Biomedical subjects

G E Langenbach

Publications and source records attributed to G E Langenbach.

9 recordsLinked to original sources

PubMed2001

Length changes in the human masseter muscle after jaw movement.

The human masseter is a multilayered, complex muscle contributing to jaw motion. Because variations in stretch may cause muscle fibers to function over different portions of their length-tension curves, the aim of this study was to determine how parts of the masseter lengthen or shorten during voluntary jaw movements made by living subjects. Magnetic resonance (MR) imaging and optically-based jaw-tracking were used to measure muscle-insertion positions for four parts of the muscle with six degrees of freedom (DOF), before and after maximum-opening, jaw protrusion and laterotrusion in four adult males. Muscle part lengths and intramuscular tendon lengths were calculated, and these data, with fiber-tendon ratios published previously, were used to estimate putative changes in fiber-length. During maximum jaw-opening, the largest increases in muscle length (34-83%) occurred in the medial part of the deep masseter, whereas the smallest changes occurred in the posterior-most, superficial masseter (2-19%). Smaller changes were found during movement to the ipsilateral side, than during protrusion and movement to the contralateral side. On maximum opening, putative fibers in the deep masseter lengthened up to 83%, whereas those of the superficial masseter stretched up to 72%. The masseter muscle does not stretch uniformly for major jaw movement. Jaw motion to the ipsilateral side causes little length change in any part, and the effect of tendon-stretch on estimated fiber lengths is not substantial. The stretch that occurs infers there are task-related changes in the active and passive tensions produced by different muscle regions.

Adult↗

PubMed2001

A longitudinal electromyographic study of the postnatal maturation of mastication in the rabbit.

At 2 weeks of age, infant rabbits show chewing movements that resemble those of the adult animal. Previous studies have shown that, at that stage, the accompanying masticatory motor pattern is clearly similar to the suckling motor pattern. As early as 4 weeks, chewing muscle activity is indistinguishable from the adult chewing motor pattern. These reports suggest that the adult chewing motor pattern is developed from the suckling motor pattern. In this study, the chewing motor pattern in the intermediate period (between 2 and 4 weeks of age) was investigated by means of fine-wire electromyography and jaw tracking. Maturation of masticatory movements was found to have two phases. Maximum gape increased in the first few days and was followed by strong development of transverse jaw excursions after the age of 17 days. The increase in jaw excursions was brought about by changes in motor behaviour and facilitated by the development of smooth occlusal surfaces. The changes in motor behaviour were: (1) the level of activity of the balancing-side muscles became more equal to that of the working side; (2) the timing of digastric muscle activity became asymmetrical at the age of 17 days; (3) the peak activity of masseter, temporalis, medial pterygoid and lateral pterygoid muscle portions was gradually shifted or prolonged into the power-stroke phase. It can be concluded that the masticatory contraction pattern shifts from one derived from the suckling contraction pattern at the age of 14 days to one almost similar to the adult chewing pattern at the age of 23 days.

Animals↗

PubMed2001

Mass properties of the pig mandible.

Specification of mass properties is an essential step in the modeling of jaw dynamics, but obtaining them can be difficult. Here, we used three-dimensional computed tomography (CT) to estimate jaw mass, mean bone density, anatomical locations of the mass and geometric centers, and moments of inertia in the pig jaw. High-resolution CT scans were performed at one-mm slice intervals on specimens submerged in water. The mean estimated jaw mass was 12% greater than the mean wet weight, and 33% more than the mean dry weight. Putative bone marrow accounted for an extra 13% of mass. There was a positive correlation between estimated mean bone density and age. The mass center was consistently in the midline, near the last molar. The mean distance between the mass center and geometric center was small, especially when bone marrow was taken into account (0.58 +/- 0.21 mm), suggesting that mass distribution in the pig jaw is almost symmetrical with respect to its geometric center. The largest moment of inertia occurred around each mandible's supero-inferior axis, and the smallest around its antero-posterior axis. Bone marrow contributed an extra 9% to the moments of inertia in all three axes. Linear relationships were found between the actual mass and a mass descriptor (product of the bounding volume and mean bone density), and between the moments of inertia and moments of inertia descriptors (products of the mass descriptor and two orthogonal dimensions forming the bounding box). The study suggests that imaging modalities revealing three-dimensional jaw shape may be adequate for estimating the bone mass properties in pigs.

Animals↗

PubMed2000

Dynamic simulation of muscle and articular properties during human wide jaw opening.

Human mandibular function is determined in part by masticatory muscle tensions and morphological restraints within the craniomandibular system. As only limited information about their interactions can be obtained in vivo, mathematical modeling is a useful alternative. It allows simulation of causal relations between structure and function and the demonstration of hypothetical events in functional or dysfunctional systems. Here, the external force required to reach maximum jaw gape was determined in five relaxed participants, and this information used, with other musculoskeletal data, to construct a dynamic, muscle-driven, three-dimensional mathematical model of the craniomandibular system. The model was programmed to express relations between muscle tensions and articular morphology during wide jaw opening. It was found that a downward force of 5 N could produce wide gape in vivo. When the model's passive jaw-closing muscle tensions were adjusted to permit this, the jaw's resting posture was lower than that normally observed in alert individuals, and low-level active tone was needed in the closer muscles to maintain a typical rest position. Plausible jaw opening to wide gape was possible when activity in the opener muscles increased incrementally over time. When the model was altered structurally by decreasing its angles of condylar guidance, jaw opening required less activity in these muscles. Plausible asymmetrical jaw opening occurred with deactivation of the ipsilateral lateral pterygoid actuator. The model's lateral deviation was limited by passive tensions in the ipsilateral medial pterygoid, which forced the jaw to return towards the midline as opening continued. For all motions, the temporomandibular joint (TMJ) components were maintained in continual apposition and displayed stable pathways despite the absence of constraining ligaments. Compressive TMJ forces were presented in all the cases and increased to maximum at wide gape. Dynamic mathematical modeling appears a useful way to study such events, which as yet are unrecordable in the human craniomandibular system.

