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IOE > cementum > Flashcards

cementum Flashcards

1
Q

what is cementum

A
  • highly responsive mineralised connective tissue
  • forms a thin layer on + lines root of tooth
  • helps attach tooth via the PDL to alveolar bone
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2
Q

which 4 tissues support the tooth in the jaw/periodontium

A

cementum
alveolar bone
PDL
lamina propria

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3
Q

what does the cementum maintain

A
  • integrity of root

- tooth in its functional position

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4
Q

how does cementum maintain root integrity and tooth position

A
  • formed slowly BUT continuously throughout life

- allowing continual reattachment of PDLs

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5
Q

where may resorption and repair of cementum occur

A

in localised small areas (associated w microtrauma) on roots of permanent teeth

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6
Q

what cells carry out cementum resorption

A
  • multinucleated odontoclasts (may continue resorption into root dentine)
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7
Q

what are cementum resorption deficiencies filled with

A

deposition of mineralised tissue

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8
Q

what seperates repair tissues from normal underlying dental tissues

A

reversal line

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9
Q

how do reversal lines appear

A
  • irregular

- dark-staining

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10
Q

when does repair of cementum occur

A

layer of cementoblasts deposit thin layer of matrix (PRECEMENTUM) in the deficiency

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11
Q

what does cementum repair tissue resemble

A

cellular cementum (with evidence of appositional growth)

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12
Q

what does the irregular rhythm of deposition of cementum result in

A

unevenly spaced incremental lines of Salter

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13
Q

what is unknown to us about cementum’s incremental lines

A

the precise periodicity between them

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14
Q

how do incremental lines appear in acellular cementum

A
  • close together
  • thin
  • even
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15
Q

how do incremental lines appear in cellular cementum

A
  • further apart
  • thicker
  • more irregular
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16
Q

which type of cementum is formed more rapidly

A

cellular cementum

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17
Q

what is the appearance of incremental lines of salter in the cementum due to

A

differences in degree of mineralisation

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18
Q

what are Sharpey’s fibres

A

ends of PDL fibres inserted into root cementum and alveolar bone of the tooth socket

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19
Q

where do the unmineralised fibres of the PDL run

A

into the organic matrix of precementum (secreted by cementoblasts)

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20
Q

what happens when the PDL fibres insert into the organic matrix of precementum

A
  • precementum mineralised + encorporates the extrinsic fibres as sharpeys fibres
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21
Q

what mineralisation properties do sharpeys fibres have

A
  • mineralised within cementum

- unmineralised in ligament

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22
Q

what forms sharpey fibres

A

periodontal fibroblasts

- orientation of sharpeys fibres differs from fibres produced by the cementoblasts

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23
Q

where are sharpeys fibres abundant

A

acellular cementum

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24
Q

why are sharpeys fibres not present in cellular cementum

A
  • its usually present at intrinsic fibre

- it doesnt act in a supportive role as no sharpeys fibres from PDL are inserted into it

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25
Q

what are structural differences between cellular and acellular cementum related to

A

faster rate of matrix formation for cellular

26
Q

what reflects the different rates of cementum formation

A

presence of cementum layer and more widely spaced incremental lines in cellular cementum

27
Q

what cells are present in

a) acellular cementum
b) cellular

A

a) NONE

b) lacunae and canaliculi (oriented toward PDL for nutrition) containing cementocytes and their processes

28
Q

what is the border of

a) acellular cementum
b) cellular

A

a) border w dentine not clearly demarcated

b) border with dentine clearly demarcated

29
Q

what is the net % of each component of cementum based on its wet weight

A

65% inorganic material
23% organic material
12% water

30
Q

explain the variety in the degree of mineralisation in the tissue

A
  • cementum generally softer + more permeable than dentine

- some acellular zones may be more highly calcified than dentine

31
Q

what is the principle inorganic component of cementum

A

HAp (crystals thin, platelike and similar to those in bone)

32
Q

how is the composition of cementum similar to that of bone

A
  • similar in chemical composition and physical properties

- organic matrix consisting of mainly type I collagen

33
Q

how is the composition of cementum dissimilar to that of bone

A
  • cementum has no blood vessels or nerves
  • cementum less readily resorbed (allowing for orthodontic tooth
    movement)
  • doesnt have lamellar appearance or marrow spaces
34
Q

what is the collagenous element of cementum’s organic matrix

A 
type I
(small amnts of III, V, VI + XII found)
35
Q

what is the noncollagenous element of cementum’s organic matrix

A
  • sialoprotein
  • dentine sialoprotein
  • fibronectic
  • osteoporin
    similar to bone
  • glycosaminooglycans (esp chondroitin sulphate)
  • proteoglycans
  • growth factors
36
Q

how does cementum derive its collagen fibres

A

from 2 sources

1) inserting sharpeys fibres of PDL
2) from cementoblasts

37
Q

how does cementum derive its collagen fibres from inserting sharpeys fibres of PDL

