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At least 1,315 records · Page 73Linked to original sources
PubMed1994

Mechanics of tensile and shear stress generation in fixed partial denture retainers.

Movements caused by the application of chewing loads to a fixed partial denture (FPD) are predictable. There are translational and rotational movements of the FPD and flexure of the structure. The location and magnitude of tensile and shear stresses affecting cement within retainers during mastication is related to the type of movement and determined by differences in mobility of abutments at each end of the FPD, length of span, and point of chewing load. The incidence of cement failure could be reduced with improved strategic stress resistance.

Bite Force↗
PubMed1984

Synovial fluid pressure determination in the temporomandibular joint.

Synovial fluid hydrostatic pressure within the temporomandibular joint of the pig, Sus scrofa domesticus, was examined, utilizing the "wick method" for the determination of fluid pressure. Acute hydrostatic pressure levels were monitored in seven surgically exposed TMJ capsules of five animals. In six out of seven of the surgically exposed TMJ capsules, synovial fluid hydrostatic pressure was subatmospheric with the jaw in the resting position (mean = -3.8 mm of mercury). Fluid pressure increased as a response to operator-manipulated jaw position and returned to original levels upon release. In addition, an attempt was made to study fluid pressure in TMJ cavities of a functioning experimental animal model by chronically implanting a wick catheter in the joint space. Successful implantation was accomplished in two animals, and fluid pressure was monitored at 10- and 14-day intervals. Similar but slightly less negative mean "resting values" were obtained. Fluid pressures were greatly elevated during mastication.

Animals↗
PubMed1990

Oral alterations in Steinert's myotonic dystrophy: a presentation of two cases.

Two patients with Steinert's myotonic dystrophy are presented. The disease was suspected because of alterations in orofacial musculature clinically manifest as difficulties in swallowing, mastication, and speech, and as occlusal anomalies and maxillary bone deformities. The presumed diagnosis was reached as a result of the presence of percussion myotonia of the tongue; confirmation was based on family antecedents, electromyographic alterations, and muscle histopathologic findings.

Adolescent↗
PubMed1988

Synaptic bases of cortically-induced rhythmical hypoglossal motoneuronal activity in the cat.

Intracellular recordings were made from hypoglossal motoneurons during cortically-induced fictive mastication in paralyzed encéphale isolé cats. Repetitive stimulation of the masticatory area of the cerebral cortex induced rhythmical tongue movements coordinated with jaw movements. After the animal was immobilized, the cortical stimulation still induced rhythmical burst activity in the hypoglossal nerve and the digastric nerve. The burst activities in the medial and lateral branches of the hypoglossal nerve alternated rhythmically, and were in and out of phase with the burst activities of the digastric nerve, respectively. All hypoglossal motoneurons showed rhythmical intracellular potentials during repetitive cortical stimulation. The rhythmical depolarizing potentials superimposed by spike bursts appeared in phase with rhythmical bursts in either the lateral or medial branch of the hypoglossal nerve. No hyperpolarization was present between consecutive depolarizing potentials. Synaptic activation noise increased coincidentally with the depolarizing potential, indicating that EPSPs were involved in the generation of the depolarizing potential. No evidence was obtained for the existence of IPSPs during the inter-depolarizing phase by intracellular current injection. It was concluded that rhythmical bombardment of excitatory impulses to hypoglossal motoneurons was responsible for the rhythmical activity induced by repetitive stimulation of the cortical masticatory area.

Animals↗
PubMed1991

A microcomputer system for collecting and processing physiological information about the masticatory system.

A software system has been written for IBM PC, XT, AT and compatible computers to be used for data collection, analysis and display. The system supports the sampling and processing of data for jaw movement tracks, myoelectrical activities of masticatory muscles, the temporomandibular joint (TMJ) and occlusal sounds and bite force, etc. The package includes the following functions: calculating displacement, velocity, curvature, and curvature center of jaw movement trace, analyzing myoelectrical signals in amplitude integration, root mean square and power spectrum, processing TMJ sounds and occlusal sounds and bite force, analysing jaw movement traces and myoelectrical activities during mastication simultaneously, determining the maxillomandibular relations, etc. The program also provides versatile formatting capability for video, printing and plotting of data, and graph creation. The most of the above programs have flexibility and adaptability to other physiological signal processes.

