Residual protein levels on reprocessed dental instruments

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Summary

Reduction of the initial bioburden on instruments, prior to sterilization, is believed to reduce transmission risks of iatrogenic Creutzfeldt-Jakob disease. Endodontic files are used in the preparation of root canals and are likely to have close contact and become contaminated with neural material from branches of the maxillary and mandibular cranial nerves. This study examined methods used by 22 dental practices to clean endodontic files, and scored visible debris and residual protein levels adhering to 220 dental endodontic files that had been used, cleaned, autoclaved and were deemed ready for re-use. Visible debris was scored after examination under a dissecting light microscope. Residual protein was quantified using a fluorescent assay based on reaction of proteins with o-phthaldialdehyde/N-acetyl cysteine. There was wide variation in the methods used by practices to clean endodontic files. The cleaning process varied from a wipe with an alcohol-impregnated cloth to hand scrubbing and/or use of an ultrasonic bath. Surface debris was visually detected on 98% of files. Residual protein was detected on all the files examined (median amount: 5.4 μg; range: 0.5–63.2 μg). These results demonstrate that the cleaning of some instruments reprocessed routinely in primary care is incomplete, and such instruments cannot be excluded as a potential source of cross-infection.

Introduction

Iatrogenic transmission of variant Creutzfeldt-Jakob disease (vCJD) has been highlighted by recent concerns over the possibility of transmission by blood transfusion.1 There is also potential for onward transmission of vCJD via re-usable medical devices, and the large volume of instruments used in dental surgery has raised the theoretical possibility of transmission in that setting.2 The disease-associated form of prion protein has been demonstrated in trigeminal ganglion, pulpal tissue and gingival tissue in animal models.3 In vCJD, the abnormal prion form has been observed using immunohistochemistry in the trigeminal ganglion but not in the salivary gland, alveolar nerve, dental pulp or gingival tissue.4 Previous risk assessments for the potential transmission of vCJD via surgical procedures have stressed the importance of cleaning instruments prior to sterilization.5

Endodontic files are used to debride and shape the root canal system following removal of the dental pulp. These instruments pose an infection control problem due to their small size and complex surface topography, which make them difficult to clean effectively. Debris may accumulate between the flutes of the instruments.6 These instruments are decontaminated and re-used routinely in UK dental practice.7 In view of the ongoing debate over the presence of abnormal prion protein in tissues out with the central nervous system and lymphoid tissues,8, 9, 10 this is a particular concern. The purpose of this study is to extend previous work by quantifying residual protein levels on endodontic files after use and reprocessing in general dental practice, and to determine whether these could be related to the cleaning method.

Section snippets

Sample collection

A random sample of 22 general dental practices was identified from a group of general dental practitioners interested in clinical research [the GRID (Glasgow Research in Dental Practice) group]. A coding system was used for each practice to maintain anonymity. A questionnaire was administered to each dental practitioner during a practice visit and completed via a face-to-face interview. The questionnaire was used to collect data on methods used to reprocess endodontic files. The visits were

Decontamination of endodontic files

All practices in this survey re-used endodontic files routinely. Files were discarded when visibly deformed or broken. There was wide variation in the methods used by practices to clean endodontic files. The cleaning process varied from a wipe with an alcohol-impregnated cloth (Azowipe®) to hand scrubbing or use of an ultrasonic bath. The most common method of cleaning was manual cleaning, and the most common method of sterilization was in a benchtop steam sterilizer (Table II). Eight of the 22

Discussion

This analysis has furthered earlier work7 by confirming and extending the information on residual debris remaining on instruments reprocessed in primary care facilities. These findings highlight that endodontic files are consistently contaminated following reprocessing methods commonly used in primary dental care facilities. The maximum amount of protein detected on a single file was 63 μg, although multiple files may be used on a patient during a single course of treatment. Similar levels of

Acknowledgements

S. Letters was the recipient of a Shirley Glasstone Hughes Award from the British Dental Association. D. Perrett acknowledges support from the Department of Health.

References (14)

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