Dental Hard Tissues 2024-25 PDF

Dental Hard Tissues BONE, ENAMEL, DENTINE & CEMENTUM Dr Alex Cresswell-Boyes [email protected] Key Clinical question. If you see this icon a question related to the clinical aspect of the topic will be asked. Clinical consideration. If you see this icon some key clinic...

Dental Hard Tissues BONE, ENAMEL, DENTINE & CEMENTUM Dr Alex Cresswell-Boyes [email protected] Key Clinical question. If you see this icon a question related to the clinical aspect of the topic will be asked. Clinical consideration. If you see this icon some key clinical considerations to be made aware of regarding the topic. Materials question. If you see this icon a question related to the materials aspect of the topic will be asked. Learning Objectives ▪ To identify key histological and structural features of the hard periodontal tissues. ▪ To identify key components of tissues of alveolar bone, periodontal ligament and cementum. ▪ To recognise the distinction between primary and secondary cementum. ▪ To recognise key histological features of these tissues in relation to some simple clinical changes. Outline ▪ Enamel. ▪ Dentine. ▪ Cementum. ▪ Bone. Introduction ▪ Dental hard tissues are specialised mineralised structures essential for tooth function. ▪ Comprise enamel, dentine, cementum, and alveolar bone. ▪ Importance: ▪ Provide protection against mechanical forces. ▪ Facilitate mastication and speech. Photo: © University of Leeds 2003 ▪ Play a role in sensory perception. Enamel – Composition and Characteristics ▪ Composition: ▪ 96% Inorganic: Primarily hydroxyapatite crystals (Ca10(PO4)6(OH)2). ▪ 1% Organic Matrix: Enamel proteins like amelogenins, ameloblastin. ▪ 3% Water. ▪ Characteristics: ▪ Hardest tissue in the human body. ▪ Acellular and avascular; cannot Photo: © Haleon 2022 regenerate. ▪ Translucent, allowing underlying dentine colour to affect tooth appearance. Why can't enamel repair itself after damage? Because it's acellular (no cells), avascular (no blood vessels, therefore, lacks the means for regenerative capacity. Enamel Formation – Amelogenesis ▪ Ameloblasts: ▪ Derived from the inner enamel epithelium of the enamel organ. ▪ Responsible for enamel matrix secretion and mineralisation. ▪ Stages of Amelogenesis: 1. Pre-secretory Stage: Ameloblast differentiation. 2. Secretory Stage: Enamel matrix protein secretion forming enamel rods. 3. Maturation Stage: Removal of organic components and water; Photo: © Hack Dentistry 2022 influx of minerals. 4. Protective Stage: Formation of the reduced enamel epithelium. Enamel Structure ▪ Enamel Rods (Prisms): ▪ Basic structural unit, extending from the dentinoenamel junction (DEJ) to the tooth surface. ▪ Arranged in a complex, interwoven pattern for strength. ▪ Interrod Enamel: ▪ Surrounds enamel rods; composed of similar material but differing crystal orientation. ▪ Key Features: ▪ Hunter-Schreger Bands: Alternating light and dark bands due to rod orientation. ▪ Striae of Retzius: Incremental growth lines representing enamel deposition cycles. Photo: © Schenider et al. 2008 ▪ Perikymata: External manifestations of Striae of Retzius on tooth surfaces. Why are Hunter-Schreger Bands significant in restorative dentistry? They indicate areas of enamel strength, guiding cavity preparation. Clinical Relevance of Enamel ▪ Caries Susceptibility: ▪ Enamel demineralisation occurs when pH drops below critical level (~5.5). ▪ Enamel Hypoplasia: ▪ Defective enamel formation leading to thin or pitted enamel. ▪ Causes include nutritional deficiencies, systemic diseases during tooth development. ▪ Fluorosis: ▪ Excess fluoride intake disrupts Photo: © Biyani 2018 enamel mineralisation. ▪ Leads to mottling or discoloration of enamel. Dentine – Composition and Properties ▪ Composition: ▪ 70% Inorganic: Hydroxyapatite. ▪ 20% Organic: Mainly Type