DENT 112 LEC | Oral Histology Enamel Lesson 3 PDF

DENT 112 LEC | ORAL HISTOLOGY LESSON 3: ENAMEL DR. EZEKIEL S. MAJAN 1ST SEMESTER A.Y. 2024-2025 OUTLINE Translucent Color of teeth is from dentin...

DENT 112 LEC | ORAL HISTOLOGY LESSON 3: ENAMEL DR. EZEKIEL S. MAJAN 1ST SEMESTER A.Y. 2024-2025 OUTLINE Translucent Color of teeth is from dentin Cervical area has thinner enamel — ENAMEL appears more yellow (reflects more 1. PHYSICAL PROPERTIES dentin) 2. CHEMICAL COMPOSITION Color can also be affected by: 3. MICROSCOPIC STRUCTURES ○ Age — enamel abrades over time, 3.1. Enamel Prisms/Enamel Rod more of the yellow dentin is seen 3.1.1. Interrod Cementing ○ Diet — enamel is semi-permeable, Substance/Interprismatic Substance 3.1.2. Prism Sheath/Rod Sheath color of food may stick 3.2. Hunter-Schreger Bands 3.3. Incremental Lines of Retzius 3.4. Structureless/Prismless Enamel 3.5. Perikymata/Imbrication Line of Pickerill 3.6. Neonatal Line/Ring 3.7. Enamel Cuticle/Nasmyth’s Membrane 3.8. Enamel Lamellae Patients of Dr. Zeke 3.9. Enamel Tufts 3.10. Enamel Spindles In the cervical area, the color is more yellow 3.11. Scalloped DEJ showing that the enamel is quite thin 4. AMELOGENESIS Naturally yellow teeth + drinks coffee often 4.1. Functional Stages 4.1.1. Pre-secretory Permeable to TFA (Topical Fluoride Application) can 4.1.2. Secretory certain ions make enamel more resistant to caries 4.1.2.1. Tome’s Process Permeability decreases with age 4.1.3. Maturation ○ Recommended fluoride 4.1.3.1. Mineralization application to kids as that’s when 4.1.3.2. Protective 4.1.3.3. Desmolytic it is most permeable 5. CLINICAL CONSIDERATIONS 6. REFERENCES Soluble in Acid attacks from caries and acid 7. TEST BANKS acids etching in restorations begin with the 8. SUMMARY dissolution of the mineral part of enamel, followed by the degradation of ENAMEL the organic part ○ Before getting tooth fillings, they put a blue na parang maasim, 1. PHYSICAL PROPERTIES that’s acid etching Hard, translucent tissue covering the anatomical 2. CHEMICAL COMPOSITION crowns of teeth Acts as a protective The enamel is very calcified and has a high mineral covering of the coronal content dentin — resist forces of mastication Mature Enamel 96% Inorganic substance Hardest calcified tissue in the body ○ Crystalline calcium Enamel phosphate, Hydroxyapatite crystals Varies in Thickest at the cusp tips, thinnest at the 4% Organic substance + Water thickness cervical third ○ Proteins (amelogenins & Incisal edge = 2 mm non-amelogenins like Premolar cusps = 2.3-2.5 mm enamelin & ameloblastin) Molar cusps = 2.5-3 mm (masticatory Largely inorganic forces) Developing 70% Enamel Proteins (organic) Hardest Hard due to its high mineral content Enamel/Premature ○ 90% amelogenins calcified Hardness decreases from enamel to DEJ Enamel ○ 10% non-amelogenins tissue in the (dentino-enamel junction) (enamelin and human body ○ As it goes towards the pulp/dentin, ameloblastin) the hardness decreases 30% minerals (inorganic) Brittle and Prone to fracture if not supported by More organic Inelastic sound dentin (Likened to glass) UPCD 2028 | AUSTRIA, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 1  D112 | LESSON 3 | ENAMEL 3. MICROSCOPIC STRUCTURES GROUND SECTION DECALCIFIED Inorganic substance Organic substance remains remains Organic is burnt Inorganic substance is dissolved → Enamel and dentin → Pulp, dentin, cementum In Cross Section: Rods appear hexagonal, oval or round, or resemble a fish scale Has a head and a tail that resembles a keyhole/paddle However, fully mature enamel are no longer perfectly hexagonal 3.1. ENAMEL PRISMS / ENAMEL RODS because enamel rods press against each other Fundamental organizational units of enamel are: causing them to lose their ○ Enamel prism/rods geometry ○ Interrod enamel/interprismatic substance Basic structural unit of enamel formed by ameloblasts In Longitudinal Section: Long slender structures with roughly 5 or 6 sides It has a segmented appearance and dark lines crossing the rod called “Cross Striations” These Cross Striations represent the daily appositional growth