Search

Opossums (marsupials of the Didelphidae family) retain a generalized masticatory apparatus and tribosphenic molars, often used as models to understand the evolution of mastication in early therian mammals. Like all marsupials, their growth goes through a stage when pups complete their development while permanently attached to the mother's teats before weaning and starting feeding on their own. Yet, while the masticatory muscles of adults are known, as is the ontogeny of the cranium and mandible, the ontogenetic changes in the masticatory muscles remain unknown. Here we describe for the first time the changes in the masticatory muscles observed in lactating pups, and weaned juveniles, subadults, and adults in the White‐eared opossum, Didelphis albiventris, through dissection of 25 specimens and quantification of relative muscle masses, lines of actions and mechanical advantages whenever possible. We also assessed the scaling patterns of muscle masses and mechanical advantages through ontogeny. The main changes, as expected, were found between suckling and weaned specimens, although some changes still occurred from juveniles to adults. The adult adductor musculature is similar to the other Didelphis species already known, with a dominant m. temporalis that originates on the lateral wall of the skull, up to the sagittal and nuchal crests, and fills the zygomatic arch when inserting into the lateral and medial surfaces of the coronoid process, respectively through the pars superficialis and pars profunda. The m. masseter is also subdivided in superficial and deep bundles which originate posteriorly in the maxilla and zygomatic arch, and insert into the angular process and masseteric fossa in the mandible. The m. pterygoideus medialis originates from the palatine, the pterygoid bone and the alisphenoid, and it inserts on the angular process medially. Suckling pups showed muscles with more restricted attachments, reduced muscle lines of action, and less diversity in the fiber orientation. The absence of the postorbital constriction also resulted in a distinct morphology of the m. temporalis pars profunda, through two bundles, one anterior and one posterior, which insert more inferiorly into the mandible. These major changes can be related to the onset of mastication and to size‐related changes in growing weaned age classes. In general, all adductor muscles grew with positive allometry, and increased their fixation areas through, in part, the development of specific regions of the cranium and mandible. Their lines of action also increase and diversify along ontogeny. These changes can be related to the functional requirements for fixation during lactation, which shift to adduction and mastication movements after weaning. [ABSTRACT FROM AUTHOR]

Objectives: Cortical bone geometry is commonly used to investigate biomechanical properties of primate mandibles. However, the ontogeny of these properties is less understood. Here we investigate changes in cortical bone cross‐sectional properties throughout capuchin ontogeny and compare captive versus wild, semi‐provisioned groups. Tufted capuchins (Sapajus spp.) are known to consume relatively hard/tough foods, while untufted capuchins (Cebus spp.) exploit less mechanically challenging foods. Previous research indicates dietary differences are present early in development and adult Sapajus mandibles can resist higher bending/shear/torsional loads. Materials and methods: This study utilized microCT scans of 22 Cebus and 45 Sapajus from early infancy to adulthood from three sample populations: one captive Cebus, one captive Sapajus, and one semi‐provisioned, free‐ranging Sapajus. Mandibular cross‐sectional properties were calculated at the symphysis, P3, and M1. If the tooth had not erupted, its position within the crypt was used. A series of one‐way ANOVAs were performed to assess differences between and within the sample populations. Results: Mandible robusticity increases across ontogeny for all three sample populations. Sapajus were better able to withstand bending and torsional loading even early in ontogeny, but no difference in shear resistance was found. Semi‐provisioned, free‐ranging Sapajus tend to show increased abilities to resist bending and torsional loading but not shear loading compared to captive Sapajus. Discussion: This study helps advance our understanding of the primate masticatory system development and opens the door for further studies into adaptive plasticity in shaping the masticatory apparatus of capuchins and differences in captive versus free‐ranging sample populations. [ABSTRACT FROM AUTHOR]

Background: It remains unclear how the salivary flow and the fat content of food affect bolus formation during mastication. Objectives: We aimed to clarify: (1) how hyposalivation affects jaw‐closing and hyoid‐elevating muscle activities in bolus formation, and (2) if the effect of hyposalivation on muscle activity depends on the fat content of food. Methods: Eighteen healthy male volunteers were instructed to freely ingest four test foods: Plain, Fat without seasoning, Fat with seasoning, and Soft rice crackers. Masseter and suprahyoid electromyographic activities were recorded before and 30 min after the administration of atropine sulfate, a muscarinic receptor antagonist that induces hyposalivation. Results: Hyposalivation extended the masticatory duration significantly in all the test foods except Fat with seasoning. Masticatory cycle time was significantly longer with vs without hyposalivation for the Soft (p =.011). Suprahyoid activity/cycle was significantly greater with vs without hyposalivation (p =.013). Masticatory cycle time was significantly longer at the late stage with vs without hyposalivation for the Soft (p <.001). Suprahyoid activity/cycle was significantly greater at the middle (p =.045) and late stages (p =.002) with vs without hyposalivation for the Soft and greater at the late stage with vs without hyposalivation for the Plain (p =.043). Changes in masticatory cycle time and suprahyoid activity/cycle for these foods had significantly positive relationship (p <.001). Conclusion: Hyposalivation‐induced changes in masticatory behaviours resulted from the middle and late stage suprahyoid activity. Fat content and seasoning compensate for salivary flow inhibition. [ABSTRACT FROM AUTHOR]

The maxillofacial region is an extremely important region of the body from birth, which is responsible for various functions such as sucking, swallowing, chewing, breathing and pronunciation. It has a complex structure and involves a variety of biological substances from the organ level to the molecular level. Since olden times, clinicians and basic researchers have been interested in the structural changes that occur when function is impaired, and numerous studies have been conducted. Nonetheless, the opposite direction, i.e., how structural disturbances, or malocclusion in orthodontics, affect function, has been less well understood. This is probably because of the methodological difficulties involved. In this review, we will first summarize the old question of whether dysfunction affects occlusion, focusing on masticatory function, especially jaw function, and then, based on this, we will outline a new concept, the proposition of whether malocclusion affects function, focusing on the "substances" that serve as the interface between structure and function. [ABSTRACT FROM AUTHOR]

