Periodontal Ligament (PDL) Flashcards
What is the periodontal ligament?
It is the dense fibrous connective tissue that occupies the periodontal space between the cementum of the root and the alveolar bone of the tooth socket
What is the average width of the periodontal space?
0.25mm
What are the 4 main functions of the periodontal ligament?
- It’s responsible for resisting displacing forces and for protecting the dental tissues form damage caused by excessive occlusal loads
- Responsible for the mechanisms whereby a tooth attains and maintains its functional position
- Its cells form, maintain and repair alveolar bone and cementum
- Its mechanoreceptors are involved in the neurological control of mastication
Which cell makes up most of the PDL
Fibroblasts
What is the PDL made up of?
Connective tissue (mainly fibroblasts) and an extracellular matrix
What is the extracellular matrix made up of?
Type I collagen Glycosaminoglycans Proteoglycans Glycoproteins Oxytalan Water
What are the 6 cells that make up the PDL?
- Fibroblasts
- Cementoblasts
- Osteoblasts
- Osteoclasts
- Epithelial cells (Rests of Malassez)
- Macrophages
What are the fibroblasts responsible for?
For the synthesis and degradation of collagen and for secretion of all components of the PDL ground substances
What type of cell and where are cementoblasts and osteoblasts found?
They are formative cells found on the surface of both the cementum and alveolar bone
Which cells are of mesenchymal origin?
Cementoblasts Osteoblasts Preosteoblasts Precementoblasts Epithelial cells
Which cells are involved in resorbing? And where are they found?
Osteoclasts and odontoclasts
They are found on the surface of bone and cementum
Which cells are of macrophage origin?
Osteoclasts
Odontoclasts
Macrophages
What are the rests of Malassez?
Epithelial cells
They are remnants of the epithelial root sheath
What are maacrophages?
Defense cells
They are blood borne cells that enter the PDL from blood vessels
They make up a small percentage of the cell population
What are the collagen fibres in the extracellular mastic gathered into?
They are gathered to form bundles called principal fibres
The region of attachment of the gingiva to the tooth is called what?
The gingival cuff
Where are elastin fibres found?
Elastin fibres are restricted to the walls of the blood vessels
Which fibres make up the periodontal fibres?
- Collagen:
Type I, III, IV, V, VI, VII, XII - Oxytalan, elastic and elaunin
- Reticulin
Which type of collagen makes up most of the PDL?
Type I (70%)
What other types of collagen (apart from type I) make up the PDL?
Type III - 20%
Types IV, V, VI, VII, XII In trace amounts
Where are elaunin fibres found?
They are found around the blood vessels
What might the elaunin fibres do?
They might provide mechanical protection for the vascular system
What are reticulin fibres now known to be?
Type III collagen
What do reticulin fibres form and what do they do?
They for crosslinks and a fine meshwork to aid tissue support
What found between the collagen fibres?
The ground substance
Where are the ground substances found and what do they do?
They are found between collagen fibres They are thought to have many important functions including: Water binding Control of collagen fibrillogenesis Fibre orientation Binding of growth factors
What is the basic unit of collagen fibres?
Triple helical tropocollagen molecules
What happens when triple helical tropocollagen molecules are secreted outside the cell?
They are cleaved and spontaneously aggregate in a staggered fashion, first as a 5 membered micro fibrils and then into classical fibrils
What is the characteristic banding of classical microfibrils?
Characteristic banding at 64nm
What are the fibrils grouped into after classical microfibrils
These fibrils are then arranged into larger structures called bundles ranging from 1 micrometer upwards
What are bundles then further arranged into?
These bundles are then arranged to give he overall tissue architecture called the principle fibre bundles
What is the diameter of small fibrils?
Approx 40nm