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Compomers
Dental compomers, also known as polyacid-modified resin composite, are used in dentistry as a filling material. They were introduced in the early 1990s as a hybrid of two other dental materials, dental composites and glass ionomer cement, in an effort to combine their desirable properties: aesthetics for dental composites (they are white and closely mimic tooth tissue, so can camouflage into a tooth very well) and the fluoride releasing ability for glass ionomer cements (helps to prevent further tooth decay). History Compomers were introduced in the early 1990s. Previous available restorative materials included dental amalgam, glass ionomer cement, resin modified glass ionomer cement and dental composites. Composition Compomers are resin-based materials like dental composites, and the components are largely the same. The setting reaction is similarly a polymerisation process of resin monomers (e.g. urethane dimethacrylate) which have been modified by polyacid groups, and is indu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dental Restoration
Dental restoration, dental fillings, or simply fillings are treatments used to restore the function, integrity, and morphology of missing tooth structure resulting from caries or external trauma as well as to the replacement of such structure supported by dental implants. They are of two broad types—''direct'' and ''indirect''—and are further classified by location and size. A root canal filling, for example, is a restorative technique used to fill the space where the dental pulp normally resides. Tooth preparation Restoring a tooth to good form and function requires two steps: # preparing the tooth for placement of restorative material or materials, and # placement of these materials. The process of preparation usually involves cutting the tooth with a rotary dental handpiece and dental burrs, a dental laser, or though air abrasion to make space for the planned restorative materials and to remove any dental decay or portions of the tooth that are structurally unsound. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dental Restorative Material
Dental products are specially fabricated materials, designed for use in dentistry. There are many different types of dental products, and their characteristics vary according to their intended purpose. Temporary dressings A temporary dressing is a dental filling which is not intended to last in the long term. They are interim materials which may have therapeutic properties. A common use of temporary dressing occurs if root canal therapy is carried out over more than one appointment. In between each visit, the pulp canal system must be protected from contamination from the oral cavity, and a temporary filling is placed in the access cavity. Examples include: * Zinc oxide eugenol—bactericidal, cheap and easy to remove. Eugenol is derived from oil of cloves, and has an obtundant effect on the tooth and decreases toothache. It is suitable temporary material providing there are no biting forces on it. It is also contraindicated if the final restorative material is composite be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glass Ionomer Cement
A glass ionomer cement (GIC) is a dental restorative material used in dentistry as a filling material and luting cement, including for orthodontic bracket attachment. Glass-ionomer cements are based on the reaction of silicate glass-powder (calciumaluminofluorosilicate glass) and polyacrylic acid, an ionomer. Occasionally water is used instead of an acid, altering the properties of the material and its uses. This reaction produces a powdered cement of glass particles surrounded by matrix of fluoride elements and is known chemically as glass polyalkenoate. There are other forms of similar reactions which can take place, for example, when using an aqueous solution of acrylic/ itaconic copolymer with tartaric acid, this results in a glass-ionomer in liquid form. An aqueous solution of maleic acid polymer or maleic/acrylic copolymer with tartaric acid can also be used to form a glass-ionomer in liquid form. Tartaric acid plays a significant part in controlling the setting characteri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tensile Strength
Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials the ultimate tensile strength is close to the yield point, whereas in ductile materials the ultimate tensile strength can be higher. The ultimate tensile strength is usually found by performing a tensile test and recording the engineering stress versus strain. The highest point of the stress–strain curve is the ultimate tensile strength and has units of stress. The equivalent point for the case of compression, instead of tension, is called the compressive strength. Tensile strengths are rarely of any consequence in the design of ductile members, but they are important with brittle members. They are tabulated for common materials such as alloys, composite materials, ceramics, plastics, and wood. Definition The ultimate tensile ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver and was formerly named hydrargyrum ( ) from the Greek words, ''hydor'' (water) and ''argyros'' (silver). A heavy, silvery d-block element, mercury is the only metallic element that is known to be liquid at standard temperature and pressure; the only other element that is liquid under these conditions is the halogen bromine, though metals such as caesium, gallium, and rubidium melt just above room temperature. Mercury occurs in deposits throughout the world mostly as cinnabar ( mercuric sulfide). The red pigment vermilion is obtained by grinding natural cinnabar or synthetic mercuric sulfide. Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float valves, mercury switches, mercury relays, fluorescent lamps and other devices, though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dental Cement
