Ask Dr. Christensen

July 1, 2002
In this monthly feature, Dr. Gordon Christensen addresses the most frequently asked questions from Dental Economics readers.

by Gordon J. Christensen, DDS, MSD, PhD

In this monthly feature, Dr. Gordon Christensen addresses the most frequently asked questions from Dental Economics readers. If you would like to submit a question to Dr. Christensen, please send an email to [email protected].


My associate has been attempting to persuade me to change our radiographic film to the new "F" speed. Is the new film that much better than our conventional "D" and "E" speed films?

Answer from Dr. Christensen

Over the past few decades, there have been numerous changes in dental radiographic film. Practitioners who began their dental careers in the 1940s and 1950s were taught using radiographic film that required a significant amount of radiation. These films made radiographs that had a significant amount of contrast, or a major differentiation between black and white. Small demineralizations were easily identified on the radiographs. Carious lesions on teeth were about the same depth as they appeared to be on the radiographs.

Over the following years, radiation was reduced and film sensitivity was increased. Consequently, the resulting radiographs had many shades of gray instead of the significant difference between black and white of earlier radiographs. The technological change from high contrast to low contrast was a slow one, spanning several years. Younger dentists did not realize that radiographs with more diagnostic potential had been available previously.

Many studies have compared "D" and "E" speed film. The diagnostic capability of both types has been shown to be about equal; however, the reduced-radiation "E" speed film has a more granular appearance.

The new "F" speed radiographic film provides a simple way to reduce radiation to patients even further (Kodak Insight film). But the diagnostic potential of the "F" radiographic film does not appear to be superior to the older "D" and "E" speed films.

I suggest that all of us attempt to use radiographic film that uses the least amount of radiation necessary. Not only do patients appreciate your attempts to reduce the amount of radiation they receive, but we all know that reduction of radiation exposure is a desirable goal.

Practical Clinical Courses' video library includes a popular, well-accepted presentation on radiographic technique, as well as a video on a device that replaces the need for radiographs in Class I and Class V areas: V 1158 - "Simple, Fast, High-Quality Dental Radiographs" (intraoral) and C 501A - "DIAGNOdent - Scientific Diagnosis of Caries." Contact us at (800) 223-6569,, or fax (801) 226-8637.


I have been told that the heat coming from the Plasma Arc Curing (PAC) lights is highly detrimental to the dental pulp, and that the lights can cause pulpal death. Is there a meter that can be used to test the output of the curing light?

Answer from Dr. Christensen

This topic can be very confusing. I suggest using a light-testing device regardless of which curing-light concept you use. Radiometers test the amount of energy coming from the light in milliwatts per square centimeter. A light may register a strong reading, but it may not have usable light at the wavelength needed to cure your specific resin. Good examples of this phenomenon are the Light Emitting Diode (LED) lights, which register low readings on radiometers, but the wavelength of the light emitted is almost exactly in the polymerization-sensitive range of the resin's initiator.

Thus, a light may register strong on a radiometer and not cure well, while another light may have a low reading and still cure the resin well. I recommend the purchase of a radiometer that tests both high- and low-intensity lights, such as the Spring 3K Light Meter - Spring Health Products, (800) 800-1680.

Test the heat of the light on your fingernail. Hold the light there until it is uncomfortable. With most PAC lights, that time is about three seconds. Use this test as a guide to see how long you can cure without damage to the tooth pulp or soft tissue.

After determining a comfortable curing time, take a small piece of the resin you are using (in a light color such as A2) and attempt to cure it using that same curing time with your PAC light. If the resin cures at least 2-3 mm, your light is functioning adequately and the heat is not dangerous.

A recently released Practical Clinical Courses video - C901B - "Curing Resin With Light State-of-The-Art" - discusses the various controversies surrounding the light-curing concept. The video also includes many clinical tips. Contact us at (800) 223-6569,, or fax (801) 226-8637.

Dr. Christensen is a practicing prosthodontist in Provo, Utah. He is the founder and director of Practical Clinical Courses, an international continuing-education organization for dental professionals initiated in 1981. Dr. Christensen is a co-founder (with his wife, Rella) and senior consultant of Clinical Research Associates, which, since 1976, has conducted research in all areas of dentistry and publishes its findings to the dental profession in the well-known CRA Newsletter. He is an adjunct professor at Brigham Young University and the University of Utah. Dr. Christensen has educational videos and hands-on courses on the above topics available through Practical Clinical Courses. Call (800) 223-6569 or (801) 226-6569.

Dr. Christensen's views do not necessarily reflect the opinions of the editorial staff at Dental Economics.

For a review of questions and answers from Dr. Christensen over the past few months, please visit

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