Histology of Enamel PDF

Histology of Enamel Lauren Stockham Oral Dental Sciences, Year 1 Intended learning outcomes By the end of the session students should be able to: Describe the composi?on and structure of enamel Describe how the structure of enamel relates to its func?on Be able to dis7nguish the clinical...

Histology of Enamel Lauren Stockham Oral Dental Sciences, Year 1 Intended learning outcomes By the end of the session students should be able to: Describe the composi?on and structure of enamel Describe how the structure of enamel relates to its func?on Be able to dis7nguish the clinical appearance of enamel over the life-course Apply this knowledge to interpret the clinical signi@cance of enamel in health and disease Assessment Forma?ve: (to support your learning) Workbooks, Quizzes Summa?ve: E-assessment for Oral Dental Sciences Histology of the ?ssues of the teeth and suppor?ng structures Enamel Den7ne Pulp Cementum Bone (alveolar) Periodontal ligament Gingiva Let’s reEect on WHY we need to learn this… To eKec7vely support, maintain and improve oral health for our pa7ents, examples: dental professional when seeing to know. expects you Patent Refresh your knowledge Where is enamel found? crown of the tooth. What is the embryonic origin of enamel? How does this link to the embryonic This Photo by Unknown Author is licensed under CC BY-SA-NC origin of enamel? Refer to Oral Embryology and Tooth Morphology lectures for more informa7on. Source: Unknown CC Enamel COMPOSITION AND STRUCTURE  very hard but brittle. Composi?on of enamel Mineral (inorganic) content: 96% inorganic minerals Majority - calcium hydroxyapa7te (Ca5(PO4)3OH) Minority – carbonate, Xuoride Organic content: 4% Fibrous material (collagen) Chemical structure of calcium hydroxyapa7te Water (Rujitanapanich et al 2014). Some proteins Overview of structure of enamel Enamel rods (prisms) Interrods Crystallites (calcium hydroxyapa7te) Link to amelogenesis Incremental lines Prismless enamel (rod-less) Dento-enamel junc7on and microscopic features The greenhouse in the Royal Opera House demonstra7ng an analogy for a strong yet bri_le structure like enamel. Image credit: Lauren Stockham  unit making Key Structural Enamel rods - enamel : Enamel Millions of enamel rods (prisms) make up the structure of enamel. They are 7ghtly packed and organised with a keyhole shape’ in cross-sec7on (b). Each rod contains millions of calcium hydroxyapa?te crystallites (the mineral/inorganic content of enamel). Zoomed in detail of the enamel rods from a molar tooth Enamel rods The key hole shape reXects diKerent parts of the enamel rod – a head and a tail (A). The orienta7on of the head of each rod is usually towards the occlusal/incisal surface rela?ve to the tail which is oriented towards the cervical region. The tail is also known as an interrod. Structure of enamel rods in cross-section and longitudinal sections Each rod and interrod is surrounded by a sheath (organic material). Enamel crystallites There are millions of crystallites (hydroxyapa7te) in each rod 7ghtly packed in keyhole shapes. These are extremely long, thin and ribbon-like, they may run the thickness of enamel. In orienta7on, the crystallites in the head = parallel with the long axis of the rod, and the tail = diverge slightly (c). The pa_ern of the crystallites within the rod adds to the strength of enamel. Structure of enamel crystallites within the enamel rods Enamel rods - orienta?on To account for the shape of the tooth, the direc?on of the rods varies. At the cervical margin they are directed more horizontally-apically and at the cusp ?ps they are almost ver?cal. O The overall thickness of enamel also varies where it is thickest at the cusp ?ps and O incisal edges and thinnest at the cervical margins. of cusps take force Strength - Why might this be?. catting. Enamel rods They run from the dento-enamel junc?on (DEJ) to the enamel surface. The rods traverse together bending right and led in an s- shape manner. At the DEJ the rods are posi7oned perpendicular (at right angles) to the den7ne in general. At the cusps, the rods are twisted forming gnarled enamel. These structural features add to the overall strength of enamel. Longitudinal section of enamel rods from the DEJ to the surface Enamel rods direc?on and clinical signi@cance The direc7on of the rods is a key considera7on in cavity prepara7on to avoid unsupported enamel that will fracture leading to failure. Diagrams showing a posterior proximal cavity preparation Enamel rods and amelogenesis Link back to Embryology of the Crown lecture enamal an formsteeth. The structure of the enamel rods is formed - by the ameloblasts during amelogenesis. S cell that produces enamal during development Each enamel rod (and associated interrod) are formed by 1 ameloblast. The lifecycle of ameloblasts is signiecant since