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

Insights into the digestive processes of normal and high-amylose rice using realistic boluses formed in the bio-inspired oral mastication simulator (iBOMS-III)

Mastication is essential for preparing food bolus for swallowing and digestion. This study employed the bio-inspired oral simulator (iBOMS-III) to investigate the effects of mastication on physical properties and starch hydrolysis of normal rice (NR) and high-amylose rice (HR), while validating its results through comparison with in vivo data from human subjects. The median particle size (d50) of NR (1.266, 0.931, 0.776 mm) and HR (1.32, 1.04, 0.928 mm) boluses from iBOMS-III at 12, 14, and 20 cycles closely matched human boluses at the swallowing threshold, particularly after 14 and 20 cycles. Starch hydrolysis in NR increased from 76.6 % to 91.3 %, while HR hydrolysis ranged from 63.4 % to 73.3 %. Boluses from iBOMS-III with 14 and 20 cycles showed starch digestibility consistent with in vivo data (84.2 % for NR, 71.3 % for HR). These findings demonstrate that iBOMS-III effectively replicated human mastication behaviors, producing boluses comparable to those observed in vivo.

A hybrid system of mixture models for the prediction of particle size and shape, density, and flowability of pharmaceutical powder blends

This paper presents a system of hybrid models that combine both mechanistic and data-driven approaches to predict physical powder blend properties from their raw component properties. Mechanistic, probabilistic models were developed to predict the particle size and shape, represented by aspect ratio, distributions of pharmaceutical blends using those of the raw components. Additionally, the accuracy of existing mixture rules for predicting the blend's true density and bulk density was assessed. Two data-driven models were developed to estimate the mixture's tapped density and flowability (represented by the flow function coefficient, FFC) using data from 86 mixtures, which utilized the principal components of predicted particle size and shape distributions in combination with the true density, and bulk density as input data, saving time and material by removing the need for resource-intensive shear testing for raw components. A model-based uncertainty quantification technique was designed to analyse the precision of model-predicted FFCs. The proposed particle size and shape mixture models outperformed the existing approach (weighted average of distribution percentiles) in terms of prediction accuracy while providing insights into the full distribution of the mixture. The presented hybrid system of models accurately predicts the mixture properties of different formulations and components with often R 2 > 0.8 , utilising raw material properties to reduce time and material resources on preparing and characterising blends.

Effect of chewing ability on in vivo oral digestive characteristics and in vitro gastrointestinal starch hydrolysis of three different types of cooked rice

Chewing ability has a strong effect on food digestion. However, little is known about the relationship between the food mastication degree and the subsequent gastric emptying. This study was to explore the effects of individual chewing ability (strong and weak) on the in vivo oral processing characteristics and in vitro dynamic gastrointestinal starch hydrolysis of three types of rice (japonica rice, indica rice and waxy rice). Results showed that the swallowable bolus in the weak chewing group had larger holes and a looser microstructure with more small rice particles, while the strong chewing ones obtained a bolus with higher saliva content (up to 28%) and starch hydrolysis degree (up to 13.55%). Moreover, the gastric retention and starch hydrolysis of the strong chewing ability group were higher in the artificial gastric dynamic system (AGDS). The indica rice particles with the higher degree of fragmentation contacted enzymes easier and hydrolyzed quicker, thus emptying through the stomach faster (81.76%). However, the oral chewing properties of rice mainly influenced the starch digestion in the stomach and the initial stage of the small intestine (∼5 min). This study suggested that the chewing ability and rice variety can influence the bolus properties, which in turn affected the gastric emptying and the degree of starch hydrolysis during digestion.

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.

Biomechanical properties of masticatory balance in cases with RPDs-The influence of preferred and nonpreferred chewing side: A pilot study

Objectives

Removable partial dentures (RPDs) are inserted with the aim to restore masticatory function. There is however inconsistent evidence supporting the alleged improvements, posterior occlusal contacts being one of the decisive factors. We hypothesized that the distribution of abutment teeth in RPDs influences masticatory performance and functional parameters. To evaluate the masticatory performance and functional parameters in patients with a RPD using a single mathematical parameter (tilting index [TI]) for both jaws that predicts biomechanical behavior on the basis of the distribution of abutment teeth.

Materials and Methods

Masticatory performance was measured in patients wearing long‐time adapted RPDs using the standardized test food optocal, yielding the mean particle size (X₅₀). Mastication on the preferred and nonpreferred chewing sides was analyzed. Total muscle work (TMW) was calculated using bipolar electromyographic recordings of the masseter and anterior temporalis muscle. Functional parameters were subjected to multiple linear regression analysis including X₅₀ as a dependent variable and functional units (FU), the number of teeth, bite forces, and sagittal and frontal components of TI (TI α and TI β) as independent variables.

