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PubMed2004

Muscle influence on postnatal craniofacial development and diagnostics.

The postnatal craniofacial development is determined by exogenous and endogenous factors that may result in morphological and functional muscle changes and influence the dentoskeletal region in terms of a physiologic or dysgnathic development. Using functional appliances, efforts are made to treat skeletal malocclusions through targeted exercise and to prevent an undesirable development of the dentition and the craniofacial structures. However, the success of the treatment and the stability of the outcome are not always adequate. To illustrate the treatment processes, clinically relevant measures for diagnosing muscle function and morphology have been developed in recent years. Electromyographic investigations and bite-force measurements show an excessively high variability and the histologic examinations applied to date are restricted in their suitability for analysis of the human masticatory muscles. Animal experimental studies have meanwhile succeeded in simulating functional jaw orthopedics and in demonstrating muscle remodeling processes at the genetic level. Despite some invasiveness, the time and the small quantity of muscle tissue involved permit molecular biological measuring in the orofacial system.

Animals↗
PubMed1991

Signs and symptoms in samples with and without temporomandibular disorders.

Factors commonly associated with signs and symptoms of temporomandibular disorder were investigated in two groups. The patient group consisted of 41 subjects seeking treatment at the UCSF Temporomandibular Disorders Clinic, and the control group consisted of 40 incoming and first-year students. Questionnaires and clinical examinations were used to identify and measure factors in the areas of history, functional signs, and occlusion. Only four factors emerged as statistically significant between groups: frequent headaches, masticatory muscle tenderness, cervical muscle tenderness, and maximum opening.

Adult↗
PubMed2003

Measurement of mechanical strain on mandibular surface with mastication robot: influence of muscle loading direction and magnitude.

OBJECTIVES: To investigate the mechanical effects of mastication on the mandible, we developed computational controlled mastication robot system with human dry skull and analyzed the strain distribution on the mandibular bone surface. DESIGN: In the mastication robot, the mandible was suspended by eight wires, which simulated masticatory muscles. A non-linear spring damper generated viscoelastic properties, and tension sensors for simulation of jaw reflection to avoid unusual biting force were applied as a biological feedback mechanism. By using this robot system, various patterns of muscle loading (change of wire direction and magnitude) were performed. RESULTS: From the results, significant differences in the amount of principal strain and its distribution were demonstrated in each condition (ANOVA, post hoc test, and p < 0.05). The value of maximum principal strain ranged from 79.66 x 10(-6) [at anterior border of ramus (Buccal side), 128 N] to -1.42 x 10(-6) [at foramen mentale (Buccal side), 32 N]. CONCLUSION: These results suggested that the muscle loading generated the mechanical strain on the mandibular bone surface and it was affected by the changes in loading direction and magnitude.

Analysis of Variance↗
PubMed1998

Triazolam improves sleep but fails to alter pain in TMD patients.

Patients with chronic orofacial pain often report disturbances in sleep, leading to the hypothesis that nocturnal motor hyperactivity of the muscles of mastication may contribute to the nociceptive process. This hypothesis was tested in a controlled study to evaluate the relationship between sleep stages, patient self-report of pain in the orofacial region, and nocturnal masticatory muscle activity. Twenty subjects participating in a two-period, within-subject, crossover study received triazolam or placebo for 4 nights. Sleep, pain, and mandibular range of motion were assessed at baseline, following the first period, and again following the second period; a 3-day washout period separated the two treatments. Subjective report of sleep quality was significantly improved following triazolam in comparison to placebo as measured by category scales for sleep quality, restfulness, and sleep compared to usual. The amount of time spent in stage-2 sleep was also significantly increased by triazolam. No improvement was seen in pain as measured by palpation with an algometer, in scales for sensory intensity and the affective component of pain, or in daily pain diaries. Mean facial muscle electromyographic activity for 30-second epochs averaged over the entire period of sleep did not reveal any differences in muscle activity across the three conditions. These data indicate that improvements in sleep quality and alterations in sleep architecture do not affect nocturnal facial muscle activity or subsequent pain report in temporomandibular patients, thereby failing to support the hypothesized relationship between sleep disturbances and chronic orofacial pain.

Adult↗
PubMed1988

Growth allometry of craniomandibular muscles, tendons, and bones in the laboratory rat (Rattus norvegicus): relationships to oromotor maturation and biomechanics of feeding.

This study addressed the problem of how growth of craniomandibular muscles, tendons, and bones influences the acquisition of oromotor skills and biomechanics of feeding in the laboratory rat (Rattus norvegicus). Rats representing a 6.6-fold size range were dissected, and muscles, tendons, and mandibles were weighed. Cross-sectional areas of tendons and bones providing attachment surfaces for muscles were estimated. Ontogenetic scaling of craniomandibular muscles, tendons, and bones was described by using linear regression models, and departures from size-required compensations were used to characterize changes in oromotor function. A two-dimensional model was developed which permitted calculation of mechanical advantages of four masticatory muscles; the model was used to show how mandibular growth and tooth eruption influence the biomechanics of rat feeding. Relative to mandible weight, most jaw muscles scaled either isometrically or positively, tendon cross-sectional areas scaled isometrically or negatively, and bone surfaces scaled negatively. With the exception of the superficial masseter and internal pterygoid muscles, mechanical advantages did not change significantly during mandible growth. Growth patterns of craniomandibular muscles, tendons, and bones contribute significantly to changes in morphology and oromotor function.

