Periodontium

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Periodontium
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• What is included in the periodontium?
• Cementum
• periodontal ligament (PDL)
• bone lining the alveolus (socket)
• the part of the gingiva that faces the tooth
• These form a gomphosis
• A specialized fiberous joint
• Are ectomesenchymal origin
• Ultimately, the periodontium is tissue that
  supports and invests the tooth.

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Cementum

• Is hard, avascular connective tissue
• Thus, no Haversian system
• Acellular extrinsic cementum is found from the
  cervical margin to the apical 1/3
• Often the predominant type of fibrillar cementum
  on anteriors (single rooted)
• Cellular intrinsic cementum is found from the
  middle to apical and in the furcation area
• Mixed cementum is found in the apical portion and
  the furcation area

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Cementum

• What is cementum made of?
• 40-55 hydroxyapatite (inorganic)
• 50 collagen and matrix proteins (organic)
• Predominately Type I collagen (90 of organic
  material)
• Other types of collagen are present
• Cementum attachment protein
• Insulin-like growth factor

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How do you make cementum?
1) Cells from the inner enamel epithelium of the
root sheath (Hertwigs epithelial root sheath)
send a signal to the dental papilla to have their
cells line up and make dentin 2) After hard
tissue (dentin) is formed, the root sheath
doesnt know what to do because there is no
stratum intermedium (rememberthis layer of cells
act as the contractor). Thus, there is
perforation in the root sheath (ie, cells
die). 3) Due to perforation, the dentin comes
into contact with cells in the dental sac
(ectomesenchyme) which stimulates some of the
dental sac cells to differentiate into
cementoblasts which will make cementum, dental
ligament, and the intercortical plate of the
tooth socket (otherwise known as the cribriform
plate of the alveolous)
As soon as cementum forms, attachment of the
ligament occurs (attachment does not wait until
cementum is fully complete but rather, attaches
as cementum is being laid down)
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Now the monkey wrench The cells of the
inner enamel epithelium that tried to make
cementum but couldnt actually make a fine line
of enameloid substance (clear and glassy)
-enameloid separates the cementum and dentin.
This layer is also known as the Hyaline layer of
Hopewell-Smith Some cells of the root sheath
persist in the periodontal ligament as epithelial
islands. These islands are also known as
Epithelial Rests of Mallasez.
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Cc cementocytes Cb cementoblasts Note
Cementocytes are trapped in the cementum whereas
cemntoblasts are free.
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Cementum

• Afibrillar cementum lacks collagen and other
  fibers.
• Afibrillar cementum occurs when the reduced
  enamel epithelium breaks down prior to the
  eruption of the tooth. Cementum is thus deposited
  over enamel just coronally to the CEJ.

60 30 10
of the time
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Alveolar Process
Alveolar Process portion of the mandible or
maxilla that contains the tooth sockets Cortical
Plates lingual and facial plates of compacted
bone that lies on either side of spongy
bone. Alveolar bone consists of inner and outer
components that contain foramina and is sometimes
referred to as the cribriform plate (called
lamina dura when looking at a radiograph) Bundle
or woven bone the inner component of the
alveolar bone that directly lines the tooth
socket. Laid down in a flat lamellar like
pattern b/c it doesnt have time to establish a
Haversian system. Spongy bone located between
the two cortical plates. The body the portion
of the mandible or maxilla that does not contain
the tooth sockets
Do you have a layer of compact bone between tooth
sockets? -No, all you have is spongy bone
in the interdental septumyou only have
compact/cortical bone on the lingual and labial
sides of it but not mesial and distal.
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Cribriform Plate (Alveolar Bone)
Inner component
Outer component
Alveolar bone has an inner and an outer
component. Remember the inner component is
called bundled or woven bone. It does not have
the Haversian systems because it is laid down
quickly in a flat lamellar pattern. The
nutrient canals in the cribriform plate are
called Zukerkandl-Hierschfield canals in which
blood vessels travel through
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Periodontal Ligament (PDL)

• We would expect to find fibroblasts, osteoblasts,
  cementoblasts, and other entities that enable the
  PDL to be classified as a connective tissue
• Relationship to bone
• Can be called periosteum
• Relationship to cementum
• Can be called pericementum

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PDL

• A soft specialized connective tissue
• Shaped like an hour glass with the thinnest
  portion in the middle third of the root. Average
  width .15 - .38 mm
• The PDL acts as a sensory receptor in that it
  gives us location to where the pain is
• Supports the teeth

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Principle Fibers of the PDL

• Alveolar crest
• Horizontal
• Oblique
• Apical
• Attach to apical foramen
• -from apex to tooth to the floor of the tooth
  socket
• Interradicular
• Between the furcations of a multi-rooted tooth
• (Transseptal) (sometimes put in with the gingival
  fiber group)
• Do not connect to bone
• Go across the interdental septum and connect the
  cementum of adjacent teeth

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Gingival Fibers

• Dentogingival group
• From the tooth to the gingiva
• Alveologingival group
• Alveolar bone (crest of) to the gingiva
• Circular group
• Purely gingival by circling the tooth
• Dentoperiosteal group
• From the cementum of the tooth at the cervix,
  across and over the alveolar crest and inserts in
  the periosteum of the aveolous of the cortical
  plates
• (Transseptal fiber system)

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PDL

• THERE ARE NO ELASTIC FIBERS IN THE PDL
• There are elastic-like (variants) fibers
• elastin, oxytalan, and elaunin
• only oxytalan are present WITHIN the PDL

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Orthotherapy

• Bone is more sensitive to pressure and tension
  than cementum
• which is why orthodontics works
• Pressure causes resorption
• Tension causes building of bone

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PDL Bone Interstitial spaces
Nutrient canals
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Cementum PDL Interdental septum
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Interstitial spaces Cementum Wall of tooth
socket
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This tooth is out of function
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Attached gingiva Oral cavity Crest of the
alveolus Alveolar crest Dentogingival
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Apical fibers Oblique fibers
Arrow points to
the apex of the tooth
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Interradicular septum Interdental septum
Transseptal fibers
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Interstitial area
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PDL Epithelial Rests of Malessez
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Large arrow shows the direction of force
Osteoclasts resorbing bone Osteoblasts
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Cellular cementum Acellular cementum
Granular layer of Tomes
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Cementocytes w/canaliculi
The canaliculi radiate towards the source of
nutrition (in this figuretowards the PDL)
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Cellular cementum
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Cementicles
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Attached cementicle