Results

When the preferred chewing side was tested, none of the investigated parameters correlated significantly with X₅₀. In contrast, chewing on the nonpreferred side was correlated significantly with performance for most variables (p < .05). This means that increased dental support improved chewing performance with RPDs under these conditions.

Conclusions

In well‐adapted RPDs, the distribution of abutment teeth as expressed by the tilting index seems to be of subordinate importance for masticatory performance.

Masticatory Adaptation to Occlusal Changes

This review deals with the frequent wide variability of masticatory capacity/incapacity. Neither researchers nor clinicians have taken sufficient account of this variability despite its implications for nutrition. Mastication in normal healthy oral conditions is first described, followed by a short presentation of the mechanisms of masticatory adaptation in the nervous system. Capacity, incapacity, and successful compensatory adaptation of mastication are then defined, along with the different methods used for their evaluation. Examples of adaptation needs are given, such as those concomitant with dental wear or occlusal changes. Finally, given its vital importance for deeply impaired mastication/deglutition function, the impact of masticatory adaptation processes on nutrition is examined.

Relating oral physiology and anatomy of consumers varying in age, gender and ethnicity to food oral processing behavior

The aim of this study was to link parameters describing oral physiology and anatomy of consumers varying in age, gender and ethnicity to food oral processing behavior. Three groups of healthy consumers were compared: Dutch, Caucasian adults (18-30 yrs, n =32), Chinese, Asian adults (18-30 yrs, n =32) and Dutch, Caucasian older adults (65-85 yrs, n =32). Mastication performance, salivary flow rate (stimulated and unstimulated) and dental status were quantified to characterize oral physiology. Volume of oral cavity, tongue dimensions, facial anthropometry, height and weight were quantified to characterize anatomy. Oral processing behavior of three solid foods (carrot, cheese and sausage) was quantified by video recordings and eating rate (g/s), average consumption time (s), chews per bite (-) and average bite size (g) were determined. Dutch, Caucasian older adults had smaller volume of oral cavity, lower number of teeth and larger head width compared to Dutch, Caucasian adults. Chinese, Asian adults showed significantly higher mastication performance and larger head width compared to Dutch, Caucasian consumers, while dental status did not significantly differ between groups. Males had significantly larger volumes of oral cavity and larger head height and width compared to females. Dutch, Caucasian adults had a shorter average consumption time (s), less chews per bite and consumed the three foods with higher eating rate (g/s) compared to Dutch, Caucasian older adults. Chinese, Asian adults had a significantly longer average consumption time (s), more chews per bite, smaller average bite size (g) and lower eating rate (g/s) compared to Dutch, Caucasian adults. Twenty-one significant relationships were found between oral physiological and anatomical parameters and oral processing behavior. Body weight resulted in the largest β-values, indicating to be the anatomical parameter of largest influence on oral processing behavior. We conclude that only few oral physiological and anatomical parameters related with food oral processing behavior. We suggest that other factors, including cultural factors contribute to variation in food oral processing behavior between different consumer groups more than saliva flow, volume of oral cavity, mastication performance and dental status.

Differences in comminution progress during mastication in healthy dentate and denture-wearing elderly people

PURPOSE

This study aimed to investigate the effect of removable denture prostheses on the comminution progress in elderly people.

METHODS

Twenty-two denture wearers of Eichner's classification B and C (75.1±5.3 years old) and 20 young fully dentate subjects (27.6±1.9 years old) participated in the masticatory examination, which used a combined test food from 5 daily food materials. Full masticatory cycles lasting until subjects needed to swallow and the half number of the cycles were adopted as masticatory conditions. Digital images of food particles under wet conditions were obtained for each bolus, and particles were analyzed by calculating the homogeneity and particle size indices.

RESULTS

The characteristic properties of the food particles were observed using a homogeneity index in the elderly denture group for half masticatory strokes. Their homogeneity index was significantly higher than that of the young dentate group. By contrast, no significant difference was observed in the indices for particles immediately before swallowing between two groups.

CONCLUSIONS

The comminuted particle size before swallowing in healthy denture wearers was not significantly different from that in the natural dentate group. The comminution of the first-half process in denture wearers was typical and could be one possible focus for meal property specifications in future studies.

