Mastication and its control by the brain stem

Computed tomography-based findings and severity of temporomandibular joint osteoarthritis are associated with the development of skeletal mandibular retrusion

The aim of this study was to clarify the relationship between the severity of condylar osteoarthritis (OA) and skeletal mandibular retrusion. Three-dimensional cephalometric characteristics of skeletal mandibular retrusion were analysed using computed tomography scans from 15 patients with OA and 15 without OA. Mandibular, dental, and condylar-related factors were evaluated. Severity was scored by counting findings of cysts, erosion, atrophy, osteophytes, and sclerosis (score of 1 for the presence of each). The OA group was further divided into mild and moderate OA according to the total severity score of both condyles. The mean condylar volume was significantly lower in OA (851.1 mm3) than in non-OA (1151.3 mm3) (P < 0.001). A decrease in volume was significantly correlated with the number of radiographic OA findings (P = 0.012). Findings seen in mild OA were mostly cysts and erosion, while all findings were identified in moderate OA. The measured factors did not differ significantly between the mild OA and non-OA groups, whereas many mandible-related factors differed significantly between the moderate OA and non-OA groups. A significantly lower volume of the condyle was observed in moderate OA compared to non-OA (P < 0.001), suggesting that the appearance of atrophy, osteophytes, and sclerosis worsened OA from mild to moderate, and correspondingly, mandibular retrusion became apparent.

Sensorimotor integration and faces recognition in a model of altered face sensory information: Neurophysiological study in patients with dentofacial deformities

OBJECTIVE

To explore the excitability and sensory motor integration of the face and masticatory primary motor cortex (M1), and recognition of face expressions in individuals with dentofacial deformities (IDD).

METHODS

Short-interval intracortical inhibition (SICI), short-afferent inhibition (SAI) of masticatory and face M1, the blink reflex and face expressions recognition (FER) ability were assessed in 18 healthy subjects (HS) (24.56 ± 1.02 years old) and in 18 IDD (27.36 ± 1.39 years) before and after 1 month from surgery.

RESULTS

In IDD, SICI (p = 0.033) and SAI (p = 0.008) were significantly reduced in the masticatory, but not face, M1 and the blink reflex was normal. IDD also exhibited deficits in FER before surgery (p = 0.033), which was still present after surgery (p = 0.015), although improved.

CONCLUSION

Results evidence that alterations of sensory afferents due to dentofacial deformities modulates sensorimotor integration of masticatory M1, with topographic specificity. The altered sensory information from face not only influences motor inhibitory control but also FER.

SIGNIFICANCE

The integration of sensory inputs with motor outputs depends topographically on the type of sensory afferents stimulated as well as on the target muscle and its respective representation area in M1. Afferent information from face also plays a role in FER ability.

Jaw-Muscle Structure and Function in Primates: Insights Into Muscle Performance and Feeding-System Behaviors

The jaw-adductor muscles drive the movements and forces associated with primate feeding behaviors such as biting and chewing as well as social signaling behaviors such as wide-mouth canine display. The past several decades have seen a rise in research aimed at the anatomy and physiology of primate chewing muscles to better understand the functional and evolutionary significance of the primate masticatory apparatus. This review summarizes variation in jaw-adductor fiber types and muscle architecture in primates, focusing on physiological, architectural, and behavioral performance variables such as specific tension, fatigue resistance, muscle and bite force, and muscle stretch and gape. Paranthropus and Australopithecus are used as one paleontological example to showcase the importance of these data for addressing paleobiological questions. The high degree of morphological variation related to sex, age, muscle, and species suggests future research should bracket ranges of performance variables rather than focus on single estimates of performance.

Development of animal model for anterior open bite and mechanism of temporomandibular joint morphological change: an implication for MAC surgery

BACKGROUND

Although mandibular autorotation concept (MAC) surgery is a novel technique for addressing long-term stability issues in patients with mandibular retrusion and open bite accompanied by temporomandibular joint osteoarthritis (TMJOA), studies on MAC surgery in animal models and its mechanisms are scarce. This study aimed to develop an animal model for anterior open bite and investigate the underlying histological and molecular mechanisms of TMJ changes, with the expectation of contributing to the MAC surgery concept.

MATERIALS AND METHODS

Thirty-six, 5-weeks-old female Wistar rats were randomly divided into three groups: (1) Bite-raise group (2-mm resin added to the upper molars at 5 weeks of age) (2), Recovery group (resin added at 5 weeks of age and removed at 13 weeks of age), and (3) Control group (normal rats). Micro-CT imaging was used to assess 3D morphology and bone structure. Histological and immunohistochemical analyses were performed to evaluate the cartilage changes, bone cell differentiation, and extracellular matrix degradation. Gene expression of inflammatory factors (IL-1β, IL-6, TNF-α), TGF-β1, and Postn were measured by qPCR.

RESULTS

At 13 weeks of age, both Bite-raise and Recovery groups exhibited TMJOA-like changes, including decreased cartilage thickness and increased inflammatory gene expression. At 21 weeks of age, the Recovery group showed improved bone volume, reduced osteoclast activity, and lower MMP-13 and Postn levels than the Bite-raise group.

CONCLUSION

These results suggest the successful development of an animal model for anterior open bite and demonstrate that MAC surgery facilitates the recovery of compromised condyles.

Masticatory performance and masticatory behavior in individuals with eating disorders: a pilot study

Aim

The brief report aims to evaluate masticatory performance and components of chewing behavior in people with anorexia nervosa and compare it with a reference group of individuals with no history of eating disorders.

Material and methods

Eighteen women participated in the study: nine with anorexia nervosa (age 20.2 ± 5.9) and nine as controls in a reference group without anorexia nervosa (age 23.6 ± 0.9). Masticatory performance was assessed with a food comminution test. The participants also ate (chewed and swallowed) a second test food while their jaw movements were recorded to evaluate their chewing behavior. The number of comminuted pieces during the food comminution test, chewing cycles, chewing duration, and components like occlusal, and jaw opening/closing duration, were evaluated.

Results

In comparison to the reference group the anorexia nervosa patients performed poorly in the food comminution test (P = 0.007), and also chewed the test food significantly longer (P = 0.004) and with significantly more chewing cycles (P = 0.014). The results also showed a significantly longer jaw-closing duration in the anorexia nervosa group compared to the reference group (P = 0.021). However, there were no significant differences in either the jaw opening or the occlusal duration between the two groups.

Conclusion

Overall, the results of the study indicate that the anorexia nervosa group shows signs of poor masticatory performance and altered chewing behavior compared to the reference group of individuals with no history of eating disorders.

Portuguese translation, cultural adaptation and psychometric properties of the temporomandibular joint scale: a cross-sectional study

BACKGROUND

The temporomandibular joint (TMJ) scale assesses the severity of temporomandibular joint disorders (TMD), yet a European Portuguese translation is lacking.

OBJECTIVES

To translate, cross-culturally adapt and to examine the psychometric properties (construct validity and reliability) of the TMJ scale.

METHODS

Translation and cultural adaptation were carried out according to international recommendations, including initial translation, evaluation of this translation and cultural adaptation by a panel of experts, and back translation. The final Portuguese version was used to examine the reliability and validity, and participants with TMD were recruited from a Portuguese outpatient clinic. Reliability measures included internal consistency with Cronbach's alpha and test-retest reliability with the intraclass correlation coefficient (ICC2,1). The Spearman correlation comparing the TMJ scale with the Fonseca and Helkimo indexes was used to assess the construct validity.

RESULTS

A total of 63 participants (23 ± 2 years; 61,9% female) were included. Similar internal consistency was observed between the two moments of application (0.921 and 0.918), and test-retest reliability was excellent, with an ICC2,1 = 0.998 (95%CI: 0.988-0.999). Robust positive correlations (rho 0.554-0.611, p < 0.001) were found between the TMJ scale and Fonseca and Helkimo indexes.

