J. Dent

1990;

281

18: 281-283

Cross-infection hazards associated with the use of pumice in dental laboratories* S. Witt* and P. Hartt Departments of Restorative Dentistry, UK

Dentistry*

and Department

of Dental Surgeryt,

University

of Leeds, School

of

ABSTRACT The bacteriological contamination of pumice slurry in polishing units in a dental clinical area (high risk), a production laboratory (medium risk), and a non-clinical teaching laboratory (low risk), was investigated. Slurry samples taken from all three areas were found to be heavily contaminated with pathogenic organisms. The investigations were repeated following the addition of a disinfectant with both bacteriocidal and virucidal properties to the pumice. Lower bacterial counts were obtained indicating that routine disinfection of pumice slurries is desirable. KEY WORDS: Cross-infection, Laboratory (dental) procedure, Pumice J. Dent. 1990;

18: 281-283

(Received 23 April 1990;

reviewed 13 June 1990;

accepted 25 July 1990)

Correspondence should be addressed to: Mrs S. Witt, Department of Restorative Dentistry, University of Leeds, School of Dentistry, Clarendon Way, Leeds LS2 9LU. UK.

INTRODUCTION Fresh stimulus has been given to the study of crossinfection and infection control measures by the recognition of the risks associated with the dental treatment of patients suffering from serious virus infections such as hepatitis B (HBV) and the acquired immune deficiency syndrome (HIV) (MoselyetaL, 1975; Mitchell and Mosely, 1982; Cottone, 1985; British Dental Association, 1986). Although HBV continues to be the major cross-infection hazard for dental practitioners and their staff, they are also at risk to many other diseases such as herpes, staphylococcal and streptococcal infections, TB, syphilis and possibly HIV (Beneson, 1980; Crawford, 1985; Runnells, 1988). The present investigation was prompted by a number of eye infections which occurred among members of staff in dental laboratories in Leeds Dental Hospital. Slurries of dental pumice were considered to be a possible source of these infections. Pumice slurry is widely used in dentistry during the polishing process of dental appliances and it has been *The poster demonstradon from which this paper is derived was the winner of the Davis Schottlander and Davis prize at the Annual Conference of the British Society for the Study of Prosthetic Dentistry. Leeds 1989. 0 1990 Butterworth-Heinemann 0300-5712/90/050281-03

Ltd.

recognized for some time that the use of such slurries poses a cross-infection risk. It has been suggested that separate pumice slurry pans be used for new and existing dental prostheses and that a liquid disinfectant be used as the mixing medium. Further more, it has been recommended that polishing wheels be soaked in a disinfectant between use and that fresh pumice and polishing agents be used for each prosthesis (Council on Dental Therapeutics, 1985: Runnells, 1988). In Leeds Dental Hospital, impressions and prostheses from the clinical area are first rinsed under running tapwater and then sent to the laboratory. Impressions and prostheses from known risk cases are separately bagged and labelled in the clinic and disinfected before admission to the laboratory. Appliances to be polished after adjustment in the clinic are polished on a lathe sited in a room adjacent to the clinical area. Such appliances are contaminated with saliva and, in some cases, with blood and are rinsed under running tapwater before polishing. For acrylic dentures pumice slurry, followed by a finer polish, is the method of choice for polishing. After polishing, such appliances are washed in tapwater and returned to the patient. The pumice slurry used for polishing can become contaminated by organisms derived from the patient, the operator, the medium used to form the slurry or the atmosphere.

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Tab/e 1. Concentrations of bacterial growth expressed in colony forming units per gram weight of pumice slurrv bv location

Production laboratory

Nature of sample Pumice/tapwater-freshly made PumiceAapwater-unused 12 h PumiceAapwater-used 4 days PumiceNirkon-freshly made PumiceNirkon-unused 12 h PumiceNirkon-used 4 days Fresh pumice powder Tapwater Pumice/sterile water-unused Pumice/tapwater-3 h exposure Pumice/sterile water-3 h exposure PumiceAlirkon-3 h exposure

No growth 4653 x 1 O3 251316 x IO3 < 1.0 No growth < 1.0 No growth 30/ml No growth 1033 K No growth No growth

Pumice slurry is also used in the School of Dentistry teaching laboratory, a non-clinical area in which prostheses are constructed on teaching models and are therefore free of patient contamination.

