Masticatory Movements Research Articles

Optogenetic activation of serotonergic neurons changes masticatory movement in freely moving mice

Optogenetic activation of serotonergic neurons changes masticatory movement in freely moving mice

Gross Anatomy of the Equine Masseter Muscle: Lamination and Intramuscular Course of the N. Massetericus.

The masticatory muscles of the horse are arranged in an asymmetrical pattern. Four individual muscles on the medial side of the mandible are opposed by one muscle (M. masseter) on the lateral side. However, recent studies on various herbivorous mammals indicate that the masseter muscle features a complex stratigraphic structure that might account for a functional diversity resembling an arrangement of several individual muscles. The functional consideration of the multidirectional equine masticatory movements leads to a similar hypothesis. In order to elucidate the detailed anatomy of the equine masseter muscle, eight cadaveric equine heads were dissected. Additional 29 skull specimens were assessed with regard to the masseteric attachment within the Fossa masseterica. A constant arrangement of nine individual muscular layers within the masseteric muscle was determined. The individual layers were clearly separated by tendon plates and their attachment areas at the masseteric fossa of the mandible were arranged in a constant pattern of bony ridges. With similar consistency, the main trunk of the masseteric nerve was found to run from dorsocaudal to ventrorostral: On that course, the nerve penetrated between the muscular layers from medial to lateral at constant positions. The findings of this study serve as a basis for further studies with the aim of developing biomechanical concepts of equine masticatory movement.

The anatomy of mastication in a toothless mammal: Morphological characteristics of the temporomandibular joint in the platypus (Ornithorhynchus anatinus)

AbstractThe temporomandibular joint (TMJ) is a distinguishing feature of mammals, and in most mammals includes an articular disc that buffers the loads placed on it by mastication. The disc is well developed in mammals with significant lateral masticatory jaw movements but is absent in toothless mammals, including extant monotremes, although histological studies of developing monotremes have shown rudimentary discs that fail to mature. Platypus (Ornithorhynchus anatinus) grind their food between keratinous pads in the maxillae and lower jaws and are the only edentulate mammals that masticate their food. In this study, we characterize the anatomy of the TMJ of the adult platypus to see if we can reconcile the anatomy, including the absence of the articular disc, with the mandibular movements observed in video recordings. We studied the gross anatomy of the maxillofacial region and the microstructure using microcomputed tomography (micro‐CT) and histological examination. Platypuses had well‐developed masticatory muscles but lacked an articular disc between the mandibular condyle and glenoid fossa. The surface of the glenoid fossa was slightly concave than that of the condylar head was correspondingly slightly convex. The pre‐ and postglenoid processes were not well developed. Micro‐CT showed dense trabecular bone in the anterior part of the condyle, where the lateral pterygoid muscle attached. Histological analysis showed that the surfaces of the condyle and glenoid fossa consisted of dense, avascular and thickened fibrous connective tissue. In addition, well‐developed synovial folds were present. These anatomical characteristics are consistent with both anterior and lateral movements of the mandible, while the thick layer of connective tissue substitutes for a disc by absorbing the mechanical stresses associated with mastication. The failure of the disc primordium to develop cannot be attributed to a lack of muscle development, but the distribution of stresses in the toothless platypus jaw is likely to be different from those in a masticating eutherian.

Ontogeny of the masticatory muscles in the opossum Didelphis albiventris (Marsupialia, Didelphimorphia, Didelphidae).

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.

