Is food particle size a criterion for the initiation of swallowing?

Effects of appetite, BMI, food form and flavor on mastication: almonds as a test food

OBJECTIVES

To investigate the effects of appetitive sensations, body mass index (BMI) and physical/sensory properties of food (almonds) on masticatory indices and resultant pre-swallowing particle sizes.

SUBJECTS/METHODS

Twelve lean (BMI=22.2+/-0.3) and 12 obese (BMI=34.3+/-0.6) adults. After collecting appetitive ratings, electromyographic recordings were used to assess participants' microstructure of eating for five almond products (raw, dry unsalted roasted, natural sliced, roasted salted and honey roasted) under fasted and satiated conditions. Duplicate samples were masticated to the point of deglutition and then were expectorated and size sorted.

RESULTS

No statistically significant effects of BMI were detected for any of the mastication measures. Maximum and mean bite forces were greater under the fasted condition. Sliced almonds required lower bite force than did the other almond varieties. The pre-swallowing particle sizes were significantly greater for the sliced almonds than all other varieties. Both the number of chews and mastication time were negatively correlated with particle size. There were no significant effects of almond form or flavor on particle size.

CONCLUSIONS

These results do not support differences in masticatory performance between lean and obese individuals, nor effects of sensory properties. Instead, the physical form of foods as well as an individuals' appetitive state may have a greater influence on masticatory behavior. The health implications of these observations warrant further investigation.

Relationship between orthodontic anomalies and masticatory function in adults

INTRODUCTION

Normal mastication requires the coordinated action of many elements, including teeth, salivary glands, tongue, and masticatory muscles. Dysfunction in any of these areas can result in impaired masticatory function. Few studies dealt with the influence of occlusal conditions on the masticatory function. Our aim in this study was to examine to what extent masticatory function is impaired in subjects with occlusal anomalies.

METHODS

Masticatory function was studied in 102 untreated adults. They were observed while chewing a standard test food for 20, 30, and 40 chewing strokes. Orthodontic condition was assessed with the index of complexity, outcome, and need (ICON). From the masticatory test, 3 variables were obtained: median particle size (MPS), broadness of the particle distribution (BPD), and masticatory frequency (F).

RESULTS

MPS was significantly larger in subjects with ICON scores >43 (definite-need subsample) than in subjects with ICON scores < or =43 (no-need subsample) when the masticatory test was performed with 20, 30, or 40 cycles (P =.05, .03, and .01, respectively). BPD also followed the same trend, but the differences were not significant (P = .33, .16, .14 for 20, 30, and 40 cycles, respectively). Also, the differences in F between the 2 subsamples were not significant (P = .26, .45, .37).

CONCLUSIONS

The results suggest that, in addition to esthetic considerations, improving a patient's chewing function by improving occlusal relationships could be an indication for orthodontic treatment.

Oral physiology and mastication

Mastication is a sensory-motor activity aimed at the preparation of food for swallowing. It is a complex process involving activities of the facial, the elevator and suprahyoidal muscles, and the tongue. These activities result in patterns of rhythmic mandibular movements, food manipulation and the crushing of food between the teeth. Saliva facilitates mastication, moistens the food particles, makes a bolus, and assists swallowing. The movement of the jaw, and thus the neuromuscular control of chewing, plays an important role in the comminution of the food. Characteristics of the food, e.g. water and fat percentage and hardness, are known to influence the masticatory process. Food hardness is sensed during mastication and affects masticatory force, jaw muscle activity, and mandibular jaw movements. When we chew for instance a crispy food, the jaw decelerates and accelerates as a result of resistance and breakage of food particles. The characteristic breakage behaviour of food is essential for the sensory sensation. This study presents a short review of the influence of oral physiology characteristics and food characteristics on the masticatory process.