I collagen and non-collagenous proteins. ▪ 10% Water. ▪ Properties: ▪ Less mineralised than enamel but more flexible. ▪ Supports enamel and absorbs occlusal forces. ▪ Capable of regeneration due to Photo: © IAAD 2024 odontoblast activity. Why is dentine capable of repair? Due to the activity of living odontoblasts lining the pulp. Dentinogenesis – Formation of Dentine ▪ Odontoblasts: ▪ Derived from dental papilla mesenchymal cells. ▪ Line the periphery of the dental pulp. ▪ Formation Process: ▪ Predentine: Unmineralised matrix secreted by odontoblasts. ▪ Mineralisation: Deposition of hydroxyapatite crystals on collagen fibers. ▪ Incremental Lines: ▪ Lines of von Ebner: Reflect daily deposition. ▪ Contour Lines of Owen: Indicate metabolic disturbances. Photo: © Hemmati 2021 Dentine Structure ▪ Dentinal Tubules: ▪ Microscopic channels running from the pulp to the DEJ. ▪ Contain odontoblastic processes and dentinal fluid. ▪ Peritubular Dentine: ▪ Highly mineralised dentine surrounding each tubule. ▪ Intertubular Dentine: ▪ Less mineralised dentine between tubules. ▪ Types of Dentine: ▪ Primary Dentine: Formed during tooth development. ▪ Secondary Dentine: Formed after root completion; reduces pulp chamber size. Photo: © Messelt 2016 ▪ Tertiary Dentine: Formed in response to stimuli; includes reactionary and reparative dentine. How do dentinal tubules contribute to caries progression? They provide pathways for bacteria to reach the pulp. Clinical Implications of Dentine ▪ Tooth Sensitivity: ▪ Exposure of dentinal tubules leads to sensitivity. ▪ Hydrodynamic Theory: Movement of fluid within tubules stimulates nerve endings. ▪ Caries Progression: ▪ Dentine demineralises at a higher pH than enamel. ▪ Caries can progress rapidly once it reaches dentine. ▪ Restorative Dentistry: ▪ Importance of preserving dentine during Photo: © Hill 2016 cavity preparation. ▪ Use of liners and bases to protect the pulp. Cementum – Overview ▪ Function: ▪ Anchors periodontal ligament fibers to the tooth. ▪ Protects root dentine. ▪ Compensates for occlusal wear by continuous deposition. ▪ Composition: ▪ 45-50% Inorganic: Hydroxyapatite. ▪ 50-55% Organic: Collagen (Type I, III) and non-collagenous proteins. ▪ Types: ▪ Acellular Cementum: First formed; covers cervical third; crucial for attachment. ▪ Cellular Cementum: Contains Photo: © Sarna-Boś et al. 2016 cementocytes; found on apical third and furcations. Cementogenesis ▪ Cementoblasts: ▪ Originated from dental follicle cells. ▪ Deposit cementum on the root dentine surface. ▪ Formation Process: ▪ Initial Layer: Acellular afibrillar cementum at the cervical region. ▪ Subsequent Layers: Photo: © Klinge 2016 Alternating acellular and cellular cementum. How does continuous cementum deposition affect orthodontic treatment? It allows for tooth movement by remodelling attachment structures. Distinction Between Primary and Secondary Cementum ▪ Primary Cementum (Acellular): ▪ Formed before tooth eruption. ▪ Lacks cells; fibres mainly extrinsic (Sharpey's fibres). ▪ Essential for tooth attachment. ▪ Secondary Cementum (Cellular): ▪ Formed after tooth eruption. ▪ Contains cementocytes in lacunae. Photo: © Future Dentistry 2020 ▪ Adaptable to functional stress; aids in repair. Clinical Considerations of Cementum ▪ Hypercementosis: ▪ Excessive cementum deposition. ▪ May complicate extractions. ▪ Cementum Resorption: ▪ Can occur due to trauma or orthodontic movement. ▪ Usually repaired by new cementum deposition. ▪ Cemental Caries: Photo: © Tanasiewicz et al. 2011 ▪ Occurs in exposed root surfaces. ▪ Prevention includes proper oral hygiene and management of periodontal disease. How does cementum resorption impact tooth integrity? It weakens tooth attachment, increasing mobility. Alveolar Bone – Structure ▪ Components: ▪ Alveolar Bone Proper: Thin layer lining the tooth