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What is the hardest substance in the body? What is it's composition (include percentages)?
- Enamel; it's also the most calcified of the dental tissues. Mainly made of inorganic salts and hydroxyapatite.
- Inorganic: 95% (hydroxyapatite and calcium)
- Organic: 1% (mostly protein ENAMELIN, which is similar to keratin in structure. Thought to aid enamel in permeability properties. This becomes calcified later on.)
- Water: 4%
Out of bone, enamel, and dentin, which one takes the longest to calcify?
- Enamel (takes off quickly, but takes years to finish.) (Bone and dentin don't start immediately, but once they do, they achieve their max fairly quickly.)
At what stage of tooth development does enamel formation occur?
Fill in the blank: Following deposition of (blank) by the odontoblasts and mineralization to form (blank), the (blank) become differentiated and being to secrete enamel.
- Predentin. Dentin. Ameloblasts (although she says "preameloblasts" during the lecture).
- She also says in lecture that full ameloblasts initiate secretion of enamelIN, which then calcifies to become enamel...
From where do ameloblasts derive?
They're differentiated cells from the inner enamel epithelium.
Describe the structure of ameloblasts and how this structure relates to cell function.
Ameloblasts are tall, columnar, 6-sided cells. This structure allows the cells to pack in close together (interlocking), which aids in the enamel secretion into set geometric patterns that are maximum in strength (allows enamelin and hydroxy crystals to close pack, with minimal organic material between them.)
What is Tome's process? Describe the physical features distinct to it.
- The secretory process that ameloblasts use to deposit enamel is termed "Tome's Process". It is shorter than an odontoblastic process, and is shovel-shaped or knife-like.
True or false: Enamel maturation begins once the enamel is completely formed.
False. Enamel maturation begins before the enamel is completely formed; begins with the depositing of hydroxyapatite crystals into the matrix that are thin and needlelike.
Why are hydroxyapatite crystals in enamel four times larger than in bone, dentin, or cementum?
- During the process of enamel maturation, the hydroxapatite crystals increase in size in all dimensions. This is possible b/c water and organic material is removed, allowing for calcium salts to enter into the newly created space and to enhance crystal growth. The resorptive properties of the ameloblast make this large size possible.
- (Enamel - 6)
Name and describe the two major phases of ameloblasts while depositing enamel.
- 1) Secretory phase: when ameloblasts deposit enamel matrix containing enamelin. Tome's process is evident.
- 2) Resorbing stage: after deposition of enamel, ameloblasts remove most of the water and organic components from the matrix. There is no visible Tome's process. The border takes on a ruffled appearance.
- (Enamel - 7)
What are "rods" or "prisms" in the context of enamel/cementum?
Enamel is composed of tightly packed masses of hydroxyapatite crystals called "rods" or "prisms".
- Enamel rod formation is related to the shape of Tome’s process and the orientation of the crystals as they are laid
- down by the ameloblasts. The prisms are rod-shaped structures that run from the DEJ to the outer edge of the enamel surface.
- (Enamel -8)
Explain the phenomenon of "key-hole shaped prism" and the hexagonal orientation of the ameloblasts and rods.
Hexagonal shape of ameloblasts causes rods to appear as a key-holed shaped prism when viewed in cross section, w top of keyhole facing occlusal or incisal edge of tooth, and tail facing the cervical portion. Keyhole side is growing out towards the oral cavity.
Decribe gnarled enamel.
- During crown maturation, enamel rods are deposied pependicular to teh DEJ to the tangent of the enamel surface --> gives maximal packing between rod units. In some areas, this isn't possible, and enamel rods become bent. The prisms become intertwined and the space between the rods is much greater (allows for greater susceptibility by microorganisms to penetrate enamel; prime sites for caries.)
- (Enamel - 10)
True or false: Gnarled enamel areas are more susceptible to caries that nicely laid, perpendicular enamel areas.
True. In gnarled enamel areas, there's a higher percentage of organic material, so there's less calcium and hydroxyapatite there, and they're MORE susceptible to caries.
Why do incremental lines form? What is another name for them?
- They're the point at which secretion of enamel paused and absorption occurred; it's indicative of a change in phase (according to lecture). Incremental lines are the result of rhythmic recurrent deposition of enamel (according to slide).
- - As matrix mineralizes, these lines follow the growth lines of enamel and are called "Striae (or Stripes) or Retzius"
- (enamel - 14)
What are Hunter-Schreger Bands? Why do we get them?
- Since enamel has such high inorganic and crystal structure, if one sections a crown longitudinally and subjects it to polarized light, imperfect (bent) crystals will not allow the light to pass through. This creates a pattern of light (permissive) and dark (non-permissive) bands in the enamel, called Hunter-Schreger Bands. They develop b/c enamel rods/prisms tend to rotate as they're laid down. There is NO CLINICAL SIGNIFICANCE to these.
