication by being one possible unit of coordination that can be recruited on a cycle-to-cycle basis.

Injury responses of Sprague-Dawley rat jaw muscles to an experimental unilateral anterior crossbite prosthesis

ObjectiveDental occlusion are frequently changed in clinic. Molecular responses in jaw muscles to aberrant dental occlusion are changes are attractive, yet remain are obscure. DesignUnilateral anterior crossbite (UAC) prostheses were applied to Sprague-Dawley rats and then ceased after two weeks to detect the reactions of the masseter, a representative jaw elevator, and the lateral pterygoid muscle (LPM), a representative jaw depressor. ResultsTwo weeks of UAC elicited mild injury of the two muscles. Myogenesis and protective reactions were detected as increases in αB-crystallin expression in the masseter after 3 days and in the LPM after 2 weeks, and increases in desmin expression in both muscles after 2 weeks. A switch in fibre types from IIb to IIx occurred in the LPM but not in the masseter. Inflammatory responses, shown by the infiltration of inflammatory cells and increases in TNF-α mRNA expression, and fibrosis responses, shown by increased mRNA expression of Type I and III collagens, appeared very mild in the two muscles. These responses were partially recovered by the cessation of UAC. During the whole process, no obvious changes were observed in mitochondrial function, as indicated by the levels of proliferator-activated receptor γ coactivator 1α, mitofusin-2 and voltage-dependent anion channel. ConclusionsUAC causes injury and very limited inflammatory and fibrosis adaption in the masseter and LPM. Both muscles respond with myogenesis and protective activity. The LPM responds also with muscle fibre isoform alternations. These alterations were partially recovered by the cessation of dental stimulation at an early stage.

Efficacy of jaw elevation device (JED®) for maintenance of upper airway patency during transcatheter aortic valve replacement under deep sedation

Introduction There has been a growing popularity of performing transcatheter aortic valve replacement (TAVR) under sedation. However, insecurity of upper airway patency caused by deep sedation poses great challenges¹. To counteract the collapse of upper airway, we have adopted Jaw Elevation Device (JED®: Hypnoz Therapeutic Devices), an externally applicable device that holds up the mandible so that the upper airway can be kept patent non-invasively. The purpose of this study was to determine whether the intraoperative use of JED® is efficacious in improving the upper airway patency during deep sedation for TAVR. Methods We retrospectively reviewed medical and anesthetic records from patients who underwent transfemoral TAVR under sedation with or without JED® between May 2018 and November 2018. The primary outcome was the intraoperative upper airway obstruction (UAO) score; 0: no snoring/obstruction, 1: snoring, 2: spontaneously resolving UAO within a few breaths, 3: UAO resolved with manual jaw thrust, 4: UAO requiring mask ventilation. This study was approved by the institutional human research committee (Approved No. 20130023) and the written informed consents for data collection were obtained from the patients prior to the procedures. Results Data were collected from 46 patients, of which 31 were anesthetized with JED® [JED (+) group] and 15 were managed without any airway device [JED (-) group]. Baseline characteristics and preoperative variables were comparable between groups. None of the patients in either group required insertion of any alternative airway devices or conversion to general anesthesia during the procedure. JED (+) group showed significantly less upper airway obstruction scores at valve deployment with median (interquartile range) of 0 (0-1) compared with 3 (2.5-3) in JED (-) group (P Discussion Our data suggest that JED® is effective in securing upper airway patency in a non-invasive manner, and therefore can be a viable option for deep sedation during TAVR procedure. Considering complicated and demanding anesthetic managements during TAVR procedure, provision of hands-free environment by JED® may significantly contribute to the improvement in safety.

