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PubMed2005

Relationship between masticatory function and internal structure of the mandible based on computed tomography findings.

INTRODUCTION: The purposes of this study were to investigate bone mineral density as a part of bone construction in human skulls and to examine the relationship between dentofacial morphology and masticatory function by using computed tomography (CT) findings. Changes in bone mineral density in the mandible because of loss of masticatory function were tested in rats by experimentally producing an environment that inhibited mastication by the molars. METHODS: Data for the human study were obtained from 27 modern male Japanese skulls (mean age, 28 years) from the University of Tokyo. Cortical bone thickness (CBT) and CT value (CV) were measured by each CT scan of the first and molars. For the animal study, a metal cap was inserted between the maxillary and mandibular incisors to prevent the molars from biting in 6-week-old male Wistar rats. The rats were killed after 2, 4, or 6 weeks, and bone mineral density was measured in cancellous and cortical bone equivalent to the first molar region by using peripheral quantitative computed tomography. RESULTS: In the human skull study, significant negative correlations were observed between CV in the regions of the buccal side of the second molar and the angle between the Frankfort horizontal and mandibular planes. Significant negative correlations were also observed between the gonial angle and CV in the buccal and basal sides. In the animal study, cancellous bone mineral density began to decline 4 weeks after the start of the experiment in the masticatory hypofunction group compared with the control group. By week 6, cancellous bone density had declined by 11.6% on the buccal side, 16.7% on the lingual side, 12.3% at the bifurcation of the root, and 38.1% at the root apex. Cortical bone density declined by 8% to 12% on the lingual side. CONCLUSIONS: The results support our hypothesis that a functional adaptive response by the mandible to mechanical stress resulting from mastication occurs not only in the muscle insertion area, but also in mandibular alveolar bone in the molar region.

Adaptation, Physiological↗
PubMed2005

Superficial and deep layer muscle fibre properties of the mouse masseter before and after weaning.

To clarify changes in the properties of the masseter muscle superficial and deep layer muscle fibres, which initiate masticatory movement, myosin heavy chain isoforms were evaluated based on immunohistochemistry at the transcription level in male mice both before and after weaning. In the results, MHC-2b isoforms, the isoforms with the fastest contraction speed, were observed in the superficial layer after weaning. However, MHC-2a isoforms with slower contraction speeds were not apparent. By contrast, in the deep layer, MHC-2a isoforms were present, as were MHC-2b isoforms, however, there were fewer MHC-2b isoforms present than in the superficial layer. The most rapid movement in the mouse mandible was observed anteroposteriorly during mastication. As the superficial layer of the masseter muscle runs parallel to the direction of mandibular movement, the presence of MHC-2b isoforms in it is consistent. The presence of MHC-2a isoforms in the deep layer, lying at right angles to the direction of mastication movement, is consistent with the positional adjustment of the mandible contributed by the deep layer muscle fibres during masticatory movement. We therefore conclude that complicated masticatory movement is achieved by the presence of various muscle bundles within the masseter, each carrying out different roles.

Animals↗
PubMed2006

Incisor and mandibular movement during retrusion.

Human mastication, respiration, speech, swallowing and suckling are directed by the jaw muscle activites, the temporo-mandibular joints, the ligaments and by the occlusal dental contacts. Mastication is usually assessed by border movements of the mandibular incisors. While the border movements of opening, protrusion and lateratrusion are often used to determine the mandibular functions, the movement of retrusion is rarely considered in the study of the human oro-facial functions. Our purpose was to evaluate the mandibular movement of retrusion in a population that did not present any symptoms nor clinical signs of temporo-mandibular disorders. The study was performed on 117 males and 121 females (age range: 17.7-65.2 years; mean age: 31.1 years) using electrognathographic registrations (Sirognatograph(*), Siemens, Benshein, Germany). Every patient was instructed and trained before recording. The measurements were calculated on the sagittal plane registrations. The results showed that the mandibular movement of retrusion was present in 233 out of the 238 studied subjects (97.9%) whatever was the dental class, the age or the sex. The width range was between 0.3 and 5.4 mm and the mean value was 1.75+/-0.91 mm. The inferential analysis performed by a 3-way ANOVA model demonstrated no significant difference in retrusion value by dental class, gender or age. The most frequent numerical value was 1.5 mm, observed in 16 subjects (6.7% of the studied population). These results suggest that, in order to respect the physiological characteristics, more attention is needed in performing dental treatments.

