Lecture 2: Dentine and Cementum 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Enamel Dentine Cementum Bone Composition of Dental Tissues as Percentages by Weight Water Organic Matrix Mineral General properties of dentine Mesenchymal in origin, less mineralised than enamel Chemical Composition of Dentine • 20% organic • Most is type I collagen • Phosphorylated phosphoproteins (phosphophoryn – this is unique to dentine) • Osteocalcin, osteonectin • Proteoglycans – similar to those in bone • Growth factors, eg bone morphogenetic protein Physical Properties of Dentine • Less hard than enamel • Has higher tensile strength than enamel • More resilient (elastic) than enamel (supports brittle enamel) • Sensitive (depends on nerves in pulp) • Pulp-dentine complex is a living organ • Can react to damage • Increases in amount with age • Porous • Structure (and physical properties) change with age Regions and Types of Dentine • Dentine types based on region – Coronal dentine • Mantle dentine • Circumpulpal dentine – Globular dentine – Intertubular dentine – Peritubular or intratubular dentine – Sclerotic dentine – Root dentine • Includes intertubular and peritubular • Granular layer of Tomes • Hyaline layer Regions and Types of Dentine • Dentine types based on time of development – Predentine – Primary dentine – Secondary dentine – Tertiary dentine • Reparative dentine • Reactionary dentine Dentinogenesis • Begins at bell stage independently in each cusp • Formed by odontoblasts – Mesenchymal – Differentiate from dental papilla – Papilla will become dental pulp – Differentiate when inner dental epithelium cells change polarity while becoming ameloblasts through cell signalling Dentinogenesis • Odontoblast secrete collagen fibres (Type III) called von Korff’s fibres at 90 degrees to edj • Begin to secrete smaller Type 1 collagen fibres parallel to edj • Odontoblast develops cell process • Secretion of matrix vesicles • Initiation of mineralisation within matrix vesicle • Crystallites burst out of vesicle and form mineralising front • Mineralising front is always behind collagen matrix front • Unmineralised area between odontoblast layer and mineralising front is called predentine Mineralisation by matrix vesicles • Small (25 – 250 nm) membrane-bound vesicle produced by odontoblast • Moves into matrix surrounding odontoblast (hence name) • Contains phospholipids that bind to calcium • Contains alkaline phosphatase that increases phosphate concentration or destroys inhibitor of mineralisation • Matrix vesicles have only been seen during mineralisation of mantle dentine • They may or may not be involved with mineralisation of circumpulpal dentine Golgi rER Fibroblast von Korff fibre Odontoblast process Matrix vesicle Dentinogenesis: mineralisation (drawing courtesy of Doug Luke) Collagen Matrix vesicles Matrix vesicles – some calcified, some not calcified Note there is no mineralisation in or near the collagen fibres, suggesting that collagen is not responsible for initiating mineralisation Crystals in matrix vesicle Dentine: oblique SEM of predentine 1 = Collagen fibres 2 = Odontoblast process 3 = Dentinal tubule Linear and Globular Mineralisation • Dentine mineralisation can be linear or globular, depending on speed of formation. • Globular – Calcospherites (globular masses of mineralised dentine) form within collagen matrix and increase in size until they fuse – when fusion incomplete, interglobular dentine forms when formation is fast. – When formation slow, mineralisation occurs gradually and mineralising front looks straight. Dentine/predentine junction Predentine has been removed and growing surface of mineralised dentine is seen using SEM Note calcospherites with dentinal tubules passing through Dentine: predentine pulp odontoblast bodies Predentine Fully mineralised dentine •Predentine is unmineralised dentine found on the growing surface of dentine •Calcospherites (mineral spheres) grow into the predentine so the predentine/dentine junction is scalloped • Globular mineralisation of dentine. • Faster rate of secretion of predentine results in calcospherite formation in advance of the mineralising front, leading to interglobular dentine formation interglobular dentine Dentine: interglobular dentine •In a region of the crown about 0.2 mm from the EDJ is usually interglobular dentine: •Leaf-like areas between spheres or globules of mineral edj • Enamel and dentine showing zone of interglobular dentine where secretion rate was fastest mantle dentine circumpulpal dentine Dentine: contains tubules with branches enamel-dentine junction (picture courtesy of Doug Luke) This is a part of a decalcified section of a tooth enamel removed by acid Enamel-dentine junction On right, the enamel has been removed and this is a high-power SEM 3D view of the edj: crater-like depressions increase the surface area of the edj and sharp edges help attachment of enamel to dentine scalloped edj in histological section E D Spindle Dentine is much more permeable than enamel Flow of red dye placed in pulp (pictures courtesy of Doug Luke) Numbers of tubules in dentine • Cross-section of 1 square mm dentine contains about 40 000 dentinal tubules – About 20 000 near enamel – About 60 000 near pulp – Because tubules are more separated near enamel and more tightly