Jaw System Research Articles

Efficiency of chewing load deficiency correction in clinical dental practice

Weakening of the chewing act, typical for modern humans due to consumption of soft food, causes a deficit of chewing load and has a negative effect on the dental system. To combat hypodynamia of the masticatory apparatus with the aim of preventing destructive processes in its structures, a gnathotraining system was developed, including electrical stimulation of the masticatory muscles themselves in physiological parameters, which develops the effect of “imaginary chewing”, and gnathotraining using chewing gum. In addition, functional training of the masticatory apparatus using chewing exercises was proposed. Considering that chewing gum practically does not compensate for the deficit of chewing load observed in modern society, the staff of the Kazan State Medical University and the Kazan National Research Technological University developed the “Denta Fit” dental trainer and a dental training system. It has been established that dental and jaw training stimulates secretion of saliva, its mineralizing potential, functional resistance of tooth enamel, allows achieving a good level of oral hygiene, reduces the rate of increase in the intensity of dental caries, as well as the severity of muscular-articular disorders of the temporomandibular joints, enhances neuromuscular activity of the masticatory muscles and regional blood flow. In children with permanent bite, dental and jaw training maintains the hydrogen index (pH) of oral fluid at a neutral level and provides, in combination with a toothbrush, optimal hygienic dental care, contributes to the formation of a correct dental occlusion. Thus, the effects of increased neuromuscular activity of the masticatory muscles, as well as regional vascular tone, arising during dental and jaw training, indirectly indicate that the dental and jaw system receives adequate mechanical loads necessary for the normal functioning of all its links. The results of the conducted studies indicate the effectiveness and feasibility of using dental training to improve dental status, which serves as a new approach to the prevention and treatment of dental diseases.

Balanced approach to correcting distal bite in children: the role of chewing-mimic therapy

Annotation. This scientific research focuses on analyzing a balanced approach to correcting distal bite in children and determining the significance of chewing-mimic therapy in this context. The article thoroughly examines key aspects related to distal bite issues and proposes effective correction strategies to achieve optimal results. The authors emphasize the importance of a comprehensive treatment approach, with chewing-mimic therapy playing a pivotal role. The research results illustrate the success of employing this method in improving the condition of patients with a distal bite, underscoring the relevance of implementing such an approach in the clinical practice of dentists and orthodontists. This not only enhances treatment outcomes but also ensures the optimal development of the dental and jaw system in children, particularly crucial in the early stages of growth and development. The analysis conducted in this article not only unveils key aspects of a balanced approach to correcting distal bite in children and the role of chewing-mimic therapy but also has the potential to chart new paths for the development of modern treatment methods in dentistry and orthodontics. The obtained results are valuable for professionals in the field, aiding them in a deeper understanding of the mechanisms involved in treating distal bite and optimizing outcomes. The coverage of this topic in the literature indicates the relevance and importance of studying this aspect in pediatric dentistry, as accurately identified and effectively applied methods can have a far-reaching impact on the oral health of children. Further scientific research and exploration of this topic in the literature can contribute to refining treatment methodologies by incorporating new knowledge and innovations. It is crucial to note that this work can serve as a foundation for future scientific research and articles, expanding our understanding of effective methods for correcting distal bite and their influence on the dental and jaw system’s health in childhood.

Accuracy and reliability for estimating jaw functional range of motion

BackgroundThree dimensional (3D) kinematic analysis based on motion capture can study synchronized data from the integrated jaw and neck motor system. Jaw function is commonly estimated on linear outcome variables of motion range. By combining jaw border movements in three planes the functional range of motion could be described by movement area and volume measures. Research questionCan we ensure the accuracy, test-retest reliability, and intra-individual variability with 3D kinematic analysis for estimating jaw functional range of motion (ROM), including jaw movement area and volume and jaw and head linear measures? MethodsAccuracy was estimated by applying the method to a set of beakers with known volume, based on the percentage deviation and Pearson correlation coefficient between target and estimated values. Test-retest reliability was then analysed on maximum jaw movements performed in a pre-determined movement sequence by 17 pain-free participants (25.4 years ± 2.4) to estimate jaw functional ROM. Intraclass correlation coefficients (ICC) were calculated, and Bland-Altman plots were constructed. Coefficient of variation (CV) tested the within session reliability. ResultsThe accuracy in volume and area measurements were high with a percentage deviation (0.03±0.59) and (1.2±0.45), respectively, with a strong linear relationship (R2=0.99) between target and estimated values. The test-retest reliability showed moderate to excellent reliability, and Bland-Altman plots showed good agreement. Overall, CVs showed high repeatability, but jaw movements in horizontal directions were less reliable and presented higher variability. SignificanceThe study with 3D kinematic analysis of jaw functional ROM, provides a methodological basis for accurate and reliable measurements. The study presents a new way to estimate jaw functional ROM measures, useful for evaluation in clinical intervention, for instance in pain and jaw dysfunction. Moreover, the natural biological movement variability and the complexity of the interplay of jaw-head movement will be emphasised.