Animals↗
PubMed2004

Electromyographic activity of lower lip muscles when chewing with the lips in contact and apart.

Masticatory muscle activity is coordinated with perioral muscle during chewing. Subjects with competent lips usually chew with the lips in light contact, whereas subjects with incompetent lips possibly have dysfunctional chewing. In this study, the electromyographic (EMG) activities of the lower lip and masseter muscles were recorded when chewing with the lips in contact and apart. At first, 37 subjects were divided into an incompetent lip group and competent lip group on the basis of EMG activity of the lower lip muscle at rest. The durations of the masseter nonactive phase and total phase when chewing with lips in contact were shorter in the incompetent lip group than in the competent lip group. In the incompetent lip group, when chewing with the lips apart, the EMG activity of lower lip in the masseter nonactive phase was significantly (P < .05) higher than in the competent lip group, but there was no difference in the EMG activity in the masseter active phase between two groups. Our results suggest that subjects with incompetent lips have difficulty chewing while their lips are relaxed. We conclude that the inability of sealing the lips and lip dysfunction could possibly affect masticatory function.

Adult↗
PubMed1986

A numerical model of temporomandibular joint loading.

A numerical model of the mandible, its articulating surfaces, and the forces exerted by the primary masticatory muscles has been developed for the purpose of investigating loading of the temporomandibular joint. Evidence is presented which shows that the temporomandibular joint. Evidence is presented which shows that the temporomandibular joint is a load-bearing joint over the normal functional range of bite-force positions and angles. In this investigation, temporomandibular joint loads were found to vary from a maximum appositional force of 60% of the bite force (when bite forces were applied to the incisors) to a distracting force of about 5% of the bite force (when applied to the distal surfaces of the third molars). TMJ loads tended to reach a minimum as a result of vertically directed bite forces positioned at the second molars. A range of conditions in which bite forces were directed parallel to or within approximately 20 degrees of the mid-sagittal plane was found to be conducive to stability of the temporomandibular joint. This stability included symmetry in the direction and in the magnitude of condylar loads as well as the presence of small forces tending to oppose the condyle and articular eminence. TMJ loads tended to reach a maximum in response to mediolaterally directed bite forces. This result is consistent with the fact that no muscle of mastication exhibits a spatial orientation in which the muscle fibers are predominantly mediolateral in direction.

Bite Force↗
PubMed1979

Craniofacial growth in olive baboons (Papio cynocephalus anubis): browridge formation.

The examination of a developmental series of skulls of olive baboons has led to the generation of a model for browridge formation. Evidence in support of the model comes from surface configuration of browridge bone as studied by scanning electron microscopy, histology of the bone by the analysis of thin sections and by measurements that reflect both depositional cycles in browridge bone and the biomechanics of mastication. The model relates sudden changes in the biomechanical system caused by the tooth eruption cycle to cyclical changes in the formation of browridge bone. We suggest that browridge bone is added during periods of peak stress caused by the positive response of the masticatory muscles to relatively sudden reduction of their biomechanical efficiency.

Animals↗
PubMed1977

The effect of muscle function in discriminating thickness differences interocclusally and the duration of the perceptive memory.

The thresholds in discriminating the thickness differences interocclusally were measured with three different mouth openings on subjects having natural dentitions. Also the duration of the perceptive memory was studied. The results showed that the functional activation or fatiguing of masticatory muscles and the degree of mouth opening affect size discrimination interocclusally. The ability to perceive thickness differences between the incisors was more accurate after 1 hour's chewing than normally. The trend was significant with 0.5 mm and 10 mm mouth openings (2 P less than 0.01) and highly significant with an 20 mm mouth opening (2 P less than 0.001). With a 20 mm mouth opening (2 P less than 0.01) and 10 mm mouth opening (2 P less than 0.05) size discrimination was less accurate after two hours' fatiguing chewing than after one hour's conventional chewing. After 30 seconds' forceful isometric contraction and with 20 mm mouth opening discrimination was more accurate than normally (2 P less than 0.01). The trend was the same with a 10 mm mouth opening, but no difference could be observed when the mouth opening was 0.5 mm. The memory tests showed that with a 0.5 mm mouth opening thickness differences of 0.3-0.5 mm were most commonly correctly perceived twenty-four hours later, but when the mouth openings were 10 and 20 mm an interval of only 1 min between the reference and test piece trial impaired the performance.

Fatigue↗
PubMed2000

Masticatory strains on osseous and ligamentous components of the temporomandibular joint in miniature pigs.