Influence of oral characteristics and food products on masticatory function

Mastication is a complex process that involves activities of the facial muscles, the elevator and suprahyoidal muscles, and the tongue. These activities result in patterns of rhythmic mandibular movements, food manipulation, and the crushing of food between the teeth. Saliva facilitates mastication by moistening food particles, making a bolus, and assisting swallowing, whereas food consistency modifies masticatory forces, the mandibular jaw movements, the duration of the mastication cycle, and the number of cycles preceding the first swallow. Jaw elevator EMG activity research shows a clear relation between muscular activity and food properties. The teeth, masticatory muscles, and temporomandibular joints are also important because together they form the mechanism by which the food particles are fragmented. Hard and dry foods require more chewing cycles and a longer time in the mouth until swallowing for sufficient breakdown to take place and for enough saliva to be added to form a coherent bolus safe enough for swallowing. Product characteristics, the amount of saliva, dentition, and bite force affect the chewing performance. This study presents an update and synopsis of the effects of saliva, food, dentition, muscle force, and temporomandibular disorders on the masticatory process.

Measuring chewing ability in randomized controlled trials with edentulous populations wearing implant prostheses*

In this article, the authors review methods commonly used to measure the masticatory ability of patients wearing conventional and implant prostheses. Measurement approaches are viewed in two broad categories: laboratory based and patient based. The laboratory based measures discussed are mastication time, particle size, force measurements, patterns of jaw movement and electromyographic (EMG) bursts and total EMG activity. Patient based measures include satisfaction and chewing difficulty. Oral health-related quality of life measures and diet/nutrition variables are briefly mentioned. Patient-based outcomes are recommended as the most appropriate variables of masticatory efficiency.

Influence of Mastication and Salivation on Swallowing in Stroke Patients

OBJECTIVE

To determine differences of the oral swallowing functions between stroke and normal subjects and to identify those factors affecting dysphagia of stroke patients.

DESIGN

Case-control study.

SETTING

University hospital.

PARTICIPANTS

Ten stroke and 10 healthy subjects.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Resting saliva flow rate, the total number of chews, and the duration of the oral phase until onset of pharyngeal swallow, and food viscosities both before and after the oral phase using diluted barium, pudding, thick rice gruel, and curd type yogurt.

RESULTS

The viscosity of all test foods was significantly reduced after the oral phase in both groups (P<.01). Resting saliva flow rate and the viscosity of thick rice gruel after the oral phase in the stroke group were significantly lower than in the control group (P<.01). However, there were no differences in the viscosities of the other foods between both groups. And a longer oral phase and a greater number of chews prior to pharyngeal swallow were revealed in the stroke group than in the control group (P<.01).

CONCLUSIONS

This study shows that the food requiring mastication demands a longer oral phase and a greater number of chews, and has more altered rheologic characteristics during the oral phase in stroke patients. These findings suggest that masticatory function is impaired in stroke patients, which may contribute to their swallowing dysfunction.

The influence of product and oral characteristics on swallowing

The urge to swallow food could be triggered by a threshold level in both food particle size and lubrication of the food bolus. Thus, both oral physiology and product characteristics may influence the swallowing threshold. We quantified the swallowing threshold in a group of 266 healthy adult subjects (age 42 +/- 12 years) by counting the number of chewing cycles needed to prepare food for swallowing. The influence of oral physiology on the swallowing threshold was determined by measuring salivary flow rate, maximum bite force and masticatory performance. We used about 10 cm(3) of bread, toast, melba toast, breakfast cake, peanuts and cheese to determine the influence on the swallowing threshold of various food characteristics, e.g. hardness, moisture and fat. Furthermore, we tested the effect of buttering the bread, toast, melba toast and breakfast cake on the swallowing threshold. Salivary flow rates were significantly and negatively correlated with the number of chewing cycles of melba toast and breakfast cake. Hence, subjects with more saliva needed less chewing cycles for these dry products. Maximum bite force and masticatory performance had an influence on the swallowing threshold for the hard products only (carrot and peanut). Although significant, the correlation coefficients were less than 0.28. Thus, the oral physiology parameters explained less than 10% of the variance in the swallowing threshold. We found significantly different numbers of chewing cycles for the various foods, ranging from 17 for cake to 63 for carrot. Hard and dry products needed more chewing cycles until swallowing. Buttering the food significantly reduced the number of chewing cycles needed before swallowing. This was especially true for the dry products cake, melba toast and toast. Hard and dry products require more chewing cycles and longer time in mouth until swallowing for sufficient breakdown to take place and for enough saliva to be added to form a coherent bolus safe for swallowing. In spite of this, more saliva, higher maximum bite force and better masticatory performance were only weakly correlated with a smaller number of chewing cycles. Butter enhanced lubrication and bolus formation of dry products, thus reducing the number of chewing cycles until swallowing. In conclusion, product characteristics and to a lesser extent oral physiology significantly affect swallowing threshold.

