Bolus Formation Research Articles

Investigation of oral gels breakdown using image analysis

Characterizing the dynamics of food oral breakdown is of interest to understand the temporal perception of food products. The present work aimed at studying the possible contribution of artificial vision for studying bolus formation. Four emulsion-filled gels were prepared from two concentrations of agar and gelatin. By combining two different layers of these gels, four samples of homogeneous composition and 6 samples of heterogeneous composition were prepared. The layers were colored independently in order to study their breakdown and mixing during oral processing. Images of spat out boluses were collected at different stages of the chewing process and studied by different image analysis methods: gray-level histograms, histogram of shape area, mathematical morphology and gray level co-occurrence matrix. Methods were compared for their ability in discriminating boluses as function of homogeneous gel composition and mastication time. Three methods were found to be relevant and mathematical morphology provided the best results. Using this method, we further analyzed the impact of heterogeneous gels composition on the evolution of boluses properties. Results showed that when two gel layers of different composition were combined, the agar layer dominated bolus properties and that the presence of gelatin impacted the dynamics of gel breakdown. The results were in agreement with results obtained previously when characterizing the physical properties of the boluses. This study showed that artificial vision provides reliable tools for evaluating the dynamics of bolus formation, which is complementary to the methods commonly used in literature while avoiding extensive manipulation of boluses.

Electro-magnetohydrodynamic Flow of Biofluid Induced by Peristaltic Wave: A Non-newtonian Model

This article aims to develop a mathematical model for peristaltic transport of magnetohydrodynamic flow of biofluids through a micro-channel with rhythmically contracting and expanding walls under the influence of an applied electric field. The couple stress fluid model is considered to represent the non-Newtonian characteristics of biofluids. The velocity slip condition at the channel walls is taken into account because of the hydrophilic/hydrophobic interaction with negatively charged walls. The essential features of the electromagnetohydrodynamic flow of biofluid through micro-channels are clearly highlighted in the variations of the non-dimensional parameters of the physical quantities of interest such as the velocity, wall shear stress, pressure gradient, pressure rise per wave length, frictional force at the channel walls and the distribution of stream function. It reveals that the flow of biofluid is appreciably influenced by the sufficient strength of externally applied magnetic field and electro-osmotic parameter. The velocity slip condition reduces the frictional force at the channel wall. Moreover, the formation of the trapping bolus strongly depends on electro-osmotic parameter and magnetic field strength.

Adjustment of Food Textural Properties for Elderly Patients

AbstractOver the next twenty years the number of people over 60 years will exceed one billion. Changes associated with ageing have an impact on food texture choices for healthy elders and those used therapeutically for people with swallowing difficulties (dysphagia). The ideal “swallow‐safe” bolus is moist, cohesive and slippery. A general reduction in muscle strength is seen throughout the ageing oropharyngeal musculature, resulting in a reduced ability to safely and efficiently manage hard or fibrous textured foods. Reduced masticatory ability combined with dental loss further compounds the issue. Dry mouth is commonly associated with old age, making it difficult to propel dry or sticky textures through the pharynx, and increases the likelihood of pharyngeal residue. An age related reduction in laryngopharyngeal sensitivity dampens the ability to detect residue, increasing choking risk. Reduced tongue pressure, increases in pharyngeal transit time, valleculae residue, number of clearing swallows and slower and less efficient oesophageal transit occur with aged swallowing. Food textures that are sticky and adhesive will require increased lingual effort to propel them into and through the pharynx. Taken in combination these factors mean that food textures prescribed to the elderly need to be soft and moist and for fibers to be easily broken. To improve moisture content, additional nutrient dense products (e.g., milk, cream or butter) may be required to artificially moisten the bolus. Careful, individualized attention to diet recommendations will result in a diet that is appealing and also provide a variety of textures that are swallow‐safe and nutrient dense.Practical ApplicationAged related changes in the oral cavity and the oral, pharyngeal and oesophageal phases of swallowing require special thought to the suitability of food textures for the elderly. Foods that are fibrous, hard or dry may be unsuitable due to difficulties with safe particle size reduction and bolus formation for swallowing. Foods that are sticky and adhesive are also problematic and increase risk for both choking and residue. Food texture properties that are ideally suited for the elderly include those that are soft, moist, and easily reduced with minimal chewing effort. Hard food textures that break down and dissolve easily with minimal chewing should be investigated. Increased aroma and flavor may improve appeal lost through reduced variety in food textures. Diet reviews need to consider both textures that can be safely managed and the nutrient density of those textures.

