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At least 1,063 records · Page 59Linked to original sources
PubMed1998

Myoelectric activity during unilateral chewing in healthy subjects: cycle duration and order of muscle activation.

STATEMENT OF PROBLEM: Craniomandibular disorders, unilateral mastication, and asymmetry of masticatory muscles appear to be related to each other. Thus, it is of interest to investigate masticatory muscle activity during unilateral mastication in healthy subjects. PURPOSE: This study monitored contractile activity of the right and left masticatory muscles during right- and left-side gum chewing. MATERIAL AND METHODS: Electromyographic techniques were used to determine chewing cycle duration and duration of contractile activity of the masticatory muscles (right and left masseter and anterior temporalis muscles) during unilateral chewing in 40 subjects without orofacial pain. The time-course of activation of the 4 muscles was also investigated. RESULTS: Electromyographic traces showed extensive interindividual variation. In both right- and left-side chewing tests, and regardless of whether the masseter or the temporalis muscles were considered, mean duration of the contraction phase did not differ significantly between the working and nonworking sides. The working side temporalis contracted first, whether alone or at the same time as the other muscles. CONCLUSIONS: In healthy subjects, no significant differences in masticatory muscle activity should be expected between either the right and left or the working and nonworking sides.

Adult↗
PubMed1999

Comparison of chin and jaw movements during gum chewing.

STATEMENT OF PROBLEM: Knowledge of mastication is based on studies that use jaw tracking equipment in nonroutine settings. Ethologists would argue that such data probably does not reflect routine masticatory function. If jaw movements could be tracked noninvasively, then the hypothesis that jaw tracking equipment and nonroutine settings alter mastication could be investigated. PURPOSE: This study quantitatively evaluated the relationship between chin and jaw movements during a gum-chewing task. MATERIAL AND METHODS: Masticatory chin and jaw movements of 50 subjects were tracked in the x-, y-, and z-axes for 15 seconds, which resulted in approximately 15 chewing cycles obtained per subject. For each chewing cycle, magnitude and timing of displacement, velocity, and acceleration extrema in each axis were computed for both jaw and chin movement data. Extrema means were calculated for each 15-second trial. The respective means representing chin versus jaw movements were compared with linear regression and correlation analyses. RESULTS: All mean extrema were significantly correlated (r range 0. 30-0.99; P <.05). Magnitude correlations were larger than timing correlations for acceleration extrema. In contrast, magnitude correlations were smaller than timing correlations for displacement extrema. The highest correlation occurred for chewing rate. CONCLUSIONS: Chin and jaw movements were correlated during chewing; however, only chewing rate was highly predictable from chin movement data.

Acceleration↗
PubMed1997

GM1 gangliosidosis type 3 with severe jaw-closing impairment.

The patient had adult GM1 gangliosidosis (type 3) with severe impairment of mastication caused by dystonia of anterior digastric muscles (jaw-opener) on clenching. This is the first report on jaw dystonia severe enough to cause the masticatory impairment in adult GM1 gangliosidosis. The discordance of closing and opening muscles during mastication might be caused by a basal ganglia lesion in this disease.

Adult↗
PubMed2004

Rhythm generation for food-ingestive movements.

In vitro block preparations of the central nervous system (CNS) are particularly valuable for study of central neuronal mechanisms controlling the respiratory and locomotor rhythms. No comparable in vitro preparation has been described previously, however, for analysis of analogous feeding rhythms. In this chapter, we present such a model. It is comprised of an in vitro brainstem-spinal cord preparation isolated from the newborn rat and mouse. Bath application to this preparation of N-methyl-D-aspartate (NMDA) induces rhythmical burst activity in the V, VII and XII nerves, which, collectively, is indicative of feeding behavior. Selected transections of the brainstem reveal that the central sucking rhythm generators for such V, VII and XII activity are separate from one another, and located segmentally in the brainstem at the level of their respective motor nuclei. We believe that use of this in vitro preparation will advance understanding of the central neuronal mechanisms controlling sucking and mastication, and the developmental transition from sucking to mastication.

Animals↗
PubMed1998

Fracture toughness determination of composite resin and dentin/composite resin adhesive interfaces by laboratory testing and finite element models.