of the enamel rods Intervals between cross striations: 5µ Alternating constrictions & expansions of the rods in some Shaped like a cylinder & regions of enamel which may account for this banded are made up of crystals appearance in ground section with long axes that run in the general direction of The appearance could also result from structural the longitudinal axis of interrelations among groups of rods rather than the rod modification of a single rod Built from closely packed & long ribbon-like hydroxyapatite crystals One enamel rod is surrounded with millions of Hydroxyapatite crystals ○ 60-70 nm in width ○ 25-30 nm in thickness The length spans ALMOST the entire enamel thickness Number of enamel rods can range from: Extending from DEJ to the ○ Around 5 million (lower lateral incisors) surface in a wavy course & ○ To 12 million (upper first molars) oblique direction In deciduous teeth, enamel rods are generally oriented Since it is wavy = Length occlusally/coronally of rods > Thickness of enamel UPCD 2028 | AUSTRIA, DACUNES, MANUEL, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 2  D112 | LESSON 3 | ENAMEL In mature enamel, the rods 3.1.2. PRISM SHEATH / ROD SHEATH are oriented at right angles to the DEJ Outermost portion of the rod; takes stain easily because Pits & Fissures: Tent-like it is more organic manner Narrow space serving as the boundary between rod and Proximal: Horizontal interrod enamel Cervical: Oblique Contains organic material ○ Permanent: face apically ○ Primary: face coronally 3.2. HUNTER-SCHREGER BANDS Alternating light and dark bands originating from the DEJ towards surface (inner ⅘) Caused by different directions of rods/crisscrossing of rods Seen in longitudinal ground section but under oblique reflected light/polarized light In cusps & incisal edges, there are bundles of rods ○ Under the microscope, these may or may intertwining irregularly from DEJ, straightens as it reaches not be seen, depending on how the slides the surface of enamel called “Gnarled Enamel” are prepared The gnarled enamel offer the greatest resistance to A manifestation of the crisscrossing of rods cusps & incisal edges Black arrow - Gnarled Enamel 3.1.1. INTERROD CEMENTING SUBSTANCE / Red Arrow - Hunter-Schreger INTERPRISMATIC SUBSTANCE Bands (alternating dark & light bands Substance that cements rods together ○ In between the rods 1µ thick Formed by the proximal part of the Tome’s process of ameloblasts 3.3. INCREMENTAL LINES / STRIAE OF RETZIUS Surround each rod & its crystals are oriented in a direction different from those making up the rod Brownish bands illustrating the incremental pattern of Rods and interrods have the same composition, just enamel/successive apposition of layers of enamel different orientations Longitudinal section: Surround tip of dentin UPCD 2028 | AUSTRIA, DACUNES, MANUEL, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 3  D112 | LESSON 3 | ENAMEL ○ Cervical parts - run obliquely from DEJ to surface 3.4. STRUCTURELESS / PRISMLESS ENAMEL occlusally Cross section: Appear as concentric dark lines (like No prisms outlines visible growth rings of a tree) 30μ thick Found in: 10 (primary) teeth and cervical region of 20 (Polarized, longitudinal section) (permanent) teeth Apatite crystals parallel to one another; perpendicular to *Shows the incremental lines Striae of Retzius of apposition More heavily mineralized than bulk of enamel beneath it Visible in scanning microscopy (not detectable in light microscopy) Found in: ○ Innermost enamel (contains rods) ○ Outermost enamel (worn-off/abraded in mature teeth) (Cross-section) Black triangles - Incremental Lines of Retzius *Appear as concentric lines A (OBLIQUE lines) - Incremental lines of Retzius 3.5. PERIKYMATA / IMBRICATION LINE OF PICKERILL Enamel Prisms (they form right angles with the Transverse, wavelike grooves dentin) Believed to be the External manifestation of Striae of B - DEJ Retzius C - Dentin Parallel to one another and CEJ ~10 perikymata/mm – occlusal/incisal Periodic bending of enamel rods ○ Seen with bare eyes (Macroscopic) Variation in basic