Background: Patients with painful temporomandibular disorders (TMD) more often experience jaw functional limitations. The study of jaw functional limitations should be primarily focused on painful TMD. Objectives: The impact of TMD pain characteristics (source, chronicity and intensity) on jaw functional limitations were evaluated using Jaw Functional Limitation Scale (JFLS). Methods: This cross‐sectional study reviewed the dental records and self‐report questionnaires of patients with painful TMD. The pain source, chronicity and intensity were evaluated to study the TMD pain characteristics. The jaw functional limitations were analysed using the Thai version of the JFLS. Results: A total of 176 patients with painful TMD were included in this study. The jaw functional limitations were affected only by pain intensity. Patients with TMD with severe pain intensity had significantly higher jaw functional limitations than those with mild‐to‐moderate pain intensity (p <.05). A significant association was observed between pain intensity and jaw functional limitations (p <.05). Mastication was highly restricted by pain intensity (odd ratio = 1.39, 95% confidence interval = 1.16–1.67). Conclusion: The present study found a significant effect of TMD pain intensity on jaw functional limitations. Patients with severe TMD pain intensity were more likely to experience jaw functional limitations, particularly mastication limitation. Management focusing on reduction of pain intensity may improve jaw functions in patients with TMD. [ABSTRACT FROM AUTHOR]

Objectives: Studies on oral processing are often snapshots of behaviors that examine feeding through individual bouts. In this study, we expand on our previous work comparing bite/chew variables per feeding bout to summed daily biting, chewing, and food intake to interpret loading that could have potential morphological effects. Materials and Methods: We observed sympatric Lemur catta and Propithecus verreauxi over two field seasons in the dry forest of Bezà Mahafaly Special Reserve in southwestern Madagascar. Bite and chew rates determined from videos filmed during observations were multiplied with time spent feeding on specific foods during focal follows to calculate daily values for each feeding bout. Food mechanical properties (FMPs) were tested on dietary items with a portable tester. We contrasted daily bite/chew numbers and intake with FMPs, species, season, and food shape. Results: Daily bite and chew numbers increased with maximum, but not average, food toughness. Daily intake decreased with average and maximum toughness. Season had a strong effect on daily bites and chews, but not on intake. Food shape influenced intake and total bite and chew numbers. The lemur species did not differ in our models. Discussion: Maximum food toughness impacted feeding behaviors and intake, which is consistent with higher loads having a greater effect on morphology. In contrast to feeding per bout, cumulative biting and chewing did not differ between species; taking feeding frequency into consideration affects interpretation of jaw loading. Finally, biting, as much as chewing, may generate strains that impact morphology. [ABSTRACT FROM AUTHOR]

In studies of mammalian mastication, a possible relationship has been proposed between bilateral recruitment of jaw adductor muscle force during unilateral chewing and the degree of fusion of the mandibular symphysis. Specifically, species that have unfused, mobile mandibular symphyses tend to utilize lower levels of jaw adductor force on the balancing (nonchewing) than the working (chewing) side of the head, when compared to related species with fused symphyses. Here, we compare jaw adductor recruitment levels in two species of musteloid carnivoran: the carnivorous ferret (unfused symphysis), and the frugivorous kinkajou (fused symphysis). During forceful chewing, we observe that ferrets recruit far more working‐side muscle force than kinkajous, regardless of food toughness and that high working‐to‐balancing side ratios are the result of increased working‐side force, often coupled with reduced balancing‐side force. We propose that in carnivorans, high working‐to‐balancing side force ratios coupled with an unfused mandibular symphysis are necessary to rotate the hemimandible for precise unilateral occlusion of the carnassial teeth and to sustain laterally oriented force on the jaw to engage the carnassial teeth during shearing of tough foods. In contrast, the kinkajou's flattened cheekteeth permit less precise occlusion and require medially‐oriented forces for grinding, thus, a fused symphysis is mechanically beneficial. Research Highlights: Ferrets' (unfused mandibular symphyses) use of asymmetrical jaw muscle activity may optimi forces for carnassial shearing. Kinkajous' more nearly equal force may be facilitated by their fused symphysis and flat cheek teeth. [ABSTRACT FROM AUTHOR]

Insects use their mandibles for a variety of tasks, including food processing, material transport, nest building, brood care, and fighting. Despite this functional diversity, mandible motion is typically thought to be constrained to rotation about a single fixed axis. Here, we conduct a direct quantitative test of this 'hinge joint hypothesis' in a species that uses its mandibles for a wide range of tasks: Atta vollenweideri leaf-cutter ants. Mandible movements from live restrained ants were reconstructed in three dimensions using a multi-camera rig. Rigid body kinematic analyses revealed strong evidence that mandible movement occupies a kinematic space that requires more than one rotational degree of freedom: at large opening angles, mandible motion is dominated by yaw. But at small opening angles, mandibles both yaw and pitch. The combination of yaw and pitch allows mandibles to 'criss-cross': either mandible can be on top when mandibles are closed. We observed criss-crossing in freely cutting ants, suggesting that it is functionally important. Combined with recent reports on the diversity of joint articulations in other insects, our results show that insect mandible kinematics are more diverse than traditionally assumed, and thus worthy of further detailed investigation. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'. [ABSTRACT FROM AUTHOR]

Anterior tooth (ANT) contacts induce a short-latency reflex inhibition of the human jaw-closing muscles. The jaw is a rigid class 1 lever for pinpoint targeting muscle force into a single bite point, the pivoting food particle. Seesaw reflex movements around the food particle fulcrum multiply the food-crushing force. Unpredictable jolts of reaction force caused by food crushing are subjected to the rostral ANT and caudally to the two articulate ends of the jaw triangle. The compression/distraction strains of food crushing must be monitored and inhibited by withdrawal reflexes. The mesencephalic ganglion (Vmes), neural myelin sheath, and muscle stretch receptors evolved subsequently to the advent of jaws to improve the velocity of proprioceptive and withdrawal reflexes. In mammalians, the spindles of the taut motor units, stretched by the food fulcrum, send excitatory monosynaptic feedback for the efferent neurons of the respective ipsilateral muscle units via the Vmes. In the Vmes, the spindle-input-mediating afferent neurons are coupled with another source of afferent feedback, which is also excitatory, from the back tooth (BAT) mechanoreceptors. The two sources of excitatory pulses are summated and targeted for the efferent neurons to boost the stretched and taut motor units. Likewise, the afferent feedback from the ANT mechanoreceptors is also coupled in the Vmes with concomitant feedback from spindles. The ANT output, however, is inhibitory to negate the excitatory feedback from the stretched jaw muscle units. The inhibitory feed from the anterior teeth temporarily blocks the excitatory potential of the masticatory motor efferent neurons to protect the anterior teeth and jaw joints from inadvertent strains. The inhibitory inputs from the anterior teeth alternate with the excitatory inputs from the BAT to determine which jaw-closing muscle units are activated or inhibited at any given instant of food crushing. The Vmes exists in all jawed vertebrates, and its evolution was probably motivated by demands for the control of bite force. The monosynaptic unilateral food-crushing excitatory and inhibitory reflexes (UFCRs) override the coexisting bilaterally executed feed for the jaw muscles from the central nervous system. The hypothesis proposed in this study is that the Vmes-mediated UFCRs combine neural inputs from tooth contacts with concomitant feedback from the muscle stretch receptors for the control of the mammalian food-crushing bite force. [ABSTRACT FROM AUTHOR]

