Oral Histology: Enamel & Cementum
PDL fibers
A
acellular cementum
A
alveolar bone
A
arrest lines
A
bone
A
cementicle
A
cementoblastic process
A
cementocytes
A
cementum
A
intermediate cementum (acellular)
A
reduced enamel epithelium
A
A--Gnarled enamel found at DEJ B--Enamel Spindle
A-? B-?
tome's granular layer intermediate cementum
A? B?
Enamel formation initiates in late bell stage- after the first deposition of dentin DENTIN ALWAYS COMES FIRST
Amelogenesis Enamel formation initiates in ____ stage- after the _____deposition of _____.
Cementum, like enamel and dentin, is laid down at intervals. Produces a banding pattern of periods of deposition and non-deposition
Arrest/resting lines
PDL
B
bone
B
cellular cementum
B
cementoblast
B
cementoblasts
B
cementoid
B
cementum
B
dentin
B
enamel
B
periodontal ligament
B
tome's granular layer
B
Sharpey's fibers
C
cementoblast
C
cementoid
C
cementum
C
cementum - the fibers here are Sharpey's
C
dentin
C
Merge point of enamel and acellular cementum at cervix of tooth Does not always achieve perfect junction Exposed dentin can be temperature sensitive, is subject to mechanical abrasion during cleaning, can be exposed by recession of gingiva, increases risk for root caries
CEJ
Small calcified oval or round nodules found in a number of sites. Similar to pulp stones in composition. Result from cellular debris, typically from degenerating remnants of Hertwig's root sheath. Most frequently found in the PDL but may be attached to the cementum surface, free in the PDL or embedded in the cementum.
Cementicles
Seals root dentin. Junction between crown enamel and root cementum—cementoenamel junction (CEJ) Acts as 1⁄2 the anchoring system for periodontal ligament (PDL) to hold tooth in the alveolar bone socket least mineralized of the calcified dental tissues
Cementum
cementoblast
D
cementum and cells from dental sac
D
dentin
D
intermediate cementum
D
odontoblasts
D
osteoblast
D (pointing left)
No.
Do the cores of Group II fibers become calcified in calcified cementum?
Yes, it thickens towards the apex. It also thickens with age and trauma. However, acellular cementum NEVER thickens.
Does cellular cementum thicken?
bone
E
cementocyte
E
remnants of root sheath
E
Hard calcified coverings over dentin of the crown and root (respectively)
Enamel and cementum
95% inorganic (Ca salts and hydroxyapatite) 1% organic (protein--enamelin) 4% H2O
Enamel composition
cellular cementum
F
Hardest substance in body, most highly calcified Withstands tremendous stresses involved in mastication Provides shape and contour of crown Part of the tooth exposed to external environment Translucent grayish white in color, may look slightly yellow due to underlying yellowish dentin
Facts about enamel
Collagen fibers from cementoblasts Form the fibrous part of cementum Run parallel to the long axis of the root Contained within the cementum
Group I Fibers
Collagen fibers from dental sac cells Comprise the PDL Insert into the cementum at right angles to the CEJ and to the Group I fibers Called Sharpey's Fibers where inserted into cementum
Group II Fibers
A smooth ground section of tooth does not have a wavy surface. Prisms curve up or down relative to the fracture plane near the dentin-enamel junction. When these areas are cut lengthwise and viewed with incident light- we see enamel prisms reflecting less light and they appear dark. The longitudinal sectioned prisms reflect more light and are lighter looking.
How does this picture explain the ability to see Hunter-Schregar Bands?
2 Group I Fibers and Group II Fibers
How many fiber types does cementum contain?
High mineral crystal structure of rods means they are visible in polarized light Imperfect bands (bent crystals) block polarized light, normal crystals pass polarized light Creates light/dark banding in longitudinal cut dry tooth—called Hunter-Schreger bands No clinical significance
Hunter-Schreger Bands
Local abnormal thickening of parts of the cementum, generally found near the apical region. Caused by: chronic inflammation, loss of an an opposing tooth in the jaw, hypereruption of a tooth or fusion of tooth to surrounding aveolar bone.