organic structure ~30/mm – CEJ Physiologic calcification rhythm ○ = periods of enamel matrix formation and of rests 20-80µm apart; 4-15µm in width Surrounds the tip of the dentin Cervically - runs obliquely 3.6. NEONATAL LINE / RING (Longitudinal section) Accentuated Incremental Line of Retzius Yellow arrow - enamel separating/differentiating prenatally developed enamel prisms/rod from postnatal enamel Yellow lines - Cross striations Believed to be the result of abrupt changes in environment White arrows - Incremental and nutrition of newborn infant lines of Retzius ○ The difference in environment and nutrition is seen in the development of the enamel after birth UPCD 2028 | AUSTRIA, DACUNES, MANUEL, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 4  D112 | LESSON 3 | ENAMEL The dark band is the 3.9. ENAMEL TUFTS neonatal line/ring It’s an accentuated ALWAYS originates from the DEJ incremental line of Retzius 1/3 to 1/5 of entire enamel thickness Separates prenatal and Filled with protein and organic material postnatal enamel Believed to occur developmentally due to abrupt changes ○ [A] prenatal enamel in the direction of rod groups originating from the DEJ. ○ [B] postnatal enamel “Tuft” – resembles blades of grass attached to a parent stem Longitudinal Ground section in polarized light Narrow, ribbon-like structure composed of bundles of poorly calcified rods & interrod cementing substance 3.7. ENAMEL CUTICLE / NASMYTH’S MEMBRANE Delicate membrane that covers the entire crown of a newly erupted tooth Protects your tooth Shortly removed by mastication ○ Erupted teeth are covered by precipitates of salivary proteins called PELLICLE -> may be colonized by bacteria & food debris -> once pellicle is colonized by bacteria, it forms PLAQUE -> once plaque calcifies, it becomes CALCULUS -> pellicle reforms within hours after mechanical Ground Section of the Enamel cleaning 3.8. ENAMEL LAMELLAE ENAMEL LAMELLAE = originates from the SURFACE ENAMEL TUFTS = originates from the DEJ Cracks in the enamel ALWAYS originates from the SURFACE Leaf-like structural defects 3.10. ENAMEL SPINDLES Filled with enamel protein or organic debris from the oral cavity -> possible avenue for dental caries Club-shaped extensions/projections of dentinal tubules/odontoblastic processes in enamel Consists of linear, Part of the dentin that penetrate the enamel longitudinally oriented May contain a living process of the odontoblast defects contributing to the vitality of the DEJ (extensions of dentin) Smaller than enamel tufts, singular UPCD 2028 | AUSTRIA, DACUNES, MANUEL, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 5  D112 | LESSON 3 | ENAMEL Randomly RECALL distributed in coronal & Advanced Bell Stage sagittal Successional lamina seen above sections blue arrow Outer Enamel Epithelium Stellate Reticulum Inner Enamel Epithelium Stratum Intermedium 2 PHASES: PROCESS OF DEVELOPMENT OF THE ENAMEL Enamel Matrix When enamel first forms, it Formation/Formative mineralizes only partially to Phase approximately 30% Enamel is ECTODERMAL in origin Enamel Spindles ARE NOT Mineralization or As the organic matrix breaks ○ They are projections of DENTINAL TUBULES. Maturation Phase down and is removed, crystals Dentin is MESODERMAL in origin grow wider and thicker Organic materials & water lost; mineral added after full thickness 3.11. SCALLOPED DEJ of enamel layer has been formed to attain 96% mineral content Dentin surface on crown, they are shallow depressions/pits where enamel caps are fitted CHEMICAL COMPOSITION OF ENAMEL Firm attachment of enamel to dentin surface (scalloped for Developing Enamel/Premature Enamel increased surface area & adhesion) ○ 70% Enamel Proteins 90% amelogenins Concavity is 10% non-amelogenins (enamelin and facing the ameloblastin) enamel ○ 30% Minerals Immediate partial mineralization on Convexity is the first increment of enamel facing the dentin 4.1. FUNCTIONAL STAGES Pacman eats the enamel :) Ground section - “enamel space” because it is decalcified A. Enamel Tufts (t for tall) B. Enamel Spindles (s for short) C. Enamel Lamellae D. Dentin