ВЛИЯНИЕ ПРОЦЕССА ЖЕВАНИЯ НА ГЕМОДИНАМИЧЕСКИЕ ПОКАЗАТЕЛИ

Chewing has been shown to have a significant effect on systemic circulation, with circulatory responses appearing to be largely regulated by autonomic nervous activity through a more complex regulatory system than responses to other activities. However, the results of studies on the relationship between masticatory movements and changes in autonomic nervous activity and systemic circulation are still rare and contradictory. We examined changes in systemic circulation during gum chewing. Blood pressure, heart rate, and chewing electromyograms were recorded during continuous gum chewing as indicators of systemic circulation in 27 healthy subjects with normal occlusion. Nonparametric matched-sample analyzes were performed to determine the chronological changes in each variable during gum chewing, and nonparametric Spearman correlations were calculated to assess the relationship between changes in hemodynamic parameters and masticatory muscle activity. Chewing gum increased heart rate and blood pressure, indicating significant changes in sympathetic activity and vagal tone. We have identified a pronounced, statistically significant strong correlation between changes in heart rate and the magnitude of contractions of the masticatory muscles. These results suggest that changes in the activity of parts of the autonomic nervous system may be due to the trigeminal nerve reflex, which explains some of the features of the autonomic nervous regulation of chewing movements.

Development of a pressure acquisition system for detecting mandibular movements in ruminants

Livestock farming is responsible for producing much of the animal protein that humans consume. Estimates of significant growth in the world population over the years highlight a demand not only for the expansion of animal production but also for an increase in livestock efficiency. To achieve this, one of the essential factors is improving the nutrition process, with the analysis of the ingestive behavior of ruminants being essential. Therefore, this work presents the development of a system for acquiring, storing, and transmitting signals from a pressure sensor for monitoring and evaluating masticatory movements in ruminants. This system employs a pressure sensor to obtain signals relating to chewing movement. A microcontroller acquires these signals at a sampling frequency of 100 Hz, and the resulting data are transmitted to a smartphone via Bluetooth and stored in a memory card for later analysis. Preliminary bench tests were carried out with the system installed on a full-size prototyped bovine head. Compression movements were applied to a silicone tube, causing pressure variations in the sensor. By transmitting the data to a smartphone via Bluetooth, it was possible to check the signal, adjust the gain of the instrumentation amplifier, and achieve the best positioning of the silicone tube in the mouthpiece. By reading the data recorded on a memory card, it was possible to obtain the signal profile, graphically demonstrating that the signal corresponds to the typical profile for this type of sensor.

Development of Highly Flexible Piezoelectric PVDF-TRFE/Reduced Graphene Oxide Doped Electrospun Nano-Fibers for Self-Powered Pressure Sensor.

The demand for self-powered, flexible, and wearable electronic devices has been increasing in recent years for physiological and biomedical applications in real-time detection due to their higher flexibility and stretchability. This work fabricated a highly sensitive, self-powered wearable microdevice with Poly-Vinylidene Fluoride-Tetra Fluoroethylene (PVDF-TrFE) nano-fibers using an electrospinning technique. The dielectric response of the polymer was improved by incorporating the reduced-graphene-oxide (rGO) multi-walled carbon nano-tubes (MWCNTs) through doping. The dielectric behavior and piezoelectric effect were improved through the stretching and orientation of polymeric chains. The outermost layer was attained by chemical vapor deposition (CVD) of conductive polymer poly (3,4-ethylenedioxythiophene) to enhance the electrical conductivity and sensitivity. The hetero-structured nano-composite comprises PVDF-TrFE doped with rGO-MWCNTs over poly (3,4-ethylenedioxythiophene) (PEDOT), forming continuous self-assembly. The piezoelectric pressure sensor is capable of detecting human physiological vital signs. The pressure sensor exhibits a high-pressure sensitivity of 19.09 kPa-1, over a sensing range of 1.0 Pa to 25 kPa, and excellent cycling stability of 10,000 cycles. The study reveals that the piezoelectric pressure sensor has superior sensing performance and is capable of monitoring human vital signs, including heartbeat and wrist pulse, masticatory movement, voice recognition, and eye blinking signals. The research work demonstrates that the device could potentially eliminate metallic sensors and be used for early disease diagnosis in biomedical and personal healthcare applications.

A Finite Element Analysis Study of Edentulous Model with Complete Denture to Simulate Masticatory Movement.

