Bone and Bones: A specialized CONNECTIVE TISSUE that is the main constituent of the SKELETON. The principle cellular component of bone is comprised of OSTEOBLASTS; OSTEOCYTES; and OSTEOCLASTS, while FIBRILLAR COLLAGENS and hydroxyapatite crystals form the BONE MATRIX.Bone Remodeling: The continuous turnover of BONE MATRIX and mineral that involves first an increase in BONE RESORPTION (osteoclastic activity) and later, reactive BONE FORMATION (osteoblastic activity). The process of bone remodeling takes place in the adult skeleton at discrete foci. The process ensures the mechanical integrity of the skeleton throughout life and plays an important role in calcium HOMEOSTASIS. An imbalance in the regulation of bone remodeling's two contrasting events, bone resorption and bone formation, results in many of the metabolic bone diseases, such as OSTEOPOROSIS.Bone Density: The amount of mineral per square centimeter of BONE. This is the definition used in clinical practice. Actual bone density would be expressed in grams per milliliter. It is most frequently measured by X-RAY ABSORPTIOMETRY or TOMOGRAPHY, X RAY COMPUTED. Bone density is an important predictor for OSTEOPOROSIS.Bone Resorption: Bone loss due to osteoclastic activity.Bone Marrow: The soft tissue filling the cavities of bones. Bone marrow exists in two types, yellow and red. Yellow marrow is found in the large cavities of large bones and consists mostly of fat cells and a few primitive blood cells. Red marrow is a hematopoietic tissue and is the site of production of erythrocytes and granular leukocytes. Bone marrow is made up of a framework of connective tissue containing branching fibers with the frame being filled with marrow cells.Bone Neoplasms: Tumors or cancer located in bone tissue or specific BONES.Bone Development: The growth and development of bones from fetus to adult. It includes two principal mechanisms of bone growth: growth in length of long bones at the epiphyseal cartilages and growth in thickness by depositing new bone (OSTEOGENESIS) with the actions of OSTEOBLASTS and OSTEOCLASTS.Bone Marrow Cells: Cells contained in the bone marrow including fat cells (see ADIPOCYTES); STROMAL CELLS; MEGAKARYOCYTES; and the immediate precursors of most blood cells.Bone Diseases: Diseases of BONES.Bone Regeneration: Renewal or repair of lost bone tissue. It excludes BONY CALLUS formed after BONE FRACTURES but not yet replaced by hard bone.Bone Matrix: Extracellular substance of bone tissue consisting of COLLAGEN fibers, ground substance, and inorganic crystalline minerals and salts.Bone Marrow Transplantation: The transference of BONE MARROW from one human or animal to another for a variety of purposes including HEMATOPOIETIC STEM CELL TRANSPLANTATION or MESENCHYMAL STEM CELL TRANSPLANTATION.Bone Transplantation: The grafting of bone from a donor site to a recipient site.Bone Substitutes: Synthetic or natural materials for the replacement of bones or bone tissue. They include hard tissue replacement polymers, natural coral, hydroxyapatite, beta-tricalcium phosphate, and various other biomaterials. The bone substitutes as inert materials can be incorporated into surrounding tissue or gradually replaced by original tissue.Bone Diseases, MetabolicFractures, Bone: Breaks in bones.Bone Morphogenetic Proteins: Bone-growth regulatory factors that are members of the transforming growth factor-beta superfamily of proteins. They are synthesized as large precursor molecules which are cleaved by proteolytic enzymes. The active form can consist of a dimer of two identical proteins or a heterodimer of two related bone morphogenetic proteins.Bone Morphogenetic Protein 2: A potent osteoinductive protein that plays a critical role in the differentiation of osteoprogenitor cells into OSTEOBLASTS.Osteogenesis: The process of bone formation. Histogenesis of bone including ossification.Temporal Bone: Either of a pair of compound bones forming the lateral (left and right) surfaces and base of the skull which contains the organs of hearing. It is a large bone formed by the fusion of parts: the squamous (the flattened anterior-superior part), the tympanic (the curved anterior-inferior part), the mastoid (the irregular posterior portion), and the petrous (the part at the base of the skull).Parietal Bone: One of a pair of irregularly shaped quadrilateral bones situated between the FRONTAL BONE and OCCIPITAL BONE, which together form the sides of the CRANIUM.Femur: The longest and largest bone of the skeleton, it is situated between the hip and the knee.Osteoblasts: Bone-forming cells which secrete an EXTRACELLULAR MATRIX. HYDROXYAPATITE crystals are then deposited into the matrix to form bone.Alveolar Bone Loss: Resorption or wasting of the tooth-supporting bone (ALVEOLAR PROCESS) in the MAXILLA or MANDIBLE.Bone Cements: Adhesives used to fix prosthetic devices to bones and to cement bone to bone in