Dentine Flashcards
Physical properties of dentine
Softer than enamel due to lower mineral content. Header than cementum and bone.
Anisotropic: Stress withstanding is directionally dependent, can withstand more pressure when tubules are perpendicular to stress
Hard but elastic —> greater compressive and flexural strength. This allows it to surround and protect pulp, and is foundation under enamel to prevent crack propagation
Permeable. Contain dentinal fluid that and transfer and dissipate occlusal force
What is the chemical composition of dentine
Mainly hydroxyapatite crystals that give compressive strength
Organic matrix 90% made up of type 1 collagen which provide elasticity and provide a scaffold for mineralisation. 10% made up of non-collagenous proteins in ECM eg osteocalcin, growth factors and cytokines that regulate dentinogenesis and tooth development
How does mineralisation of dentine occur
Matrix vesicles with high concentration of calcium and phosphate bud off osteoblasts. Alkaline phosphatase from odontoblast liberates phosphate ions from organic phosphates
Globular calcification: crystals form and break through vesicle membrane to form calcospherites. Calcospherites grow and fuse to form mineralisation front eg mantle dentin
Linear calcification: slower, more uniform rate of formation of mineralisation, apposition onto mineralisation front eg circumpulpal dentin
Compare intertubular and peritubular dentine
Intertubular dentine is found between dentine tubules and peritubular dentine is found within dentine tubules.
Intertubular dentine formed via mineralisation of dentine while peritubular dentine formed via aposition of apatite crystals on walls of tubules.
Peritubular dentine is more mineralised (hypermineralised, 40% more mineralised)
Intertubular dentine provides hardness and elasticity while peritubular dentine provides mechanical properties and durability of dentine.
What is mantle dentine
Outer layer of primary dentin in the crown synthesised at initiation of dentinogenesis, it is the first predentin that forms and matures. Collagen fibrils are perpendicular to EDJ
What is hyaline layer of hopewell smith
Outermost layer of root dentine. Bonds cementum to dentine
What is granular layer of tomes
Narrow dark layer immediately beneath hyaline layer (Seen in root not crown!!). Dentinal tubules in this area branch more profusely and loop back on themselves
What is interglobular dentine
Throughout crown and root. Below granular layer in root and below mantle dentine in crown. Separates circumpulpal and mantle dentine
Uncalcified. Formed due to incomplete fusion of calcospherites.
What is circumpulpal dentine
Central circumpulpal dentine is mineralising front, representing ongoing mineralisation
Peripheral circumpulpal dentine marks incomplete initial mineralisation
Describe enamel dentine junction
Enamel spindles, enamel tufts, enamel lamellae
Enamel spindles interlock enamel and dentine structures
Scalloped pattern beneath cusp surface, smooth on lateral surface. Scalloped surface increases surface area for bonding of enamel to dentine to prevent tissue from collapsing under masticatory forces (withstand shearing forces). Increased masticatory loads results in more pronounced scallops.
Gradual change in properties and discontinuous stress concentration at EDJ helps to prevent delamination of enamel and crack propagation.
What are the incremental lines in dentine
Lines of von ebner: alternate light and dark bands perpendicular to dentinal tubules. 4µm apart at cuspal dentine (rapid deposition), 3µm at root. Dirunal rhythym, daily increment
Andresen lines:
Perpendicular to dentinal tubules. Changes in collagen fibril orientation. Weekly rhythm of dentine formation
What are neonatal lines
Accentuated contour liens separating prenatal and postnatal dentine. This is due to variation in matrix composition due to abrupt change in environment
Seen in primary teeth and first permanent molar
Describe secondary dentine
Circumpulpal dentine formed in continuity with primary dentine (just that formed post eruptively.
Formed by downregulated odontoblasts (which have fewer RER and GA). Less regular tubular pattern with incremental markings closer together due to increased crowding of odontoblasts
Greater deposition on roof and floor of pulp chamber due to increased occlusal forces (higher stimuli for deposition)
Delineated from primary dentine by pronounced line of owen (change in direction of dentinal tubule)
What happens to dentine when it ages
It becomes translucent with physiological aging. Peritubular dentine (whitlockite crystals) completely occlude tubules. More prone to fracture than normal dentine
Describe tertiary dentine
Deposited at specific sites in response to external more severe stimuli. Increased severity of injury leads to greater rate of deposition, greater distortion of tubular pattern. Tertiary dentine is less tubular and less permeable.
Reactionary dentine is formed by upregulation of existing odontoblasts where tooth integrity is breached. Respond to mild stimulus. May be tubular.
Reparative dentine formed by newly differentiated odontoblast-like cells following death of original odontoblasts. Formed in response to strong stimulus. Usually atubular because rapidly deposited
