Histology - Periodontium Structure Flashcards
What are the 4 connective tissues of type I collagen origin in the PDL?
Cementum
– Bone like material (acellular/cellular)
Lamina propria
– Underlying connective tissue
Alveolar bone
– (Lamina dura) many gaps to allow passage of nerves + arteries
Periodontal ligament
– Fills periodontal space between root and socket wall
What are the benefits of the periodontium?
Mammals require excellent occlusion for mastication (meat + vegetables) teeth must be retained within socket for occlusion ( wear from opposing teeth)
Acts as a shock absorber protects the hard and brittle enamel surface of tooth
Allows for eruption to take place
Describe the lamina propria
Dense and fibrous tissue inserts into booth tooth & and alveolar crest
Fibres run in many different directions fibres act in supporting free gingiva & holding gingiva to tooth surface
Describe the junction epithelium
Junction epithelium also form part of the gingival cuff
- Mucogingival junction (MGJ) where keratinised mucosa around tooth meets soft mucosa that form support teeth
- Cementoenamel junction (CEJ) junction between enamel and cementum
Describe the structure of cementum
Composition: Inorganic= 65% Organic- 23% Water=12%
Structurally similar to bone (calcified & Hydroxylapatite)
Acellular region covers the whole of the root formed first
Cellular region is formed last and covers root apex (contains Cementocytes)
Cementoblasts are found on surface of cementum and produce cementum matrix HAP
Describe the cementoenamel junction
3 types of junction
Cementum overlaps with enamel (70%)
Butt join between cementum and enamel (20%)
Gap between cementum and enamel (10%)
Incremental growth lines are observed in enamel (lines of salter)
Describe the periodontal ligament – dentine boundary
Cementum between this boundary
Lines of salter are observed within the cementum
Cementoblasts line the periodontal ligament, they form cementum (part of PDL not cementum)
Pale area can be observed; this is pre cementum (unmineralised)
Describe the cementum and periodontal ligament boundary
Periodontal ligament project Sharpey’s fibres into the cementum (extrinsic fibres)
Sharpey’s fibre is unmineralised in PDL & mineralised in cementum
Cementum between the mineralised Sharpey’s fibres are termed intrinsic cementum formed by Cementoblasts
Sharpey’s fibres are formed from periodontal fibroblasts
Describe the bone and periodontal ligament boundary
Periodontal ligament protrudes Sharpey’s fibres into bone known as bundle bone continuous with transalveolar fibres these insert into base of adjacent tooth
Osteocytes/osteoid/ osteoblasts are seen
What cells are present in the periodontium?
Fibroblasts Cementoblasts Osteoblasts Osteoclasts Cell rests of mallasez Macrophages
What is the role of Fibroblasts?
Responsible for producing/degrading extracellular matrix (type 1 collagen)
What is the role of Cementoblasts?
form cementum
What is the role of Osteoblasts?
form bone
What is the role of Osteoclasts?
remove bone
What is the role of Cell rests of mallasez?
periodontal epithelial cells
What is the role of macrophages?
act as white blood cells
What are the periodontal fibres?
Crestal (Alveolar crest upwards inserts into cementum)
Horizontal (run horizontally from bone to tooth)
Apical (Radiate from root apex)
Oblique (Largest group of fibres)
Interradicular (Run from Interradicular bone (beneath tooth in multirooted tooth))
Describe collagen structure
Tropopcollagen – helical structure Microfibrils Classic fibres – classical banding of 64nm, individual fibre length= 8-400nm, width= 40-50nm Bundles length = 1 micron upwards Principle fibre bundles
Describe oxytalan fibres
Run from cementum to terminate in periodontal capillaries
Little/no elastin found within the fibres
Stained purple when sectioned
Explain the high cellularity of the peridontium
Many cells are seen within the ligament (mostly fibroblasts) so many nuclei observed.
Ligament is 50% matrix of this only 60% is ground substance & 40% is collagen.
Tendons reduce in cellularity as they mature
What are fibroblasts?
Have large amounts of RER which is used in production/transportation of proteins for e.g. collagen production
Metabolically co-ordinated as contain gap junctions between them to help co ordinate collagen production turnover.
Contain vacuoles within cells that store collagen
Fibroblasts can degrade surrounding collagen by degrading extracellularly using collagenases (this occurs in connective tissue).
Within the periodontal ligament fibroblasts break down collagen phagocytically, lysosomes fuse with the phagosome forms phago lysosome leads to degradation.
What are rests of mallasez?
Cells that are remainders of tooth developing process
No role so may play a role in peri apical cysts
What are macrophages?
Contain lysosomes + membrane bound organelles
Found mostly in areas of blood vessels
Describe the blood supply of the periodontium
Blood supply from superior and inferior alveolar arteries
Blood from apex of tooth or intrabony spaces (form arterioles in gingivae)
Capillaries and arterioles form a plexus around tooth
Capillaries have fenestrations
Fenestrations are small holes in side of capillary of 50 nm
Capillaries with fenestrations have more efficient filtering + diffusion and number of fenestrations is proportional to tooth eruption
Volksmans canals carry blood between intrabony spaces and ligament