CONCLUSION

The European Portuguese version of TMJ scale is now available to improve the assessment of severity of TMD in routine clinical practice. This version is also reliable and valid.

Masticatory simulators based on oral physiology in food research: A systematic review

A masticatory simulator is a mechanical device that mimics the physiological structures of the human oral cavity, chewing movement system, and functions. The advantage of this device lies in real-time tracking and analysis of food boluses within a sealed oral space, offering a direct validation platform for food experiments without constraints related to time, space, and individual variations. The degree to which the masticatory simulator simulates physiological structures reflects its efficacy in replicating oral physiological processes. This review mainly discusses the physiological structures of the oral cavity, the simulation of biomimetic components, and the development, feasibility assessment, applications, and prospects of masticatory simulators in food. The highlight of this review is the analogy of biomimetic component designs in masticatory simulators over the past 15 years. It summarizes the limitations of masticatory simulators and their biomimetic components, proposing potential directions for future development. The purpose of this review is to assist readers in understanding the research progress and latest literature findings on masticatory simulators while also offering insights into the design and innovation of masticatory simulators.

Rehabilitation with dental prostheses and its influence on brain activity: A systematic review

STATEMENT OF PROBLEM

The consequences of edentulism depend on its complexity and are far-reaching, but limited evidence regarding its association with neurologic health is available.

PURPOSE

The purpose of this systematic review was to establish the relationship between oral prosthetic rehabilitation and the regional increase in brain activity.

MATERIAL AND METHODS

This systematic review was registered in the International Prospective Register of Systematic Reviews (CRD42021262247), and the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guideline was followed. Randomized clinical trials, prospective studies comparing the brain activity of patients rehabilitated with and without the use of dental prostheses, and studies that analyzed the human brain by using noninvasive techniques were used as inclusion criteria. The risk of bias in each study was assessed by using the Risk Of Bias In Non-randomized Studies-of Interventions (ROBINS-I).

RESULTS

The search was carried out in the PubMed/MEDLINE, Embase, Cochrane Library, and https://clinicaltrials.gov databases up to June 2021. After a search conducted by 2 reviewers, 8 articles were included in the review. A regional increase in blood flow and regional cerebral activity during dental prosthesis use was identified in the studies.

CONCLUSIONS

A positive association was found between the different types of prosthetic rehabilitation and brain function. Prostheses may preserve and restore neurological health.

Biomechanical and Cortical Control of Tongue Movements During Chewing and Swallowing

Tongue function is vital for chewing and swallowing and lingual dysfunction is often associated with dysphagia. Better treatment of dysphagia depends on a better understanding of hyolingual morphology, biomechanics, and neural control in humans and animal models. Recent research has revealed significant variation among animal models in morphology of the hyoid chain and suprahyoid muscles which may be associated with variation in swallowing mechanisms. The recent deployment of XROMM (X-ray Reconstruction of Moving Morphology) to quantify 3D hyolingual kinematics has revealed new details on flexion and roll of the tongue during chewing in animal models, movements similar to those used by humans. XROMM-based studies of swallowing in macaques have falsified traditional hypotheses of mechanisms of tongue base retraction during swallowing, and literature review suggests that other animal models may employ a diversity of mechanisms of tongue base retraction. There is variation among animal models in distribution of hyolingual proprioceptors but how that might be related to lingual mechanics is unknown. In macaque monkeys, tongue kinematics-shape and movement-are strongly encoded in neural activity in orofacial primary motor cortex, giving optimism for development of brain-machine interfaces for assisting recovery of lingual function after stroke. However, more research on hyolingual biomechanics and control is needed for technologies interfacing the nervous system with the hyolingual apparatus to become a reality.

Sensorimotor integration in cranial muscles tested by short- and long-latency afferent inhibition

OBJECTIVE

To compressively investigate sensorimotor integration in the cranial-cervical muscles in healthy adults.

METHODS

Short- (SAI) and long-latency afferent (LAI) inhibition were probed in the anterior digastric (AD), the depressor anguli oris (DAO) and upper trapezius (UT) muscles. A transcranial magnetic stimulation pulse over primary motor cortex was preceded by peripheral stimulation delivered to the trigeminal, facial and accessory nerves using interstimulus intervals of 15-25 ms and 100-200 ms for SAI and LAI respectively.

RESULTS

In the AD, both SAI and LAI were detected following trigeminal nerve stimulation, but not following facial nerve stimulation. In the DAO, SAI was observed only following trigeminal nerve stimulation, while LAI depended only on facial nerve stimulation, only at an intensity suprathreshold for the compound motor action potential (cMAP). In the UT we could only detect LAI following accessory nerve stimulation at an intensity suprathreshold for a cMAP.

CONCLUSIONS

The results suggest that integration of sensory inputs with motor output is profoundly influenced by the type of sensory afferent involved and by the functional role played by the target muscle.

SIGNIFICANCE

Data indicate the importance of taking into account the sensory receptors involved as well as the function of the target muscle when studying sensorimotor integration, both in physiological and neurological conditions.

Three-dimensional mandibular kinematics of mastication in the marsupial Didelphis virginiana

Didelphis virginiana (the Virginia opossum) is often used as an extant model for understanding feeding behaviour in Mesozoic mammaliaforms, primarily due to their morphological similarities, including an unfused mandibular symphysis and tribosphenic molars. However, the three-dimensional jaw kinematics of opossum chewing have not yet been fully quantified. We used biplanar videofluoroscopy and the X-Ray Reconstruction of Moving Morphology workflow to quantify mandibular kinematics in four wild-caught opossums feeding on hard (almonds) and soft (cheese cubes) foods. These data were used to test hypotheses regarding the importance of roll versus yaw in chewing by early mammals, and the impact of food material properties (FMPs) on jaw kinematics. The magnitude of roll exceeds that of yaw, but both are necessary for tooth-tooth or tooth-food-tooth contact between complex occlusal surfaces. We confirmed the utility of the four vertical kinematic gape cycle phases identified in tetrapods but we further defined two more in order to capture non-vertical kinematics. Statistical tests support the separation of chew cycle phases into two functional groups: occlusal and non-occlusal phases. The separation of slow close into two (occlusal) phases gives quantitative kinematic support for the long-hypothesized multifunctionality of the tribosphenic molar. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

The relationships between mastication and cognitive function: A systematic review and meta-analysis

Masticatory function such as chewing is expected to modify human cognitive function, and/or the possibility of improving cognitive function is also predicted. This systematic review investigated whether masticatory function affects cognitive function for older/young adults. Full articles written in English from January 2000 to April 2022 were collected using PubMed and Cochrane Library. Target outcomes were cognitive function test scores, cognitive processing speed (reaction time), and masticatory function. For each research question, two independent reviewers conducted the search and screening, data extraction, quality assessment, and risk of bias assessment. The reviewers resolved any disagreements by discussion. From 226 articles retrieved, 20 were included in this review. Older adults with lower scores on the cognitive function test had lower masticatory performance, lower chewing ability, chewing difficulty, and decreased number of teeth. An increased risk of cognitive impairment was found in older adults with masticatory dysfunction. For young adults, gum chewing significantly reduced the processing speed of cognitive tasks compared to no gum chewing. Although most of the evidence included had a low level of evidence and a high risk of bias because of the research designs, the results still suggest that mastication may be a factor in improving cognitive function.