Chewing behavior and salivary secretion

We determined the salivary flow rate in 16 healthy subjects in rest and while chewing artificial and natural foods (Parafilm, Melba toast with and without margarine, and three different volumes of breakfast cake and cheese). We also determined the duration of a chewing cycle, the number of chewing cycles until swallowing, and the time until swallowing. The physical characteristics of the foods were quantified from force-deformation experiments. The flow rates of the saliva as obtained without stimulation, with Parafilm stimulation, and with chewing on the various foods were significantly correlated. An increase in chewing cycle duration, number of chewing cycles until swallowing, and time until swallowing was observed as a function of the volume of the food. More chewing cycles were required for Melba toast than for an equal volume of cake or cheese. This may be caused by the low water and fat percentage of the Melba toast. The number of chewing cycles and the time until swallowing significantly decreased when the Melba toast was buttered. The decrease may be caused by facilitation in bolus formation and lubrication of the food due to buttering the toast. The number of chewing cycles until swallowing was not correlated to the salivary flow rate.

Chewing behaviour and bolus formation during mastication of meat with different textures

During chewing, meat is mashed under compression and shear bite forces whilst saliva is incorporated. The resulting mixture is shaped into a cohesive bolus by agglomeration of small particles, and triggers a swallow. This study aimed to investigate the relationship between chewing behaviour and bolus formation of meat with different textures. Twenty-five consenting young adults participated in this study. Electromyographic activity was recorded from surface electrodes on the elevator muscles (masseter and temporalis) during mastication of cold beef. Two different textures (T(1): tough and dry; T(2): tender and juicy) were studied, and subjects were asked to chew the beef and then spit out the bolus either: (1) after a constant chewing period of 7s or (2) when the bolus was ready to be swallowed. Meat samples were weighed before and after chewing to determine weight changes due to saliva incorporation and the release of meat juice. Cutting tests were applied to measure the maximum shear force. The mechanical shear force was maximal for meat before chewing (T(1)=124 N/cm(2); T(2)=83 N/cm(2)) and decreased with increased chewing duration. Texture differences analysed from mechanical measurements remained significant even when the boli were ready for swallowing (T(1)=39 N/cm(2); T(2)=32 N/cm(2)); the toughest meat gave the toughest bolus. Muscular activity adapted to the texture of the meat as soon as chewing began, and remained constant over the observed chewing period. Mean muscular activity was higher during the chewing of tough meat than during the chewing of tender meat. As a consequence, by the time a bolus was ready to be swallowed, more saliva had been incorporated into the tough meat samples (mean weight increase: 36%) than the tender meat samples (mean weight increase: 30%).

Saliva and gastrointestinal functions of taste, mastication, swallowing and digestion

Saliva has multiple essential functions in relation to the digestive process taking place in the upper parts of the gastrointestinal (GI) tract. This paper reviews the role of human saliva and its compositional elements in relation to the GI functions of taste, mastication, bolus formation, enzymatic digestion, and swallowing. The indirect function of saliva in the digestive process that includes maintenance of an intact dentition and mucosa is also reviewed. Finally, pathophysiological considerations of salivary dysfunction in relation to some GI functions are considered.