Bite Force↗
PubMed1993

A comparative animal experimental study of differently dimensioned osteosynthesis screws used in the mid-face.

The soft tissue covering most of the midfacial skeleton is relatively thin. On account of this plates and screws of the 2 mm systems used in the osteosynthesis of this region can bulge and/or be palpable through the thin integument. This shortcoming has prompted the need to develop smaller systems. The present study was designed to investigate whether these more delicate systems are capable of withstanding the midfacial forces that come to bear during functional mastication. For the study a Le Fort I osteotomy was carried out in 10 sheep. The mobile maxilla was fixed with osteosynthesis plates and screws. This paper reports on 40 plates and 170 screws of two AO titanium systems. It compares the strength of 1.5 mm and 2.0 mm AO screws. The anchorage of the screws was assessed by evaluating the nature of contact between the screw and interfacial bone. The loaded screws showed no discernible differences in postoperative bone remodelling that could be correlated to the osteosynthesis systems. Although the experimental situation may not be directly comparable to the trauma or osteotomy case, this study lends credibility to the assumption that the 1.5 mm screw system could be used instead of the 2.0 mm system, even in mid-face areas associated with high masticatory loads.

Analysis of Variance↗
PubMed1991

Development of masticatory muscles and oral behavior from suckling to chewing in dogs.

1. At the age of 20 postnatal days, more than a half of the dogs (13/20) showed incisor eruption. At the age of 25 postnatal days, half of the dogs (10/20) showed molar eruption. 2. At the age of 24 postnatal days, half of the dogs (10/20) started chewing behavior. 3. EMG amplitudes of temporal muscle were larger than that of masseter muscle until 26.5 days after birth, but they were reversed at 26.5 days after birth. 4. This suggests that in dogs the earlier teeth erupted, the earlier the dominant oral behavior was changed from suckling to mastication, and concomitantly the dominant muscle for the oral behavior was changed from the temporal to the masseter muscle.

Animals↗
PubMedDate not supplied

New approaches to the pathogenesis of peptic ulcer based on the protective action of saliva with special reference to roughage, vegetable fibre and fermented milk products.

Epidemiologic studies have shown differences in the prevalence of peptic ulcer disease among various communities to be related to variation in diet and eating patterns. Results of studies of the effect of diet and pattern of eating on saliva, on gastric juice, and on the amount of bile are reviewed. It is suggested that bile, and not hydrochloric acid, plays the causative role in pathogenesis of peptic ulceration. The role of saliva in the prevention of peptic ulcer is emphasized. The salivary mucus swallowed with food is protective because it decreases the flow rate of bile which, when held in the gall bladder longer, loses its alkalinity and therefore its ability to damage the mucous cells. Roughage, cellulose and vegetable fibres and fermented milk products act in a similar manner. When food is well masticated, containing plenty of vegetable fibres and fermented milk products such as ghee and yoghurt, resulting in an increase in the amount of salivary mucus, peptic ulceration may be prevented and cured and relapses may be prevented. This does not require a big change in the pattern of diet but only a change in the manner of eating so that hasty eating is avoided and good is chewed well. The pattern of diet, especially the relative dietary preponderance of short-chain fatty acids, such as those present in milk, yoghurt and other fermented milk products, have a protective action; the short-chain fatty acids retard gall bladder contraction and thus diminish the amount of bile entering the duodenal lumen.

Bile↗
PubMed2006

Masticatory muscle pain and disordered jaw motor behaviour: Literature review over the past decade.