- (Enamel - 15)
There are points on a tooth that are the end point for incremental lines/Stripes of Retzius on the outer surface of enamel. These lines are produced by hesitation of ameloblasts before the next group of rods contacts the enamel surface (they are the heads of the enamel prisms). What are these end points called?
- Note: perikymata are seen only in fairly newly erupted teeth; they smooth out quickly.
- (Enamel - 18)
What are cracks in enamel cystalization called? When and where can these form?
- Enamel lamellae. They can be the result of defective enamel formation during development or after eruption from impact or from temperature related trauma (breathing cold air, drastic oral temp differences). They can extend all the way through enamel or only part way, and come from either crown of tooth or from DEJ.
- (Enamel -19)
What are the three main defects in enamel?
What enamel defect is described by location near the DEJ, forms between groups of enamel rods that are oriented slightly apart from one another, not in a straight line, the spaces tend to fill w enamelin, and it's indicative of areas of poorer secretion of enamel, hence, more organic material here?
- Enamel tufts
- (Enamel - 20)
True or false: Enamel spindles ALWAYS occur at DEJ.
- True. Enamel spindles form at DEJ and extend into the enamel. They're extensions of overambitious odontoblastic processes, where the odontoblast in the pulp has processes upward and outward pas the DEJ; they become trapped due to a failure to withdrawl back into the dentinal tubule before amelogenesis occurs.
- Note: they can functionally secrete dentin in some cases!
- (Enamel - 21)
How does adding fluoride change enamel?
- Enamel is semi-permeable tissue. Flouride ions are absorbed onto the hydroxyapatite crystals, changing the hydroxyapatite into fluorapatite. Fluorapatite is much more resistant to bacterial acids secreted onto the enamel surface, which makes teeth more impervious to caries.
- Drinking water fluoride is also thought to alter the environment of the teeth, particularly w respect to the oral bacterial flora, and has been the single most important intervention in preventing tooth decay.
- (Enamel - 29)
How does acid etching affect teeth?
- Acid etching penetrates the enamel surface for a short distance (30 micrometers) and attacks the mineral matrix at the periphery of the sheaths. It can also attack the rod core and have the same effect.
- (Enamel - 29)
True or false: Individual keyhole prisms of enamel has more coating on outside and edge of head, so it's not susceptible to acid etching.
- False. Individual keyhole prisms of enamel have little coating on outside and at the edge of the head. This makes the surface more susceptible to acid etching, due to slightly higher organic composition here.
- (Enamel - 30)
What effect does the broad spectrum antibiotic Tetracycline have on teeth?
- The organic and inorganic components of bone and dentin try to bind to the drug. For pregnant women and young children, developing dentin and bone will bind and incorporate tetracycline permanently within the mineralized matrix. It appears clinically as dark bands through the enamel, where it is the thinnest, as a result of binding to dentin. The stains are nearly impossible to bleach out, as it's dentin stain, not enamel...
- (Enamel - 31)
Why do enamel pits and fissures form developmentally?
- P & Fs form where ameloblasts become crowded between adjacent areas (cusps), causing incomplete maturation of enamel (higher concentration of calcified material). Such teeth are at increased risk for dental caries (they collect food material here as well) and require sealants for preventative purposes.
- (Enamel - 32)
What are two functions of dental cementum?
- 1) Provides a protective covering to the tooth.
- 2) Serves to keep tooth suspended in its bone socket by forming attachments with the PDL on one end while the other end of the PDL is attached to the alveolar bone proper --> allows teeth to be suspended in the jaw.
- (Enamel - 33)
What is the composition of cementum?
- Cementum is the LEAST MINERALIZED of the calcified dental tissues:
- 65% inorganic
- 23% organic
- 12% water
- Type I collagen fibers
- (Enamel - 33)
True or false: Cementum development begins mid-way through crown formation.
- False. Cementum is formed after crown formation is complete.
- (Enamel - 34)
From which two epithelial layers do Hertwig's Root Sheath Cells derive? What role does HRS play in the development of cementum?
- - The Outer Enamel Epithelium and the Inner Enamel Epithelium.
- - HRS grows downward, shaping the root of the tooth. Root dentin begins to be deposited and the cells from the inner layer of HRS deposit a 10 micrometer layer of INTERMEDIATE CEMENTUM (also called CEMENTOID or PRIMARY CEMENTUM).
- (Enamel - 34)
Intermediate Cementum is deposited on what layer, prior to the root sheath breaking apart?