An optimization model for mastication and swallowing in mammals

Mammalian mastication is a process combining simultaneous food comminution and lubrication. The initiation of swallowing, which is voluntary, has been thought to depend on separate thresholds for food particle size and for particle lubrication. Instead of this duality, we suggest that swallowing is initiated when it is sensed that a batch of food particles is binding together under viscous forces so as to form a bolus. Bolus formation ensures that when the food mass is swallowed, it will pass the pharyngeal region safely without risk of inhaling small particles into the lower respiratory tract. Crucial for bolus formation is food particle size reduction by mastication. This allows the tongue to pack particles together tightly by pressure against the hard palate. A major function of salivation is to fill the gradually reducing spaces between particles, so increasing viscous cohesion and promoting bolus formation. If swallowing is delayed, excessive saliva floods the bolus, separating particles and reducing cohesion. Swallowing then becomes more precarious. Our model suggests that there is an optimum moment for a mammal to swallow, defined in terms of a peak cohesive force between food particles. The model is tested on human mastication with two foods, brazil nut and raw carrot, which have very different particle size breakdown rates. The peak cohesive force is much greater with brazil nuts but both foods are predicted to be swallowed after similar numbers of chews despite the very different food particle size reductions achieved at that stage. The predicted number of chews to swallow is in broad agreement with published data.

Tongue-jaw linkages in human feeding: a preliminary videofluorographic study

Motions of the tongue and jaw are closely coupled during feeding in mammals, but this relation has not been studied in humans. A videofluorographic method for measuring tongue movement relative to jaw motion using small radiopaque markers affixed to the tongue with dental adhesive was developed and tested in five individuals. Sagittal movements of the anterior tongue marker (ATM) and the lower jaw were measured for complete feeding sequences with a computerized image-analysis system. The ATM and jaw moved in loosely linked, semirhythmic cycles. Vertical and horizontal maxima of ATM motion were determined for each motion cycle in relation to maximum and minimum gape (greatest jaw opening and closing, respectively). The amplitude of tongue movements and their timing differed between hard and soft foods (p < 0.001). For both food types, motions varied as the feeding sequence progressed from ingestion to terminal swallow (p < 0.001). A basic temporal sequence was found in 70% of the 224 cycles analysed. On average, the ATM reached its most inferior position just after maximum gape, its most posterior during jaw closing, its most superior just after minimum gape, and its most anterior during jaw opening (p < 0.001). This study confirms that tongue and jaw movements are linked during human feeding, as they are in other mammals.

Mastication and swallowing in patients with postirradiation xerostomia

PURPOSE

Very little objective data has been reported on mastication and swallowing in xerostomic patients, which would substantiate presumed causal relationships between xerostomia and patient complaints. The purpose was to elucidate which components of mastication and swallowing were abnormal, and most directly related to xerostomia, and which appeared unaffected.

METHODS AND MATERIALS

A retrospective analysis of timing events in mastication and swallowing was done using videofluoroscopic data for 15 cancer patients with xerostomia, and 20 normal controls. Scintigraphy was also used to determine oropharyngeal residue after a water swallow. Cancer treatment modalities included radiation therapy or chemoradiation therapy.

RESULTS

For barium liquid and paste substances, timing measures were equivalent for controls and patients. Xerostomic patients took 46% longer to masticate a shortbread cookie, and timing for the initiation of swallowing was shorter, but duration of swallowing appeared unaffected. Oral and pharyngeal residues following the swallow were greater in the patient group.

CONCLUSIONS

Xerostomia primarily affected mastication and oral manipulation of a dry, absorbent food material. Increased oral and pharyngeal residues after a water swallow are ambiguously related to xerostomia. The initiation and duration of the pharyngeal swallow was not abnormal.

