5. SUPPORTING STRUCTURE prof Tilak2024.pdf
- 1. Structure and function of Dental hard tissues and Tooth supporting structures Professor WM Tilakaratne BDS, MS, FDSRCS, FRCPath, PhD
- 2. Learning outcomes Understand the structure of dental hard tissues and tooth supporting structures Review properties of tooth supporting structures. Relate the significance of various structures to clinical dentistry Summarize the age changes in dental hard tissues
- 3. Enamel • Enamel is the protective covering of the tooth and the hardest tissue in the human body secreted by ameloblasts. These cells are lost after enamel formation hence no renewal of enamel.
- 4. Ameloblasts • Secrete matrix proteins which are responsible for creating extracellular environment favourable for mineral deposition. • Shows a unique life cycle with different phenotypic changes according to the stage of development.
- 5. Chemical composition of enamel • Inorganic: 96% (Permanent), 93% (Deciduous) • Mineral composition: Hydroxyapatite, Fluoapatite and carbonate apatite • Intercrystalline spaces: Amorphous calcium carbonate, Mn, Zn, Cu, Mg, Al etc
- 6. Enamel Proteins (Organic matrix) • Amelogenin • Ameloblastin • Enamelin • Tuftlin • Other macromolecules: Phosphoproteins, glycoproteins, sialoproteins • Enzymes: MMPs, Phosphatases, Serine proteinase
- 7. Morphology of enamel • Enamel rods • Enamel inter-rod space • Rod sheath • Striae of Retzius • Hunter-Schreger bands • Cross striation of rods • Gnarled enamel • DEJ and enamel spindles • Enamel lamellae and tufts • Surface enamel
- 8. Striae of Retzuis Striae of Retzuis represents incremental growth. In ground cross sections they appear like concentric growth rings similar to those found in trees. In ground longitudinal sections they appear to be dark lines extending from the DEJ to the tooth surface, where they end in shallow furrows known as perikymata (or
- 9. Enamel Tufts, Lamellae and Spindles • Enamel tufts originate from the DEJ, run a short distance in the enamel. They represent protein (enamelin) rich areas in the enamel matrix that fail to mature. They are formed during the formative stages of enamel. • Lamellae extend from the enamel surface toward the dentinoenamel junction and may sometimes extend to dentin. Consist of organic material, with little mineral content. Usually developed in planes of tension. • Enamel spindles originate from odontoblastic process which cross the DEJ. Before enamel forms, some developing odontoblastic processes extend into the ameloblast layer, and when enamel formation begins become trapped to form enamel spindles.
- 10. A: Lamellae B: Tufts A: Spindles
- 11. Dentinoenamel Junction Scalloped in appearance
- 12. Enamel surface • Perikymata: Striae of Retzius extend from DEJ to the outer surface and end in shallow furrows. • Surface consists of a structure less surface layer without rods. • As the tooth erupts, it is covered by pellicle consisting of debris from enamel organ and soon replaced by salivary pellicle.
- 13. Enamel Rod structure • Rods extend from DEJ to the outer surface. • Each rod is formed by secretory products of four ameloblasts. • One forms the rod head. • A part of two ameloblasts form the neck. • Tail is formed by four ameloblasts.
- 14. Reduced enamel epithelium • It represents the epithelial covering of the enamel after its formation is completed. REE is derived mainly from the ameloblast and stratum intermedium layers of the enamel organ, but it also may include remnants of stellate reticulum and outer enamel epithelium. Primary enamel cuticle, also called Nasmyth's membrane, is a thin membrane of tissue also known as reduced enamel epithelium
- 15. Clinical implications • Leads to diseases with structural abnormalities (Amelogenesis imperfecta). • Chronological hypoplasia • Changes in chemical structure and composition. • Remnants such as REE lead to cyst formation.
- 16. Dentine Physical properties • Pale yellow • Darker with age • Harder than bone and cementum, softer than enamel. • Much more resistant to propagation of cracks than enamel (higher fracture toughness) • Greater compressive, tensile and flexural strength than enamel • Permeable (permeability depends on the size and patency of the tubules) • Permeability decline with age. • Elastic (slight deformation) • Less mineralized than enamel (more radiolucent)
- 17. Chemical properties • 70% inorganic, 20% organic and 10% water by weight. • 50% inorganic, 30% organic and 20% water by volume. Inorganic matrix • Inorganic mineral component: calcium hydroxyapatite crystals. • Hydroxyapatite similar in shape, but very much smaller than those in enamel. • Trace elements: fluoride. • Crystallites in the mineralised dentine are found on and between the collagen fibrils.