Transverse magnetic field driven modification in unsteady peristaltic transport with electrical double layer effects

The influence of transverse magnetic field on time-dependent peristaltic transport of electrically-conducting fluids through a microchannel under an applied external electric field with induced electric field effect is considered, based on lubrication theory approximations. The electrohydrodynamic (EHD) problem is also simplified under the Debye linearization. Closed-form solutions for the linearized dimensionless boundary value problem are derived. With increasing Hartmann number, the formation of bolus in the regime (associated with trapping) is inhibited up to a critical value of magnetic field. Flow rate, axial velocity and local wall shear stress are strongly decreased with greater Hartmann number whereas pressure difference is enhanced with higher Hartmann number at low time values but reduced with greater elapse in time. With greater electro-osmotic parameter (i.e. smaller Debye length), maximum time-averaged flow rate is enhanced, whereas the axial velocity is reduced. An increase in electrical field parameter (i.e. maximum electro-osmotic velocity) causes an increase in maximum time-averaged flow rate. The simulations find applications in electromagnetic peristaltic micro-pumps in medical engineering and also ⿿smart⿿ fluid pumping systems in nuclear and aerospace industries.

Age-related changes in mastication are not improved by tongue exercise in a rat model.

Aging results in progressive changes in deglutitive functions, which may be due in part to alterations in muscle morphology and physiology. Mastication is a critical component of bolus formation and swallowing, but aging effects on masticatory function have not been well studied. The purpose of this study was to 1) quantify the effects of aging on mastication, and 2) determine the effects of tongue exercise on mastication in young adult and old rats. We hypothesized that there would be significant differences in mastication characteristics (number of bites, interval between bites, time to eat) as a function of age, and that tongue exercise would resolve preexercise differences between age groups. We expanded the established model of progressive, 8-week tongue exercise to include a mastication measurement: acoustic recordings of vermicelli pasta biting from 17 old and 17 young adult rats, randomized into exercise and control groups. We found the following: 1) Mastication characteristics were impacted by age. Specifically in older rats, there was an increase in time to eat and number of bites and intervals between bites decreased, suggesting increased oral motor-processing requirements for bolus formation. 2) tongue exercise did not impact mastication behaviors in young adult or old rats. Tongue exercise may not have been specific enough to result in behavioral changes in mastication or exercise dose may not have been sufficient. Nevertheless, results were noteworthy in expanding the established rat model of aging and have relevant clinical implications for future translation to human populations. NA Laryngoscope, 127:E29-E34, 2017.

Exploring the Links Between Texture Perception and Bolus Properties Throughout Oral Processing. Part 2: Bolus Mechanical and Rheological Properties

AbstractThis study explored links between texture perception, breakdown path, and bolus properties throughout oral processing. Five subjects chewed biscuits to three stages of bolus formation (early, mid, and point of swallow). Bolus properties were measured using back extrusion (BE) (yield stress) and a modified texture profile analysis, consecutive double compression (CDC) (peak force, “adhesiveness”, and “cohesiveness”). The validity of the testing methods was discussed and BE was found to be better suited than CDC for testing boluses of varying size. In addition, results indicated that a greater understanding of the properties being measured by the CDC parameters is required. The bolus properties were linked to texture perception and breakdown path results presented in Part 1 of this study.At a panel‐level, yield stress and peak force decreased and “adhesiveness” and “cohesiveness” increased throughout oral processing. Interindividual differences were found in bolus mass, yield stress, peak force, “adhesiveness”, “cohesiveness”, and description of bolus properties using texture terms. A panel‐level analysis agreed with the “Mouth Process” and “Optimum Swallow” models. However, not all individuals' results were consistent with the latter model. A universal swallowing threshold for this biscuit recipe in terms of the measured properties was not found. Results suggest consumers can potentially be grouped by sensory experience, breakdown path, or bolus properties.Practical ApplicationsThe relationships between masticatory behavior, perceived texture, bolus structure, and mechanical and rheological properties throughout oral processing are still not fully understood. This study applies modified texture profile analysis and back extrusion methods for the testing of boluses at different stages of oral processing and discusses their validity. This study indicates that analyzing texture‐bolus property relationships at a panel – rather than individual – level may not provide a full picture of consumer experience. Although there are differences between consumers, they can potentially be grouped by sensory experience, food breakdown path, or bolus properties (including bolus moisture content and rheology). These groupings could be used to design studies that are more applicable to a general population and may be useful in tailoring foods to specific target groups.

