Radiography plays an important role in the diagnosis, treatment planning and prognosis of dental diseases. Perhaps, there is no speciality of dentistry that can do without the use of x-radiation. In day to day practice every dentist handles a dental x-ray machine. The construction and operation of an x-ray machine is taught at great length in the dental curriculum. Most of the teaching is based on schematic diagrams of the machine found in radiology text books.

But, one never gets to see the inside of an x-ray machine. Not even the pictures of it! So we decided to open up a defunct dental x-ray machine to take a good look inside. What we found inside mostly corresponded with what is described in the text books. But, there were some differences between the theory and reality.

The tube head, as expected was filled with oil. A rubberized pouch, with an opening on the undersurface was found placed over a plastic container that housed the transformer coils and other circuitry. The pouch provides the extra space required when the oil expands due to the heat generated during generation of x-rays. Generation of x-rays, remember, is not a very efficient process. Only about 1% of the energy of the electrons incident on the tungsten focal spot gets converted into x-radiation. The remaining into heat!