it means that enamel is inert – it has no cell during its life. The pa_ern of amelogenesis results in tries incremental lines. ma. Line & that appear in ecretsmineral Zoomed in longitudinal section of enamel rods Source: dent-wiki.com enamal. S and associated with the ameloblast. Incremental lines Incremental lines represent the paZern of amelogenesis that occurs in waves reXec7ng ac7ve and rest phases of growth Similar to growth rings (lines) of a tree, the rings of growth in teeth are called Stria of Retzius (line of retzius) These lines may be detected clinically on the surface of enamel as normal subtle Tree in cross-section features and as more dis7nct features Incremental lines within ↑ Stria of Retzius - are visible under a microscope in sitey ground sec7ons of enamel as growth rings/lines Perkymata – The edge of the stria of retzius that is visible as a shallow furrow on the enamel surface showing where the incremental lines reach the surface on the labial/buccal surfaces. These are most marked when newly erupted and gradually wear over 7me. Visible clinically. Diagram of the incremental lines in enamel Looking at the pa-ern of the Stria of Retzius - can you remember where amelogenesis starts?  1. Identify the teeth present in each clinical image LLI LRI 2. Identify the perkymata in each – note that the teeth have been air-dried to Take a look… enable visibility of these features Arrow 2 3. Identify the morphological features indicated by the arrows at the incisal edges Arrow 3 4. Consider why there might be a difference in the size of the features between 3. both images. Wear First photo newly erupted teeth.. 2 ↓ url ULI 2. LRI LLI s ‘Prismless’ Enamel Although enamel rods (prisms) are the main structural unit of enamel, there are some area of enamel where it is unstructured known as prismless/aprisma7c. Surface – The very erst and last formed enamel shows no usual prism no prisms structure where the crystals are parallel with the surface. a Body – -moderas prisms/ It is 30 microns wide at the surface, highly radio-opaque, rods harder and less soluable – includes more Xuoride and carbon thus key for demineralisa7on/ remineralisa7on. Light microscopy image showing the distinction between the surface enamel (no rods/prisms) and body (rods) of enamel It is seen in the primary den77on and 70% of the permanent den77on, greatest in the cervical regions. Clinical signiecance  may interfere with op7mal etching. Den?ne-Enamel Junc?on (DEJ) The junc7on between enamel and den7ne that forms once den7nogenesis and amelogenesis have started. Scalloped appearance under a microscope thought to strengthen the bond between the two materials almost locking them together. The dento-enamel junction between enamel and dentine Structural features at the DEJ Enamel Tu` Thought to result from abrupt changes in direction of the enamel rods This is because of the scalloped boundary of enamel at DEJ Possibly supports bond between dentine and enamel? No known clinical significance Seen in traverse sections of enamel Cross-section of DEJ Structural features at the DEJ Enamel Spindles extension of dentine tubules into enamel May result from odontoblast processes extending into the ameloblast layer becoming trapped since dentine starts to form before enamel Possibly contribute to minor sensitivity Cross-section of DEJ Structural features visible under a microscope Features are only visible under a microscope, they help to grasp the histological structure light and dark bands under light microscope = Hunter Schreger Bands longitudinal section run upwards from dentine – see image cross-section appear as growth rings Cross-section of enamel and dentine Structural features at the enamel surface Lamella Appear as cracks in enamel - developmental defects appear as jagged lines in surface of crown clinically extend inwards maybe as far as dento- enamel junction result of ameloblast ceasing production of enamel Can be mistaken for cracks in enamel and vice versa Cross-section of enamel and dentine Link to structure FUNCTIONS OF ENAMEL So` boiled egg analogy to explain the func?ons and link with structure Protect - related to tooth. pentine - Pulp - Enamas Func?ons Inability to Ion Protection Eating repair or Smile exchange feel injury I Highlyralised Moose er take How the func?ons of enamel link to the structure Func?ons Structure Protec7on of the tooth/pulp Thickest at cusp 7ps, occlusal and # Ea7ng: chewing, bi7ng etc incisal surfaces Inability to repair or feel injury Covers the en7re tooth crown Able to remineralise and demineralise Inert 7ssue (no living cell due to – ion exchange ameloblasts’ limited lifecycle Smile - Aesthe7cally appealing ‘pearly Hardest biological 7ssue whites’ Highly mineralized 7ssue White translucent crystallite Permeable ‘micropores’ Link to functions and clinical appearance