Enamel, cementum Jan Křivánek 3. 4. 2024 Enamel (enamelum, enamel, email, substantia adamantina, s. vitrea) ENAMEL (enamelum, email, substantia adamantina, s. vitrea, sklovina) - Tissue covering tooth crowns - Ectodermal origin - Hardest tissue (fragile) in the vertebrates bodies - Acelular Thickness:Permanent dentition +- 2,5 mm Primary dentition +- 1,3 mm Tooth neck +- 0,1 mm Physical properties - Refractive index: 1,62; density: 2,9 g.cm-3, - Mohs scale hardness 5 - Translucent, color – white shades – depends on thickness and mineralization degree Grey-white – occlusion sides White – middle part of crown Yellowish – near the neck (dentin bellow) High resistence to abrasion - Denser, harder and less porous in the surface (aprismatic) - Hardness is decreasing towards DEJ (dentino-enamel junction) and from top of crown towards the neck Chemical composition Inorganic 96 - 97 % • Hydroxyapatite building hexagonal crystals • Fluoroapatite (more on the surface of enamel), it is harder • Main elements: Calcium, fluoride, magnesium, phosphorus (and others). • Deposition of other elements (e.g. lead) due to environmental pollution – once depositite, always there. Water 2 - 3 % Organic 1 % NON-collagenous proteins a) Amelogenins - 90 % - Main product of ameloblasts secretory stage - Spherical polymers, regulation of enamel prisms growth b) Non-amelogenins: - Enamelin – Nucleation and direction of growth regulation of crystals - Ameloblastin – Adhesive molecule - Kalikrein 4 – Protease secreted by ameloblasts in the final sectretory stage - Tuftelin – Stabilizes connection to dentin c) Proteins with enzymatic activity - Metaloproteases (MMP20) – amelogenin degradation - Alkalic phosphatase, phosphomonoesterase and serinprotease 1 Chemical composition Inorganic 96 - 97 % Water 2 - 3 % Organic 1 % Microscopis structure Complicated and species-specific inner structure Enamel prisms (prisms and interprismatic substance), +-1 µm wide Direction: from DEJ up to the surface, approx. 8,5 milions (incisivi) Prisms ultrastructure Consists of longitudinal arranged crystals of hydroxyapatite, inserted into proteinous matrix (amelogenins, non-amelogenins) Interprizmatic substance structure is the same, but crystals are laid down under different angle Enamel decussation pattern (rodents) • Very precise and homogeneous organization of enamel microstructure • Little differences within different species • Fundamental mechanisms controlling decussation pattern formation are evolutionary conserved Daniela C. Kalthoff, 2007 Wood Mouse (Apodemus sylvaticus) Daniela C. Kalthoff Goldberg et al, 2014 Mus musculusHeterosminthus gansus (late Miocene) External characteristics of enamel Striae of Retzius Perikymata Hunter - Schreger bands Neonatal line Enamel tuffs External characteristics of enamel Hunter - Schreger bands Lynch et al., British dental journal, 2010 Course of Hunter-Schreger bands (HSB) on: the buccal side of M 2 from Ursus spelaeus (A), the buccal side of P 4 from Felis catus (B), the U. wenzensis M 2 viewed from the lingual and occlusal side (C) and the buccal side of M 1 from U. wenzensis. Nowakowski et al., 2010 • Consequence of changes in the direction of prisms • The course of enamel prisms changes in all directions, especially in premolars and molars. • Optically, they appear as alternating lighter and darker bands Incremental enamel bands The enamel grows periodically: the influence of circadian rhythms Manifestation of periodic activity of ameloblasts or joint mineralization of a larger number of daily incremental lines Based on the incremental lines, we distinguish the characteristic types of incremental bands a) Daily incremental lines - Cause prisms cross-striation, very thin (2,5 - 6 μm) - Circardial rhytms influenced - Alternation of the phase of intense secretion with the resting phase b) Stripes of Retzius (Retzium lines; enamel striae) - Can be observed under optical microscope on ground sections (25-35 μm) - From DEJ to enamel surface - Forms perikymata c) Neonatal line - A distinctive stripe of less mineralized enamel - In primary dentition and M1 - It belongs to the Retzius line - Due to abrupt change in nutrition at birth (Timothy G. Bromage et al., 2015, American Journal of Physical Anthropology; Hard Tissue Biology, Metabolomics, and Life History) Daily incremental lines Daily (circadian) growth lines, or cross-striations (short arrows) are observed between adjacent long-period (multidien) striae of Retzius (long arrows) Striae of Retzius may be seen to course across the horizontal field of view. The number of crossstriations between adjacent striae of Retzius is termed the "repeat period" (RP). (Timothy G. Bromage et al., 2015, American Journal of Physical Anthropology; Hard Tissue Biology, Metabolomics, and Life History) Swine enamel circadian and multidien rhythms. Dark banding across the horizontal field are striae of Retzius (long arrows), while 5 daily events may be seen between adjacent striae (short arrows) Daily