Exploring the Links Between Texture Perception and Bolus Properties Throughout oral Processing. Part 1: Breakdown Paths

AbstractThis study explored links between texture perception and breakdown path throughout oral processing. Five subjects chewed a short dough biscuit recipe. Dynamic textural perception was followed using Temporal Dominance of Sensations. Subjects expectorated at three stages of bolus formation (early, mid, and point of swallow). Visual inspection and moisture content (MC) provided a description of breakdown path. Interindividual differences in perceived texture and breakdown paths were observed. This study indicated differences between how individuals used sensory texture terms to describe bolus structure. The dry‐to‐sticky dominance transition corresponded to increased mixing and MC. However, there was not a significant change in MC for all subjects.A panel‐level analysis agreed with the “Mouth Process” model but there were interindividual differences at the point of swallow. This study suggests that there may not be a universal swallowing threshold for this biscuit recipe in terms of the measured properties but does indicate it may be possible to group consumers using bolus structure swallowing thresholds.Practical ApplicationsOral processing of a solid food involves food breakdown and reassembly with saliva into a deformable bolus that can be swallowed safely. The relationships between masticatory behavior, perceived texture, bolus structure, and mechanical and rheological properties throughout oral processing are still not fully understood. This study provides evidence of the subjective nature of oral processing and texture perception but indicates that each individual is not necessarily unique. Consumers may be able to be categorized into different groups based upon sensory dominance, bolus structure, and moisture content swallowing thresholds. Understanding these groupings could aid in the design of foods that follow a desired oral processing path and therefore provide consumers with a specific sensory experience.

Chemical Sensing Regulates Mastication/Swallowing.

Mastication and swallowing are the first stage of digestion involving several motor processes such as food intake, intra-oral food transport, bolus formation and chewing and swallowing reflex. These complicated motor functions are accomplished by the well-coordinated activities in the jaw, hyoid, tongue, facial and pharyngeal muscles. Although the basic activity patterns of these movements are controlled by the brainstem pattern generators, these movements generate various peripheral sensory inputs. Among the sensory inputs, it is well-known that somatic sensory inputs play important roles in reflexively modulating the movements so that the final motor outputs fit the environmental demand. However, little is known about the effects of chemical sensory inputs such as taste and olfaction originating from the ingested foods by these movements. A possible reason could be raised that cognition of the chemical sensory inputs at the higher brain also influences the movements, so it is difficult to discuss the neural mechanisms underlying the observed effect. In this review, we focus on the effects of chemical sensory inputs on the masticatory movements and initiation of swallowing. We first summarize chemical sensory inputs occurring during mastication and swallowing, and their receptive mechanisms. In addition, we will introduce the effect of application of monosodium L-glutamate (MSG) solution as an umami taste to the oropharynx on the swallow initiation which is involuntary controlled and the possible neural mechanisms underlying this effect is discussed.

Surgical anatomy and physiology of swallowing

Deglutition, the act of swallowing, is an extremely complex process involving approximately 50 pairs of muscles and nerves that are responsible for preparing and transferring food and liquids from the mouth to the stomach. A problem with any of these structures can lead to dysphagia and a decrease in the quality of life in patients suffering from it. To successfully diagnose and treat dysphagia, a thorough understanding of deglutition is essential. The anatomy and physiology of the swallowing process is reviewed as it pertains to operative approach and technique.

Characteristics of bolus formation and propagation from breaking internal waves on shelf slopes

A series of laboratory experiments was conducted to study the formation of internal boluses through the run up of periodic internal wave trains on a uniform slope/shelf topography in a two-layer stratified fluid system. In the experiments, the forcing parameters of the incident waves (wave amplitude and frequency) are varied for constant slope angle and layer depths. Simultaneous particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) measurements are used to calculate high resolution, two-dimensional velocity and density fields. Over the range of wave forcing conditions, four bolus formation types were observed: backward overturning into a coherent bolus, top breaking into a turbulent bolus, top breaking into a turbulent surge and forward breaking into a turbulent surge. Wave forcing parameters, including a wave Froude number $Fr$, a wave Reynolds number $Re$ and a wave steepness parameter $ka_{0}$, are used to relate initial wave forcing to a dominant bolus formation mechanism. Bolus characteristics, including the bolus propagation speed and turbulent components, are also related to wave forcing. Results indicate that for $Fr>0.20$ and $ka_{0}>0.40$, the generated boluses become more turbulent in nature. As wave forcing continues to increase further, boluses are no longer able to form.

