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Post And Core
A post and core crown is a type of dental restoration required where there is an inadequate amount of sound tooth tissue remaining to retain a conventional crown. A post is cemented into a prepared root canal, which retains a core restoration, which retains the final crown. The role of the post is firstly to retain a core restoration and crown, and secondly to redistribute stresses down onto the root, thereby reducing the risk of coronal fracture. The post does not play any role in reinforcing or supporting the tooth and can in fact make it more likely to fracture at the root. When deciding whether or not a tooth requires a post and core crown rather than a conventional crown, the following must be established: # Presence of an adequate ferrule (coronal tooth structure) # Sufficient length of canal to retain a post # Curvature and overall anatomy of root canal system # Sufficient root (radicular) dentine thickness for post preparation # Restorability of tooth The benefit of placing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crown (dentistry)
In dentistry, a crown most commonly refers to a dental cap, a type of dental restoration that completely caps or encircles a tooth or dental implant. A crown may be needed when a large cavity threatens the health of a tooth. A crown is typically bonded to the tooth by dental cement. They can be made from various materials, which are usually fabricated using ''indirect methods''. Crowns are used to improve the strength or appearance of teeth and to halt deterioration. While beneficial to dental health, the procedure and materials can be costly. The most common method of crowning a tooth involves taking a dental impression of a tooth prepared by a dentist, then fabricating the crown outside of the mouth. The crown can then be inserted at a subsequent dental appointment. This ''indirect method'' of tooth restoration allows use of strong restorative material requiring time-consuming fabrication under intense heat, such as casting metal or firing porcelain, that would not be possib ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crown-to-root Ratio
Crown-to-root-ratio is the ratio of the length of the part of a tooth that appears above the alveolar bone versus what lies below it. It is an important consideration in the diagnosis, treatment planning and restoration of teeth, one that hopefully guides the plan of treatment to the proper end result. Perspectives of different terminologies Anatomical terms All teeth have two general sections, the crown and the root. Because the crown is covered with enamel and the root is covered with cementum, the line at which these two sections join is called the cementoenamel junction. In health, the roots of teeth are entirely surrounded by and submerged in the alveolar bone of either the maxilla or the mandible, depending on whether the tooth in question is an upper or a lower tooth, up until the cementoenamel junction. Overlying the bone is the gingival soft tissue, which is, on average, about 1 millimeter in thickness. Because of this gingiva, the crown, which exists entirely outside ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nankali Post-system
The Nankali post system is a post and cores prosthesis, which is used in prosthodontology and dental restoration. This post and core consists of a single ''smooth'' or ''serrated post'' and core which has an additional ''circle ring'' (counter sink) around it. The additional single-circle ring increases the contact surface area between the core and involved part of tooth significantly. Increased contact surface area decreases the pressure between the two objects (remaining part of the tooth and post-core) and is followed by ''a declining in the number of failures'' in treatments.Nankali A.(2006)Usage the New Post System with Insertion Ring, Soveremenaia Stomatologia Journal/ Kyiv, Ukraine 2(34) 2006, p142-144 General indications The main indications are: *Severely damaged crown *Trauma *Tooth wear (erosion) *Hypoplastic conditions *As part of another restoration *Combined indication *Non-vital teeth Disadvantages The disadvantages are as follows: * Requires an exact castin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dental Implant
A dental implant (also known as an endosseous implant or fixture) is a prosthesis that interfaces with the bone of the jaw or skull to support a dental prosthesis such as a crown, bridge, denture, or facial prosthesis or to act as an orthodontic anchor. The basis for modern dental implants is a biologic process called osseointegration, in which materials such as titanium or zirconia form an intimate bond to bone. The implant fixture is first placed so that it is likely to osseointegrate, then a dental prosthetic is added. A variable amount of healing time is required for osseointegration before either the dental prosthetic (a tooth, bridge or denture) is attached to the implant or an abutment is placed which will hold a dental prosthetic/crown. Success or failure of implants depends on the health of the person receiving the treatment, drugs which affect the chances of osseointegration, and the health of the tissues in the mouth. The amount of stress that will be put on the impla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyvinyl Siloxane
Polyvinyl siloxane (PVS), also called poly-vinyl siloxane, vinyl polysiloxane (VPS), or vinylpolysiloxane, is an addition-reaction silicone elastomer (an addition silicone). It is a viscous liquid that cures (solidifies) quickly into a rubber-like solid, taking the shape of whatever surface it was lying against while curing. As with two-part epoxy, its package keeps its two component liquids in separate tubes until the moment they are mixed and applied, because once mixed, they cure (harden) rapidly. Polyvinyl siloxane is widely used in dentistry as an impression material. It is also used in other contexts where an impression similar to a dental impression is needed, such as in audiology (to take ear impressions for fitting custom hearing protection or hearing aids) or in industrial applications (such as to aid in the inspection of interior features of machined parts, for example, internal grooves inside bores). Polyvinyl siloxane was commercially introduced in the 1970s. To create ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lost-wax Casting