CHANGES IN ENAMEL OVER THE LIFE- COURSE Enamel changes over the life-course Over 7me enamel is subject to tooth wear including: AZri?on Abrasion Erosion For example, perkymata are worn away, scratches and cracks develop. Colour changes – reduced translucency and increase in underlying den7ne makes enamel appear yellower – normal aging process. Enamel changes over the life-course Over 7me enamel is subject to: Reduced ‘permeability’ – exchange of ions such as Ca, PO, F- Clinical signi@cance for exposure to topical Xuoride as a younger tooth and in the progression of early enamel lesions. Demineralisa?on-Remineralisa?on cycle As a mineralised structure, enamel is subject to Link to Aetiology of Caries Lecture demineralisa7on (loss of mineral) and remineralisa7on (uptake of mineral) In acidic condi7ons the balance favours demineralisa7on In alkaline condi7ons the balance favours remineralisa7on enabling uptake of Euoride and calcium phosphate to The cri?cal pH of enamel is 5.5 Enamal Start - Acid Alkaline Demineralize. What substance in the mouth is alkaline and thus favours remineralisa@on? Saliva Demineralisa?on-Remineralisa?on cycle Since enamel does not contain any living cell, it is not able to repair itself with the immune system and therefore it can not feel injury This allows the progression of the early stages of dental caries to occur unno?ced to the host The composi7on and structure of enamel is relevant for the clinical preven7on and treatment of dental caries Cross-section of DEJ Clinical applica?on – preven?ve and restora?ve Fluoride – enamel that has Xuoride incorporated (Xuorapa7te) has a cri7cal pH of 4.5, lower than hydroxyapa7te thus more resistant to acids and demin. Acid etch – acid removes minerals from the enamel surface crea7ng ‘tags’ that enable the bond to ell in and s7ck the composite to. Link to Histopathology of Enamel Caries lecture in Year 1. The signi@cance of the DEJ and caries Take close look at: The breakdown of enamel The progression into den7ne and to the pulp Note the diKerence in size of the lesion in enamel compared to the lesion in go den7ne at the DEJ… tows Demineralisaca a an se Destine. in the Clinical image showing the progression of caries Radiographic view of dental caries in enamel Take a close look at the radiopaque structures of enamel, den7ne and alveolar bone – the whiter it is, the more mineralized it is. The circle iden7ees a radiolucent area of enamel that is consistent with interproximal caries clinically although not breached the DEJ. Radiograph showing the LR56 Enamel STRUCTURAL ABNORMALITIES Structural abnormali?es - Incremental Lines Clinically dis?nct: Neo-natal line an exaggerated line represen7ng the dis7nc7on between enamel that has formed before birth and ader birth It usually reXects a disturbance in the amelogenesis at birth (perinatal) Other exaggerated lines ReXect systemic disturbances during amelogenesis ie fever, tetracycline staining Primary dentition showing the distinction between when enamel forms in the crown. Structural abnormali?es in enamel Link to Embryology of the Crown lecture As a result of disturbances during amelogenesis, defects in the enamel structure may result from: Local disturbances – aKect individual teeth such as trauma systemic disturbances – aKect all the teeth forming at the 7me such as Xuorosis (too much Xuoride), or exposure to tetracycline, nutri7onal deeciencies, molar-incisor hypomineralisa7on Gene?c factors – may aKect all teeth such as amelogenesis imperfecta These defects may result in signiecant clinical Tetracycline staining of the primary dentition. implica7ons. Structural abnormali?es in enamel Defects during amelogenesis can result in enamel hypoplasia or enamel hypomineralisa?on collec7vely known as molar-incisor hypomineralisa?on. The impact for pa7ents can range from Showing enamel hypomineralisation (Patel et al minimal to signi@cant clinical 2019). implica?ons. Further information in articles. Link to Developmental Anomalies lecture. Structural abnormali?es in enamel O Can you iden7fy: Any colour changes in speciec teeth? Any morphology discrepancies with speciec teeth? O O Image showing Molar incisor-hypomineralisation in an 8 year old child. (Seow 2014). Summary Enamel The clinical Composition Structure Functions significance How functions organic and structural enamel rods link to inorganic abnormalities structure changes over caries the life-course prevention Knowledge and understanding of enamel structure is essen7al to promote the preven7on of dental caries - most prevalent chronic condi7on globally. Key area of research focus to understand how enamel can be regenerated. Reading Highly recommend reading – included in post-session on moodle. First ar7cle gives detailed and succinct explana?on of amelogenesis and den?nogenesis Both ar7cles discuss the clinical impact