MATERIALS AND METHODS Aliquots of fresh unused pumice slurry were collected from the slurry pans in the polishing room off the clinical area and from the production and teaching laboratories and weighed. Ten-fold serial dilutions were prepared and 0.2 ml of each dilution was inoculated onto fresh blood agar and Sabouraud’s dextrose agar in duplicate. Incubation was aerobic at 37 “C for 48 h. Colonies were counted and results expressed as mean colony forming units (c.f.u.) per gram weight of pumice slurry. Representative colonies were subcultured and identified by standard methods. Streptococci were identified using the API-20 strep system and Gram-negative bacilli by the API-20 E and 20 NE systems (API-bioMCrieux (UK) Ltd, Basingstoke, UK). After the pumice had been used for one working day further samples were collected and treated as before. All of the polishing lathes were then stripped down, thoroughly cleaned and disinfected with a 2 per cent solution of Virkon (Antec International, Sudbury, UK) which is a proprietary disinfectant that is both bacteriotidal and virucidal. Fresh pumice slurry was made up using 2 per cent Virkon solution as the suspension agent. Further samples were collected before use and after 4 days’ use. These samples were treated in the manner described above. Fresh pumice powder and tapwater from each of the three sites were also cultured. In addition, samples of pumice made up in tapwater from each of these sites, distilled water and 2 per cent Virkon solution were exposed to the air for 3 h at each site to test the effects of environmental contamination.

Prosthetics clinical area No growth 5125 x IO3 284410 x lo3 < 1.0 No growth < 1.0 No growth 170/ml No growth 997 K No growth No growth

Student teaching laboratory No growth 5747 x 103 210448 x lo3 < 1.0 No growth < 1.0 No growth 60/ml No growth 400 K No growth No growth

RESULTS A wide range of microorganisms was isolated from all of the samples of used pumice mixed with tapwater. Aerobic Gram-positive bacilli including B. cereus, B. brevis and B. licheniformis with members of the coli-aerogenes group predominated. Also present were members of the viridans group of streptococci with S. salivarius, S. mitis and S. sanguis being represented. In addition to these Staphylococcus aureus andS. epidermis were also present together with Branhamella catarrhalis and Neisseria sicca.

All these samples were heavily contaminated, with counts ranging from 210.45 to 280.0 X 106c.f.u./g wt of pumice slurry. Replacing tapwater with 2 per cent Virkon solution in the preparation of the pumice slurry had an effect on the concentration of microorganisms. All samples collected within 10 min of preparation yielded counts of < 1.0 c.f.u./ g wt of slurry. These concentrations were unchanged following 4 days’ use. Samples of fresh pumice powder were sterile. The tapwater from each of the three locations contained coliaerogenes organisms in low concentrations. The tapwater in the prosthetics adjustment room yielded 170 c.f.u./ml, that in the production laboratory 30 c.f.u./ml, and in the teaching laboratory 60 c.f.u.lml. Table I summarizes the counts at each location. Fresh pumice slurry prepared in tapwater and exposed in open petri dishes to atmospheric contamination yielded low counts from each of the three locations. The range of microorganisms was restricted to Gram-positive aerobic sporing bacilli, members of the coli-aerogenes group, staphylococci andAcinetobactercalcoaceticus var. anitratus. Similar petri dishes made up with sterile distilled water and 2 per cent Virkon gave no growth.