The purposes of this study are to establish and validate a finite element (FE) model using finite element analysis methods and to identify optimal loading conditions to simulate masticatory movement. A three-dimensional FE model of the maxillary and mandibular cortical bone, cancellous bone, and gingiva was constructed based on edentulous cone-beam-computed tomography data. Dental computer-aided design software was used to design the denture base and artificial teeth to produce a complete denture. Mesh convergence was performed to derive the optimal mesh size, and validation was conducted through comparison with mechanical test results. The mandible was rotated step-by-step to induce movements similar to actual mastication. Results showed that there was less than a 6% difference between the mechanical test and the alveolar bone-complete denture. It opened 10° as set in the first stage, confirming that the mouth closed 7° in the second stage. Occlusal contact occurred between the upper and lower artificial teeth as the mouth closed the remaining angle of 3° in the third stage while activating the masseter muscle. These results indicate that the FE model and masticatory loading conditions developed in this study can be applied to analyze biomechanical effects according to the wearing of dentures with various design elements applied.

Factors Related to Masticatory Rhythm in Patients with Oral Tumors.

Background: Older adults who have undergone surgery for oral tumors are at increased risk of impaired masticatory rhythm. This study investigated the correlations between masticatory rhythm, objective masticatory performance, and subjective masticatory performance as well as factors related to masticatory rhythm. Methods: The participants were 44 adults (24 men, 20 women; age range 42~90 years old) who had undergone maxillectomy, mandibulectomy, or glossectomy and were rehabilitated with a maxillofacial prosthesis. The number of functional contact teeth pairs was confirmed by intraoral examination. Chewing rate, cycle duration, coefficient of variation (CV) for cycle duration (reflecting the stability of masticatory rhythm), and mixing ability were measured simultaneously using a mastication movement rhythm tracking device during gum chewing. Maximum occlusal force was measured using the dental prescale system. Patients' perception of chewing ability was rated using a questionnaire. Results: The Spearman's rank correlation test revealed that mixing ability, patient-rated masticatory scores, cycle duration, CV for cycle duration, and maximum occlusal force showed significant correlations with chewing rate. Multiple linear regression analysis identified mixing ability and the CV for cycle duration as significant predictors of masticatory rhythm. Conclusions: Factors associated with a faster chewing rate were higher mixing ability and masticatory scores, greater maximum occlusal force, shorter cycle duration, and smaller CV for cycle duration. Stable masticatory rhythm and mixing ability are significant predictors of chewing rate. Poor masticatory performance and unstable masticatory rhythm can result in slower chewing and thus a higher risk of inadequate dietary intake.

The impact of an approach incorporating myofunctional therapy of the masticatory system movement on the motor efficiency of a patient after a subarachnoid hemorrhage to the left hemisphere of the brain – A case study

This paper analyzes the case of a 46-year-old woman who suffered a subarachnoid hemorrhage to the left hemisphere of the brain with penetration into the ventricular system from a ruptured aneurysm of the left middle cerebral artery (cardiac arrest, critical condition, GCS 4), followed by subsequent paralysis of the lower and upper right limbs and aphasia. Data collected during a 2-year therapy process were analyzed, including examinations of the stomatognathic system, analysis of the axes and planes of the facial cranium in relation to the joint structures of the movement system, observations of the interactions of tissue structures as well as mandibular-hyoid and lingual structures, analysis of Angle’s classifications, analysis of imaging studies of the orofacial zone and neck muscle tension, results of periodic functional tests, including manual functional analysis of the masticatory system movement. A vision analysis of the material was performed using ShapeCare.Physio equipment with Blaze Pose software based on a model for detecting the skeleton of a moving person. It was found that treatment including myofunctional therapy of the masticatory system movement contributed to the improvement of the patient's motor efficiency after suffering a subarachnoid hemorrhage to the left hemisphere of the brain and after a frontotemporo-parietal craniotomy.

Progressive thalamic nuclear atrophy in blepharospasm and blepharospasm-oromandibular dystonia.

