Dental hard tissues Flashcards
Examples of mineralised (hard) tissues
Alveolar bone, cementum, dentine and enamel
Examples of non- mineralised (soft) tissues
Oral mucosa, dental pulp, gingivae, periodontal ligament
Colour of dentine
Pale yellow
Organisation of dentine
Fine, parallel tubules within a collagenous matrix, tubules are S shaped (primary curvature), tubules connect pulp chamber to enamel and dentine junctions, contain long processes of cell bodies (odontoblasts), dentine at the junction is unmineralised and known as predentine
Is dentine vital or non vital
Vital
Function of dentine
Acts as a shock absorber - dissipating large loads throughout the tooth structure
Composition of dentine
70% inorganic
20% organic
10% water
Sigmoid route of dentine
Primary curvature - Schreger lines
What is dentine between tubules called
Intertubular dentine
Small changes in direction of dentine
Secondary curvature - Lines of Owen
When does secondary dentine appear
After completion of tooth and root formation
What is translucent dentine
Forms with ageing
Caused by tubule occlusion by deposits of peritubular dentine
What is tertiary dentine
Occurs in reaction to a pathological change
Different types of tertiary dentine
Reactionary: Formed in response to injury/ insult. Made from existing odontoblasts
Reparative: Formed in response to a stimulus. Made from new plural progenitor cells
What is sclerotic dentine
Tubule occlusion by an external stimulus
What are dead tracts
Odontoblasts are killed by an external stimulus, or retract leaving empty tubules
What is peritubular dentine
Located in the wall of tubules
What is intertubular dentine
Located between tubules
What is mantle dentine
Outermost layer, 1st dentine formed
What is circumpulpal dentine
Located around the pulp - bulk of dentine
What is primary dentine
Formed prior to root completion. Formed more rapidly and more mineralised than secondary dentine
What is secondary dentine
Formed after completion of root and tooth formation, formed more slowly and is less mineralised than primary dentine
What are lines of von ebner
Represent cyclic activity of odontoblasts during dentine formation
5-6 um per day - crown
3.5 um per day - root
What are ameloblasts
Enamel producing cells
Where is enamel thickest
Cuspal/ incisal regions
2.5mm @ thickest point
Hardness index (knoop no) of enamel and dentine
Enamel - 296
Dentine - 64
Composition of enamel
96-97% inorganic
3-4% organic
Structure of enamel
Organised into rods (prisms)and interiors
Built from closely packed hydroxyapatite crystals
Hexagonal symmetry
Rod = cylinder shaped
Organisation is tighter around the centre of each rod
What are striae of retzius
A series of dark lines extending from the DEJ towards the surface of the tooth
They form due to a weekly rhythm of enamel production resulting in structural alterations of the rods
What are bands of hunter and schreger
They are produced by the changing orientations of adjacent groups of rods
What is gnarled enamel
Where the rods appear twisted around in each other in a complex arrangement
What is perikymata
Transverse waves like grooves, external manifestations of striae of retzius