Among mammals, hippopotamids ('hippos') have been described as the species with the lowest chewing efficacy despite elaborate enamel folds on the occlusal surface or their cheek teeth, which was hypothesized to result from the lack of a grinding chewing motion. We investigated the chewing and dentition of the two extant hippo species, the common hippo (Hippopotamus amphibius) and the pygmy hippo (Choeropsis liberiensis), making (video) observations of live animals and gathering data on museum specimens (n = 86 H. amphibius and 26 C. liberiensis skulls). Hippos have a low degree of anisodonty (differences in width between maxillary and mandibular cheek teeth) and anisognathy (difference in width between the upper and the lower jaw), corresponding to a mainly orthal (up-and-down) chewing motion. The two hippo species differ slightly, but distinctively, in their anterior dental morphology and chewing mode. In both species, the canines do not completely prevent a lateral jaw movement but would, in theory, permit this movement until the mandibular canines get into contact with the maxillary protruding snout. This movement is only realized, to a small extent, in pygmy hippos, leaving distinct wear traces on their incisors and creating relatively wider wear facets on the maxillary canines. In common hippos, the interlocking upper and lower incisors prevent lateral jaw movement. Corresponding contact wear facets are evident on the medial aspect of the upper, and on the lateral aspect of the lower incisors–unless museal reconstructions mispositioned these teeth. If these facets are interpreted as an indication for a relic of a lateral jaw movement that was probably more prominent in hippo ancestors, i.e. if we assume that hippos evolved orthal chewing secondarily, several other characteristics of hippos can be explained, such as a low degree of hypsodonty (in the absence of distinct attrition due to a grinding chewing movement), a secondary loss of complexity in their enamel schmelzmuster, a secondary evolution of a wide mouth gape, a reduction in anisodonty compared to their ancestors, and the evolution of a bilaterally symmetrical ('trifoliate') enamel folding pattern on the molar occlusal surface from an ancestral bunoselenodont condition. As an underlying driving force, selection for intraspecific combat with canines and incisors, necessitating a wide gape and a rigid jaw, has been suggested. [ABSTRACT FROM AUTHOR]

Objectives: The link between diet and the masticatory apparatus in primates is complex. We investigated how food mechanical properties (FMPs) and food geometry affect feeding behaviors and subsequent jaw loading. We compared oral processing in two sympatric lemur species with distinct diets and mandibular morphologies. Materials and Methods: All‐day focal follows of Lemur catta (Lc) and Propithecus verreauxi (Pv) were conducted in both the dry and wet seasons at Beza Mahafaly Special Reserve. We collected activity budget data, filmed feeding bouts, and collected food items to measure their mechanical properties with an FLS‐1 portable tester. Feeding videos for the top food items they spent the most time consuming were analyzed frame‐by‐frame to assess bite and chew numbers and rates. Results: Lc bite more and at a slower rate on tougher (maximum) foods, chew more for tougher (average) foods, and chew less for stiffer leaves. Pv initially increase chew number for tougher (average) foods, but their behavior is less affected as food toughness increases. Pv chew less and more slowly but spend more of the day feeding than Lc. Additionally, they have a tougher (maximum) diet than Lc. Discussion: Lc adjust their feeding behaviors depending on the FMPs of their top food items, while Pv feed more consistently. The more robust masticatory apparatus of Pv may not require them to adjust their feeding behaviors for more mechanically challenging foods. Furthermore, the two species show distinct differences in chewing. Exploring chewing on a daily scale could aid in understanding its impact on the loading of the masticatory apparatus. [ABSTRACT FROM AUTHOR]

The near‐global distribution of hadrosaurid dinosaurs during the Cretaceous has been attributed to mastication, a behaviour commonly recognized as a mammalian adaptation. Its occurrence in a non‐mammalian lineage should be accompanied by the evolution of several morphological modifications associated with food acquisition and processing. This study investigated morphological variation in the dentary, a major element of the hadrosauroid lower jaw. Eighty‐four hadrosauroid dentaries were subjected to geometric morphometric and statistical analyses to investigate their taxonomic, ontogenetic, and individual variation. Results suggest increased food acquisition and processing efficiency in saurolophids through a complex pattern of evolutionary and growth‐related changes. The edentulous region grew longer relative to dentary length, allowing for food acquisition specialization anteriorly and processing posteriorly, and became ventrally directed, possibly associated with foraging low‐growing vegetation, especially in younger individuals. The saurolophid coronoid process became anteriorly directed and relatively more elongate, with an expanded apex, increasing moment arm length, with muscles pulling the jaw more posteriorly, increasing mechanical advantage. During growth, all hadrosauroids underwent anteroposterior dental battery elongation by the addition of teeth, and edentulous region ventralization decreased. The dental battery became deeper in saurolophids by increasing the number of teeth per tooth family. The increased coronoid process anterior inclination and relative edentulous region elongation in saurolophids are hypothesized to have evolved through hypermorphosis and/or acceleration, peramorphic heterochronic processes; the development of an anteroposteriorly shorter but dorsoventrally taller saurolophid dentary, is probably due to post‐displacement in dental battery elongation and edentulous region decreased ventral orientation, a paedomorphic heterochronic process. [ABSTRACT FROM AUTHOR]

Background and objective: Patients with dentofacial deformity often present with impaired masticatory function, orofacial pain and temporomandibular disorders (TMD). This study investigates the relationship between TMD, pain, jaw and masticatory function at different stages of orthognathic surgical (OS) treatment. Methods: A total of 120 OS patients were prospectively recruited and grouped as pre‐orthodontic (group 1), pre‐surgery (group 2), 4‐month post‐surgery (group 3), 24‐month post‐surgery (group 4), in addition to 30 controls (group 0). Outcomes were assessed using: Jaw Function Limitation Scale (JFLS), McGill pain questionnaire, DC/TMD instrument, voluntary maximum bite force (MVBF), and masticatory efficiency (ME) using two‐coloured chewing gum. Data were analysed using structural equation modelling. Results: The prevalence of non‐painful TMD did not differ between groups (p =.827). However, the prevalence of painful TMD differed between groups (p =.001). Among the painful TMDs, the highest prevalence was observed for masseter myalgia in group 2 (p =.031), and importantly group 4 did not differ from group 0 (p =.948). The MPQ score was significantly higher in group 1 (p =.001) compared to group 0, and the JFLS score was significantly higher in groups 1, 2 and 3 compared to group 0. Notably, MPQ (p =.756) and JFLS (p =.572) scores in group 4 were not different from group 0. However, MVBF (p =.996) and ME (p =.991) did not differ between groups 1 and 4. The association of self‐reported pain and jaw function with the masticatory function was observed in OS patients. Conclusion: OS was not associated with a negative impact on TMD. Jaw function and pain levels were similar to controls at the 24‐month follow‐up. The masticatory function was further affected by the surgery and seems to require a longer recovery time. Moreover, it was confirmed that pain and TMD were associated with limitations in jaw function and impacts on masticatory function. [ABSTRACT FROM AUTHOR]