E. Enamel ↑ DEJ Life Cycle of an Ameloblast 4. AMELOGENESIS 3 MAIN FUNCTION STAGES + 6 FUNCTIONAL STAGES: AMELOBLAST Presecretory Cells responsible for enamel formation 1. Morphogenetic Derived from inner enamel epithelium of the enamel 2. Histodifferentiation organ Secretory/Formative Ameloblast secrete matrix proteins & are responsible 3. Initial secretory + secretory for creating & maintaining an extracellular environment Maturation favorable for mineral deposition 4. Ruffle ended ameloblast maturation Ameloblast has a unique life cycle in the formation of (transition), Smooth ended ameloblast enamel maturation (modulation) 5. Protective (reduced) 6. Desmolytic UPCD 2028 | AUSTRIA, DACUNES, MANUEL, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 6  D112 | LESSON 3 | ENAMEL 4.1.1. PRE-SECRETORY innermost portion of the tooth Differentiating ameloblasts: ○ Acquire phenotype ○ Change polarity ○ Develop an extensive protein synthetic apparatus ○ Prepare to secrete the organic matrix RECIPROCAL INDUCTION The short columnar cells of IEE become tall columnar, polarized cells known as pre-ameloblasts The first enamel that is laid down (you can ○ Polarized because the nuclei moves away to see it on the top portion) is NOT PART of one side from the dental papilla the rod and interrod enamel They then induce the peripheral cells of the dental papilla to increase in size and become polarized and Secretory As the early secretory ameloblast become odontoblasts Ameloblasts produces enamel, it forms a process -> ○ Peripheral cells move away from the enamel TOME’S PROCESS organ ○ Polarized Odontoblasts then lay down pre-dentin ○ Picket-fence or saw tooth appearance Pre-dentin is mineralized to become dentin (mantle dentin) ○ Pre-dentin sends signals to the pre-ameloblasts This induces the pre-ameloblasts to become ameloblasts, which are now ready to secrete enamel protein matrices Amelogenesis: Pre-secretory 4.1.2. SECRETORY Secretions of enamel proteins become staggered and The basal lamina disintegrates, forming the DEJ confined to 2 sites: (dentino-enamel junction) The cells of the IEE, now ameloblasts, begin to secrete Proximal Forms enamel partitions that delimit a pit more actively enamel proteins that accumulate and Portion (creates a space) immediately participate in the formation of a partially Not distinct units and form a continuum mineralized (30%) initial layer of enamel that HAS NO throughout enamel -> INTERROD RODS ENAMEL As enamel is laid down, ameloblasts will move away from the dental papilla Distal Secretions with matrix forms ENAMEL Portion ROD that later fills the pit ○ Ameloblasts will then develop cytoplasmic projections called TOME’S PROCESS 1.1.1.1. TOME’S PROCESS Juts into and interdigitates with newly forming enamel Gives ameloblasts a picket-fence or saw-toothed appearance The ROD & INTERROD CONFIGURATION of enamel crystals is a property of the AMELOBLASTS & TOME’S PROCESS Ameloblasts in their secretory stage Early Ameloblasts initially looked like this The proximal portion of the Tome’s process will lay Secretory No tome’s process present -> no rods -> down enamel matrix first, leaving a pit or space that Ameloblasts structureless/prismless enamel in the will be filled out by the distal portion of the process UPCD 2028 | AUSTRIA, DACUNES, MANUEL, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 7  D112 | LESSON 3 | ENAMEL ○ Cells from SI, SR, and OEE fuse into 1 layer -> ○ Proximal -> INTERROD ENAMEL blood vessels invaginate deeply into this layer ○ Distal -> ROD ENAMEL to form a convoluted structure Enamel rod and interrod enamel have identical SI + SR + OEE = Papillary Layer composition but differs only in orientation of their Ameloblasts attach to enamel by means of crystals hemidesmosomes ○ Different crystal orientation of enamel gives When enamel is fully mature -> mature ameloblasts and increased resistance to fracture papillary layer regress together ○ Ameloblasts + Papillary Layer = Reduced Enamel Epithelium (REE) The distal portion of Tome’s process ○ Lengthens as enamel thickens ○ Becomes thinner as the rod