An open forum for our readers to express their valued opinions (April 01, 2000)

Re: Dangers of dental unit waterlines.At this time there is a controversy brewing concerning the dangers of dental unit waterlines. Recent articles (JADA, Nov. ’99 and Oral Health, Dec. ’99) have stated that there is a serious problem. The JADA article mentions continued concern over Legionella as the prime, potential source of water-related dental infections. I find it interesting that dentistry, unlike medicine, continues to produce faulty research focusing on the presence of Legionella microbes as a serious problem, which it is not. There are 23 species of Legionella and many more sub-species with only one, L. pneumophila, having been associated with serious illness.

Measuring harmless ‘Legionella’ in waterlines and biofilm and equating this to disease risk is poor science. What researchers must do is to identify and measure pathogenic L. pneumophila… the agent that causes harm. Few authors/articles do this due to ignorance or the expense and difficulty in identification and isolation of this type of Legionella among dozens of similar but relatively harmless Legionella microbes that do not produce endotoxin. If this were done, ‘Legionella’ would appear as a minuscule problem.

Legionella (family Legionellacea) is a common and widespread group organisms located in most water and soil samples. For example, around the time of the Mt. St. Helens volcanic eruptions, half of all air samples taken contained airborne Legionella.

Readers should be aware that the presence of garden variety ‘Legionella’ does not pose significant hazards to our patients. Large numbers of one particular variety, L. pneumophilia, do. This distinction somehow has missed the attention of many dental waterline alarmists.

Dean Swift, in Oral Health, Dec. ’99, focuses on Pseudomonas as a deadly hazard in waterlines and quotes a flawed British study as prime evidence of its infectivity in the dental office. Pseudomonades are relatively harmless and found in great quantities in the soil, water and on plant foliage. The few cases of contamination noted in the dental literature have not distinguished the source of so-called dental unit Pseudomonas from Pseudomonas species that exist normally in the environment (e.g. on patient’s shoes), which also can cause the occasional colony on tested equipment.

I believe research and reports (especially those promoting financial benefits of the authors) that fail to make the distinction between individual microbiologic species and their non-pathological microbe relatives is suspect. Often, these reports paint all related organisms (e.g. Legionella) with the same ‘toxic’ brush and thus, are misleading, if not blatant junk science. The discriminating dentist must be alert.

E. J. Neiburger, DDS

Director, Centre for Dental Aids Research

Waukegan, IL

Editor’s Note.

Dr. E. Neiburger’s letter to the editor is built on the premise that he can be a critic of so-called ‘flawed’ research on Pseudomonas, noted in the 1987 study in the British Dental Journal,1 yet offer no studies to prove the allegation. It is easier to blow up the bridge than to build it.

Contrary to Dr. Neiburger’s statement, Dean Swift did differentiate between pathogenic and non-pathogenic Pseudomonas. In the 1999 Summary section of his article he pointed out that in testing 4,000 dental waterlines on a wide geographical basis, 10% of them were contaminated with Pathogenic Pseudomonas Aeruginosa — not the ‘relatively harmless’ type — not ‘junk science.’

It is noteworthy that the U.S. Federal Water Quality Regulation for drinking purposes requires a level of no more than 500 cfu/ml with no pseudomonas aeruginosa–probably not the ones on the patient’s shoes. The concern is what type and how many are in the dental waterline.

Thirty-five different bacterial organisms, four fungal organisms and four protozoa have been isolated from dental unit water.2 Clinical Research Associates, in a study of 246 dental unit waterlines,3 found 350.0 to 7 million cfu/ml with a mean of 444,040 cfu/ml. Admittedly these are mainly heterotrophic bacterial organisms — possibly some pathogenic. It is a long way from the ADA goal of 200 cfu/ml. With cfus/ml sometimes in the millions, bacterial products in the water (endotoxins) can be high.

In surgical procedures this factor is part of the decision to utilize sterile water. For routine, non-invasive procedures I’ll put my money on attainable low cfu/ml counts.

“It’s just not prudent public dental health practice to expose patients during dental treatment to water that wouldn’t pass standards for swimming pool water.”4 To quote Chris Miller: “Microorganisms are present in dental unit water. We need to appreciate that this is documented evidence. It is not just a couple of indications, a couple of little research efforts or abstracts; it is clearly documented nationwide and worldwide.”5

R.A. Clappison, DDS, FRCD(C)

Oral Health Consultant, Infection Control/Health Issues


1.Martin, M.V., The Significance of the Bacterial Contamination of the Dental Water System, Br. Dent Journal – J 163:15204, 1987

2.Microbial Contamination of Dental Unit Waterlines – Williams, J.F.; Molinari, John A.; Andrews, Nancy. Pg. 538, Compendium, June 1996

3.Clinical Research Associates Newsletter, Vol. 23, Issue 10 October, 1999

4.Cleveland, Jennifer, DDS, MPH, Centre for Disease Control and Prevention, “Waterlines ’98, Will We Meet the Goal for 2000,” Public Health Implications for Contaminated Dental Unit Water – OSAP

5.Chris Miller, PhD, Infection Control, Indiana University. Overview 1998 OSAP Annual Symposium.