Sterilization of New Endodontic Hand Files Stored in Dental Office Inventory: An In Vitro Study

Abstract

Background and objective Endodontic files, as supplied by the manufacturers to the endodontists, are not pre-sterile routinely. For both new and used equipment, rotary as well as manual, autoclaving is the standard sterilization protocol used in clinical and academic practice. In dentistry, instrument sterilization aims to safeguard patients from cross-contamination through instruments. Hence, every device should be thoroughly cleaned and sterilized. In this study, we aimed to evaluate the presence of various microorganisms in sealed and unsealed stored packs in dental offices and the probable impact of pre-sterilization procedures on the survival of these microorganisms. Materials and methods Two groups of root canal files varying in their packing method, boxes (Mani stainless steel K-files, ISO 25, length 25 mm) and blister packs (UGD, ISO 25, length 25 mm), pre-sterile, opened/unopened were chosen and stored for about two weeks in the dental office and were classified into three groups based on their storage and further classified into subgroups depending on their packing modes as follows: Group-1 (unopened and stored in shelf for two weeks), Subgroup-1A (boxes), Subgroup-1B (blister packs); Group-2 (unopened and stored on the countertop for two weeks), Subgroup-2A (boxes), Subgroup-2B (blister packs); Group-3 (opened and stored on the countertop for two weeks). After two weeks of storage, a set of three new files from each pack, both boxes and blisters, were placed in the nutrient broth to assess the turbidity and later cultured to assess the presence/absence and type of any bacterial growth. All the instruments in the three groups and subgroups were placed separately in the nutrient broth and carried to the microbiology lab for bacterial cultures. The entire procedure was carried out under the laminar flow. All these files in the nutrient broth were incubated for about 72 hours and the turbidity was assessed, and then the turbid bacteria were cultured on blood agar and MacConkey agar plates for the presence/absence and the type of bacteria in each group and subgroups. Results All specimens, both opened/unopened boxes and blister packs, after about two weeks of storage, were cultured and observed for contamination. All the tested files groups showed bacterial culture growth both on blood agar and MacConkey agar plates. Group-1 (Subgroups 1A, 1B) boxes and blister packs unopened and stored on the shelf for two weeks demonstrated aerobic spore bacilli; Group-2 (Subgroups 2A, 2B) boxes and blister packs unopened and stored on the countertop for two weeks demonstrated Gram-positive bacilli; Group-3 opened boxes and blisters stored on the countertop for two weeks demonstrated Micrococci and Gram-negative bacilli. Conclusion In the present study, all the packs, blisters and boxes, demonstrated the presence of bacterial growth irrespective of their storage in the dental office. Hence, in order to prevent any new infections from the operating field, sterilization of not only the old files but also the pre-sterilization of new files should be made mandatory.

Keywords: bacteria; blisters; blood agar plates; boxes; macckonkey agar plates; microorganisms; nutrient broth; root canal files; sterilization; turbidity.

Figure 1. Group-1, Group-2 (Subgroups 1A, 1B, 2A, 2B), and Group-3 files placed in the nutrient broth after two weeks of storage

Figure 2. Turbidity in the nutrient broth evaluated after 72 hours

Figure 3. Bacterial culture growth on blood agar plates

Figure 4. Microscopic image of aerobic spore bacilli

Figure 5. Bacterial culture growth on MacConkey agar plates

Figure 6. Microscopic image of Gram-positive cocci

Figure 7. Bacterial culture growth on MacConkey agar plates

Figure 8. Microscopic image of Gram-negative bacilli