OBJECTIVES: The reliability and validity of the adhesive bond toughness of dentin/composite resin interfaces were studied from the standpoint of fracture mechanics. METHODS: The fracture toughness (KIC) and fracture energy (JIC) values of two different composite resins (Brilliant Dentin and P50) were determined by using single edge notch (SEN) specimens loaded in three point bending and the results were analyzed by the t-test method (p < 0.1). The fracture loads of dentin/composite resin interface with different initial crack lengths were obtained experimentally. The adhesive fracture energy (J(adh)), residual fracture energy (J(res)) and effective (total) fracture energy (J(eff)) for the symmetrical bimaterial (SBM) joint specimen for dentin/composite resin interfaces were calculated and the applied fracture energy (J(appl)) values under the mastication force were obtained for the axisymmetric tooth models. All numerical calculations were carried out by the finite element method and software programs were prepared according to fortran 77. RESULTS: The fracture toughness and energy values obtained experimentally for Brilliant Dentin were found to be higher than those for P50. It was seen that, calculated J values (J(adh) and J(res)++) changed with the crack length; but the effective fracture energy (J(eff)++) was independent of the crack length, as expected. The applied fracture energy (J(appl)) and effective fracture energy (J(eff)) are considerably smaller than the experimentally determined JIC values of composite resins. SIGNIFICANCE: The bonded interface tends to produce microscopic flaws which could act as critical stress risers promoting interfacial failures. The initiation and propagation of such flaws under the mastication forces can be followed by fracture toughness (KIC) or fracture energy (JIC) in linear elastic fracture mechanics (LEFM).

Bicuspid↗
PubMed1996

Comparative evaluation of function after surgery for cancer of the alveolobuccal complex.

PURPOSE: The current study was undertaken to assess the functional deficit after hemiresection of the mandible and to determine whether lateral segment resection with reconstruction was a functionally superior alternative in the management of patients suffering from alveolobuccal cancer. PATIENTS AND METHODS: Eighty-three patients were assigned to one of two main groups: Group I, hemiresection of the mandible (n = 47), and group II, lateral segment defects (n = 36). Functional assessment of patients included subjective evaluation of overall well-being, feeding, and cosmesis, as well as objective assessment of mastication, speech, and cosmesis. Mean scores for each of these categories were compared across groups using the Duncan Multiple Range Test with .01 confidence intervals. RESULTS: Subjective assessment of overall well-being, feeding, and cosmesis did not yield statistically significant differences between groups. Objective evaluation of mastication showed significantly better function after hemiresection in dentate patients as compared with their edentulous counterparts. However, masticatory scores for hemimandibulectomy patients with intact residual dentition were not significantly different from those for patients whose lateral segmental defects had been reconstructed. Although objective cosmetic scores for reconstruction of lateral segment defects were significantly better than those for hemiresection of the mandible, most patients in the latter group accepted the resultant deformity as a consequence of their treatment and did not let it affect their routine activities. CONCLUSION: Until functional results in patients undergoing lateral segmental resection for alveolobuccal cancer can be improved by better prosthetic techniques, hemiresection of the mandible remains a simple, safe, reliable, and cost-effective option that produces acceptable postoperative function.

Adult↗
PubMed1999

Biomechanical testing of resorbable screws used for mandibular sagittal split osteotomies.

PURPOSE: The object of the study was to determine the suitability of specific resorbable screws for fixation of mandibular sagittal split osteotomies by in vitro biomechanical strength testing. MATERIALS AND METHODS: Resorbable screws (2.5 mm diameter) composed of a polylactic acidpolyglycolic acid copolymer were placed in an inverted L-pattern in overlapping urethane blocks representative of sagittal split mandibular surgery. In an in vitro model at room temperature, the test specimens were statically loaded until tensile failure occurred. On a different set of test specimens, dynamic testing was done in an in vitro water bath at body temperature through cyclic loads representative of mastication until failure. RESULTS: In static testing, three 2.5-mm resorbable screws sustained an average peak load of 131 Kiloponds (Kp) (standard deviation, 5.2 Kp) with 5.5% strain at yield. In dynamic testing, the resorbable screws tolerated a 45.3-Kp load for an average of 340,675 cycles (22,783 standard deviation). Several of these test specimens did not ultimately fail and were further evaluated by static testing with an average load of 77.4 Kp until fixation failure occurred. CONCLUSIONS: These laboratory results indicate a relatively high resistance to biomechanical loads representative of mastication and suggest that 2.5-mm resorbable screws of this particular polylactic acid-polyglycolic acid copolymer may be effective in fixation of the postoperative unrestrained sagittal split mandibular osteotomy.