- 18. Organic matrix • Composition similar to bone. • Fibrils (collagen)embedded in an amorphous ground substance. • 90% collagen ( mostly type 1) • Traces of type III and type V collagen • Most of the collagen fibrils in dentine run parallel to the pulpal surface. • In mineralised dentine collagen fibrils are of larger diameter (100 nm) and are more closely packed than in predentine.
- 19. Dentinal tubule
- 20. Types of Dentine
- 21. Regional variations in dentine structure and composition • The properties and composition of mineralised dentine vary with distance from the predentin to the enamel–dentine junction. • The mineral content of dentine decreases and the thickness of mineral crystals increases towards the enamel–dentine junction. • Hardness and elastic modulus decrease towards the DEJ. • The most peripheral region beneath the enamel: mantle dentine. • Predentin is the innermost unmineralised layer
- 22. MANTLE DENTINE • It is slightly (approx. 5%) less mineralised. • The collagen fibrils are largely oriented perpendicular to the enamel–dentine junction. • The dentinal tubules branch profusely in this region • Mineralisation in the presence of matrix vesicles • Varies in width from 20 μm to 150 μm
- 23. Interglobular dentine • Incomplete fusion of calcospherites. • Beneath the mantle layer in the crown and the granular layer in root. • Dentinal tubules pass without deviation through interglobular areas
- 24. Circumpulpal dentine • Basic structure of dentine • Forms the bulk of the dentine and is uniform in structure except at its edges
- 25. Predentine • Pale-staining appearance • Globular or a linear outline • Width vary from 10 μm to 40 μm • Thicker in young teeth.
- 26. Age-related and posteruptive changes • Related to age: secondary dentine and translucent dentine. • Response to a stimulus (caries or attrition): tertiary dentine, sclerotic dentine and dead tracts.
- 27. Secondary dentine • Structure is very similar to that of primary dentine • Change in direction of the dentinal tubules • The same odontoblasts continue to lay down similar dentine and the tubules of primary and secondary dentine are continuous. • Slower rate of deposition • Secondary dentine formation begins at the completion of root formation as the tooth comes into occlusion. • Secondary dentine forms most rapidly on the pulpal floor. • Its continuing deposition leads to smaller pulp chambers and narrower root canals
- 28. Translucent Dentine • With ageing, tubules become completely occluded with peritubular dentine to form translucent dentine. • At the root apex and increases linearly with age • Used in forensic dentistry to help determine the age of a person
- 29. Tertiary dentine • Due to external stimuli. • Few and/or irregularly arranged tubules; or it may be relatively atubular. • No continuity of dentinal tubules between normal dentine and tertiary D. • Variety of names (irregular secondary dentine, reparative dentine, reactionary dentine, and osteodentine) • production by newly differentiated mesenchymal cells
- 31. Sclerotic dentine • Dentinal tubules fill in response to external stimuli (slowly advancing caries or severe attrition)
- 32. Clinical considerations Permeability of dentine • Tubular structure allows substances applied to its outer surface being able to reach and affect the dental pulp. • Ex: bacteria of dental caries and the toxins – dental materials, or etchants depends on: • Exposure of the dentine surface ( caries, attrition, abrasion or trauma) • Patency of the tubules (peritubular dentine, exogenous material) • Sealed off from the pulp (tertiary dentine) • Outward movement of interstitial ‘dentinal’ fluid • Intact odontoclasts layer ( barrier)
- 33. Response to external stimuli Caries, attrition • Deposition of tertiary dentine provides a barrier to the progress of caries and toxins. • Secondary dentine -barrier Cavity preparation • Drilling through dentine open a pathway towards the pulp. • Depth, age (younger less dentine thickness, less amount of peritubular dentine). • Heat during drilling
- 34. Adhesion of dental materials to dentine • New materials adhere to enamel and dentine. • Less pulpal injury and improved aesthetic results. • Adhesion to dentine is more complex than that to enamel. – high organic and water content – tubular architecture, – Its heterogeneity, – its age changes and its reactions to caries. – a smear layer
- 35. Endodontics • The continuous deposition of secondary dentine throughout life • Deposition of tertiary dentine • Leads to oobliteration of the pulp chamber and root canals Endodontics applications
- 36. Sensitivity • Three main hypotheses • Nerves in dentine • The odontoblast processes • Fluid movements in the dentinal tubules
- 37. 1st hypothesis: • No free nerve endings in outer parts of dentine. • Application of local anaesthetics to the surface does not abolish the sensitivity. 2nd hypothesis: • No evidence to show odontoblast process is analogous to a nerve fibre and conduct impulses.. • Odontoblast procesess do not extend to the enamel–dentine junction. • Application of local anaesthetics to the surface does not abolish the sensitivity. • Odontoblasts have not been shown to be synaptically connected to nerve fibres. 3rd hypothesis: • The most plausible hypothesis • Fluid movement through the dentinal tubules depolarise nerve endings at the pulp–predentine junction and in the subodontoblastic neural plexus
- 39. Role of the supporting apparatus? • Protects the teeth from masticatory forces – facilitates normal oral function preventing premature loss of teeth
- 40. Periodontium - Components 1) Investing gingival complex (Gingiva & dentogingival junction) 2) Periodontal Ligament (PDL) 3) Alveolar Bone 4) Root Cementum
- 41. Gingiva • Part of the masticatory mucosa which covers the alveolar process and surrounds the cervical portion of the tooth.
