Hard tissue biology Flashcards
state the ideal properties of teeth
- strong/hard
- wear-resistant
- resistant to chemical wear
- aesthetics
- ability to respond to damage
- ability to repair
describe how the hard tissues in the oral cavity are mineralised
minerals such as phosphate and calcium make a 2D mosaic called hydroxyapatite, which stacks on each other to make a 3D structure which are the different parts of the teeth. the enamel is the most mineralised part of the teeth.
describe the structure of pure hydroxyapatite
Ca10(PO4)6(OH)2
- OH- ion surrounded by 3 Ca2+
- Surrounded by 3 PO4 3-
- Enclosed by 6 Ca2+
the outer 6 Ca2+ is shared with other mosaics.
describe the ionic replacement in hydoxyapatite mosaics
- Any ions within the structure can be substituted
- Fluoride ion (F-) may replace OH-
Explain how F- replacing OH- in hydroxyapatite prevents tooth decay
F- ions are smaller than OH- ions, therefore when replacing the OH- ions, the now called flurohydroxyapatite is denser than pure hydroxyapatite therefore it stabilises the lattice, making it more acid-resistant and prevents tooth decay.
state the features of enamel
- covers the anatomical crown
- product of epithelium
- 96% inorganic material (HAP)
- Translucent
- Hard/strong
- brittle
- non-vital
describe the structure of enamel
- tightly packed with HAP crystals
- basic unit = enamel prisms
- prisms are visible in-ground section
describe the structure of enamel prisms
2 parts:
- enamel core: tightly packed
- enamel sheet: more susceptible to acid attack
how is surface enamel different to sub-surface enamel?
surface enamel is more mineralised (more HAP crystals) and is more subject to HAP ionic replacement, so more F-, therefore more resistant to acid attack (caries/erosion) and acid etch
how do dentists cut through the enamel
high-speed diamond or tungsten carbide bur can cut through the hard enamel. the high-speed air turbine but requires a water coolant due to high friction
state the difference between cutting through enamel supported with sound dentine and enamel not supported by sound dentine
- enamel supported by sound dentine is hard and requires a high-speed bur.
- enamel unsupported by sound dentine is brittle and can easily be broken off by a hand instrument such as a cheisel.
state the features of dentine
- specialised connective tissue
- vital
- highly tubular (more tubular towards the pulp)
- hard and resilient
- 20% collagen, 70% minerals (HAP crystals)
state the features of pre-dentine
- non-mineralised
- sits beside the pulp
- more tubular than dentine
describe the structure of dentine
collagen fibres run parallel to the AMJ
how do dentists cut through the carious dentine?
carious dentine is soft and can be scoped out by hand excavators or bladed burs.