Chewing Analysis by Means of Electromagnetic Articulography: Current Developments and New Possibilities

Chewing is a complex procedure that involves sensory feedback and motor impulses controlled by the trigeminal system in the brainstem. The analysis of mandibular movement is a first approximation to understanding these mechanisms. Several recording methods have been tested to achieve this. Video, ultrasound, the use of external markers and kinesiographs are examples of recording systems used in research. Electromagnetic articulography is an alternative method to those previously mentioned. It consists of the use of electromagnetic fields and receiver coils. The receiver coils are placed on the points of interest and the 3D coordinates of movement are saved in binary files. In the Oral Physiology Laboratory of the Dental Sciences Research Center (Centro de Investigación en Ciencias Odontológicas-CICO), in the Faculty of Dentistry at the Universidad de La Frontera (Temuco, Chile) several research studies have been carried out using the AG501 3D EMA articulograph (Carstens Medizinelektronik, Lenglern, Germany). With this device, they developed a series of protocols to record mandibular movement and obtain new information, such as the 3D Posselt polygon, the area of each polygon, individualized masticatory cycles and speed and acceleration profiles. Other investigations have analyzed these parameters, but separately. The AG501 allows for holistic analysis of all these data without altering natural movement. A limitation of this technology is the interference generated by its metallic elements. The aim of the present work is to show the developed methods used to record mandibular movement in the CICO, using the AG501 and compare them with others used in several research studies.

Chewing and its influence on swallowing, gastrointestinal and nutrition-related factors: a systematic review

The study aimed to evaluate the hypothesis that chewing is a mechanical and physiological contributor to swallowing, physiologic/pathologic processes of the gastrointestinal tract (GIT), and nutrition-related factors. A search strategy was applied to three different databases to investigate if chewing function in adults affects the swallowing, physiologic/pathologic processes of the GIT, and nutrition-related factors compared to controls with no exposure. The included studies were evaluated for methodological quality and risk of bias and certainty of evidence. The results showed 71 eligible studies. Overall, the results showed that 46 studies supported the hypothesis while 25 refuted it. However, the GRADE analysis showed low to very low certainty of the evidence to support the hypothesis that chewing is an important contributor in the swallowing process, and physiologic/pathologic processes in the GIT. The GRADE analysis also showed a moderate to very low certainty of the evidence to suggest that chewing function contributes to nutrition-related parameters. The overall results of the current study showed that a majority (64.7%) of the studies (46 out of 71) supported the hypothesis. However, robust studies with proper design, adequate sample size, and well-defined outcome parameters are needed to establish conclusive evidence.

Modulation of reflex responses of the anterior and posterior bellies of the digastric muscle in freely moving rats

BACKGROUND

Chewing and licking are primarily activated by central pattern generator (CPG) neuronal circuits in the brainstem and when activated trigger repetitive rhythmic orofacial movements such as chewing, licking and swallowing. These CPGs are reported to modulate orofacial reflex responses in functions such as chewing.

OBJECTIVE

This study explored the modulation of reflex responses in the anterior and posterior bellies (ant-Dig and post-Dig, respectively) of the digastric muscle evoked by low-intensity trigeminal stimulation in conscious rats.

METHODS

The ant-Dig and post-Dig reflexes were evoked by using low-intensity electrical stimulation applied to either the right or left inferior alveolar nerve. Peak-to-peak amplitudes and onset latencies were measured.

RESULTS

No difference was observed between threshold and onset latency for evoking ant-Dig and post-Dig reflexes, suggesting that the latter was also evoked disynaptically. The peak-to-peak amplitude of both reflexes was significantly reduced during chewing, licking and swallowing as compared to resting period and was lowest during the jaw-closing phase of chewing and licking. Onset latency was significantly largest during the jaw-closing phase. Inhibitory level was similar between the ant-Dig and post-Dig reflex responses and between the ipsilateral and contralateral sides.

CONCLUSION

These results suggest that both the ant-Dig and post-Dig reflex responses were significantly inhibited, probably due to CPG activation during feeding behaviours to maintain coordination of jaw and hyoid movements and hence ensure smooth feeding mechanics.

Food consumption and masticatory performance of normal weight, overweight and obese children aged 7 to 12 years old

Childhood obesity is a significant public health problem. Studies show that obese children are more likely to become obese adults. In an attempt to ascertain the factors associated with childhood obesity, research has shown that this condition is associated with changes in food consumption and masticatory performance. The aim of this study was thus to evaluate food consumption and masticatory performance in normal weight, overweight and obese children aged 7 - 12 years. A cross-sectional study was carried out with 92 children aged 7 - 12 years, of both sexes, from a public school in a Brazilian municipality. The children were divided into the following groups: normal weight (n = 48), overweight (n = 26) and obese (n = 18). Anthropometric parameters, food consumption, food consistency preference, and masticatory performance were evaluated. Pearson's chi-square test was used to compare categorical variables. To compare numerical variables, the one-way ANOVA test was applied. For variables not conforming to a normal distribution, the Kruskal-Wallis test was used. The level of statistical significance was set at p ≤ 0.05. Our results show that the children with obesity consumed fewer fresh foods (median = 3, IQI = 4.00-2.00, p = 0.026), consumed more ultra-processed foods (median = 4, IQI = 4.00-2.00, p = 0.011), performed fewer mastication sequences (median = 2, IQI = 3.00-2.00, p = 0.007), and ate faster (median = 58.50, IQI = 69.00-48.00, p = 0.026) compared to children of normal weight. We conclude that children with obesity exhibit differences in food consumption and masticatory performance compared to children of normal weight.

Application of numerical simulation studies to determine dynamic loads acting on the human masticatory system during unilateral chewing of selected foods

Introduction: This paper presents its kinematic-dynamic computational model (3D) used for numerical simulations of the unilateral chewing of selected foods. The model consists of two temporomandibular joints, a mandible, and mandibular elevator muscles (the masseter, medial pterygoid, and temporalis muscles). The model load is the food characteristic (i), in the form of the function F_i = f(Δh_i)-force (F_i) vs change in specimen height (Δh_i). Functions were developed based on experimental tests in which five food products were tested (60 specimens per product). Methods: The numerical calculations aimed to determine: dynamic muscle patterns, maximum muscle force, total muscle contraction, muscle contraction corresponding to maximum force, muscle stiffness and intrinsic strength. The values of the parameters above were determined according to the mechanical properties of the food and according to the working and non-working sides. Results and Discussion: Based on the numerical simulations carried out, it can be concluded that: (1) muscle force patterns and maximum muscle forces depend on the food and, in addition, the values of maximum muscle forces on the non-working side are 14% lower than on the working side, irrespective of the muscle and the food; (2) the value of total muscle contraction on the working side is 17% lower than on the non-working side; (3) total muscle contraction depends on the initial height of the food; (4) muscle stiffness and intrinsic strength depend on the texture of the food, the muscle and the side analysed, i.e., the working and non-working sides.

Food Hardness Modulates Behavior, Cognition, and Brain Activation: A Systematic Review of Animal and Human Studies

Food hardness is one of the dietary features that may impact brain functions. We performed a systematic review to evaluate the effect of food hardness (hard food versus soft food diet) on behavior, cognition, and brain activation in animals and humans (PROSPERO ID: CRD42021254204). The search was conducted on 29 June 2022 using Medline (Ovid), Embase, and Web of Science databases. Data were extracted, tabulated by food hardness as an intervention, and summarized by qualitative synthesis. The SYRCLE and JBI tools were used to assess the risk of bias (RoB) of individual studies. Of the 5427 studies identified, 18 animal studies and 6 human studies met the inclusion criteria and were included. The RoB assessment indicated that 61% of animal studies had unclear risks, 11% had moderate risks, and 28% had low risks. All human studies were deemed to have a low risk of bias. The majority (48%) of the animal studies showed that a hard food diet improved behavioral task performance compared to soft food diets (8%). However, 44% of studies also showed no differential effects of food hardness on behavioral tests. It was also evident that certain regions of the brain were activated in response to changes in food hardness in humans, with a positive association between chewing hard food, cognition performance, and brain function. However, variations in the methodologies of the included studies hindered the meta-analysis execution. In conclusion, our findings highlight the beneficial effects of dietary food hardness on behavior, cognition, and brain function in both animals and humans, however, this effect may depend on several factors that require further understanding of the causality.

Subjective and objective evaluation of masticatory function in patients with bimaxillary implant-supported prostheses

BACKGROUND

People perform poorly in masticatory function tests despite well-functioning prostheses. However, it is unclear whether there is an agreement between subjective and objective measures of mastication.

