Boundary-layer Features in Limit of Conservative Nonlinear Oscillators

In the double limit of high amplitude (xmax → ∞) and high leading power (x2 N+1, N → ∞), (1+1) dimensional conservative nonlinear oscillatory systems exhibit characteristics akin to boundary layer phenomena. The oscillating entity, x(t), tends to a periodic saw-tooth shape of linear segments, the velocity, x′(t), tends to a periodic step-function and the x − x′ phase-space plot tends to a rectangle. This is demonstrated by transforming x and t into proportionately scaled variables, η and θ, respectively. η(θ) is (2-π) periodic in θ and bounded (|η(θ)| ≤ 1). The boundary-layer characteristics show up by the fact that the deviations of η(θ), η′(θ) and the η − η′ phase-space plot from the sharp asymptotic shapes occurs over a range in θ of O(1/N) near the turning points of the oscillations.

Influence of phylogeny on the estimation of diet from dental morphology in the Carnivora

Because teeth are the most easily preserved part of the vertebrate skeleton and are particularly morphologically variable in mammals, studies of fossil mammals rely heavily on dental morphology. Dental morphology is used both for systematics and phylogeny as well as for inferences about paleoecology, diet in particular. We analyze the influence of evolutionary history on our ability to reconstruct diet from dental morphology in the mammalian order Carnivora, and we find that much of our understanding of diet in carnivorans is dependent on the phylogenetic constraints on diet in this clade. Substantial error in estimating diet from dental morphology is present regardless of the morphological data used to make the inference, although more extensive morphological datasets are more accurate in predicting diet than more limited character sets. Unfortunately, including phylogeny in making dietary inferences actually decreases the accuracy of these predictions, showing that dietary predictions from morphology are substantially dependent on the evolutionary constraints on carnivore diet and tooth shape. The “evolutionary ratchet” that drives lineages of carnivorans to evolve greater degrees of hypercarnivory through time actually plays a role in allowing dietary inference from tooth shape, but consequently requires caution in interpreting dietary inference from the teeth fossil carnivores. These difficulties are another reminder of the differences in evolutionary tempo and mode between morphology and ecology.

Identifying Handsaw Tooth Shape Based on the Micro- and Macroscopic Analysis of the Kerf Floor Contour

Skeletal trauma analysis is a major facet of forensic anthropology casework and can entail interpretation of sharp force saw trauma. Hand-powered saws are commonly used in cases of dismemberment and analysis requires differentiating class characteristics. Features of the kerf walls and floor provide information utilized in identifying set, shape, size, power, and direction of sawing motion of the tool. The focus of this study is to examine validity and reliability of determining tooth shape class characteristic (rip versus crosscut) from features of the kerf floor. Two crosscut and three rip handsaws, ranging from 6 to 16 teeth per inch, were used to make 30 incomplete cuts per saw for a total of 150 cuts. Each kerf floor was analyzed macroscopically and microscopically using a digital microscope at 30 × magnification by three observers of different experience levels (expert, experienced, and novice). Profile shapes were classified as U-shaped/concave (rip) or W-shaped/convex (crosscut) by each observer for all 150 cuts. Reliability tests using Cohen’s kappa ranged from substantial in the two less experienced observers to almost perfect in pairwise comparisons with the expert. Microscopic classification accuracy was 94.0% (423/450) for all three observers and macroscopic examination increased accuracy to 99.8% (449/450). Saw wear and tooth size were not a significant determiner in correct identification of saw tooth type. Overall, tooth shape can be reliably and accurately determined from incomplete cuts.

Contribution to the study of improving the aesthetics of the smile by repairing and reshaping the incisors with composite materials.

