Iran Dental Basic Sciences Exam key terms

A tightly packed column of hydroxyapatite crystals running from the dentinoenamel junction toward the enamel surface, formed by one ameloblast; its cross-sectional keyhole shape and decussation pattern determine how enamel behaves under occlusal stress and acid attack.

The two-stage process in which ameloblasts first secrete a partially mineralized organic matrix and later resorb it while pumping mineral ions, yielding mature enamel that is over 95% mineral by weight and contains no collagen.

The scalloped interface where enamel meets dentin. Its interlocking contour spreads occlusal forces and resists crack propagation, and it is the reference landmark used to judge whether a cavity preparation or lesion has reached dentin.

A postmitotic, columnar cell lining the pulp periphery that secretes predentin and maintains the dentinal tubules. Its process occupies the tubule, so the cell is the final common pathway for dentin formation, dentinogenesis, and pulpal response to injury.

A narrow, S-shaped channel running from the pulp to the dentinoenamel junction, containing an odontoblast process and fluid. Fluid movement within tubules is the basis of dentin hypersensitivity and a route for bacterial penetration.

Tubular tertiary dentin deposited by surviving primary odontoblasts beneath a mild, slowly progressing stimulus such as a shallow carious lesion or attrition. It is distinguished from reparative dentin, which is atubular and secreted by newly recruited odontoblast-like cells.

Atubular, irregular dentin formed by odontoblast-like cells derived from pulp progenitor cells after severe injury destroys the original odontoblast layer; it seals the pulp but lacks the organized structure of primary or reactionary dentin.

A transient cartilaginous rod of the first pharyngeal arch around which the mandible forms by intramembranous ossification. It largely disappears, but its perichondrium contributes to the sphenomandibular ligament and its dorsal end forms malleus and incus ossicles.

One of six paired mesodermal bars on the embryonic foregut, each with its own cartilage, muscle, nerve, and aortic arch artery. The first arch gives most of the face, and arch nerve-to-muscle mapping is a standard exam target.

The motor nerve of the second pharyngeal arch, supplying the muscles of facial expression, stapedius, and posterior digastric; it also carries taste from the anterior tongue via the chorda tympani and parasympathetic fibers to salivary glands through the pterygopalatine ganglion.

The principal sensory nerve of the face and teeth, with ophthalmic, maxillary, and mandibular divisions. Its mandibular division alone carries motor fibers, supplying the muscles of mastication, mylohyoid, anterior digastric, tensor veli palatini, and tensor tympani.

A branch of the mandibular division of the trigeminal nerve that enters the mandibular canal through the mandibular foramen and supplies mandibular teeth and gingiva, exiting as the mental nerve to serve the lower lip and chin.

A branch of the mandibular division of the trigeminal nerve that carries general sensation from the anterior two-thirds of the tongue and floor of the mouth, and is joined by the chorda tympani for taste and secretomotor fibers.

A parasympathetic ganglion suspended from the lingual nerve. Preganglionic fibers arrive through the chorda tympani and synapse here, and postganglionic fibers innervate the submandibular and sublingual glands.

A bilateral synovial joint in which a fibrocartilage-covered condyle articulates with the temporal bone through an articular disc, allowing both rotation and translation; it is the only human joint with a fibrocartilaginous, not hyaline, articular surface.

The only muscle of mastication that opens the jaw; its inferior head protrudes the mandible and its superior head stabilizes the disc during closure. It is supplied by the mandibular division of the trigeminal nerve.

A rapid, all-or-none reversal of membrane potential produced when depolarization opens voltage-gated sodium channels, followed by potassium efflux and refractoriness. Its propagation along axons and muscle fibers underlies nerve conduction and excitation-contraction coupling.

The steady voltage across a cell membrane at rest, typically about -70 mV in neurons, set mainly by potassium permeability and the sodium-potassium pump. Its value determines how easily a stimulus can reach threshold.

Fast, jumping propagation of an action potential between nodes of Ranvier in myelinated axons. Because excitation is regenerated only at nodes, conduction velocity rises with axon diameter and myelin thickness and falls when myelin is lost.

The widely accepted explanation that pain from exposed dentin arises when stimuli move fluid within dentinal tubules, deforming mechanosensitive nerve endings near the pulp. Tubule occlusion and reduced fluid flow are therefore treatment goals.

The volume of plasma filtered by the kidneys per unit time, normally about 125 mL/min in adults. It is estimated from creatinine clearance or cystatin C and guides dose adjustment for renally excreted drugs such as aminoglycosides and penicillins.

The quantitative description of enzyme-catalyzed reaction rate as a function of substrate concentration, summarized by Km and Vmax. Competitive inhibitors raise apparent Km, while noncompetitive inhibitors lower Vmax; this distinguishes inhibition types on exams.

Reversible inhibition in which an inhibitor resembling the substrate binds the enzyme active site, raising apparent Km without changing Vmax. It can be overcome by increasing substrate concentration, unlike noncompetitive inhibition.

The cytoplasmic pathway converting one glucose into two pyruvate molecules with net gain of two ATP and two NADH. It supplies energy to erythrocytes and, in the absence of oxygen, to skeletal muscle, and it is the target of fluoride-mediated enolase inhibition in bacteria.

The mitochondrial cycle in which acetyl-CoA is oxidized to carbon dioxide, generating NADH, FADH2, and GTP. It is the central hub of oxidative metabolism and links carbohydrate, fat, and amino acid catabolism to the electron transport chain.

ATP synthesis driven by a proton gradient across the inner mitochondrial membrane, built by electron transport and consumed by ATP synthase. It yields most cellular ATP and is the target of uncoupling agents and cyanide.