Dental cements have a wide range of dental and orthodontic applications. Common uses include temporary restoration of teeth, cavity linings to provide pulpal protection, sedation or insulation and cementing fixed prosthodontic appliances. Recent uses of dental cement also include two-photon calcium imaging of neuronal activity in brains of animal models in basic experimental neuroscience. Traditional cements have separate powder and liquid components which are manually mixed to form a viscous liquid. The liquid sets to form a brittle solid after application on the treated surface. More advanced cements, such as GIC, can come in capsules and are mechanically mixed using rotating or oscillating mixing machines. Ideal cement properties * Non irritant – many cements are acidic and irritate the pulp. However, on setting there is a rapid increase in pH. Polycarboxylate cement is considered the most biocompatible type due to having the most rapid pH rise. * Provide a good marginal se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Compressive Strength
In mechanics, compressive strength or compression strength is the capacity of a material or structure to withstand loads tending to reduce size (as opposed to tensile strength which withstands loads tending to elongate). In other words, compressive strength resists compression (being pushed together), whereas tensile strength resists tension (being pulled apart). In the study of strength of materials, tensile strength, compressive strength, and shear strength can be analyzed independently. Some materials fracture at their compressive strength limit; others deform irreversibly, so a given amount of deformation may be considered as the limit for compressive load. Compressive strength is a key value for design of structures. Compressive strength is often measured on a universal testing machine. Measurements of compressive strength are affected by the specific test method and conditions of measurement. Compressive strengths are usually reported in relationship to a specific ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flexural Strength
Flexural strength, also known as modulus of rupture, or bend strength, or transverse rupture strength is a material property, defined as the stress in a material just before it yields in a flexure test. The transverse bending test is most frequently employed, in which a specimen having either a circular or rectangular cross-section is bent until fracture or yielding using a three-point flexural test technique. The flexural strength represents the highest stress experienced within the material at its moment of yield. It is measured in terms of stress, here given the symbol \sigma. Introduction When an object is formed of a single material, like a wooden beam or a steel rod, is bent (Fig. 1), it experiences a range of stresses across its depth (Fig. 2). At the edge of the object on the inside of the bend (concave face) the stress will be at its maximum compressive stress value. At the outside of the bend (convex face) the stress will be at its maximum tensile value. These ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wear Resistance
Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in machine elements, together with other processes such as fatigue and creep, causes functional surfaces to degrade, eventually leading to material failure or loss of functionality. Thus, wear has large economic relevance as first outlined in the Jost Report. Abrasive wear alone has been estimated to cost 1-4% of the gross national product of industrialized nations. Wear of metals occurs by plastic displacement of surface and near-surface material and by detachment of particles that form wear debris. The particle size may vary from millimeters to nanometers. This process may occur by contact with other metals, nonmetallic solids, flowing liquids, solid particles or liquid droplets entrained in flowing gasses. The wear rate is affected by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dental Caries
Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complications may include inflammation of the tissue around the tooth, tooth loss and infection or abscess formation. The cause of cavities is acid from bacteria dissolving the hard tissues of the teeth ( enamel, dentin and cementum). The acid is produced by the bacteria when they break down food debris or sugar on the tooth surface. Simple sugars in food are these bacteria's primary energy source and thus a diet high in simple sugar is a risk factor. If mineral breakdown is greater than build up from sources such as saliva, caries results. Risk factors include conditions that result in less saliva such as: diabetes mellitus, Sjögren syndrome and some medications. Medications that decrease saliva production include antihistamines and anti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