DISCUSSION The results demonstrate that once pumice slurry is used to

S. Witt

et al.: Cross-infection hazards associated with the use of pumice in dental laboratories

polish dental appliances it becomes heavily contaminated and therefore poses a cross-infection risk. A series of eye infections occurred among members of the laboratory staff and although no causative organisms had been isolated in any of the cases, circumstantial evidence incriminating the aerosol from the pumice slurry is available from the presence of pseudomonas and staphylococci in all of the used untreated samples. Both of these groups of organisms are associated with eye infection. Pumice powder from all three areas investigated was shown to be sterile, the tapwater contributed low counts of coli-aerogenes and the environment produced Grampositive sporing bacilli, staphylococci and acinetobacter. In addition to these, the untreated used pumice slurry from all three areas contained bacteria which could only have come from human oral and nasal tracts. The pumice freshly made with Virkon solution showed no growth after 12 h. The slurry made with tapwater was found after 12 h to be a good growth medium for bacteria. Contamination appears to originate from four possible sources: tapwater, the atmosphere, the appliance and the clinician. In view of the results from the non-clinical slurry samples, care must be taken to ensure that, in particular, immunologically compromised patients and patients having prostheses inserted into or over open wounds, such as implants or immediate replacement dentures, do not become infected by organisms introduced from the dental laboratory. In the clinical areas the bacterial counts of pathogenic organisms in pumice slurries may be found to be high. Although the risk of infection depends upon the minimum infective dose of any given organism, counts of the magnitude reported pose a significant risk.

283

Virkon was used as the disinfectant, as it is non-toxic and has proven virucidal properties. A prosthesis may be sterilized after 10 min immersion in a 2 per cent solution of Virkon which inactivates hepatitis B virus in 10 min (1 per cent solution). At these concentrations Virkon is inactive against stainless steel and cobalt chromium. However, as with all procedures where there is aerosol generation, safety spectacles and face mask should be worn. It is concluded that untreated pumice slurries present an unacceptable risk of cross-infection between clinician, patient, technician, dental surgery assistant and ancilliary personnel. The use of a virucidal disinfectant solution to form pumice slurries considerably reduces the risks identified by the present work. References Beneson A S. (1980)Control of Communicable Diseases in Man. Washington DC, American Public Health Association. British Dental Association (1986) Guide to Blood-borne Viruses and the Control of Cross-infection in Dentistry. BDA, London Cottone J. (1985) Hepatitis B and the dental profession. J. Am. Dent. Assoc. 110,615-650. Council on Dental Therapeutics (1985) Council on Prosthetic Services and Dental Laboratory Relations. Guidelines for infection control in the dental office and the commercial dental laboratory. J. Am. Dent. Assoc. 110,969-972. Crawford J. J. (1985) State of the art: practical infection control in dentistry. J. Am. Dent. Assoc. 110,629-633. Mitchell E. and Mosley J. (1982) ADA council recommends hepatitis vaccine for dentists, students, auxiliary personnel. ADA News 13, (17), 1, 8. Mosley J., Edwards V. M., Casey G., Redeker A. G. and White E. (1975) Hepatitis B virus infection in dentists. N. Engl. J. Med. 293, 729-734. Runnells R. R. (1988) An overview of infection control in dental practice. J. Prosthet. Dent. 59, 625-629.

Book Review Periodontology Today. Edited by B. Guggenheim. Pp. 350. Hardback, f 54.60

1988.

Basel, Karger.

This book reports the proceedings of a conference held in Zurich in May 1988. There are 32 chapters by eminent workers in their field plus summaries of the panel discussions at the end of the book. It covers anatomy and physiology of the periodontium throughout life, epidemiology, microbiology, the host-defence systems with a relatively short section on treatment. An unusual feature, which I found most refreshing, is the attention paid to those areas of periodontology which are contentious. These include chapters on statistical models, what constitutes a periodontal pathogen, the specific

plaque hypothesis, microbial invasion of the periodontal tissues, a critical appraisal of the burst hypothesis and a review of the suitability of various animal models for the study of periodontal diseases. The number of contributors to this book makes commenting on the style of presentation difficult because it varies so much. The different types of print used make the book particularly difficult and tiring to read. Many of the diagrams and tables would have been clearer if they had been enlarged. However, such is the price for rapid publication of a conference report. Overall, this was an enjoyable book to read. It will probably appeal most to specialists in the field of periodontology but other workers may also find some parts worthwhile. F. C. Smales

Cross-infection hazards associated with the use of pumice in dental laboratories.

The bacteriological contamination of pumice slurry in polishing units in a dental clinical area (high risk), a production laboratory (medium risk), an...
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