The Relationship Between Tongue Pressure and Oral Dysphagia in Stroke Patients.

ObjectiveTo evaluate the relationships between tongue pressure and different aspects of the oral-phase swallowing function.MethodsWe included 96 stroke patients with dysphagia, ranging in age from 40 to 88 years (mean, 63.7 years). Measurements of tongue pressure were obtained with the Iowa Oral Performance Instrument, a device with established normative data. Three trials of maximum performance were performed for lip closure pressure (LP), anterior hard palate-to-tongue pressure (AP), and posterior hard palate-to-tongue pressure (PP); buccal-to-tongue pressures on both sides were also recorded (buccal-to-tongue pressure, on the weak side [BW]; buccal-to-tongue pressure, on the healthy side [BH]). The average pressure in each result was compared between the groups. Clinical evaluation of the swallowing function was performed with a videofluoroscopic swallowing study.ResultsThe average maximum AP and PP values in the intact LC group were significantly higher than those in the inadequate lip closure group (AP, p=0.003; PP, p<0.001). AP and PP showed significant relationships with bolus formation (BF), mastication, premature bolus loss (PBL), tongue to palate contact (TP), and oral transit time (OTT). Furthermore, LP, BW, and BH values were significantly higher in the groups with intact mastication, without PBL and intact TP.ConclusionThese findings indicate that the tongue pressure appears to be closely related to the oral-phase swallowing function in post-stroke patients, especially BF, mastication, PBL, TP and OTT.

Swallowing after non-surgical treatment (radiation therapy / radiochemotherapy protocol) of laryngeal cancer

AbstractRadiation therapy and radiochemotherapy protocols can cause swallowing difficulties.Aim: To evaluate swallowing in patients undergoing radiation therapy and radiochemotherapy protocol only for the treatment of laryngeal tumors.Methods: A prospective study of 20 patients, with a mean age of 62 years, at the end of oncological therapy. Six patients (30%) underwent radiation therapy, and 14 patients (70%) underwent combined therapy. The mean time between treatment and an evaluation of swallowing was 8.5 months. Videofluoroscopy was done to assess the preparatory, oral and pharyngeal phases of swallowing.Results: All patients had only an oral diet. Normal swallowing was present in only 25% of patients. The swallowing videofluoroscopic examination identified the following changes: bolus formation (85%), bolus ejection (60%), oral cavity stasis (55%), changes in the onset of the pharyngeal phase (100%), decreased laryngeal elevation (65%), and hypopharyngeal stasis (80%). Laryngeal penetration was observed in 25% of the cases; 40% presented tracheal aspiration. The grade of penetration/ aspiration was mild in 60% of cases. Aspiration was silent in 35% of patients. Although 75% of patients had dysphagia, only 25% complained of swallowing difficulties.Conclusion: Patients with laryngeal cancer that underwent radiation therapy/combined treatment can present changes in all swallowing phases, or may be asymptomatic.

Changes in jaw muscle activity and the physical properties of foods with different textures during chewing behaviors

This study aimed to investigate how the activity of the masseter (Mas) and suprahyoid (Hyoid) muscles is influenced by the physical properties of food, how changes in the rheological properties of food differ between different foods during the process of food reduction, and how different salivary flow rates affect bolus-making capability during masticatory behavior in healthy humans. Ten healthy adults participated in this study. Electromyographic (EMG) recordings were obtained from the Mas and Hyoid muscles, and 15g of steamed rice and rice cake was prepared as test foods. In the ingestion test, the subjects were asked to eat each food in their usual manner. The chewing duration, number of chewing cycles before the first swallow, Mas and Hyoid EMG activity, and chewing cycle time were compared between the foods. Total chewing duration was divided into three substages: early, middle, and late; chewing cycle time and EMG activity per chewing cycle of each substage were compared between the foods and among the substages. In the spitting test, the rheological properties of the bolus at the end of each substage were compared between the foods and among the substages. Finally, stimulated salivary flow rates were measured and the relationships between salivary flow rate and chewing duration, EMG activity, and changes in physical food characteristics were investigated. There were significant differences in total chewing duration and the number of chewing cycles, but not in chewing cycle time, between the foods, which had similar hardness values. The EMG activity levels of the Mas and Hyoid per chewing cycle for the rice cake were significantly greater than for the steamed rice throughout the recording periods. While Mas activity did not change among the substages during chewing, Hyoid EMG activity decreased as chewing progressed. Chewing cycle time also gradually decreased as chewing progressed. The hardness of both foods initially increased, then gradually decreased back to baseline. The adhesiveness of the rice cake initially increased, and did not fall throughout the recording period; the adhesiveness of the steamed rice did not significantly change. Cohesiveness barely changed in either of the two foods during chewing, but was significantly greater for the rice cake than for the steamed rice. Finally, a correlation between the stimulated salivary flow rate and chewing performance was evident only in a change in Mas EMG activity. The current results demonstrate that the activities of the Mas and Hyoid muscles changed as chewing progressed, and were affected by hardness, adhesiveness, and cohesiveness. Salivary flow rate may affect the changes in Mas activity during the process of bolus formation.