A
  • EXTRINSIC FIBRES (when derived from pdl)
  • sharpeys fibres continue into cementum in same direction as the principle fibres of the pdl ligament (perpendicular or oblique to root surface)
38
Q

how does cementum derive its collagen fibres from the cementoblasts

A
  • INTRINSIC FIBRES (when derived from cementoblasts)
  • run parallel to root surface and at right angles to extrinsic fibres
  • do NOT extend into the PDL
39
Q

what is the name of cementum where both

extrinsic and intrinsic fibres are present

A

mixed fibre cementum

40
Q

when does cementum form

A
  • once crown fully formed
  • internal + external enamel epithelia proliferate
    downwards as a double-layered sheet of flattened epithelial cells (epithelial
    root sheath (of Hertwig) that outlines the shape
    of the root)
  • epithelial root sheath induces peripheral cells of the dental papilla to differentiate into odontoblasts + begin producing predentine
  • epithelial root sheath in contact with initial predentine layer for short time before continuity of its cells is lost
41
Q

how is acellular cementum formed

A
  • mesenchymal cells of inner layer of dental follicle, come lie close to surface of newly formed un-mineralised dentine
  • differentiate into cementoblast like cells
  • secrete collagen fibrils
  • begin forming it
42
Q

what is the role at the deep and superficial surfaces of the collagen fibrils secreted by cementoblast like cells

A
  • deep = intermingle with those of the hyaline layer

- superficial = extend perpendicularly into periodontal space to provide attachment for PDL fibres

43
Q

when does cellular cementum appear

A
  • following formation of acellular cementum
    in cervical portion of root
  • it appears in the apical region of root at time tooth erupts
44
Q

how is cellular cementum formed

A
  • large basophilic cells differentiate from the adjacent cells of the
    dental follicle against the surface of the root
    dentine (or acellular cementum) following loss of continuity of epithelial
    root sheath
  • they form distinct cuboidal layer of cementoblasts adjacent to the root surface and secrete the collagen that forms the intrinsic
    fibres of the cellular cementum
45
Q

what is precementum

A
  • thin layer of uncalcifed matrix on surface of the cellular cementum
  • on stained section: appears as pale section between dark pink cementum and light pink pdl
46
Q

how does precementum stay at a constant thickness

A

more matrix deposited on its periodontal surface at same rate as mineral deposited on its inner surface

47
Q

what classifications of cementum exist based on the origin of its organic matrix

A
  • extrinsic
  • intinsic
  • mixed fibre
  • afibrillar
48
Q

what are acellular and cellular cementum also called

A 
acellular = primary cementum (formed 1st)
cellular = secondary cementum
49
Q

how do acellular and cellular cementum appear on the root in most common arrangement

A 
acellular = thin covering over whole root
cellular = predominantly at/around the root apex and overlies the acellular cementum, its also common in interradicular areas
50
Q

how may acellular and cellular cementum deviate from their most common arrangement

A
  • several layers of each
    variant alternate (representing variations
    in rate of deposition)
  • the acellular may overly the cellular
51
Q

what does acellular cementum appear to be

A
  • relatively structureless
52
Q

explain Acellular extrinsic fibre cementum: AEFC and its location

A
  • all the collagen = derived as Sharpey fibres from the pdl (ground substance produced by cementoblasts)
  • corresponds w primary acellular cementum
  • is formed slowly
  • mainly over cervical half of root
  • bulk of cementum in some teeth ie premolars
53
Q

explain Cellular intrinsic fibre cementum: CIFC and its location

A
  • composed only of intrinsic
    fibres
  • absence of Sharpey
    fibres means it has NO role in tooth attachment
  • layer of cementoid on its outer surface (similar to
    osteoid seen in bone)
  • found in patches in apical 3rd + interradicular areas
  • may be a temporary phase w extrinsic fibres subsequently gaining a
    reattachment OR may represent a permanent region without
    attaching fibres
54
Q

explain Cellular mixed stratified cementum and its location

A
  • shows alternation
    of AEFC and CIFC
  • in apical and furcation areas of posterior teeth
55
Q

explain Cellular mixed fibre cementum

A

occasionally normal cellular intrinsic cementum gives attachment to some extrinsic fibres arising
from the pdl

56
Q

explain Afibrillar cementum

A
  • deposited as thin layer overlying enamel at cervical margin of tooth
  • bc reduced enamel epithelium overlying +
    protecting this cervical enamel in an unerupted tooth = damaged or
    lost allowing cells of the dental follicle to come into contact with the enamel surface where they are induced to form
    cementoblast
57
Q

what is the clinical consideration with exposed root dentine

A
  • Developmentally cementum may not completely cover dentine around entire circumference of
    cervical margin
  • SO patients complain of hypersensitivity (no obvious clinically detectable cause)
58
Q

what is another common cause of hypersensitivity complaints

A
  • root cementum exposed due to gingival recession
  • softness of the mineralised tissue + its thinness cervically = frequent abrasion by mechanical friction
  • results in exposure of dentinal tubules to oral
    environment
59
Q

what is the clinical consideration with root caries

A
  • risk of these in pts w cariogenic diet following gingival recession and exposure of root
    cementum
  • ESP elderly (poor saliva flow + oral health)
60
Q

what is the clinical consideration with non surgical periodontal therapy

A
  • chronic periodontitis = bacterial biofilm +
    related mineralised calculus = associated with
    cementum surface of the root deep inside an
    active periodontal pocket
  • evidence indicates bacterial endotoxin is loosely adherent to cementum
  • SO do root surface
    debridement (RSD)
61
Q

what is the aim of ; root surface

debridement (RSD) treatment

A 
- disrupt and remove
the subgingival biofilm
- remove plaque-retentive
factors including calculus
- while preserving
cementum

IOE (22 decks)

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