Hypercementosis
Initial secretion is amelogenin Later, secretion changes to enamelin (after 3d)
Initial secretion is _______ Later, secretion changes to _________ after 3d)
Mature ameloblasts are tall, columnar 6-sides cells
Mature ameloblasts are tall, _____-sides cells
Reversal lines Cementicles Arrest/Resting lines Hypercementosis
Name some cementum abnormailities
End point for incremental lines (striae, or stripes,of Retzius) visible on the outer surface of the enamel. Visible to the naked eye--called perikymata. Perikymata are produced by hesitation of ameloblasts before the next group of rods contacts the enamel surface. Generally only visible on newly erupted teeth, disappear due to attrition
Perikymata
Presence of dentin (mineralized predentin) initiates completion of differentiation into ameloblasts (columnar shape)
Presence of _____ (mineralized predentin) initiates completion of differentiation into _______ (columnar shape)
lines that reflect active areas of resorption (remodeling). Not as common as in bone, and typically occurs with extreme movement of the teeth by orthodontics or trauma to the teeth.
Reversal lines
pre-ameloblasts (cuboidal shape)
The cells of the inner enamel epithelium differentiate to ____
Perikymata or imbrication lines
What are the fine ridges on enamel surface of crown called?
cementocytes (the shadows of them)
What are these?
secrete cellular and acellular cementum
What do cementoblasts do?
Group II
What group of fibers comprise the PDL?
Group I
What group of fibers form the fibrous part of the cementum?
dental pick probably scraped the dentin
What happened here?
60% small overlap of cementum over enamel 30% perfect sealing edge-to-edge of enamel and cementum 10% failure to meet, small area of Tome's granular layer of root dentin (clinical issue)
What happens at each CEJ level?
cementum in which the cementoblasts have been incorporated into the matrix, they are then called cementocytes
What is cellular cementum?
65% inorganic components 23% organic components 12% water cementoblasts cementocytes type I collagen fibers
What is cementum made of?
The thin layer of cementum deposited by Hertwig's root sheath on Tome's granular layer of root dentin before the root sheath starts to dissolve. Intermediate cementum does not contain collagen fibers but is made up of enamelin It is more highly calcified than either later cementum or Tome's granular layer dentin It is acellular.
What is intermediate cementum?
tome's granular layer
What is the dark line?
initial secretion is amelogenin mature ameloblasts Later, secretion changes to enamelin
What is the initial secretion in amelogenesis? Which cell does this? What is the later secretion?
intermediate cementum (acellular)
What is the white line above the dark line?
Sealant
What is the white-ish material on the left border?
??
What is this area?
Hunter-Schreger Bands
What is this showing?
High mag perfect meeting of enamel and cementum
What is this?
Hypercementosis
What is this?
Perfect meeting of enamel and cementum
What is this?
Perikymata
What is this?
Cross section, hexagonal outline of ameloblast. Ratio of ameloblasts:prisms = 1:1 4 ameloblasts
What is this? How many ameloblast contribute to each rod or prism?
Ameloblasts
What produces keyhole shaped oulines in the enamel prisms?
Presence of dentin (mineralized predentin) initiates completion of differentiation into ameloblasts (columnar shape)
When dentin is present, it initiated completion of differentiation into ________.
After it deposits the intermediate cementum.
When does Hertwig's rooth sheath break up?
Initiates following deposition of predentin
When does amelogenesis initiate?
After the crown is completed.
When does cementum deposition start?
Mesenchymal cells of the dental sac migrate over and attach to intermediate cementum. These cells differentiate into cementoblasts
Where do cementoblasts originate from?
the more cervical areas of root
Where is acellular cementum found?
the more apical area of root
Where is cellular cementum found?
Group II
Which cementum fibers are more coarse?
Acellular, and it is usually covered by a layer of cellular cementum.
Which forms more slowly, cellular or acellular cementum?
Hexagonal shape allows for tight packing in interlocking pattern Interlocking pattern aids in secretion of enamel in set geometric pattern which is maximal in strength
Why are mature ameloblasts hexagonal?
Enamelin similar to keratin in structure, thought to aid in permeability of enamel
_______ similar to keratin in structure, thought to aid in ______ of enamel.