The clinically important relationship between masticatory muscle pain (MMP) and disordered jaw motor behaviour is subject of this concise, evidence-based review of the literature that was published during the past 10 years. Mainly based on studies that used some sort of experimental MMP (e.g., the intramuscular injection of noxious substances like hypertonic saline), it was concluded that MMP has pronounced effects on jaw motor functions like maximal clenching and mastication. The pain-related modulation of oral reflexes further illustrated the effects of MMP on masticatory motor control. Protecting the painful muscle tissues against further damage and allowing for time to heal the damaged tissues by immobilization of the masticatory system seem to be the key outcomes of these effects. Further, MMP was shown to influence the cervical motor system, which may partly explain the mechanism behind the frequently observed co-occurrence of pain in the neck and the jaw. Finally, it was concluded that, even though the evidence is not yet conclusive, also remote pain (non-MMP) can modulate jaw motor behaviour, which indicates the involvement of central mechanisms in this modulation.

Facial Pain↗
PubMed2006

Developmental and functional considerations of masseter muscle partitioning.

The masseter muscle participates in a wide variety of activities including mastication, swallowing and speech. The functional demands for accurate mandibular positioning and generation of forces during incising or a power stroke require a diverse set of forces that are determined by the innate muscle form. The complex internal tendon architecture subdivides the masseter into multiple partitions that can be further subdivided into neuromuscular compartments representing small motor unit territories. Individual masseter compartments have unique biomechanical properties that, when activated individually or in groups, can generate a wide range of sagittal and off-sagittal torques about the temporomandibular joint. The myosin heavy chain (MyHC) fibre-type distribution in the adult masseter is sexually dimorphic and is influenced by hormones such as testosterone. These testosterone-dependent changes cause a phenotype switch from slower to faster fibre-types in the male. The development of the complex organization of the masseter muscle, the MyHC fibre-type message and protein expression, and the formation of endplates appear to be pre-programmed and not under control of the muscle nerve. However, secondary myotube generation and endplate maturation are nerve dependent. The delayed development of the masseter muscle compared with the facial, tongue and jaw-opening muscles may be related to the delayed functional requirements for chewing. In summary, masseter muscle form is pre-programmed prior to birth while muscle fibre contractile characteristics are refined postnatally in response to functional requirements. The motor control mechanisms that are required to coordinate the activation of discrete functional elements of this muscle remain to be determined.

Animals↗
PubMed2006

Functional roles of oral reflexes in chewing and biting: phase-, task- and site-dependent reflex sensitivity.

Because loading during chewing is not totally predictable and jaw-closing muscles are strong and act over short distances, feedback from oral receptors is important in the control of mastication. Information on such feedback can be obtained by studying reflexes in jaw muscle EMGs. This review will deal with the contribution of reflex mechanisms to modifying motor neuron activity during chewing, and the dependency of reflex sensitivity on motor task, phase of movement, and site of stimulation.

Bite Force↗
PubMed2006

The effect of saliva composition on texture perception of semi-solids.

Saliva is expected to be of significance for the perception of food stimuli in the mouth. Mixing the food with saliva, including breakdown and dilution, is considered to be of large importance for semi-solids as these products are masticated without chewing. It is known that there are large variations in composition of saliva originating from different glands and different subjects. In this study we investigated how variations in salivary characteristics affect sensory perception. Eighteen trained subjects participated in the study. Saliva was collected at rest and during three types of stimulation (odour, parafilm chewing and citric acid), and flow rates were determined. The collected saliva was analyzed for protein concentration, buffer capacity, mucin level and alpha-amylase activity. The salivary components measured in this study varied considerably among subjects, but also within subjects as a result of different means of stimulation. Variations in salivary components were correlated with sensory perception of a number of flavour, mouth feel and after feel attributes in the semi-solids mayonnaise and custard dessert. Total protein concentration and alpha-amylase activity were observed to correlate most strongly with texture perception.

Adult↗
PubMed2004

Effect of different masticatory functional and mechanical demands on the structural adaptation of the mandibular alveolar bone in young growing rats.