socket. ▪ Supporting Alveolar Bone: Comprises cortical and trabecular bone. ▪ Histology: ▪ Compact Bone: Dense outer layer; provides strength. ▪ Cancellous Bone: Spongy inner layer; contains marrow spaces. ▪ Cells: ▪ Osteoblasts: Bone-forming cells. ▪ Osteocytes: Mature bone cells. Photo: © Ramalingam et al. 2020 ▪ Osteoclasts: Bone-resorbing cells. Alveolar Bone Remodelling ▪ Bone Turnover: ▪ Continuous process of resorption and formation. ▪ Influenced by mechanical forces and systemic factors. ▪ Orthodontic Movement: ▪ Application of force leads to bone resorption on pressure side and Photo: © Lisowska et al. 2018 formation on tension side. ▪ Periodontal Disease: ▪ Inflammation leads to alveolar Why is alveolar bone remodelling important bone loss. ▪ Detection via radiographs showing in orthodontics? It allows teeth to move within the jawbone in response to decreased bone height. forces.  Comparison Tissue Formation Composition Properties Key Histological Features Type - Formed by ameloblasts during - 96% Inorganic: Hydroxyapatite crystals - Hardest and most mineralized tissue in the - Enamel Rods (Prisms): Basic structural units running from the dentinoenamel junction amelogenesis. (Ca₁₀(PO₄)₆(OH)₂). body. (DEJ) to the surface. - Ameloblasts originate from the - 1% Organic Matrix: Enamel proteins - Acellular, avascular, and non- inner enamel epithelium of the - Interrod Enamel: Surrounds enamel rods with differing crystal orientation. like amelogenins and enamelins. regenerative. Enamel enamel organ. - Brittle and requires underlying dentine for - Hunter-Schreger Bands: Alternating light and dark bands due to changes in rod - Enamel formation occurs before support. orientation. tooth eruption and stops once the - 3% Water. - Translucent, affecting tooth colour based on - Striae of Retzius: Incremental growth lines indicating enamel deposition cycles. tooth erupts. underlying dentine. - Perikymata: External manifestations of Striae of Retzius on tooth surfaces. - Formed by odontoblasts during - Dentinal Tubules: Microscopic channels containing odontoblastic processes and fluid, - 70% Inorganic: Hydroxyapatite. - Less mineralized and softer than enamel. dentinogenesis. extending from the pulp to the DEJ. - Odontoblasts derive from dental - 20% Organic: Mainly Type I collagen - Provides elasticity and supports enamel. - Peritubular Dentine: Highly mineralized dentine surrounding tubules. papilla mesenchymal cells. and non-collagenous proteins. Dentine - Vital tissue with the ability to repair and - Intertubular Dentine: Located between tubules; less mineralized. - Dentine formation is lifelong due respond to stimuli. to secondary and tertiary dentine - 10% Water. - Incremental Lines: - Sensitive due to innervation through dentinal deposition. - Lines of von Ebner: Indicate daily deposition. tubules. - Contour Lines of Owen: Reflect metabolic disturbances during formation. - Formed by cementoblasts during - 45-50% Inorganic: Hydroxyapatite. - Covers the root surface of the tooth. - Types of Cementum: cementogenesis. - Cementoblasts originate from - 50-55% Organic: Mainly Type I - Anchors periodontal ligament (PDL) fibres - Acellular (Primary) Cementum: First formed; lacks cells; mainly in the cervical third. dental follicle cells. collagen and proteoglycans. to the tooth. Cementum - Cellular (Secondary) Cementum: Contains cementocytes in lacunae; found in the apical - Cementum formation continues - Capable of repair and adaptation. - Similar composition to bone but third and furcations. throughout life, especially in without vascularization. - Avascular and receives nutrients from the - Cementocytes: Cells trapped within the cementum matrix. response to occlusal forces. PDL. - Sharpey's Fibers: Collagen fibres from the PDL embedded in cementum. - Formed and remodeled by - Forms