Components of the Teeth - Cementum Flashcards
what are the features of cementum
- cementum covers the root dentine
- it has a very similar structure to bone
- provides attachment for some periodontal fibres
- laid down by cementocytes
in what way is the structure of cementum similar to bone
both have a collagen matrix as well as a lamellar arrangement, which means they go around in circles
what are the two different types of cementum
cellular and acellular
give a brief description of cellular cementum
this form of cementum contains cementocytes, is present in the apical part of the root and is later formed (known as secondary cementum)
give a brief description of acellular cementum
there are no cells, it lies adjacent to dentine and is the primary cementum, ie the first formed cementum
what is furcation
this is where the roots of molars will fork
give a brief description of the acellular extrinsic fibre cementum
this means that the fibres are coming from outside into the cementum, anchoring onto it.
these fibres are collagen fibres known as Sharpey’s fibres, and are equivalent to primary acellular cementum
they are present on cervical roots.
what is the key difference between acellular and cellular cementum
acellular does not have cells within, but it does have Sharpey’s fibres. cellular does have cells but it does not have Sharpey’s fibres
give a brief description on cellular, intrinsic fibre cementum
there are no collagen fibres, but there are intrinsic collagen fibres that run parallel to the surface. this is equivalent to the secondary cellular momentum.
this has no role in tooth attachment, as the fibres can not get out of the cementum, therefore meaning the collagen fibres are not able to attach to the bone on the other side
what are cementocytes
these are the cells that form cementum, and can also be called cementoblasts, although this is not recommended.
in what form of cementum are the cementocytes actively building up cementum
the cellular cementum
how can the production of cementum be described
in waves, which leads to the mixture of cellular and acellular
how can cementum, enamel and dentine be linked
- cementum can be covering the enamel at the cervix of the tooth
- cementum can be just meeting enamel
- there can be a space between the cementum and the enamel which leads to exposed dentine
how is the tooth attached to the bone
via periodontal fibres known as sharpey fibres which attach to the alveolar bone
does the formation of cementum stop once the tooth has erupted
no, it is slowly formed throughout life which allows for the reattachment of periodontal ligament
what is one of the features of cemental growth that allows for the reattachment of periodontal ligament
it is slowly formed throughout life
what can occur to cementum if exposed to the oral environment
due to the relative softness of cementum, combined with its thinness cervically, it can be readily removed by abrasion when gingival recession exposes the root surface to the cellular cementum
what are the lacunae in the cementum
these are the spaces that cementocytes occupy in the cellular cementum
how does cementum compare with the other dental tissues
its crystallinity of apatite is lower, and it can be demineralised more easily
what are the four tissues responsible for supporting the tooth in the jaw
- cementum
- alveolar bone
- periodontal ligament
- gingivae
describe the regional thicknesses of cementum
it is thickest at the root apex and thinnest cervically
is cementum permeable
yes, more so than dentine is, however this permeability declines with age
what is the prime function of cementum
give attachment to the collagen fibres of the periodontal ligament
what is cementoid
the layer of unmineralised matrix
which area of the root is cellular cementum found
in the apical area of the root
where is acellular cementum found
covering the toot adjacent to dentine
what are the structural differences between cellular and acellular cementum though to be related to
the faster rate of matrix formation
where are extrinsic fibres derivded from
the periodontal ligament
where are intrinsic fibres derived from
cementoblasts
what feature of cementum allows the reattachment of the periodontal ligament throughout life
it is slowly formed throughout life
what features of cementum mean it is readily removed by abrasion when the gingival recession exposes the root surface to the oral environment
it is relatively soft and thin cervically
what are lacunae
the spaces that cementocytes occupy in the cellular cementum
how does the crystallinity of the hydroxyapatite in cementum compare to the other dental tissues
it is lower
where is the thickest region of cementum located
root apex
where is the thinnest region of cementum located
cervical region
is cementum more or less permeable than dentine
more
what is the prime function of cementum
to give attachement to collagen fibres of the periodontal ligament
what is the cementoid
the layer of unmineralised matrix in the cementum
where are extrinsic fibres derived from
periodontal ligament
where are intrinsic fibres thought to be derived from
cementoblasts
where is cementum located and what is its function
it is found lining the root of the tooth to help the attach the tooth to the alveolar bone via the periodontal ligament
what does the organic matrix of cementum consist primarily of
type one collagen
what kind of tissue can cementum be described as
calcified
what is cementum derived from
the investing layer of the dental follicle
describe the appearance of cementum
pale yellow, dull surface
is cellular less permeable than acellular cementum
no
how much of the weight of cementum is inorganic material
65%
how much of the weight of cementum is organic material
23%
how much of the weight of cementum is water
12%
what is the principle inorganic component of cementum
hydroxyapatite
does cementum demineralise easier than the other dental tissues
yes
describe the fluoride levels of cementum
high
what is cementum derived attachment protein
a collagenous protein that promotes the attachment of mesenchymal cells to the extracellular matric.