Tongue strength, masticatory and swallowing dysfunction in patients with chronic temporomandibular disorder

BackgroundThe possible factors related to functional impairment and limitations in patients with temporomandibular disorders (TMDs) still need to be clarified because recovery of orofacial functions is a goal of their treatment. ObjectiveTo investigate whether chronic TMD patients had any changes in tongue strength, besides the difficulty in chewing and orofacial functional impairment, compared to a control group. Moreover, to examine whether tongue strength, chewing difficulties, and orofacial functions were associated. MethodsTwenty-three patients with chronic TMD according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) and volunteers without TMD (control group) were compared. Strength measures were obtained using the Iowa Oral Performance Instrument (IOPI) during tongue protrusion (TPS) and swallowing of saliva (SS) tasks. A scale was used to investigate self-reported chewing difficulties, and the orofacial muscles and functions were evaluated using the orofacial myofunctional evaluation with scores protocol (OMES). ResultsCompared to the control group, TMD patients showed reduced TPS and SS, higher difficulty in chewing and worse myofunctional orofacial conditions. Tongue strength was correlated with mastication and swallowing behaviors, as well as with general myofunctional status. Chewing difficulty increased with decreasing tongue strength and with worsening of orofacial muscles and functions. ConclusionPatients with chronic TMD showed reduced tongue strength and worse masticatory and swallowing functions, and these aspects were interrelated. Clinical relevanceThe present results contribute additional evidence regarding the impairment of orofacial muscles other than jaw elevator muscles in patients with chronic TMD.

Swallowing changes related to chronic temporomandibular disorders.

To investigate whether chronic temporomandibular disorder (TMD) patients showed any changes in swallowing compared to a control group. Moreover, it was examined whether swallowing variables and a valid clinic measure of orofacial myofunctional status were associated. Twenty-three patients with chronic TMD, diagnosed with disc displacement with reduction (DDR) and pain, according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD), and 27 healthy volunteers (control group) were compared. Surface electromyography (EMG) of the temporalis, masseter, sternocleidomastoid, and suprahyoid muscles was performed during swallowing tasks of thin liquid (10 and 15mL) and spontaneous saliva. Data were normalized. Compared to the control group, TMD patients showed a prolonged duration of swallowing for liquid and saliva and required a longer time to reach the activity peak and half the integral. While the overall mean value of the relative peaks was similar for the groups, the suprahyoid peak was significantly lower in the TMD group during swallowing of liquid. Moreover, TMD patients recruited the jaw elevator muscles proportionally more than controls. The orofacial myofunctional status was moderately correlated with EMG parameters. Patients with chronic TMD showed temporal prolongation and changes in the relative activity of the muscles during the swallowing tasks. The present results contribute additional evidence regarding the reorganization of muscle activity in patients with chronic TMD.

Ultrasonographic evaluation of jaw elevator muscles in young adults with bruxism and with and without attrition-type tooth wear: A pilot study

ABSTRACT Objective This pilot study was planned to analyze masticatory activation in bruxism patients with and without attrition by ultrasonographic evaluation of mandibular adductor muscles. Methods Sixty bruxism patients (group 1: 30 without attrition, group 2: 30 with attrition) and an age-sex matched control of 30 (group 3) were clinically examined. The thickness of bilateral temporalis and masseter muscles during clench and rest was measured by ultrasonography. Results The mean muscle thicknesses were higher in bruxing patients than in controls. In group 2, the clench/rest ratio (C/R) of the right and left masseter and temporal muscles were higher than the control group (p = 0.03, p = 0.01, p = 0.04, p = 0.03, respectively). Conclusion The thickness of chewing muscles increases with bruxism. The occlusal forces in the teeth increase, and therefore, the tooth wear increases. Ultrasonographic muscle thickness can be used to determine muscle activity in bruxism patients.

Evaluating the triplet hypothesis during rhythmic mastication in primates.

