Age-related changes in mastication.

The paper reviews human mastication, focusing on its age-related changes. The first part describes mastication adaptation in young healthy individuals. Adaptation to obtain a food bolus ready to be swallowed relies on variations in number of cycles, muscle strength and volume of emitted saliva. As a result, the food bolus displays granulometric and rheological properties, the values of which are maintained within the adaptive range of deglutition. The second part concerns healthy ageing. Some mastication parameters are slightly modified by age, but ageing itself does not impair mastication, as the adaptation possibilities remain operant. The third part reports on very aged subjects, who display frequent systemic or local diseases. Local and/or general diseases such as tooth loss, salivary defect, or motor impairment are then indistinguishably superimposed on the effects of very old age. The resulting impaired function increases the risk of aspiration and choking. Lastly, the consequences for eating behaviour and nutrition are evoked.

Tongue-mandible coupling movements during saliva swallowing.

The purpose of this study was to measure the tongue and mandible positions and displacements in relation to the maxilla in the midsagittal plane to characterize the different saliva swallowing patterns by recording their kinematics. A 2D electromagnetic articulograph using four transducer coils, three attached to the upper surface of the tongue midline plus one attached to the chin anterior part allowed continuous evaluation of tongue and chin movements in twelve young adults in good general health. During 170 s sequences recorded at a frequency of 100 Hz, subjects were at rest, silently reading a text they had chosen. The subjects were free to swallow during the sequence. Deglutition of accumulated saliva was analysed after averaging all values obtained during successive 250 ms periods. We identified three elementary swallowing patterns. Mean duration of tongue-mandible movements were 1·51 ± 0·17 s, 1·63 ± 0·14 s and 2·00 ± 0·08 s for the first, second and third patterns respectively. In the light of other studies based on intra-oral pressure recordings, our results help to understand the tongue-mandible coupling behaviours involved in managing an in-mouth saliva bolus during the three elementary swallowing patterns identified.

Mood-induced variations of mandible and tongue postures.

Twelve young adults in a good general health were observed during habitual posture of tongue and jaw in different emotional conditions induced by watching three video sequences. The position of the mandible was tracked by the displacements of an electromagnetic sensor glued to the chin. The tongue-to-palate distance was obtained by 2-D location of three electromagnetic sensors placed on the tongue upper midline surface. Head displacements were evaluated with a sensor fixed to an upper central incisor and were subtracted from corresponding displacements of tongue and chin sensors to obtain the real tongue and mandible positions during continuous recording sequences. Emotional conditioning by a fear movie influenced the vertical position of the mandible: the mean interarch distances during the fear movie (2·34 ± 0·24 mm) were significantly different from those measured during the tender (3·13 ± 0·35) and neutral (3·42 ± 0·80) movies, respectively (anova repeated measure, SNK; P < 0·05). anova repeated measure indicated that the tongue-to-palate distance differed significantly when the subjects were watching the conditioning movies (P = 0·003), the tip of the tongue taking a lower position during the fear movie than during the tender and neutral movies.

Changes in mastication after an immediate loading implantation with complete fixed rehabilitation.

OBJECTIVE: This study aimed to measure modifications of mastication after immediate loading full-arch prosthesis (ILFAP) rehabilitation. MATERIALS AND METHOD: Fourteen patients were observed before and 6 months after ILFAP rehabilitation when masticating two natural, standardized foods (peanut and carrot) and three model foods with increasing hardness. The granulometry of the expectorated boluses from carrot and peanuts was characterized by median particle size (D50), determined at the natural point of swallowing. Chewing time (CT), number of chewing cycles (CC), and chewing frequency (CF) were video recorded. A self-assessment questionnaire for oral health-related quality of life [Geriatric Oral Health Assessment Index (GOHAI)] was also used. RESULTS: After ILFAP rehabilitation, the mean D50 values for carrot and peanuts were smaller [Repeated Model Procedures (RMP), F = 41, p < 0.001]. Mean CT and CC values recorded with the three model foods decreased, while CF increased regardless of the model food hardness (RMP, F = 14, F = 10, and F = 11, respectively, p < 0.001). The GOHAI score increased from 43 ± 9 to 56 ± 3 (t test, p < 0.001). CONCLUSION: ILFAP rehabilitation improves the ability to reduce the bolus particle size and the ability to discriminate between different food hardnesses in the 6 months post-surgery period. CLINICAL RELEVANCE: This study encourages the clinical development of immediate loading implantation with a fixed full-arch prosthesis protocol.