Lost-wax casting (also called "investment casting", "precision casting", or ''cire perdue'' which has been adopted into English from the French, ) is the process by which a duplicate metal sculpture (often silver, gold, brass, or bronze) is cast from an original sculpture. Intricate works can be achieved by this method. The oldest known examples of this technique are approximately 6,500-year-old (4550–4450 BC) and attributed to gold artefacts found at Bulgaria's Varna Necropolis. A copper amulet from Mehrgarh, Indus Valley civilization, in Pakistan, is dated to circa 4,000 BC. Cast copper objects, found in the Nahal Mishmar hoard in southern Israel, which belong to the Chalcolithic period (4500–3500 BC), are estimated, from carbon-14 dating, to date to circa 3500 BC. In Other examples from somewhat later periods are from Mesopotamia in the third millennium BC. Lost-wax casting was widespread in Europe until the 18th century, when a piece-moulding process came to predomi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in sea water, aqua regia, and chlorine. Titanium was discovered in Cornwall, Great Britain, by William Gregor in 1791 and was named by Martin Heinrich Klaproth after the Titans of Greek mythology. The element occurs within a number of minerals, principally rutile and ilmenite, which are widely distributed in the Earth's crust and lithosphere; it is found in almost all living things, as well as bodies of water, rocks, and soils. The metal is extracted from its principal mineral ores by the Kroll and Hunter processes. The most common compound, titanium dioxide, is a popular photocatalyst and is used in the manufacture of white pigments. Other compounds include titanium tetrachloride (TiCl4), a component of smoke screens and catalysts; and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile metal in a pure form. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. Gold often occurs in free elemental ( native state), as nuggets or grains, in rocks, veins, and alluvial deposits. It occurs in a solid solution series with the native element silver (as electrum), naturally alloyed with other metals like copper and palladium, and mineral inclusions such as within pyrite. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides). Gold is resistant to most acids, though it does dissolve in aqua regia (a mixture of nitric acid and hydrochloric acid), forming a soluble tetrachloroaurate anion. Gold is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sprue (manufacturing)
A sprue is the vertical passage through which liquid material is introduced into a mold and it is a large diameter channel through which the material enters the mold. It connects the pouring basin to the runner. In many cases it controls the flow of material into the mold. During casting or molding, the material in the sprue will solidify and need to be removed from the finished part. It is usually tapered downwards to minimize turbulence and formation of air bubbles. Casting In casting, a sprue is the passage through which a molten material is introduced into a mold, and the term also refers to the excess material which solidifies in the sprue passage. Function Sprues can serve as filters, as heat sinks, and as feeders. Bronze, in particular, has a high shrinkage rate as it is cooling. A sprue is tapered with its bigger end at the top to receive the liquid metal, the smaller end is connected to the runner. Sprue design The design of the sprue gating and runner is also essent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vertical Root Fracture
Vertical root fractures are a type of fracture of a tooth. They can be characterized by an incomplete or complete fracture line that extends through the long axis of the root toward the apex. Vertical root fractures represent between 2 and 5 percent of crown/root fractures. The greatest incidence occurs in endodontically treated teeth, and in patients older than 40 years of age. The occurrence of a complete vertical root fracture is often catastrophic for the individual tooth as tooth extraction is usually the only reasonable treatment. Vertical root fracture is more likely where teeth have undergone extensive prior treatment. It is thought that excessive removal of dentine during procedures such as root canal treatment weakens the tooth. For this reason excessive canal shaping should be avoided. Fracturing may be caused by excessive forces placed on the tooth, such as during compaction of gutta-percha during the obturation phase of endodontics. Trauma can also cause crack formatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fibre
Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate fibers, for example carbon fiber and ultra-high-molecular-weight polyethylene. Synthetic fibers can often be produced very cheaply and in large amounts compared to natural fibers, but for clothing natural fibers can give some benefits, such as comfort, over their synthetic counterparts. Natural fibers Natural fibers develop or occur in the fiber shape, and include those produced by plants, animals, and geological processes. They can be classified according to their origin: *Vegetable fibers are generally based on arrangements of cellulose, often with lignin: examples include cotton, hemp, jute, flax, abaca, piña, ramie, sisal, bagasse, and banana. Plant fibers are employed in the manufacture of paper and textile (cloth), and dietar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