The influence of masticatory functional and mechanical demands on the structural adaptation of the alveolar bone has not been investigated in both animals and humans. The effect of two experimental factors, the insertion of a bite-opening appliance and the alteration of food consistency, was investigated in young growing rats, with a particular emphasis on three-dimensional (3D) bone microstructure. Thirty-six male albino rats were divided into two equal groups, fed with either the standard hard diet or soft diet, at the age of 4 weeks. After 2 weeks, half of the animals in both groups had their upper molars fitted with an upper posterior bite block, an appliance similar to those used in clinical orthodontics. The remaining animals served as a control. After another 4 weeks, the animals were sacrificed, and their left hemimandibles were excised. Bone mineral density (BMD) and bone microstructure parameters of the alveolar process were subsequently measured, using dual-energy X-ray absorptiometry (DXA) and micro-computed tomography (micro-CT). The alveolar process width was also measured. Both experimental factors led to significant shape and structure modification of the mandibular alveolar bone in the growing rat. The bite block applied a continuous light force, which was associated with an inhibition of alveolar process vertical growth and a significant increase of cortical thickness. Soft diet and the consequent reduction of the intermittent forces applied to the alveolar bone during mastication resulted in a reduction of bone mineral density, accompanied by decreased trabecular bone volume and thickness. This rat model could prove to be a useful tool for the in vivo investigation of the role of muscular forces on the shape and structure adaptation of bone.

Absorptiometry, Photon↗
PubMed2006

The mesencephalic trigeminal sensory nucleus is involved in acquisition of active exploratory behavior induced by changing from a diet of exclusively milk formula to food pellets in mice.

Post-weaning mice fed exclusively milk display low-frequency exploratory behavior [Ishii, T., Itou, T., and Nishimura, M. (2005) Life Sci. 78, 174-179] compared to mice fed a food pellet diet. This low-frequency exploratory behavior switched to high-frequency exploration after a switch from exclusively milk formula to a food pellet diet. Acquisition of the high-frequency exploratory behavior was irreversible. Recently, we demonstrated that the mesencephalic trigeminal nucleus (Me5) is involved in the control of feeding and exploratory behavior in mice without modulating the emotional state [Ishii, T., Furuoka, H., Itou, T., Kitamura, N., and Nishimura, M. (2005) Brain Res. 1048, 80-86]. We therefore investigated whether the Me5 is involved in acquisition of high-frequency exploratory behavior induced by the switch in diet from an exclusively milk formula to food pellets. Mouse feeding and exploratory behaviors were analyzed using a food search compulsion apparatus, which was designed to distinguish between the two behaviors under standard living conditions. Immunohistochemical analysis of immediate early genes indicated that the Me5, which receives signals from oral proprioceptors, is transiently activated after the diet change. The change from low-frequency to high-frequency exploratory behavior was prevented in milk-fed mice by bilateral lesion of the Me5. These results suggest that the Me5 is activated by signals associated with mastication-induced proprioception and contributes to the acquisition of active exploratory behavior.

Afferent Pathways↗
PubMed2006

How to qualify and validate wear simulation devices and methods.

The clinical significance of increased wear can mainly be attributed to impaired aesthetic appearance and/or functional restrictions. Little is known about the systemic effects of swallowed or inhaled worn particles that derive from restorations. As wear measurements in vivo are complicated and time-consuming, wear simulation devices and methods had been developed without, however, systematically looking at the factors that influence important wear parameters. Wear simulation devices shall simulate processes that occur in the oral cavity during mastication, namely force, force profile, contact time, sliding movement, clearance of worn material, etc. Different devices that use different force actuator principles are available. Those with the highest citation frequency in the literature are - in descending order - the Alabama, ACTA, OHSU, Zurich and MTS wear simulators. When following the FDA guidelines on good laboratory practice (GLP) only the expensive MTS wear simulator is a qualified machine to test wear in vitro; the force exerted by the hydraulic actuator is controlled and regulated during all movements of the stylus. All the other simulators lack control and regulation of force development during dynamic loading of the flat specimens. This may be an explanation for the high coefficient of variation of the results in some wear simulators (28-40%) and the poor reproducibility of wear results if dental databases are searched for wear results of specific dental materials (difference of 22-72% for the same material). As most of the machines are not qualifiable, wear methods applying the machine may have a sound concept but cannot be validated. Only with the MTS method have wear parameters and influencing factors been documented and verified. A good compromise with regard to costs, practicability and robustness is the Willytec chewing simulator, which uses weights as force actuator and step motors for vertical and lateral movements. The Ivoclar wear method run on the Willytec machine shows a mean coefficient of variation in vertical wear of 12%. Force measurements have revealed that in the beginning of the stylus/specimen contact phase the force impulse is 3-4 times higher during dynamic loading than during static loading. When correlating material properties to the wear results of 23 composite resins subjected to the Ivoclar method, some parameters could be identified and incorporated into a wear formula to predict wear with the Ivoclar method. A round robin test evaluating the wear of ten dental materials with five wear simulation methods showed that the results were not comparable, as all methods follow different wear testing concepts. All wear methods lack the evidence of their clinical relevance because prospective studies correlating in vitro with long-term in vivo results with identical materials are not available. For direct restorative materials, amalgam seems to be a realistic reference material. For indirect, namely crown and bridge materials, low strength ceramic is appropriate.