Can temporomandibular disorder symptoms and headaches be prevented in 13- to 15-year-old girls by information provided in a school setting?

Temporomandibular disorders (TMD) may develop, especially among girls, during the adolescence period. The aim of this study was to study if information and advice in a school setting could prevent development of TMD symptoms and headaches during the early teenage period. Thirteen-year-old girls, at 19 upper elementary schools were invited to participate in a study with structured information about the jaw system, TMD symptoms and risk factors, as well as advice how to manage risk factor and TMD. Six hundred and fifty-one girls enrolled, of which 507 girls were followed for 2-2.5 years. Half received information on three occasions (cases), and the other half served as controls. Included in the analysis of incidence of TMD symptoms were those without frequently occurring TMD symptoms (not including headaches) at baseline (n = 396) and included in the analysis of incidence of headaches were those without frequent headaches at baseline (n = 297). The 2-year incidence of TMD symptoms was significantly lower in the information cohort (19%) compared to the controls (28%) (p = .03). The 2-year incidence of headaches was lower among those who were allocated to information (30%) compared to controls (40%), but the difference was not statistically significant (p = .099). Cases who had headaches at baseline reported a significantly lower prevalence at follow-up compared to controls (p = .03). Standardized information in school settings can prevent development of TMD symptoms and headaches among young girls.

Cranial muscle architecture in wild boar: Does captivity drive ontogenetic trajectories?

The jaw system in mammals is complex and different muscle morphotypes have been documented. Pigs are an interesting group of animals as they are omnivorous and have a bunodont crushing dentition. Moreover, they have interacted with humans for over 10,000 years and grow nearly two orders of magnitude in size. Despite being a model system for studies on cranial form and function, data on the growth of the jaw adductor muscles are scant. Moreover, whether captivity impacts the growth and architecture of the jaw adductors remains unknown. Based on dissection data of the jaw adductors of 45 animals ranging from less than 1 kg to almost 100 kg, we show that muscle masses, muscle fiber lengths, and cross-sectional areas scale as predicted for geometrically similar systems or with slight negative allometry. Only the fiber length of the lateral pterygoid muscle grew with slight positive allometry. Animals raised in captivity in stalls or in an enclosure were overall very similar to wild animals. However, some muscles were larger in captive animals. Interestingly, variation in bite force in captive animals was well predicted by the variation in the size of the superficial masseter muscle relative to the overall jaw adductor mass.

Вивчення кореляційних зв’язків між стоматологічною патологією та головним болем у дорослих пацієнтів (огляд літератури)

Introduction. Headache is the sixth leading cause of disability worldwide and the third leading cause of disability among people aged 50 years and older. Primary headaches are accompanied by a complex of musculoskeletal orofacial pain known as temporomandibular disorders (TMD). At the same time, the Diagnostic Criteria for TMD (DC/TMD) defined the category of secondary “headache associated with TMD” (HATMD). Purpose: based on the analysis of literary sources, to determine correlations between pathological conditions of the dental and jaw system and headache in adult patients. Materials and methods. Information search and analysis of scientific sources was carried out using scientometric databases Web of Science, PubMed, Google Scholar over the past 15 years. Conclusion. The results of numerous scientific studies presented in the review confirm the existence of correlations between pathological conditions of the maxillofacial system and headache in adult patients and the need for a multidisciplinary approach to their complex treatment. Key words: headache, orofacial pain, temporomandibular disorders, periodontal tissue pathology, bruxism.