difficult fractures. Synthetic resins are commonly used as cements. A mixture of monocalcium phosphate, monohydrate, alpha-tricalcium phosphate, and calcium carbonate with a sodium phosphate solution is also a useful bone paste.Tibia: The second longest bone of the skeleton. It is located on the medial side of the lower leg, articulating with the FIBULA laterally, the TALUS distally, and the FEMUR proximally.Bone Cysts: Benign unilocular lytic areas in the proximal end of a long bone with well defined and narrow endosteal margins. The cysts contain fluid and the cyst walls may contain some giant cells. Bone cysts usually occur in males between the ages 3-15 years.Osteoclasts: A large multinuclear cell associated with the BONE RESORPTION. An odontoclast, also called cementoclast, is cytomorphologically the same as an osteoclast and is involved in CEMENTUM resorption.Osteoporosis: Reduction of bone mass without alteration in the composition of bone, leading to fractures. Primary osteoporosis can be of two major types: postmenopausal osteoporosis (OSTEOPOROSIS, POSTMENOPAUSAL) and age-related or senile osteoporosis.Frontal Bone: The bone that forms the frontal aspect of the skull. Its flat part forms the forehead, articulating inferiorly with the NASAL BONE and the CHEEK BONE on each side of the face.Calcification, Physiologic: Process by which organic tissue becomes hardened by the physiologic deposit of calcium salts.Bone Morphogenetic Protein 7: A bone morphogenetic protein that is widely expressed during EMBRYONIC DEVELOPMENT. It is both a potent osteogenic factor and a specific regulator of nephrogenesis.Bone Marrow DiseasesOsteocalcin: Vitamin K-dependent calcium-binding protein synthesized by OSTEOBLASTS and found primarily in BONES. Serum osteocalcin measurements provide a noninvasive specific marker of bone metabolism. The protein contains three residues of the amino acid gamma-carboxyglutamic acid (Gla), which, in the presence of CALCIUM, promotes binding to HYDROXYAPATITE and subsequent accumulation in BONE MATRIX.X-Ray Microtomography: X-RAY COMPUTERIZED TOMOGRAPHY with resolution in the micrometer range.Leg Bones: The bones of the free part of the lower extremity in humans and of any of the four extremities in animals. It includes the FEMUR; PATELLA; TIBIA; and FIBULA.Bone Marrow Neoplasms: Neoplasms located in the bone marrow. They are differentiated from neoplasms composed of bone marrow cells, such as MULTIPLE MYELOMA. Most bone marrow neoplasms are metastatic.Bone Marrow Examination: Removal of bone marrow and evaluation of its histologic picture.Pelvic Bones: Bones that constitute each half of the pelvic girdle in VERTEBRATES, formed by fusion of the ILIUM; ISCHIUM; and PUBIC BONE.Metacarpal Bones: The five cylindrical bones of the METACARPUS, articulating with the CARPAL BONES proximally and the PHALANGES OF FINGERS distally.Absorptiometry, Photon: A noninvasive method for assessing BODY COMPOSITION. It is based on the differential absorption of X-RAYS (or GAMMA RAYS) by different tissues such as bone, fat and other soft tissues. The source of (X-ray or gamma-ray) photon beam is generated either from radioisotopes such as GADOLINIUM 153, IODINE 125, or Americanium 241 which emit GAMMA RAYS in the appropriate range; or from an X-ray tube which produces X-RAYS in the desired range. It is primarily used for quantitating BONE MINERAL CONTENT, especially for the diagnosis of OSTEOPOROSIS, and also in measuring BONE MINERALIZATION.Alkaline Phosphatase: An enzyme that catalyzes the conversion of an orthophosphoric monoester and water to an alcohol and orthophosphate. EC 3.1.3.1.Skull: The SKELETON of the HEAD including the FACIAL BONES and the bones enclosing the BRAIN.Bone Morphogenetic Protein 4: A bone morphogenetic protein that is a potent inducer of bone formation. It also functions as a regulator of MESODERM formation during EMBRYONIC DEVELOPMENT.Metatarsal Bones: The five long bones of the METATARSUS, articulating with the TARSAL BONES proximally and the PHALANGES OF TOES distally.Tarsal Bones: The seven bones which form the tarsus - namely, CALCANEUS; TALUS; cuboid, navicular, and the internal, middle, and external cuneiforms.Osteocytes: Mature osteoblasts that have become embedded in the BONE MATRIX. They occupy a small cavity, called lacuna, in the matrix and are connected to adjacent osteocytes via protoplasmic projections called canaliculi.Diphosphonates: Organic compounds which contain P-C-P bonds, where P stands for phosphonates or phosphonic acids. These compounds affect calcium metabolism. They inhibit ectopic calcification and slow down bone resorption and bone turnover. Technetium complexes of diphosphonates have been used successfully as bone scanning agents.Cell Differentiation: Progressive restriction of the developmental potential and increasing specialization of function that leads to the formation of specialized cells, tissues, and organs.