Marcus Gunn jaw wink phenomenon or Trigeminal oculomotor synkinesis, is a congenital disorder in which the upper lid moves synkinetically in response to jaw movement during chewing. The term synkinesis describes the simultaneous movement or a coordinated sequence of movements of muscles, which are supplied by different nerves or by separate peripheral branches of the same nerve. Although it rarely manifests bilaterally, it is typically unilateral. In 1883, Dr Robert Marcus Gunn, a Scottish Ophthalmologist described a 15-year-old girl with a peculiar type of congenital ptosis that included an associated winking motion of the affected eyelid on the movement of the jaw. It is known to affect both men and women equally. This phenomenon has been reported to be a similar phenomenon affecting 2-13% of all cases of congenital ptosis. It can be congenital or acquired, for example through trauma. The Congenital Marcus Gunn jaw wink phenomenon is thought to arise from the connection between the branch of the trigeminal nerve (responsible for chewing) supplying the middle or lateral pterygoid muscle and the branch of the oculomotor nerve supplying the upper superior levator ocular defect. Here we present a case report of Marcus Gunn's Jaw-Winking Synkinesis in congenital ptosis. [ABSTRACT FROM AUTHOR]

The evolutionary shift from a single-element ear, multi-element jaw to a multi-element ear, single-element jaw during the transition to crown mammals marks one of the most dramatic structural transformations in vertebrates. Research on this transformation has focused on mammalian middle-ear evolution, but a mandible comprising only the dentary is equally emblematic of this evolutionary radiation. Here, we show that the remarkably diverse jaw shapes of crown mammals are coupled with surprisingly stereotyped jaw stiffness. This strength-based morphofunctional regime has a genetic basis and allowed mammalian jaws to effectively resist deformation as they radiated into highly disparate forms with markedly distinct diets. The main functional consequences for the mandible of decoupling hearing and mastication were a trade-off between higher jaw stiffness versus decreased mechanical efficiency and speed compared with non-mammals. This fundamental and consequential shift in jaw form–function underpins the ecological and taxonomic diversification of crown mammals. This article is part of the theme issue 'The mammalian skull: development, structure and function'. [ABSTRACT FROM AUTHOR]

Background: Individuals with impaired oral sensation report difficulty chewing, but little is known about the underlying changes to tongue and jaw kinematics. Methodological challenges impede the measurement of 3D tongue movement and its relationship to the gape cycle. Objective: The aim of this study was to quantify the impact of loss of oral somatosensation on feeding performance, 3D tongue kinematics and tongue‐jaw coordination. Methodology: XROMM (X‐ray Reconstruction of Moving Morphology) was used to quantify 3D tongue and jaw kinematics during feeding in three rhesus macaques (Macaca mulatta) before and after an oral tactile nerve block. Feeding performance was measured using feeding sequence duration, number of manipulation cycles and swallow frequency. Coordination was measured using event‐ and correlation‐based metrics of jaw pitch, anterior tongue length, width and roll. Results: In the absence of tactile sensation to the tongue and other oral structures, feeding performance decreased, and the fast open phase of the gape cycle became significantly longer, relative to the other phases (p <.05). The tongue made similar shapes in both the control and nerve block conditions, but the pattern of tongue‐jaw coordination became significantly more variable after the block (p <.05). Conclusion: Disruption of oral somatosensation impacts feeding performance by introducing variability into the typically tight pattern of tongue‐jaw coordination. [ABSTRACT FROM AUTHOR]

Background: Obese individuals may have impaired oral sensory functioning and abnormal oral motor function, a consequence of fat deposition in muscles. Objective: To evaluate the oral motor function in obese individuals. Material and Methods: Three observational cross‐sectional studies were performed. In total, 140 participants were evaluated: (1) orofacial myofunctional evaluation (OMES) was performed in 26 obese and 26 control subjects; (2) time taken for suction of 50 ml of water through straws of 3 mm and 6 mm of diameter was measured in 30 obese and 30 control subjects; (3) the oral phase of swallowing of 5 ml moderately thick and 5 ml extremely thick boluses was analysed by videofluoroscopy in 14 obese and 14 control subjects. Obese and non‐obese control subjects had body mass index ≥40 kg/m2 and <30 kg/m2, respectively. Results: Obese subjects had worse oral myofunctional evaluation scores in posture/appearance (lips, jaw, cheeks, tongue and hard palate), in mobility (lips, tongue, jaw and cheeks) and in breathing, deglutition and mastication functions (p ≤.020). The OMES total score was 73.5 ± 5.5 in obese and 92.8 ± 3.7 in controls subjects (p <.001). There was no difference between the groups in the time taken for 50 ml of water suction through the 3‐mm‐ or 6‐mm‐diameter straw. Videofluoroscopic evaluation of the bolus swallowed demonstrated a longer oral preparation time in obese individuals for both boluses (p ≤.040) and no difference in oral transit time (p ≥.140). Conclusion: A moderate change in oral motor function was observed in obese individuals with BMI ≥40 kg/m2. [ABSTRACT FROM AUTHOR]

Objective: To investigate the effects of dental/skeletal malocclusion and orthodontic treatment on four main objective parameters of chewing and jaw function (maximum occlusal bite force [MOBF], masticatory muscle electromyography [EMG], jaw kinematics, and chewing efficiency/performance) in healthy children. Materials and methods: Systematic searches were conducted in MEDLINE (OVID), Embase, and the Web of Science Core Collection. Studies that examined the four parameters in healthy children with malocclusions were included. The quality of studies and overall evidence were assessed using the Joanna Briggs Institute and GRADE tools, respectively. Results: The searches identified 8192 studies; 57 were finally included. The quality of included studies was high in nine studies, moderate in twenty-three studies, and low in twenty-five studies. During the primary dentition, children with malocclusions showed similar MOBF and lower chewing efficiency compared to control subjects. During mixed/permanent dentition, children with malocclusion showed lower MOBF and EMG activity and chewing efficiency compared to control subjects. The jaw kinematics of children with unilateral posterior crossbite showed a larger jaw opening angle and a higher frequency of reverse chewing cycles compared to crossbite-free children. There was a low to moderate level of evidence on the effects of orthodontic treatment in restoring normal jaw function. Conclusions: Based on the limitations of the studies included, it is not entirely possible to either support or deny the influence of dental/skeletal malocclusion traits on MOBF, EMG, jaw kinematics, and masticatory performance in healthy children. Furthermore, well-designed longitudinal studies may be needed to determine whether orthodontic treatments can improve chewing function in general. Clinical relevance: Comprehensive orthodontic treatment, which includes evaluation and restoration of function, may or may not mitigate the effects of malocclusion and restore normal chewing function. [ABSTRACT FROM AUTHOR]