- 42. The gingivae – Comprise: • Free Gingival margin (the visible edge of the gingiva) • Gingival sulcus (crevice):0.5-3 mm deep • Free gingiva (FG) – a mobile cuff of gingiva, above alveolar crest • Free gingival groove (FGG) • Attached gingiva (AG) – a band of 1-9 mm in height, bound to the underlying alveolus & cementum by collagen fibres of DG complex • Muco-gingival junction (MJG)
- 43. The gingiva
- 44. Alveolar mucosa & MGJ • Alveolar mucosa- Dark red, located apical to the MGJ. Loosely bound to the underlying bone – movable • MGJ – Where AG joins the oral mucosa.
- 45. Gingival Crevice & GCF • Gingival sulcus (crevice) – Between FG and tooth crown in health. • Clinical probing depths 0.5-3mm (20 –25 g probing pressures). • Crevice washed out by GCF (GCF flows out at a rate of 0.2 µl / hour. GCF contributes about 1ml / day to saliva)
- 46. Contents of the GCF in health? • Same as serum, except for RBC • Viable neutrophils (PMNLs) can be collected • With inflammation, GCF Transudate ------>More like an Inflammatory exudate during inflammation (Increased flow rate & volume due to local components of inflammatory process)
- 47. The epithelium covering the free gingiva - 1 Oral epithelium (OE) - faces the oral cavity. 2 Oral sulcular epithelium (OSE) - faces the tooth without being in contact with the tooth surface. 3 Junctional epithelium (JE) - provides the contact between gingiva and the tooth.
- 48. Microscopic Anatomy of gingiva
- 49. How is structure of JE related to function? • Non-keratinized JE – permeable (tissue defence mechanisms possible) –permeability allows GCF carrying PMNLs, complement & antibody as components of immune-inflam: response ). Manifested by infiltration of inflammatory cells How is the integrity of the JE maintained? • High cellular turn over (Divides faster than any other normal epithelium) • 2-6 days (JE) Vs 1 month (OE)
- 50. Clinical relevance of JE: • Apical migration of JE – 1st clinical indicator of periodontal attachment loss; Results in formation of a true pocket. • JE – key to determine when gingivitis progresses to periodontitis.
- 51. Gingival Connective Tissue predominant tissue component of gingiva (also in PDL) Components • Ground substance, blood, lymph & neural tissue. • Major components of CT fibres - collagen fibre bundles.
- 52. Fibres in GCT • Collagen fibres - most predominant and most important type • Reticulin fibres - found at the epithelium-CT and endothelium-CT interface • Oxytalan fibres - in gingiva & PDL. Function is unknown • Elastic fibres - only in association with blood vessels
- 53. Collagenous fibre bundle groups- 1) Dento-gingival fibres 2) Dento-periosteal 3) Alveolar-gingival 4) Circular (circumferential) 5) Transeptal (interdental)
- 54. Dento-gingival fibres (DGF) • Embedded in the cementum of the supra- alveolar portion of the root. Project from the cementum into the free gingival tissue of facial, lingual & interproximal surfaces, in a fan-like configuration.
- 55. • Dento-periosteal fibres (DPF)- Embedded on the same portion of the cementum as DGF, but run their course apically in the tissue of attached gingiva.
- 56. Alveolar gingival fibres • Run from the alveolar crest to the free gingival tissue.
- 57. Circular fibres (CF) – • Run their course in the free gingiva and encircle the tooth in a cuff- or ring-like fashion.
- 58. Trans-septal fibres (TF) Embedded in the cementum of adjacent teeth. Run straight across supra- alveolar cementum of approximating teeth.