Результат комплексного подхода к диагностике и лечению коморбидного пациента: клинический случай

AIM. Show the feasibility and possibility of diagnosing and treating a comorbid patient (neurology, dentistry) MATERIAL AND METHODS. Clinical example of a patient with concomitant pathology; dynamic observation for 5 years. CASE PRESENTATION. A male patient has been observed in the clinic for 5 years. The positive dynamics of neurological and dental statuses as a result of therapeutic measures is shown. Undifferentiated connective tissue dysplasia was revealed, manifested by the following symptom complex: asthenic physique, Gothic palate, distal occlusion, ingrown earlobes, hypermobility of joints. Dynamic monitoring throughout the entire period of observation, diagnosis and treatment. In the neurological status, emotional and vegetative lability can be distinguished (the patient gets tired quickly, there is daytime drowsiness, there is a violation of concentration, and as a result, memory problems), sleep disturbance — insomnia. Manifested by difficulties falling asleep, frequent awakenings, restless sleep, with vivid dreams, as well as difficulties waking up (a symptom of sleep intoxication). RESULTS AND DISCUSSION. The dynamics and the result of the treatment process are presented using the example of a patient with comorbid pathology in the dental and jaw system. CONCLUSION. Patients with undifferentiated connective tissue dysplasia who have neurological and dental disorders should be observed as part of comorbid pathology, jointly by neurologists and dentists, to obtain successful results. KEYWORDS: emotional disorders, distal occlusion, sagittal fissure, connective tissue dysplasia, clinic, diagnosis, treatment

Comparative analysis of the influence of the shapes and dimensions of dental arches on the morphotopogeometric characteristics of the facial area.

Aim: The aim of the article is a comparative analysis of the main aspects of existing medical and diagnostic measures in patients with abnormal types of occlusal relationships and methods of mathematical and graphic reproduction of the shape of the dental arches, taking into account the individual characteristics of the maxillofacial area. Materials and Methods: The search for relevant publications related to the objective topic was carried out through scientific databases: Scopus, PubMed, BVS and Scielo. Conclusions: The analysis of regression models of the reproduction of individual characteristics of the dental arch of the jaws will avoid errors that occur when comparing the actual sizes with their statistical norm, which will allow to correctly determine the proportionality and ratio of dif f erent departments of the dental and jaw system, the necessary amount of orthodontic measures in the treatment of anomalies of the dental arches.

Тимчасові незнімні ортопедичні конструкції виготовлені із використанням CAD/CAM системи методом фрезерування, як альтернатива постійним на тривалий термін

Relevance. Prevalence of partial loss of teeth in the population of Ukraine is from 62.3% to 84.5%. The war in Ukraine significantly affected the provision of timely and high-quality dental care. However, the restoration of the destroyed crown part of the tooth and the integrity of the tooth rows must take place in a timely manner, as it leads to the development of secondary deformations of the dental and jaw system. One of the options for solving the problem of timely orthopedic treatment, in these conditions, can be the use of temporary fixed orthopedic structures made using the CAD/CAM system by the milling method. The aim is to investigate the possibility of using non-removable temporary orthopedic structures made using the CAD/ CAM system by the milling method and cements for their temporary fixation for a period exceeding that established by the general protocols of orthopedic treatment and declared by the manufacturer. Materials and methods. The study was conducted in the period from September 2022 to April 2024 at the Department of Orthopedic Stomatology of the National Medical University named after O.O. Bogomolets For the study, 60 patients aged 25-59 years were selected, with the destruction of the crown part of the tooth, which required replacement with a fixed orthopedic structure and included dentition defects of various lengths. All supporting elements were divided into groups, depending on the cement used for fixation: Group I – Freegenol (GC, Japan), Group II – Provicol (Voco, Germany), Group III – RelyX Temp NE (3M ESPE, Germany), IV group – Temp-Bond NE (KERR, USA). Re-examinations of patients were carried out in periods from two weeks to six months. Results. Depending on the selected cement for temporary fixation of a non-removable orthopedic structure, the percentage of decementing of temporary single crowns, in terms of two weeks to six months, was from 2.22% to 32.65%, structures with support on two elements from 5.55% to 52.94% and based on three elements from 7.14% to 77.78%. A direct relationship was established between the appearance of mobility of the temporary fixed orthopedic structure, the sensitivity of the vital tooth and bleeding gums in all groups of subjects. Conclusions. Temporary non-removable orthopedic structures made using the CAD/CAM system by the milling method, depending on the selected cement for temporary fixation, can be used to restore the crown part of the tooth and included defects of the dentition for a period that exceeds that established by the general protocols of orthopedic treatment and declared by the manufacturer. Key words: temporary non-removable orthopedic structures, CAD/CAM systems, milling, cements for temporary fixation.