- Tome's granular layer (or dentin)
- (Enamel - 34)
Like the enamel in the DEJ, this layer of hard tissue seals the tubules of dentin in the root area ...
- Intermediate cementum
- (Enamel - 34)
True or False: Since it is epithelial in origin, intermediate cementum does not have collagen fibers as its organic matrix but uses enamelin like ameloblasts for enamel formation.
True or False: Intermediate cementum calcifies to a lesser extent than the adjacent dentin or the next layer of cementum to be deposited.
- False. Intermediate cementum calcifies to a GREATER extent than the adjacent dentin or the next layer of cementum to be deposited.
- (Enamel - 34)
What cells are responsible for laying down secondary cementum in the root area? From which cellular origin do these hail?
- Following intermediate cementum, the Hertwig's Root Sheath breaks up and cells from the dental sac (mesenchymal in origin) migrate in and attach to the intermediate cementum. These cells differentiate into cementoblasts and begin to produce BOTH cellular and acellular cementum (depending on whether cementoblasts are incorporated into the matrix).
- (Enamel - 35)
What do you call cells that are stuck in cellular cementum? (This sounds like the beginning of a bad joke... but it's not... or it is... and the joke's on us...)
- Cementocytes (hmmm... not so funny, really)
- (Enamel - 35)
Are cementocytes more like dead cells in cellular cementum or are they still productive?
- Cementocytes continue to produce cellular cementum in a lacunae (just like osteocytes).
- (Enamel - 35)
True or False: Cellular cementum is generally found in the more cervical regions of the root, while acellular cementum is in the lower areas and is deposited after tooth eruption.
- False (this is the sentence that was jacked in the lecture...):
- ACELLULAR cementum is generally found in the more cervical regions of the root, whereas CELLULAR cementum is in the lower areas and is deposited after tooth eruption.
- (Enamel - 35)
True or false: At the time of tooth eruption, one would have both intermediate and secondary cementum completed on the root.
- False. Cellular cementum is deposited after tooth eruption. Cellular cementum tends to grow w age and is a vital tissue.
- (Enamel - 34 & 35)
Contrast the thicknesses, location, and developmental rates of acellular and cellular cementum.
- Acellular: 10 micrometers thickness, on the cervical 1/3 of tooth, forms more slowly than cellular cementum, and is covered with a layer of cellular cementum to a total thickness of 50 micrometers, and never thickens.
- Cellular: reaches 100-150 micrometers, thickens apically down the root, continues to grow w age, is a vital tissue.
What cells produce Group II Fibers? Are these fibers part of the cementum or the PDL? Are these fibers parallel or perpendicular to the long axis of the root? Are they coarser or smoother than Group I Fibers? What is another name for these fibers?
- -Produced by dental sac cells
- - Comprise the PDL
- - Insert into cementum at right angles to CEJ or at right angles to long axis of tooth (Group I orientation)
- - Coarser than Group I fibers
- - Cores DO NOT calcify in the calcified cementum
- - Also called Sharpey's Fibers (the fiber portion in the cementum and not the exposed portion)
What cell type produces Group I fibers? Do they form the fibrous part of the cementum or the PDL? Do they run perpendicular or parallel to the long axis of the root? Are they internal or external fibers?
- - Produced by cementoblasts
- - Form the fibrous part of the cementum
- - Run parallel to the long axis of the root
- - Internal fibers (in the cementum)
Why would teeth show signs of reversal lines?
Reversal lines reflect areas of active resorption (remodeling). This is not as frequent as in bone, and typically occurs w extreme movement of teeth by ortho or trauma.
What are cementicles?
These are small calcified oval or round nodules found in the PDL, attached to the cementum surface, or embedded in the cementum. Similar to pulp stones (in dentin). They're the result of cellular debris, typically degenerating remnants of HRS, epithelial rests, or Rests of Mailez that've become calcified.
What do "arrest" or "resting lines" refer to, in the context of cementum?
- They are a banding pattern, which reflects periods of deposition and non-deposition of enamel.
- (Enamel - 45)
What can produce hypercementosis, or a local thickening of parts of the cementum?
- Chronic inflammation
- Loss of an opposing tooth in the jaw
- Hypereruption of a tooth
- Fusion of tooth to surrounding alveolar bone
- (enamel - 45)
The cementoenamel junction does not always achieve a consistent abutment of crown enamel to root cementum. What percentage of time does this junction overlap, meet, or gap, respectively? What is the most serious concern when probing?
- 60% overlap
- 30% meet
- 10% gap
- - gap is main probing concern of the three, as the cementum does not meet the enamel and dentin is exposed.
- Note: gingival recession also leaves exposed cementum of dentin, creating root sensitivity and increased risk for root carries.
- (Enamel - 47)