Adolescent↗
PubMed2006

Postnatal changes of local neuronal circuits involved in activation of jaw-closing muscles.

Feeding behaviour in mammals changes from suckling to mastication during postnatal development and the neuronal circuits controlling feeding behaviour should change in parallel to the development of orofacial structures. In this review we discuss the location of excitatory premotor neurons for jaw-closing motoneurons (JCMNs) and postnatal changes of excitatory synaptic transmission from the supratrigeminal region (SupV) to JCMNs. We show that neurons located in SupV and the reticular formation dorsal to the facial nucleus most likely excite JCMNs. Excitatory inputs from SupV to JCMNs are mediated by activation of glutamate and glycine receptors in neonatal rats, whereas glycinergic inputs from SupV to JCMNs become inhibitory with age. We also show that the incidence of post-spike afterdepolarization increases during postnatal development, whereas the amplitude and half-duration of the medium-duration afterhyperpolarization decrease with age. Such postnatal changes in synaptic transmission from SupV to JCMNs and membrane properties of JCMNs might be involved in the transition from suckling to mastication.

Animals↗
PubMed2006

Functional significance of strain distribution in the human mandible under masticatory load: numerical predictions.

A common feature of studies of mandibular morphology is the assumption that there is some functional relation between the form of the lower jaw and masticatory stress. It was noted that the local variation in cortical bone thickness in the mandibular corpus appears to be stereotypical among anthropoids. This occurs at sections under the molars, where the lingual cortical plate is thinner than buccal one. In this study we investigate and contrast the strain pattern along buccal and lingual surfaces of the mandibular corpus during mastication using a numerical model of a human mandible. We show that strain distribution differs in alveolar and mid-corpus segments of the mandible and that the latter develops an alternate pattern between the buccal and lingual aspects of the working and balancing sides of the jaw. We then relate the magnitude of these strains to Frost's mechanostat. Our results suggest that the cortical asymmetry of the human mandible is in fact not related to strain patterns generated during mastication.

Adult↗
PubMed2005

Effect of treatment of dentofacial deformities on the electromyographic activity of masticatory muscles.

Individuals with dentofacial deformities present changes in masticatory muscles. The objective of the present study was to determine the influence of interdisciplinary treatment in cases of class III dentofacial deformities regarding the EMG activity of the temporal (T) and masseter (M) muscles. The study was conducted on 15 patients with class III dentofacial deformities who were submitted to orthodontic, oromyofunctional and surgical treatment and assigned to groups P1 (before surgery) and P2 (6-9 months after surgery). Fifteen individuals with no alterations in facial morphology or dental occlusion and without signs or symptoms of temporomandibular joint dysfunction were used as controls (CG). The T and M muscles were submitted to EMG bilaterally in the situations of mastication and mastication plus biting, with analysis of amplitude interval and root mean square. For all muscles tested, there was a difference between CG, P1 and P2; CG was higher than P2 and P2 higher than P1 in all situations assessed. We conclude that there was an increase in EMG activity in the T and M muscles after surgical correction of the dentofacial deformity accompanied by interdisciplinary treatment, although the values were still lower than those obtained for CG.

Adult↗
PubMed2006

Load transmission in the nasofrontal suture of the pig, Sus scrofa.