The cichlid pharyngeal jaw novelty enhances evolutionary integration in the feeding apparatus.

The modified pharyngeal jaw system of cichlid fishes is widely viewed as a key innovation that substantially facilitated the evolutionary exuberance of this iconic evolutionary radiation. We conduct comparative phylogenetic analyses of integration, disparity, and rate of evolution among feeding-related, skeletal structures in Neotropical cichlids and North American centrarchids, which lack the specialized pharyngeal jaw. Contrasting evolutionary patterns in these two continental radiations, we test a classic decoupling hypothesis. Specifically, we ask whether the modified pharyngeal jaw in cichlids resulted in enhanced evolutionary independence of the oral and pharyngeal jaws, leading to increased diversity of trophic structures. Contrary to this prediction, we find significantly stronger evolutionary integration between the oral and pharyngeal jaws in cichlids compared to centrarchids, although the two groups do not differ in patterns of integration within each jaw system. Further, though we find no significant differences in disparity, centrarchids show faster rates of morphological evolution. Our results suggest that the modified pharyngeal jaw resulted in less evolutionary independence and slower rates of evolution within the feeding system. Thus, we raise the possibility that the cichlid novelty enhances feeding performance, but does not prompt increased morphological diversification within the feeding apparatus, as has long been thought.

Multiple pathways to herbivory underpinned deep divergences in ornithischian evolution

The extent to which evolution is deterministic is a key question in biology,1,2,3,4,5,6,7,8,9 with intensive debate on how adaptation6,10,11,12,13 and constraints14,15,16 might canalize solutions to ecological challenges.4,5,6 Alternatively, unique adaptations1,9,17 and phylogenetic contingency1,3,18 may render evolution fundamentally unpredictable.3 Information from the fossil record is critical to this debate,1,2,11 but performance data for extinct taxa are limited.7 This knowledge gap is significant, as general morphology may be a poor predictor of biomechanical performance.17,19,20 High-fiber herbivory originated multiple times within ornithischian dinosaurs,21 making them an ideal clade for investigating evolutionary responses to similar ecological pressures.22 However, previous biomechanical modeling studies on ornithischian crania17,23,24,25 have not compared early-diverging taxa spanning independent acquisitions of herbivory. Here, we perform finite-element analysis on the skull of five early-diverging members of the major ornithischian clades to characterize morphofunctional pathways to herbivory. Results reveal limited functional convergence among ornithischian clades, with each instead achieving comparable performance, in terms of reconstructed patterns and magnitudes of functionally induced stress, through different adaptations of the feeding apparatus. Thyreophorans compensated for plesiomorphic low performance through increased absolute size, heterodontosaurids expanded jaw adductor muscle volume, ornithopods increased jaw system efficiency, and ceratopsians combined these approaches. These distinct solutions to the challenges of herbivory within Ornithischia underpinned the success of this diverse clade. Furthermore, the resolution of multiple solutions to equivalent problems within a single clade through macroevolutionary time demonstrates that phenotypic evolution is not necessarily predictable, instead arising from the interplay of adaptation, innovation, contingency, and constraints.1,2,3,7,8,9,18.

Relationship of odontometric and cephalometric indicators. Review of literary sources

Annotation. The construction of a correct orthodontic intervention that will satisfy the aesthetic and functional needs of the patient requires the perception of the craniofacial region as a single complex. At the same time, it is necessary to understand the relationship of each component of this complex and its influence on each other in order to better predict the expected result of treatment and its planning. The purpose of this study is to review modern scientific sources devoted to the study of the relationship between odontometric and cephalometric indicators. For this, a search for literary sources related to the research topic in the period 2012-2022 was performed on the basis of Google Scholar using keywords and inclusion/exclusion criteria, in particular, the presence of previous review of articles, the representativeness of the sample, and the presence of statistical analysis of the obtained data. The analysis of selected literary sources showed that the vast majority of publications are devoted to the topic of studying the relationship of odontometric and cephalometric indicators under the conditions of pathology of the dental and jaw system. Also, in most sources, researchers do not prefer the use of one or two methods of cephalometric analysis of lateral teleroentgenograms, but use complex analysis methods. At the same time, scientists pay attention to its ethnicity, gender and age when drawing up a sample. Thus, taking into account the relevance of this research topic and at the same time the lack of studies aimed at determining the relationship of cephalometric and odontometric indicators under the conditions of orthognathic bite, there is a need to conduct this kind of clinical experimental study on the Ukrainian population using several of the most common methods of cephalometric analysis.