is growing in diameter and presses it against the wall of the interrod cavity Advanced bell stage As it lays down more enamel, parang kamay siya na nage-extend until it thins C - Stellate Reticulum out since as more enamel is laid down, Before the IEE become ameloblasts, they get their nap-press siya against the interrod blood supply from the dental papilla enamel As enamel forms, the IEE moves away from the ○ As the distal Tome’s process disappears, a dental papilla because of dentin and enamel narrow space is created along the IEE will then get blood supply from the oral circumference between rod & interrod enamel epithelium -> stellate reticulum becomes thinner as -> formation of the PRISM/ROD SHEATH enamel matures The space that was formerly the distal D - Outer Enamel Epithelium portion of the Tome’s process is filled E - Ameloblasts by organic material and now it forms Produce enamel the surrounding prism sheath G - Inner Enamel Epithelium SI + SR + OEE = PAPILLARY LAYER Papillary Layer + Mature Ameloblasts = REDUCED ENAMEL EPITHELIUM When enamel layers are formed, ameloblasts become shorter and lose distal portion of Tome’s process but they still continue to secrete enamel -> Once the ameloblasts lose the Tome’s process and still secrete enamel, will the outermost layer of enamel have rods? NO, because there is no distal portion of the Tome’s process that’s why the innermost and outermost Decalcified Section Preparation enamel are prismless Two Forms of Maturation (Ruffle or Smooth-Ended) 1.1.1. MATURATION Ruffle-Ended Adds minerals to enamel When full thickness of enamel is complete, ameloblasts Maturation enter the maturation stage Stage ○ Post-secretory transition ameloblasts shorten and restructure into maturation cells (ruffle-ended or smooth-ended) UPCD 2028 | AUSTRIA, DACUNES, MANUEL, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 8  D112 | LESSON 3 | ENAMEL Smooth-Ended Removes water and proteins from enters their system and can be incorporated into Maturation enamel enamel during this maturation stage Stage 4.1.3.3. DESMOLYTIC After enamel and dentin reach the CEJ (crown Protective Stage formation finishes) and root formation begins, cells of Part of REE to protect the tooth the REE produce enzymes that cause lysis of the connective tissue (desmolysis) above it RECALL: REE = OEE + SI + SR + ameloblasts The REE then unites with the oral epithelium (OE) to form the EPITHELIAL CUFF, where the tooth will pass as it erupts REE remains until tooth erupts As tooth passes OE (or as it erupts), ○ INCISALLY: the part of REE joined with the OE is destroyed ○ CERVICALLY: REE interacts with OE to become the primary epithelial attachment and form the JUNCTIONAL EPITHELIUM Once the tooth erupts, the inner part of REE (made of reduced ameloblasts) will lose its blood supply and die ○ Disappearance of REE -> formation of GINGIVAL SULCUS That’s why 30% becomes 96% minerals due to BLEEDING AND TOOTH ERUPTION ruffle-ended and smooth-ended ameloblasts Blood vessels can be found in connective tissues. However, REE destroys CT as tooth erupts. 1.1.1.1. MINERALIZATION There are also no blood vessels in the epithelium; hence, we don't bleed when our tooth is erupting. First to mineralize - cusp tips Last to mineralize - cervical areas, fissures, and bottom of pits DIAGRAM *aralin daw to sabi ni sir Primary and Secondary Calcification 1o Calcification Partial mineralization of the segments of matrix as it reaches a certain thickness About 25-30% of mineral salts may be deposited into the matrix 2o Calcification Gradual completion of the mineralization where the rest of the mineral contents are deposited by Completion of crown formation ruffle-ended and smooth-ended A Layers (bottom up): dentin, enamel, regressed REE ameloblasts REE produces enzymes that destroy connective B, C, D 4.1.3.2. PROTECTIVE tissue above it, then merges with OE and forms cuff REE continues to cover the tooth and has a protective E REE is destroyed incisally, but persists cervically function At this phase, the tooth has still not erupted and enamel Inner REE will disappear