Radiographs are important to treatment planning a patient because they allow us to see the bones and teeth which are covered by the skin and gums. With this information, one can determine the extent to which a patients malocclusion is the result of bony defects versus dental defects.

To produce radiographic x-rays you need a power supply or voltage (kVp) and a length of time (t) to expose an object to the radiation. The object can be of any thickness (q). By adjusting any of theses three parameters, you change the quality of the image.

How X-Rays are Formed - An in depth look at the science.

What is Radiation?

• Radiographs are formed for the transmission of energy through space and matter in the form of radiation.
• There are two types of radiation - particulate and electromagnetic.
• Particulate radiation consists of atomic nuclei or subatomic particles moving at high velocities.
• Examples of particulate radiation include alpha rays, beta rays and cathode rays.
• Alpha rays high speed double ionized Helium nuclei consisting or two protons and two neutrons with an atomic number of 2 and atomic mass of 4.
• Protons have positive 1 charge and weigh 1 atomic mass unit
• Neutrons have no charge and weigh 1 atomic mass unit.
• Electrons have a negative 1 charge and are so small that their mass can be ignored.
• Alpha rays result from the decay of many radioactive elements naturally.
• Beta and Cathode rays are both high speed electrons coming from radioactive nuclei or some manufactured device (e.g. X-ray tube to make radiographs).
• Alpha rays have such large mass that high charge that they give up their energy very quickly and can only penetrate a few microns on body tissue (an ordinary sheet of paper absorbs them).
• Beta and cathode rays are very light and travel at speeds close to the speed of light. They can penetrate about 1.5 cm of body tissue. This is because electrons are smaller, lighter, and carry only 1 negative charge.

The X-ray machine

• An X-ray machine consists of a x-ray tube, its power supply and the tube head, support arm and control panel.
• The X-ray tube is positioned within the tube head along with some components of the power supply.
• The X-ray tube is able to generate x-rays because of the cathode which consists of a focusing cup and a filament (the source of the electrons) and an anode.
• The filament composed of a coil of tungsten wire. The filament is heated to cause the release of electrons at a rate proportional to the temperature.
• A milliampere (mA) control provides fine adjustment of the voltage across the filament and in turn adjusts the flow of heating current through the filament.
• The filament lies in a focusing cup which is a negatively charged concave reflector of molybdenum. Since negative repels negative, the focusing cup electrostatically focuses the electrons emitted by the filament into a narrow beam directed at a small rectangular area on the anode known as the focal spot.
• The anode is positively charged and attracts the negatively charged electrons.
• The anode is made of a copper stem and tungsten target which the beam of electrons is directed.
• The purpose of the target is to convert the kinetic (energy of motion) of the electrons into x-ray photons.
• This process is very inefficient and results in 99% of the kinetic energy being turned into heat.
• Tungsten is used as the target because is has many important properties: High melting point, low vapor pressure, and high atomic mass.
• Since so much heat is produced by this process, tungsten must have a high melting temperature so that it does not melt.
• The low vapor pressure allows tungsten to function as a solid at high operating temperatures.
• The high atomic mass makes a material more effective at producing x-rays.