ABSTRACT
Background: The emergence and spread of SARS-CoV-2 has increased environmental disinfectant usage to reduce the transmission of this virus. Ethanol 70%-90% and 5% sodium hypochlorite have the highest consumption for disinfection of various environmental surfaces during the COVID-19 pandemic. Dental unit waterlines (DUWLs) are more susceptible to microbial contamination due to their particular structure. This study aimed to investigate the effect of increasing the use of disinfectants during the COVID-19 pandemic on the bacterial contamination of DUWLs. Methods: During November (before the COVID-19 pandemic) and December (during the COVID-19 pandemic), a questionnaire was used to assess the frequency of disinfection of unit surfaces and other environmental surfaces and the type of disinfectants used. The water samples were collected from different parts of DUWLs. The gram staining method followed by the biochemical method was used to identify the desired bacteria. Results: The results showed that the frequency of disinfection of dental units increased 8 times in December compared to November. There is a significant inverse relationship between the frequency of disinfection of dental units surfaces and the bacterial contamination of DUWLs. Conclusion: The microbial load in different parts of the DUWLs was less than 200 CFU/mL. The American Dental Association (ADA) recommended and indicated the allowable microbial concentration and the appropriate quality and water used in these units. © 2022 The Author(s).