AIMS: An animal study of functional biomechanics was undertaken to understand normal loading of the temporomandibular joint (TMJ) and to provide insight into the pathogenesis of TMJ disorders. METHODS: Bone strain and ligamentous deformation were measured during mastication in 26 10-month-old minipigs. Half the subjects had undergone a surgical disruption of the left lateral capsular and disc attachments to the condyle 5 to 6 weeks previously. Rosette strain gauges were bonded to the left lateral surfaces of the squamosal bone near the TMJ, the condylar neck, and the mandibular corpus below the molar region. Differential variable reluctance transducers (DVRTs) were placed bilaterally in the lateral capsular tissue of the joints. Bone strains, ligamentous deformations, and the electromyographic activities of the masseters and lateral pterygoids were recorded during natural mastication. RESULTS: In all animals on both working and balancing sides, mastication caused bone strains that were dominated by tension in the squamosal bone site and by compression in the other sites. Measurements from the DVRT revealed elongation of the lateral capsular tissue in the last phase of the power stroke and shortening in the initial phase of opening, which was almost simultaneous with the development of bone strain. Strain in the capsule ranged from 3 to 25%, with the strain of the balancing side exceeding that of the working side. The surgical disruption did not alter chewing side preference or bone strain, but a tendency toward more extensive ligamentous deformation on the intact side was observed. Furthermore, the ratio of masseter to lateral pterygoid activity was smaller on the disrupted side and larger on the intact side, in comparison to control pigs. CONCLUSION: Both osseous and ligamentous components of the TMJ are strained during mastication, and the latter are more deformed on the balancing side. Disruption of the lateral attachment had little effect on strain in the osseous components but appeared to increase strain in the capsule and to modify the balance of masticatory muscle activity.

Analysis of Variance↗
PubMed1983

The effect of head position upon jaw reflexes in the rat.

The vestibular apparatus of the decerebrate rat was stimulated by tilting the head dorsally or ventrally, with or without an associated stimulation of neck afferents i.e. either the head alone, or the head and body together, was tilted. The effect of such conditions, upon short latency reflexes elicited in antagonistic jaw and hyoid muscles, was examined. Reflexes in the different jaw and hyoid muscles were affected differently when the head was tilted, whether or not neck movement was permitted. Variations in the pattern of response in different animals were explicable on the basis of the known variable recovery of neck reflexes opposing the influence of the vestibular afferents. Head position can therefore be an important but complex factor which may enhance or depress reflex activity differentially in the different masticatory muscles, at least in the experimental situation.

Animals↗
PubMed1996

Comparison of computed tomography imaging before and after functional treatment of bilateral condylar fractures in adults.

Bilateral condylar fractures in 10 adult patients were successfully treated nonsurgically. The patients were studied with computed tomography (CT). In all patients, the pretreatment images of both condyles showed medially displaced or dislocated condyles which were accompanied clinically by an anterior open bite. In all patients, the anterior open bite was eliminated and the occlusion was normal 2-3 months after treatment, while jaw function was normal and the patients were free of pain. Follow-up CT images showed that the fractured condyles had healed by bony consolidation but were still displaced or dislocated. The relationships with the glenoid fossa had not improved. The reestablishment of occlusion and function appears to occur not as a result of anatomic restitution of condylar height, but as a result of adaptation of the masticatory muscles.

Adaptation, Physiological↗
PubMed1981

Neuromuscular problems in the orofacial region: diagnosis-classification, signs and symptoms.

In the light of recent findings, it is clear that organic changes in the tissues of the temporomandibular joint commonly occur simultaneously with neuromuscular problems. It is suggested that the term "masticatory disorder' should be adopted in order that diagnosis will fully reflect this inter-relationship. Patients with masticatory disorders will exhibit one or more of the following signs and symptoms: (a) pain and tenderness in the region of the masticatory muscles and TMJ, (b) incoordination and sounds during condylar movement and (c) limitation of mandibular movement. Diagnosis which relies solely on subjective symptoms is incomplete and the progressive nature of the condition requires careful attention to the prognosis. A diagnostic classification of masticatory disorders is given in Table II and the characteristics of each of the conditions listed is described in greater detail in the text.

Diagnosis, Differential↗
PubMed1995

Visualization and quantitative analysis using normalized electromyographic linear envelopes of muscle contraction patterns during gum chewing.

Surface electromyography (EMG) has been widely used in clinical dentistry, although interpretation of the raw data is difficult owing to its low reproducibility. Linear EMG envelopes, also known as EMG profiles, which are normalized with respect to raw EMG amplitudes and stride, have been developed to analyze the time course of gait stride. Normalized EMG contraction patterns can be used for comparing individuals or recording sessions on the same individual made at different times. We made EMG profiles during unilateral gum chewing for the masticatory muscles of five asymptomatic volunteers. EMG signals were recorded from the anterior temporal (Ta), masseter (M) and anterior belly of the digastric (Da) muscles on the subject's preferred chewing side. The mandibular kinesiograph was used for tracking incisal point movement during chewing. EMGs and kinesiometric data were simultaneously recorded for 90 seconds. Ensemble averages of EMG profiles were made from 10 stable strokes after 60 seconds of initiation of chewing. Phasic characteristics of the EMG profiles were evaluated by product-moment correlation and intraclass correlation coefficients. Although the EMG profiles for Ta and M were very similar, those for Da were different from the elevator muscles.

Adult↗