the tooth sockets (alveoli) in the - Alveolar Bone Proper (Cribriform Plate): Thin layer lining the tooth socket; contains osteoblasts (formation) and - 65% Inorganic: Hydroxyapatite. jaws. Volkmann's canals. osteoclasts (resorption). - Originates from mesenchymal - 35% Organic: Mostly Type I collagen - Dynamic tissue with high remodelling Alveolar - Supporting Bone: Includes cortical (compact) bone and trabecular (cancellous) bone. cells of the dental follicle. and non-collagenous proteins. capacity. Bone - Bone remodelling is continuous - Osteons (Haversian Systems): Structural units of compact bone with concentric lamellae - Provides support and protection for teeth. throughout life, influenced by - Contains bone marrow spaces with around central canals. mechanical forces and systemic hematopoietic cells. - Responds to mechanical stress, such as - Bundle Bone: Area where Sharpey's fibres of the PDL insert into bone. factors. occlusal forces and orthodontic treatment. - Lacunae and Canaliculi: House osteocytes and allow nutrient exchange. Periodontal Ligament (PDL) – Anatomy and Function ▪ Anatomy: ▪ Connective tissue between cementum and alveolar bone. ▪ Contains collagen fibers, cells, and ground substance. ▪ Functions: ▪ Supportive: Anchors tooth in alveolus. ▪ Sensory: Transmits tactile and pain sensations. ▪ Nutritive: Supplies nutrients via blood vessels. ▪ Formative and Resorptive: Involved in repair and regeneration. Photo: © Wagner et al. 2018 Components of the PDL ▪ Principal Fiber Groups: ▪ Alveolar Crest Fibres: Resist lateral movements. ▪ Horizontal Fibres: Resist horizontal pressure. ▪ Oblique Fibres: Absorb vertical forces. ▪ Apical Fibres: Prevent tooth extrusion. ▪ Interradicular Fibres: Stabilise multirooted teeth. ▪ Cell Types: ▪ Fibroblasts: Produce and remodel collagen fibers. ▪ Cementoblasts and Osteoblasts: Maintain cementum and bone. ▪ Epithelial Cell Rests of Malassez: Remnants of root sheath. Photo: © Satish et al. 2010 Histological Features of the PDL ▪ Blood Supply: ▪ Rich vascular network from superior and inferior alveolar arteries. ▪ Nerve Supply: ▪ Sensory fibers for pain and proprioception. ▪ Ground Substance: ▪ Amorphous material containing proteoglycans and glycoproteins. Photo: © Wagner et al. 2018 ▪ Cellular Elements: ▪ Defense Cells: Macrophages, mast cells for immune response. ▪ Stem Cells: Undifferentiated cells How does the rich vascular supply benefit the for regeneration. PDL? It provides nutrients and aids in healing. Clinical Relevance of the PDL ▪ Tooth Mobility: ▪ Increased mobility indicates PDL or bone loss. ▪ Orthodontic Treatment: ▪ PDL remodels under applied forces, allowing tooth movement. ▪ Periodontal Disease: ▪ Inflammation leads to destruction of PDL fibers. ▪ Trauma from Occlusion: ▪ Excessive force can damage the PDL. Photo: © McCormack et al. 2014 Cementum-PDL-Alveolar Bone Interface ▪ Sharpey's Fibres: ▪ Collagen fibres embedded in cementum and bone. ▪ Essential for tooth stability. ▪ Continuity: ▪ Integration of these tissues provides a functional unit. ▪ Clinical Importance: ▪ Damage to one component affects Photo: © Satish et al. 2010 the entire periodontium. ▪ Regeneration requires coordinated Why are Sharpey's fibres thicker at the alveolar healing of all tissues. bone and thinner at the cementum? Because the alveolar bone accommodates thicker Sharpey's fibres due to its structure and remodelling capacity, while the cementum, being thinner and less vascularised, incorporates thinner fibres. Histological Changes in Disease ▪ Periodontitis: ▪ Characterised by loss of attachment and bone. ▪ Histology shows inflammatory infiltrate, collagen breakdown. ▪ Cementum Exposure: ▪ Leads to root sensitivity and caries. ▪ Ankylosis: ▪ Fusion of cementum to bone; loss Photo: © Sima 2021 of PDL space. ▪ Tooth becomes immobile; complicates