incremental lines Striae of Retzius Striae of Retzius Perikymata Neonatal line Incremental enamel bands The enamel grows periodically: the influence of circadian rhythms Manifestation of periodic activity of ameloblasts or joint mineralization of a larger number of daily incremental lines Based on the incremental lines, we distinguish the characteristic types of incremental bands a) Daily incremental lines - Cause prisms cross-striation, very thin (2,5 - 6 μm) - Circardial rhytms influenced - Alternation of the phase of intense secretion with the resting phase b) Stripes of Retzius (Retzium lines; enamel striae) - Can be observed under optical microscope on ground sections (25-35 μm) - From DEJ to enamel surface - Forms perikymata c) Neonatal line - A distinctive stripe of less mineralized enamel - In primary dentition and M1 - It belongs to the Retzius line - Due to abrupt change in nutrition at birth Aprismatic enamel • 20-70 um wide layer on the surface of crown enamel • Harder and more mineralized. Contains more fluoride • Is formed just before the end of ameloblasts aktivity • Hydroxyapatite crystals are hightly packed and perpendicular to enamel surface DEJ (Dentino-Enamel Junction) • The boundary between the enamel and the dentin, forms the functional connection of these two hard tissues • Developmentally, it is located at the site of the (disintegrated) basal membrane of ameloblasts • It has wavy structure • Multiple small holes where enamel prisms bundles are connected Cuticula dentis (Nasmyth's membrane) • Covers a newly erupted tooth, after eruption its remnants can only be seen near the tooth neck • A thin cuticular structure - remains of the enamel organ • Formed by proteins and polysaccharides • 1 um wide, remains on the surface of primary dentition nearby the neck Enamel spindles (fuzus enameli) Up to 100 um prolongation of dentin tubules into enamel Cementum-enamel border 3 types: Cementum overlap over enamel sharp line with gap 15 % (60 %) 52 % (30 %) 33 % (10 %) Enamel regeneration Enamel do NOT regenerate! Ameloblasts became apoptotic during eruption Enamel hypoplasia Enamel is soft and fragile Etiology: • Ameloblasts damage and/or premature end of their function • Genetical disorders (amelogenesis imperfecta) • Longterm increase of fluorides income (5x higher increase of fluorides in drinking water) • Tetracykline antibiotics – incorporation into enamel during calcification • High fevers Enamel reparation Remineralization of damaged enamel by the action of saliva Age related changes in enamel - Abrasion - in more advanced stages, dentin exposure may occur - Change of chemical composition - increasing the content of fluorides, reducing of the water and organic compounds - Change in enamel pigmentation - incorporation of organic material into the enamel, dentin thickening and darkening - Permeability changes - decreases with age, crystals grow during life and the pores between them shrink Cementum (cementum, substantia petrosa) • Hard, bone-like tissue covering the root of the tooth • Yellowish color • Avascular tissue • Does NOT rebuild (in contrast to bone) • Can be resorbed by cementoclasts - during the tooth replacement • It is continuously deposited by new layers formation. Growth related to circardial rhytms – incremental lines. • Development from ectomesenchyme Composed of: • Cellular part • ECM Cementum • Collagen fibers (especially collagen 1) of periodontal ligaments, which are immersed on the one side in cementum and on the other side in the periosteum of alveolar bone • It forms a functional attachment of the tooth in the alveolus • They run all the way to acellular cementum, where they are fully mineralized Sharpey fibers Microscopic anatomy Cementocytes, Cementoblasts, (Cementoclasts) Extracellular matris (ECM) = Cementum Cementoblasts Actively involved in ECM formation Cementocytes Cells surrounded by cementous tissue, bodies placed in cavities (lacunae), processes in small tubules (similar to Osteocytes in Bone) - canaliculi cementi Cementoclasts Involved in cementum resorbation in temporary teeth Acelular (primary) Celular (secondary)Cells Cementum matrix Collagen fibres and calcified amorphous mass Collagen fibres run in bundles (orientation is determined by the forces on teeth) Cementum is divided by origin into: Primary (acellular) Does not contain cementocytes In the range of the entire tooth root Directly connected to the dentine Thickness: 10 to 200 µm Secondary (cellular) Contains cementocytes Especially on dental apexes Grows up to 500 µm thick Cementum hyperplasia (hypercementosis) Abnormal cement thickening Occurs either in single tooth/teeth or in a whole dentition (Paget's disease) The most frequent cause of hypercementosis is long-term and excessive tooth load Cementicles – in PDL Attachment of hypsodont teeth in the jaw High „crowned“ Low „crowned“ Development of hypsodont teeth in animals with highly abrasive diets. Gradual, uneven abrasion of the "crown" part. What is the crown?