Purpose: This study was performed to examine how denture wearing improves jaw and neck muscle coordination during chewing in partially edentulous elderly patients. Methods: Sixteen patients classified as Eichner’s index B2 or B3 and 16 young dentate subjects were enrolled. Jaw and neck muscle activities during chewing were recorded using electromyography with and without denture wearing, then analyzed using intermuscular Electromyography (EMG)-EMG transfer and EMG-EMG coherence function analyses to clarify quantitative, temporal, and functional coordination of jaw and neck muscle activities while chewing. Occlusal force and masticatory scores were also determined. Results: Denture wearing increased the power values for jaw closing muscle activities, and improved occlusal area and force, and masticatory score. Gain values for jaw closing and opening muscle activities were decreased in those wearing dentures compared to those not wearing dentures. Denture wearing resulted in equivalent gain values for jaw closing and opening muscle activities as compared to the young subjects. Coherence values for chewing and nonchewing side neck muscle activities were increased as compared to not denture wearing. Conclusions: The suitability of denture wearing can be evaluated from the viewpoint of gain as a quantitative parameter showing coordination between jaw closing and opening muscle activities. Such evaluation can be performed from the viewpoint of coherence as a parameter of functional coordination between jaw and neck muscle activities during chewing in partially edentulous elderly patients. The gain parameter in regard to jaw muscle activities may be compensated to a state equivalent to that seen in young subjects by wearing an appropriate denture. [ABSTRACT FROM AUTHOR]

Objective: To examine jaw muscle activity of women with chronic temporomandibular myalgia (mTMD). It was hypothesized that mTMD patients had a different masticatory muscle activity, increased work during isometric clenching, and a reduced chewing frequency as compared to TMD-free subjects.Methods: The electromyographic (EMG) activity of temporalis anterior (TA) and masseter (MM) of 27 women with mTMD and 18 TMD-free women was recorded during clenching tasks and while chewing. EMG indices comparing the activity of paired jaw muscles were computed.Results: Women with TMD myalgia had greater muscular work than controls (p = 0.025). The activity of TA and MM were similar between right and left sides in both groups. mTMD patients had a greater activity of MM than TA (p = 0.028). No between-groups differences were found in chewing rate.Conclusion: Women with mTMD showed an abnormal recruitment of the jaw-closing muscles during functional tasks, which may predispose to further tissue injury. [ABSTRACT FROM AUTHOR]

Purpose: Dental implants are used to stabilize, support, and retain prostheses in the mandible following fibula free flap reconstruction. A previous longitudinal prospective study showed that an implant-supported prosthesis (IP) provided additional improvement in masticatory performance compared to a conventional prosthesis (CP). Therefore, in this paper, the impact of implant retention and support of mandibular prostheses on neuromuscular function is reported via a within-subject analysis. Materials and Methods: Forty-six participants were enrolled in the study. Prosthetic treatment with a CP was completed in 33 subjects following oromandibular resection and fibula free flap reconstruction. Twenty-five subjects completed evaluation of the CP after an adaptation period. Standardized masticatory tests with peanuts were given to subjects on the defect and nondefect chewing sides. Electromyography (EMG) of masseter muscles and jaw movement was performed and recorded simultaneously in 19 of these subjects. IP treatment was then completed in 16 of these subjects, and 15 of them participated in the IP evaluation after an adaptation period. Of these 15 subjects, 13 completed EMG and jaw movement recordings for both CP and IP. Results: EMG activity of the defect-side masseter muscle increased significantly from CP to IP conditions when chewing on either side, but no significant change was found for nondefect-side muscle activity. Jaw movement parameters showed no significant changes from CP to IP. Conclusion: In patients restored with mandibular fibula free flap reconstruction, implant support for mandibular prostheses has the benefit of permitting greater muscle effort on the defect side, irrespective of the side on which the bolus is being chewed. The impact of an IP on jaw movements is limited. [ABSTRACT FROM AUTHOR]

Medicated chewing gum has been recognised as a new advanced drug delivery method, with a promising future. Its potential has not yet been fully exploited because currently there is no gold standard for testing the release of agents from chewing gum in vitro. This study presents a novel humanoid chewing robot capable of closely replicating the human chewing motion in a closed environment, incorporating artificial saliva and allowing measurement of xylitol release from the gum. The release of xylitol from commercially available chewing gum was quantified following both in vitro and in vivo mastication. The chewing robot demonstrated a similar release rate of xylitol as human participants. The greatest release of xylitol occurred during the first 5 minutes of chewing and after 20 minutes of chewing only a low amount of xylitol remained in the gum bolus, irrespective of the chewing method used. Saliva and artificial saliva solutions respectively were collected after 5, 10, 15 and 20 minutes of continuous chewing and the amount of xylitol released from the chewing gum determined. Bioengineering has been implemented as the key engineering strategy to create an artificial oral environment that closely mimics that found in vivo. These results demonstrate the chewing robot with built-in humanoid jaws could provide opportunities for pharmaceutical companies to investigate and refine drug release from gum, with reduced patient exposure and reduced costs using this novel methodology. [ABSTRACT FROM AUTHOR]

Introduction The role of the occlusal quality as a relevant factor for mastication is controversially discussed. This paper aims to determine the role of the occlusion given the influencing factors. The correlation between the subjective evaluation of treatment needs and objective chewing test results are assessed. Methodology 842 participants (female n=460, 54.5%; male n=382, 45.4%) performed a standardized chewing test. The participants' occlusal quality, angle classification, age, gender, treatment needs and intraoral status were recorded. The participants were instructed to break down the standardized chewing tests units. The particles were collected in a sieve and placed on a calibrated acquisition board. Standardized images were analysed, measuring the areas of each particles in mm2. Null Hypotheses were tested with the Kruskal-Wallis tests and post hoc tests with Bonferroni correction, to be rejected at p≤0.01. Results The occlusion quality has a significant impact on the chewing efficiency (p=0.001), but angle classification only to some extent. Age (p≤0.001) and gender (p≤0.001) are important intrinsic factors. Fixed prosthodontics do not reach the chewing performance of natural occlusion (p≤0,01). The subjective clinical assessment of treatment needs correlates in categories with strong differentiations (p=0,001), but not if only minor differences are asserted (p≤0,515). Conclusion The occlusion quality has a significant impact on the chewing efficiency. Masticatory performance is highly dependent on the natural or artificial chewing surface morphology. Age, gender and the intraoral status are important intrinsic factors. The maintenance of a sufficient functional oral status is a crucial task in the care of the aging population. [ABSTRACT FROM AUTHOR]