to form gingival sulcus F composition can still be modified observable at G ○ Fluoride*, if available, can still be incorporated NOT topical (directly applied/ 5. CLINICAL CONSIDERATIONS pinapahid), but systemic fluoride (e.g. taken orally through tablets) Since the tooth is unerupted! ENAMEL HYPOPLASIA & ENAMEL HYPOCALCIFICATION SYSTEMIC FLUORIDE Hypoplasia – defective enamel matrix Hypocalcification – defective enamel maturation In the US, children take fluoridated water. Fluoride UPCD 2028 | AUSTRIA, DACUNES, MANUEL, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 9  D112 | LESSON 3 | ENAMEL Maybe caused by: ATTRITION S̀ystematic ○ Vitamin D Deficiency - Ca & Ph deposition Physiologic wearing (Minerals found in enamel) away of teeth due to Can even occur in the womb, if the mother has occlusion, diet and Vitamin D deficiency mastication ○ Vitamin A Deficiency - Affects ectodermal tissues Physiologic – part of (enamel); if severe = no enamel formation the teeth’s function ○ Febrile Illness - formation is disturbed that all teeth is characterized by distinctive bands of malformed enamel As a kid is growing up, getting a fever can affect enamel formation ○ Tetracycline Antibiotics - May also cause bands of ABRASION brown pigmentation Local Pathologic wearing away of teeth through ○ Caused by very extensive carious lesion such that an abnormal 2° successor is affected mechanical process causing severe loss of CLINICAL SCENARIO: tooth structure A child has a febrile Toothbrush abrasion – illness caused by brushing too During the development hard of their teeth, they got sick SEEN: normal enamel + zone of defective ATTRITION AND ABRASION enamel (developed enamel when the patient Both are wearing away of the teeth was sick) + tetracycline Differentiated through taking history stains EROSION SIDE NOTE Loss of tooth Parents often assume that baby teeth don’t need substance by attention because they will eventually be replaced by chemical process permanent teeth. However, it is the responsibility of the (acids) without dentist to inform them that neglecting to treat issues in bacterial action baby teeth can impact the development of the permanent tooth underneath If a lesion is extensive, it can lead to conditions like local enamel hypoplasia or hypocalcification, known as Turner’s Tooth CARIES If carious lesion reaches the developing permanent tooth before it erupts, it can adversely affect the quality Action of acids formed by microorganisms that dissolves of the enamel enamel Direction of enamel rods affects the spread of caries ○ Pit and fissure caries appear like small lesions outside, but because of the direction of enamel rods and AMELOGENESIS IMPERFECTA dentinal tubules, once you drill up that area, a bigger cavity inside is revealed Group of inherited defects that cause disruption to the ○ Spread of carious lesion on DEJ because of the tufts structure and clinical appearance of tooth enamel (organic, less material for acids to break down → Almost no enamel is visible spreads) UPCD 2028 | AUSTRIA, DACUNES, MANUEL, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 10  D112 | LESSON 3 | ENAMEL ○ Deposited in calcified tissues (bones and teeth) ACID ETCHING The fluoride ion enhances the precipitation of fluorapatite crystals from calcium and phosphate in the saliva Apply acids (phosphoric acid) to enamel to create micro ○ As the tooth is demineralized from bacterial acid porosities to fill with composite, sealant and bond ortho attacks, the hydroxyapatite are broken down brackets (for bonding) ○ Fluorapatite crystals replace the hydroxyapatite Etchant is acid and removes organic film on the tooth crystals surface and creates a rougher surface for bonding ○ Fluorapatite crystals are less soluble and more resistant to acid Too much fluoride (> 1 ppm) can affect ameloblasts while the tooth is developing ○ Will form mottled enamel, seen as white patches of hypomineralized and altered enamel. Still able to resist caries WILL FLUORIDE MAKE ENAMEL HARDER? → No. Fluoride makes the enamel more resistant to acid attacks (won’t demineralize