Mammalian mastication involves precise jaw movements including transverse movement of the mandible during the power stroke. Jaw elevation and transverse movement are driven by asymmetrical jaw elevator muscle activity, which is thought to include a phylogenetically primitive and conserved triplet motor pattern consisting of: triplet I (balancing side: superficial masseter and medial pterygoid; working side: posterior temporalis), which reaches onset, peak and offset first; and triplet II (working side: superficial masseter and medial pterygoid; balancing side: posterior temporalis), which is active second. Although the presence of a triplet motor pattern has been confirmed in several primate species, the prevalence of this motor pattern - i.e. the proportion of masticatory cycles that display it - has not been evaluated in primates. The present study quantifies the presence and prevalence of the triplet motor pattern in five different primate species, Eulemur fulvus, Propithecus verreauxi, Papio anubis, Macacafuscata and Pan troglodytes, using mean onset, peak and offset time relative to working superficial masseter. In all five of the species studied, the mean triplet motor pattern was observed at peak muscle activation, and in four out of the five species the triplet motor pattern occurred more frequently than expected at random at peak muscle activation and offset. Non-triplet motor patterns were observed in varying proportions at different time points in the masticatory cycle, suggesting that the presence or absence of the triplet motor pattern is not a binomial trait. Instead, the primate masticatory motor pattern is malleable within individual cycles, within individual animals and therefore within species.

The effect of craniokinesis on the middle ear of domestic chickens (Gallus gallus domesticus).

The avian middle ear differs from that of mammalians and contains a tympanic membrane, one ossicle (bony columella and cartilaginous extra-columella), some ligaments and one muscle. The rim of the eardrum (closing the middle ear cavity) is connected to the neurocranium and, by means of a broad ligament, to the otic process of the quadrate. Due to the limited number of components in the avian middle ear, the possibilities of attenuating the conduction of sound seem to be limited to activity of the stapedius muscle. We investigate to what extent craniokinesis may impact the components of the middle ear because of the connection of the eardrum to the movable quadrate. The quadrate is a part of the beak suspension and plays an important role in craniokinesis. Micro-computed tomography was used to visualize morphology and the effect of craniokinesis on the middle ear in the domestic chicken (Gallus gallus domesticus). Both hens and roosters are considered because of their difference in vocalization capacity. It is hypothesized that effects, if present, of craniokinesis on the middle ear will be greater in roosters because of their louder vocalization. Maximal lower jaw depression was comparable for hens and roosters (respectively 34.1±2.6° and 32.7±2.5°). There is no overlap in ranges of maximal upper jaw elevation between the sexes (respectively 12.7±2.5° and 18.5±3.8°). Frontal rotation about the transversal quadrato-squamosal, and inward rotation about the squamosal-mandibular axes of the quadrate were both considered to be greater in roosters (respectively 15.4±2.8° and 11.1±2.5°). These quadrate rotations did not affect the columellar position or orientation. In hens, an influence of the quadrate movements on the shape of the eardrum could not be detected either; however, craniokinesis caused slight stretching of the eardrum towards the caudal rim of the otic process of the quadrate. In roosters, an inward displacement of the conical tip of the tympanic membrane of 0.378±0.21mm, as a result of craniokinesis, was observed. This is linked to a flattening and slackening of the eardrum. These changes most likely go along with a deformation of the extra-columella. Generally, in birds, larger beak opening is related to the intensity of vocalization. The coupling between larger maximal upper jaw lifting in roosters and the slackening of the eardrum suggest the presence of a passive sound attenuation mechanism during self-vocalization.

Sex differences in jaw muscle duty factors during exercise in two environments: A pilot study

It is unknown if females and males use jaw muscles similarly during exercise. This pilot study assessed jaw elevator muscle duty factors (DFs=time of muscle activity/total recording time) at repeated sessions to test if DFs are reliable and different between sexes during exercises in two environments. Ten female and seven male subjects recruited from university soccer teams provided informed consent. Surface electromyography was recorded from masseter and temporalis muscles during biting and leg-extension laboratory exercises. Average activities to produce 20N bite-forces for each muscle and subject determined thresholds (5–80%·T20N) for subject-specific DF calculations during exercises performed in laboratory and natural environments. Subjects self-recorded via portable electromyography equipment during in-field leg-extension and weight-lifting exercises. Effects of variables on DFs were assessed via ANOVA (α=0.05) and simple effects testing (Bonferroni-adjusted p⩽0.012). All subjects used jaw muscles during exercises in both environments. DFs between laboratory sessions were reliable (R=0.84). During laboratory exercises, male temporalis DFs were significantly higher than female DFs from both muscles (p⩽0.001). During in-field exercises females had higher DFs during weight-lifting while males had higher DFs during leg-extensions. In-field sex differences were significant at most thresholds and showed larger effect sizes for leg-extension compared to weight-lifting exercises.