Which variables should be controlled when measuring the granulometry of a chewed bolus? A systematic review

The distribution of food particles in a chewed bolus characterizes the food destruction after food oral processing (FOP). Previous reviews report that it could be affected by a lot of parameters as the number of chewing strokes, the dental status, but the conditions for producing reproducible data allowing inter-studies comparison have not been clearly described yet. This systematic review aims to identify the variables that can affect bolus granulometry determination, and to calculate their relative weights in the median particle size (D₅₀ ) variations. The systematic review focuses on granulometry expressed as D50 of the most used foods (peanuts, carrots, and almonds) and materials (Optosil and Optocal). Based on 58 studies, 5 variables among 60 being extracted could explain the D₅₀ variations. Conceptual differences between the conditions for FOP should be considered. After Chewing-test, the bolus is collected after a predefined number of strokes and its granulometry characterizes the effects of the dental and muscular apparatus on food destruction, while after Mastication-test the bolus is collected at the swallowing threshold, and its granulometry reflects the outcome of the abilities of the subject to adapt his/her mastication behavior to food texture. Experimental conditions related either to physical sieving or image analysis used to analyze the collected boluses impact the D₅₀ values. Finally, when type of test, sieving conditions, type of food or material, number of chewing strokes, and the oral status of the subjects are controlled, mean D₅₀ values are reproducible and could be used for inter-studies comparisons. PRACTICAL APPLICATIONS: This review provides tables that could be useful to control mean D₅₀ variations in further research.

A comparative evaluation of chewing efficiency, masticatory bite force, and patient satisfaction between conventional denture and implant-supported mandibular overdenture: An in vivo study

Purpose:

The purpose of this within-subject crossover clinical trial was to compare and evaluate the chewing efficiency, masticatory bite force, and patient satisfaction with conventional dentures and two implant-retained mandible overdentures after 4 weeks of usage.

Method:

This within-subject crossover clinical trial was carried out in the Department of Prosthodontics in K.D Dental College and Hospital. A total 15 patients were selected for the study. To report the changes in chewing efficiency by chewing 6gms of peanuts with 40 chewing strokes and comparing the particle size of the chewed material between two implant retained mandibular overdenture with that of conventional denture using micro vu excel gantry type visual measurement machine. To report changes in masticatory bite force after transition of conventional complete denture patient to implant retained overdenture after using the prosthesis for four weeks each and recorded by digital transducer. To assess the patient satisfaction after transition of conventional complete denture patient to implant retained mandibular overdenture with help of OHIP edent patient satisfaction questionnaire.

Results:

The chewing efficiency for implant retained overdenture increased significantly than that of conventional denture. The particle size decreased to 76.34% for implant supported overdenture than that of conventional denture. The chewing strokes required by conventional denture was 69 strokes and that by implant supported overdenture which was 40 strokes to get the same mean particle size. The patients satisfaction after receiving the implant retained overdenture was significantly higher than that of complete denture.

Conclusion:

The provision of two mandibular implants significantly improves measures of oral function and better quality of life for edentulous patients.

Masticatory Function with Implant-supported Overdentures

The type of attachment that is used in implant-supported mandibular overdentures may influence the retention and stability of the prosthesis and, thus, masticatory function. In this within-subject cross-over clinical trial, we examined the hypothesis that greater retention and stability of the overdenture improve the masticatory function. Eighteen edentulous subjects received 2 oral implants, a new overdenture, and, successively, 3 different suprastructure modalities: magnet, ball, and bar-clip. Masticatory performance, masticatory efficiency, and swallowing threshold were measured. The masticatory function significantly improved after implant treatment with each of the 3 attachments. We observed small differences in masticatory function among the 3 attachment types: slightly better masticatory performance with ball and bar-clip than with magnet attachments. The number of chewing cycles until swallowing hardly decreased after implant treatment. We conclude that significantly better masticatory performance, combined with a slightly smaller number of chewing cycles after implant treatment, results in smaller food particles being swallowed.

