How are enamel rods arranged at the ADJ?
Perpendicular to junction - at right angle
What is the composition of enamel?
Hydroxyapatite crystals - 95%
Water - 4%
Organic matrix (proteins) - 1%
What are the characteristics of enamel?
Very brittle, can resist abrasion. Requires underlying dentine to provide support or would be too brittle. translucent - line shines through, no colour
How are enamel rods formed?
Projections of cells at amelo-dentino junction, tomes processes found, contains ameloblasts. Contains many Rough ER and golgi apparatus, produces proteins which are then secreted into vesicles. Vesicles contain and release hydroxyapatite crystals into matrix of enamel, mineralising the matrix. forms enamel rods. crystallites are deposited at right angles to ameloblast membrane.
What is a dead tract?
When enamel becomes worn away, it can expose dentine. This forms a tract in which air and bacteria can get in to dentine, which then appears black.
what are the oblique lines seen in enamel?
Striae of retzius - these are oblique lines, running from surface to ADJ. They represent the growth pattern of enamel during crown formation.
What surface variations can be seen in enamel?
In anterior teeth, enamel is thickest at the incisal edge and thinnest at the cervical region. In posterior teeth, enamel is thickest at occlusal surfaces and thinnest at fissures. The thick regions are areas with a lot of wear. The thin regions are most vulnerable to caries.
What is the difference in composition and characteristics between enamel and dentine?
Dentine has a higher composition of water and organic matrix, and a lower composition of HA crystals. This allows it to be more resistant to tensile and compressive forces as it is much less brittle.
What area of the teeth is dentine thickest?
Areas where teeth are sliding on one another, e.g. cingulum
How is dentine arranged?
In dentinal tubules, which are laid down by odontoblasts at the pulp region. These tubules are enclosed by peritubular capsule. Between tubules is the inter-tubular space
What is the difference between dentine at the pulp and dentine closer to enamel?
Dentinal tubules at the pulp have a large diameter but are also very compact. This is because they are just fresh. At the enamel, the tubules have started to die so are much thinner and there is a lot less of them.
What is the primary and secondary curvature of dentine?
Primary curvature - tubules run in an s-shape from ADJ to pulp.
Secondary curvature - the curves of individual tubules
What is the difference between primary and secondary dentine?
Primary dentine is produced when the tooth is forming. It is laid down rapidly. Secondary dentine is continually produced once the tooth is formed. This replaces dead dentinal tubules. Secondary is at a much slower rate as there would not be enough space to accommodate the rate of primary dentine formation.
When is tertiary dentine produced?
After trauma, when dentine is damaged
What cells can be found in dentine?
odontoblasts, nerve cells (unmyelinated, often nociceptors), dendritic cells for immune function - never blood vessels
What is the function of the pulp?
To produce unmineralised dentine - predentine
provide nutrients to the tooth and contains immune cells to fight infection
What nerve fibres can be found in the pulp?
Sensory - for detecting pain and inflammation
autonomic - constriction of blood vessels, via sympathetic NS
What are calcospherites?
Clumps of pre-dentine which then becomes mineralised to become dentine
What structure is similar to cementum?
Bone - it is arranged in lamellae but linear instead of circular which is found in bone
What is the role of cementum?
To cover root dentine and for attachment of periodontal fibres
What is the difference between acellular and cellular cementum and where can each be found?
Cellular cementum contains cementocytes in lacunae, whereas acellular cementum has no cementocytes. Cellular can be found at the apex and in furcation areas. Acellular can be found adjacent to dentine at the cervical 2/3rds of the root.
What different fibres can be found in cementum?
Intrinsic fibres - often found in cellular cementum, as these fibres are produced within the cementum.
Extrinsic fibres - not produced in the cementum, arise from structures elsewhere. Often found in acellular cementum, also known as Sharpey’s fibres. These have an important role in stabilising the tooth
Describe the extracellular matrix of the periodontium.
Composed of long chain proteoglycans and glycoproteins. Makes the matrix gel-like, allowing it to absorb forces.
Where can plaque bacteria attack in the periodontium?
It can attack the side chains of the proteoglycans or glycoproteins, destroying the periodontium makes the tooth more mobile
What nerve fibres are present in the periodontal ligament?
Nociceptors - have a reflex loop, activated when we bite on something too hard, immediately open mouth.
