Foundation m3 Flashcards
What is a Radiograph?
An image produced by X-rays passing through an object and interacting with the photographic emulsion on a film. If a digital image is being formed, the x-rays affect a sensor or a phosphor plate.
Why is radiographs useful in dentistry?
Allow us to look at mineralised tissues.
Teeth are mineralised - enamel more than dentine.
Caries and other dentally related disease often cause demineralisation.
Who discovered X-rays?
Wilhelm Conrad Roentgen, November 1895
What is an atom?
Nucleus
- Protons +ve charge
- neutrons no charge
Electrons
- -ve charge
- Orbit around nucleus in different energy shells - K, L, M, etc.
What are electrons?
- Move in predetermined shells with different energy levels
- shells contain maximum number of electrons
- K=2, L=8, M=18, N=32, O=50
- can move from shell to shell but cannot exist between shells - forbidden zone
- energy is required to remove electron from atom and overcome binding energy which keeps it in its shell
What is the atomic structure?
i.e. atomic number, neutron number, isotopes, radio-isotopes
- Atomic number Z = protons
- Neutron number N = neutrons
- Atomic mass number A = Z+N
- Isotopes: atoms with same Z but different N
- Radio-isotopes: Isotopes with unstable nuclei which undergo radioactive disintegration
What is an ion?
- charged atom or molecule
- number of electrons do not equal the number of protons
- -ve charge if there are more electrons - anion
- +ve charge if there are more protons - cation
What are Alpha particles?
- 2 protons + 2 neutrons (helium nucleus)
- size: large
- +ve charge
- slow speed
- penetration: 1-2mm in tissue
- energy: 4-8 MeV
- damage potential: extensive ionisation
What are Beta particles?
- Electrons
- small size
- -ve charged
- fast
- penetration: 1-2cm in tissue
- energy: 100keV- 6MeV
- damage potential: ionisation
What are Gamma rays?
- Electromagnetic radiation
- very fast
- penetration: can pass through tissue
- energy: 1.24keV- 12.4MeV
- damage potential: ionisation
What X-rays are used in dentistry?
- Not involved in radioactive decay
- identical to gamma rays - with lower energy values
- not particulate - no weight or mass
- no charge
- very fast
- cause ionisation
When is ionisation a problem?
- when it occurs in living cells
- can cause damage to tissue - cataracts for example
- can cause damage to DNA diretly or produce chemicals that do this damage - tumours or cancer
What is the electromagnetic spectrum?
How is energy, frequency, wavelength measured?
Range of all types of EM radiation.
- Energy is measured in electron volts - eV
- frequency is measured in cycles per second or Hertz
- wavelength is measured in metres or nanometres = 10-9
- visible light 400 - 700 nanometres
- X-rays and others so small - described by their energy - eV
What is Voltage?
Voltage is the “power” or “force” that causes a current to move along a wire or for electrons to move across a gap from cathode to anode
How does an electrical circuit work?
- current passed along wire by vibration of electrons
- passes from -ve to +ve
- battery has a direct current