Aims: To determine whether mucosal pain, evoked through a novel topical capsaicin model, has an effect on jaw movement and whether psychologic factors have an association with any pain-induced movement effects. Methods: Mandibular movement was recorded from 26 asymptomatic subjects during free opening and closing, resistant opening jaw movements, and free and standardized chewing, at baseline and in test sessions while the subjects were wearing a custom maxillary mouthguard coated with either capsaicin cream (pain group, 13 subjects) or placebo cream (control group, an additional 13 subjects). All subjects completed the Depression Anxiety Stress Scales (DASS) and the Pain Catastrophizing Scale (PCS). Statistical analyses were made with independent t tests and bivariate correlation analyses. Results: Capsaicin induced moderate pain in the pain group, but there were no significant differences between the two groups in the change of kinematic variables from baseline except for a significantly greater increase from baseline in the number of chewing cycles per second (chewing rate) for free (t = 2.74, P = .011) and standardized chewing (t = 2.10, P = .047) in the pain group compared with the control group. In the pain group, the DASS anxiety score was negatively correlated (r = -.70, P = .007), with the change of mean opening velocity from the baseline to the test session in the free opening task, and the DASS depression score was negatively correlated to the increase of chewing rate in the free chewing task from the baseline to the test session (r = -.56, P = .046). Conclusion: Capsaicin-induced mucosal pain resulted in a significant increase in chewing rate but had no effect on amplitude or velocity in opening/closing jaw movements and chewing. Anxiety and depression scores correlated negatively with velocity in free opening jaw movement and chewing rate, respectively. [ABSTRACT FROM AUTHOR]

Aims: To determine the effects of experimental jaw-muscle pain on jaw movements. Methods: Mandibular mid-incisor point was tracked in 22 asymptomatic subjects during standardized (at 2.2 mm/s) protrusion, contralateral excursion, and open jaw movements, as well as free, right-sided chewing and chewing standardized for timing (900 ms/cycle). Tonic infusion of 4.5% hypertonic saline into the right masseter muscle maintained pain intensity between 30 and 60 mm on a 100-mm visual analog scale. Subjects performed tasks in 3 sessions on the same experimental day: control condition (baseline trials), test condition 1 (during hypertonic or 0.9% isotonic saline infusion), and test condition 2 (during isotonic or hypertonic saline infusion). Results: In comparison with control, there were no significant effects of hypertonic saline infusion on amplitude or velocity for protrusion or contralateral jaw movements or on velocity for jaw opening. Jaw-opening amplitude was significantly smaller in comparison with control during hypertonic, but not isotonic, saline infusion. During free but not standardized chewing, subjects chewed faster and exhibited larger amplitude gapes during hypertonic and isotonic infusion in comparison with control. Therefore, it was unlikely that pain had an effect on the kinematic parameters of jaw movement during free chewing. Qualitatively, individual subject data revealed considerable variability in the effects of hypertonic saline on movement parameters, which suggests that the effect of pain on jaw movement may not be uniform between individuals. Conclusions: The data indicate that the effect of pain on jaw movement may vary with the task performed. [ABSTRACT FROM AUTHOR]

Purpose: This study assessed the duration of different phases of the chewing cycle and the height of the masticatory cycle in relation to the type of lateral guidance. Materials and Methods: Fifty-three subjects with the same type of lateral guidance on both sides were categorized into 3 groups: anterior protected articulation, canine protection, and group function. Overbite was measured clinically. Border jaw movements were recorded using a Sirognathograph, and the lateral guidance angle in the frontal plane was measured. Jaw movements during unilateral chewing of peanuts were recorded on the frontal plane using the Sirognathograph connected to an electrocardiograph used for transcription. A single masticatory cycle was divided into opening, closing, and occlusal-level phases. Masticatory parameters were analyzed by one-way analysis of variance, correlations, the paired Student ttest, and multiple linear regression. Results: Women showed significantly longer total cycle duration than men. Subjects with canine protection showed the highest lateral guidance angle and the highest chewing cycle duration. Subjects with anterior protected articulation exhibited significantly longer occlusal-level phases. Fifty-nine percent of the variation in duration of the occlusal-level phase can be explained by the type of lateral dental guidance, gender, and lateral guidance angle. Only overbite was a predictor of height of mastication. Conclusion: The type of lateral guidance, gender, and frontal guidance angle are correlated with the duration of the occlusal-level phase during unilateral chewing of peanuts. The height of mastication cannot be explained by the type of lateral guidance. [ABSTRACT FROM AUTHOR]

Purpose:Dentists may be the first health care professionals to recognize unusual and abnormal oral movements collectively termed oral dyskinesias. The aims of this clinical overview are to raise the dental community's awareness about this important and complex topic and describe the clinical features and management of the main entities. Materials and Methods: A MEDLINE search of the different entities reported in the English and French literature was conducted. The main findings of a field study on oral dyskinesia were also reviewed. Results: Involuntary movement disorders are often drug related. In other cases, excessive oral movements may occur at any age in relation to various neuropsychiatric conditions. Orofacial dystonia apparently triggered by dental procedures has also been reported. Edentulousness has been associated with oral stereotypes. In a survey of 352 edentulous elderly individuals attending daycare centers, only 7% displayed visible oral sterotypes, and ill-fitting dentures were suggested as a possible triggering factor for the majority. Conclusion: A multidisciplinary evaluation is desirable in the care of individuals with oral dyskinesia and in the selection of those who may benefit from a prosthodontic approach. A good knowledge of potentially offending drugs may allow avoidance of unnecessary procedures. [ABSTRACT FROM AUTHOR]