A three dimensional free body analysis describing variation in the musculoskeletal configuration of the cynodont lower jaw.

The evolution of the middle ear from the cynodont craniomandibular bones is one of the key mammalian innovations, and the mechanics underlying this anatomical transformation represents an intriguing paradox. Because the jaw joint of nonmammalian cynodonts was functionally coupled to the inner ear, auditory performance would favor low joint reaction forces. However, this could not be achieved at the expense of feeding performance, favoring high bite forces. The balance of these two seemingly incompatible performance criteria in the context of the morphological diversity of the cynodont lower jaw is poorly understood. Here we derive a series of equations using three dimensional free body analysis that describe the relationship between the orientation and position of the jaw elevator muscles, the position of the jaw articulation relative to the bite point, the joint reaction forces and the bite force in the lower jaw of the nonmammalian cynodont Probainognathus. These equations permit the effects of variation in each variable to be tested independently, yielding three terms that act to limit joint reaction forces without substantially impacting bite force: the reorientation of the resultant muscle force more vertically, shifting the position of the bite point medial to the jaw articulation, and elevating the jaw articulation above the level with the tooth row only when the muscles are oriented principally in the anterior direction. The predictions from our equations provide insights for functional interpretations of patterns of morphological diversity in the cynodont fossil record. They also illustrate that the musculoskeletal configuration of the cynodont lower jaw can be evolutionarily labile without negatively impacting the dual performance criteria of the auditory and feeding system.

THU0343 Visual Feedback of Bilateral Bite Force Coordination to Assess Motor Control of the Mandible

BackgroundThe muscle impairment in Temporomandibular disorders (TMDs)1, frequently observed in patients with different rheumatic diseases, contribute to diminished recruitment and force tuning ability. The quantitative assessment of the motor function...

Jaw Elevation Device (JED) is able to maintain jaw trust and keep the airway open

Itosu, M.1; Yogo, H.1; Shimajiri, T.1; Fujimura, T.1; Shinzato, T.1; Isono, S.2 Author Information

Convergence in morphology and masticatory function between the pharyngeal jaws of grass carp,Ctenopharyngodon idella, and oral jaws of amniote herbivores

The cellulose-rich walls that protect plant cells are difficult to digest, and therefore mechanical food processing is a key aspect of herbivory across vertebrates. Cell walls are typically broken down by translation of flattened teeth in the occlusal plane (i.e. grinding) as part of a complex, rhythmic chewing stroke. The grass carp, Ctenopharyngodon idella, is a voracious, invasive herbivorous fish that relies solely on its pharyngeal teeth, located in the back of the throat, for mechanical processing of plant material. Here, we describe the musculoskeletal anatomy of the pharyngeal jaws of grass carp and use XROMM to quantify chewing kinematics and muscle strain. The pharyngeal jaws are suspended in a sling of 11 muscles and maintain no bony articulation with any other skeletal elements in the head. The jaws bear long, serrated teeth that are worn during use into flattened tooth cusps. Our kinematic data show that this wear is the result of the teeth being elevated into occlusion against the basioccipital process and keratinous chewing pad, not tooth-on-tooth occlusion. Pharyngeal jaw elevation results from large strains in the jaw elevator muscle, the levator arcus branchialis V, to drive a pulley-like mechanism that rotates the jaws about a pivot point at the symphysis between the left and right pharyngeal jaws. These complex, rhythmic jaw rotations translate the teeth laterally across the chewing surface throughout the occlusion phase. The grass carp chewing system is strikingly similar in gross morphology and masticatory function to herbivorous chewing strategies in other vertebrates.