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.Foot Bones: The TARSAL BONES; METATARSAL BONES; and PHALANGES OF TOES. The tarsal bones consists of seven bones: CALCANEUS; TALUS; cuboid; navicular; internal; middle; and external cuneiform bones. The five metatarsal bones are numbered one through five, running medial to lateral. There are 14 phalanges in each foot, the great toe has two while the other toes have three each.Ilium: The largest of three bones that make up each half of the pelvic girdle.Radius: The outer shorter of the two bones of the FOREARM, lying parallel to the ULNA and partially revolving around it.Bone Cysts, Aneurysmal: Fibrous blood-filled cyst in the bone. Although benign it can be destructive causing deformity and fractures.Technetium Tc 99m Medronate: A gamma-emitting radionuclide imaging agent used primarily in skeletal scintigraphy. Because of its absorption by a variety of tumors, it is useful for the detection of neoplasms.Bone Morphogenetic Protein 6: A bone morphogenetic protein that is a potent inducer of BONE formation. It plays additional roles in regulating CELL DIFFERENTIATION of non-osteoblastic cell types and epithelial-mesenchymal interactions.RANK Ligand: A transmembrane protein belonging to the tumor necrosis factor superfamily that specifically binds RECEPTOR ACTIVATOR OF NUCLEAR FACTOR-KAPPA B and OSTEOPROTEGERIN. It plays an important role in regulating OSTEOCLAST differentiation and activation.Mice, Inbred C57BLHematopoietic Stem Cells: Progenitor cells from which all blood cells derive.Bone Plates: Implantable fracture fixation devices attached to bone fragments with screws to bridge the fracture gap and shield the fracture site from stress as bone heals. (UMDNS, 1999)Osseointegration: The growth action of bone tissue as it assimilates surgically implanted devices or prostheses to be used as either replacement parts (e.g., hip) or as anchors (e.g., endosseous dental implants).Periosteum: Thin outer membrane that surrounds a bone. It contains CONNECTIVE TISSUE, CAPILLARIES, nerves, and a number of cell types.Arm Bones: The bones of the free part of the upper extremity including the HUMERUS; RADIUS; and ULNA.Bone Screws: Specialized devices used in ORTHOPEDIC SURGERY to repair bone fractures.Parathyroid Hormone: A polypeptide hormone (84 amino acid residues) secreted by the PARATHYROID GLANDS which performs the essential role of maintaining intracellular CALCIUM levels in the body. Parathyroid hormone increases intracellular calcium by promoting the release of CALCIUM from BONE, increases the intestinal absorption of calcium, increases the renal tubular reabsorption of calcium, and increases the renal excretion of phosphates.Facial Bones: The facial skeleton, consisting of bones situated between the cranial base and the mandibular region. While some consider the facial bones to comprise the hyoid (HYOID BONE), palatine (HARD PALATE), and zygomatic (ZYGOMA) bones, MANDIBLE, and MAXILLA, others include also the lacrimal and nasal bones, inferior nasal concha, and vomer but exclude the hyoid bone. (Jablonski, Dictionary of Dentistry, 1992, p113)Hyoid Bone: A mobile U-shaped bone that lies in the anterior part of the neck at the level of the third CERVICAL VERTEBRAE. The hyoid bone is suspended from the processes of the TEMPORAL BONES by ligaments, and is firmly bound to the THYROID CARTILAGE by muscles.Cells, Cultured: Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.Giant Cell Tumor of Bone: A bone tumor composed of cellular spindle-cell stroma containing scattered multinucleated giant cells resembling osteoclasts. The tumors range from benign to frankly malignant lesions. The tumor occurs most frequently in an end of a long tubular bone in young adults. (From Dorland, 27th ed; Stedman, 25th ed)Humerus: Bone in humans and primates extending from the SHOULDER JOINT to the ELBOW JOINT.Osteolysis: Dissolution of bone that particularly involves the removal or loss of calcium.Osteoporosis, Postmenopausal: Metabolic disorder associated with fractures of the femoral neck, vertebrae, and distal forearm. It occurs commonly in women within 15-20 years after menopause, and is caused by factors associated with menopause including estrogen deficiency.Fracture Healing: The physiological restoration of bone tissue and function after a fracture. It includes BONY CALLUS formation and normal replacement of bone tissue.Lumbar Vertebrae: VERTEBRAE in the region of the lower BACK below the THORACIC VERTEBRAE and above the SACRAL VERTEBRAE.Mesenchymal Stromal Cells: Bone-marrow-derived, non-hematopoietic cells that support HEMATOPOETIC STEM CELLS. They have also been isolated from other organs and tissues such as UMBILICAL CORD BLOOD, umbilical vein subendothelium, and WHARTON JELLY. These cells are considered to be a source of multipotent stem cells because they include subpopulations