Mineral heterogeneity affects predictions of intratrabecular stress and strain.

Knowledge of the influence of mineral variations (i.e., mineral heterogeneity) on biomechanical bone behavior at the trabecular level is limited.

Age-related changes in collagen properties and mineralization in cancellous and cortical bone in the porcine mandibular condyle.

Collagen is an important constituent of bone, and it has been suggested that changes in collagen and mineral properties of bone are interrelated during growth. The aim of this study was to quantify age-related changes in collagen properties and the degree of mineralization of bone (DMB). The DMB in cancellous and cortical bone samples from the mandibular condyle of 35 female pigs aged 0-100 weeks was determined using micro-computed tomography.

The adaptive response of jaw muscles to varying functional demands.

Jaw muscles are versatile entities that are able to adapt their anatomical characteristics, such as size, cross-sectional area, and fibre properties, to altered functional demands. The dynamic nature of muscle fibres allows them to change their phenotype to optimize the required contractile function while minimizing energy use. Changes in these anatomical parameters are associated with changes in neuromuscular activity as the pattern of muscle activation by the central nervous system plays an important role in the modulation of muscle properties.

Ae2(a,b)-deficient mice exhibit osteopetrosis of long bones but not of calvaria.

Extracellular acidification by osteoclasts is essential to bone resorption. During proton pumping, intracellular pH (pH(i)) is thought to be kept at a near-neutral level by chloride/bicarbonate exchange. Here we show that the Na(+)-independent chloride/bicarbonate anion exchanger 2 (Ae2) is relevant for this process in the osteoclasts from the long bones of Ae2(a,b)(-/-) mice (deficient in the main isoforms Ae2a, Ae2b(1), and Ae2b(2)).

Postnatal development of fiber type composition in rabbit jaw and leg muscles.

We examined the difference in fiber type composition and cross-sectional areas during postnatal development in male rabbit jaw muscles and compared these with changes in leg muscles. The myosin heavy chain (MyHC) content of the fibers was determined by immunohistochemistry. No fiber type difference was found between the jaw muscles in 20-week-old rabbits.

Biomechanical effect of mineral heterogeneity in trabecular bone.

Due to daily loading, trabecular bone is subjected to deformations (i.e., strain), which lead to stress in the bone tissue.

Jaw-muscle activity changes after the induction of osteoarthrosis in the temporomandibular joint by mechanical loading.

Aims: To examine the effect of mechanical loading on the induction of temporomandibular joint osteoarthrosis (TMJ OA).

Methods: Mechanical stress was applied to the rat TMJ by forced jaw opening of 3 hours a day for 5 days. The electromyographic (EMG) activity of the masseter and digastric muscles was continuously monitored by radio-telemetry.

Spatial orientation in bone samples and Young's modulus.

Bone mass is the most important determinant of the mechanical strength of bones, and spatial structure is the second. In general, the spatial structure and mechanical properties of bones such as the breaking strength are direction dependent. The mean intercept length (MIL) and line frequency deviation (LFD) are two methods for quantifying directional aspects of the spatial structure of bone.

Development of the micro architecture and mineralization of the basilar part of the pig occipital bone.

In this study, the development of the architecture and the degree and distribution of mineralization in the basilar part of the pig occipital bone, one of the contact points between the spine and skull base, was investigated. Multiple regions of the basiocciput of pig specimens of different gestational ages were examined with three-dimensional microcomputed tomography (microCT). The cortex of the basilar part developed from a structure with a large intertrabecular separation into a more compact one, whereas its center maintained a trabecular structure.

Modeling of the effect of friction in the temporomandibular joint on displacement of its disc during prolonged clenching.

Purpose: The effect of the frictional coefficient in the temporomandibular joint on the disc during prolonged clenching was examined.

Materials And Methods: For this purpose, a finite element model of the temporomandibular joint based on magnetic resonance images from a volunteer subject was used. Muscle forces applied for clenching were used as a loading condition for stress analysis during 10 minutes.

Is fiber-type composition related to daily jaw muscle activity during postnatal development?

Aim: Muscles containing large numbers of slow-contracting fibers are generally more active than muscles largely composed of fast fibers. This relationship between muscle activity and phenotype suggests that (1) changes in fiber-type composition during postnatal development are accompanied by changes in daily activity and (2) individual variations in fiber-type composition are related to similar variations in daily muscle activity.

Methods: The masseter and digastric muscles of 23 New Zealand White rabbits (young, juvenile and adult) were examined for their phenotype (myosin heavy chain content) and their daily activity (total daily number of activity bursts).

Effect of hyperactivity of the lateral pterygoid muscle on the temporomandibular joint disk.

In this study, the effect of hyperactivity of the lateral pterygoid muscle (LPM) on the temporomandibular joint (TMJ) disk during prolonged clenching was examined with a mathematical model. Finite element models of the TMJ were constructed based on magnetic resonance images from two subjects with or without internal derangement of the TMJ. For each model, muscle forces were used as a loading condition for stress analysis for 10 min clenching.

Consequences of viscoelastic behavior in the human temporomandibular joint disc.