Mechanoreceptors - to determine if food is soft or hard, detect load of PDL and alter bite
Autonomic - for vasoconstriction of blood vessels
What are the two types of PDL fibres and what is the difference between the two?
True fibres - attach alveolar bone to cementum of tooth.
Gingival fibres - run in the gingiva, attach tooth to tooth or tooth or bone to gingiva
What PDL fibres have a sling effect?
Oblique fibres, preventing stretching
In which 2 ways is oral mucosa protective?
Mechanical - many layers
Infection and immunity
where can lining mucosa be found?
buccal areas, soft palate
Where can masticatory mucosa be found?
gingiva and hard palate
What is the structure of lining mucosa and why does this suit the function?
Has a loose lamnia propria and submucosa, allows it to be distendible, crucial for the surrounding muscles and for impression taking
What is the structure of masticatory mucosa and why does this suit the function?
Has a thick lamnia propria, and no submucosa, lamnia propria attaches to bone via mucoperiosteum - this allows it to be rigid as it is subjected to compression
What type of papillae can be found on the tongue?
Filiform - at front, most numerous
fungiform - at lateral borders, mushroom shape
Vallate - 5-7 large in shape, divides tongue to anterior and posterior
What is para-keratinised?
Where the nuclei are still present at the top layer as the turn over of cells is so fast the cells at the top are not dead yet
What is geographical tongue?
areas of pink and white separated by a red line. pink areas have no filliform papillae whereas white areas have lots of the papillae, trapping bacteria and giving the white appearance. the pattern can change over time
What is the structure of the ducts salivary glands?
What salivary gland is most active when sleeping?
Submandibular - 70%, sublingual and minor - 15% each, parotid - 0%
What salivary gland is most active when awake but at rest?
Submandibular - 72%, parotid - 20%, sublingual and minor - 4% each
What salivary gland is most active when eating?
Parotid - 50%, submandibular - 40%, sublingual 2%, minor - 8%
What is the average salivary flow per day?
How does the flow rate of saliva affect the ionic composition?
Bicarbonate ion is greatly increased (most important buffer), as is Na ion. Chloride ion is slightly increased whereas, potassium is decreased
What buffers are important in saliva?
Bicarbonate most important, increased during eating, phosphate also helps
What factors affect flow rate in unstimulated saliva?
Previous stimulation, hydration levels, medications, any salivary gland disease
Describe primary saliva production in acinar cells.
ATP produced from Na/K pump, this is used to exchange Cl into acinar cells and K out. Acetylcholine then binds, stimulating second messenger system resulting in the opening of Cl pores from cells into lumen. To balance the ions, Na travels through gap junctions into the lumen. This then increases the salt concentration, causing water to flow into the lumen. Acinar cells also use carbonic anhydrase to produce carbonic acid from H2O and CO2, which can then produce bicarbonate ions.
Describe secondary saliva production.
As saliva from acinar cells is produced, it travels through inter-calated ducts into striated ducts. Here, it is modified. Na and Cl ions are reabsorbed here, and bicarbonate inos and K ions are secreted. Plasma proteins may be secreted from cells into saliva, this is the final saliva
What fluid is an indication of gingivitis?
Gingival crevicular fluid
Which of the following does not have antimicrobial properties? Lactoferrin, Lactoperoxidase, Cystatin, Gustin
Gustin - zinc protein important in taste and producing bicarbonate
What salivary protein can protect against candida albicans and streptococcus mutans?
How do muco-proteins protect the oral cavity?
They are a polypeptide with polysaccharide side chains, they bind to oral mucosa and enamel, and only specialised bacteria can bind to this. If bacteria binds, it can colonise on the mucins. This can then be swallowed and kills the bacteria
Describe 2 mechanisms of unconditioned stimulation of saliva
Mechanical - loading of the periodontal ligament, biting and chewing stimulates salivation on that side
Gustatory - taste stimulates saliva
What tastes stimulate more saliva?
Acidic > salt = unami > sweet > bitter
How can salivation be conditioned?
A normal stimuli (e.g. a bell) can be associated with an unconditioned stimuli (e.g. orange juice). After a while, the bell can cause salivation without the juice.
does this conditioned response last?
No, without reinforcement, the response becomes extinct
What effect does the sympathetic NS have on salivation?
