Tooth Demineralization: A tooth's loss of minerals, such as calcium in hydroxyapatite from the tooth matrix, caused by acidic exposure. An example of the occurrence of demineralization is in the formation of dental caries.Microradiography: Production of a radiographic image of a small or very thin object on fine-grained photographic film under conditions which permit subsequent microscopic examination or enlargement of the radiograph at linear magnifications of up to several hundred and with a resolution approaching the resolving power of the photographic emulsion (about 1000 lines per millimeter).Tooth: One of a set of bone-like structures in the mouth used for biting and chewing.Dental Enamel: A hard thin translucent layer of calcified substance which envelops and protects the dentin of the crown of the tooth. It is the hardest substance in the body and is almost entirely composed of calcium salts. Under the microscope, it is composed of thin rods (enamel prisms) held together by cementing substance, and surrounded by an enamel sheath. (From Jablonski, Dictionary of Dentistry, 1992, p286)Bone Demineralization, Pathologic: Decrease, loss, or removal of the mineral constituents of bones. Temporary loss of bone mineral content is especially associated with space flight, weightlessness, and extended immobilization. OSTEOPOROSIS is permanent, includes reduction of total bone mass, and is associated with increased rate of fractures. CALCIFICATION, PHYSIOLOGIC is the process of bone remineralizing. (From Dorland, 27th ed; Stedman, 25th ed; Nicogossian, Space Physiology and Medicine, 2d ed, pp327-33)Tooth Remineralization: Therapeutic technique for replacement of minerals in partially decalcified teeth.Cariostatic Agents: Substances that inhibit or arrest DENTAL CARIES formation. (Boucher's Clinical Dental Terminology, 4th ed)Hardness Tests: A test to determine the relative hardness of a metal, mineral, or other material according to one of several scales, such as Brinell, Mohs, Rockwell, Vickers, or Shore. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Dental Caries Activity Tests: Diagnostic tests conducted in order to measure the increment of active DENTAL CARIES over a period of time.Bone Demineralization Technique: Removal of mineral constituents or salts from bone or bone tissue. Demineralization is used as a method of studying bone strength and bone chemistry.Fluorides, Topical: Fluorides, usually in pastes or gels, used for topical application to reduce the incidence of DENTAL CARIES.Dentin: The hard portion of the tooth surrounding the pulp, covered by enamel on the crown and cementum on the root, which is harder and denser than bone but softer than enamel, and is thus readily abraded when left unprotected. (From Jablonski, Dictionary of Dentistry, 1992)Dental Caries: Localized destruction of the tooth surface initiated by decalcification of the enamel followed by enzymatic lysis of organic structures and leading to cavity formation. If left unchecked, the cavity may penetrate the enamel and dentin and reach the pulp.Tooth, Deciduous: The teeth of the first dentition, which are shed and replaced by the permanent teeth.Tooth Erosion: Progressive loss of the hard substance of a tooth by chemical processes that do not involve bacterial action. (Jablonski, Dictionary of Dentistry, 1992, p296)Root Caries: Dental caries involving the tooth root, cementum, or cervical area of the tooth.Tooth Root: The part of a tooth from the neck to the apex, embedded in the alveolar process and covered with cementum. A root may be single or divided into several branches, usually identified by their relative position, e.g., lingual root or buccal root. Single-rooted teeth include mandibular first and second premolars and the maxillary second premolar teeth. The maxillary first premolar has two roots in most cases. Maxillary molars have three roots. (Jablonski, Dictionary of Dentistry, 1992, p690)Dental Enamel Solubility: The susceptibility of the DENTAL ENAMEL to dissolution.Cariogenic Agents: Substances that promote DENTAL CARIES.Fluorides: Inorganic salts of hydrofluoric acid, HF, in which the fluorine atom is in the -1 oxidation state. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed) Sodium and stannous salts are commonly used in dentifrices.Tooth Loss: The failure to retain teeth as a result of disease or injury.Tooth Germ: The collective tissues from which an entire tooth is formed, including the DENTAL SAC; ENAMEL ORGAN; and DENTAL PAPILLA. (From Jablonski, Dictionary of Dentistry, 1992)Toothpastes: Dentifrices that are formulated into a paste form. They typically contain abrasives, HUMECTANTS; DETERGENTS; FLAVORING AGENTS; and CARIOSTATIC AGENTS.Acidulated Phosphate Fluoride: A sodium fluoride solution, paste or powder, which has been acidulated to pH 3 to 4 and buffered with a phosphate. It is used in the prevention of dental caries.Tooth Crown: The upper part of the tooth, which joins the lower part of the tooth (TOOTH ROOT) at the cervix (TOOTH CERVIX) at a line called the cementoenamel junction. The entire surface of the crown is covered with enamel which is thicker at the extremity and becomes progressively thinner toward the cervix. (From Jablonski, Dictionary of Dentistry, 1992, p216)Microscopy, Polarization: Microscopy using polarized light in which phenomena due to the preferential orientation of optical properties with respect to the vibration plane of the polarized light are made visible and correlated parameters are made measurable.Dentifrices: Any preparations used for cleansing teeth; they usually contain an abrasive, detergent, binder and flavoring agent and may exist in the form of liquid, paste or powder; may also contain medicaments and caries preventives.Radiography, Dental, Digital: A rapid, low-dose, digital imaging system using a small intraoral sensor instead of radiographic film, an intensifying screen, and a charge-coupled device. It presents the possibility of reduced patient exposure and minimal distortion, although resolution and latitude are inferior to standard dental radiography. A receiver is placed in the mouth, routing signals to a computer which images the signals on a screen or in print. It includes digitizing from x-ray film or any other detector. (From MEDLINE abstracts; personal communication from Dr. Charles Berthold, NIDR)Photography, Dental: Photographic techniques used in ORTHODONTICS; DENTAL ESTHETICS; and patient education.Hardness: The mechanical property of material that determines its resistance to force. HARDNESS TESTS measure this property.Tooth Eruption: The emergence of a tooth from within its follicle in the ALVEOLAR PROCESS of the MAXILLA or MANDIBLE into the ORAL CAVITY. (Boucher's Clinical Dental Terminology, 4th ed)Molar: The most posterior teeth on either side of the jaw, totaling eight in the deciduous dentition (2 on each side, upper and lower), and usually 12 in the permanent dentition (three on each side, upper and lower). They are grinding teeth, having large crowns and broad chewing surfaces. (Jablonski, Dictionary of Dentistry, 1992, p821)Neodymium: Neodymium. An element of the rare earth family of metals. It has the atomic symbol Nd, atomic number 60, and atomic weight 144.24, and is used in industrial applications.Erbium: Erbium. An element of the rare earth family of metals. It has the atomic symbol Er, atomic number 68, and atomic weight 167.26.