OBJECTIVES

To investigate the association between subjective and objective measures of masticatory function in patients with bimaxillary implant-supported prostheses.

MATERIALS AND METHODS

An experimental group (n = 25, age = 70.6 ± 7.5 years, eight women) with bimaxillary implant-supported fixed prostheses and a control group (n = 25, age = 69.0 ± 5.3, 13 women) with natural dentition were recruited. The participants in the experimental group were included if they had been using the prosthesis for at least a year and had no obvious complaints with their prostheses. The control group was people with natural dentition and without any prostheses or complaints related to the masticatory system. The masticatory function was evaluated objectively with food comminution and mixing ability tests, and subjectively with jaw function limitation scale (JLFS) and oral health impact profile (OHIP).

RESULTS

The experimental group performed poorly in both objective tests (p < .001). However, there was no significant differences between the two groups in total JFLS (p = .114) and OHIP (p = .312) scores. Though, there were certain positive correlations between the food comminution test and JFLS subdomains in the control group, and a positive correlation between food comminution test and specific subdomains of OHIP in the experimental group indicating poor correlation between the subjective and objective measures.

CONCLUSION

Although patients with implant prostheses show poor masticatory performance, there is no agreement in the objective and subjective measures of mastication.

Deglutition and the Regulation of the Swallow Motor Pattern

Despite centuries of investigation, questions and controversies remain regarding the fundamental genesis and motor pattern of swallow. Two significant topics include inspiratory muscle activity during swallow (Schluckatmung, i.e., "swallow-breath") and anatomical boundaries of the swallow pattern generator. We discuss the long history of reports regarding the presence or absence of Schluckatmung and the possible advantages of and neural basis for such activity, leading to current theories and novel experimental directions.

Regeneration of sensory nerve branches in extraction socket and surrounding alveolar bone in rat: immunohistochemical observation of the axon and myelin sheath changes

The purpose of this study was to investigate the process and derivation of the distribution of the sensory nerves that appear in the extraction socket and surrounding alveolar bone following tooth extraction. The right mandibular first molar of rats and periodontal ligament were extracted as a single mass, and the mandible was harvested after days 1, 3, 5, and 7 after extraction. Serial sections of 7 µm thickness were prepared for the proximal root (Section A), buccolingual root (Section B), and centrifugal root (Section C) of the first molar. H–E staining and immunohistochemical staining with anti-S100 antibody and anti-NF-L antibody were carried out. The presence of nerve fiber bundles in the blood clot was already evident on post-extraction day 3, and on post-extraction day 7. On day 3, the number of axons in Sections B and C had greatly decreased, indicating that, after extraction, the connection between peripheral nerve tissue and the trigeminal ganglion was temporarily markedly reduced in the region of the alveolar branch. Although the myelin sheaths were regenerating on day 5, the majority of the axons of the alveolar branches extending from the inferior alveolar nerve were seen to be extremely thin and scattered, despite their further regeneration. The above results suggest that the newly myelinated nerves are actually derived from the bone marrow to the extraction socket, so few nerves, rather than being derived from the alveolar branches that had innervated the extracted tooth.

Masticatory performance in patients with jaw muscle pain: A case control study

Introduction

Masticatory function is often impaired in patients with painful temporomandibular disorders (TMD) therefore more detailed studies on comminution and mixing ability are warranted in well-defined TMD patients with chronic myalgia. Moreover, there is a need to explore the correlation between any changes in perceived pain or fatigue in such patients and the masticatory function.

Materials and methods

Self-assessments using questionnaires regarding pain, oral health, jaw function, masticatory ability, fear of movement and psychosocial signs were answered by all the participants. A series of chewing tasks involving viscoelastic food and two-colored gum was performed. Optical imaging and analyzing was conducted. Bite force as well as characteristics of pain and fatigue were assessed.

Results

In patients, the fragmented soft candy particles were less in number and had larger median of area and minimum Feret's diameter after standardized chewing compared to healthy individuals (P = 0.02). Surprisingly, the two-colored Hue-Check gum was less mixed by the healthy controls since they displayed a greater variance of the hue (P = 0.04). There were significant differences between the patients and the healthy controls in the self-assessed masticatory ability mainly regarding pain-related variables.

Conclusions

Objectively, TMD patients with chronic myalgia exhibited an impaired masticatory performance with less efficiency in comminuting soft viscoelastic food compared to the pain-free healthy control group. There was an agreement between the patients' self-assessed masticatory ability and the efficiency of their masticatory function.

Chewing side preference and laterality in patients treated with unilateral posterior implant-supported fixed partial prostheses

BACKGROUND

It is not clear to what extent chewing is improved by unilateral oral rehabilitation with implant-supported fixed partial prostheses (ISFPPs).

OBJECTIVES

This study aimed to investigate whether patients treated with unilateral ISFPPs in the maxilla use their prostheses during mastication to the same extent as they used their contralateral natural teeth. A further aim was to investigate whether there is a correlation between preferred chewing side and laterality.

METHODS

Chewing side preference was assessed in 15 participants treated with unilateral ISFPPs in the maxilla. The first, second, third, fifth and tenth chewing cycles were assessed, and the test was repeated 10 times. All participants also answered a questionnaire about their chewing side preference.

RESULTS

Most of the participants presented bilateral chewing, but two (13%) chewed only on the ISFPP. There was no statistically significant association between the objectively assessed chewing side and dental status (natural teeth or ISFPPs) during any of the recorded chewing cycles (p > .1). There were statistically significant correlations between both the subjectively reported usually preferred chewing side and the subjective chewing side preference during the test and the objectively assessed chewing side for the first three chewing cycles (p < .01). No correlation was found between handedness and the objectively assessed chewing side.

CONCLUSION

In the present study, most participants chewed bilaterally, and chewing was performed both on the ISFPP and on the natural teeth. No correlation was found between the preferred chewing side, objectively or subjectively determined and laterality.

Neural Basis of Etiopathogenesis and Treatment of Cervicogenic Orofacial Pain

(1) Background and Objectives: The aim of this narrative review was to analyze the neuroanatomical and neurophysiological basis of cervicogenic pain in cervico-cranial pain syndromes, focusing particularly on cervico-orofacial syndromes as a background for the proper diagnosis and non-surgical treatment. Relevant literature on the topic from past 120 years has been surveyed. (2) Material and Methods: We surveyed all original papers, reviews, or short communications published in the English, Spanish, Czech or Slovak languages from 1900 to 2020 in major journals. (3) Results: The cervicogenic headache originates from the spinal trigeminal nucleus where axons from the C₁–C₃ cervical spinal nerves and three branches of the trigeminal nerve converge (trigeminocervical convergence) at the interneurons that mediate cranio-cervical nociceptive interactions. The role of the temporomandibular joint in the broad clinical picture is also important. Despite abundant available experimental and clinical data, cervicogenic orofacial pain may be challenging to diagnose and treat. Crucial non-surgical therapeutic approach is the orthopedic manual therapy focused on correction of body posture, proper alignment of cervical vertebra and restoration of normal function of temporomandibular joint and occlusion. In addition, two novel concepts for the functional synthesis of cervico-cranial interactions are the tricentric concept of mouth sensorimotor control and the concept of a cervicogenic origin of bruxism. (4) Conclusions: Understanding the basis of neuroanatomical and neurophysiological neuromuscular relations enables an effective therapeutic approach based principally on orthopedic manual and dental occlusal treatment.

