PAP2- the periodontium anatomy and function Flashcards
what makes up the periodontal ligament?
- Principal Fibres (collagen/fibroblasts/ ground substances)
- Loose Connective Tissue •Blast & Clast cells
- Oxytalan Fibres
- Cell Rests of Malassez
what does the periodontal ligament attach?
Attachment of cementum (root) to the bone :
-sharpey fibres
Name the groups of fibres that make up the periodontal ligament.
-Oblique fibres
-Apical fibres
-Horizontal fibres
-Alveolar crest
-Inter-radicular
(look at diagram for direction)
where are inter-radicular fibres found?
furcation area
what are the most common types of collagen in periodontal ligament?
- Type I
- Type III
- Type V
- Small amounts of Type IV in basement membranes of blood vessels
what is the difference between type III and type I ?
Type III collagen is more fibrillar and extensible than type I collagen
(this property important for accommodating tooth movement )
what is collagen turned over by?
Fibroblast cells:
- formation
- Broken down
what is the rate of collagen turnover?
-Very high rate
half life approx 3 days around the apex
what is found in the loose connective tissue of the periodontal ligament?
•Fibres •Extracellular matrix •Cells: >fibroblast >undifferentiated mesenchymal cells >defence cells •Nerves •Vessels: >blood >lymphatic
what is the extracellular matrix of the periodontal ligament similar to?
gingival tissue matrix
what is the extracellular matrix turned over by?
Fibroblasts
what does the extracellular matrix include?
- Hyaluronic acid
- heparin sulphate
- chondroitin 4-6 sulphates
what is the extracellular matrix important for binding?
Important for binding H2O:
>hydrostatic cushion
>helps to withstand force of mastication
what is the autonomic nerve supply of the periodontal ligament?
-Sympathetic :
>C fibres (unmyelinated)
>Vasoconstrictor
what is the primary afferent (sensory) supply of the periodontal ligament?
- Mechanoreceptors (AB fibres -large myelinated)
- Nociceptors ( C fibres -unmyelinated and Ad fibres -small myelinated)
Why is a rich nerve supply to the periodontal ligament important?
Important for monitoring masticatory loading + reflex salivation during chewing
What are the 3 principal sources of blood vessels in the heavy anastomosis in the periodontal ligament?
-Apical vessels :
>from the vessels that supply the pulp
>run occlusal vertical direction
-Perforating vessels/ lamina dura origin :
>perforating socket wall (cribriform plate)
-Gingival vessels :
>from gingival tissue
what do the lymphatic vessels tend to follow?
the venous supply
why is the a rich blood supply to the periodontal ligament?
cells are very active and require a kot of energy to be brought to the tooth but they also produce a lot of toxins that must be carried away
what are blasts cells?
- Derived from adjacent undifferentiated connective tissue cells
- producing cells
what do cementoblasts do?
- line the surface cementum
- lay down cementum
What do osteoblasts do?
- line the end-steal and periosteal alveolar bone surfaces
- lay down bone
what are clast cells?
-derived from bone marrow cells
-remove tissue :
>multinucleate cells
>appear on resorbing surfaces
what do cementoclasts do?
- line the surface cementum
- breakdown cementum
what do osteoclasts do?
- line the end-steal and periosteal alveolar bone surfaces
- breakdown bone
what fibres are unique to the PDL?
oxytalan fibres
what is oxytalan fibres nature?
-Elastic in nature :
>variant of elastic fibres
>Immature elastin
where do oxytalan fibres insert?
into cementum
in what 2 directions do oxytalan fibres run?
- parallel to root surface
- oblique to root surface (across oblique principal fibres)
what is the function of oxytalan fibres?
- thought to maintain latency of blood vessels during occlusal loading
- direct fibroblast migration during eruption
what are cell rests of malassez?
remnants of epithelial root sheath of hertwig
what do cell rests of malassez form?
a plexus which surrounds the tooth ( close to the cementum )
what are the cell rests of malassez thought to prevent?
ankylosis - pathology where there is no PDL just straight attachment bone to teeth
what can possibly form from cell rests of malassez?
cyst formation later in life
what is the alveolar bone?
Maxillary & mandibular bone that surrounds + Supports the tooth roots
what does the alveolar bone consist of?