The nasofrontal suture links the nasal complex with the braincase and is subject to compressive strain during mastication and (theoretically) tensile strain during growth of nasal soft tissues. The suture's ability to transmit compressive and tensile loads therefore affects both cranioskeletal stress distribution and growth. This study investigated the in vitro viscoelastic and failure properties of the nasofrontal suture in the pig, Sus scrofa. Suture specimens from two ages were tested in compression and tension and at fast and slow rates. In additional specimens, strain gauges were applied to the suture and nasal bone for strain measurement during testing. Relaxation testing demonstrated higher elastic moduli in tension than compression, regardless of test rate or pig age. In contrast, maximum elastic moduli from failure tests, as well as peak stresses, were significantly higher in compression than in tension. Sutures from older pigs tended to have higher elastic moduli and peak stresses, significantly so for tensile relaxation moduli. Strain gauge results showed that deformation at the suture was much greater than that of the nasal bone. These data demonstrate the viscoelasticity and deformability of the nasofrontal sutural ligament. The suture achieved maximal resistance to tensile deformation at low loads, corresponding with the low tensile loads likely to occur during growth of nasal soft tissues. In contrast, the maximal stiffness in compression at high loads indicates that the suture functions with a substantial safety factor during mastication.

Animals↗
PubMed2004

A device for investigating neuromuscular control in the human masticatory system.

A new apparatus has been developed to study the control of mastication in humans. The subject places his/her teeth on fixed upper and mobile lower bite plates; the device then enables opening and closing movements of the lower jaw against a controlled resistance. It is also possible to vary the number of teeth in contact with the device during an experiment from the entire dental arcade to a single tooth. The specially designed lower bite plate is dynamic and allows for both rotation and translation of the lower jaw during movement, thus, permitting the natural curvilinear trajectory of the jaw. The lower bite plate can follow chewing initiated by the subject without resisting the movement ('no force' mode) via a dedicated microprocessor controlled compensation mechanism. Another function of the device is to inject a constant predetermined load onto the lower bite plate so that the subject 'chews' against a fixed resistance simulating rapidly yielding food bolus ('fixed force' mode). The device can be programmed to increase or decrease the force during the closing or opening phase of chewing by feeding the position information into the force compensation system so both position and force change in parallel, hence, simulating a bite onto a non-yielding, or sticky, food bolus ('normal chewing' mode). By use of a jaw position compensation mechanism, the device can actively move the lower jaw, following any imposed position pattern ('position controlled' mode). The chewing simulator also has a mode that holds the position at a fixed level and allows the force to change ('position hold' mode). Furthermore, the device can inject additional rapid or slow forces or displacements onto the lower bite plate in order to elicit reflexes so that the response of jaw muscles to such stimuli can be examined at various jaw positions, force levels, phases of motion and velocities. The different modes of the apparatus can be used to study the operation and feedback control of human mastication; in particular whether modulations in jaw muscle activity and reflexes are due to changes in force, velocity, position, chewing cycle phase or a combination of these factors.

Afferent Pathways↗
PubMed2004

Masticatory motion after surgical or nonsurgical treatment for unilateral fractures of the mandibular condylar process.

PURPOSE: We sought to compare mandibular motion during mastication in patients treated in either an open or a closed fashion for unilateral fractures of the mandibular condylar process. PATIENTS AND METHODS: Eighty-one male patients with unilateral condylar process fractures were treated either with (n = 37) or without (n = 44) surgical reduction and rigid fixation of their condylar process fractures. At 6 weeks, 6 months, 1 year, and 2 years after treatment, the subjects' chewing cycles were recorded using a magnetic sensor array (Sirognathograph; Siemens Corp, Bensheim, Germany) while chewing Gummi-Bears (HARIBO, Bonn, Germany) unilaterally on the same side as the fracture and on the opposite side. The chewing cycles were analyzed using a custom computer program, and the duration, excursive ranges, and 3-dimensional cycle shape were compared between the 2 treatment groups at each time interval using multilevel linear modeling statistics. RESULTS: The 2 treatment groups did not differ significantly for any measure of cycle duration or any excursive range (except lateral excursions at 1 year post-treatment) at any of the time intervals. However, the 3-dimensional cycle shapes of the 2 groups did differ significantly at all time intervals. CONCLUSION: Surgical correction of unilateral condylar process fractures has relatively little effect on the more standard measures (duration and excursive ranges) of masticatory function. However, surgical correction better normalizes opening incisor pathways during mastication on the side opposite the fracture.

Adolescent↗
PubMed2004

A fronto-parietal network for chewing of gum: a study on human subjects with functional magnetic resonance imaging.