Diadococinesia oral e função mastigatória em idosos saudáveis

Objetivo Relacionar os achados da diadococinesia (DDC) oral com a função mastigatória em idosos saudáveis.Métodos Análise de prontuários e arquivos de imagens de 35 idosos saudáveis, entre 60 e 74 anos de idade. Considerou-se o tipo mastigatório e outros comportamentos associados à mastigação de uma fatia de pão francês de 1cm de espessura, análise da apreensão do alimento, formação do bolo alimentar e mensuração do tempo de mastigação, utilizando cronômetro. Para avaliação da DDC, foram analisadas as emissões silábicas "pa", "ta", "ka" e a trissílaba "pataka", quanto aos parâmetros fornecidos automaticamente pelo programaMotor Speech Profile Advanced -KayPentax®. Para correlação entre os aspectos qualitativos da função mastigatória e a DDC, foi realizada estatística pertinente.Resultados A análise estatística demonstrou correlação entre o tempo mastigatório e os parâmetros coeficiente de variação do pico da intensidade da sílaba ‘'ta'' e perturbações do período da sílaba ‘'ka'', indicando instabilidade da DDC. Para o tipo mastigatório, apreensão e formação do bolo alimentar não houve correlação com os dados da DDC oral.Conclusão A DDC oral correlacionou-se com o tempo mastigatório em idosos saudáveis, evidenciando que, quanto maior a instabilidade na repetição dos movimentos de ponta e dorso de língua durante a produção articulatória, maior o tempo necessário para a preparação do alimento para a deglutição.

Influence of Metallic Nanoparticles on Blood Flow Through Arteries Having Both Stenosis and Aneurysm.

The main objective of the present paper is to discuss the blood flow analysis through inclined arteries by treating its nature as viscous fluid. The effects of both dilatation and constriction are considered to investigate the behavior of the both abnormal wall segments with variable nanofluid viscosity. The nonlinear momentum equation for proposed model is simplified by considering the nondimensionless parameters to find the exact solutions of the formulated problem. The main hemodynamic effects of stenosis and aneurysm are discussed for different values of the interest by plotting the graphs of wall shear stress and resistance impedance to flow and opposite behavior is observed for both cases. The results also reveal that the nanoparticles with high concentration are important to reduce the resistance impedance to blood flow. The graphs of stream lines show the formation of bolus appears in the aneurysm segment but no formation is observed or seen in the stenotic segment.

Specific features of the head region in euconodont animals

New data on morphology of the head region of euconodonts are discussed based on a study of its imprint from the Lower Carboniferous deposits of the Polar Urals (Russia); on its external ventral surface, the animal had an oval expansion of the head region, supposedly, a mouth food sac. A similar structure is also described in one of the imprints from Granton (Great Britain) exposed from internal surfaces. A hypothesis is put forward on the mechanism of functioning of the feeding apparatus in euconodonts which consists of hard S, M, and P tooth elements and H attaching skeletal elements as well as soft connective structures. The food sac probably served for filtering food particles from the water which was removed through special openings and for formation of the food bolus and transferring the latter into the alimentary canal (gut). These data gave to reasons for a new interpretation of feeding behaviour of euconodonts. It is suggested that the euconodont animals were filter feeders adapted to the near-bottom dwelling over substrates, where there was greatest concentration of small food items available for filtration.

Analysis of bolus formation in micropipette ejection systems.

