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CHAPTER 38 Week 10.

LEARNING OBJECTIVES. Pronounce, define, and spell the Key Terms..

INTRODUCTION. The dental assistant must have a thorough knowledge and understanding of the importance and uses of dental imaging..

DISCOVERY OF X-RADIATION. Wilhelm Conrad Roentgen (pronounced rent-ken), a Bavarian physicist, discovered the x-ray on November 8, 1895..

PIONEERS IN DENTAL RADIOGRAPHY. Otto Walkoff made the first dental radiograph..

RADIATION PHYSICS. All things in this world are composed of energy and matter..

ATOMIC STRUCTURE. Central nucleus Orbiting electrons.

NUCLEUS. The nucleus, or dense core, of the atom is composed of particles known as protons and neutrons..

ELECTRONS. Electrons are tiny negatively charged particles with very little mass..

IONIZATION. The electrons remain stable in their orbits around the nucleus until x-ray photons collide with them. (A photon is a minute bundle of pure energy that has no weight or mass.).

A molecule of water (h2o) consists of two atoms of hydrogen connected to one atom of oxygen..

PROPERTIES OF X-RAYS. The dental assistant must be familiar with the unique characteristics of x-rays..

X-ray a has a long wavelength; that is, the distance between its peaks is greater than for x-ray b. X-ray b has a shorter wavelength and is therefore more energetic and more penetrating..

Dental x-ray machines may vary somewhat in size and appearance, but all machines will have three primary components:.

TUBEHEAD. The x-ray tubehead is tightly sealed; heavy metal housing contains the x-ray tube that produces dental x-rays..

COMPONENTS OF THE TUBEHEAD. The metal body of the tubehead that houses the x-ray tube is called the metal housing. It is filled with insulating oil..

THE X-RAY TUBE. The vacuum environment allows the electrons to flow with minimum resistance between the electrodes:.

THE CATHODE. The cathode consists of a tungsten filament in a focusing cup made of molybdenum..

THE ANODE. The anode is the target for the electrons..

The production of dental images occurs in the x-ray tube..

THE POSITION INDICATOR DEVICE (PID). The open end of the lead-lined PID is placed against the patient’s face during x-ray exposure..

THE EXTENSION ARM. The extension arm encloses the wire between the tubehead and the control panel..

THE CONTROL PANEL. The control panel of an x-ray unit contains: The master switch Indicator light Exposure button Control devices (time, milliamperage [mA] selector, and kilovoltage [kVp] selector).

X-RAY PRODUCTION. The x-ray machine is plugged into the wall outlet, and when the machine is turned on the electric current enters the control panel..

TYPES OF RADIATION. Primary radiation is the x-rays that come from the target of the x-ray tube..

Types of radiation interaction with the patient. 1, primary. 2, secondary. 3, scatter..

CHARACTERISTICS OF THE X-RAY BEAM. Three qualities are necessary for a good radiograph:.

RADIOLUCENT AND RADIOPAQUE CHARACTERISTICS. Radiolucent structures allow x-rays to pass through them..

Bite-wing radiograph showing a radiopaque (white, a) area of amalgam restoration and radiolucent (black, b) area of air and cheek tissue..

CONTRAST. The ideal contrast of an image clearly shows the radiopaque white of a metal restoration, the radiolucent black of air, and the many shades of gray between..

Image produced with lower kilovoltage exhibits high contrast. Many light and dark areas are seen..

Image produced with higher kilovoltage exhibits low contrast. Many shades of gray are seen instead of black and white..

DENSITY. Density is the overall blackness or darkness of an image..

OTHER FACTORS INFLUENCING DENSITY. The distance from the x-ray tube to the patient: If the operator lengthens the source-image distance without changing the exposure settings, the resulting radiographs will be light or less dense..

GEOMETRIC CHARACTERISTICS. Three geometric characteristics affect the quality of the radiograph:.

SHARPNESS. The sharpness of an image is influenced by three things:.

RADIATION EFFECTS. The dental assistant must understand how the harmful effects of radiation occur and how to discuss the risks of radiation with patients..

IONIZATION. The atoms that lose electrons become positive ions; as such, they are unstable and capable of interacting with (and damaging) other atoms, tissues, or chemicals..

CUMULATIVE EFFECTS. Tissues have the capacity to repair some of the damage; however, they do not return to their original state..

BIOLOGIC EFFECTS OF RADIATION. This time lag is called the latent period..

ACUTE AND CHRONIC RADIATION EXPOSURE. Acute radiation exposure occurs when a large dose of radiation is absorbed in a short period, such as in a nuclear accident..

GENETIC AND SOMATIC EFFECTS. X-rays affect both genetic and somatic cells. Genetic cells are the reproductive cells (sperm and ova). Damage to genetic cells is passed on to succeeding generations. These changes are referred to as genetic mutations..

CRITICAL ORGANS. Skin Thyroid gland Lens of the eye Bone marrow.

RADIATION MEASUREMENT. Radiation can be measured in a manner similar to that used to measure time, distance, and weight..

RADIATION MEASUREMENT. Radiation can be measured in a manner similar to that used to measure time, distance, and weight..

MAXIMUM PERMISSIBLE DOSE. The maximum permissible dose (MPD) of whole-body radiation for those who are occupationally exposed to radiation is 5000 mrem (5.0 rem) per year, or 100 mrem per week..

RADIATION SAFETY. Background radiation comes from natural sources such as radioactive materials in the ground and cosmic radiation from space..

PROTECTIVE DEVICES. The dental tubehead must be equipped with certain appropriate components:.

ALUMINUM FILTRATION. The purpose of the aluminum filter is to remove the low-energy, long-wavelength, and least penetrating x-rays from the x-ray beam..