Bite force

Stress distribution in human tooth structure can be visualized through the use of Moiré fringes, which has improved the clinical understanding of recently identified anatomical structures in molar occlusal surfaces. This article discusses the concept of a "peripheral rim of enamel" and describes the manifestation of compressive and tensile fractures within the peripheral rim of enamel and dentin. It also emphasizes the benefits of microdentistry techniques and minimally invasive preparation designs in the long-term preservation of the natural tooth structure.

The purpose of this paper is to analyse the effects of cranial size and shape in domestic dogs (Canis familiaris) on predicted forces of biting. In addition to continuous size-shape analysis, nine size-shape groups were developed based on three skull shape categories and three skull size categories. Bite forces were predicted from measurements made on dried skulls using two lever models of the skull, as well as simple models derived by regression analysis. Observed bite force values were not available for the database used in this study, so only comparisons between categories and models were undertaken. The effects of shape and size on scaled predicted bite forces were evaluated. Results show that bite force increases as size increases, and this effect was highly significant (P < 0.0001). The effect of skull shape on bite force was significant in medium and large dogs (P < 0.05). Significant differences were not evident in small dogs. Size × shape interactions were also significant (P < 0.05). Bite force predictions by the two lever models were relatively close to each other, whereas the regression models diverged slightly with some negative numbers for very small dogs. The lever models may thus be more robust across a wider range of skull size-shapes. Results obtained here would be useful to the pet food industry for food product development, as well as to paleontologists interested in methods of estimating bite force from dry skulls.

Assessments of masticatory performance and occlusal force for wearers of obturator prostheses were performed as clinical objective assessments and reported in an earlier study. The purpose of the present study was to evaluate clinically the chewing function of obturator prosthesis wearers by self-evaluations and to examine their relationship to the objective assessments. Twenty patients with maxillofacial obturator prostheses who were having a periodic checkup at the maxillofacial rehabilitation clinic in Kyushu University Hospital were recruited for this study. Chewing function was evaluated by 3 assessment tools: a self-assessment mastication scale, a chewing function score, and a mastication score. In addition, correlations among these assessments and objective tests--ie, masticatory performance and maximum occlusal force--were analyzed by the Spearman rank correlation coefficient. The mean self-assessment mastication scale was 63.2 (SD 31.8), the chewing function score was 54.0 ...

Tyrannosaurs, the group of dinosaurian carnivores that includes Tyrannosaurus rex and its closest relatives, are icons of prehistory. They are also the most intensively studied extinct dinosaurs, and thanks to large sample sizes and an influx of new discoveries, have become ancient exemplar organisms used to study many themes in vertebrate paleontology. A phylogeny that includes recently described species shows that tyrannosaurs originated by the Middle Jurassic but remained mostly small and ecologically marginal until the latest Cretaceous. Anatomical, biomechanical, and histological studies of T. rex and other derived tyrannosaurs show that large tyrannosaurs could not run rapidly, were capable of crushing bite forces, had accelerated growth rates and keen senses, and underwent pronounced changes during ontogeny. The biology and evolutionary history of tyrannosaurs provide a foundation for comparison with other dinosaurs and living organisms.

It is widely accepted that the orthodontist should have a thorough understanding of the craniofacial musculature and its association with the growth and development of the dentofacial complex. There is still much controversy regarding the influence of the mandibular muscles on normal growth and development, and on orthodontic treatment and stability. This review presents an outline of the mandibular muscles and the vertical facial pattern. The different methods by which the mandibular muscles have been investigated are discussed. The potential influence of these muscles on normal morphologic variation in different people is also discussed, along with the implications for contemporary orthodontic treatment and stability.

Finite element analysis (FEA) was used to generate 3-dimensional models of a human mandible with impacted third molars. The aim was to analyze the effects of removing various amounts of bone around an impacted mandibular third molar and to predict the possibility of iatrogenic fracture. Data were acquired from cone beam computed tomography (CBCT) scans of a patient using numerically calculated mechanical parameters. Virtual surgery was then performed on the mandibular models, and standardized chewing forces were applied to the resulting simulations. The modelling showed that the highest stress during normal clenching occurred if the surgical procedure involved the external oblique ridge. The peak stress occurred at the site of removal of the third molar, during contralateral loading of the mandible. Use of CBCT allowed production of high-quality models of an individual patient and simulation of various surgical scenarios. FEA identified the accumulation of stress and strain at speci...