Biomechanical Phenomena↗
PubMed2006

Intra-oral restorative materials wear: rethinking the current approaches: how to measure wear.

OBJECTIVE: To determine what wear parameter(s) have clinical relevance and what factors are important for accurate measurement of these parameters in vivo and in vitro. METHOD: Describe biomechanical factors affecting mastication and the mechanics of wear. Investigate how they impact the wear of teeth and restorative materials. Based on this information, define the advantages and disadvantages of using volume, depth, and area parameters to quantify wear. Describe direct and indirect methods of measuring wear and point out advantages and disadvantages of each. RESULTS: The preferred parameter for quantifying wear is volume. It is independent of occlusal factors and is a measure of work done. If material and environmental factors remain constant, volume loss is linear with time. Depth and area have limited clinical value because of their dependence on occlusal factors; plus, they are not linear with time. When measuring wear the material of interest and the opposing material must be considered; especially if the opposing material is enamel. Wear is best measured by comparing sequential 3D images. Measuring systems should be calibrated with their error reported using sigma values rather means and standard deviations. The quality of the alignment of the sequential images should be included in the error analysis. Cost and availability of 3D imaging systems has severely limited their use in clinical studies. SIGNIFICANCE: Wear is an important consequence of occlusal interactions. If not controlled, wear could lead to poor masticatory function with a concomitant reduction in quality of life and possible deterioration of systemic health.

Biomechanical Phenomena↗
PubMed2006

Differential effects of hypoglossal and facial nerve injuries on survival and growth of rats at different developmental stages.

The hypoglossal (XII) nerve is made up of functionally different nerve branches: the medial branch related to protrusion of the tongue and the lateral branch related to its retraction. The present study was performed to determine the effects of facial (VII) and XII nerve injuries on the survival and growth of rats in which the unilateral or bilateral VII and XII nerve components (main trunk, XII-trunk; medial branch, XII-med; lateral branch, XII-lat) had been resected at different developmental stages. In the suckling period, unilateral as well as bilateral injuries in the XII-trunk or XII-med nerve produced disturbed milk intake, lower survival rates and growth retardation in the nerve-injured rats. In the transition and mastication periods, only bilateral injury in the XII-trunk or XII-med nerve produced disturbed food intake followed by lower survival rates and growth retardation in those animals. The unilateral XII-lat nerve injury did not have significant effects on milk and food intake, whereas the bilateral injury caused disturbance in milk intake especially at the early neonatal stage. The unilateral VII nerve injury at the early neonatal stage caused deteriorating effects on food intake resulting in lower survival rate and severe growth retardation in the nerve-injured rats. The results indicate that the survival and growth of XII and VII nerve-resected rats differ considerably depending on the nerves injured and the developmental ages of the animals at the time of nerve insult.

Age Factors↗
PubMed2006

A novel approach to bite force measurements in a porcine model in vivo.

A novel device for a bite force measurement system in a porcine model is described. A single polyethylene layer was vacuum-formed into a splint, and a force sensor was fitted on to the splint occlusal surface and seated with a silicone layer. This design enabled the measurement of bite forces on selected teeth in a large animal model with either natural dentition or single implant crowns and could be used in assessing information on biomechanical adaptation of the bone-implant interface to masticatory loads. Preliminary recordings of force values obtained during mastication in the premolar region (200-560 N) and various limiting factors of the technical design are discussed.

Animals↗