Periodontium: intro + cementum

• what is the periodontium?


  ("around the tooth") tissues that support it and anchor it into the jaws

  
• what are the 4 tissues of the periodontium?

  - gingiva

  - cementum

  - the periodontal ligament (PDL)

  - alveolar bone

  
• The developmental origins of the periodontal tissues are from the teeth, not from the jaw

  
  

  TRUE/FALSE

  TRUE
• what is cementum?

  bone-like material that coats the roots of our teeth and grows slowly throughout life

  
• is cementum avascular?

  It is avascular (no blood vessels in it).
• can cementum repair itself?

  it has limited ability to remodel or repair itself.
• what is the external appearance of cementum?

  yellowish
• what is cementum made up of?

  About 45-50% mineral (hydroxyapatite), the rest is mostly type I collagen (90% of the organic material).
• what are the two main types of cementum?

  - acellular (primary)

  - cellular (secondary) cementum.
• describe acellular cementum

  A thin, clear tissue (no cells inside) in ground thin sections covering and protecting the dentine

  
  

  • May contain incremental growth lines as well as Sharpey's fibers

  
• what are the sharpeys fibers in acellular cementum like?

  they are partially mineralised collagen fiber bundles (in this case, derived from the periodontal ligament)

  
• when does acellular cementum develop?

  Acellular cementum develops first prior to tooth eruption
• where is acellular cementum?


  it is the principal cementum type along the cervical 2/3 (or more) of the tooth root

  
• what is the main function of acellular cementum?

  to provide the site of attachment for the fibers of the periodontal ligament.

  -> crucial for anchoring a tooth into its socket
• what are the type types of acellular cementum?

  1. AEFC

  Acellular Extrinsic Fiber Cementum

  
  

  2. AEFC

  Acellular Extrinsic Fiber Cementum

  
• what is acellular cementum that contains the Sharpey's fiber bundles from the periodontal ligament called?

  AEFC

  Acellular Extrinsic Fiber Cementum

  ("Fibers from outside")

  
• what is a second, rarer form of acellular cementum which occurs along the cervical margin of the tooth and sometimes along the cervical most region of the crown called?

  AAC

  Acellular Afibrillar Cementum

  ("No fibers")

  
  

  - does not have an attachment function

  - not found in every person

  
• describe cellular cementum

  • has cementocytes throughout

  (these are former cementoblasts that are now entombed in the cementum matrix)

  • Cementocytes reside in spaces within the cementum, called lacunae (singular: lacuna).

  • Cellular cementum often contains numerous incremental growth lines as well.

  
• show cementocytes in lacunae in cellular cementum

  
• in cellular cementum, what are the tiny projections from the cementocytes called?

  canaliculi

  
• where do the canaliculi point?

  mostly towards the outer surface of the cementum

  
• why do canaliculi point towards the outer surface of the cementum?

  because they will get their nourishment from blood vessels in the periodontal ligament which is around the outer surface of the cementum.
• when does cellular cementum develop?

  it begins forming after ~half of the tooth root has begun to form
• where is cellular cementum?

  Cellular cementum coats the apical 1/3 of the tooth root

  
• which is thicker- acellular or cellular cementum?

  cellular is often thicker than the acellular cementum.
• Cellular cementum is deposited more rapidly than acellular forms, and it is more mineralized.

  TRUE/FALSE

  FALSE

  
  

  
  

  Cellular cementum is deposited more rapidly than acellular forms, and it is LESS mineralized.
• cellular cementum is found in all teeth

  TRUE/FALSE

  FALSE

  Not found in all teeth! May be absent in incisors and canines
• what is the primary function of cellular cementum?

  adaptive:

  • Continuous deposition along the root apex as a tooth slowly erupts and moves within its socket.

  • Minor role in attachment and re-attachment of the PDL fiber bundles.

  
  

  -> Because of this adaptive role, the rates of cementum deposition can change over time, and so can its matrix (lots of Sharpey's fibers vs. none).
• cellular cementum can also have acellular regions within it

  TRUE/FALSE

  TRUE
• what are the two types of cellular cementum?

  1. CMSC

  Cellular Mixed Stratified Cementum

  
  

  2. CIFC

  Cellular Intrinsic Fiber Cementum

  
• what is it called when cellular cementum has a mixture of cementum layers within its regions?

  CMSC

  Cellular Mixed Stratified Cementum

  ("Layers of different kinds of cementum")

  
• what is it called where the layers of cellular cementum have no Sharpey's fibers from the PDL?

  CIFC

  Cellular Intrinsic Fiber Cementum

  ("Fibers are from cementum itself")

  
• what are cementoblasts?

  An osteoblast-like cell responsible for deposition of collagenous cementum matrix (cementoid).
• what are cementoblasts derived from?

  the dental follicle
• what is the function of cementoblasts?

  - Cementoblasts deposit cementum matrix centrifugally (outwards from the tooth) and will migrate with the thickening cementum to avoid being entombed in the matrix (acellular cementum)

  - Cementoblasts may also become entombed in the matrix to form cellular cementum
• how do cementoblasts become entombed in the matrix to form cellular cementum?

  cementoblasts undergo a differentiation process to become cementocytes (cells responsible for maintaining the cellular cementum).