The purpose of this study is to investigate human brain activity during mastication using fMRI. Twelve right-handed normal subjects performed two tasks: chewing of gum at their own pace, and imitating the movements of chewing gum. In order to reveal which areas of the brain are more strongly activated while chewing gum, we performed the conjunction analyses of gum chewing minus sham chewing with gum chewing minus rest. The common activity in the orofacial sensorimotor and premotor cortex was subtracted out since it was common to both tasks, but there were some differences in activity in some prefrontal and posterior parietal cortex areas. Our results suggest that a fronto-parietal network for mastication exists and may contribute to higher cognitive information processing.

Adult↗
PubMed2004

Assessment of the nutrition status of patients with Huntington's disease.

OBJECTIVE: The purpose of the present study was to compare the nutrition status of patients with Huntington's disease (HD) with that of control subjects by analyzing anthropometric and biochemical indicators, energy, and macronutrient intake and to determine which indicators are most altered in HD patients. METHODS: We assessed the nutrition status of 25 HD patients and 25 age- and sex-matched controls by measuring anthropometric and biochemical indicators. Food intake data were obtained by the 3-d record method to assess mean daily energy and macronutrient intake. We studied variables reported by the patients such as increased or decreased appetite, mastication difficulties, and solid food and liquid food dysphagia. A neurologist assessed the clinical features of HD patients by using the Unified Huntington's Disease Rating Scale. RESULTS: HD patients showed significantly lower anthropometric variables but significantly higher kilocalorie intake. Among the subjective variables analyzed, patient-referred weight loss, increased appetite, mastication, and solid food dysphagia were significantly more frequent in HD patients than in controls. We also found relations between motor disability and some anthropometric parameters in HD patients. In particular, we found a significant correlation between total motor disability score and body mass index and arm muscle circumference (r = -0.464 and -0.445, respectively; P < 0.05) and with percentage of body fat (r = -0.496, P = 0.012). CONCLUSIONS: It is of the utmost importance to identify nutritional alterations in HD patients and to find strategies to cover their kilocalorie and nutrient requirements to improve their quality of life.

Adult↗
PubMed2005

Comparison of quality of life after surgical endodontic treatment using two techniques: a prospective study.

OBJECTIVE: The purpose of this prospective study was to compare patient experience of quality of life following surgical endodontic treatment using 2 different techniques: a technique that included the use of a dental operating microscope, root resection with minimal bevel and retrograde preparation with ultrasonic tips, and a traditional technique that included root resection with a 45 degrees bevel and retrograde preparation by bur performed without magnification. STUDY DESIGN: The study consisted of 66 patients referred for surgical endodontic treatment. One operator (I.T.) carried out all treatment. An equal number of patients were assigned to each group. Group 1 was treated by the traditional technique without an operating microscope and Group 2 by a technique using an operating microscope and minimal osteotomy. All patients were given a questionnaire with 15 questions to evaluate their quality of life for 7 days postsurgery. RESULTS: On day 5, patients in Group 1 reported significantly more pain and took significantly more analgesics (P < .05). On days 1 and 2, patients in Group 2 reported significantly more difficulty in mouth opening, mastication, and the ability to speak (P < .05). CONCLUSION: Patients in both groups reported a high incidence of symptoms. The technique using the operating microscope provided significantly less postoperative pain, but more difficulties in mouth opening, mastication, and the ability to speak immediately postoperatively.

Adult↗
PubMed2000

Correlations between functional and occlusal tooth-surface areas and food texture during natural chewing sequences in humans.