Natural bites, food consistency and feeding behaviour in man

Complete feeding sequences (bite to terminal swallow) were recorded in 11 individuals (Class I occlusions) feeding on apple, banana and biscuit (hard cookie) to establish whether jaw movements characteristic of the stage I transport, chewing, stage II transport and swallowing processes found in non-human mammals could be identified in man. All participants took large natural bites (known weight) of each food, but seven were supplied standard 6-g pieces of apple. Jaw movements (three axes) were recorded using a locally calibrated Sirognathograph. Discrete stage I transport movements (bite moved from incisors to postcanines), were found in most records, but least frequently for banana. The number of chewing cycles before the first in-sequence swallow increased in the order: banana, ( = ) apple without peel, apple with peel, biscuit. Chewing cycles showed subtle changes in gape profile but significant variation in mediolateral movement cycle to cycle. Morphologically distinct stage II transport cycles could not be identified. Swallows occurred intermittently during chewing (79% of all sequences, n = 146) with cycle durations in excess of 1 s in contrast to the range for chewing (0.6-0.7 s). Almost all sequences ended with a period, clearance, of highly irregular jaw movements often including swallows. Clearance has not been described in other mammals. Food consistency affected feeding behaviour. The "chew/swallow' ratio (total number of chews/total number of swallows) increased with food hardness. The number of chewing cycles before the first in-sequence swallow also increased. Food type significantly affected sequence duration. The duration of clearance was also affected by bite weight and food hardness. It is concluded that initial food consistency determines the number of chewing cycles before the first swallow and overall sequence duration. The change in the pattern of jaw movement in both the vertical and mediolateral directions cycle to cycle suggests continuous sensory modulation of the motor output to the mandibular musculature.

Oral bolus kneading and shaping measured with chewing gum

A masticatory test using two-colored chewing gum is presented and analyzed. Two separate parameters of chewing were studied on the same chewing gum bolus after 10 strokes of oral preparation, color mixing, and bolus shaping. The two parameters were evaluated in indices 1-5. A test series should preferably contain three chewing gums, and color mixing can be evaluated on six sides and shape-indexed for each bolus. The medians characterize the subjects' masticatory ability. Color mixing may relate, for example, to ensalivation of the food during chewing, and bolus shape may relate to preparation into a form suitable for swallowing. The tests were used on test subjects with different dental and denture status. Significant differences in both color mixing and shape indices were found between groups with different status. The method is discussed in relation to earlier types of tests, e.g., the comminution test mostly used hitherto.

Within-subject comparisons of implant-supported mandibular prostheses: evaluation of masticatory function

In the past, fixed prostheses were believed to be more efficient implant-supported devices than removable types for edentulous patients. However, this hypothesis was never properly tested. Therefore, a within-subject crossover clinical trial was designed in which 145 completely edentulous subjects were tested wearing implant-supported mandibular fixed prostheses and long-bar overdentures. Eight subjects received the fixed appliance first and seven the removable type. The patients' perceptions of various characteristics of the implant-supported prostheses were measured after a minimum of two months' adaptation. Mandibular movements and jaw muscle electromyographic activity were recorded while the patients chewed five standard-sized test foods: bread, apple, hard cheese, sausage, and raw carrot. The prostheses were then changed, worn for the same period of adaptation, and the procedures repeated. There were three test sessions per prosthesis, and each included five trials per food. The measurements were repeated three times at one-week intervals. Mastication time was found to be shorter for three foods (bread, cheese, and sausage) when subjects wore the long-bar overdenture. The vertical amplitude of the masticatory strokes was significantly less with the overdenture for all foods except carrot. Cycle duration was significantly longer with the overdenture for sausage and carrot. Contrary to what might be expected, the long-bar overdenture appears to be no less efficient than the fixed prosthesis. Furthermore, these data suggest that patients are capable of adapting their masticatory movements to the characteristics of the two prostheses.