Absorbable Implants↗
PubMed2000

Identification of brainstem interneurons projecting to the trigeminal motor nucleus and adjacent structures in the rabbit.

Neurons of several nuclei within the medial pontomedullar reticular formation are active during mastication, but their relationship with other elements of the pattern generating circuits have never been clearly defined. In this paper, we have studied the connection of this area with the trigeminal motor nucleus and with pools of last-order interneurons of the lateral brainstem. Retrograde tracing techniques were used in combination with immunohistochemistry to define populations of glutamatergic and GABAergic neurons. Injections of tracer into the Vth motor nucleus marked neurons in several trigeminal nuclei including the ipsilateral mesencephalic nucleus, the contralateral Vth motor nucleus, the dorsal cap of the main sensory nucleus and the rostral divisions of the spinal nucleus bilaterally. Many last-order interneurons formed a bilateral lateral band running caudally from Regio h (the zone surrounding the Vth motor nucleus), through the parvocellular reticular formation and Vth spinal caudal nucleus. Injections of tracer into Regio h, an area rich in last-order interneurons, marked, in addition to the areas listed above, a large number of neurons in the medial reticular formation bilaterally. The major difference between injection sites was that most neurons projecting to the Vth motor nucleus were located laterally, whereas most of those projecting to Regio h were found medially. Both populations contained glutamatergic and GABAergic neurons intermingled. Our results indicate that neurons of the medial reticular formation that are active during mastication influence Vth motoneurons output via relays in Regio h and other adjacent nuclei.

Animals↗
PubMed1998

Physical and chemical transformations of cereal food during oral digestion in human subjects.

Chemical and physical transformations of solid food begin in the mouth, but the oral phase of digestion has rarely been studied. In the present study, twelve healthy volunteers masticated mouthfuls of either bread or spaghetti for a physiologically-determined time, and the levels of particle degradation and starch digestion before swallowing were compared for each food. The amounts of saliva moistening bread and spaghetti before swallowing were, respectively, 220 (SEM 12) v. 39 (SEM 6) g/kg fresh matter. Particle size reduction also differed since bread particles were highly degraded, showing a loss of structure, whereas spaghetti retained its physical structure, with rough and incomplete reduction of particle size. Starch hydrolysis was twice as high for bread as for spaghetti, mainly because of the release of high-molecular-mass alpha-glucans. The production of oligosaccharides was similar after mastication of the two foods, respectively 125 (SEM 8) and 92 (SEM 7) g/kg total starch. Starch hydrolysis, which clearly began in the mouth, depended on the initial structure of the food, as in the breakdown of solid food. These significant physical and chemical degradations of solid foods during oral digestion may influence the entire digestive process.

Adult↗
PubMed2003

The influence of gel strength on aroma release from pectin gels in a model mouth and in vivo, monitored with proton-transfer-reaction mass spectrometry.

The course of events from taking a food into the mouth to the perception of the food's flavor involves many steps, from dilution with saliva, mastication, and transportation of the compounds to the olfactory epithelium to transformation into signals that go to the brain. In addition, there are also the effects of the food's structure and properties. In this study, a proton-transfer-reaction mass spectrometer (PTR-MS) was used to investigate how four pectin-containing systems with different structures and strengths affected the release of aroma compounds in a model mouth and in the nose of an assessor. Both the model mouth and the in-nose measurements showed that the strength and structure of pectin-containing systems are important with regard to the quantity of aroma compounds that are released. Mastication and saliva were also shown to have a large influence on how much of the aroma compound is released from the mouth to the nose.

Chemical Phenomena↗
PubMed2005

Aroma release and retronasal perception during and after consumption of flavored whey protein gels with different textures. 1. in vivo release analysis.

