28. Histology of Perio, Gingiva and Oral Mucosa Flashcards
Compare and describe pattern of cementum distribution at different parts of the root and how this relates to age?
- normally in young people, slowly formed acellular cementum predominates the root as teeth have been exposed to comparably less mechanical stress than in older people
- in older people, occlusal wear and compensatory tooth movement induced formation of thicker layer of fast forming cellular cementum especially at apical and interradicular regions
What is the significance of cementum not meeting enamel at CEJ?
- in 10% of cases
- get exposure of root dentine
- patients have a higher risk of dentine sensitivity and root caries
- especially where gingiva recedes
Why are cementocytes shaped peculiarly?
- long cellular processes creating small canals (canaliculi) in cementum
- cellular processes/canaliculi are interconnected and directed towards periodontal ligament from which cementocytes get their nutrients
- cementum is avascular with no blood vessels
What do Lines of Salter represent?
periodic activity of cementocytes
- i.e pauses in cementum deposition
What do Sharpey’s fibres do?
- collagen fibres that insert into cementum and bone
- become mineralised to anchor fibres of PDL in hard tissues
Differences in PDL between young and old patient
- thicker in younger patients
- contains more cells in younger (fibroblasts)
- collagen fibre bundle in older people are thicker and tissue appears fibrotic
Function of oblique fibres in PDL
- most abundant group
- resist compressive forces i.e occlusal forces caused by mastication
What are the main types of collagen in PDL and functions?
- type 1 (80%) and type 3 (15%)
- type 1 forms majority of fibre bundles in PDL
- type 3 forms reticular fibres that crosslink to form fine meshwork of collagen fibres implicated in supporting blood vessels when PDL compressed
- type 3 interacts with platelets to form blood clots and important to wound healing
how do osteons form and how are they linked to osteocytes?
- consist of central Haversian canal surrounded by concentric layers of lamellar bone
- osteoblasts enter inside of them through blood vessel in Haversian canal and produce bone matrix later mineralised to bone
- osteoblasts aligned along bone so results in formation of concentric layers of bone (lamellar bone)
- when an osteoblasts gets trapped in bone, termed ‘osteocyte’
How are osteons different in adjacent region? Compare with with Sharpey’s fibres - what are these?
- osteon is adjacent to bundle bone characterised by presence of Sharpey’s fibres
- bundle bone always found near PDL as PDL fibres insert here and constantly remodel as part of normal physiology or in response to tooth movement
- regions further away from PDL consist of lamellar bone that form majority of alveolar process
What is bone remodelling at reversal stage?
- osteoclasts have stopped resorbing bone
- have disappeared from region, leaving behind resorption bays termed ‘Howship’s lacunae’
Compare reversal line and resting line
- reversal line is where a change from bone resorption to bone deposition had occurred, scalloped to show positions of Howship’s lacunae before bone deposition resumed
- resting line caused by pauses in bone deposition. lines are straighter because osteoblasts align along existing bone
Keratinisation in gingival epithelium?
- orthokeratinised in cats as functional adaptation to increased abrasion by tougher diet
- in humans, gingiva mainly parakeratinised and only partially ortho (in areas of increased action)
Keratinisation of sulcular epithelium?
- nonkeratinised
- bounds the gingival sulcus and acts as epithelial barrier
- development of correct depth of sulcus induced by masticatory forces acting on gingiva
Keratinisation in Nasmyth’s membrane?
- epithelial tag composed of primary enamel cuticle and cell remnants of reduced enamel epithelium
- primary enamel cuticle is internal basal lamina produced by REE cells and attached to enamel
Keratinisation of junctional epithelium
- nonkeratinised
- derived from REE that covers enamel of erupting tooth
- REE/junctional ep cells attach tightly to enamel surface via primary enamel cuticle and hemidesmosomes
- keratin would prevent this
Which gingival fibres are associated with dento-gingival, alveo-gingival and transseptal fibres? Give function
- dento-gingival and alveo-gingival fibres connect tooth and alveolar crest to lamina propria of free and attached propria
- these strong fibres establish and maintain a tight association between gingiva and tooth
- transseptal fibres form an interdental fibre system connecting all teeth of jaw - controls mesio-distal spacing of teeth
Why is there no bleeding when a tooth erupts? Relate to forming of DGJ
- fusion of REE of an erupting tooth with oral epithelium creates DGJ resulting in epithelial continuum
- connective tissue including blood vessels are never exposed to oral cavity, therefore no bleeding
- junctional epithelium remains tightly attached to enamel surface
Surface cells of all epithelia are sloughed off. What happens to surface cells of junctional epithelium?
- sloughed off/desquamated into gingival sulcus
- become component of gingival crevicular fluid
Describe effect of gingival inflammation of sulcular and junctional epithelium. Why?
- inflammation has caused the sulcular and junctional epithelium to form long, irregular rete processes that project lamina propria (epithelial hyperplasia)
- pathological response may compensate for loss of connective tissue mainly collagen
- intercellular spaces between epithelial cells also become larger and basal lamina may be damaged allowing for easier penetration by microorganisms and toxins
Describe effect of gingival inflammation on connective tissue. What’s the role of neutrophils, macrophages and lymphocytes?
- area of inflammation characterised by lots of neutrophils, macrophages and lymphocytes
- number of collagen fibres dramatically reduced compared to healthy gingiva
- chronic inflam leads to destruction of gingival collagen fibres resulting in damage to gingiva and bleeding
- during inflam, cytokine secretion e.g IL-6 and metalloproteinases/MMPs
- MMPs normally involved in remodelling of connective tissue by degrading damaged collagen fibres that need to be renewed during subsequent wound repair of damaged tissue
- however, in chronic, wound healing suppressed and continuous activity of MMPs results in excessive collagen degradation and increased tissue damage
- for example, in chronic periodontitis, overproduction of MMP8 by neutrophils results in excessive degradation of collagen
Examine gingival and palatal epithelium. What is their keratinisation status? Describe function of keratin here in monkeys
- in monkeys, both orthokeratinised
- much thicker keratinised layer in palatal epithelium than in humans
- functional adaptation to consumption of tougher food such as fibrous plants
- keratinised layer of oral epithelia to resist abrasion caused by masticatory forces
What is the functional significance of folding in epithelial-connective tissue interface?
- interdigitation of epithelial ridges (rete pegs) and papillae of lamina propria increases surface area and stability of epithelium-connective tissue interface
- prevents separation of these two tissue layers, especially if exposed to masticatory forces
Function of submucosa and hard palate
What cells do they contain to achieve function?
- submucosa found in lateral/posterior regions of hard palate
- consists of loose connective tissue (fibroblasts), adipose tissue (adipocytes), minor salivary glands and larger blood vessel and nerves
- submucosa provides motility and acts as cushion in mucosae not directly exposed to masticatory forces e.g buccal mucosa
- in contrast, gingiva forms a mucoperiosteum that provides stability and functions to withstand masticatory forces
- in mucoperiosteum, highly fibrous lamina propria is directly attached to periosteum of bone
Which type of collagen is predominant in mucosa of gingiva and palate and what properties does it provide?
- collagen type 1
- produces long strong fibres for tensile strength to resist shearing forces