Development of a system to analyze oral frailty associated with Alzheimer's disease using a mouse model

The rapid aging of the population makes the detection and prevention of frailty increasingly important. Oral frailty has been proposed as a novel frailty phenotype and is defined as a decrease in oral function coexisting with a decline in cognitive and physical functions. Oral frailty has received particular attention in relation to Alzheimer's disease (AD). However, the pathomechanisms of oral frailty related to AD remain unknown. It is assumed that the mesencephalic trigeminal nucleus (Vmes), which controls mastication, is affected by AD pathology, and as a result, masticatory function may be impaired. To investigate this possibility, we included male 3 × Tg-AD mice and their non-transgenic counterpart (NonTg) of 3-4 months of age in the present study. Immunohistochemistry revealed amyloid-β deposition and excessive tau phosphorylation in the Vmes of 3 × Tg-AD mice. Furthermore, vesicular glutamate transporter 1-immunopositive axon varicosities, which are derived from Vmes neurons, were significantly reduced in the trigeminal motor nucleus of 3 × Tg-AD mice. To investigate whether the AD pathology observed in the Vmes affects masticatory function, we analyzed electromyography of the masseter muscle during feeding. The 3 × Tg-AD mice showed a significant delay in masticatory rhythm compared to NonTg mice. Furthermore, we developed a system to simultaneously record bite force and electromyography of masseter, and devised a new method to estimate bite force during food chewing in mice. Since the muscle activity of the masseter showed a high correlation with bite force, it could be accurately estimated from the muscle activity. The estimated bite force of 3 × Tg-AD mice eating sunflower seeds was predominantly smaller than that of NonTg mice. However, there was no difference in masseter weight or muscle fiber cross-sectional area between the two groups, suggesting that the decreased bite force and delayed mastication rhythm observed in 3 × Tg-AD mice were not due to abnormality of the masseter. In conclusion, the decreased masticatory function observed in 3 × Tg-AD mice was most likely caused by AD pathology in the Vmes. Thus, novel quantitative analyses of masticatory function using the mouse model of AD enabled a comprehensive understanding of oral frailty pathogenesis.

Chewing modulates the human cortical swallowing motor pathways

When eating, mastication is always followed by swallowing. The present study assessed the effect of mastication on swallowing-related neural pathways in humans. Twenty healthy volunteers participated and underwent baseline transcranial magnetic stimulation to evaluate cortico-pharyngeal and cortico-hand motor-evoked potentials (MEPs). Next, they performed a chewing task and a swallowing task. Repeated-measures ANOVA revealed that pharyngeal MEPs were significantly higher after the swallowing task than after the chewing task, even though the number of swallows across tasks was matched. This implies that chewing movements suppress swallowing-related activity in the pharyngeal motor circuit.

The Effect of a Masticatory Muscle Training Program on Chewing Efficiency and Bite Force in People with Dementia

Until now, no study has investigated the effects of masticatory muscle training on chewing function in people with dementia. This study aimed to investigate whether physiotherapeutic exercises for the masticatory muscles have an influence on chewing efficiency and bite force in people with dementia. In a clinical trial with stratified randomization subjects were assigned to three groups based on the Mini Mental State Examination (MMSE: group 1—28–30, group 2—25–27, group 3—18–24). Each group was divided into an experimental (ExpG, intervention) and control group (ConG, no intervention). As intervention a Masticatory Muscle Training (MaMuT) (part 1: three physiotherapeutic treatments and daily home exercises, part 2: daily home exercises only) was carried out. Chewing efficiency and bite force were recorded. The MaMuT influenced the masticatory performance regardless of the cognitive state. Bite force increased in ExpG 1 and 2. Without further training, however, the effect disappeared. Chewing efficiency increased in all ExpG. After completion of the training, the ExpG 2 and 3 showed a decrease to initial values. Subjects of ExpG 1 showed a training effect at the final examination, but a tendency toward the initial values was observed. ExpG 3 seemed to benefit most from the physiotherapeutic exercises in terms of improving chewing efficiency by the end of the intervention phase. ExpG 1 showed the greatest gain in bite force. The MaMuT program is a potential method of improving masticatory performance in people with cognitive impairment or dementia when used on a daily basis.

Effect of malocclusion on jaw motor function and chewing in children: a systematic review

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.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-021-04356-y.

Postnatal Maturation of Glutamatergic Inputs onto Rat Jaw-closing and Jaw-opening Motoneurons

Motoneurons that innervate the jaw-closing and jaw-opening muscles play a critical role in oro-facial behaviors, including mastication, suckling, and swallowing. These motoneurons can alter their physiological properties through the postnatal period during which feeding behavior shifts from suckling to mastication; however, the functional synaptic properties of developmental changes in these neurons remain unknown. Thus, we explored the postnatal changes in glutamatergic synaptic transmission onto the motoneurons that innervate the jaw-closing and jaw-opening musculatures during early postnatal development in rats. We measured miniature excitatory postsynaptic currents (mEPSCs) mediated by non-NMDA receptors (non-NMDA mEPSCs) and NMDA receptors in the masseter and digastric motoneurons. The amplitude, frequency, and rise time of non-NMDA mEPSCs remained unchanged among postnatal day (P)2-5, P9-12, and P14-17 age groups in masseter motoneurons, whereas the decay time dramatically decreased with age. The properties of the NMDA mEPSCs were more predominant at P2-5 masseter motoneurons, followed by reduction as neurons matured. The decay time of NMDA mEPSCs of masseter motoneurons also shortened remarkably across development. Furthermore, the proportion of NMDA/non-NMDA EPSCs induced in response to the electrical stimulation of the supratrigeminal region was quite high in P2-5 masseter motoneurons, and then decreased toward P14-17. In contrast to masseter motoneurons, digastric motoneurons showed unchanged properties in non-NMDA and NMDA EPSCs throughout postnatal development. Our results suggest that the developmental patterns of non-NMDA and NMDA receptor-mediated inputs vary among jaw-closing and jaw-opening motoneurons, possibly related to distinct roles of respective motoneurons in postnatal development of feeding behavior.

Children who have more toothache-related behaviors have worse masticatory performance

Inadequate masticatory function can be linked to oral problems and result in functional limitation. In children, this function is extremely important for their development, and therefore efforts are made to keep it adequate. To evaluate whether dental pain-related behaviors are associated with masticatory performance (MP). A cross-sectional study was conducted with a sample of 123 children from 3 to 5 years old. Toothache was evaluated using the Dental Discomfort Questionnaire. Anthropometric data, predominant type of breathing, presence of malocclusion, number of posterior teeth cavitated by dental caries, and masticatory units were collected. MP was measured by the median size of the crushed particles (X₅₀ ) after 20 cycles of chewing the Optocal test material and was calculated with the Rosin-Rammler equation. Data analysis involved a description of variable frequencies, as well as simple and multiple linear regression, and a confidence level set at 95%. The mean scores of dental pain-related behaviors were 1.14 (±1.90) points, and the mean X₅₀ value was 3.96 mm (±1.34). In the multiple linear regression, a larger median size of the particles remained associated with a higher score of dental pain-related behaviors (β = +.81, p = .01); mouth breathing (β = +.22, p = .01); and a smaller number of masticatory units (β = -.22, p = .02). Greater dental pain-related behavior scores are associated with worse MP, regardless of the presence of associations with predominantly oral breathing and fewer chewing units.

Adhesive Management of Anterior Tooth Wear in Combination with the Dahl Concept-A 27-Month Observational Case Series

Localized anterior maxillary tooth wear caused by erosion and attrition with loss of interocclusal space is difficult to manage. This observational case-series study reports six cases with worn anterior dentition treated with labial ceramic and palatal direct resin composite veneers at an increased vertical dimension of occlusion without restoration of unaffected posterior teeth. Thirty-six palatal direct veneers were made in six patients from a nanohybrid resin composite with the help of a wax-up-based template at an increased vertical dimension. After the complete re-establishment of posterior occlusion, 40 labial lithium-disilicate ceramic veneers were fabricated with a mock-up-guided method. The sandwich veneers were evaluated according to the United States Public Health Service (USPHS) criteria after a mean service time of 22.7 months. Re-establishment of posterior contacts as well as subjective patient satisfaction and function were evaluated. The overall success of the labial ceramic veneers was excellent. The quality of the palatal resin composite restorations was found to be good with predominantly "Alpha" scores. The marginal quality (11.1% and 33.3% of integrity and discoloration, respectively) and surface roughness (16.7%) showed small deteriorations indicated by "Beta" scores. The resin composite showed, in general, signs of wear facets which resulted in "Beta" scores in 44.4% of the cases. Posterior contacts re-established firmly within 4 weeks in all cases. Patient satisfaction with esthetics and function was high. The short-term outcome of this non-invasive treatment option is favorable and promising.

