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Enamel Tufts
Enamel tufts are hypomineralized ribbon-like structures that run longitudinally to the tooth axis and extend from the dentinoenamel junction (DEJ) one fifth to a third into the enamel. They are called ‘‘tufts’’ due to their wavy look within the enamel microstructure. Biomechanically, enamel tufts are ‘‘closed cracks’’ or defects which, in their manner of propagating, act to prevent enamel fractures. This aspect of them is being studied to see how to make more fracture-resistant materials. However, they can also form without stress during enamel development. Enamel tufts are most common in the enamel of molars of animals that crush hard food objects, such as nuts (crushed by apes) and shellfish (crushed by sea otters). Microstructure Each tuft consists of several unconnected leaves that start near the dentinoenamel junction. These defects as they pass through the enamel rods to the surface become progressively more fragmented and fibrillar. Scanning electron ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Odontology
Dentistry, also known as dental medicine and oral medicine, is the branch of medicine focused on the teeth, gums, and mouth. It consists of the study, diagnosis, prevention, management, and treatment of diseases, disorders, and conditions of the mouth, most commonly focused on dentition (the development and arrangement of teeth) as well as the oral mucosa. Dentistry may also encompass other aspects of the craniofacial complex including the temporomandibular joint. The practitioner is called a dentist. The history of dentistry is almost as ancient as the history of humanity and civilization with the earliest evidence dating from 7000 BC to 5500 BC. Dentistry is thought to have been the first specialization in medicine which have gone on to develop its own accredited degree with its own specializations. Dentistry is often also understood to subsume the now largely defunct medical specialty of stomatology (the study of the mouth and its disorders and diseases) for which reason ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Newton (unit)
The newton (symbol: N) is the unit of force in the International System of Units (SI). It is defined as 1 kg⋅m/s, the force which gives a mass of 1 kilogram an acceleration of 1 metre per second per second. It is named after Isaac Newton in recognition of his work on classical mechanics, specifically Newton's second law of motion. Definition A newton is defined as 1 kg⋅m/s (it is a derived unit which is defined in terms of the SI base units). One newton is therefore the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in the direction of the applied force. The units "metre per second squared" can be understood as measuring a rate of change in velocity per unit of time, i.e. an increase in velocity by 1 metre per second every second. In 1946, Conférence Générale des Poids et Mesures (CGPM) Resolution 2 standardized the unit of force in the MKS system of units to be the amount needed to accelerate 1 kilogram of mass at the rate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chewing
Chewing or mastication is the process by which food is crushed and ground by teeth. It is the first step of digestion, and it increases the surface area of foods to allow a more efficient break down by enzymes. During the mastication process, the food is positioned by the cheek and tongue between the teeth for grinding. The muscles of mastication move the jaws to bring the teeth into intermittent contact, repeatedly occluding and opening. As chewing continues, the food is made softer and warmer, and the enzymes in saliva begin to break down carbohydrates in the food. After chewing, the food (now called a bolus) is swallowed. It enters the esophagus and via peristalsis continues on to the stomach, where the next step of digestion occurs. Increasing the number of chews per bite increases relevant gut hormones. Studies suggest that chewing may decrease self-reported hunger and food intake. Chewing gum has been around for many centuries; there is evidence that northern Europeans ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of the molten form; some glasses such as volcanic glass are naturally occurring. The most familiar, and historically the oldest, types of manufactured glass are "silicate glasses" based on the chemical compound silica (silicon dioxide, or quartz), the primary constituent of sand. Soda–lime glass, containing around 70% silica, accounts for around 90% of manufactured glass. The term ''glass'', in popular usage, is often used to refer only to this type of material, although silica-free glasses often have desirable properties for applications in modern communications technology. Some objects, such as drinking glasses and eyeglasses, are so commonly made of silicate-based glass that they are simply called by the name of the material. Despite bei ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brittle
A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a sharp snapping sound. When used in materials science, it is generally applied to materials that fail when there is little or no plastic deformation before failure. One proof is to match the broken halves, which should fit exactly since no plastic deformation has occurred. Brittleness in different materials Polymers Mechanical characteristics of polymers can be sensitive to temperature changes near room temperatures. For example, poly(methyl methacrylate) is extremely brittle at temperature 4˚C, but experiences increased ductility with increased temperature. Amorphous polymers are polymers that can behave differently at different temperatures. They may behave like a glass at low temperatures (the glassy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peccaries