Introduction. Dental aesthetics, although it seems something relative and difficult to evaluate, it is governed by a series of laws and rules that connect the dental disciplines, creating a unitary whole. It is structured by rules, perfected by artistic sense and by the inclination towards beauty of all specialists in dento-facial cosmetics. The aim of the study is to highlight an overview of aesthetic factors to consider when restoring anterior teeth with direct composite materials. Material and methods. A total of 25 patients were included in the study where the anterior teeth were restored using Gradia Direct Anterior (from GC) and Filtek Z550 (from3M-ESPE) composite kits, in perfect isolation using rubber damn, with a separate appointment after 24 hours for the polishing step, for which Rainbow Kit Technic and polishing Platina Hi-Gloss (from Prevest) paste were used. While the replacement of the tooth defect, we ensured that the composite increment, which we used should not be more than 2mm in thickness, and light cured for 20 seconds as the producer recommends. In none of all tooth shape modification (elongation in incisal zone) we did not modify the occlusion, by eliminating all premature contacts. All patients included in the study have signed the informed consent and agreed to participate in this research. Results. From a total of 25 patients, we repaired 20 central incisors with the mesial (18 cases) or distal (2 cases) angles fractured, in different accidents, 5 cases with diastema by small shape of the crown or malposition of one of the central incisors. Conclusions. Restoring the incisal angle or the incisal edge and refining a natural and improved smile of the patient is e very frequent dental intervention, especially nowadays when aesthetics plays an important role in the social society.

Linking tooth shape to strike mechanics in the Boa constrictor

Snakes, with the obvious exception of the fangs, are considered to lack the regional specialization of tooth shape and function that are exemplified by mammals. Recent work in fishes has suggested the definition of homodont and heterodont are incomplete without a full understanding of the morphology, mechanics, and behavior of feeding. We investigated this idea further by examining changes in tooth shape along the jaw of Boa constrictor and integrating these data with the strike kinematics of boas feeding on rodent prey. We analyzed the shape of every tooth in the skull, from a combination of anesthetized individuals and CT scanned museum specimens. For strike kinematics, we filmed eight adult boas striking at previously killed rats. We determined the regions of the jaws that made first contact with the prey, and extrapolated the relative positions of those teeth at that moment. We further determined the roles of all the teeth throughout the prey capture process, from the initiation of the strike until constriction began. We found that teeth in the anterior third of the mandible are the most upright, and that teeth become progressively more curved posteriorly. Teeth on the maxilla are more curved than on the mandible, and the anterior teeth are more linear or recurved than the posterior teeth. In a majority of strikes, boas primarily made contact with the anterior third of the mandible first. The momentum from the strike caused the upper jaws and skull to rotate over the rat. The more curved teeth of the upper jaw slid over the rat unimpeded until the snake began to close its jaws. In the remaining strikes, boas made contact with the posterior third of both jaws simultaneously, driving through the prey and quickly retracting, ensnaring the prey on the curved posterior teeth of both jaws. The curved teeth of the palatine and pterygoid bones assist in the process of the swallowing.

Optimal Position of Attachment for Removable Thermoplastic Aligner on the Lower Canine Using Finite Element Analysis

Malocclusion is considered as a developmental disorder rather than a disease, and it may be affected by the composition and proportions of masseter muscle fibers. Orthodontics is a specialty of dentistry that deals with diagnosis and care of various irregular bite and/or malocclusion. Recent developments of 3D scanner and 3D printing technology has led to the use of a removable thermoplastic aligner (RTA), which is widely used due to its aesthetic excellence, comfortableness, and time efficiency. However, orthodontics using only an RTA has lower treatment efficacy and accuracy due to the differing movement of teeth from the plan. In order to improve these disadvantages, attachments were used, and biomechanical analyses were performed with and without them. However, there is insufficient research on the movement of teeth and the transfer of load according to the attachment position and shape. Therefore, in our study, we aimed to identify the optimal shape and position of attachments by analyzing various shapes and positions of attachments. Through 3D finite element analysis (FEA), simple tooth shape and mandibular canine shape were extracted in order to construct the orthodontics model which took into account the various shapes and positions of attachments. The optimal shape of a cylinder was derived through the FEA of simple tooth shape and analyzing various positions of attachments on teeth revealed that fixing the attachments at the lingual side of the tooth rather than the buccal side allowed for torque control and an effective movement of the teeth. Therefore, we suggest fixing the attachments at the lingual side rather than the buccal side of the tooth to induce effective movement of teeth in orthodontic treatment with the RTA in case of canine teeth.