Aims: To evaluate the effect of temporomandibular arthralgia on mandibular mobility, chewing, and bite force. Methods: Twenty female patients (ages 19 to 45 years) with unilateral temporo-mandibular joint (TMJ) pain during chewing (49 ± 27 mm on a 100-mm visual analog scale) and provocation, as well as TMJ tenderness, were studied. The TMJ conditions were classified as disc derangement disorders (n = 9), osteoarthritis (n = 7), and inflammatory disorders (n = 4). The patients were com pared with matched healthy volunteers without orofacial pain or tenderness. Exclusion criteria were the presence of fewer than 24 teeth or malocclusion. The methods used were (1) algometric assessment of the pressure pain threshold (PPT) over the TMJ; (2) clinical recordings of maximum jaw opening; (3) computerized kinematic assessment of maximum vertical distance, velocity, and cycle duration during chewing of soft gum; and (4) measurement of unilateral molar bite force. Results: The mean (± SD) PPT in the patients' painful side (69 ± 20 kPa; P = .000001) was significantly lower than in the control subjects (107 ± 22 kPa). Jaw opening was also significantly less (P = .00003) in the patients (42 ± 9 mm) than in the controls (52 ± 4 mm). Chewing cycle duration and maximum closing velocity were significantly different (P ≤ .03) in the patients (948 ± 185 milliseconds and 142 ± 46 mm/s, respectively) versus the controls (765 ± 102 milliseconds and 173 ± 43 mm/s, respectively), and bite force was significantly lower (P = .000003) in the patients (238 ± 99 N) than in the controls (394 ± 80 N). Both bite force and jaw opening in patients were significantly correlated (P ≤ .02) with PPT (r = 0.53 and 0.63, respectively). Conclusion: These systematic findings supplement results from acute pain experiments and confirm indications from unspecified patient groups that the clinical presence of long-standing TMJ pain is associated with marked functional impairment. This impairment might be a result of reflex adaptation and long-term hypoactivity of the jaw muscles. [ABSTRACT FROM AUTHOR]

Aims: To test the hypotheses that, in comparison to control, the effects of simultaneous noxious stimulation of the right masseter and anterior temporalis muscles on jaw muscle activity (1) vary with the task; (2) are different between different agonist or antagonist muscles involved in a task; and (3) are correlated with mood or pain-related cognition scores. Methods: In 15 asymptomatic participants, recordings were made of jaw movement and electromyographic (EMG) activity of the right digastric and bilateral masseter and anterior temporalis muscles during standardized open/close and free and standardized chewing tasks. The tasks were repeated in three blocks: block 1 (baseline), block 2 (during simultaneous infusion of 5% hypertonic or 0.9% isotonic saline infusion into the right masseter and anterior temporalis muscles), and block 3 (infusion sequence reversed). The Depression, Anxiety and Stress Scales questionnaire was completed prior to the experiment, and the Pain Catastrophizing Scale was completed before and after the experiment. Linear mixed-effects model analysis compared root mean square (RMS) EMG activity under baseline, hypertonic saline, and isotonic saline (control), and Spearman correlations between RMS and psychologic scores were calculated. P < .05 was considered significant. Results: The significant effects of pain on the activity of a jaw muscle varied with the task, were different between different agonist and antagonist muscles in a task, and were significantly correlated with some of the psychologic scores. Qualitatively, the effects noted in a particular muscle could be different between different participants. Conclusion: Simultaneous noxious masseter and anterior temporalis stimulation results in changes in jaw muscle activity that can vary with the task, the muscle, the participant, and some psychologic variables. [ABSTRACT FROM AUTHOR]

Background: Mastication is one of the most fundamental functions for the conservation of life. The demand for devices for evaluating stomatognathic function, for instance, recording mandibular movements or masticatory muscle activities using animal models, has been increasing in recent years to elucidate neuromuscular control mechanisms of mastication and to investigate the etiology of oral motor disorders. To identify the fundamental characteristics of the jaw movements of mice, we developed a new device that reconstructs the three-dimensional (3D) movement trajectories on an arbitrary point on the mandible during mastication.Methods: First, jaw movements with six degrees of freedom were measured using a motion capture system comprising two high-speed cameras and four reflective markers. Second, a 3D model of the mandible including the markers was created from micro-computed tomography images. Then, the jaw movement trajectory on the certain anatomical point was reproduced by integrating the kinematic data of the jaw movements with the geometric data of the mandible.Results: The 3D movements at any points on the mandible, such as the condyle, molar, and incisor during mastication, could be calculated and visualized with an accuracy > 0.041 mm in 3D space. The masticatory cycle was found to be clearly divided into three phases, namely, the opening, closing, and occlusal phases in mice.Conclusions: The proposed system can reproduce and visualize the movements of internal anatomical points such as condylar points precisely by combining kinematic data with geometric data. The findings obtained from this system could facilitate our understanding of the pathogenesis of eating disorders or other oral motor disorders when we could compare the parameters of stomatognathic function of normal mice and those of genetically modified mice with oral behavioral dysfunctions. [ABSTRACT FROM AUTHOR]

The article provides information on the field of orthodontics, focusing on children suffering from malocclusion, prevention and correction of malpositioned teeth and jaws, improvement of the chewing function and treatment of malocclusion. Topics include use of dental screws, molars and position of anterior tooth.

Copyright of Journal of Craniomandibular Disorders is the property of Quintessence Publishing Company Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Orofacial Pain is the property of Quintessence Publishing Company Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Orofacial Pain is the property of Quintessence Publishing Company Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Orofacial Pain is the property of Quintessence Publishing Company Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Image analysis was used to determine masticatory efficiency and performance before and after placement of immediate dentures. Sections of cored carrot were used as the test food and the particle size of chewed expectorated food was measured using image analysis. Measurements were shown to be accurate and reproducible. Masticatory function of immediate-denture patients was also compared with a similar number of dentate individuals and experienced complete-denture wearers. Dentate subjects were significantly (P < .01) more efficient at masticating the test food than were the completeor immediate-denture wearers. The new method of measurement removes the necessity for the unpleasant and unhygienic sieving process previously used in this type of study. [ABSTRACT FROM AUTHOR]

To investigate the chewing patterns of patients with TMJ disorders, analysis of mandibular movement was performed in 25 normal subjects and 150 patients with stomatognathic dysfunction using the Sirognathograph analyzing system. Patients with TMJ disorders demonstrated different chewing patterns than those of normal subjects. Chewing patterns in the frontal, horizontal, and sagittal projections were classified into four, two, and two different patterns, respectively, and each distinct chewing pattern appeared to be associated with a specific TMJ disorder. [ABSTRACT FROM AUTHOR]

In this investigation of the relationship between mastication and TMJ abnormalities, the movements of the incisal point and condyles during mastication were analyzed in two normal subjects and six patients with unilateral TMJ abnormalities. The path of the nonworking condyle was shorter than that of the working condyle when patients chewed on the side of the normal TMJ, causing the mandible to deviate to the abnormal side at the point of transition from opening to closing. Also, the mobility of the abnormal condyle influenced the convexity of the opening path, and posterior dislocation of the condyle resulted in a crossover chewing pattern. [ABSTRACT FROM AUTHOR]

Mandibular movements and muscle activities during chewing were analyzed in normal subjects under two experimental situations: (1) chewing food with different physical properties (marshmallow, crisp bread, carrot, cheese, and dried cuttlefish) and (2) chewing gum at rates paced by audio signals. Whatever the type of food, both masseteric and digastric bursts were shortened as the chewing rate increased, though the former was more closely related to the chewing rate than the latter. However, when the chewing rate was altered voluntarily, the duration of the digastric burst varied more than the masseteric burst. [ABSTRACT FROM AUTHOR]

The article presents information on orthofunction therapy in complete denture construction. Orthofunction means a denture reconstruction keeping in view the patient's masticatory pattern. In this procedure, occlusion is marked at the midline and by lateral lines in such a way that the marks are visible in the maxillary and in the mandibular rim. After determining the static jaw relations, the patient is asked to make articulation movements. It is stated that the patient's masticatory pattern is very important in making the orthofunction denture. During the mastication test, the patient is fitted with his old denture and given a biscuit to eat. His biting and chewing are observed, and muscle function and mandibular movements are visually assessed.