The thalamus is considered a key region in the neuromechanisms of blepharospasm. However, previous studies considered it as a single, homogeneous structure, disregarding potentially useful information about distinct thalamic nuclei. Herein, we aimed to examine (i) whether grey matter volume differs across thalamic subregions/nuclei in patients with blepharospasm and blepharospasm-oromandibular dystonia; (ii) causal relationships among abnormal thalamic nuclei; and (iii) whether these abnormal features can be used as neuroimaging biomarkers to distinguish patients with blepharospasm from blepharospasm-oromandibular dystonia and those with dystonia from healthy controls. Structural MRI data were collected from 56 patients with blepharospasm, 20 with blepharospasm-oromandibular dystonia and 58 healthy controls. Differences in thalamic nuclei volumes between groups and their relationships to clinical information were analysed in patients with dystonia. Granger causality analysis was employed to explore the causal effects among abnormal thalamic nuclei. Support vector machines were used to test whether these abnormal features could distinguish patients with different forms of dystonia and those with dystonia from healthy controls. Compared with healthy controls, patients with blepharospasm exhibited reduced grey matter volume in the lateral geniculate and pulvinar inferior nuclei, whereas those with blepharospasm-oromandibular dystonia showed decreased grey matter volume in the ventral anterior and ventral lateral anterior nuclei. Atrophy in the pulvinar inferior nucleus in blepharospasm patients and in the ventral lateral anterior nucleus in blepharospasm-oromandibular dystonia patients was negatively correlated with clinical severity and disease duration, respectively. The proposed machine learning scheme yielded a high accuracy in distinguishing blepharospasm patients from healthy controls (accuracy: 0.89), blepharospasm-oromandibular dystonia patients from healthy controls (accuracy: 0.82) and blepharospasm from blepharospasm-oromandibular dystonia patients (accuracy: 0.94). Most importantly, Granger causality analysis revealed that a progressive driving pathway from pulvinar inferior nuclear atrophy extends to lateral geniculate nuclear atrophy and then to ventral lateral anterior nuclear atrophy with increasing clinical severity in patients with blepharospasm. These findings suggest that the pulvinar inferior nucleus in the thalamus is the focal origin of blepharospasm, extending to pulvinar inferior nuclear atrophy and subsequently extending to the ventral lateral anterior nucleus causing involuntary lower facial and masticatory movements known as blepharospasm-oromandibular dystonia. Moreover, our results also provide potential targets for neuromodulation especially deep brain stimulation in patients with blepharospasm and blepharospasm-oromandibular dystonia.

Jawline Aesthetic Definition: Enhancement with Masseteric Augmentation Using Ultrasound-Guided Fat Transfer

Background: The rejuvenation and restoration of a well-defined jawline contour are crucial for enhancing facial aesthetics in both men and women. Within the jawline aesthetic unit (mandibular angle), the masseter muscle plays a significant role, as it is responsible for mandibular masticatory movements. We propose a new approach using ultrasound-guided intramuscular fat transfer to enhance the mandibular angle and jawline. Methods: The multicenter study included 20 patients from three countries (Peru, Brazil, and Mexico). After fat harvesting, the ultrasound-guided masseteric fat transfer was performed with a 1.5-mm Viaro cannula from an incision beneath the ear lobule. The fat was then injected intramuscularly into the masseter at each side of the mandibular angle. Results: Masseter ultrasound-guided fat transfer was performed on 10 men and 10 women between 2021 and 2022. The patients had a mean age of 34.4 ± 6.39 years and a mean body mass index of 22.39 ± 2.59 kg per m2. The mean injected volume was 5.83 mL and 5.58 mL on the right and left sides, respectively. Muscle thickness increased in patients immediately postsurgery, but decreased after 1 month. The muscle remained significantly thicker on each side than the presurgery measurements in patients regardless of gender (both P < 0.0001). Conclusions: Ultrasound-guided intramuscular fat transfer is a safe and reproducible technique for enhancing the jawline contour at the mandibular angle. We believe that it could be a more durable solution than other procedures, although further evaluation of long-term results is necessary.