of mesenchymal stem cells.Diaphyses: The shaft of long bones.Bone Marrow Purging: Techniques for the removal of subpopulations of cells (usually residual tumor cells) from the bone marrow ex vivo before it is infused. The purging is achieved by a variety of agents including pharmacologic agents, biophysical agents (laser photoirradiation or radioisotopes) and immunologic agents. Bone marrow purging is used in both autologous and allogeneic BONE MARROW TRANSPLANTATION.Osteoprotegerin: A secreted member of the TNF receptor superfamily that negatively regulates osteoclastogenesis. It is a soluble decoy receptor of RANK LIGAND that inhibits both CELL DIFFERENTIATION and function of OSTEOCLASTS by inhibiting the interaction between RANK LIGAND and RECEPTOR ACTIVATOR OF NUCLEAR FACTOR-KAPPA B.Femur Neck: The constricted portion of the thigh bone between the femur head and the trochanters.Biomechanical Phenomena: The properties, processes, and behavior of biological systems under the action of mechanical forces.Hand Bones: The CARPAL BONES; METACARPAL BONES; and FINGER PHALANGES. In each hand there are eight carpal bones, five metacarpal bones, and 14 phalanges.Collagen Type I: The most common form of fibrillar collagen. It is a major constituent of bone (BONE AND BONES) and SKIN and consists of a heterotrimer of two alpha1(I) and one alpha2(I) chains.Spine: The spinal or vertebral column.Bone Diseases, Infectious: Bone diseases caused by pathogenic microorganisms.Occipital Bone: Part of the back and base of the CRANIUM that encloses the FORAMEN MAGNUM.Petrous Bone: The dense rock-like part of temporal bone that contains the INNER EAR. Petrous bone is located at the base of the skull. Sometimes it is combined with the MASTOID PROCESS and called petromastoid part of temporal bone.Tomography, X-Ray Computed: Tomography using x-ray transmission and a computer algorithm to reconstruct the image.Osteitis Deformans: A disease marked by repeated episodes of increased bone resorption followed by excessive attempts at repair, resulting in weakened, deformed bones of increased mass. The resultant architecture of the bone assumes a mosaic pattern in which the fibers take on a haphazard pattern instead of the normal parallel symmetry.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Integrin-Binding Sialoprotein: A highly glycosylated and sulfated phosphoprotein that is found almost exclusively in mineralized connective tissues. It is an extracellular matrix protein that binds to hydroxyapatite through polyglutamic acid sequences and mediates cell attachment through an RGD sequence.Ulna: The inner and longer bone of the FOREARM.Weight-Bearing: The physical state of supporting an applied load. This often refers to the weight-bearing bones or joints that support the body's weight, especially those in the spine, hip, knee, and foot.Alveolar Process: The thickest and spongiest part of the maxilla and mandible hollowed out into deep cavities for the teeth.Minerals: Native, inorganic or fossilized organic substances having a definite chemical composition and formed by inorganic reactions. They may occur as individual crystals or may be disseminated in some other mineral or rock. (Grant & Hackh's Chemical Dictionary, 5th ed; McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Metacarpus: The region of the HAND between the WRIST and the FINGERS.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)Calcium Phosphates: Calcium salts of phosphoric acid. These compounds are frequently used as calcium supplements.Mandible: The largest and strongest bone of the FACE constituting the lower jaw. It supports the lower teeth.Alendronate: A nonhormonal medication for the treatment of postmenopausal osteoporosis in women. This drug builds healthy bone, restoring some of the bone loss as a result of osteoporosis.Bone Banks: Centers for acquiring, characterizing, and storing bones or bone tissue for future use.Haversian System: A circular structural unit of bone tissue. It consists of a central hole, the Haversian canal through which blood vessels run, surrounded by concentric rings, called lamellae.Transplantation, Homologous: Transplantation between individuals of the same species. Usually refers to genetically disparate individuals in contradistinction to isogeneic transplantation for genetically identical individuals.Hematopoiesis: The development and formation of various types of BLOOD CELLS. Hematopoiesis can take place in the BONE MARROW (medullary) or outside the bone marrow (HEMATOPOIESIS, EXTRAMEDULLARY).Mice, Knockout: Strains of mice in which certain GENES of their GENOMES have been disrupted, or "knocked-out". To produce knockouts, using RECOMBINANT DNA technology, the normal DNA sequence of the gene being studied is altered to prevent synthesis of a normal gene product. Cloned cells in which this DNA alteration is successful are then injected into