easily). Makes it stronger, not harder. CAVITY PREPARATION Cavity preparation should follow the course of enamel rods Enamel rods at pit and fissure areas run at right angles from the DEJ. Enamel rods close to CEJ run in a more horizontal direction Mottled enamel It is important that unsupported enamel rods are not left in cavity margins due to risk of fracture and possible CAN ENAMEL REGENERATE? leakage. Bacteria will lodge in these spaces inducing → No. At the end of amelogenesis, no ameloblast are left. Enamel secondary or recurring dental caries. cannot regenerate but it can be remineralized because of the Enamels are brittle and inelastic and needs dentin for calcium and phosphate in saliva, even better if fluoride is present. support, without it, enamel will break SIDE NOTE Too much fluoride can affect the ameloblast when the tooth is developing mottled enamel (fluorosis) Mottled enamel – white patches of hypomineralized outer enamel Cavite has the most cases of fluorosis because fluoride exists naturally in their water sources Unsupported Enamel 6. REFERENCES Rods – do not have underlying dentin support [RECORDING] 112 Enamel.m4a = prone to fracture [PPT] ENAMEL-Lecture-2024.pdf In cavity preparations (esp. In cervical areas) 7. TEST BANK maintaining 90o at the enamel margin can 1. T or F. Ameloblasts and amelogenin are important cells increase the risk of in enamel formation. enamel fracture, which 2. T or F. Enamel lamellae make the tooth more leads to microleakage and susceptible to caries. bacterial infiltration A beveled margin 3. Which of the following does NOT play a role in the (15-20o) is recommended hardness of enamel? a. Orientation of enamel rods b. Fluoride incorporation into enamel FLUORIDATION c. Amelogenin degradation during enamel maturation Fluoride ions have the same charge and radius as d. Degree of mineralization hydroxide ions and can replace each other in mineral structures UPCD 2028 | AUSTRIA, DACUNES, MANUEL, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 11  D112 | LESSON 3 | ENAMEL 4. Enamel spindles are formed by which of the following AMELOGENESIS mechanisms? Ameloblast a. Dislocation of dentin during the secretory ○ Enamel formation phase ○ From IEE ○ Secrete matrix proteins b. Extension of odontoblastic processes into the 2 Phases enamel layer ○ Formative c. Irregular deposition of enamel proteins ○ Maturation d. Microfractures in the enamel during FUNCTIONAL STAGES mastication ○ Pre-secretory: Differentiation of ameloblast 5. Identify the pointed structure(s) below. Morphogenetic Histodifferentiation ○ Secretory/formative: formation of DEJ; Tome’s process; rod and interrod enamel form Initial secretory + secretory ○ Maturation: post-secretory ameloblast restructure; mineralization reached 96% Ruffle ended ameloblast maturation (transition), smooth ended ameloblast maturation (modulation) Protective (reduced) Desmolytic CLINICAL CONSIDERATIONS Enamel hypoplasia and enamel hypocalcification Amelogénesis imperfecta 6. What cells are responsible for removing water and Attrition proteins from the enamel as it matures? Abrasion 7. Erupted teeth are covered by precipitates of salivary Erosion proteins called ___? Caries Acid etching ANSWERS: 1F, 2T, 3C, 4B, 5Retzius, Cavity preparation 6Smooth-ended mat. cells, 7pellicle Fluoridation 8. SUMMARY ENAMEL PHYSICAL PROPERTIES Thickness Hardest calcified tissue Brittle and Inelastic Translucent Permeable to certain ions Soluble in acids CHEMICAL COMPOSITION Mature 96% Inorganic substance Enamel 4% Organic substance + Water Largely inorganic Developing 70% Enamel Proteins (organic) Enamel 30% minerals (inorganic) More organic MICROSCOPIC STRUCTURES Enamel rods ○ Interrod Cementing Substance/Interprismatic Substance ○ Rod Sheath\ Hunter-Schreger Bands Incremental Lines of Retzius Structureless/Prismless Enamel Perikymata/Imbrication Line of Pickerill Neonatal Line/Ring Enamel Cuticle/Nasmyth’s Membrane Enamel Lamellae Enamel Tufts Enamel Spindles Scalloped DEJ UPCD 2028 | AUSTRIA, DACUNES, MANUEL, ONG, ORIO, ORLEANS, PACHECO, PERALTA, PLACIDO, SUNICO, TANAGON 12