Characterization of red algae (Gracilaria verrucosa) on potential application for topical treatment of oral mucosa wounds in Rattus norvegicus.

Wound healing in the mouth has its challenges due to masticatory movements and the presence of bacteria that can inhibit its process. The aim of this study was to analyze the contents of red algae (Gracilaria verrucosa) from Indonesia, and its potential as a wound-healing agent for oral wounds using animal model. Red algae content was determined by phytochemical tests and gas chromatography-mass spectroscopy (GC-MS). The wound was made by making an incision on the gingival mucosa of Rattus norvegicus and the parameters assessed were bleeding time, number of fibroblast cells, and time of wound closure. Three doses of G. verrucosa gel were used (2.5%, 5%, and 10%) and the gels were applied twice a day, at 6:00 and 18:00. Application was carried out topically by applying 0.1 ml of gel to the incision wound using a 1 mL syringe. Our phytochemical test indicated that the G. verrucosa contained alkaloids, steroids, flavonoids, and phenols. The dominant contains of the G. verrucosa were glycerol (36.81%), hexadecenoic acid (20.74%), and cholesterol (7.4%). The hemostasis test showed that the 2.5% G. verrucosa extract gel had the shortest bleeding time, 33.98±2.66 seconds. On the seventh day of the initial proliferation phase, the number of fibroblasts was not significantly different among groups. On day 14, the number of fibroblasts was only significantly different between 10% G. verrucosa and untreated group (p=0.007). On day 28, however, both 5% and 10% G. verrucosa were significantly higher compared to untreated group, both had p=0.010. Daily clinical examination showed that animals that were given 2.5% and 5% of G. verrucosa extract gel experienced wound closure on day 10. Animals treated with 10% of extract gel, all wounds healed on day 9. This study suggested that G. verrucosa extract could accelerate wound closure and wound healing.

Temporomandibular joint biomechanics and equine incisor occlusal plane maintenance.

In equine dentistry, the physiological incisor occlusal surface is visually perceived as a plane with a distinct inclination to the head's coronal plane, extending rostro-ventrally to caudo-dorsally. To better understand the formation of this inclined plane and its connection to dental wear, we investigated the hypothesis that it arises from masticatory movements and the considerable distance between mandibular articular heads and the incisor occlusal surfaces, acting as the three points of support for the mandibles. Leveraging data from a large-scale clinical study involving static and dynamic orthodontic measurements in horses, we approximated the mandibular movement range where incisor occlusion and dental wear occur. By introducing and testing a segment coordinate system, we explored possible angular deviations from the occlusal plane caused by mandibular roll and pitch rotations during two lateral mandibular movement patterns, protrusion and retrusion. Theoretical biomechanical calculations and simulations confirmed the visual perception of the incisor occlusal surface as a plane. To further examine our assumptions, we employed a simple mechanical simulator to assess incisor normal occlusion and provoked malocclusions (diagonal, smile, and frown bite) by modifying temporomandibular joint (TMJ) movement patterns. The results from clinical investigations were corroborated by both the theoretical analysis and mechanical simulations, strengthening our understanding of the biomechanical basis behind the physiological incisor occlusal plane maintenance in horses. These findings have significant implications for equine dental health and contribute to a thorough understanding of TMJ dynamics.

Kinematics of lateral tongue-pushing movement in coordination with masticatory jaw movement: An anteroposterior projection videofluorographic study

ObjectiveDuring 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. MethodsVideofluorography (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. ResultsThe 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. ConclusionTP 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.

Effect of masticatory movements on head and trunk sways, and sitting and foot pressure distributions during sitting position.