The effect of missing postcanine teeth on chewing performance in man

The masticatory performance of a group of subjects missing on average 5.7 postcanine teeth and of a control group with complete dentitions were compared. There were significant differences in performance between the two groups. Within the patient group the number of occluding units significantly influenced performance. The average number of chewing cycles needed to prepare the food for swallowing was significantly larger for the patient than for the control group. Despite this, subjects in the patient group swallowed, on average, significantly larger food particles. Correlations between chewing performance and the number of chews up to swallowing within each of the two groups did not reach significance. However, combining the data from the two groups and thus increasing the range of chewing performances yielded a highly significant correlation. Subjects with reduced performance needed more chewing cycles before swallowing the food. Significant correlations were also found between chewing performance and the size of the swallowed food; subjects with poor performance swallowed larger particles. The numbers of chewing cycles made to swallow a natural (peanut) and an artificial (Optosil) test food were highly correlated, indicating that both foods are suitable for testing chewing performance.

A comparison between data analysis methods concerning particle size distributions obtained by mastication in man

Three mixtures of chewed food particles (coarse, medium and fine) were quantified by measuring the particle sizes with an optical scanning device. The particle sizes were described by three different particle-size distributions: a cumulative volume, a volume and a number distribution. The median particle size was determined from each of the distribution functions. Suitability for characterizing a mixture of chewed food particles was tested, showing that the median particle size as obtained from a cumulative volume (or weight) distribution should be preferred. It was shown to be the most sensitive measure for characterizing mixtures of chewed food.

Masticatory ability in experimentally induced xerostomia

The masticatory ability of 15 nondysphagic volunteers with complete natural dentition was tested using different chewing parameters including preparation of a two-color plastic chewing gum (bolus shape, and color mixture), particle reduction of a piece of silicone, and number of strokes before swallow of almonds. The tests were performed under conditions of normal salivation and experimental oral dryness caused by intramuscular injection of methylscopolamine. The chewing gum tests as well as the silicone particle reduction tests were not influenced by lack of salivation. The number of chewing strokes prior to the initiation of swallowing of almonds was significantly increased. Oral dryness seems to cause accumulation of particles in the oral cavity from friable food and the particulate material is not transported posteriorly into a "ready-to-swallow" positioning. The absorption of saliva by dry oral content such as an almond further impaired oral manipulation of food.

Swallow thresholds using dentures made on different types of articulator

The purpose of this study was to determine whether edentate subjects achieved different performance when using dentures constructed on different articulators. A cross-over experimental design was employed to evaluate these swallow thresholds using complete dentures constructed on the hinge and free plane articulators. Seven subjects completed the study. Swallow threshold tests were performed 3 months after the insertion of dentures. The overall particle size distribution achieved with the dentures constructed on free plane articulators was significantly better at the end of the 3-month period (P less than 0.01 to P less than 0.0001), but significantly more strokes were used to achieve this success rate (P less than 0.04). A questionnaire revealed that the subjects had a preference for the denture constructed on the free plane articulator. It is concluded that patients performed better with dentures constructed on the free plane articulator.

Effects of anaesthesia of human oral structures on masticatory performance and food particle size distribution

Ten persons with intact dentitions performed a series of 6 masticatory tests, employing 5, 10, 20, 40, 80 and 160 strokes to chew standard quantities of peanuts on their preferred chewing side for each of three test conditions: (1) before anaesthesia: (2) after maxillary anaesthesia; and, (3) after maxillary and mandibular anaesthesia (unilateral). A seventh test employing 20 strokes was also repeated on the non-anaesthetized contralateral side. The chewed food was sieved through 5, 10, 20, 40, 80 and 100 mesh screens. The percentage of the ratio of the volume of peanuts that passed through the sieve and the total volume of recovered food provided the performance score for the given sieve. The performance scores increased significantly with the number of stokes and dropped markedly after anaesthesia. The maximum reduction of 19.6% in the mean masticatory performance and 46% in the mean masticatory efficiency occurred after unilateral anaesthesia at 10 mesh particle size in the 20-stroke test. An average of 40 strokes was required after unilateral anaesthesia to achieve almost the same performance achieved with 20 strokes before anaesthesia. The regression slopes, derived from the 5, 10 and 20 mesh particle distributions showed that coarse particles were ground more rapidly than fine particles before anaesthesia. This preferential comminution became less evident after maxillary anaesthesia and was least evident after unilateral anaesthesia. The regression slope for the control peaked at 10 strokes as compared to 20 strokes after unilateral anaesthesia. Thus peripheral sensory impairment affects masticatory efficiency in dentate persons.