packed near pulp – More tubules per unit area near pulp and tubules are wider (2-3µm) here than near enamel (1 µm) – So permeability of dentine increases as get nearer pulp Dentine permeability increases from EDJ towards pulp (drawing courtesy of Doug Luke) Image courtesy of Charuwan Manmee Lead concentration in child’s primary molar; lead is low but increases dramatically at pulp. Ablation pits in dentine; white arrows show daily von Ebner lines 28 EDJ Circumpulpal dentine S-shaped tubules here because odontoblasts are pushed apically as dentine grows inwards towards pulp Hyaline layer – outermost layer of root dentine Mantle dentine – outermost layer of crown dentine Drawing courtesy of Doug Luke Primary (left) and secondary (right) curvature of dentinal tubules • Primary cuvature involves whole tubules seen at low power; Secondary involves single tubules at very high power magnification Dentine: peritubular dentine 1 = T.S. tubule 2 = peritubular dentine 3 = intertubular dentine • Forms on the walls of dentinal tubules • About 90 % mineral • Contains no collagen • Forms by precipitation of mixed calcium phosphates from calcium-rich dentinal fluid • Begins to form in older dentine (outer dentine) • Can fill tubule •Dentine tubules that are completely occluded with material are called sclerotic dentine. Intertubular and peritubular dentine (sections same scale) A Appearance in transverse ground section. Tubule space appears black, ringed with white highly-mineralised peritubular dentine, with grey intertubular dentine between. B Appearance in transverse demineralised section. Demineralisation has completely removed the peritubular dentine leaving a peritubular space: ‘tubule’ therefore appears wider, separated only by the intertubular dentine Peritubular dentine SEMs of dentine: odontoblast process and organic material have been removed wall of original tubules peritubular dentine (90% mineral) tubule Dentine: incremental growth lines (drawing courtesy of Doug Luke) Long-period lines (Andresen lines) – equivalent to striae of Retzius in enamel Angle at which they intersect the surface is a reflection of the rate of root extension. Differs between molars. The naming of the lines in dentine varies from book to book Short period or daily lines (von Ebner lines) – equivalent to cross striations in enamel Contour lines of Owen – due to ill health, poor diet – stress lines Incremental lines in dentine Coronal (crown) dentine is deposited at 1-2 µm per day near edj, rises to 4-5 µm per day, and then falls again approaching pulp cavity. A growth line is left in the dentine each 24 h; this is called a von Ebner line and corresponds to the cross striations in enamel. Longer period lines correspond to the striae of Retzius in enamel. These are called Andresen lines. Neonatal line in dentine Neonatal line in enamel of deciduous molar tooth Dentine: neonatal line In deciduous teeth and the first permanent molar, a neonatal line is found in dentine corresponding to the neonatal line in enamel. Contour lines of Owen Bends in tubules coincide to produce Owen line; accentuated markings that reflect a disturbance in dentine formation; correspond to accentuated lines in enamel. Secondary dentine • Normal continuation of dentine formation that occurs throughout life by the odontoblasts lining the pulp and root canals. • Irregular: found mostly on roof and floor of pulp chamber Tertiary Dentine • Reactionary or Reparative • Produced in response to stimuli – Reparative: new odontoblast-like cells induced from pulp stem cells; caries or restoration, rapid response, little structure – Reactionary: slower response from odontoblasts lining pulp, few tubules, response to attrition Dentine: response to wear Attrition has worn through the enamel of cusps (photo courtesy of Doug Luke) Slow, natural wear of the crown stimulates peritubular dentine to form so the dentine is hard, impermeable and insensitive when it is exposed. This is an important adaptation because it allows teeth to be useful even if enamel is worn away. Dentine that forms in response to attrition is reactionary tertiary dentine. Dead tracts occur when dentine is sealed off from pulp by a calcified barrier. Dentine that is formed in response to caries is called reparative tertiary dentine. (Pictures courtesy of Doug Luke) trapped air causes dark appearance in histological sections tertiary dentine calcified barrier Reactionary Tertiary Dentine Two primary incisors; left, little wear, ‘sharp’ pulp horn, little resorption – right, worn, significant root resorption, and pulp horn filled in by reactionary dentine in response to attrition Histology of the tooth root Hertwig’s epithelial root sheath (HERS) Decalcified unerupted first permanent molar from a 5-year-old child Cementoblasts are formed by descendants of undifferentiated mesenchymal cells in the dental follicle. However, HERS cells can undergo epithelial-mesenchymal transition and partially contribute to cementoblast formation. Fig. 9-1: Ten Cate’s Oral Histology Two transverse ground sections of a human tooth root (cervical and periapical region) Fig. 11.6: Berkovitz Fig. 11.7: Berkovitz Fig. 11.8: Berkovitz Cementocytes Fig. 11.13: Berkovitz Incremental growth lines in cementum Different types of cementum overlap Fig. 11.3: Berkovitz