Substantiation of an artificial saliva formulated for use in a masticatory apparatus.

The aim of this work was to substantiate artificial saliva prepared for use in a masticator apparatus. Mastication's goal is to produce a viscous and plastic food bolus where these properties authorize a safe swallow. Apart from its biochemical contribution, saliva is mainly used in this kind of apparatus to provide a viscous component to the bolus. Artificial saliva was prepared with water and minerals, and completed with mucin and amylase. Different physico-chemical conditions were applied and the resultant viscosity was compared to that of human saliva. Mechanically- or chemically-stimulated salivas of ten healthy subjects were collected. Viscosity was measured with a capillary viscometer in response to changes in measurement's temperature, air exposure or pH. The effects of circadian saliva collection and the stimulation type on viscosity of human saliva were also studied. Viscosity of artificial and human salivas was comparable. An increase in the measurement's temperature or a 30 min-exposure of saliva to air led to a significant decrease in viscosity of both types of saliva. Amylase in artificial saliva did not change viscosity. The viscosity of human saliva displayed important subject variability as well as a dependence on the stimulation type of saliva production. This work allowed a useful evaluation of the formulated artificial saliva. It exhibited similar viscosity as the natural saliva in response to different methodological conditions. Therefore the proposed artificial saliva satisfies the major requirement of viscosity for a use in the masticator apparatus designed to prepare a food bolus.

A description of oral health in three French jails.

UNLABELLED: Prisoners display many features suggestive of a higher risk of poorer oral health than the general population. They have many risk factors: disadvantaged social background, consumption of psychoactive substances and a high proportion of persons with mental illness. The oral health of prisoners is handled by different care providers such as hospital doctors together with some students, interns, and some dedicated dental practitioners. There are few data describing the outcomes of this activity. OBJECTIVE: The objective of this descriptive study was to determine the oral health of prisoners in the current care system as observed in three French jails. PARTICIPANTS: 84 male prisoners were allocated to two subgroups according to the duration of incarceration: a short-term group (< or = 2 years; 31 subjects, mean age: 31 (sd 13) years) and a long-term group (> 2 years; 53 subjects, mean age: 43 (sd 11) yearss). One investigator performed a semi-guided interview and a dental examination. MAIN OUTCOME MEASURES: The DMFT index, the Global Oral Health Assessment Index, the number of dental functional units and some specific indicators on mastication were collected. RESULTS: Duration of incarceration explained more variability than age for numbers of missing teeth (26%; p < 0.001) and functional units (24%; p < 0.001). Long-term prisoners had greater chewing difficulties than short-term prisoners. CONCLUSIONS: This study suggested that, in the French jails studied, a stable level of oral infection including untreated caries was obtained at the cost of a degraded masticatory function.

Development and validation of a mastication simulator.

More and more research are being done on food bolus formation during mastication. However, the process of bolus formation in the mouth is difficult to observe. A mastication simulator, the Artificial Masticatory Advanced Machine (AM2) was developed to overcome this difficulty and is described here. Different variables can be set such as the number of masticatory cycles, the amplitude of the mechanical movements simulating the vertical and lateral movements of the human lower jaw, the masticatory force, the temperature of the mastication chamber and the injection and the composition of saliva. The median sizes of the particles collected from the food boluses made by the AM2 were compared with those of human boluses obtained with peanuts and carrots as test foods. Our results showed that AM2 mimicked human masticatory behavior, producing a food bolus with similar granulometric characteristics.

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.

Is the tongue position influenced by the palatal vault dimensions?

The influence of the palatal vault dimensions on tongue position is here studied through evaluation of the in-mouth air cavity (IMAC) volume when the mandible is in maximal intercuspal position. A sample of 35 women (mean age 21.2 +/- 1.0) and 15 men (mean age 22.1 +/- 0.9) was selected. The sagittal cross-section area of the IMAC, which is modulated by the tongue position, was measured on lateral cephalograms. Dental casts were used to measure the palatal vault volume, which was defined by the occlusal plane, the hard palate and the posterior face of the second molars. Palatal vault volume allowed deduction of the IMAC volume through a rule of three procedure relating volume to area ratios. No IMAC could be calculated from cephalograms of 10 subjects who had the tongue stuck to the palate. For the 40 other subjects, the IMAC volume was 8.9 +/- 4.8 mL. It was 2 mL larger in men (n = 14) than in women (n = 26) and was the largest in skeletal Class III and the smallest in skeletal Class II (P > 0.05). IMAC volume was strongly correlated with palatal vault height but neither with palatal width nor length. It was thus assumed that the height of the palatal vault could influence the most observed position of the tongue but this does not exclude a possible growth influence of the tongue on its surrounding skeletal structures.