An innovative masticatory efficiency test using odour intensity in the mouth as a target marker: a feasibility study

A large number of studies have reported the findings for masticatory efficiency tests; however, some objective masticatory efficiency tests have a drawback, in that subjects are required to spit out the test material. This study examined the possibility of a masticatory efficiency test that evaluates the intensity of odours released when chewing an odour compound-containing material. A total of 20 volunteers were used in this study. The odour intensity in the breath after chewing a gum was measured by portable odour sensor device. The odour intensity after chewing the gum was measured over four chewing durations and at four intervals between spitting out and measurement of the odour intensity. The volume of stimulated saliva was measured by calculating the difference in the weight of the gauze before and after chewing to examine the effect of saliva flow. With an increase in chewing duration, odour intensity reduced. The odour intensity was the highest immediately after chewing. There was a positive correlation between odour intensity and gummy jelly-related masticatory efficiency test value (G-METV), which was significant for 10-s chewing. The regression equation was calculated from three objective variables of odour intensity and G-METV as dependent variable. Pearson's correlation coefficient between G-METV and the odour intensity-related masticatory efficiency value (O-METV) was 0·68. The coefficient of variation of O-METV was significantly lower than that of G-METV. These results suggest that the masticatory performance can be estimated by measuring the odour intensity immediately after chewing food containing odour compounds for 10 s.

Review: the Use of Electromyography on Food Texture Assessment

Sensory evaluation (SE) involves evoking, measuring and interpreting human responses to the properties of foods. Among these properties texture is an important one for food acceptability. Texture is mainly perceived through mastication, a process that changes food characteristics throughout time by comminuting and salivation. Electromyography (EMG) has emerged as a new tool in sensory evaluation mainly for assessing texture characteristics. Thus, it is interesting to analyze the knowledge so far generated and the procedures employed. Bipolar surface electrodes are placed on the four main masticatory muscles (masseter right-left and temporalis right-left) and their electric activity recorded during mastication. The signals need to be amplified and filtered, and afterwards their acquisition by a computer allows conditioning and analysis. The output is a series of bursts corresponding to the chews during mastication. EMG parameters include the area under the curve (linked to masticatory work) and voltage (linked to the force exerted) at different moments of the process. Many other parameters are derived from the recording and related to food texture characteristics. EMG allows the study of changes throughout the masticatory process, these changes in EMG parameters permit a better assessment of sensory characteristics than mechanical measurements. Nevertheless, close-fitting correlations have been found between sensorymechanical-EMG measurements. In the literature, texture assessment by using EMG includes many products like carrots, biscuits, cooked meat, cooked rice, cheese, etc., as well as different texture characteristics like tenderness, hardness, crunchiness, juiciness, among others. Nowadays, texture studies involving EMG are mainly linked to describing changes or differences in the signals, good descriptors of perceived differences. Nevertheless for quantifying purposes, in order to allow comparisons among authors, a first step should be undertaken to standardize EMG parameters definition and procedures used in SE.

Effect of mastication on lipid bioaccessibility of almonds in a randomized human study and its implications for digestion kinetics, metabolizable energy, and postprandial lipemia

BACKGROUND

The particle size and structure of masticated almonds have a significant impact on nutrient release (bioaccessibility) and digestion kinetics.

OBJECTIVES

The goals of this study were to quantify the effects of mastication on the bioaccessibility of intracellular lipid of almond tissue and examine microstructural characteristics of masticated almonds.

DESIGN

In a randomized, subject-blind, crossover trial, 17 healthy subjects chewed natural almonds (NAs) or roasted almonds (RAs) in 4 separate mastication sessions. Particle size distributions (PSDs) of the expectorated boluses were measured by using mechanical sieving and laser diffraction (primary outcome). The microstructure of masticated almonds, including the structural integrity of the cell walls (i.e., dietary fiber), was examined with microscopy. Lipid bioaccessibility was predicted by using a theoretical model, based on almond particle size and cell dimensions, and then compared with empirically derived release data.

RESULTS

Intersubject variations (n = 15; 2 subjects withdrew) in PSDs of both NA and RA samples were small (e.g., laser diffraction; CV: 12% and 9%, respectively). Significant differences in PSDs were found between these 2 almond forms (P < 0.05). A small proportion of lipid was released from ruptured cells on fractured surfaces of masticated particles, as predicted by using the mathematical model (8.5% and 11.3% for NAs and RAs, respectively). This low percentage of lipid bioaccessibility is attributable to the high proportion (35-40%) of large particles (>500 μm) in masticated almonds. Microstructural examination of the almonds indicated that most intracellular lipid remained undisturbed in intact cells after mastication. No adverse events were recorded.

CONCLUSIONS

Following mastication, most of the almond cells remained intact with lipid encapsulated by cell walls. Thus, most of the lipid in masticated almonds is not immediately bioaccessible and remains unavailable for early stages of digestion. The lipid encapsulation mechanism provides a convincing explanation for why almonds have a low metabolizable energy content and an attenuated impact on postprandial lipemia.

