QUIZ 3 Periodontium II Flashcards
cementum serves to do what 2 things?
- cover the root
- provide PDL attachment
what are the origins of cementum?
describe the composition of cementum
- very similar to bone
- 50% organic, 50% inorganic
- inorganice component: hydroxyapatite
- organic component around 90% collagen type I
- other collagens: type III and XII
- bone-associated non-collagenous proteins
what are the bone-associated non-collagenous proteins of cementum?
- bone sialoprotein (BSP)
- osteopontin (OP)
- osteocalcin (OC)
- osteonectin (ON)
cementum is thinner at the CEJ and thicker at the apex. what are the relative thicknesses?
- CEJ: 20-50um
- apex: 150-200um
cells in the ___ become cementoblasts
dental follicle
HERS cells that break off become ___. HERS cells that remain attached to roots can form ___, which is ___.
- cell rests of malassez
- enamel pearls, which is enamel like material that remains attached to roots
what are two possible scenarios to explain how cells in the dental follicle become cementoblasts?
- HERS or dentin induces cells in the dental follicle to beome cementoblasts
- some HERS cells become cementoblasts themselves
describe the frequency of the 3 types of CEJs
- cementum overlaps enamel - 60% (this is the ideal CEJ because dentin is not exposed)
- cementum and enamel meet to form a blunt end - 30%
- there is a gap between cementum and enamel - 10%
what are the two cementum subtypes?
- acellular (primary)
- cellular (secondary)
describe the differences between acellular and cellular cementum
- classified by the presence of encapsulated cells (cementoblasts) and the predominant origin of the collagen fibers
- collagen fiber origin: extrinsic from the PDL, or intrinsic from the cementoblasts themselves
- acellular has extrinsic fibers, cellular has intrinsic fibers
- primary cementum - acellular extrinsic fiber cementum
- secondary cementum - cellular intrinsic fiber cementum
where is acellular and cellular cementum located?
- acellular extrinsic fiber cementum - coronal 2/3 of root
- cellular intrinsic fiber cementum - apical 1/3 of root
describe AEFC formation
- predentin (unmineralized) forms in the roots
- cementoblasts send processes into this predentin and produce collagen fibers, termed the “fibrous fringe”
- mineralization occurs internally in the dentin and spreads into the cementum
- thus cementum and dentin are mingled forming the CDJ
- after 15-20um of deposition, collagen synthesis stops, and only non-collagenous protein is produced (to induce mineralization)
- collagen fibers from the developing PDL fibroblasts merge with the fibrous fringe and mineralize in place forming Sharpey’s Fibers (hence extrinsic fiber)
- cementoblasts end up only on the surface of the cementum (hence acellular)
describe CIFC formation
- starts very similar to AEFC with intermingling to create the CDJ
- cementoblasts become entrapped in the advancing cementum and become cementocytes
- form lacunae as in bone, but do not establish a complex cellular network like osteocytes (hence cellular)
- cementoid visible at the surface
- there is an initial rapid phase of cementum production, followed by a slower more regular deposition
- the collage fibers present are produced by cementoblasts, not PDL fibroblasts (hence intrincis)
- Sharpey’s fibers can still be present: cementum forms around PDL collagen fibers
- mixed cementum is also possible: alternating layers of AEFC and CIFC with both intrinsic and extrinsic fibers
inner cementoblasts are generally ___
non-vital (no vasculature)
describe the main differences between AEFC and CIFC
- AEFC:
- no cells inside, no cementoid, slower deposition, more mineralized
- functionality: attachment of PDL to cementum
- CIFC:
- more laminar, cells encapsulated, cementoid visible, often absent in canines and incisors
- functionality: some attachment, adaptation and adjustment for wear
what is intermediate cementum?
- between granular layer of tomes and dnetal cementum proper
- mineralization level higher
- may function to seal the surface of root dentin: reduce sensitivity
what is mixed cementum?
- alternating layers of AEFC and CIFC
- extrinsic and intrinsic fibers, generally located apically
- perhaps quite a lot of the secondary cementum is actually mixed
what is hypercementosis?
- abnormal thickening of cementum
- diffuse or circumferential around the whole root
- can affect entire dentition, single tooth, or portions of one tooth
- tooth can become ankylosed
in physiological and orthodontic tooth movement, cementum is more resistant to ___ than alveolar bone
resorption
thus, bone tends to be remodeled first, effectively moving teeth “through” bone
the periodontium is generally affected by what 5 types of tooth movements?
- tipping
- bodily movement
- extrusive movement
- intrusive movement
- rotational movement
orthodontists effectively manipulate the ___
periodontium
in tooth movements, what are the 3 factors that determine the degree of the effect of an applied force?
- tranduction: efficiency of the conversion of physical force into biologic response
- time: effect is time-dependent
- magnitude of force: degree of force determines response
what are the 4 net results of tooth movements?
- compression
- tension
- hyalinization
- undermining resorption