[Nociception and chronic oral and cervicofacial pain]. / Nociception et douleur chronique orale et cervicofaciale.

This short review focuses on the main properties of the nervous system responsible for pain originating from oral, nasal and pharyngeal cavities. First, the major roles of the somatic sensations coming from the orofacial and pharyngeal areas are emphasized. Then, the description of the respective peripheral fields of the different cranial nerves involved in these somatic sensations is followed by the description of the primary afferent neurons and the central nuclei and pathways. The review emphasizes that pain does not result from a simple transmission of nervous impulses that would follow a fixed "hardwire" pathway but, on the contrary, results from an ever-changing balance between excitatory and inhibitory influences. These descending influences and other mechanisms may lead acute pain to become chronic through plastic changes of the nervous system and possible neuropathic changes. Finally, certain psychosocial factors that may facilitate chronic pain arousal are discussed.

Mastication of model products in complete denture wearers.

OBJECTIVE: The aim of this study was to define the characteristics of muscular activity in complete denture wearers and in dentate subjects during mastication of model foods differing in hardness but similar in terms of rheologically properties. MATERIAL AND METHODS: The foodstuffs used in this study were laboratory-developed gumdrops demonstrating viscoelastic properties. The test foods cover a range of four hardness levels. The group of complete denture wearers included 15 subjects, while the control group included 9 subjects with normal dentition. Electromyograph (EMG) recordings were taken from the masseter and temporal muscles during mastication of the test foods. The results were evaluated by one-way and two-way ANOVA followed by means comparisons using a Student-Newman-Keuls post hoc test (alpha=0.05). RESULTS: Preparing the same food bolus for swallowing required a greater number of masticatory cycles and a longer duration of mastication for complete denture wearers than for dentate subjects. In addition, complete denture wearers failed to increase EMG activity per cycle in response to hardness of the food. CONCLUSION: Denture wearers experienced difficulties during mastication, as indicated by a decreased masticatory rate and the observed failure to increase EMG activity per cycle in response to increased food hardness. The increases in number of cycle and masticatory duration appear to be a response to this impaired masticatory function.

The regulation of masticatory function and food bolus formation.

This review emphasizes the following points: 1. The values of the physiological parameters of mastication (number of cycles and total electromyographic activity in the sequence, sequence duration, cycle frequency in the sequence, kinetic characteristics of the cycles) are characteristic of each individual and vary widely from one individual to another. In a given individual their modification reflects an adaptation of mastication to the size of the food bolus, and the hardness and rheological characteristics of the food. 2. The ready-to-swallow food boluses produced by different individuals nevertheless display similar particle size distributions. 3. Ageing entails adaptation of the masticatory function and does not impair swallowing. 4. Observed increase in total electromyographic activity shows that more energy is expended in mastication by full denture wearers. Despite this increased muscle activity, loss of teeth, even if compensated for by complete dentures, hinders the formation of a normal bolus. The food boluses made by denture wearers thus contain many large-size particles. The impaired mastication observed in denture wearers approaches the masticatory disabilities found in persons with neuromotor deficiencies.

Effect of texture of plastic and elastic model foods on the parameters of mastication.

Mastication is continually modified throughout the chewing sequence in response to the texture of the food. The aim of this work was to compare the effects of an increase in hardness of two model food types, presenting either elastic or plastic rheological properties, on mastication. Each model food type consisted of four products of different hardness. Sensory testing experiments conducted with one group of 14 subjects showed significant perceived differences between products in terms of their increasing hardness. Fifteen other volunteers were asked to chew three replicates of each elastic and plastic product during two sessions. EMGs of masseter and temporalis muscles were recorded simultaneously with jaw movement during chewing. Numerous variables were analyzed from these masticatory recordings. Multiple linear regression analyses were used to assess the respective effects of food hardness and rheological properties on variables characterizing either the whole masticatory sequence or different stages of the sequence. Muscle activities were significantly affected by an increase in hardness regardless of the food type, whereas the shape of the cycles depended on the rheological properties. The masticatory frequency was affected by hardness at the initial stage of the sequence but overall frequency adaptation was better explained by a change in rheological behavior, with plastic products being chewed at a slower frequency. A dual hypothesis was proposed, implicating first a cortical-brain stem preprogrammed mechanism to adapt the shape of the jaw movements to the rheological properties of the food, and second, a brain stem mechanism with mainly sensory feedback from the mouth to adapt muscle force to the food hardness.