Effect of chewing training on masticatory efficiency

A special, hard chewing gum was used to study the effects of chewing training on masticatory efficiency. An experimental group of 17 individuals used this chewing gum 1 h daily for 28 days, while a control group of 8 individuals performed no chewing-gum training. The percentage of masticatory efficiency was measured with a special sieve system, and the time for 10 chewing cycles was taken from EMG recordings. These measurements were made in trained and untrained condition before and after 30 min of intense chewing. The results indicate that intense chewing for 30 min decreased the masticatory efficiency and increased the frequency of the chewing cycles significantly in both trained and untrained individuals, possibly due to fatigue of the masticatory muscles. However, chewing training for 28 days did not influence these factors significantly.

Feeding disorders research and teams: a new challenge for dentistry

Feeding disorders, which include masticatory and cerebral disabilities, present a major problem for disabled persons, but only in the last decade have health professionals shown an increased interest in the diagnosis and management of patients with such problems. Dentists are experts in the diagnosis and treatment of disorders of the oral-facial region, yet they have either worked in intradisciplinary isolation or have not demonstrated their interest in patients with feeding disorders. Consequently, those involved in the assessment and treatment of persons with feeding disorders are not aware of the contributions dentists have made to the basic and clinical data base of feeding assessment and therapy. Dentistry is simply not mentioned in rehabilitation. The opportunity now exists for dentistry to inform others of our expertise in the field from both a research and a clinical perspective. The basic and clinical base of dental therapeutics and its role in the diagnosis and treatment of disorders of the masticatory apparatus and of swallowing are reviewed here. It is hoped that this review will stimulate interest among dentists to take part in the rehabilitation of patients with feeding disorders through the use of the extensive data base within the profession.

Subjective assessment of liquid volumes by humans during swallowing

To test the hypothesis that during drinking the appreciation of a volume of fluid in the mouth (VM) is important in determining the volume swallowed (VS), we assessed how well subjects recognized different volumes taken into the mouth and swallowed. Five volumes of tap water (5-25 cm3) were drunk in random order with the eyes closed and the subjects assessed these by selecting from an assortment of cylindrical blocks those with volumes which were thought to correspond visually or manually to the test volumes. Two known reference volumes and cylinders each of 15 cm3 were included in the test. Scores for total error magnitude, correct responses and bias showed that subjective assessment of volumes, though poor, was reproducible and that a student group performed better than children and elderly subjects who consistently underestimated VM. Of the factors studied which might contribute to perception of VM, the time taken for water to enter the mouth, but not the interval before swallowing, seemed most important. Raising the water temperature to 37 degrees C, surface anaesthesia of tongue and palate, and sipping as opposed to gulping, did not alter scores in students. The mean VS in unrestricted drinking was 12.6 cm3 for 44 students; repeat measurements in an individual varied by only about 11 per cent.

Food breakdown patterns produced by human subjects possessing artificial and natural teeth

The abilities of thirty-two complete denture wearers and thirty-two dentate subjects to break down raw carrot particles were compared. The particle size distributions produced were broader in those subjects that broke down food rapidly per chew and, conversely, narrower in those that were slower. This did not appear to depend on dental status. An analysis of mastication as composed of two separable processes, one describing the means by which particles come to be broken (selection) and the other, the size distributions of a particle upon fracturing (breakage), indicated that both processes were variable. It is concluded that no qualitative differences in the manner by which the two groups reduce food is apparent. To support this, a small study on dentate subjects suggests the covering of the palatal mucosa with an acrylic plate does not affect masticatory performance.