Influence of disinfectant solutions on test materials used for the determination of masticatory performance

Masticatory function can be evaluated objectively as the capacity of an individual to fragment solid food after a fixed number of chewing cycles, the so-called masticatory performance (MP). The objective of this study was to evaluate the reliability of four different test materials (Optosil, Optocal, Zetapuls, and Perfil) and five disinfection protocols by aspersion and immersion (no disinfection, 2% glutaraldehyde, 2% chlorhexidine, 5.25% sodium hypochlorite, and 70% alcohol) on the MP, determined at three moments (24 hours, 15 and 60 days) after storing the fragmented blocks. MP was evaluated by calculating X50 through the sieving technique and the Rosim-Ramler equation. The weight and microbiologic count (colony forming units, CFUs) of chewed blocks were measured to identify any variations that would make MP determination unfeasible. Differences in MP were observed among the materials (p < 0.01). Perfil presented the highest X50 value (worst MP determination), followed by Zetaplus (both p < 0.05), Optosil, and Optocal (both p > 0.05). The time and disinfection type had no influence on MP (p > 0.05). The number of CFUs differed between the nondisinfected group and all other disinfection groups at all time points (p < 0.01). No other significant difference in CFU count between disinfection groups was observed. In conclusion, disinfection did not alter the reliability of the test materials for the MP calculation for up to 60 days.

The relationship between oral conditions, masticatory performance and oral health-related quality of life in children

OBJECTIVE

To evaluate the association between oral conditions, masticatory performance (MP) and oral health-related quality of life (OHRQoL) in 8-12 year-old children.

DESIGN

150 Brazilian scholars were examined for caries and malocclusions. MP was evaluated based on the ability to comminute an artificial test food followed by the determination of the median particle size (X50) and particle distribution in different-sized sieves ("b"). OHRQoL was measured using the Brazilian versions 8-10 and 11-14 of the child perceptions questionnaire (CPQ), considering the following domains: oral symptoms (OS), functional limitations (FL), emotional well-being (EW) and social well-being (SW). Higher scores indicated worse OHRQoL. Data were submitted to Spearman's correlation test and multiple linear regression analysis.

RESULTS

There were significant positive correlations between the psychosocial and OS domains scores of the CPQ8-10 and the number of decayed and missing teeth, respectively. The number of decayed teeth positively correlated with the number of missing teeth and the CPQ11-14 scores. The number of decayed and missing teeth was significantly associated with higher CPQ8-10 scores. Higher CPQ11-14 overall scores were associated with female gender, higher FL domain scores were associated with the number of missing teeth, and higher X50 values and EW domain scores were associated with female gender and the number of decayed teeth.

CONCLUSIONS

A higher number of missing teeth correlated with an inferior MP in older children. Children with a higher number of caries rated their oral health less favourably. Older females and those who broke the test material into smaller sizes were also more likely to report a worse OHRQoL, suggesting that the time allowed to reduce food appears to be a more influential factor on children' perception of oral health than their ability to break down the test material into smaller sizes. Moreover, the subjectivity of functional domain and artificial nature of chewable test material could have influenced the test sensitivity.

The masticatory normative indicator

There is no established quantitative, objective method to differentiate individuals with good masticatory function from those lacking this attribute. The aim of this study was to specify a normal range of median particle size values for masticated raw carrots collected just before being swallowed. The masticatory normative indicator (MNI) value thus obtained was based on seven studies carried out by different investigators using different methods for measuring particle size in carrot boluses. A simple mathematical transformation of variables and the choice of an interval of +/-1.96 times the standard deviation gave 4.0 mm as the upper limit of normal median particle size for carrots in a population of young persons with good oral health. This value identifies boluses that may be considered as resulting from impaired mastication, as illustrated in healthy individuals with experimentally hampered mastication, denture wearers, and individuals presenting with obesity or Down syndrome.

Influence of occlusal vertical dimension on the masticatory performance during chewing with maxillary splints

Changing the occlusal vertical dimension is a common procedure in restorative dentistry, during treatment of patients with cranio-mandibular disorders, and during orthodontic and orthognathic treatment. The treatment may alter the length of the main jaw elevator muscles and the position of the mandibular head in the fossa temporalis. These changes may influence the bite forces that are generated during chewing and thus may affect the masticatory function. We measured the objective masticatory function, defined as masticatory performance, by determining an individual's capacity to pulverize a test food. The immediate influence of the increase in the occlusal vertical dimension on the masticatory performance was determined using three anatomical maxillary splints in a group of seven dentate subjects. The splints gave an increase in the occlusal vertical dimension of 2, 4 and 6 mm, respectively. Before we started the experiments the subjects practiced chewing with the splints during about 5 min. No significant differences were observed in masticatory performance among the conditions without and with the three splints. Thus, an increase in the occlusal vertical dimension up to 6 mm did not have a significant effect on the masticatory performance. Maxillary splints may be used to study the effect of occlusal factors on the chewing process by manipulating tooth shape and occlusal area of the splint.