Adaptation of healthy mastication to factors pertaining to the individual or to the food.

Mastication is a physiological process controlled by the central nervous system and modulated by inputs from the mouth. Both the intrinsic characteristics of the subject and the extrinsic characteristics of the chewed food are responsible for variations of the masticatory function. Age, gender and dental state constitute the most studied intrinsic factors whereas hardness, rheological characteristics such as plasticity or elasticity, and food size are the better known extrinsic factors. These factors cause physiological adaptations which can occur during individual cycles or the whole sequence of mastication. Electromyographic and jaw movements (kinematic) recordings are commonly used to study mastication, from which, several variables can be measured. Vertical and lateral amplitudes and, velocities of jaw movements, are only given by kinematic recordings. Bioelectrical activities per cycle or per sequence are closely linked to masticatory forces and are measured from electromyographic recordings. Number of cycles, sequence duration and masticatory frequency can be measured from both types of recordings. The objective of this review is to provide an overview of the variations of the measured masticatory variables that occur when mastication adapts to changes in characteristics of the individual or the food.

[Adaptation of mastication in response to the characteristics of the individual or the food]. / Adaptation de la mastication en réponse aux caractéristiques de l'individu ou de l'aliment.

This article describes how all individuals formulate an individual masticatory adaptation process to deal with the special characteristics of the food they are chewing. It begins by briefly reviewing the act of mastication and the principal techniques that are used to observe it, focusing especially on electromyography. An overall study of mastication must include an analysis of its result, that is, the bolus of food that it prepares for swallowing. The masticatory act varies with each individual; it has been clearly established that people do not effect the same mandibular movements when they chew. Some people will need more chewing cycles to treat the same bolus of food than others will and the amplitude and duration of muscular contraction will vary from individual to individual. But a certain reproducibility does exist for each subject. The patients' dental condition will, to a large extent, dictate how they chew. The more prosthetic replacements they have in their mouths, the more cycles they will require for mastication. Age, too, plays a role. Older people have diminished perception thresholds and, therefore, take longer to react. If their dentitions are relatively complete and healthy, they simply need to increase the number of chewing cycles for a given portion of food. And, of course, the texture of the foodstuff plays a part; the harder it is the greater the number of cycles will be.

Impact of teaching requirements for students on the activity of a university dental hospital.

OBJECTIVES: This study aimed at investigating the influence of teaching requirements on the clinical activity of a dental hospital. METHOD: The annual clinical activity of seven classes of fifth-year students (n = 294) was monitored between 1994 and 2001 within the conservative dentistry and endodontic departments of a French dental hospital. The variables chosen were: (i) the mean number of procedures performed per student, and (ii) the proportion of different types of treatment within the global activity (i.e. endodontic treatment, anterior, and posterior restorations). These data were analysed in relation to changes in student assessment criteria over time. RESULTS: Quantitative clinical teaching requirements were removed for the academic year 1998-99 and student clinical activity subsequently decreased by 32.7%, going from 51.9 +/- 12.2 dental procedures on average per student in 1997-98, to 29.1 +/- 7.2 in 2000-01. The mean number of patients treated per student also declined significantly during this period. The size of the minimum clinical requirement altered over the years prior to being removed altogether and a positive correlation existed between the volume of activity and the minimum requirement over this time. The types of treatment provided changed independently from the assessment criteria over the study period. There was a decrease in the percentage of amalgams placed and an increase in the number of posterior composites. A negative correlation existed between the evolution of these two types of treatment. CONCLUSION: This study demonstrates that the clinical activity of a department in a dental teaching hospital is directly related to the assessment criteria fixed by the university. This may have repercussions for hospital services.

Particle size distribution of food boluses after mastication of six natural foods.