The purpose of this study was to test the hypothesis in healthy subjects that masticatory movements affect head and trunk sways, and sitting and foot pressure distributions during sitting position. A total of 30 healthy male subjects with an average age of 25.3 years (range, 22-32 years) were evaluated. The CONFORMatTM and MatScanTM system were used to analyze changes in sitting pressure distribution (center of sitting pressure: COSP) and changes in foot pressure distribution (center of foot pressure: COFP) respectively, and the 3-dimensional motion analysis system was used to analyze changes in head and trunk postures while subjects remained sitting position with rest position, centric occlusion, and chewing. The total trajectory length of COSP/COFP, COSP/COFP area, and head and trunk sway values were compared between the three conditions to evaluate whether masticatory movement affected the stability of head and trunk sways, and sitting and foot pressure distributions. Total trajectory length of COSP and COSP area during chewing were significantly shorter and smaller respectively than it was in rest position and centric occlusion (p < 0.016). Head sway value during chewing was significantly larger than it was in rest position and centric occlusion (p < 0.016). Masticatory movements affect sitting pressure distribution and head movements during sitting position.

Masticatory mechanisms, dental function, and diet in Triassic trilophosaurids (Reptilia: Allokotosauria)

Documenting evidence of feeding behavior in extinct vertebrates is crucial to understanding trophic structure and stability of ecosystems over periods of Earth's history. Direct evidence of trophic interactions in the fossil record is rare, but proxies like dental microwear enable testable hypotheses of feeding behavior in extinct taxa. Here we present new evidence on the masticatory apparatuses and feeding behaviors of Late Triassic (Norian) trilophosaurid reptiles from southwestern North America based on Scanning Electron Microscope (SEM) observation and quantitative analysis of dental microwear in isolated teeth and dentigerous elements. Trilophosaurids are a Late Triassic archosauromorph group known from Europe and North America with distinctive labiolingually expanded teeth that are usually tricuspid; this clade is hypothesized to be herbivorous based on qualitative comparisons of their dentition to those of living taxa. Our study is among the first to infer their diet within a quantitative comparative framework. Analysis of pit-to-scratch ratios (a proxy for the hardness/toughness of dietary intake) indicate dietary disparity between the three examined trilophosaurid taxa, possibly driven by differing plant preferences. Analysis of scratch orientations, caused by contact between opposite teeth during jaw closure (a proxy for the direction of masticatory movements), may suggest derivation of a masticatory mechanism including labiolingual movement in Trilophosaurus, differing from the orthal jaw closure mechanism ancestral to archosauromorphs that is likely conserved in the sister group to Trilophosauridae, the Azendohsauridae. Variance in dental microwear patterns between the sampled taxa suggests potential herbivore niche space partitioning amongst North American trilophosaurids during the Norian. Furthermore, microwear evidence for complex masticatory movement in trilophosaurids may suggest previously unknown craniomandibular specializations, highlighting the need for reexamination of trilophosaurid craniomandibular morphology and jaw closure mechanics.

Mechanical Resistance of Different Implant Suprastructures: A Laboratory Study

Background: Appropriate abutment selection according to the individual specificities of each patient is a leading factor in achieving high aesthetic results. Standardized titanium abutments are the most widely used due to their easy use and low cost. It is considered that customized abutments can eliminate many of the complications seen with factory abutments in prosthetic treatment. The purpose of this study is to evaluate whether customized abutments have better mechanical behavior in laboratory settings than standard ones. The null hypothesis is that customized abutments have better resistance to cyclic load and compression than factory abutments. Methods: The study model includes thirty implant suprastructure samples, fabricated digitally, divided into three groups according to the type of implant abutment and the used material: Group A (control group) comprised monolithic implant crowns made of zirconium dioxide and a titanium base; Group B (test group) comprised monolithic implant crowns made of zirconia implant crowns and a customized titanium alloy abutment; and Group C (test group) comprised monolithic implant crowns made of lithium disilicate and a customized titanium alloy abutment. The samples were subjected to dynamic load in a computer-controlled 2-axis machine that simulated masticatory movements, Chewing Simulator CS-4 (SD-Mechatronik, Westerham, Germany), for 250,000 cycles at a frequency of 2 Hz. The samples were then subjected to compressive strength testing in an Instron M 1185 universal testing machine. A metal steel disc was used as an antagonist, exerting pressure at a rate of 2 mm/min at room temperature on each sample. After conducting the laboratory tests, the samples were examined by an experienced expert under a Carl Zeiss microscope (Carl Zeiss Microscopy GmbH, Jena, Germany). Results: All samples were found to have passed the fatigue test in the masticatory simulator without any of the listed complications. The average value of the compressive strength at which the structures in each group fracture is as follows: Group A, 5669.2; Group B, 3126.5; and Group C, 1850.6. Based on the average values, it can be concluded that the combination of materials used in Group A has the greatest resistance. Conclusion: The weak link in the prosthetic complex consisting of a crown and abutment seems to be the crown. No abutment failure was found regardless of the type. However, monolithic zirconia crowns over standard titanium abutments withstand higher mechanical forces compared with zirconia and lithium disilicate crowns over customized ones. Detailed studies in clinical settings may provide more in-depth information on this issue.