mouse EMBRYOS to produce chimeric mice. The chimeric mice are then bred to yield a strain in which all the cells of the mouse contain the disrupted gene. Knockout mice are used as EXPERIMENTAL ANIMAL MODELS for diseases (DISEASE MODELS, ANIMAL) and to clarify the functions of the genes.3-Oxo-5-alpha-Steroid 4-Dehydrogenase: An enzyme that catalyzes the reduction of TESTOSTERONE to 5-ALPHA DIHYDROTESTOSTERONE.Bone Morphogenetic Protein 3: A bone morphogenetic protein that is found at high concentrations in a purified osteoinductive protein fraction from BONE. Bone morphogenetic protein 3 is referred to as osteogenin, however it may play a role in variety of developmental processes.Sesamoid Bones: Nodular bones which lie within a tendon and slide over another bony surface. The PATELLA (kneecap) is a sesamoid bone.Etidronic Acid: A diphosphonate which affects calcium metabolism. It inhibits ectopic calcification and slows down bone resorption and bone turnover.Pubic Bone: A bone that forms the lower and anterior part of each side of the hip bone.Stress, Mechanical: A purely physical condition which exists within any material because of strain or deformation by external forces or by non-uniform thermal expansion; expressed quantitatively in units of force per unit area.Bone Morphogenetic Protein Receptors, Type I: A subtype of bone morphogenetic protein receptors with high affinity for BONE MORPHOGENETIC PROTEINS. They can interact with and undergo PHOSPHORYLATION by BONE MORPHOGENETIC PROTEIN RECEPTORS, TYPE II. They signal primarily through RECEPTOR-REGULATED SMAD PROTEINS.Compressive Strength: The maximum compression a material can withstand without failure. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed, p427)Disease Models, Animal: Naturally occurring or experimentally induced animal diseases with pathological processes sufficiently similar to those of human diseases. They are used as study models for human diseases.Ovariectomy: The surgical removal of one or both ovaries.Biological Markers: Measurable and quantifiable biological parameters (e.g., specific enzyme concentration, specific hormone concentration, specific gene phenotype distribution in a population, presence of biological substances) which serve as indices for health- and physiology-related assessments, such as disease risk, psychiatric disorders, environmental exposure and its effects, disease diagnosis, metabolic processes, substance abuse, pregnancy, cell line development, epidemiologic studies, etc.Transplantation, Autologous: Transplantation of an individual's own tissue from one site to another site.Bone Nails: Rods of bone, metal, or other material used for fixation of the fragments or ends of fractured bones.Cartilage: A non-vascular form of connective tissue composed of CHONDROCYTES embedded in a matrix that includes CHONDROITIN SULFATE and various types of FIBRILLAR COLLAGEN. There are three major types: HYALINE CARTILAGE; FIBROCARTILAGE; and ELASTIC CARTILAGE.Calcaneus: The largest of the TARSAL BONES which is situated at the lower and back part of the FOOT, forming the HEEL.Osteomalacia: Disorder caused by an interruption of the mineralization of organic bone matrix leading to bone softening, bone pain, and weakness. It is the adult form of rickets resulting from disruption of VITAMIN D; PHOSPHORUS; or CALCIUM homeostasis.Mice, Transgenic: Laboratory mice that have been produced from a genetically manipulated EGG or EMBRYO, MAMMALIAN.Osteosclerosis: An abnormal hardening or increased density of bone tissue.Bony Callus: The bony deposit formed between and around the broken ends of BONE FRACTURES during normal healing.Bone Morphogenetic Protein Receptors: A family of CELL SURFACE RECEPTORS that bind BONE MORPHOGENETIC PROTEINS. They are PROTEIN-SERINE-THREONINE KINASES that mediate SIGNAL TRANSDUCTION PATHWAYS through SMAD PROTEINS.Renal Osteodystrophy: Decalcification of bone or abnormal bone development due to chronic KIDNEY DISEASES, in which 1,25-DIHYDROXYVITAMIN D3 synthesis by the kidneys is impaired, leading to reduced negative feedback on PARATHYROID HORMONE. The resulting SECONDARY HYPERPARATHYROIDISM eventually leads to bone disorders.Epiphyses: The head of a long bone that is separated from the shaft by the epiphyseal plate until bone growth stops. At that time, the plate disappears and the head and shaft are united.Scaphoid Bone: The bone which is located most lateral in the proximal row of CARPAL BONES.Tissue Scaffolds: Cell growth support structures composed of BIOCOMPATIBLE MATERIALS. They are specially designed solid support matrices for cell attachment in TISSUE ENGINEERING and GUIDED TISSUE REGENERATION uses.Collagen: A polypeptide substance comprising about one third of the total protein in mammalian organisms. It is the main constituent of SKIN; CONNECTIVE TISSUE; and the organic substance of bones (BONE AND BONES) and teeth (TOOTH).Calcium, Dietary: Calcium compounds used as food supplements or in food to supply the body with calcium. Dietary calcium is needed during growth for bone development and for maintenance of skeletal integrity later in life to prevent osteoporosis.Acid Phosphatase: An enzyme that catalyzes the conversion of an orthophosphoric monoester and water to an alcohol and orthophosphate. EC 3.1.3.2.Stem Cells: Relatively undifferentiated cells that retain the ability to divide and proliferate throughout postnatal life to provide progenitor cells that can differentiate into specialized cells.Treatment Outcome: Evaluation undertaken to assess the results or consequences of management and procedures used in combating disease in order to determine the efficacy, effectiveness, safety, and practicability of these interventions in individual cases or series.Bone Conduction: Transmission of sound waves through vibration of bones in the SKULL to the inner ear (COCHLEA). By using bone conduction stimulation and by bypassing any OUTER EAR or MIDDLE EAR abnormalities, hearing thresholds of the cochlea can be determined. Bone conduction hearing differs from normal hearing which is based on air conduction stimulation via the EAR CANAL and the TYMPANIC MEMBRANE.Phosphorus: A non-metal element that has the atomic symbol P, atomic number 15, and atomic weight 31. It is an essential element that takes part in a broad variety of biochemical reactions.Receptor Activator of Nuclear Factor-kappa B: A tumor necrosis factor receptor family member that is specific for RANK LIGAND and plays a role in bone homeostasis by regulating osteoclastogenesis. It is also expressed on DENDRITIC CELLS where it plays a role in regulating dendritic cell survival. Signaling by the activated receptor occurs through its association with TNF RECEPTOR-ASSOCIATED FACTORS.Biocompatible Materials: Synthetic or natural materials, other than DRUGS, that are used to replace or repair any body TISSUES or bodily function.Flow Cytometry: Technique using an instrument system for making, processing, and displaying one or more measurements on individual cells obtained from a cell suspension. Cells are usually stained with one or more fluorescent dyes specific to cell components of interest, e.g., DNA, and fluorescence of each cell is measured as it rapidly transverses the excitation beam (laser or mercury arc lamp). Fluorescence provides a quantitative measure of various biochemical and biophysical properties of the cell, as well as a basis for cell sorting. Other measurable optical parameters include light absorption and light scattering, the latter being applicable to the measurement of cell size, shape, density, granularity, and stain uptake.Ossification, Heterotopic: The development of bony substance in normally soft structures.Growth Plate: The area between the EPIPHYSIS and the DIAPHYSIS within which bone growth occurs.Core Binding Factor Alpha 1 Subunit: A transcription factor that dimerizes with CORE BINDING FACTOR BETA SUBUNIT to form core binding factor. It contains a highly conserved DNA-binding domain known as the runt domain and is involved in genetic regulation of skeletal development and CELL DIFFERENTIATION.Tissue Engineering: Generating tissue in vitro for clinical applications, such as replacing wounded tissues or impaired organs. The use of TISSUE SCAFFOLDING enables the generation of complex multi-layered tissues and tissue structures.Multiple Myeloma: A malignancy of mature PLASMA CELLS engaging in monoclonal immunoglobulin production. It is characterized by hyperglobulinemia, excess Bence-Jones proteins (free monoclonal IMMUNOGLOBULIN LIGHT CHAINS) in the urine, skeletal destruction, bone pain, and fractures. Other features include ANEMIA; HYPERCALCEMIA; and RENAL INSUFFICIENCY.Implants, Experimental: Artificial substitutes for body parts and materials inserted into organisms during experimental studies.Osteosarcoma: A sarcoma originating in bone-forming cells, affecting the ends of long bones. It is the most common and most malignant of sarcomas of the bones, and occurs chiefly among 10- to 25-year-old youths. (From Stedman, 25th ed)Sphenoid Bone: An irregular unpaired bone situated at the SKULL BASE and wedged between the frontal, temporal, and occipital bones (FRONTAL BONE; TEMPORAL BONE; OCCIPITAL BONE). Sphenoid bone consists of a median body and three pairs of processes resembling a bat with spread wings. The body is hollowed out in its inferior to form two large cavities (SPHENOID SINUS).Porosity: Condition of having pores or open spaces. This often refers to bones, bone implants, or bone cements, but can refer to the porous state of any solid substance.Bones of Upper Extremity: The bones of the upper and lower ARM. They include the CLAVICLE and SCAPULA.Bones of Lower Extremity: The bones of the upper and lower LEG. They include the PELVIC BONES.Calcium: A basic element found in