Impaired mastication modifies the dynamics of bolus formation

Mastication is a complex sensory-motor activity whereby a food product is transformed into a bolus. Consumers mainly perceive the sensory properties of the food during the intra-oral manipulation of the product. Consequently, the quality of the chewing process could have consequences on the perception of sensory properties and food choice. By focusing on meat products, this study aimed to analyze the influence of dental status on (i) dynamic adaptation of the chewing behavior (evaluated by electromyography) to the changes in texture during bolus formation and (ii) bolus properties (mechanical resistance and saliva incorporation) obtained from meat of different initial textures. Two groups of subjects (dentate subjects and denture wearers), known to present highly different chewing efficiency, were compared. For both groups, salivary flow rates were evaluated at rest and after stimulation by chewing (paraffin and meat). The salivary flow rates, assessed during chewing of a nonedible matrix (paraffin), were a good predictor of salivary flow rates induced by meat chewing for both groups of subjects. Salivary flow rates were not affected by the dental status. In contrast, the chewing behavior varied between groups. For denture wearers, the chewing pattern was strongly impaired and not adapted to the changes in meat structure during bolus formation. Denture wearers swallowed less fragmented boli than dentate subjects, but boli had a similar level of moisture for both groups of subjects.

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.

Comparison of single and multiple sieve methods for the determination of masticatory performance

In the majority of studies on masticatory performance, the degree of food breakdown has been determined by sieving the food with one or more sieves. The aim of the present study was to compare the results obtained with a single and a multiple sieve method, as these methods have never been compared. We analysed the chewed food of 176 dentate subjects with a single and a multiple sieve method. Furthermore, we quantified the influence of age, gender, and dental status on the masticatory performance in order to compare the sensitivity of both methods. We observed a significant influence of the number of occlusal units on the masticatory performance for both methods. The single sieve method is less reliable than the multiple sieve method if the sieve diameter is not close enough to the median particle size of the chewed food. Therefore, we recommend the multiple sieve method.

Swallowing thresholds of mandibular implant-retained overdentures with variable portion sizes

We analysed the effect of three portion sizes Optocal Plus (small, medium and large) on swallowing thresholds in subjects with either conventional complete dentures or mandibular implant-retained overdentures (transmandibular and permucosal cylindric implants). Tests were carried out in 52 women and 15 men (mean age 59 years) 4 years after treatment in a randomised controlled clinical trial. The results indicated that the degree of mucosal support for the mandibular denture did not affect the number of chewing strokes, time till swallowing or swallowed particle size. Only the chewing rate differed: subjects wearing mandibular implant-retained overdentures chewed the food at a higher rate than complete-denture wearers. With larger portion sizes, subjects needed significantly more chewing strokes and time until swallowing and they would have swallowed larger particles. Men chewed their food more efficiently than women, as they used the same number of chewing strokes and time, but achieved a greater particle size reduction at the swallowing moment.

Comparison of single and multiple sieve methods for the determination of masticatory performance

In the majority of studies on masticatory performance, the degree of food breakdown has been determined by sieving the food with one or more sieves. The aim of the present study was to compare the results obtained with a single and a multiple sieve method, as these methods have never been compared. We analysed the chewed food of 176 dentate subjects with a single and a multiple sieve method. Furthermore, we quantified the influence of age, gender, and dental status on the masticatory performance in order to compare the sensitivity of both methods. We observed a significant influence of the number of occlusal units on the masticatory performance for both methods. The single sieve method is less reliable than the multiple sieve method if the sieve diameter is not close enough to the median particle size of the chewed food. Therefore, we recommend the multiple sieve method.