- 59. Purpose of collagen fibres in GCT Maintain a tight gingival cuff & tight adaptation of gingiva to tooth – restrict subgingival microbial colonization. All fibre bundle groups reinforce the interdental papilla and provide resilience and tone necessary for maintaining integrity of the dentogingival attachment.
- 60. Age changes of gingiva Age and inflammation related changes • The level of the junctional epithelium relative to the tooth surface shifts apically with age and it is believed inflammation is an important factor that contributes to this apical migration. This apical shift is gradual and if it is accelerated then it is a pathological condition referred to as gingival recession.
- 61. Age changes of gingiva • With age – progressive apical migration of the dento-gingival junction. • Increased height.
- 62. Root Cementum • Thickness - varies at different levels of the root. Thinner coronally (0.05-0.1mm at CEJ) and thicker apically (0.2-1mm) • Thickest at the root apex • Thinnest cervically
- 63. Root Cementum • Bone-like tissue (about 50% mineral) • No blood, lymph or neural tissue
- 64. Classification of cementum • 1) Acellular (primary) cementum • 2) Cellular (secondary) cementum Primary/Acellular Cementum • Forms next to the dentine & around inserting PDL fibres (sharpey’s fibres)
- 65. Secondary Cementum • Found mainly in the apical area & overlying the acellular cementum • Formed during functional needs (e.g. compensatory tooth eruption due to attrition) • Cementocytes are numerous
- 66. Cementum formation • Cementum formation - occurs throughout life, slowly (surface being covered by a layer of uncalcified matrix or precementum) -This allows for continual reattachment / new attachment of the PDL fibres.
- 67. Incremental lines of cementum Rhythmic deposition. • Periods of activity alternating with periods of quiescence. • Periods of decreased activity - associated with incremental lines.
- 68. Functions of the cementum • Prime function: To give attachment to collagen fibres of PDL (Anchors the PDL fibres to root surface) • Protects root dentine
- 69. • Scan 338 pg: 156
- 70. • Pattern 1 - cementum overlaps (60%- predominant arrangement). • Pattern 2 - C & E meet at a butt joint (30%) • Pattern 3 - C&E fail to meet (10%). • Clinical implication ?- Pattern 3 will lead to sensitivity with the slightest root exposure. • (In a given tooth, can have even all 3 types, but one type can predominate).
- 71. Resorption and repair of cementum • Cementum - less susceptible for resorption than bone under same pressure (eg: with orthodontic loading) • But, most roots of permanent teeth, show small localized areas of resorption - by odontoclasts) • Cause of resorption ? Not clear, Micro- trauma? – a possibility
- 72. Cementicles • Small globular masses of cementum found on 35% (appro.) of human roots. • Not always attached to the cemental surface. • May be located free in the PDL.
- 73. Cementicles FC – Free cementicle SC-sessile cementicle May result from micro-trauma (When extra stress on the Sharpey’s fibres causes a tear in the cementum. Commoner in apical and middle 1/3 of the root and root furcation areas.
- 74. Hypercementosis • Cementum deposits continuously and slowly throughout life. • Chronic periapical inflammation - hypercementosis (localized) • Hypercementosis in all teeth - Paget’s disease • Clinical implications :Difficult extractions.
- 75. Periodontal Ligament (PDL) • Dynamic structure • Soft, richly vascular, dense & fibrous cellular connective tissue • Occupies between the root of the tooth & the alveolus. • PDL : 0.2-0.4 mm wide.
- 76. PDL- boundaries & structural relationship with tissues around • Above alveolar crest, PDL is continuous with the connective tissue of the gingiva. • At the apical foramen- continuous with the dental pulp.
- 77. Clinical implications • Gingivitis sometimes progresses to periodontitis. • Any pulpal infection through apical foramen – infection of apical PDL (endo-perio lesion).
- 78. Functions of PDL 1) Provides attachment between tooth (via cementum) & alveolar bone. 2) Resists, displaces occlusal forces. 3) Protects dental tissues from damage caused by excessive occlusal load (especially at the apex)
- 79. 4) Allows normal function by “physiological” mobility (up to 0.2 mm). This slight mobility of teeth – essential for function. Tooth mobility - largely determined by the width, height & quality of the PDL 5) Provides sensory input for reflex jaw activities via mechanoreceptors 6) PDL- responsible for mechanisms to maintain the functional position of a tooth. Functions of the PDL, cont--
- 80. Functions of the PDL, cont-- • 7) Its cells form alveolar bone & cementum (also maintain & repair both structures). • 8) Neurological control of mastication (by mechano-receptors). Type II mechano-receptors: primary mechano- receptors in PDL
- 81. • Shape of the PDL space - hour-glass appearance (Narrowest at the mid root level - where it acts as a fulcrum during orthodontic load). • Width of the PDL - varies according to functional state of the periodontal tissues.