Jaw mechanics in macrophagous lamniform sharks and their evolutionary and functional implications.

Jaw mechanics of lamniform sharks were examined three-dimensionally to analyze the variability in jaw shape and the evolution of the jaw system based on the extant macrophagous species. Three-dimensional lever analysis was applied to lamniform jaws to calculate bite force at each tooth relative to maximum input force from jaw adductor muscles for interspecific comparison of efficiency in lamniform jaws. When total input force from the jaw adductor muscles on both working and balancing sides of the skull is considered, input force varies along the jaw because the contribution by balancing side muscles is not constant. The phylogenetically basal-most species, Mitsukurina owstoni, has the least efficient jaws due to posteriorly positioned jaw adductor muscles. Our study shows that the higher efficiency of jaws is regarded as apomorphic in lamniform phylogeny owing to the anterior extension of jaw adductor muscles relative to M. owstoni and a relative decrease in jaw length in relation to width seen in some species, both of which increase leverage. Differences in the efficiency of jaws among derived genera or species are due to the morphology of their jaws. The relationship between calculated bite force relative to maximum input force and tooth morphology indicates low relative bite forces being exerted at anteriorly located, narrow, piercing teeth, whereas high relative bite forces at posteriorly located, broad, cutting, or crushing-type teeth. As a result, the biting pressure during feeding is maintained throughout the tooth series.

Functional Trade-Offs Asymmetrically Promote Phenotypic Evolution.

Trade-offs are thought to bias evolution and are core features of many anatomical systems. Therefore, trade-offs may have far-reaching macroevolutionary consequences, including patterns of morphological, functional, and ecological diversity. Jaws, like many complex anatomical systems, are comprised of elements involved in biomechanical trade-offs. We test the impact of a core mechanical trade-off, the transmission of velocity versus force (i.e., mechanical advantage), on rates of jaw evolution in Neotropical cichlids. Across 130 species representing a wide array of feeding ecologies, we find that the velocity-force trade-off impacts the evolution of the surrounding jaw system. Specifically, rates of jaw evolution are faster at functional extremes than in more functionally intermediate or unspecialized jaws. Yet, surprisingly, the effect on jaw evolution is uneven across the extremes of the velocity-force continuum. Rates of jaw evolution are 4- to 10-fold faster in velocity-modified jaws, whereas force-modified jaws are 7- to 18-fold faster, compared to unspecialized jaws, depending on the extent of specialization. Further, we find that a more extreme mechanical trade-off resulted in faster rates of jaw evolution. The velocity-force trade-off reflects a gradient from specialization on capture-intensive (e.g., evasive or buried) to processing-intensive prey (e.g., attached or shelled), respectively. The velocity extreme of the trade-off is characterized by large magnitudes of trait change leading to functionally divergent specialists and ecological stasis. By contrast, the force extreme of the trade-off is characterized by enhanced ecological lability made possible by phenotypes more readily co-opted for different feeding ecologies. This asymmetry of macroevolutionary outcomes along each extreme is likely the result of an enhanced utility of the pharyngeal jaw system as force-modified oral jaws are adapted for prey that requires intensive processing (e.g., algae, detritus, and mollusks). The velocity-force trade-off, a fundamental feature of many anatomical systems, promotes rapid phenotypic evolution of the surrounding jaw system in a canonical continental adaptive radiation. Considering that the velocity-force trade-off is an inherent feature of all jaw systems that involve a lower element that rotates at a joint, spanning the vast majority of vertebrates, our results may be widely applicable across the tree of life. [Adaptive radiation; constraint; decoupling; jaws; macroevolution; specialization.].