Masticatory performance in patients with anterior disk displacement without reduction in comparison with symptom-free volunteers

Masticatory function can be impaired by craniomandibular disorders. The aim of this study was to assess masticatory performance in patients with an anterior disc displacement (ADD) without reduction. In the experiments, 29 patients and 33 age- and gender-matched volunteers chewed artificial test food for 60 chewing strokes. The collected remains of the test food were filtered, dried, fractionated by a sieving procedure, and weighed. The particle size distribution was then described using a cumulative distribution function. Patients and controls were clinically examined, and patients were asked to complete a pain questionnaire. Comparison with controls, patients showed significantly reduced masticatory performance. Patients that had had a disorder longer than 3 yr tended to display less reduction of their masticatory performance. Neither the treatment methods used, nor restriction of daily life activities or pain intensity were significantly correlated with masticatory performance. Jaw mobility was significantly reduced in patients. More than half of the patients and none of the controls had joint noises and trigger points in the masticatory muscles. Pain was present, in particular, during chewing and maximal opening of the mouth. It was concluded that patients with ADD without reduction have a significantly reduced masticatory performance.

Influence of impaired mastication on nutrition

It has been suggested that people who suffer from impaired masticatory function may adapt food consistency to their oral status (which may lead to deficient nutrient intake) or rely on the digestive system to compensate for the lack of oral preparation of food (which may increase the likelihood of digestive diseases and decrease gut absorption). Masticatory deficiency thus may be detrimental to health. This article reviews evidence of the effects of masticatory deficiency on nutrition. The selection of relevant literature was based on Medline queries using the following key words: mastication, nutrition, digestion, diet, and disease risk. Earlier work not listed in Medline but related to the subject also was reviewed. Only publications available in English were selected for inclusion. It is difficult to draw conclusions from many of the reviewed studies due to issues related to study design, confounding variables, and the subjective nature of the measurements. In particular, data supporting a link between masticatory function and deficient dietary intake often are based on relatively weak correlations and cannot confer a causal relationship.

Masticatory performance in patients with myasthenia gravis

Masticatory muscle electromyograms (EMGs) were recorded while patients with bulbar myasthenia gravis chewed artificial food and compared with those of patients with ocular myasthenia gravis, patients in clinical remission who had previously suffered from bulbar myasthenia gravis and healthy individuals. Masticatory performance and EMGs were significantly smaller in the bulbar group. There were no indications of subclinical masticatory muscle weakness in patients with bulbar myasthenia gravis in remission and in patients with ocular myasthenia gravis. Patients with bulbar myasthenia gravis barely compensated for muscular weakness by chewing at a higher percentage of their maximal EMG. These quantitative findings, when combined with subjective reports of masticatory muscle weakness, show that a need to support the jaw is characteristic of patients with bulbar myasthenia gravis who produce low EMG activity.

Biting and chewing in overdentures, full dentures, and natural dentitions

It has been suggested that the provision of dental implants can improve the oral function of subjects with severely resorbed mandibles, possibly restoring function to the level experienced by satisfied wearers of conventional complete dentures. Nevertheless, a quantitative comparison has never been made and can be drawn from the literature only with difficulty, since studies differ greatly in methodology. To make such a comparison, we measured bite force and chewing efficiency by using identical methods in subjects with overdentures, complete full dentures, and natural dentitions. Our results indicated that bite forces achieved with overdentures on dental implants were between those achieved with artificial and natural dentitions. Chewing efficiency was significantly greater than that of subjects with full dentures (low mandible), but was still lower than that of subjects with full dentures (high mandible) and overdentures on bare roots. Differences in the height of the mandible revealed significant differences in chewing efficiency between the two full-denture groups. Furthermore, subjects with a shortened dental arch exerted bite forces similar to those of subjects with a complete-natural dentition, but their chewing efficiency was limited due to the reduced occlusal area. For all groups combined, a significant correlation was found between maximum bite force and chewing efficiency. Nearly half of the variation in chewing efficiency was explained by bite force alone.

Mechanical properties of foods responsible for resisting food breakdown in the human mouth

The fragmentation of foods (breakage function) was measured in five humans on "bagged' single particles of 28 foods from three food groups. The change in the square root of the specific surface of the particles (the specific surface being the area of particle silhouettes, measured by image analysis, divided by original particle volume) produced by one bite, averaged for all participants, was inversely linearly related to the square root of the toughness of the foods divided by the square root of their Young's moduli(r = -0.86; p < 0.00001). This relation is predicted by an analysis based on food fragmentation within a limited jaw displacement. Thus, resistance to jaw movement appears to provide sensory information on the deformation fracture and fragmentation of foods. It is believed that this is the first time that a relation between the breakage of food particles by the teeth and their material properties has been found, and the finding has considerable implications for human masticatory studies, for the analysis of dentition and diet in mammals and for texture studies in food science.