The influence of gel texture on retronasal aroma release during mastication was followed by means of real-time proton-transfer reaction mass spectrometry and compared to sensory perception of overall aroma intensity. A clear correlation was found between individual-specific consumption patterns and the respective physicochemical release patterns in vivo. A modified data analysis approach was used to monitor the aroma changes during the mastication process. It was found that the temporal resolution of the release profile played an important role in adequate description of the release processes. On the basis of this observation, a hypothesis is presented for the observed differences in intensity rating.

Adult↗
PubMed2000

Variability of the masticatory process during chewing of elastic model foods.

Many studies show a consistent individual chewing pattern; chewing being governed by a pattern generator and regulated by sensory feedback. The aim of this study was to determine the variation in chewing between sessions, replicates and subjects using elastic model foods. Fifteen young male subjects were selected to chew four food products differing in hardness. Four sessions were performed at 1-wk intervals for each subject and, within each session, the four model foods were presented 3 times each. Jaw movement was recorded simultaneously with masseter and anterior temporalis electromyographic activities. Several chewing characteristics increased progressively from one session to the next; the largest increase occurred from the 1st to the 2nd session, with little difference between the last two sessions. No differences were observed between the samples of the same food product within a session. As mastication progressed, the amplitude and speed of the cycles and the muscular work decreased progressively. The first cycle appeared to be very different from the subsequent for all parameters except for occlusal duration. Thus, under our experimental conditions, the origin and amount of variation in chewing patterns were identified and provide information to improve the accuracy and comparability of results in studies of mastication.

Adult↗
PubMed2003

Biomechanics of craniofacial sutures: orthopedic implications.

Sutures are soft connective tissue articulations between craniofacial bones. Suture mechanics deals with patterns of mechanical stress experienced in sutures resulting from natural activities such as mastication and exogenous forces such as orthopedic loading. Patterns of sutural mechanical stress can be delineated readily as sutural strain using strain gages attached over the suture. In mastication, complex sutural strain patterns have been elucidated in a few species. Mechanical stresses are not transmitted in the skull as a continuing gradient, for different sutures are capable of redefining a propagating mechanical force as predominately tensile or compressive strain. Exogenous mechanical forces with engineering waveforms such as static and sine wave at different frequencies induce corresponding waveforms and rates of sutural strain, providing the basis for applying novel mechanical stimuli to engineer sutural growth. The available data on suture mechanics converge to a hypothetical theme that mechanical forces regulate sutural growth by inducing sutural mechanical strain. Various orthopedic therapies, including headgear, facemask, and functional appliances may induce sutural strain, leading to modification of otherwise natural suture growth.

Biomechanical Phenomena↗
PubMed2006

Functional relationships between the masseter and sternocleidomastoid muscle activities during gum chewing:.

The purpose of this study was to investigate the functional relationship between masseter muscle (MM) and sternocleidomastoid muscle (SCM) activities and between mandibular and head movements during mastication, under experimental muscle fatigue. The sample consisted of 12 adults with individually normal occlusion. The subjects were asked to chew gum at three different times: before maximum clenching, immediately after maximum clenching, and 3 minutes after maximum clenching. At these times, we examined the activity of the MM and SCM as well as the movement of the mandible and head. The activity and movement were simultaneously measured using both electromyography and the motion capture system. The MM activity time after clenching was significantly shorter than that before clenching, whereas the SCM activity time was significantly longer after clenching. There was no significant difference in the changes of three-dimensional distance of the mandibular movement between the respective times. On the other hand, the changes in the three-dimensional distance of head movement after clenching increased when compared with before clenching. Furthermore, the difference in the time of MM and SCM activity onset and of mandibular and head movement onset after clenching was shorter than that before clenching. A functional relationship exists between the MM and SCM activities and between mandibular and head movements during mastication.

Adult↗
PubMed1993

Symmetry of mandibular muscle activity as an index of coordinative strategy.