Evolutionary Innovations of the Feeding Apparatus in Herbivorous Dinosaurs

Although most studies in feeding biology of non‐avian dinosaurs have investigated feeding function and ecology in carnivorous dinosaurs, the complex diversity of feeding in herbivorous dinosaurs has recently been explored in much greater detail. Herbivorous non‐avian dinosaurs, composed of nearly all sauropodomorphs and ornithischians as well as a few theropod groups (i.e., ornithomimosaurs, therizinosaurs, and oviraptorosaurs), show a wide range of craniomandibular feeding mechanisms, each with unique adaptations for processing various forms of plant‐life. Here, I will review over a century of feeding studies in herbivorous dinosaurs, with particular focus on more recent advancements in our knowledge of their feeding evolution and ecology. These studies have primarily focused on the many components influencing the functional morphology of the head and neck of these animals, including: dental morphology, with studies in dental microwear and macrowear, overall morphological analysis of the skull and cervical vertebrae, reconstruction of cranial musculature and other soft tissues of the head, and biomechanics of the skull, with comparative analyses of mechanical advantage of the jaw system and 3D computer modeling in the form of finite element analyses and multibody dynamics analyses with the use of laser scans and CTs of dinosaur skulls. All these studies are instrumental in our understanding of the evolution and diversity of bite forces as well as feeding mechanisms that range from orthal to palinal feeding motions as well as bilateral hemi‐mandibular long‐axis rotation (especially in a variety of ornithischians). The similarities and differences between herbivorous dinosaurs and the herbivores of today (especially mammalian megaherbivores) show a great deal about how evolutionary opportunities and constraints have made a significant impact on the diverse nature of herbivory and its importance in ecosystems around the world.

Mapping the vocal circuitry of Alston's singing mouse with pseudorabies virus.

Vocalizations are often elaborate, rhythmically structured behaviors. Vocal motor patterns require close coordination of neural circuits governing the muscles of the larynx, jaw, and respiratory system. In the elaborate vocalization of Alston's singing mouse (Scotinomys teguina) each note of its rapid, frequency-modulated trill is accompanied by equally rapid modulation of breath and gape. To elucidate the neural circuitry underlying this behavior, we introduced the polysynaptic retrograde neuronal tracer pseudorabies virus (PRV) into the cricothyroid and digastricus muscles, which control frequency modulation and jaw opening, respectively.Each virus singly labels ipsilateral motoneurons (nucleus ambiguus for cricothyroid, and motor trigeminal nucleus for digastricus). We find that the two isogenic viruses heavily and bilaterally colabel neurons in the gigantocellular reticular formation, a putative central pattern generator. The viruses also show strong colabeling in compartments of the midbrain including the ventrolateral periaqueductal gray and the parabrachial nucleus, two structures strongly implicated in vocalizations. In the forebrain, regions important to social cognition and energy balance both exhibit extensive colabeling. This includes the paraventricular and arcuate nuclei of the hypothalamus, the lateral hypothalamus, preoptic area, extended amygdala, central amygdala, and the bed nucleus of the stria terminalis. Finally, we find doubly labeled neurons in M1 motor cortex previously described as laryngeal, as well as in the prelimbic cortex, which indicate these cortical regions play a role in vocal production. The progress of both viruses is broadly consistent with vertebrate-general patterns of vocal circuitry, as well as with circuit models derived from primate literature.

The relationship between head shape, head musculature and bite force in caecilians (Amphibia: Gymnophiona).

Caecilians are enigmatic limbless amphibians that, with a few exceptions, all have an at least partly burrowing lifestyle. Although it has been suggested that caecilian evolution resulted in sturdy and compact skulls as an adaptation to their head-first burrowing habits, no relationship between skull shape and burrowing performance has been demonstrated to date. However, the unique dual jaw-closing mechanism and the osteological variability of their temporal region suggest a potential relationship between skull shape and feeding mechanics. Here, we explored the relationships between skull shape, head musculature and in vivo bite forces. Although there is a correlation between bite force and external head shape, no relationship between bite force and skull shape could be detected. Whereas our data suggest that muscles are the principal drivers of variation in bite force, the shape of the skull is constrained by factors other than demands for bite force generation. However, a strong covariation between the cranium and mandible exists. Moreover, both cranium and mandible shape covary with jaw muscle architecture. Caecilians show a gradient between species with a long retroarticular process associated with a large and pennate-fibered m. interhyoideus posterior and species with a short process but long and parallel-fibered jaw adductors. Our results demonstrate the complexity of the relationship between form and function of this jaw system. Further studies that focus on factors such as gape distance or jaw velocity will be needed in order to fully understand the evolution of feeding mechanics in caecilians.