Increases secretion from salivary glands, vasoconstriction on blood vessels
What effect does the parasympathetic NS have on salivation?
Increases secretion from salivary glands, vasodilation on blood vessels
What regions of the oral cavity have a high salivary flow rate?
What regions of the oral cavity have a low salivary flow rate?
buccal and labial
What does the term clearance mean?
The removal of substances (both harmful and beneficial) from the oral cavity
When is a high clearance rate desired?
After eating, high clearance desired to remove cariogenic sugar. Regions with low salivary flow rate will have a low clearance rate and will be vulnerable to caries
When is a low clearance rate desired?
After brushing teeth, mouth full of fluoride which we want to retain for more mineralisation
What would be the ideal fluoride tablet (in terms of lowering saliva rate)?
A tasteless tablet which is sucked - not chewed
What does the Stephan curve show?
The pH of plaque bacteria over time
What happens to the stephan curve when a sugary drink is taken?
The pH is decreased, past 5 - meaning there is more solubilisation than remineralisation occurring. This takes a long time to recover,
How is the Stephan curve altered with chewing gum? How is this achieved?
Chewing gum reduces the pH drop and the pH is increased and recovered much faster. This is due to stimulating mechanoreceptors by increasing load on PDL, activating salivation. Saliva contains bicarbonate which is an important buffer and restricts the pH change
What is unusual about the flow rate when chewing gum?
It is only increased initially, after this the flow rate is similar to unstimulated however the pH is increased
How can the stephan curve illustrate why behavioural changes can improve a patients oral health?
If drinking sugary drinks - drink at meal times, saliva rate is highest so less cariogenic effect seen. Also reduce snacking as the drop in pH doesnt drop more the more you eat but a continual pH drop can increase incidence of caries
Why can sweeteners be seen as better than sugar for the oral health?
Sweeteners give a sweet taste but cannot be fermented by bacteria, thus no acid produced and no pH change
What is the difference in the plaque formation in fermentation of sucrose compared to fructose?
sucrose - mature plaque formed, cannot be penetrated by saliva
fructose - immature plaque formed, saliva can penetrate through this
formation of 3 germ layers, as cells from epiblast migrate through the primitive streak to form mesoderm and endoderm layers, epiblast renamed to ectoderm
What is the difference between the morula and the blastocyst
Each are a ball of 16 cells, however in the morula these are all packed together. Whereas, in the blastocyst, there are 2 separate cell types - inner cell mass and outer trophoblast cells
What tissues develop from the ectoderm layer
skin, glands and enamel
What tissues develop from the mesoderm layer
paraxial - somites, skeletal muscle, bones, cartilage
intermediate - urogenital, lateral - visceral muscle
what tissues develop from the endoderm layer
respiratory and gastrointestinal tracts, visceral organs
what can be described as the 4th germ layer
neural crest cells, lying next to neural tube, can be described as ectomesenchymal - dentine, pulp, cementum and periodontal ligament all derived from here
describe morphogenesis in tooth development
the tooth germ forms a cap like shape from the bud. this has an external enamel epithelium and internal enamel epithelium, which meet at the cervical loop. this is surrounded by ectomesenchymal cells, particularly near the IEE, forming the dental papilla
describe cytodifferentiation in tooth development
a bell shape is formed here. as the enamel organ develops, another 2 layers are prominent. the stellate reticulum lies in the middle of the organ to provide structural support, and the stratum intermedium lies between the reticulum and the IEE or EEE.
What is seen around week 16?
A lingual extension of the dental papilla - forming the tooth bud of the permanent tooth.
Describe matrix secretion in tooth development
The developing IEE stimulates odontoblast formation in the underlying dental papilla. These then produce pre-dentine, mainly just a collagen matrix which is yet to be mineralised. As this is formed, it stimulates ameloblast differentiation from cuboidal to columnar. These then secrete a protein matrix, forming an un-mineralised enamel. As the ameloblasts mature, the proteins are removed and the matrix becomes much more mineralised and crystallites are deposited
Describe root formation in tooth development
EEE, IEE and the cervical loop migrate down, forming the hertwig’s epithelial root sheath. This stimulates the odontoblasts at the adjacent dental papilla to produce dentine. Once dentine produced, the HERS is regressed. Dentine then contacts the dental follicle, these mesenchymal cells differentiate to cementoblasts. Cementum is then formed around the root dentine