Comminution of food with mandibular implant-retained overdentures

When complete-denture wearers are treated with from four to six implants and mandibular implant-borne prostheses, masticatory performance improves. No significant improvement has been observed with two implants and implant-mucosa-borne overdentures, suggesting that the masticatory performance of edentulous subjects depends on the degree of support for their mandibular prostheses by implants or alveolar mucosa. To verify this hypothesis, we studied, in a randomized clinical trial, the comminution of an artificial test food during mastication. The trial involved the provision of a new maxillary denture and either a new conventional mandibular denture, a mandibular overdenture retained by two permucosal cylindric implants through a single bar-clip attachment, or a mandibular overdenture retained by a transmandibular implant through five clips on a triple-bar construction with cantilever extensions. In comparison with the subjects wearing mandibular implant-retained overdentures, the subjects with conventional complete dentures needed between 1.5 and 3.6 times more chewing strokes to achieve an equivalent reduction in particle size. No differences in masticatory performance and efficiency were found between the subjects who had received two permucosal cylindric implants and those who had received a transmandibular implant. The results suggest that the increased retention and stability of the mandibular denture, rather than the degree of support by implants or alveolar mucosa, determine the wearer's ability to comminute food during mastication.

Chewing performance before and after rehabilitation of post-canine teeth in man

Missing teeth are often replaced by fixed or removable prosthodontic appliances to improve masticatory function. However, there have been few studies directly determining the influence of prosthodontic treatment on masticatory function. Our aim was to obtain information on the objective and subjective masticatory function of partially edentulous subjects before and after prosthetic restoration. In this way, the improvement of the masticatory function as a result of the treatment could be quantified. The objective and subjective masticatory function of a group of 15 subjects was determined before and after replacement of an average of 3.1 post-canine teeth. The results were compared with data from a control group of 26 subjects having a complete dentition. The total number of occluding post-canine teeth increased as a result of the prosthodontic treatment, yielding a significantly improved objective masticatory function. The average masticatory performance was found to approach the level of the control group if all occlusal units of the longest posterior side were replaced. Subjects with an incomplete dentition tended to chew predominantly on the side of the longest posterior arch. The average subjective masticatory function improved as a result of the treatment. The appreciation of the masticatory function after treatment was equal to that of the control group, despite an average of 2.7 missing teeth. However, no correlation was found between the additional number of occlusal units and the change in subjective masticatory performance. Rehabilitation of post-canine teeth restores some objective masticatory function and leads to an increased appreciation of the masticatory function, although no correlation was found between the changes in objective and subjective masticatory function.

The association between chewing efficiency and occlusal contact area in man

Chewing is influenced by a number of factors, which include jaw and tongue movements, the activity of circumoral muscles, bite force and hard oral surfaces, but it is not clear which of these factors is most crucial to efficiency. The mere presence of surfaces such as the hard palate, or teeth, does not insure that chewing will be efficient. The purpose of this study was to explore the relationship between occlusal contact area, and chewing efficiency and to observe the influence of chewing-side preference on efficiency. These variables were recorded for both left- and right-hand sides, in a sample of 26 normal young adults. Chewing efficiency was estimated by the size of food particles collected after a predetermined number of chewing strokes. The particles were measured using image analysis and the median size calculated. Comparisons were made, firstly within subjects, between the left- and right-hand side, and secondly between subjects. Correlations were found between chewing efficiency and occlusal contact area which were more pronounced within, than between, subjects. It was concluded that while occlusal contact area influenced chewing efficiency within the same individual, it could not account for the differences in chewing efficiency found between individuals. Differences in the movement of the jaw and in the bite force may have a greater influence on chewing efficiency than occlusal contact area.

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 sieving and optical scanning for the determination of particle size distributions obtained by mastication in man

Mixtures of particles of different sizes, as obtained after chewing, were analysed. Coarse, medium and fine mixtures of particles of an artificial (Optosil) test food were used. Mixtures of Optosil particles of known form and size (half-cubes) were used to validate the analytical methods. The results of both methods were described by particle size distributions based on the volume of the particles. Complete agreement between methods was found for the mixtures of half-cubes. In order to determine the median particle size by volume from the results of optical scanning an assumption on the form of the chewed particles had to be made. Using the assumption that, on average, the particles resemble spheres a slight overestimate of the median particle size was obtained for scanning as compared to sieving. It can be concluded that, although different aspects of the fragmented particles are measured, sieving and optical scanning are both adequate methods for quantifying mixtures of chewed food particles and yield similar results for the degree of particle size reduction.