There is a large variability between and among individuals in the physiology of mastication, but it is not known whether this produces a similar variability in the particle sizes of food boluses at the end of the chewing process. Food boluses obtained just before swallowing were analyzed in ten subjects (aged 36.7 +/- 9.5 yrs) with normal dentition. Food samples of 3 nuts (peanut, almond, pistachio) and 3 vegetables (cauliflower, radish, and carrot) were chewed and expectorated after self-estimated complete mastication. Measurements with sieving and laser diffraction methods indicated that particles were much larger in vegetables than in nuts. Particle size distributions were similar among nuts and among vegetables. Surprisingly, no inter-individual variability was observed in the particle distributions for the 6 foods, although several sequence variables differed markedly. A need for a bolus to be prepared with a precisely determined texture before it can be swallowed may explain the inter-subject variability of the masticatory function.

Gonadectomy induces site-specific differences in nociception in rats.

High prevalence of chronic orofacial pain in women and its relationship with ovarian states suggest that ovarian hormones may be involved in the control of orofacial nociception. Since the interaction between ovarian hormones and nociception seems more evident in the orofacial area than in many other parts of the body, a possible site specificity of an ovarian hormone effect on nociception was tested in rats. Two nociceptive tests were applied to three groups of male rats (n=46) and three groups of female rats (n=46), that were gonadectomised (n=17), sham-operated (n=15) or intact (n=14). Each rat in each group received a local subcutaneous injection of formalin in the upper lip and in the hindpaw. Upper lip injection resulted in an increased occurrence of upper lip rubbing for more than 45 min and hindpaw injection resulted in an increased occurrence of hindpaw licking for about 1h. The duration of the nociceptive behaviours was measured at 3 months after surgery. No significant difference was found between intact and sham-operated animals. A significant increase (54%) in the upper lip rubbing but not the hindpaw licking was observed in gonadectomised females. No difference was observed in castrated males for upper lip rubbing, but a tendency towards an increased duration (102%) of hindpaw licking was noted. The depletion in gonadal hormones was confirmed 3 months after gonadectomy and after the sacrifice of the animals, by the observed decline in the bone mineral density measured on the femur of 40 rats belonging to the six groups. A role of ovarian hormones was also suggested after immunostaining of oestrogen receptors in the lamina II of Caudalis subnucleus of the trigeminal sensory complex and cervical (C1-C2) spinal dorsal horn. The number of cells expressing oestrogen receptors displayed a small (13.6%) but significant (P=0.037) increase in ovariectomised compared with sham-operated rats. These results suggest that the lack of ovarian hormones induces a site-specific increase in the sensitivity to orofacial nociceptive stimulation, and that an up-regulation of oestrogen receptors in the Caudalis subnucleus and C1-C2 dorsal horn may be one of the factors involved in this effect.

Ascending connections from the caudal part to the oral part of the spinal trigeminal nucleus in the rat.

The brainstem trigeminal somatosensory complex, while sharing many common aspects with the spinal somatosensory system, displays features specific to orofacial information processing. One of those is the redundant representation of peripheral structures within the various subnuclei of the complex. A functional redundancy also exists since a single sensory modality, e.g. nociception, may be processed within different subnuclei. In the present study, we addressed the question whether anatomical connections from the caudal part to the oral part of the spinal trigeminal nucleus may support topographical and functional redundancy within the rat trigeminal somatosensory complex. The retrograde tracer tetramethylrhodamine-dextran was injected iontophoretically into the oral subnucleus of anaesthetised rats. Cell bodies labelled retrogradely from the oral subnucleus were observed in laminae III-IV and V of the ipsilateral caudal subnucleus consistently, and to a lesser degree in lamina I. Such a distribution of retrogradely labelled cells suggested that specific subsets of neurones may relay nociceptive information, and others non-nociceptive information. Furthermore, intratrigeminal connections conserved the somatotopic distribution of primary afferents in the two subnuclei. First, injections of tracer in the dorsomedial and ventrolateral parts of the oral subnucleus resulted in retrograde labelling of the dorsal and ventral parts of the caudal subnucleus respectively. Second, animals that received tracer into the ventrolateral oral subnucleus displayed more caudal labelling than animals that were injected into the dorsomedial oral subnucleus. These findings show the existence of anatomical connections from the caudal part to the oral part of the spinal trigeminal nucleus in the rat. The connections conserve the somatotopic distribution of primary afferents in the two subnuclei. They provide an anatomical substrate for the indirect activation of trigeminal oral subnucleus neurones by somatosensory stimuli through the caudal subnucleus.