A peccary (also javelina or skunk pig) is a medium-sized, pig-like hoofed mammal of the family Tayassuidae (New World pigs). They are found throughout Central and South America, Trinidad in the Caribbean, and in the southwestern area of North America. They usually measure between in length, and a full-grown adult usually weighs about . They represent the closest relatives of the family Suidae, which contains pigs and relatives. Together Tayassuidae and Suidae are grouped in the Suina within the Artiodactyla (even toed ungulates). Peccaries are social creatures that live in herds. They eat roots, grubs, and a variety of foods. They can identify each other by their strong odors. A group of peccaries that travel and live together is called a "squadron". A squadron of peccaries averages between six and nine members. Peccaries first appeared in North America during the Miocene, and migrated into South America during the Pliocene-Pleistocene as part of the Great American Interchang ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bear
Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the Northern Hemisphere and partially in the Southern Hemisphere. Bears are found on the continents of North America, South America, Europe, and Asia. Common characteristics of modern bears include large bodies with stocky legs, long snouts, small rounded ears, shaggy hair, plantigrade paws with five nonretractile claws, and short tails. While the polar bear is mostly carnivorous, and the giant panda feeds almost entirely on bamboo, the remaining six species are omnivorous with varied diets. With the exception of courting individuals and mothers with their young, bears are typically solitary animals. They may be diurnal or nocturnal and have an excellent sense of smell. Despite their heavy build and awkward gait, they are adept runners, cli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gorilla
Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or five subspecies. The DNA of gorillas is highly similar to that of humans, from 95 to 99% depending on what is included, and they are the next closest living relatives to humans after chimpanzees and bonobos. Gorillas are the largest living primates, reaching heights between 1.25 and 1.8 metres, weights between 100 and 270 kg, and arm spans up to 2.6 metres, depending on species and sex. They tend to live in troops, with the leader being called a silverback. The Eastern gorilla is distinguished from the Western by darker fur colour and some other minor morphological differences. Gorillas tend to live 35–40 years in the wild. The oldest gorilla known is Fatou (b. 1957), who is still alive at the advanced age of 65 years. Gorillas' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orangutan
Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus ''Pongo'', orangutans were originally considered to be one species. From 1996, they were divided into two species: the Bornean orangutan (''P. pygmaeus'', with three subspecies) and the Sumatran orangutan (''P. abelii''). A third species, the Tapanuli orangutan (''P. tapanuliensis''), was identified definitively in 2017. The orangutans are the only surviving species of the subfamily Ponginae, which diverged genetically from the other hominids (gorillas, chimpanzees, and humans) between 19.3 and 15.7 million years ago. The most arboreal of the great apes, orangutans spend most of their time in trees. They have proportionally long arms and short legs, and have reddish-brown hair covering their bodies. Adult males weigh about , while female ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chimpanzee
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative the bonobo was more commonly known as the pygmy chimpanzee, this species was often called the common chimpanzee or the robust chimpanzee. The chimpanzee and the bonobo are the only species in the genus ''Pan''. Evidence from fossils and DNA sequencing shows that ''Pan'' is a sister taxon to the human lineage and is humans' closest living relative. The chimpanzee is covered in coarse black hair, but has a bare face, fingers, toes, palms of the hands, and soles of the feet. It is larger and more robust than the bonobo, weighing for males and for females and standing . The chimpanzee lives in groups that range in size from 15 to 150 members, although individuals travel and forage in much smaller groups during the day. The species lives in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Primate
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including humans). Primates arose 85–55 million years ago first from small terrestrial mammals, which adapted to living in the trees of tropical forests: many primate characteristics represent adaptations to life in this challenging environment, including large brains, visual acuity, color vision, a shoulder girdle allowing a large degree of movement in the shoulder joint, and dextrous hands. Primates range in size from Madame Berthe's mouse lemur, which weighs , to the eastern gorilla, weighing over . There are 376–524 species of living primates, depending on which classification is used. New primate species continue to be discovered: over 25 species were described in the 2000s, 36 in the 2010s, and three in the 2020s. Primates have large bra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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