Dental X Rays

Definition

Dental x rays are pictures taken of the mouth area using high energy photons with very short wave-lengths. They show the teeth and surrounding bone.

Purpose

Dental x rays are effective in discovering tooth decay, broken fillings, fractured teeth, tumors, occlusal trauma, or impacted or ectopic teeth that would otherwise be unseen by the eye, in between the teeth and below the gum tissue.

Description

Dental x rays are part of the dental examination for aiding in the diagnostic process. X rays are vital in the diagnosis of root canal treatment on checking the apical of the tooth and the surrounding structures for abscesses or bone loss. Without the aid of dental x rays, 60% of dental decay would be missed. Diagnostic x rays are essential in providing accurate information. The most common x rays taken are:

• bitewing x rays (vertical and horizontal bitewings)
• panoramic x rays
• periapical x rays
• occlusal x rays

Each is used in its own respective degree of diagnosis, with the bitewing x ray being the most common. Bitewings are the most effective in discovering tooth decay in between the teeth and on adjacent teeth. A bitewing shows only the top crown portion of the tooth structure. It is called a bitewing due to the way the patient can bite down and hold the film securely in place. The bitewing is good in diagnosing and evaluating periodontal conditions and bone levels between the teeth. They are also good in detecting tartar buildup.

The panoramic (a type of film used), or Panorex (brand name) is also commonly taken on the initial visit to the dental office. This type of x ray makes a complete circle of the head from one ear to the other, to produce a complete two-dimensional representation of all the teeth. This x ray will also show bone structure beneath the teeth and the temporomandibular joint (TMJ). The panoramic is the most commonly used x ray in the aid of diagnostic decisions regarding third molar extractions (wisdom teeth) for people who are edentulous (the tooth is not there/has not erupted). This special x ray, however, has its advantages and disadvantages.

One advantage of the panoramic is that a broad area is imaged, showing many structures. Furthermore, the exposure level emits low radiation. The panoramic is excellent for evaluation of trauma, tooth development, and certain anomalies. A 1999 study at the University of Buffalo School of Dental Medicine demonstrated that calcifications in the carotid arteries, which were exposed on standard panoramic x rays, served as predictors of death from cardiovascular disease.

The main disadvantage of panoramic x rays is that the image shown does not provide the fine detail of a bitewing x ray. The procedure for taking a panoramic x ray is also somewhat confining to the patient, as the x-ray machine takes a minute or more to fully encircle the head for the complete picture. These films are not good in aiding the diagnosis of decay, bone level, and certain types of periapical pathosis.

A periapical x ray is similar to a bitewing. This type of x ray shows the entire tooth area, from crown to root, and the bone surrounding the root from a side view. This type of film will reveal any root anomalies, changes in the bone and surrounding tissue, cysts, bone tumors, and abscesses. The fine detail in the periapical film is necessary in diagnosis and treatment planning, and is commonly taken during root canal treatment and crown restoration procedures.

Occlusal films are least common. These films show the whole bite of the lower or upper jaw. Occlusal x rays, when taken, are mainly taken on children to show the eruption order of the permanent teeth.

X rays pass through hard and soft tissue in the mouth. The x-ray beam is blocked by denser structures, such as teeth, fillings, jaws, and bones. Teeth appear lighter because fewer x rays go through the teeth to reach the film. Cavities and gum disease appear darker (shown by a dark spot in the tooth or loss of bone structure around the tooth) because of more x-ray penetration. On the film, the white images are the dense structures.

Operation

William Roentgen, a German scientist, discovered the x ray in 1895. He found that x rays are energy in the form of waves, similar to visible light. The only difference between light and x rays is that light does not have the ability to penetrate the body as x ray energy does. Light makes pictures of the outside of objects, while x rays have the ability to make pictures of the inside of objects. The roentgen represents the amount of exposure given off by one single energy photon. The amount of absorbed x ray in the body is a unit called a rad. A unit called "rem" accounts for the difference in biological effectiveness of different types of radiation, such as secondary radiation, or cosmic radiation. One rem equals one rad. One rad equals one R and one thousand milliroentgens, more commonly known as mrad; it is equal to one roentgen (R).