Adult↗

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↗

PubMed1995

Functional movements of putative jaw muscle insertions.

BACKGROUND: The craniomandibular muscles control jaw position and forces at the teeth and temporomandibular joints, but little is known regarding their biomechanical behaviour during dynamic function. The objective of this study was to determine how jaw muscle insertions alter position during different jaw movements in living subjects. METHODS: Computer 3D reconstruction of MR images and jaw-tracking were combined to permit the examination of movement with six degrees of freedom. Maximum mandibular opening, protrusive and laterotrusive positions were recorded in four subjects, and the translation and rotation of the putative insertions of masseter, temporal, medial, and lateral pterygoid muscles were measured. RESULTS: The sizes and shapes of regional attachments varied markedly among subjects, and their displacement patterns were different in specific muscles. For instance, when the jaw closed to the dental intercuspal position from maximum gape, the region near the superior insertion site of the masseter moved backward and upward, whereas the region near the inferior insertion site displaced mainly forward. In three subjects, the jaw's rotational center during this act was approximately 26-34 mm below the mandibular condyles. CONCLUSIONS: Since the movements of each muscle part differ according to variations in the size and shape of insertion areas, individual musculoskeletal form, and patterns of jaw motion during function, the prediction of motion-related muscle mechanics in any one subject is unlikely to be possible without direct measurement of the motion of visualized muscle parts. The present study shows that this information can be obtained.

Adult↗

PubMed1992

Preweaning feeding mechanisms in the rabbit.

Muscle contraction patterns and mandibular movements of infant rabbits during suckling and chewing were compared. Oral muscle activity was recorded by fine-wire electromyography, while jaw movements and milk bottle pressure were registered. Suckling and mastication have a comparable cycle duration and share a common pattern of oral muscle activity which consists of a succession of a jaw closer burst, during which the jaw closes and undergoes a power stroke (in mastication), a suprahyoid burst with a stationary or slightly opening jaw and a digastric burst with fast jaw opening (the power stroke of suckling). Compared to suckling, mastication shows decreased jaw opener activity, increased jaw closer activity, development of jaw closing activity in the lateral pterygoid, and increased asymmetry in the masseter by development of a new differentiated motor pattern on the working side. The study shows that the suckling motor pattern enables the infant rabbits to change to chewing with just a few modifications.

Animals↗

PubMed1991

Biomechanical changes in the rabbit masticatory system during postnatal development.

Using dissection, biometry, and two three-dimensional mechanical models, the postnatal changes of the rabbit masticatory muscles were studied by analyzing their three-dimensional orientation, their strength and fiber lengths, and certain functional consequences of these changes. The first mechanical model uses length-tension relationships of the muscles and predicts the maximum bite force as a function of mandibular position. It shows that young rabbits are able to generate large bite forces at a wider gape than adult animals and that the forces are directed more vertically. In spite of the postnatal changes the mechanical advantage of the system remains about equal. However, the muscles are reoriented so that they exert a larger degree of parallel action, suggesting a larger bite force magnitude but a smaller range of bite force directions. The second model-predicts this range. It shows that during postnatal development a relative gain occurs in the possibilities for the system to exert forces directed rostrodorsally. In all other directions the capability to exert force decreases. The results suggest that during development the possibility of the system to generate large bite forces is increased at the cost of a restriction in the range of jaw excursion and that a restriction takes place in the range of possible force directions that can be exerted at the molars.

Animals↗

PubMed1990

Growth patterns of the rabbit masticatory muscles.

The post-natal growth of the masticatory muscles in the rabbit was examined. By means of anatomical dissection and measurement, total muscle length, muscle fiber length, and muscle weight were determined in animals varying in age between one week and 36 months and exhibiting a 50-fold weight increase. Growth data were fitted by linear regression models with facial skull length used as the independent variable. Many deviations occur from size-dependent isometric growth. The muscles can be divided into three groups, according to their pattern of weight increase: The jaw openers grow negatively allometrically, and their contribution to total muscle weight decreases with time; the temporal muscle grows negatively allometrically, but its relative weight proportion remains about the same; the masseter and medial pterygoid muscles have positively allometric growth, and their contribution to total muscle weight increases strongly. Generally, the length of the muscles and of their fibers increases at lower rates than does the length of the facial skull. After weaning, the rate of longitudinal growth drops steeply in some muscles. Total fiber area or physiological cross-section (PCS) of muscles is computed from weight and fiber length. It increases positively allometrically in the jaw closers and negatively allometrically in the jaw openers. In the lateral pterygoid muscle, the increase of PCS changes from negatively- to positively-allometric growth after weaning. The study demonstrates that individual oral muscles follow different patterns of longitudinal and cross-sectional growth, so that their functional capacities (force, range of contraction) and mutual functional relationships are age-dependent.

Animals↗