Reliability and validity of a new colour-changing test food with an acid-base reaction for the clinical assessment of masticatory performance

The aim of this study was to determine the reliability and validity of a new test food for the clinical assessment of masticatory performance. The test food had two overlapping acidic/basic halves. Ten dentate subjects chewed one unit for 10-100 cycles. One subject chewed ten units for the same number of cycles. Differences in the L*, a* and b* colour axes were determined before and after chewing by ANOVA. Colour guides were created based on the values of these axes and matched with the number of cycles. The reliability of the guides was evaluated using 30 images, where three examiners indicated the number of cycles in which the colour closest to that of a chewed material was found. The data were contrasted with the real values of the guides to determine the validity (Kappa coefficients). The equivalence of the guides with the median particle size (X₅₀) was determined using equidimensional curves. The test food progressively changed from green to pink during chewing. As the number of cycles increased, the a* values increased and the b* values decreased (p < 0.05). Overall, the guides showed a Kappa value >0.8 for the intra-examiner and inter-examiner reliability and the validity comparisons. The a* and X₅₀ values were inversely proportional to each other, and the b* values showed a direct relationship with the X₅₀ values. The L* values did not show correspondence. The new test food showed high reliability and validity for the assessment of masticatory performance through clinical colour guides matched with the number of cycles and X₅₀.

A Qualitative and Comprehensive Analysis of Caries Susceptibility for Dental Fluorosis Patients

Dental fluorosis (DF) is an endemic disease caused by excessive fluoride exposure during childhood. Previous studies mainly focused on the acid resistance of fluorotic enamel and failed to reach a consensus on the topic of the caries susceptibility of DF patients. In this review, we discuss the role of DF classification in assessing this susceptibility and follow the “four factors theory” in weighing the pros and cons of DF classification in terms of host factor (dental enamel and saliva), food factor, bacteria factor, and DF treatment factor. From our analysis, we find that susceptibility is possibly determined by various factors such as the extent of structural and chemical changes in fluorotic enamel, eating habits, fluoride levels in diets and in the oral cavity, changes in quantity and quality of saliva, and/or oral hygiene. Thus, a universal conclusion regarding caries susceptibility might not exist, instead depending on each individual’s situation.

Technical note: Artificial Resynthesis Technology for the experimental formation of dental microwear textures

Dental microwear formation on the posterior dentition is largely attributed to an organism's diet. However, some have suggested that dietary and environmental abrasives contribute more to the formation process than food, calling into question the applicability of dental microwear to the reconstruction of diet in the fossil record. Creating microwear under controlled conditions would benefit this debate, but requires accurately replicating the oral environment. This study tests the applicability of Artificial Resynthesis Technology (ART 5) to create microwear textures while mitigating the challenges of past research. ART 5 is a simulator that replicates the chewing cycle, responds to changes in food texture, and simulates the actions of the oral cavity. Surgically extracted, occluding pairs of third molars (n = 2 pairs) were used in two chewing experiments: one with dried beef and another with sand added to the dried beef. High-resolution molds were taken at 0, 50, 100, 2500, and 5000 simulated chewing cycles, which equates to approximately 1 week of chewing. Preliminary results show that ART 5 produces microwear textures. Meat alone may produce enamel prism rod exposure at 5000 cycles, although attrition cannot be ruled out. Meat with sand accelerates the wear formation process, with enamel prism rods quickly obliterated and "pit-and-scratch" microwear forming at approximately 2500 cycles. Future work with ART 5 will incorporate a more thorough experimental protocol with improved controls, pH of the simulated oral environment, and grit measurements; however, these results indicate the potential of ART 5 in untangling the complex variables of dental microwear formation.

Stability of masticatory movements after placement of implant-supported denture

The purpose of this study was to clarify the stability of masticatory movement after placement of implant-supported denture. Fourteen patients (patient group) with mandibular implants denture and maxillary complete denture and 30 dentate adults (control group) were asked to chew a boiled fishpaste, and the masticatory movement was recorded using MKG. For the 10 cycles beginning with the 5th cycle of mastication, the parameters representing the stability of masticatory movement were calculated. Data collected at 1, 3, 6, 9 months and 1, 2, 3 years after insertion of implants denture were compared between sessions and also between the patient and control groups. The mean and standard deviation of the values in the patient group at 1 month after insertion of implants denture were large, but gradually decreased 6 to 9 months after insertion of implants denture. Each parameter maintained almost the same value from 1 to 3 years. The parameter values of the patient group were significantly larger than those of control group from 1 to 9 months after insertion of implants denture, but 1 year after insertion of implants denture, there was no significant difference between the two groups in 5 out of 7 parameters. From these results, it was suggested that a certain duration, about 9 months to 1 year, was necessary for patients with implants denture to adapt to the new masticatory function and that the timing of functional evaluation should be set to 1 year after insertion of implants denture.

Masticatory function in children with Down syndrome

The objective was to study masticatory function of 8 to 10-year-old children with Down syndrome (DS) through the evaluation of maximum occlusal force and masticatory performance (via medium particle size) and compare it to that of children of the same age without DS.

METHODS

A convenience sample of eight, 8-10-year-old children with DS were included in this cross-sectional study. The study had ethical approval and parents provided informed consent. Exclusion criteria were large carious lesions, dental pain or previous orthodontic/orthopedic treatment. Masticatory performance was evaluated with an artificial test food (Optosil Comfort®) after 20 cycles and at swallowing threshold. The chewed material was collected, dried and sieved. The material on each sieve was weighed; the weights were used to calculate medium particle size. Maximum occlusal force (1st permanent molars) was determined using the GM10 Nagano Keiki Co.™ portable transducer. The number of cycles until swallowing threshold, cycle and sequence durations were also compared. The data for the reference group (n = 32) came from a previous study in children of the same age. Descriptive statistics as well as comparisons with Mann-Whitney tests and simple and multiple regression analysis were performed. Cutoff was set at p≤.05.

RESULTS

Medium particle size is larger by 44% after 20 chewing cycles and 75% at swallowing threshold (p<.05) in children with DS. Median maximum occlusal force was 254 kN in DS children and 499 kN in children without the syndrome (p<.001). 48% of the variance in maximum occlusal force is explained by having DS. There were also significant differences in sequence and cycle durations. All significant differences had large effect sizes (˃1). Although the children with DS chewed more cycles before swallowing threshold the difference was not significant.

CONCLUSIONS

Children with DS have approximately 50% of the masticatory performance and maximum occlusal force of children of the same age without DS. These findings can be associated to the feeding problems reported in children with DS.

Effect of dental malocclusion on cerebellar neuron activation via the dorsomedial part of the principal sensory trigeminal nucleus

Occlusion has been proposed to play a role for body posture and balance, both of which are mediated mainly by the cerebellum. The dorsomedial part of the principal sensory trigeminal nucleus (Vpdm) has direct projection to the cerebellum. The experimental unilateral anterior crossbite (UAC) has an impact on the motor nuclei in the brain stem via trigeminal mesencephalic nucleus (Vme). The current aim was to explore whether UAC has an impact on Vpdm‐cerebellum circuit. The inferior alveolar nerve was injected into cholera toxin B subunit (CTb), the cerebellum was injected into fluoro‐gold (FG), and the Vpdm was injected into biotinylated dextran amine (BDA) to identify the activation of Vpdm‐cerebellum circuit by UAC. Data indicated that there were more neuronal nuclei (NeuN)/CTb/FG triple‐labelled neurons and NeuN/CTb/vesicular glutamate transporter 1(VGLUT1) triple‐labelled neurons in the Vpdm, and more NeuN/BDA/ VGLUT1 triple‐labelled neurons in the cerebellum of rats with UAC than in control rats. The VGLUT1 expression in the Vpdm and cerebellum in the UAC group was higher than that in control rats. These findings indicate an excitatory impact of UAC on the Vpdm‐cerebellum pathway and support the role of occlusion for body posture and balance.

