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
2
Q
which 4 tissues support the tooth in the jaw/periodontium
A
cementum
alveolar bone
PDL
lamina propria
3
Q
what does the cementum maintain
A
- integrity of root
- tooth in its functional position
4
Q
how does cementum maintain root integrity and tooth position
A
- formed slowly BUT continuously throughout life
- allowing continual reattachment of PDLs
5
Q
where may resorption and repair of cementum occur
A
in localised small areas (associated w microtrauma) on roots of permanent teeth
6
Q
what cells carry out cementum resorption
A
- multinucleated odontoclasts (may continue resorption into root dentine)
7
Q
what are cementum resorption deficiencies filled with
A
deposition of mineralised tissue
8
Q
what seperates repair tissues from normal underlying dental tissues
A
reversal line
9
Q
how do reversal lines appear
A
- irregular
- dark-staining
10
Q
when does repair of cementum occur
A
layer of cementoblasts deposit thin layer of matrix (PRECEMENTUM) in the deficiency
11
Q
what does cementum repair tissue resemble
A
cellular cementum (with evidence of appositional growth)
12
Q
what does the irregular rhythm of deposition of cementum result in
A
unevenly spaced incremental lines of Salter
13
Q
what is unknown to us about cementum’s incremental lines
A
the precise periodicity between them
14
Q
how do incremental lines appear in acellular cementum
A
- close together
- thin
- even
15
Q
how do incremental lines appear in cellular cementum
A
- further apart
- thicker
- more irregular
16
Q
which type of cementum is formed more rapidly
A
cellular cementum
17
Q
what is the appearance of incremental lines of salter in the cementum due to
A
differences in degree of mineralisation
18
Q
what are Sharpey’s fibres
A
ends of PDL fibres inserted into root cementum and alveolar bone of the tooth socket
19
Q
where do the unmineralised fibres of the PDL run
A
into the organic matrix of precementum (secreted by cementoblasts)
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
21
Q
what mineralisation properties do sharpeys fibres have
A
- mineralised within cementum
- unmineralised in ligament
22
Q
what forms sharpey fibres
A
periodontal fibroblasts
- orientation of sharpeys fibres differs from fibres produced by the cementoblasts
23
Q
where are sharpeys fibres abundant
A
acellular cementum
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
25
what are structural differences between cellular and acellular cementum related to
faster rate of matrix formation for cellular
26
what reflects the different rates of cementum formation
presence of cementum layer and more widely spaced incremental lines in cellular cementum
27
what cells are present in
a) acellular cementum
b) cellular
a) NONE
| b) lacunae and canaliculi (oriented toward PDL for nutrition) containing cementocytes and their processes
28
what is the border of
a) acellular cementum
b) cellular
a) border w dentine not clearly demarcated
| b) border with dentine clearly demarcated
29
what is the net % of each component of cementum based on its wet weight
65% inorganic material
23% organic material
12% water
30
explain the variety in the degree of mineralisation in the tissue
- cementum generally softer + more permeable than dentine
| - some acellular zones may be more highly calcified than dentine
31
what is the principle inorganic component of cementum
HAp (crystals thin, platelike and similar to those in bone)
32
how is the composition of cementum similar to that of bone
- similar in chemical composition and physical properties
| - organic matrix consisting of mainly type I collagen
33
how is the composition of cementum dissimilar to that of bone
- cementum has no blood vessels or nerves
- cementum less readily resorbed (allowing for orthodontic tooth
movement)
- doesnt have lamellar appearance or marrow spaces
34
what is the collagenous element of cementum's organic matrix
```
type I
(small amnts of III, V, VI + XII found)
```
35
what is the noncollagenous element of cementum's organic matrix
- sialoprotein
- dentine sialoprotein
- fibronectic
- osteoporin
similar to bone
- glycosaminooglycans (esp chondroitin sulphate)
- proteoglycans
- growth factors
36
how does cementum derive its collagen fibres
from 2 sources
1) inserting sharpeys fibres of PDL
2) from cementoblasts
37
how does cementum derive its collagen fibres from inserting sharpeys fibres of PDL
- 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
how does cementum derive its collagen fibres from the cementoblasts
- 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
what is the name of cementum where both
| extrinsic and intrinsic fibres are present
mixed fibre cementum
40
when does cementum form
- 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
how is acellular cementum formed
- 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
what is the role at the deep and superficial surfaces of the collagen fibrils secreted by cementoblast like cells
- deep = intermingle with those of the hyaline layer
| - superficial = extend perpendicularly into periodontal space to provide attachment for PDL fibres
43
when does cellular cementum appear
- following formation of acellular cementum
in cervical portion of root
- it appears in the apical region of root at time tooth erupts
44
how is cellular cementum formed
- 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
what is precementum
- 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
how does precementum stay at a constant thickness
more matrix deposited on its periodontal surface at same rate as mineral deposited on its inner surface
47
what classifications of cementum exist based on the origin of its organic matrix
- extrinsic
- intinsic
- mixed fibre
- afibrillar
48
what are acellular and cellular cementum also called
```
acellular = primary cementum (formed 1st)
cellular = secondary cementum
```
49
how do acellular and cellular cementum appear on the root in most common arrangement
```
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
how may acellular and cellular cementum deviate from their most common arrangement
- several layers of each
variant alternate (representing variations
in rate of deposition)
- the acellular may overly the cellular
51
what does acellular cementum appear to be
- relatively structureless
52
explain Acellular extrinsic fibre cementum: AEFC and its location
- 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
explain Cellular intrinsic fibre cementum: CIFC and its location
- 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
explain Cellular mixed stratified cementum and its location
- shows alternation
of AEFC and CIFC
- in apical and furcation areas of posterior teeth
55
explain Cellular mixed fibre cementum
occasionally normal cellular intrinsic cementum gives attachment to some extrinsic fibres arising
from the pdl
56
explain Afibrillar cementum
- 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
what is the clinical consideration with exposed root dentine
- Developmentally cementum may not completely cover dentine around entire circumference of
cervical margin
- SO patients complain of hypersensitivity (no obvious clinically detectable cause)
58
what is another common cause of hypersensitivity complaints
- 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
what is the clinical consideration with root caries
- risk of these in pts w cariogenic diet following gingival recession and exposure of root
cementum
- ESP elderly (poor saliva flow + oral health)
60
what is the clinical consideration with non surgical periodontal therapy
- 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
what is the aim of ; root surface
| debridement (RSD) treatment
```
- disrupt and remove
the subgingival biofilm
- remove plaque-retentive
factors including calculus
- while preserving
cementum
```