To prevent relapse after orthodontic treatment, retention is often considered indispensable. Soft tissues are thought to have a significant influence on dental movements. To quantify the influence of masticatory muscles on post-treatment relapse, and in an attempt to avoid unnecessary procedures, 2 male orthodontic patients (13 and 30 years old at debonding) were followed up. The patients completed 2 years of fixed orthodontic treatment and received no post-orthodontic retention. After 1 week and again after 6 months, alginate impressions of dental arches and a surface electromyographic (EMG) assessment of the masseter and temporalis muscles during maximum voluntary clenching were performed. The younger patient received surface EMG monitoring once a month for the first 6 months and at the 1-year follow-up appointment. Arch dimensions and the 3-dimensional inclination of the facial axis of the clinical crown (FACC) were measured using a computerized digitizer. Symmetry in muscular co...

This study analyzed detailed models of human mandibles at 3 different stages of life with simulation of supra normal chewing forces at static conditions. Finite element analysis (FEA) was used to generate models from cone-beam computerized tomograms (CBCT) of 3 patients aged 12, 20, and 67 years, using numerically calculated material parameters. Estimated chewing forces were then applied to the simulations. The results reflect higher elasticity in younger models in all regions of the mandible. The experimental models show that physiologic load stress and strain distributional changes of the mandible vary according to age. The CBCT-based model generation used in this study provided high-quality model definition of the 3 individual patients of different ages. FEA has great potential to predict bone responses to paradigms of mechanical activity. Future applications of FEA will include surgical planning, surgical hardware testing, and the design of scaffolds and tissue-engineered constructs.

The Carnivora spans the largest ecological and body size diversity of any mammalian order, making it an ideal basis for studies of evolutionary ecology and functional morphology. For animals with different feeding ecologies, it may be expected that bite force represents an important evolutionary adaptation, but studies have been constrained by a lack of bite force data. In this study we present predictions of bite forces for 151 species of extant carnivores, comprising representatives from all eight families and the entire size and ecological spectrum within the order. We show that, when normalized for body size, bite forces differ significantly between the various feeding categories. At opposing extremes and independent of genealogy, consumers of tough fibrous plant material and carnivores preying on large prey both have high bite forces for their size, while bite force adjusted for body mass is low among specialized insectivores. Omnivores and carnivores preying on small prey have more moderate bite forces for their size. These findings indicate that differences in bite force represent important adaptations to and indicators of differing feeding ecologies throughout carnivoran evolution. Our results suggest that the incorporation of bite force data may assist in the construction of more robust evolutionary and palaeontological analyses of feeding ecology.

The feeding behavior of the theropod dinosaur Tyrannosaurus
rex is investigated through analysis of two
variables that are critical to successful predation, bite
force and prey body mass, as they scale with the size of
the predator. These size-related variables have important
deterministic effects on the predator’s feeding strategy,
through their effects on lethal capacity and choice of
prey. Bite force data compiled for extant predators
(crocodylians, carnivorans, chelonians and squamates)
are used to establish a relationship between bite force
and body mass among extant predators. These data are
used to estimate the maximum potential bite force of
T. rex, which is between about 183,000 and 235,000N for a
bilateral bite. The relationship between maximum prey
body mass and predator body mass among the same
living vertebrates is used to infer the likely maximum
size of prey taken by T. rex in the Late Cretaceous. This
makes it possible to arrive at a more rigorous assessment
of the role of T. rex as an active predator and/or scavenger
than has hitherto been possible. The results of this
analysis show that adult Triceratops horridus fall well
within the size range of potential prey that are predicted
to be available to a solitary, predaceous T. rex. This
analysis establishes boundary conditions for possible
predator/prey relationships among other dinosaurs, as
well as between these two taxa.

Starch and mucilage extracts of sweet cassava tubers were incorporated into wheat flour–cassava starch (WF–CS) composite mix to make Chinese noodle. CS was extracted from fresh 1- and 2-yr-old sweet cassava tubers and was mixed at an optimized ratio of 70:30 into patent hard red Spring wheat (HRSW) flour. Noodles of proportional substitution of cassava mucilage in WF–CS blends were