Effects of low occlusal loading on the neuromuscular behavioral development of cortically-elicited jaw movements in growing rats

The effect of altered occlusal force on masticatory-related neuromuscular control, which projects from the anterior part of the cortical masticatory area (A-CMA), during growth remains unclear. This study sought to evaluate the effect of occlusal hypofunction on neuromuscular development of jaw muscle activities and cortically-induced rhythmic jaw movements (RJMs) in growing rats. Sixty-four 2-week-old male albino Wistar rats were divided into the control (fed normal diet) and experimental (fed soft diet) groups soon after weaning. Electromyographic activity was recorded at 5, 7, 9, and 11 weeks from the right masseter and anterior digastric along with RJMs. We found a significantly longer onset latency and smaller peak-to-peak amplitude in the experimental group than that in the control group. The RJMs showed an increase in gape size and lateral excursion until up to 9 weeks in both groups. However, both the average gape size and lateral excursion were significantly smaller in the experimental group than that in the control group after 9 weeks. The jaw movement pattern also showed a significant decrease at the maximum opening period in the experimental group. Our findings indicate that inadequate occlusal function during growth alters neuromuscular control of masticatory behaviors and impairs the pattern of RJMs.

Consensus on the terminologies and methodologies for masticatory assessment

A large number of methodological procedures and experimental conditions are reported to describe the masticatory process. However, similar terms are sometimes employed to describe different methodologies. Standardisation of terms is essential to allow comparisons among different studies. This article was aimed to provide a consensus concerning the terms, definitions and technical methods generally reported when evaluating masticatory function objectively and subjectively. The consensus is based on the results from discussions and consultations among world‐leading researchers in the related research areas. Advantages, limitations and relevance of each method are also discussed. The present consensus provides a revised framework of standardised terms to improve the consistent use of masticatory terminology and facilitate further investigations on masticatory function analysis. In addition, this article also outlines various methods used to evaluate the masticatory process and their advantages and disadvantages in order to help researchers to design their experiments.

Increase in masseter muscle activity by newly fabricated complete dentures improved brain function

PURPOSE

To reveal effects of improvement of masseter muscle activity on brain function in elderly people wearing complete dentures.

METHODS

Subjects were 14 edentulous patients with a chief complaint of the inconvenience of their complete dentures. The surface electromyographic (EMG) activity of the masseter muscles was measured. Brain activities were analyzed with functional magnetic resonance imaging (fMRI), employing chewing gum as the task program. Cognitive functions were evaluated with Trail Making Test Part A (TMT-A), Rey Auditory Verbal Learning Test (RAVLT) and Rey-Osterrieth Complex Figure Test (R-OCFT). Those evaluations were performed in which subjects wore their old dentures (OD) or newly fabricated dentures (ND).

RESULTS

We compared ND condition with OD condition. The masseter muscle activity significantly increased in ND condition (p < 0.05, Wilcoxon signed rank test). The brain activity increased significantly in the superior frontal gyrus, precentral gyrus, putamen, inferior parietal lobule, cerebellum, inferior frontal lobe, and middle frontal gyrus under the ND condition than under the OD condition (p < 0.01, uncorrected, cluster size > 10 voxels). Results of TMT-A, RAVLT, and R-OCFT were also significantly improved (p < 0.05, Wilcoxon signed rank test).

CONCLUSIONS

In the edentulous elderly, the brain activity was increased following the improvement of the masseter muscle activity. Consequently, it is possible that the improvement of the masseter muscle activity might influ ence on the attention, verbal skills, and visual memory.

Mapping research trends of temporomandibular disorders from 2010 to 2019: A bibliometric analysis

BACKGROUND

Because of various clinical manifestations and complicated courses, temporomandibular disorders (TMDs) are difficult to treat. Current knowledge about this disease remains insufficient for precise treatment after diagnosis.

OBJECTIVES

The objective of this study is to obtain and map the overall literature trends and most cited keywords in TMDs research.

METHODS

Many indicators, including annual number of publications, country distribution, global cooperations, author contributions, original journals, cited references and keywords, were calculated and evaluated using VOSviewer v.1.6.13, which visualised many results, from the WoSCC database.

RESULTS

A total of 3121 papers on TMDs research were retrieved from 2010 to 2019. The United States produced the most articles published, but the most productive institution was the University of Sao Paulo (Brazil). Researchers and institutions conducting TMDs research have shown a very widespread and close connection. TMDs have been studied worldwide by many research centres. Professor Svensson P was the most published researcher in TMDs research and the Journal of Oral Rehabilitation published the most TMDs research articles. The top cited references mainly presented diagnostic criteria of TMDs. The most cited keywords formed clusters: (a) Anatomical factor of TMDs, (b) Symptoms of TMDs and (c) RDC/TMD, the risk factors, biopsychosocial factors and epidemiology of TMDs.

CONCLUSIONS

The research results provide very valuable data for a thorough understanding of the research status of TMDs and demonstrated international cooperation.

Effects of preventing intercuspation on the precision of jaw movements

BACKGROUND

Closing movements are among the jaw's basic physiological motor actions. During functional movements, the jaw changes position continually, which requires appropriate proprioception. However, the significance of the various proprioceptive receptors involved and how they interact is not yet fully clear.

OBJECTIVES

This study's main objective was to test whether preventing intercuspation (IC) for 1 week would affect the precision of jaw-closing movements into IC and the functional space of habitual chewing movements (HCM). A secondary objective was to compare precision of jaw-closing movements into IC with the precision of movements into a target position (TP) far from IC.

METHODS

Fourteen participants' HCM and jaw-closing movements into IC were recorded on two sessions (T1 and T2) 1 week apart. Between sessions, participants wore posterior bite plates to prevent IC. They also received a 10-minute training session at T1 to guide their jaw-closing movements into TP. The precision of the closing movements into IC and TP was analysed. For HCM, the vertical amplitude, lateral width and area of chewing cycles were evaluated.

RESULTS

The precision of jaw movements into IC increased as the jaw gap decreased, but precision did not differ significantly between T1 and T2. For HCM, the vertical amplitude and area of chewing cycles increased significantly between T1 and T2. The precision of the closing trajectory into TP increased significantly during the training session.

CONCLUSION

Our results confirm the excellent adaptability of the craniomandibular system, controlled by stringent motor programmes that are supported by continuous peripheral sensory input.

The reciprocal jaw-muscle reflexes elicited by anterior- and back-tooth-contacts-a perspective to explain the control of the masticatory muscles

AIMS

Tooth-contact sensations are considered essential to boost jaw adductor muscles during mastication. However, no previous studies have explained the importance of the inhibitory reflex of human anterior-tooth (ANT)-contacts in mastication. Here I present the "reciprocal reflex-control-hypothesis" of mammalian mastication.

SUBJECTS AND SETTING OF THE STUDY

I demonstrate the hypothesis with the live kinematics of free jaw-closures as inferred from T-Scan recordings of dental patients.

RESULTS

The jaw-closures started with negligible force, predominantly with ANT-contacts (the AF-bites). The first ANT-contact inhibited the first kinematic tilt of the mandible, whereas the bites starting from a back-tooth (BAT)-contact (the BF-bites) accelerated the first tilt. The second tilt established a low-force static tripod of the ANT- and bilateral BAT-contacts for a fixed mandible-maxilla relation. Thereafter, semi-static bite force increased rapidly, relatively more in the BAT-area.