The dental-arch surfaces preferentially used in mastication were studied by measuring functional and occlusal surface areas and comparing these to the number of chews required to swallow foods of different texture properties. The functional surface of the teeth was defined as the total area of visible wear facets on post-incisal teeth, adding to it the contacting areas of restored teeth where no facets were visible. Occlusal surface area was taken as the total area of the occluding parts of post-incisal teeth. Both surfaces were measured with computer image processing on dental-stone casts of the teeth of 31 young adults. Functional surface areas (mean 168 mm(2), four quadrants) were positively correlated with occlusal surface areas (mean 739 mm(2), four quadrants). The left:right area ratios were more variable for functional than for occlusal surfaces. Functional surface-area ratios markedly different from 1.0 might reflect functional side-preponderance of masticatory activity. Correlations between tooth surface area and the number of cycles were examined with five different food samples of known texture during side-imposed mastication. Depending on the elastic moduli of the foods, significant negative correlations were found between the left:right ratios of functional or occlusal surface areas and the left:right ratios of cycle numbers. The rheological properties of the food particles chewed were assumed to be the key factor in the correlations with either the functional or anatomical occlusal surfaces.

Adult↗
PubMedDate not supplied

Quantitative and somatotopic mapping of neurones in the trigeminal mesencephalic nucleus and ganglion innervating teeth in monkey and baboon.

Neurones of the trigeminal mesencephalic nucleus (Mes V) and ganglion innervating the periodontium of incisor, canine and molar teeth in 10 monkeys and 10 baboons were counted and mapped using the horseradish peroxidase (Hrp), retrograde axonal transport method. Periodontal afferent neurones of all these teeth were well represented in the Mes V, although the incisors had a significantly higher number of labelled neurones than the canines or molars. The primary cell bodies of the periodontal afferents were located mainly in the caudal part of the ipsilateral Mes V from the level of the inferior colliculus to the floor of the fourth ventricle in the pons. The caudal periodontal Mes V neurones may be favourably located to make collateral connections with the trigeminal motor nucleus for jaw reflexes. Incisors and canines had a large and predominantly ipsilateral representation of Hrp-labelled neurones in the ganglion. In contrast, molar representation in the ganglion was sparse and all labelled neurones supplied ipsilateral teeth. The maxillary and mandibular teeth had a somatotopic distribution within the respective maxillary (middle) and mandibular (posterolateral) compartments of the trigeminal ganglion. It is suggested that the anterior teeth with greater connections to the Mes V and the ganglion may impart greater sensory perception and be involved in jaw reflexes to ensure a good occlusal relation during mastication, while the afferent connections of the molars may initiate complex jaw reflexes during the occlusal phase of mastication.

Animals↗
PubMed1999

The role of passive muscle tensions in a three-dimensional dynamic model of the human jaw.

The role of passive muscle tensions in human jaw function are largely unknown. It seems reasonable to assume that passive muscle-tension properties are optimized for the multiple physiological tasks the jaw performs in vivo. However, the inaccessibility of the jaw muscles is a major obstacle to measuring their passive tensions, and understanding their effects. Computer modelling offers an alternative method for doing this. Here, a three-dimensional, dynamic model was used to predict active and passive jaw-muscle tensions during simulated postural rest, jaw opening and chewing. The model included a rigid mandible, two temporomandibular joints, multiple dental bite points, and an artificial food bolus located between the right first molars. It was driven by 18 Hill-type actuators representing nine pairs of jaw muscles. All anatomical forms, positions and properties used in the model were based on previously published, average values. Two states were stimulated, one in which all optimal lengths for the length-tension curves in the closing muscles were defined as their fibre-component lengths when the incisor teeth were 2 mm apart (S2), and another in which the optimal lengths were set for a 12.0 mm interincisal separation (S12). At rest, the jaw attained 3.6 mm interincisal separation in S2, and 14.8 mm in S12. Activation of the inferior lateral pterygoid (ILP) and digastric (DG) muscles in various combinations always induced passive jaw-closer tensions, and compressive condylar loads. Maximum midline gape (from maximum bilateral co-activation of DG and ILP) was 16.2 mm in S2, and 32.0 mm in S12. When both model states were driven with muscle patterns typical for human mastication, recognizable unilateral and vertical "chopping" chewing cycles were produced. Both states revealed condylar loading in the opening and closing phases of mastication. During unilateral chewing, compressive force on the working-side condyle exceeded that on the balancing side. In contrast, during the "chopping" cycle, loading on the balancing side was greater than that on the working side. In S2, chewing was limited in both vertical and lateral directions. These results suggest that the assumptions used in S12 more closely approximated human behaviour than those in S2. Despite its limitations, modelling appears to provide a useful conceptual framework for developing hypotheses regarding the role of muscle tensions during human jaw function.