Jaw-neck motor strategy during jaw-opening with resistance load.

The jaw and neck motor systems have a close functional integration but the effect of resistance load to the mandible during jaw opening on the jaw-neck integration is not known. To evaluate the effect of resistance load compared to no load on integrated jaw and neck motor function in individuals free from pain and dysfunction in the jaw and neck regions. Jaw and head movements during continuous jaw opening were recorded with an optoelectronic system (MacReflex® ) in 26 pain-free individuals (14 women, 12men, mean age 22years). Jaw opening was performed with and without resistance load (1600g) to the mandible. The relationship between jaw movement amplitude, head movement amplitude, head/jaw ratio (quotient of head and jaw movement amplitude) and resistanceload were modelled using linear mixed-model analysis. A p-value <.05 was considered statistically significant. The expected head/jaw ratio mean was increased by 0.05 (95% CI: 0.03, 0.08, p<.001) with resistance load as compared to no load. This corresponds to an increase in expected mean by 55.6%. With resistance load, expected mean head movement amplitude increased by 1.4mm (95% CI: 0.2, 2.5, p=.018), and expected mean jaw movement amplitude decreased by 3.7mm (95% CI: -7.0, -0.5, p=.025). There is a compensation and adaptation of integrated jaw-neck motor function with an altered jaw-neck motor strategy during jaw opening with resistance load compared to no load. The head/jaw ratio demonstrates increased proportional involvement of the neck during increased load on the jaw system.

The cichlid oral and pharyngeal jaws are evolutionarily and genetically coupled

Evolutionary constraints may significantly bias phenotypic change, while “breaking” from such constraints can lead to expanded ecological opportunity. Ray-finned fishes have broken functional constraints by developing two jaws (oral-pharyngeal), decoupling prey capture (oral jaw) from processing (pharyngeal jaw). It is hypothesized that the oral and pharyngeal jaws represent independent evolutionary modules and this facilitated diversification in feeding architectures. Here we test this hypothesis in African cichlids. Contrary to our expectation, we find integration between jaws at multiple evolutionary levels. Next, we document integration at the genetic level, and identify a candidate gene, smad7, within a pleiotropic locus for oral and pharyngeal jaw shape that exhibits correlated expression between the two tissues. Collectively, our data show that African cichlid evolutionary success has occurred within the context of a coupled jaw system, an attribute that may be driving adaptive evolution in this iconic group by facilitating rapid shifts between foraging habitats, providing an advantage in a stochastic environment such as the East African Rift-Valley.

Ecological Limits on the Decoupling of Prey Capture and Processing in Fishes.

Ray-finned fishes have two jaw systems, the oral and pharyngeal jaws, which perform functions associated with prey capture and processing, respectively. The structural independence of the jaw systems is recognized as having broad implications for the functional and ecological diversity of the radiation. Cichlids (and a few other lineages) possess a modified pharyngeal jaw system that enhances prey processing versatility and capacity. This innovation, pharyngognathy, is hypothesized to have freed the oral jaws to diversify in terms of prey capture. We test the relative role of prey capture properties (e.g., evasiveness) and prey processing (e.g., crushing) in driving divergent selection in the oral and pharyngeal jaws using a macroevolutionary model fitting framework. Evolutionary outcomes were asymmetric. All transitions between different properties of prey capture had a corresponding transition in properties of prey processing. In contrast, fewer than half the transitions in the properties of prey processing had a corresponding prey capture transition. This discrepancy was further highlighted by multi-peak models that reflect the opposing function of each jaw system, which fit better than null models for oral jaw traits, but not pharyngeal jaw traits. These results suggest that pharyngeal jaw function can change independently from the function of the oral jaws, but not vice versa. This finding highlights the possibility of ecological limits to the evolutionary decoupling of jaw systems. The independent actions of prey capture and processing may be decoupled, but their respective functional demands (and evolution) are not. Therefore, prey likely impose some degree of coordinated evolution between acquisition and processing functional morphology, even in decoupled jaw systems.