A nonprotein molecule or ion required for enzyme activity, such as NAD+, FAD, or a metal ion. Tightly bound organic cofactors are called prosthetic groups, and many vitamins serve as precursors of coenzymes.

A water-soluble vitamin required as a cofactor for prolyl and lysyl hydroxylases in collagen synthesis. Deficiency causes scurvy with bleeding gums, poor wound healing, and tooth mobility, making it a classic dental-relevant deficiency.

A structured community of microorganisms embedded in a self-produced extracellular matrix and adherent to a surface. Its species composition shifts from Gram-positive streptococci in early plaque to Gram-negative anaerobes in mature plaque, driving caries and periodontitis.

A Gram-positive, facultatively anaerobic coccus that ferments sucrose to lactic acid and produces glucosyltransferases making sticky glucans. These properties make it a principal cariogenic organism in human dental plaque.

A Gram-negative, black-pigmented anaerobic rod and a keystone pathogen in chronic periodontitis. It expresses gingipains and fimbriae that degrade host proteins and dysregulate complement, promoting tissue destruction.

The lipopolysaccharide component of the outer membrane of Gram-negative bacteria, recognized by Toll-like receptor 4. It triggers cytokine release and inflammation and is implicated in pulpal and periodontal tissue destruction.

A multifactorial, biofilm-mediated, diet-modulated disease in which bacterial acids demineralize tooth hard tissues over time. It progresses from a subsurface enamel lesion to dentin and ultimately pulp involvement if the balance is not reversed.

Inflammation of the dental pulp, usually in response to bacterial invasion from caries, trauma, or restorative procedures. Because the pulp is enclosed by rigid dentin, edema raises tissue pressure, and the condition may be reversible or progress to irreversible necrosis.

A chronic inflammatory disease initiated by dysbiotic plaque biofilm that destroys the periodontal attachment apparatus, producing clinical attachment loss, pocket formation, and alveolar bone loss; it is a leading cause of adult tooth loss.

A group of inherited defects of enamel formation classified as hypoplastic, hypomineralized (hypocalcified), or hypomaturation types. Enamel is thin or soft and discolored, while dentin and pulp are normal, distinguishing it from dentinogenesis imperfecta.

An autosomal dominant disorder of dentin formation, usually associated with osteogenesis imperfecta, producing opalescent bluish-brown teeth with obliterated pulp chambers and short roots. Enamel is structurally normal but tends to chip off the weak dentin.

A developmental cyst of the jaws with a thin, corrugated parakeratinized lining and basal palisading, known for locally aggressive behavior and high recurrence. Multiple lesions suggest nevoid basal cell carcinoma syndrome.

A benign but locally aggressive epithelial odontogenic tumor, most often in the posterior mandible, showing islands of odontogenic epithelium with reverse polarity and stellate reticulum. It requires wide resection to prevent recurrence.

A drug that reversibly blocks voltage-gated sodium channels in nerve membranes, preventing depolarization and pain transmission. Amides such as lidocaine are metabolized in the liver, whereas esters are hydrolyzed by plasma pseudocholinesterase.

An intraoral injection that deposits local anesthetic near the mandibular foramen to anesthetize the inferior alveolar nerve and its branches. Failure is most often due to inaccurate needle placement or accessory innervation, not drug choice.

An anion that prevents caries by forming fluorapatite, enhancing remineralization, and inhibiting bacterial enolase. Topical exposure is the main mechanism of benefit; chronic excess during development causes dental fluorosis.

Presystemic elimination of an orally administered drug by gut wall and liver before it reaches systemic circulation, reducing bioavailability. Drugs with strong first-pass effects, such as lidocaine, require parenteral or alternative routes.

The study of how the body handles a drug, described by absorption, distribution, metabolism, and excretion. Key parameters include bioavailability, volume of distribution, clearance, and half-life, which together set dosing regimens.

A tooth-colored restorative material of resin matrix, silane-treated inorganic filler, and coupling agent. Filler content controls strength, wear, and shrinkage; polymerization shrinkage and its associated stress are its main clinical limitation.

Contraction that occurs as resin monomer converts to polymer, producing stress at bonded interfaces. In deep cavities with high configuration factor it can debond the restoration, cause marginal leakage, and produce postoperative sensitivity.

The process by which adhesive resins attach to dentin after acid etching or self-etching conditioning removes smear layer and exposes collagen, followed by resin infiltration into etched dentin and tubules to form a hybrid layer.

An alloy of mercury with silver, tin, copper, and zinc that sets by reaction of alloy particles with mercury. It is strong and durable but does not bond, and its corrosion products can discolor marginal tooth structure.

The portion of maxilla and mandible that houses tooth roots, consisting of alveolar bone proper (cribriform plate) and supporting trabecular bone. It forms and resorbs in response to tooth function and is lost after extraction or in periodontitis.

A dense connective tissue between the tooth root cementum and alveolar bone proper, containing principal collagen fiber bundles, vessels, and nerve endings. It suspends the tooth, transmits occlusal force, and provides proprioception.

Reduced mineral content of enamel, often from developmental disturbance or fluorosis, producing soft, opaque, or discolored areas. Affected enamel is more prone to caries and wear and bonds poorly to resin.

An odontogenic cyst that encloses the crown of an unerupted tooth and attaches at the cementoenamel junction, most often around impacted mandibular third molars. It is the most common developmental jaw cyst and can expand the bone.

A multifactorial, biofilm-mediated, diet-modulated disease in which bacterial acids demineralize tooth hard tissues over time. It progresses from a subsurface enamel lesion to dentin and ultimately pulp involvement if the balance is not reversed.