Analysis of Feeding Behavior Characteristics in the Cu/Zn Superoxide Dismutase 1 (SOD1) SOD1G93A Mice Model for Amyotrophic Lateral Sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is a progressive disease affecting upper and lower motor neurons. Feeding disorders are observed in patients with ALS. The mastication movements and their systemic effects in patients with ALS with feeding disorders remain unclear. Currently, there is no effective treatment for ALS. However, it has been suggested that treating feeding disorders and improving nutritional status may prolong the lives of patients with ALS. Therefore, this study elucidates feeding disorders observed in patients with ALS and future therapeutic agents. We conducted a temporal observation of feeding behavior and mastication movements using an open-closed mouth evaluation artificial intelligence (AI) model in an ALS mouse model. Furthermore, to determine the cause of masticatory rhythm modulation, we conducted electrophysiological analyses of mesencephalic trigeminal neurons (MesV). Here, we observed the modulation of masticatory rhythm with a prolonged open phase in the ALS mouse model from the age of 12 weeks. A decreased body weight was observed simultaneously, indicating a correlation between the prolongation of the open phase and the decrease observed. We found that the percentage of firing MesV was markedly decreased. This study partially clarifies the role of feeding disorders in ALS.

Functional Differences between Chewing Sides of Implant-Supported Denture Wearers

Humans are said to have habitual and non-habitual chewing sides; however, the functional differences between the chewing sides of implant-supported denture wearers have not been sufficiently clarified. This study aimed to clarify the presence or absence of functional differences between the chewing sides in implant-supported denture wearers. Forty-five patients with bilateral posterior implants were included in this study. The participants were asked to chew a gummy jelly on one side, and the masticatory movement was recorded using a Motion Visi-trainer (MVT V1). For 10 cycles from the fifth cycle after the start of mastication, the pattern of the movement path, the opening distance, the masticatory width, and the cycle time were calculated as parameters of masticatory movement. The amount of glucose eluted during the chewing of gummy jelly was measured and used as a parameter of masticatory performance. Each parameter representing masticatory movement and masticatory performance was compared between the right and left chewing sides and between the habitual and non-habitual chewing sides using a chi-squared test or a paired t-test. There was no difference in the frequency of masticatory path patterns between the right and left chewing sides. Most participants had a normal pattern on the habitual chewing side; however, abnormal patterns were also observed on the non-habitual chewing side. When comparing right and left chewing, no significant difference was observed between chewing sides in terms of opening distance, masticatory width, cycle time, or amount of glucose eluted (p &gt; 0.05). When comparing the habitual and non-habitual chewing sides, masticatory movement on the habitual chewing side showed a larger opening distance (p &lt; 0.001) and masticatory width (p = 0.008), shorter cycle time (p = 0.004), and higher masticatory performance (p &lt; 0.001). It was suggested that there is a functional difference between the habitual and non-habitual chewing sides in the masticatory movement and masticatory performance of implant-supported denture wearers.