DENT 5315/DH 2215 February 8, 2008 Dr. Sandra Myers myers025@umn.edu

What are elephant tusks made of? Enamel Dentin Enamel & Dentin Chalk Marble

Ectoderm & Enamel Enamel: an epithelially derived protective covering for the teeth derived from ectoderm Fig. 2-12 p. 26

What happens when ectoderm fails to form or form properly? Ectoderm & Enamel What happens when ectoderm fails to form or form properly?

Enamel & Amelogenesis Enamel: most highly mineralized extracellular matrix 96% mineral 4% organic material & water

Enamel & Amelogenesis Hard Tissue Formation Amelogenesis Structure of Enamel Clinical Correlations

Hard Tissue Formation “Bell Stage” Amelogenesis Structure of Enamel Clinical Correlations

Amelogenesis 3 Main Functional Stages: 1. Presecretory 2. Secretory 3. Maturation Presecretory Ameloblasts: Differentiate (acquire phenotype) Change polarity (nuclei) Develop enamel synthesis apparatus Morphodifferentiation (shape) Histodifferentiation (microscopic)

Amelogenesis Begins first at cusp tips Then sweeps down crown slopes Stops at CEJ

Amelogenesis - Secretory Stage pcw = proximal cell web dcw= distal cell web cell webs hold cells in formation

Amelogenesis - Secretory Stage Hallmarks: Intense synthetic & secretory activity Secretion is continuous Secretory granules not stored Almost immediate mineralization Initial layer does not contain rods Enamel Matrix: Note Tomes’ processes & picket-fence appearance.

Amelogenesis - Secretory Stage IGS = interrod, RGS = rod growth sites sg = secretory granules, ppTP = proximal dp = distal portion of Tomes process

Amelogenesis - Secretory Stage Enamel crystals: What are these composed of? Initial enamel: “no rods” crystalline calcium phosphate (hydroxyapatite) substituted with carbonate ions “pits filling with enamel”

Enamel - Amelogenesis (Note how trajectory of enamel rods changes)

Amelogenesis - Life Cycle of Ameloblasts Functional stages in life cycle of ameloblasts: Morphodifferentiation Histodifferentiation 3. Secretory (initial) 4. Secretory (Tomes’ process) Maturation (ruffle-ended) Maturation (smooth-ended) Protective

Amelogenesis - Maturation Stage Maturation Process: Removal of water & organic material Introduction of additional inorganic material Process = “Modulation” cyclic creation, loss, and recreation of highly invaginated ruffle-ended apical surface on ameloblasts

Amelogenesis - Maturation Stage Ruffle-ended Smooth-ended Ameloblasts incorporation of inorganic material exit of protein fragments & water Ameloblasts

Amelogenesis - Maturation Stage

Ameloblast Modulation (a visually dramatic activity) regional pH variations maturing enamel (rat incisors) Large bands = ruffle-ended cells Smaller bands = smooth-ended cells

Amelogenesis - Maturation Stage Enamel hardens before tooth erupts Results from growth in width, thickness of crystals Amelogenesis slow process almost mature enamel, most mineral removed

Amelogenesis - Enamel Proteins Enamel Proteins: (Table 7-2 text) 1. Contributing to appositional growth, thickness enamel * Amelogenin (main protein in forming enamel) * Ameloblastin * Enamelin 2. Postsecretory processing & protein degradation 3. Related to basal lamina covering maturing, preeruptive enamel 4. Legacy proteins

Amelogenesis - Enamel Proteins Amelogenin protein (stained red) Ameloblasts http://dentistry.uic.edu/CraniofacialGenetics/ResearchTED.htm

Amelogenesis - Enamel Proteins Amelogenin vs Ameloblastin

What is the enamel space? Protective Stage Full thickness of enamel complete, enamel mature Ameloblast layer & papillary layer form “reduced enamel epithelium” What is the enamel space?

Scanning Electron Microscopy Enamel - Structure Hard Tissue Formation Amelogenesis Structure of Enamel Clinical Correlations Scanning Electron Microscopy R = Rod & IR = Interrod Areas

Note: rod, interrod crystals same, but divergent orientation Enamel - Structure Aapd.org/publications/peddent/ Note: rod, interrod crystals same, but divergent orientation

Enamel: hydroxyapatite crystals Enamel - Structure Enamel: hydroxyapatite crystals Young Enamel Older Enamel Transmission EM: rod surrounded by interrod enamel

Enamel - Structure Crystals hexagonal contour to older mature crystals recently formed thin crystals

Enamel - Structure Crystal Profiles hexagons with unequal-sided peaks (un) & equal-sided peaks (eq) x 300,000 (rat incisor)

Enamel - Structure enamel rod orientation A: alternating orientations B: row arrangement C: note thin, long apatite crystals

Enamel - Structure rod sheath rod sheath = boundary between rod & interrod enamel, contains organic material Cat Secretory Stage Enamel Mature Cat Enamel

Enamel - Structure 3 Faces of an Enamel Block cross-section of rod-interrod area appearance compared to “keyhole”