Cancellous (Trabecullar /Spongy) bone covered by a thin layer of compact (cortical) bone
what inserts into alveolar bone?
PDL fibres (sharply fibres)
what bone is more dense?
cortical bone
what is the bundle bone?
- Part of the bone to which the tooth attaches (tooth socket)
- bundle bone is heavily perforated by blood vessels
what is the alternative name for bundle bone?
cribriform plate
what do the cribriform plate (bundle bone) look like on the radiograph?
shows up as a narrow radio-opaque white line around the root called the lamina dura
what does the loss of the lamina dura suggest?
pathology
Describe the turnover of alveolar bone.
-Constant turnover :
under influence of systemic and local factors
How does alveolar bone remodel?
Can remodel in response to functional demands
What effect does resorption factors have?
target osteoblasts which then instruct osteoclasts to remove bone
what is cementum?
Mineralised tissue with a similar composition to bone which covers the root surface
what are the features of the cementum?
- less mineralised than bone and dentine
- avascular (no blood vessels or lymph vessels)
- not innervated
what is the cementum site of anchorage?
PDL fibres onto teeth ( sharpeys fibres)
what are the 2 types of cementum?
- cellular cementum
- acellular cementum
What tissue homeostasis?
- Controlled synthesis & breakdown of tissue which ensures the maintenance of the composition, volume & it’s integrity.
- Also allows ability to respond to functional demands
Describe the tissue homeostasis of epithelium.
- Oral epithelial keratinocytes are continually shed.
* In health these are replaced by an equal number of cells from cell division in the basal cell layer
what do stem cells in the epithelium have the ability to do?
cells in the basal layer retain an ability to divide throughout life
what are stem cells essential for?
for renewal of the epithelium = Turnover
Epithelial turnover is influenced by factors that affect the rate of what?
- cell division
- maturation
- movement of cell through the prickle cell layer
- desquamation
what systemic hormones affect epithelial turnover?
- oestrogens (increases)
- adrenaline (reduces)
- corticosteroids (reduces)
what are more important than systemic hormones?
local factors
what are cytokines produced by and what effect do they have?
Cytokines are proteins/glycoproteins produced by various cell types which can regulate growth & differentiation of other cells (at least 3 cytokines affect epithelial turnover)
what cytokines stimulate keratinocytes division?
- transforming growth factor alpha (TGFa)
- Epidermal growth factor (EGF)
what cytokines inhibit keratinocytes division?
-Transforming growth factor beta (TGFB)
what on top of epithelium , undergoes continuous turnover?
connective tissue
what is threat of turnover of connective tissue?
- PDL 5x > alveolar bone
- PDL 15x > skin
what are fibroblasts responsible for?
-synthesis & degradation of collagen + extracellular matrix
(secrete enzymes that breakdown collagen = collagenases)
what do collagenous cleave?
- cleave segments off the collagen fibrils which are taken up by the fibroblasts.
- Fibroblasts then degrade these intracellularly (lysosomal enzymes).
what do fibroblasts regulate the activity of?
Metalloproteinase enzymes, such as collagenases, by also releasing Tissue inhibitors of metalloproteinases (TIMP):
(TIMPs prevent unwanted /uncontrolled tissue damage by collagenases)
what is involved in the regulation of connective tissue turnover?
cytokines are probably important ( little known)
what cytokines stimulate connective tissue turnover?
- platelet derived growth factor (PDGF)
- Fibroblast growth factor (FGF)
- Transforming growth factor beta (TGF-B)
what cytokines inhibit connective tissue turnover?
- interleukin - 1
- interferon gamma
Describe the homeostasis of bone.
•Turns over throughout life. •Volume relatively constant. •Able to remodel which is important for: >maintaining blood calcium levels >adaption to changes in mechanical loading
Describe the homeostasis of local periodontal bone resorption.
-Factors thought to stimulate local bone resorption (in vitro) :> prostaglandin
>interleukin
>tumour necrosis factor alpha
>tumour necrosis factor beta
when are these factors produced in bone resorption?
•These factors are produced during inflammatory & immune responses.
(•Important in periodontal disease?
•Important in normal tissue homeostasis?)