The article presents a study of mandibular movements and self-propelled changes in proprioceptive movement of mandible as effected by some clinical procedures. The study involved 67 patients with traumatized teeth, cuspal fracture, and general occlusal imbalance problems where K-5 Mandibular Kineseograph, an instrument which use a magnet affixed to mandibular incisors along with acrylic were used to evaluate the presence or absence of non-detectable slides. After few steps, patients were given a solid cracker to chew and their chewing motions were recorded with K-5 Mandibular Kineseograph. The study found that most tooth sliding ceased during mastication and in each cases slide was notably reduced with opening slides and the vertical chewing pattern appeared.

• Tongue-pushing: tongue pushes ingesta laterally during chewing. • We used videofluorography (VFG) in the anteroposterior projection to examine tongue-pushing. • VFG was performed with radiopaque tongue and jaw markers. • Tongue-pushing comprises lateral shift and rotation of the tongue. • The frequency and displacement of tongue-pushing are affected by food consistency. During the mastication of solid food, the tongue pushes the bolus laterally to place it onto occlusal surfaces as the jaw is opened. This movement is referred to as tongue-pushing (TP). TP has an important role in efficient chewing, but its kinematic mechanisms remain unclear. The present study quantified the kinematics of TP and its coordination with masticatory jaw movements. Videofluorography (VFG) in anteroposterior projection was recorded while 14 healthy young adults ate 6 g each of cookies and meat. Small lead markers were glued to the tongue surface (left, right, and anterior) and buccal tooth surfaces (upper molars and lower canines). The position of the tongue and lower canine markers relative to the upper occlusal plane was quantified with Cartesian coordinates, using the right upper molar as the origin. Jaw motion during chewing was divided into TP and Non-TP cycles, based on the lateral movement of the food and tongue markers. The side of the jaw that compressed food particles was defined as the working side, while the other side was termed the balancing side. Horizontal and vertical displacements of tongue and jaw markers were compared between TP and Non-TP cycles, as well as between food types. The mediolateral displacement of all tongue markers was significantly larger in TP than in Non-TP cycles. Vertical displacement was also significantly greater in TP than in Non-TP cycles for the anterior and working side tongue markers. TP cycles occurred more frequently with meat-chewing than with cookie-chewing. TP is accomplished by rotation and lateral movements of the tongue surface on the working side and the anterior tongue blade, along with medial movement on the balancing side. These movements produce lateral shift and rotation of the tongue surface toward the working side in concert with jaw opening. Designing exercises to improve the strength of the lateral motion and rotation of the tongue body may be useful for individuals with impaired tongue function for eating and swallowing. [ABSTRACT FROM AUTHOR]

The article presents case studies of a 46-year-old woman, a 70-year-old woman, and a 38-year-old woman who were diagnosed with medication-related osteonecrosis of the jaw (MRONJ), trigeminal neuralgia (TN), and myogenous pain involving the masticatory muscles. It mentions information on use of lumpectomy and radiation for treatment of MRONJ. It also presents information on importance of the history and clinical examination for determining appropriate treatment.

The occlusal vertical dimension (OVD) in guinea pigs is maintained by tooth eruption and grinding. It has been reported that the experimentally raised OVD recovers to the innate OVD within a few days in guinea pigs. However, the mechanisms underlying OVD adjustment are not entirely understood. This study thus aimed to clarify whether the experimentally reduced OVD would recover. Bite-reduced guinea pigs were created by applying bilateral intermaxillary elastics for 10 days. Guinea pigs without elastics were used as a control. The OVD after removal of the elastics in the experimental group was compared with that of the control group. Jaw movement during chewing was also compared between the experimental and control groups. After removal of the elastics, the experimentally reduced OVD did not recover fully and a significant difference was observed between the experimental and control groups for up to 25 days during the recording period. The minimum closed position during chewing was significantly higher in the experimental group than in the control group, whereas the maximum open position was no different between the groups. The present findings indicated that the experimentally reduced OVD could not be fully recovered, suggesting that reduction of the OVD may have limited influence on jaw movement. [ABSTRACT FROM AUTHOR]

Disorder in chewing food is a major problem in patients with stroke, some of those who suffer from brain lesion, multiple sclerosis, and other diseases such as head and neck cancer. This kind of disorder causes significantly decreased food consumption and consequently malnutrition or dehydration and in severe cases leads to suffocation. It can also increase the rate of death during the first year after the stroke to 45%. Therefore, finding an appropriate and common pattern of cooperation of jaw muscles in the act of chewing can have a very important role in assisting the process of rehabilitation in these patients. In this article, to improve current rehabilitation techniques for patients with chewing problems, attempts have been made to investigate the physiology of human chewing and involved muscles in this process. Extracting synergy patterns of jaw muscles during chewing action was also carried out in this article using analysis of the main components of electromyogram signal and quantification of muscle activity. The results show that each individual applies the same motion during different times for chewing action. Moreover, cooperation and interaction of the involved muscles are maintained in this process during various times in which the share of masseter muscle is more than temporal one in this collaboration. [ABSTRACT FROM AUTHOR]

Objective This study assessed the reliability and validity of masticatory function assessment using a new test food, Optozeta. Design Thirty-five adults participated in the cross-sectional clinical part of the study; ten of them performed a retest. They performed two free-style masticatory tests consisting of five trials of 20 cycles each chewing three pieces of Optosil or Optozeta placed in a latex bag. Optozeta was created by mixing 50% Optosil with 50% of Zetalabor. Masticatory performance, masticatory laterality and chewing rate were assessed. Reliability and construct validity were assessed using the intraclass correlation coefficient (ICC) and Spearman correlations, respectively. Results Higher ICC values were observed for each aspect of masticatory function as assessed using Optozeta compared with Optosil. All the participants showed a lower median particle size value using Optozeta than Optosil. For each masticatory parameter, a high correlation was observed between using Optosil or Optozeta. Conclusions Optozeta seems to have good construct validity and appears to be more reliable than Optosil as a test food to assess masticatory function. [ABSTRACT FROM AUTHOR]