extraction. Regenerative Potential and Clinical Applications ▪ Guided Tissue Regeneration (GTR): ▪ Barrier membranes used to direct growth of new bone and PDL. ▪ Stem Cell Therapy: ▪ Research into using stem cells for periodontal regeneration. ▪ Bone Grafting: ▪ Used to restore alveolar bone height and volume. ▪ Biomimetic Materials: ▪ Development of materials that mimic natural tissues for repair. Summary ▪ Enamel: Highly mineralised; acellular; cannot regenerate. ▪ Dentine: Vital tissue; capable of repair; sensitive due to tubules. ▪ Cementum: Anchors teeth; two types with distinct features. ▪ Alveolar Bone: Dynamic tissue; remodels in response to forces. ▪ PDL: Essential for tooth support and sensory function. References ▪ Nanci, A. (2018). Ten Cate's oral histology: Development, structure, and function (8th ed.). Elsevier. ▪ Nanci, A., & Ten Cate, A. R. (2014). The cellular biology of oral tissues. Journal of Dental Research, 93(3), 292-300. https://doi.org/10.1177/0022034513519855 ▪ Shoaib, M., & Hayat, M. (2018). Histology of oral mucosa in relation to disease progression. Journal of Oral Pathology and Medicine, 47(7), 576-582. https://doi.org/10.1111/jop.12752 ▪ Koch, G. R., & Michelsen, B. M. (2014). Oral histology: Embryology, structure, and function. Oxford University Press. ▪ Kumar, C. L., & Kumar, V. (2016). A textbook of oral histology. Jaypee Brothers Medical Publishers. ▪ Nelson, S. J. (2015). Wheeler's dental anatomy, physiology, and occlusion (10th ed.). Elsevier. MCQs – Question 1 What is the main inorganic component of enamel? A) Calcium carbonate B) Hydroxyapatite C) Collagen D) Fluoride E) Magnesium phosphate MCQs – Question 1 What is the main inorganic component of enamel? A) Calcium carbonate B) Hydroxyapatite C) Collagen D) Fluoride E) Magnesium phosphate MCQs – Question 2 Why can’t enamel repair itself once damaged? A) It has no nerve supply B) It lacks dentinal tubules C) It is brittle D) It is acellular and avascular E) It undergoes resorption MCQs – Question 3 Which type of dentine is formed in response to injury or external stimuli? A) Primary dentine B) Secondary dentine C) Reactionary dentine D) Reparative dentine E) Sclerotic dentine MCQs – Question 4 Which cells are responsible for the formation of dentine? A) Osteoclasts B) Cementoblasts C) Odontoblasts D) Fibroblasts E) Ameloblasts MCQs – Question 5 What happens to alveolar bone during orthodontic tooth movement? A) It undergoes necrosis B) It remains unchanged C) It remodels with resorption on the pressure side D) It calcifies at a faster rate E) It forms secondary cementum MCQs – Answers 1. B) Hydroxyapatite. Enamel is composed primarily of hydroxyapatite crystals, making up 96% of its structure, providing it with its hardness and durability. 2. D) It is acellular and avascular. Enamel is acellular, meaning it contains no living cells, and avascular, meaning it has no blood supply. Without cells, it lacks the ability to regenerate.​ 3. D) Reparative dentine. Reparative dentine, a type of tertiary dentine, is formed by odontoblasts in response to injury or external stimuli, such as caries or restorative procedures. 4. C) Odontoblasts. Odontoblasts are responsible for forming dentine. They line the pulp chamber and produce the dentine matrix, which then mineralises to form dentine​. 5. C) It remodels with resorption on the pressure side. During orthodontic tooth movement, the alveolar bone remodels by resorbing on the side of pressure and forming new bone on the tension side, allowing the tooth to move. Feedback – YourVoice We are continuously improving your learning experience through plenaries and their delivery. We would appreciate your feedback on what you found effective and what could be improved. Please scan the QR code below or click on the yellow icon to visit the YourVoice site.