Electromyographic activity of bilateral mandibular muscle pairs in humans was studied during several tasks: mastication, voluntary oscillation of the jaw, and speech production, as a replication and extension of an earlier investigation by Moore, Smith, and Ringel (1988). The synchrony of activity within and across these paired muscles (masseter, medial pterygoid, and the anterior belly of the digastric) was evaluated by statistical comparison of zero-lag cross-correlation coefficients between all possible pairs. Paired comparisons were classified and combined according to anatomical and biomechanical properties into comparisons of homologous pairs (e.g., synchrony of activity in right masseter with left masseter), ipsilateral synergists (e.g., right masseter with right medial pterygoid), contralateral synergists (e.g., right masseter with left medial pterygoid), ipsilateral antagonists (e.g., right masseter with right digastric), and contralateral antagonists (e.g., right masseter with left digastric). Statistical comparison of the coactivation within muscle groups (across tasks) and across these muscle groups (within tasks) revealed significantly different groups of coactivated groups for each of the three tasks studied. The grouping of these muscles into coactivated groups always included homologous pairs among those most synchronously active. During mastication, homologous pairs and ipsilateral synergists were coactivated to a degree significantly greater than either of the antagonistic groups or the contralateral synergists. During voluntary oscillation of the jaw, coactive muscle groups were shown to be primarily the homologous pairs; synergists were coactivated to a significantly lesser degree, and antagonistic muscles were reciprocally active. During speech production, only homologous pairs emerged as a highly coactive group, although synergists and antagonistic pairs were coactive to a lesser degree. This finding was interpreted as a further indication of the coordinative plasticity among mandibular muscles, and as a demonstration of the vast differences in the apparent coordinative strategies for speech and nonspeech tasks. Speculation regarding the root of these differences is focused on the differences in kinematic and force-generating requirements of each task.

Adult↗
PubMed1998

Self-assessed masticatory ability in relation to maximal bite force and dental state in 80-year-old subjects.

By means of a questionnaire, clinical examination and force recordings, the relationships between self-assessed masticatory ability, dental state and bite force were studied in 160 80-year-old persons, 74 men and 86 women. The subjects were in general satisfied with their masticatory ability and 70% had no problems, while 6% reported three or more problems with mastication. Half of the subjects were dentate without removable prostheses and almost one-third had 20 or more natural teeth. The edentulous persons (about one-fifth of all) reported more problems related to mastication than the other dentition groups. The maximal bite force varied much and exhibited a significant correlation to the number of remaining teeth and dental state. The self-assessed masticatory ability was only weakly correlated with dental state and bite force. It was concluded that many subjects with few or no remaining teeth and/or removable dentures had only few complaints of impaired masticatory function and showed a good adaptation to an impaired dental status and small maximal bite force.

Adaptation, Physiological↗
PubMed1998

Evaluation of chewing activity in the elderly person.

In the present study, we examined the chewing performance of 70 elderly persons. Self-assessment of chewing problems and clinical classification using the modified Eichner index showed little correlation (Kappa value = 0.28; 95% confidence interval (CI) = 0.05-0.51). The sensitivity and specificity were 0.52 and 0.76, respectively. On the other hand, the mastication score determined by evaluation of a questionnaire on food intake and classification using the modified Eichner index showed high agreement (Kappa value = 0.73; 95% CI = 0.50-0.96). The sensitivity and specificity were 0.76 and 0.95, respectively. The mastication score showed significant correlation with other masticatory functions such as maximum biting force, occlusal contact area and the number of missing teeth (P < 0.01). These results suggest that the use of a questionnaire on food intake would be informative for epidemiological surveys of chewing activity in the elderly.

Aged↗
PubMed1999

Energy-based evaluation of occlusion.

The purpose of this study was to establish an index for evaluating occlusal conditions using energy levels. For this purpose, first, the movement of mastication under five occlusal conditions in which the positional relationship varied mesiodistally was simulated and the energy applied to the food being masticated was calculated, based on theoretical values of computing mechanics using finite element static analysis. As a model experiment, the energy generated under each occlusal condition was then measured using the electrical output from an occlusion pressure sensor composed of pressure-sensitive rubber. By comparing the theoretical values of computing mechanics and the measured values, the changes in the energy level under occlusal conditions were consistent with the trends, and the maximum value of the energy was obtained under the occlusal condition of Angle Class I and consisting of rigid interdigitation. In conclusion, our results demonstrated that occlusal conditions can be evaluated using the energy level as an index.

Bite Force↗