nearly all organized tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.Fractures, Spontaneous: Fractures occurring as a result of disease of a bone or from some undiscoverable cause, and not due to trauma. (Dorland, 27th ed)Osteopetrosis: Excessive formation of dense trabecular bone leading to pathological fractures; OSTEITIS; SPLENOMEGALY with infarct; ANEMIA; and extramedullary hemopoiesis (HEMATOPOIESIS, EXTRAMEDULLARY).Bone Morphogenetic Protein 5: A bone morphogenetic protein that may play a role in CARTILAGE formation. It is a potent regulator of the growth of CHONDROCYTES and the synthesis of cartilage matrix proteins. Evidence for its role in cartilage formation can be seen in MICE, where genetic mutations that cause loss of bone morphogenetic protein 5 function result in the formation of small malformed ears.Femoral Fractures: Fractures of the femur.Osteogenesis, Distraction: Bone lengthening by gradual mechanical distraction. An external fixation device produces the distraction across the bone plate. The technique was originally applied to long bones but in recent years the method has been adapted for use with mandibular implants in maxillofacial surgery.Cell Proliferation: All of the processes involved in increasing CELL NUMBER including CELL DIVISION.Dental Implants: Biocompatible materials placed into (endosseous) or onto (subperiosteal) the jawbone to support a crown, bridge, or artificial tooth, or to stabilize a diseased tooth.Mice, Inbred BALB CHip: The projecting part on each side of the body, formed by the side of the pelvis and the top portion of the femur.Radiation Chimera: An organism whose body contains cell populations of different genotypes as a result of the TRANSPLANTATION of donor cells after sufficient ionizing radiation to destroy the mature recipient's cells which would otherwise reject the donor cells.Ribs: A set of twelve curved bones which connect to the vertebral column posteriorly, and terminate anteriorly as costal cartilage. Together, they form a protective cage around the internal thoracic organs.Immunohistochemistry: Histochemical localization of immunoreactive substances using labeled antibodies as reagents.Fibula: The bone of the lower leg lateral to and smaller than the tibia. In proportion to its length, it is the most slender of the long bones.Whole-Body Irradiation: Irradiation of the whole body with ionizing or non-ionizing radiation. It is applicable to humans or animals but not to microorganisms.Cell Lineage: The developmental history of specific differentiated cell types as traced back to the original STEM CELLS in the embryo.Tibial FracturesRNA, Messenger: RNA sequences that serve as templates for protein synthesis. Bacterial mRNAs are generally primary transcripts in that they do not require post-transcriptional processing. Eukaryotic mRNA is synthesized in the nucleus and must be exported to the cytoplasm for translation. Most eukaryotic mRNAs have a sequence of polyadenylic acid at the 3' end, referred to as the poly(A) tail. The function of this tail is not known for certain, but it may play a role in the export of mature mRNA from the nucleus as well as in helping stabilize some mRNA molecules by retarding their degradation in the cytoplasm.Bone Morphogenetic Protein Receptors, Type II: A subtype of bone morphogenetic protein receptors with low affinity for BONE MORPHOGENETIC PROTEINS. They are constitutively active PROTEIN-SERINE-THREONINE KINASES that can interact with and phosphorylate TYPE I BONE MORPHOGENETIC PROTEIN RECEPTORS.Reverse Transcriptase Polymerase Chain Reaction: A variation of the PCR technique in which cDNA is made from RNA via reverse transcription. The resultant cDNA is then amplified using standard PCR protocols.Tooth Socket: A hollow part of the alveolar process of the MAXILLA or MANDIBLE where each tooth fits and is attached via the periodontal ligament.Sialoglycoproteins: Glycoproteins which contain sialic acid as one of their carbohydrates. They are often found on or in the cell or tissue membranes and participate in a variety of biological activities.Transforming Growth Factor beta: A factor synthesized in a wide variety of tissues. It acts synergistically with TGF-alpha in inducing phenotypic transformation and can also act as a negative autocrine growth factor. TGF-beta has a potential role in embryonal development, cellular differentiation, hormone secretion, and immune function. TGF-beta is found mostly as homodimer forms of separate gene products TGF-beta1, TGF-beta2 or TGF-beta3. Heterodimers composed of TGF-beta1 and 2 (TGF-beta1.2) or of TGF-beta2 and 3 (TGF-beta2.3) have been isolated. The TGF-beta proteins are synthesized as precursor proteins.Titanium: A dark-gray, metallic element of widespread distribution but occurring in small amounts; atomic number, 22; atomic weight, 47.90; symbol, Ti; specific gravity, 4.5; used for fixation of