DISCUSSION AND CONCLUSIONS

In the vertical-closure phase of chewing, the primate joint-fulcrum (class 3 lever) conflicts with the food-bolus-fulcrum in the BAT-area (class 1 lever). The resilient class 3 and 1 lever systems are superseded by an almost static mechanically more advantageous class 2 lever with a more rigid fulcrum at the most anterior ANT-contact. For humans, the class 2 levered delivery of force also enables forceful horizontal food grinding to be extended widely to the BAT-area.

Functional changes in the temporomandibular joint mechanoreceptors associated with experimentally induced condylar resorption in rats

OBJECTIVES

To evaluate the influence of experimentally induced progressive condylar resorption (PCR) on temporomandibular joint (TMJ) mechanoreception.

MATERIALS AND METHODS

Twenty 13-week-old male albino Wistar rats were divided equally into control and PCR groups. A compressive force was loaded on the left TMJ of PCR group rats to induce condylar resorption. Single-unit activities of TMJ mechanoreceptors were also induced through passive jaw movement. Recording was performed for the left Gasserian ganglion at 3 days and 1 week after the establishment of PCR group. The effects of PCR on TMJ units were assessed by measuring the firing threshold, maximum instantaneous firing frequency, and average firing frequency.

RESULTS

Compared with the control group, there were no significant differences in the firing threshold of the PCR group after 3 days. The thresholds were significantly higher 1 week after compressive force loading on the condyle. The maximum instantaneous firing frequencies and the average firing frequencies showed no significant differences after 3 days. However, these were significantly lower 1 week after compressive force loading.

CONCLUSIONS

The findings suggest that compressive force loading on the condyle may influence the function of TMJ mechanoreceptors.

Age-related changes in oral motor-control strategies during unpredictable load demands in humans

To investigate age-related changes in oral motor strategies in response to unpredictable load demands. Sixty-five healthy children (aged 3-17 yr) were divided into five age-groups based on their dental eruption stages and compared with a group of healthy adults (aged 18-35 yr). Each participant was asked to perform a standardized motor control task involving 'pulling' and 'holding' a force transducer with the anterior teeth. Different loads were attached to the force transducer in an unpredictable manner. The temporal force profile was divided into two time-segments (an initial segment and a later segment). The peak force and peak force rate during the initial time-segment, and the holding force and intra-trial variability (coefficient of variation) during the later time-segment, were measured. The results showed no differences in the peak force, peak force rate, holding force, and force variability in children compared with adults. However, the trends in the data evaluated using a segmented regression analysis showed that a breakpoint (abrupt change) consistently occurred in the late-mixed dentition group (age 9-11 yr) for most of the outcome variables. The results indicate that while the motor control strategies in children appear to be similar to those in adults, there is a shift in the oral motor developmental trend during the late-mixed dentition stage.

Modulation of Intermuscular Beta Coherence in Different Rhythmic Mandibular Behaviors

Introduction

Jaw movement during chewing and speech is facilitated by neural activation patterns for opening and closing movements of the mandible. This study investigated anatomic- and task-dependent differences in intermuscular coherence (IMC) and their association with the parameters of jaw muscle activity using surface electromyography (sEMG).

Methods

We recorded sEMG activation from bilateral and ipsilateral jaw-closing muscle pairs during non-nutritive and nutritive chewing, and during a syllable repetition task. IMC and cross-correlational analyses between bilateral and ipsilateral muscle pairs were performed.

Results

Intermuscular coherence in the beta band was statistically significant between agonist jaw-closing muscle pairs, with beta IMC weaker for rapid syllable repetition compared to chewing tasks. Cross-correlational analysis of muscle co-activation, as well as sEMG burst amplitude, was positively associated with beta IMC strength.

Discussion

Beta IMC was influenced heavily by task-dependent behavioral goals and physiologic demands, which was interpreted as evidence of shared neural drive among jaw-closing muscles.

Effect of food hardness on chewing behavior in children

Objective

To investigate the effects of food hardness on chewing behavior in children compared with adults.

Materials and methods

Healthy children (3–17 years) were equally divided into five groups based on their dental eruption stages. Each participant ate soft and hard viscoelastic test food models (3 each), while the three-dimensional jaw movements and electromyographic (EMG) activity of the bilateral masseter muscles were recorded. The data from the children were compared with a control group of healthy adults (18–35 years). The data were analyzed with nonparametric tests.

Results

There was no significant difference in the number of chewing cycles and the duration of the chewing sequence between children groups and adults. Children with primary dentition (3–5 years) showed shorter lateral jaw movement and higher muscle activity at the end of the chewing sequence, compared with adults. Further, children’s age-groups (3–14 years) failed to adapt their jaw muscle activity to food hardness. However, at the late-permanent dentition stage (15–17 years), children were capable of performing adult-like chewing behavior.

Conclusions

Overall, it seems that children as young as 3-year-old are quite competent in performing basic chewing function similar to adults. Yet, there are differences in the anticipation or adaption of jaw muscle activity and jaw kinematics to food hardness.

Clinical relevance

The study may have clinical implication in the diagnosis and management of children with chewing impairment associated with dental malocclusions and other orofacial dysfunctions.

Natural food mastication capability in preschool children according to their oral condition: A preliminary study

This study investigated, for the first time, the masticatory capability of preschool children using natural foods, and the impact of an early oral health alteration (early childhood caries: ECC) on the granulometry of ready-to-swallow food boluses. Thirteen children with ECC were compared to 13 preschool children with a healthy oral condition. Oral health criteria and NOT-S scores (Nordic Orofacial dysfunction Test-Screening) were recorded. For each child, number of masticatory cycles (Nc), chewing time (Ti), and frequency (Fq = Nc/Ti) were recorded during mastication of raw carrot (CAR), cheese (CHS) and breakfast cereals (CER) samples. Food boluses were collected by stopping children at their food-dependent individual swallowing threshold (Nc), and the median food bolus particle size value (D50) was calculated. Correlations were sought between oral health and masticatory criteria. In the ECC group, mean Fq values were significantly decreased for all three foods (p ≤ .001) and mean D50 values were significantly increased (p ≤ .001) compared to the control group (i.e., D50 CAR = 4,384 μm ± 929 vs. 2,960 μm ± 627). These alterations were related to the extent of ECC. The NOT-S mean global score was significantly increased in children with ECC (2.62 ± 1.37 vs. 1 ± 0.91 in the control group, p ≤ .01), due to "Mastication and swallowing" domain impairment. This study gives granulometric normative values for three foods in preschool children and shows the impact of ECC on D50 values. The progression of children's masticatory capability after dental treatment, and the impact of such modifications of sensory input on future eating habits should be explored.

Effect of foods on selected dynamic parameters of mandibular elevator muscles during symmetric incisal biting

The paper focuses on research that enables the relationship between food and selected mechanical parameters do be determined. The main aim of the study was to designate, depending on the food: (1) the work of a single muscle (i.e. masseter, medial pterygoid, temporalis), and (2) the energy balance of mandibular elevator muscles based on the dynamic patterns of muscles. In turn, the indirect goal was to determine: (1) the muscle contraction, and (2) the average muscle contraction velocity based on the specified kinematic parameters, i.e. incisal biting velocity and incisal biting time. A hybrid model, consisting of a phenomenological model of the masticatory system and a behavioural model of incisal biting, was used in the calculations. The phenomenological model was based on an anatomically and physiologically normal mandible and healthy muscles, while the behavioural model was represented by the dynamic patterns of food. Calculations showed that muscle force is an important, but not the only, parameter that enables the quantitative and qualitative assessment of the functioning of the mandibular elevator muscles during symmetric incisal biting. Based on the obtained results, it can be stated that the dynamic patterns of muscles are a very important parameter, because on their basis, among others, muscle contraction, contraction time, work, and energy can be determined. The conducted calculations and analyses showed that the above-mentioned parameters depend on the mechanical properties of food (the dynamic patterns of food).