where is the cementum derived attachment protein found
in the matrix of mature cementum and in cementoblasts
describe the presence of growth factors in cementum
there are many, and they are normally locked up and remain inactive due to low turnover rate
how is cementum deposited
in an irregular rhythm
what are there unevenly spaced incremental lines on cementum
because it is deposited in an irregular rhythm.
what is the appearance of incremental lines mainly due to
the differences in the degree of mineralisation, which must also reflect the differences in composition of the underlying matrix, since the lines are readily visible in decalcified sections
give a summary on cellular cementum
- contains cementocytes
- covers the apical area of the root, overlying the acellular cementum
- also called secondary cementum
- in rapidly formed cellular cementum, the incremental lines tend to be closer together, thin and even
give a summary on acellular cementum
- does not contain cementocytes
- covers the root adjacent to the dentine
- also called primary dentine
- structureless
- dark line may be discerned between the hyaline dentine and the acellular cementum
which cementum is formed first
acellula
what is the function of canaculi
connecting the lacunae together
how are the canaculi of the acellular cementum orientated
preferentially toward the periodontal ligament
what is the chief source of nutrients for the canaculi of the acellular cementum
the periodontal ligament
what is the organic matrix derived from
two different sources
- sharpey fibres of the periodontal ligament
- cementoblasts
what are extrinsic fibres
fibres derived from the periodontal ligament that continue into the cementum in the same direction as the principle fibres of the ligament
what are intrinsic fibres
fibres derived from cementoblasts that run parallel to the root at right angles to the extrinsic fibres
what is the name of the cementum where both extrinsic and intrinsic fibres are located
mixed fibre cementum
what are the differences between acellular and cellular cementum
acellular:
- no cells
- no clear border with dentine
- slow development
- close incremental lines
- almost absent precementum
cellular:
- cementocytes and processes found in lacunae and canaculi
- border with dentine is clear
- fast rate of development
- wide incremental lines
- precementum layer is present
describe the acellular extrinsic fibre cementum
all collagen derived from sharpey fibres from the periodontal ligament
corresponds with acellular cementum
covers the cervical two thirds of the root
formed slowly
describe the cellular intrinsic fibre cementum
composed only of intrinsic fibres running parallel to the root surface
absence of sharpey fibres means the intrinsic fibre cementum has no role in tooth attachment
found in patches in the apical region
generally corresponds to the secondary cellular cementum
describe mixed fibre cementum
collagen fibres of the organic matrix are derived from both extrinsic and intrinsic fibres
acellular mixed fibre cementum is the name if the formation is slow
describe afibrillar cementum
no collagen fibres, instead consists of a well minerailsed ground substance that may be of epithelial origin
thought to be formed at this site following the loss of reduced enamel epithelium
how do the periodontal ligament fibres attach to the cementum
the fibres of the periodontal ligament run into the organic matric of the precementum is secreted by cementoblasts, and the subsequent mineralisation of the precementum will incorporate the extrinsic fibres as sharpey fibres
why is the cementum dentine junction of clinical importance
because of the processes involved in maintaining tooth function while repairing a diseased root surface
describe the mineral content of the cementum dentine junction
low
describe the resorption of cementum
- less susceptible to resorption than bone under the same pressures
- carried out by multinucleated odontoclasts
- may continue into the root dentine
- different levels of fluoride in cementum and bone may explain why cementum is less susceptible to resorption
why is the surface of cementum relatively inaccessible
the surface of cementum is covered by a layer of tightly packed collagen
what does cementum repair tissue resemble
cellular cementum
describe exposed root dentine
the cementum may not completely cover the dentine around the entire circumference of the cervical margin, and can be easily abraded away. these conditions lead to the exposure of the dentine tubules to the oral environment. if the tubules are patent, this may give rise to the painful symptoms of hypersensitivity
describe root fractures
the most common cause of root fractures is physical trauma from sports, falls or fights. most often it involves anterior teeth. the plane of fracture may be horizontal or vertical and may lead to mobility in the fractured part of the tooth. dental pulp often retains its vitality
what are cementicles
small, globular masses of cementum found in approximately 35% of human roots. it may be located on the cementum surface or be free within the periodontal ligament. they can occur from microtrauma when extra stress on the sharpey fibres cause a tear in the cementum.
they are more common in the apical and root furcation areas
describe how cementum is involved in regeneration of the periodontal ligament
in the removal of subgingival calculus, care must be taken to limit the removal of cementum.
stem cells associated with the formatio of cementum resides in the periodontal ligament
is cementum harder than dentine
no it is softer
is cementum vascualar
no
what is precementum
a thin layer of uncalcified matrix on the surface of the cellular cementum
is cementum innervated
no