Computer Simulation↗
PubMed1999

Stimulation of the chewing area of the cerebral cortex induces inhibitory effects upon swallowing in sheep.

Mastication and swallowing are two tightly integrated components of food intake behavior. We investigated the effects of stimulating the chewing area of the fronto-orbital cortex (CCx) on some muscles and medullary interneurons (Ins) or motoneurons (Mns) active during swallowing. For the purpose of comparison, the lingual nerve (LN) was also stimulated during the experiments. Electromyography (EMG) and extracellular neuronal recording were used, and swallowing was reflexly induced (RIS) by stimulation of the superior laryngeal nerve (SLN). RIS was almost totally abolished during long-lasting repetitive stimulation of CCx or LN, and was strongly facilitated after stimulation cessation. Short-duration stimulation (one or a few pulses) of both the CCx and LN also inhibited triggering of deglutition when delivered just before the onset of RIS. This inhibition appeared as a delay or total suppression of the EMG and neuronal swallowing activities. It was obvious at the level of the muscles, the hypoglossal Mns and the premotoneurons (PMns; Ins of the ventral medulla near the nucleus ambiguus), as well as at the level of the Ins of the dorsal medulla (within or around the solitary tract nucleus) which are assumed to be the core of the 'central pattern generator' (CPG) for swallowing. In addition to the 'chewing-related inhibition', many ventral Ins exhibited a short latency synaptic activation after CCx and/or LN stimulation. Therefore, these Ins may play a pivotal role for reflex or cortical fast control of tongue (and jaw) muscles, and for coordinating their contractions in the context of mastication-deglutition interactions.

Animals↗
PubMed1999

Effects of controllable stress on masticatory behaviour and muscle structure: partial protective effect of clomipramine.

The influence of controllable painless stress and clomipramine treatment was evaluated on masticatory behaviour and myosin heavy chain expression in masticatory rat muscles: anterior digastric, anterior temporalis and masseter superficialis. The adult fast isoforms of myosin heavy chains detected were myosin heavy chains 2A, 2X and 2B. The myosin heavy chains composition of anterior temporalis muscle was unchanged by stress or by treatment. In anterior digastric and masseter superficialis muscles, stress induced an increase in 2B and a decrease in 2X and 2A. Under stress, whereas the myosin heavy chains composition of anterior temporalis and anterior digastric muscles was unaffected by clomipramine, this drug modified significantly the myosin heavy chains composition of masseter superficialis muscle which became comparable to that of control muscle. Stress-induced myosin heavy chains transformations led to an increased velocity of anterior digastric and masseter superficialis muscles but not anterior temporalis muscle. Gnawing and mastication were increased by stress and incisor grinding was reduced. Stress shortened the duration of gnawing and increased the fatigability of anterior digastric and masseter superficialis muscles, whereas clomipramine increased the duration of mastication and reduced the fatigability of masseter superficialis muscle. Stress produces selective changes in masticatory muscles and behaviour. This study demonstrates the muscle type-specific protective effect of clomipramine against stress-induced structural transformations of masseter superficialis muscle and the specific concomitant behavioural modifications.

Animals↗
PubMed2003

Description of a photoelastic coating technique to describe surface strain of a dog skull loaded in vitro.

There are several methods of determining strain in the facial skeleton on loading in vitro. This article describes an alternative photoelastic coating technique adapted from the commonly accepted method used by engineers to study surface strains in objects. In applying this method to the stomatognathic system, because the masticatory apparatus is loaded by muscular contraction an opposite reaction load should be distributed throughout the skeletal structure. This load distribution should slightly deform the bones to which the muscles of mastication are attached. An understanding of the resulting strain generated in the facial skeleton is important because strain distribution on loading reflects how the loads applied during mastication are partially dissipated. Preliminary descriptive results are presented, suggesting that anatomic structures influence the distribution of strain on loading. The technique described should allow in vitro investigation of the mechanical environment into which osseointegrated implants are placed and may aid in understanding their behavior.

Animals↗