The ejection of drugs from micropipettes is practiced frequently in biomedical research and clinical studies however, little is known about the dynamics of this process. The fundamentals of disperse fluid injection via a capillary into an ambient immiscible fluid have been investigated extensively. Here, we experimentally investigate the bolus formation in micropipette ejection systems, where the injection and ambient fluid are the same. We experimentally measure the temporal evolution of the bolus formation in the same fluid. There are three different bolus formation mechanisms that arise from different Re t regimes: a) a nearly spherical bolus, b) a pear-like bolus, and c) a large distortion or axial jet. We examine the scaled dimensions of the bolus, R b/D t, L b/D t, H/D t, and α, as a function of the dimensionless parameters such as tip Reynolds number, Re t, dimensionless value of g/(D t (.) V t), the dimensionless time, tV t/D t, and the distance between the edge of the micropipette and the free surface, D/D t. The bolus radius for 0.2 < Re t < 30 grows according to t (1/2) in the entire time range, which allows us to estimate the time for complete bolus formation.

Ultrasonographic examination of how occlusal support is established by tongue movements during mastication

Mastication is achieved through the action of multiple organs working together, including the teeth, periodontal tissue, masticatory muscles, temporomandibular joints, lips, cheeks, palate and tongue. In particular, the tongue plays a major role in the preparation phase of mastication, which includes the transport of food to the occlusal surfaces of molars and transferring the food bolus to the pharynx once it has been chewed. Loss of teeth not only reduces masticatory efficiency, but also affects tongue form. This indicates that the provision of suitable dentures for the edentulous portion of the alveolar ridge may affect bolus formation and transport by the tongue. In other words, when the dentures are grinding food, it becomes a barrier between the oral vestibule and oral cavity proper, as well as the natural dentition and the residual ridge, followed by additional help from the tongue in bolus formation. It is believed that this movement is programmed automatic movement by central pattern generator. However, if a state of partial or complete edentulism is left without prosthetic treatment, tongue function will be impaired. Observation of tongue movements during mastication has been studied using a variety of instruments. It has been suggested that these movements can be observed indirectly using a tongue pressure gauge Ultrasonographic examination of how occlusal support is established by tongue movements during mastication

Dynamic texture perception and oral processing of semi-solid food gels: Part 2: Impact of breakdown behaviour on bolus properties and dynamic texture perception

Food texture perception depends on food structure and oral processing behaviour. The aim of this study was to explain dynamic texture perception of emulsion-filled, semi-solid gels by properties of the boli formed during three stages of oral processing. Texture perception of emulsion-filled gels varying in fracture stress and strain was found to be a dynamic process. Specific texture attributes were perceived as dominant sensations in the beginning (firm), middle (moist, refreshing, elastic, sticky) and end of oral processing (grainy, melting, creamy). In the beginning of oral processing mechanical properties of the boli, such as first penetration peak force and flowability, were correlated to sensory firmness. In the middle of oral processing, correlations between boli properties and texture perception were more complex. Perception of moist and refreshing was related to mechanical properties of the boli, such as flowability, rather than to the amount of saliva incorporated into the boli. Perception of elastic and sticky was related to the mechanical bolus properties resilience and adhesiveness. In the end of oral processing, emulsion-filled gels were perceived either as creamy or grainy. Gels perceived as creamy revealed a high bolus flowability while gels perceived as grainy consisted of boli with a high number of broken down particles. We conclude that bolus formation and changes in the properties of the bolus underlay the changes in texture perception during oral processing.

Endoscopic evaluation of food bolus formation and its relationship with the number of chewing cycles

It is known that solid food is transported to the pharynx actively in parallel to it being crushed by chewing and mixed with saliva in the oral cavity. Therefore, food bolus formation should be considered to take place from the oral cavity to the pharynx. In previous studies, the chewed food was evaluated after the food had been removed from the oral cavity. However, it has been pointed out that spitting food out of the oral cavity interferes with natural food bolus formation. Therefore, we observed food boluses immediately before swallowing using an endoscope to establish a method to evaluate the food bolus-forming function, and simultaneously performed endoscopic evaluation of food bolus formation and its relationship with the number of chewing cycles. The subject was inserted the endoscope nasally and instructed to eat two coloured samples of boiled rice simultaneously in two ingestion conditions ('as usual' and 'chewing well'). The condition of the food bolus was graded into three categories for each item of grinding, mixing and aggregation and scored 2, 1 and 0. The score of aggregation was high under both ingestion conditions. The scores of grinding and mixing tended to be higher in subjects with a high number of chewing cycles, and the score of aggregation was high regardless of the number of chewing cycles. It was suggested that food has to be aggregated, even though the number of chewing cycles is low and the food is not ground or mixed for a food bolus to reach the swallowing threshold.