- 82. • Non-functional & un-erupted teeth - narrower space – minimal physiological mobility. • Teeth subjected to heavy occlusal stress - increased space. • Age changes ? PDL narrows with age slightly.
- 83. Structure of the PDL 1) Fibres: • Arranged collagen fibre system
- 84. PDL fibres A) Transseptal (Gin), (B) Alveolar crest, (C) Horizontal, (D) Oblique, (E) Apical, and (F) Interradicular Structure of the PDL
- 85. Specific functions of oblique fibres: • Form a suspensory ligament which translate pressure on the tooth into tensional forces on the alveolar wall.
- 86. • Other than distinctive bundles -numerous randomly oriented collagen fibres - makes a fibrous plexus. • Rate of turn over of collagen in PDL - faster than virtually all other connective tissues. Highest turnover towards the apex. • Reason for high turn over? Maybe functional demands - occlusal stress needing remodeling.
- 87. All Fibres of the PDL • Mainly collagenous (90% of all PDL fibres) • Oxytalan & reticuline fibres (small amounts) • Collagen of the PDL - Mainly type I • (Type I- major protein component of most connective tissues (including bone & skin).
- 88. Main components in ground substance in PDL • Hyaluronidase; glycosaminoglycans- mainly. • Proteoglycans • Glycoproteins • All ground subs components - secreted by fibroblasts.
- 89. Functions of Ground substance - 1) Ion and water binding & exchange. 2) Control of collagen fibrillogenesis. 3) Fibre orientations.
- 90. Cells of the PDL • Fibroblasts: most predominant connective tissue cell • Osteoblasts • Cementoblasts • Osteoclasts • Cementoclasts • Undifferentiated mesenchymal cells • Defense cells • Epithelial cells (Cell Rests of Malassez).
- 91. Bone resorption • During orthodontic tooth movement? • A PDL placed under pressure will result in bone resorption whereas PDL under tension results in bone formation.
- 92. Alveolar Bone • That part of the maxilla or mandible which supports and protects the teeth. • Arbitrary boundary - level of the root apices (separates alveolar bone from the body of the mandible / maxilla).
- 93. Alveolar bone- • Finer at the margins (coronally), thicker towards the root apex. • Dense facial & lingual cortical plates – meet at the alveolar crest. • Al crest situated 1-1.5 mm apical to CEJ. • Radiographically, radio opaque line (lamina dura)- dense cortical bone lining the alveolar socket).
- 94. • Lamina dura
- 95. • Radiographyically, loss of continuity of lamina dura- The 1st sign of bone demineralization, often occurs at interdental alveolar crest • Cortical bone thickness varies – • Thinnest - mandibular incisor region • Thickest - mandibular molar
- 96. Functions of alveolar bone • Distribute and absorb forces generated by mastication and other tooth contacts. • Serves as an attachment apparatus for the teeth. • Provides a framework for bone marrow. • Acts as a reservoir for ions (especially Ca).
- 97. Alveolar bone • Alveolar bone - provides strength (allows it to remodel according to functional demands. • Al bone - tooth-dependent bone. • Anodontia - poorly developed. • Following tooth extraction - atrophies.
- 98. Cell types in bone - 5 types 1) Bone forming cells- osteoblasts Found on the surface. Cells are “trapped” in their own secretions. 2) Osteocytes - When osteoblasts subsequently get incorporated into the matrix – called osteocytes.
- 99. • 3) Large multi-nucleated cells - osteoclasts - responsible for bone resorption. • 4) Osteoprogenitor cells - mesenchymal fibroblast-like cells. Regarded as forming a stem cell population to generate osteoblasts (Situated near blood vessels of the PDL).
- 100. • 5) Bone-lining cells (flattened, undifferentiated, inactive osteoblasts)- • Provide a lining to the bone surface, when al bone is not being deposited or resorbed (throughout a considerable part of adult life). • No important function - may be related to ion exchange.
- 101. Bone resorption • Bone turnover is controlled by the RANK/RANK-L/OPG system. • RANK expressed by osteoclasts. • RANK-L (RANK-ligand) is a ligand that binds to RANK, and is expressed by bone stromal cells, osteoblasts and fibroblasts. • Binding of RANK-L to RANK results in osteoclast differentiation and activation, leading to bone resorption. • IL-1β and TNF-α regulate the expression of RANK-L. • OPG (osteoprotegerin): binding inhibits resorption.