fractures. (Dorland, 28th ed)Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.Bone Morphogenetic Protein 1: A bone morphogenetic protein family member that includes an active tolloid-like metalloproteinase domain. The metalloproteinase activity of bone morphogenetic protein 1 is specific for the removal of the C-propeptide of PROCOLLAGEN and may act as a regulator of EXTRACELLULAR MATRIX deposition. Alternative splicing of MRNA for bone morphogenetic protein 1 results in the production of several PROTEIN ISOFORMS.Osteitis: Inflammation of the bone.Femur Head: The hemispheric articular surface at the upper extremity of the thigh bone. (Stedman, 26th ed)Prostheses and Implants: Artificial substitutes for body parts, and materials inserted into tissue for functional, cosmetic, or therapeutic purposes. Prostheses can be functional, as in the case of artificial arms and legs, or cosmetic, as in the case of an artificial eye. Implants, all surgically inserted or grafted into the body, tend to be used therapeutically. IMPLANTS, EXPERIMENTAL is available for those used experimentally.Finite Element Analysis: A computer based method of simulating or analyzing the behavior of structures or components.Curettage: A scraping, usually of the interior of a cavity or tract, for removal of new growth or other abnormal tissue, or to obtain material for tissue diagnosis. It is performed with a curet (curette), a spoon-shaped instrument designed for that purpose. (From Stedman, 25th ed & Dorland, 27th ed)Mesenchymal Stem Cell Transplantation: Transfer of MESENCHYMAL STEM CELLS between individuals within the same species (TRANSPLANTATION, HOMOLOGOUS) or transfer within the same individual (TRANSPLANTATION, AUTOLOGOUS).Femoral NeoplasmsFractures, Ununited: A fracture in which union fails to occur, the ends of the bone becoming rounded and eburnated, and a false joint occurs. (Stedman, 25th ed)Aging: The gradual irreversible changes in structure and function of an organism that occur as a result of the passage of time.Follow-Up Studies: Studies in which individuals or populations are followed to assess the outcome of exposures, procedures, or effects of a characteristic, e.g., occurrence of disease.Decalcification Technique: Removal of minerals from bones during bone examination.Osteopontin: A negatively-charged extracellular matrix protein that plays a role in the regulation of BONE metabolism and a variety of other biological functions. Cell signaling by osteopontin may occur through a cell adhesion sequence that recognizes INTEGRIN ALPHA-V BETA-3.Vitamin D: A vitamin that includes both CHOLECALCIFEROLS and ERGOCALCIFEROLS, which have the common effect of preventing or curing RICKETS in animals. It can also be viewed as a hormone since it can be formed in SKIN by action of ULTRAVIOLET RAYS upon the precursors, 7-dehydrocholesterol and ERGOSTEROL, and acts on VITAMIN D RECEPTORS to regulate CALCIUM in opposition to PARATHYROID HORMONE.Mandibular DiseasesOsteonecrosis: Death of a bone or part of a bone, either atraumatic or posttraumatic.Antigens, CD34: Glycoproteins found on immature hematopoietic cells and endothelial cells. They are the only molecules to date whose expression within the blood system is restricted to a small number of progenitor cells in the bone marrow.Graft vs Host Disease: The clinical entity characterized by anorexia, diarrhea, loss of hair, leukopenia, thrombocytopenia, growth retardation, and eventual death brought about by the GRAFT VS HOST REACTION.Retrospective Studies: Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons.Ceramics: Products made by baking or firing nonmetallic minerals (clay and similar materials). In making dental restorations or parts of restorations the material is fused porcelain. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed & Boucher's Clinical Dental Terminology, 4th ed)Body Weight: The mass or quantity of heaviness of an individual. It is expressed by units of pounds or kilograms.Hyperostosis: Increase in the mass of bone per unit volume.Wound Healing: Restoration of integrity to traumatized tissue.Macrophages: The relatively long-lived phagocytic cell of mammalian tissues that are derived from blood MONOCYTES. Main types are PERITONEAL MACROPHAGES; ALVEOLAR MACROPHAGES; HISTIOCYTES; KUPFFER CELLS of the liver; and OSTEOCLASTS. They may further differentiate within chronic inflammatory lesions to EPITHELIOID CELLS or may fuse to form FOREIGN BODY GIANT CELLS or LANGHANS GIANT CELLS. (from The Dictionary of Cell Biology, Lackie and Dow, 3rd ed.)Anemia, Aplastic: A form of anemia in which the bone marrow fails to produce adequate numbers of peripheral blood elements.Rats, Sprague-Dawley: A strain of albino rat used widely for experimental purposes because of its calmness and ease of handling. It was developed by the Sprague-Dawley Animal Company.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).