Research conducted in 2000 by the Idaho Radiation Network sets a maximum permissible x ray dose for one year at 5R (roentgens). A full mouth set of dental x rays consists of 18 to 20 films (bitewings, periapicals, occlusalsm and panoramic x rays). The amount of radiation for receiving the full-mouth set of x rays is 10 to 20 mrads (milliroentgens). The benefits derived from x rays greatly outweigh the radiation concerns. In 1999, the National Council on Radiation Protection reported that the amount of radiation an average person receives each year from background sources (e.g., outer space, materials in the earth, foods consumed, and naturally radioactive materials in the body) is 360 mrads.

Secondary radiation consists of the radiation waves left over after the source of radiation is stopped. Most secondary waves can penetrate tissue and are the most damaging waves from radiation. Measures taken to prevent damaging rays are:

• setting radiation exposure to lower settings depending on the patient's age, height, build and structure
• using high-speed films to minimize exposure time

• using lead-filled aprons to shield sensitive body parts, such as thyroid glands and gonads
• x-ray badges worn by dental staff to monitor the amount of radiation exposure in the workplace

Maintenance

Dental x rays are essential in diagnosing and treating oral disease, abnormal tooth development, or trauma. At the initial dental examination, a full-mouth set of x rays may be taken (bitewings and panoramic). Thereafter, it is the dentist who should determine when and how often x rays will be required. Children are usually more cavity prone than adults; x rays may be taken with regard to degree of risk, or at the check-up examination every six months.

An adult presenting a dental trauma will need x rays to diagnose what the treatment should be. More x rays may be needed depending on the treatment plan and the extent of the injury.

The American Dental Association (ADA) recommends basic guidelines on taking dental x rays. On average, bitewing x rays should be taken approximately once a year. This is mainly to detect and treat any conditions early in their development. If the overall general health of the mouth is good, x rays can be taken every 18 to 24 months. The ADA also recommends that the type and frequency of dental x rays taken at an examination be based upon clinical judgment after the examination and consideration of the dental health and the general health of the patient.

Health care team roles

A registered dental assistant (RDA) or registered dental hygienist (RDH) commonly takes the x rays during a dental examination. They review the health and dental history, chart, and age of the patient to be x rayed. Adjustments are made to the x-ray unit depending on the size and age of the patient. The RDA then develops and mounts the x rays and presents them to the dentist. The dentist will interpret the x rays and complete the oral examination. A treatment plan will follow.

KEY TERMS

Apical— Rounded end of the root of a tooth that is embedded in hard tissue (bone); toward the apex of the root.

Crown— 1. The upper part of the tooth, covered by enamel. 2. A dental restoration that is a protective shell fitting over a tooth.

Eruption— The process of a tooth breaking through the gum tissue to grow into place in the mouth.

Pulp— The soft, innermost part of a tooth containing blood and lymph vessels, and nerves.

Root canal treatment— The process of removing diseased or damaged pulp tissue from a tooth, then filling and sealing the pulp chamber and root canals.

Training

An RDA and an RDH must have an x-ray certification in order to take and develop x rays. To become certified, full-mouth sets of x rays need to be taken. Knowledge of the x-ray machine unit is needed, as is the number of roentgens emitted from a variety of different x-ray machines. Furthermore, a working knowledge of angles and height of the x-ray unit is needed; this is necessary for taking fine-detailed images. Certification also requires knowledge of the principles of radiation safety.

Classes leading to certification as an RDA or RDH are available outside the work setting. Each state has different bylaws regarding x-ray licensing for technicians. The rules of the state in which one is interested in working should be consulted.

Resources

BOOKS

Westcott, Gerry D. "Radiology Safety." In University of California Davis Radiology News 2001. 〈http://www.ehs.ucdavis.edu/hp/pmanuals.html〉 (January 2000).

PERIODICALS

Seemuth, Robert, D.D.S. "Dental Health." New Horizons Family Dentistry (February 2001): 2-3.

ORGANIZATIONS

American Dental Association. 211 East Chicago Avenue, Chicago, IL 60611. (312) 440-2500. 〈http://www.ada.org〉.

University of California Davis Radiology. 178 Mark Hall, University of California, Davis, CA 95616. (530) 752-3710 〈http://www.ehs.usdavis.edu〉.

OTHER

Dental x rays television clip. ADA Dental Minutes July 30, 2000.

Rima, Steve D. CHP, "How Much Radiation Do You Get From Dental X Rays?" Idaho State Physics Dept. 2001. 〈http://www.physics.isu.edu/radinf/dental.htm〉 (October 2000).