The consequences of the viscoelastic behavior of the temporomandibular joint disc were analyzed in simulated jaw open-close cycles. It was hypothesized that viscoelasticity helps protect the underlying bone, while augmenting the smoothness of articular movements. Simulations were performed with a dynamic model of the masticatory system, incorporating the joints' cartilaginous structures as Finite Element Models.

Regional variations in mineralization and strain distributions in the cortex of the human mandibular condyle.

The strain (i.e. deformation) history influences the degree of mineralization of cortical bone (DMB) as well as its osteonal microstructure.

Heterogeneity of fiber characteristics in the rat masseter and digastric muscles.

The functional requirements in muscle use are related to the fiber type composition of the muscles and the cross-sectional area of the individual fibers. We investigated the heterogeneity in the fiber type composition and fiber cross-sectional area in two muscles with an opposing function, namely the digastric and masseter muscles (n = 5 for each muscle) of adult male rats, by means of immunohistochemical staining according to their myosin heavy chain (MyHC) content. The digastric and masseter muscles were taken from Wistar strain male rats 10 weeks old.

Biomechanical response of condylar cartilage-on-bone to dynamic shear.

Shear stress can result in fatigue, damage, and irreversible deformation of the mandibular condylar cartilage. However, little information is available on its dynamic properties in shear. We tested the hypothesis that the dynamic shear properties of the condylar cartilage depend on the frequency and amplitude of shear strain.

Relationship between tissue stiffness and degree of mineralization of developing trabecular bone.

It is unknown how the degree of mineralization of bone in individual trabecular elements is related to the corresponding mechanical properties at the bone tissue level. Understanding this relationship is important for the comprehension of the mechanical behavior of bone at both the apparent and tissue level. The purpose of the present study was, therefore, to determine the tissue stiffness and degree of mineralization of the trabecular bone tissue and to establish a relationship between these two variables.

The influence of mineralization on intratrabecular stress and strain distribution in developing trabecular bone.

The load-transfer pathway in trabecular bone is largely determined by its architecture. However, the influence of variations in mineralization is not known. The goal of this study was to examine the influence of inhomogeneously distributed degrees of mineralization (DMB) on intratrabecular stresses and strains.

Intratrabecular distribution of tissue stiffness and mineralization in developing trabecular bone.

The purpose of this study was to investigate the relation between bone tissue stiffness and degree of mineralization distribution and to examine possible changes during prenatal development. Understanding this may provide insight into adaptation processes and into deformation mechanisms of the bone microstructure. Mandibular condyles from four fetal and newborn pigs were used.

Effect of food consistency on the degree of mineralization in the rat mandible.

A switch to a soft diet, associated with reduced forces applied to the mandible during mastication, may result in an alteration of the degree of mineralization in the mandible. This alteration may be regionally different. The aim of this study was to analyze this alteration by examination of the degree of mineralization in the mandible of growing rats fed with a hard or soft diet.

Porosity of human mandibular condylar bone.

Quantification of porosity and degree of mineralization of bone facilitates a better understanding of the possible effects of adaptive bone remodelling and the possible consequences for its mechanical properties. The present study set out first to give a three-dimensional description of the cortical canalicular network in the human mandibular condyle, in order to obtain more information about the principal directions of stresses and strains during loading. Our second aim was to determine whether the amount of remodelling was larger in the trabecular bone than in cortical bone of the condyle and to establish whether the variation in the amount of remodelling was related to the surface area of the cortical canals and trabeculae.

Daily jaw muscle activity in freely moving rats measured with radio-telemetry.

The jaw muscle activity of rats has been investigated for specific tasks. However, the daily jaw muscle use remains unclear. The purpose of the present study was to examine daily jaw muscle activity, and its variability over time, in the rat (n = 12) by the use of radio-telemetry.

Age-related changes in microarchitecture and mineralization of cancellous bone in the porcine mandibular condyle.

The mandibular condyle is considered a good model for developing cancellous bone because of its rapid growth and high rate of remodeling. The aim of the present study was to analyze the simultaneous changes in microarchitecture and mineralization of cancellous bone during development in a three-dimensional fashion. Eight mandibular condyles of pigs aged 8 weeks prepartum to 108 weeks postpartum were scanned using microCT with an isotropic spatial resolution of 10 microm.

Development and implementation of new educational concepts in a dental curriculum.

The Academic Centre for Dentistry Amsterdam introduced a fully renewed 5-year dental curriculum in September 2003. In this article, the educational principles and didactic choices that form the basis of the curriculum development are presented and attention is given to the process of development and the implementation strategy that constitute such an important part of the success of introducing a new curriculum. Special characteristics of the new curriculum are the clinical training practice, professional conduct, the elective profiles and academic education.

Viscoelastic material model for the temporomandibular joint disc derived from dynamic shear tests or strain-relaxation tests.

Viscoelastic material models for the temporomandibular joint disc, based upon strain relaxation, were considered to underestimate energy absorption for loads with time constants beyond the relaxation time. Therefore, the applicability of a material model that takes the viscous behavior at a wide range of frequencies into account was assessed. To that purpose a non-linear multi-mode Maxwell model was tested in cyclic large-strain compression tests.