Challenging dental unit water biofilms:Clean, treat, repeat

Biofilm formation within dental unit waterlines and subsequent microbial contamination could be a potential health-risk for immune-compromised and elderly patients. In this thesis the degree of microbial contamination and which microbes are present in the dental unit waterlines in the Netherlands was examined. Furthermore, an in-vitro dynamic flow model was developed to be able to study treatment regimens and antimicrobial products. Results from a field study revealed that of 213 dental units tested only 39% complied with hygiene standards based on heterotrophic plate counts. Molecular DNA techniques, however, revealed that 43%, 71%, 98% of the units tested positive for the presence of amoebae, Legionella spp. and fungi. Analysis of confounding factors indicated that units, treated daily with a low concentration of hydrogen peroxide in combination with a weekly high dose disinfectant were acceptably low in the microbial load. This result was validated and confirmed by testing four different treatment regimens in the newly developed in-vitro dynamic flow model. Further evaluation of commercially available high-dose disinfectants revealed that most products were unable to clean a biofilm-contaminated surface within a single treatment. To control biofilm formation within the dental unit waterlines and safe-guard the patients’ health, these units should be redesigned, dental staff to be educated on the reasons why strict adherence to infection control measures is important and to frequently test the dental unit water. Additionally, the current method of testing the dental unit water and how to control microbial contamination in the dental unit water is discussed

Challenging dental unit water biofilms: Clean, treat, repeat

Biofilm formation within dental unit waterlines and subsequent microbial contamination could be a potential health-risk for immune-compromised and elderly patients. In this thesis the degree of microbial contamination and which microbes are present in the dental unit waterlines in the Netherlands was examined. Furthermore, an in-vitro dynamic flow model was developed to be able to study treatment regimens and antimicrobial products. Results from a field study revealed that of 213 dental units tested only 39% complied with hygiene standards based on heterotrophic plate counts. Molecular DNA techniques, however, revealed that 43%, 71%, 98% of the units tested positive for the presence of amoebae, Legionella spp. and fungi. Analysis of confounding factors indicated that units, treated daily with a low concentration of hydrogen peroxide in combination with a weekly high dose disinfectant were acceptably low in the microbial load. This result was validated and confirmed by testing four different treatment regimens in the newly developed in-vitro dynamic flow model. Further evaluation of commercially available high-dose disinfectants revealed that most products were unable to clean a biofilm-contaminated surface within a single treatment. To control biofilm formation within the dental unit waterlines and safe-guard the patients’ health, these units should be redesigned, dental staff to be educated on the reasons why strict adherence to infection control measures is important and to frequently test the dental unit water. Additionally, the current method of testing the dental unit water and how to control microbial contamination in the dental unit water is discussed

Determination of arginine catabolism by salivary pellet

To determine the formation of ammonium from arginine by oral bacteria residing in saliva and dental plaque, an arginolytic activity assay based on the work described by Nascimento et al. [2] was developed. Following the original methodology, insufficient ammonium production could be determined. To improve the method for our research goal, the following modifications were made to the original protocols: • The following changes were made to the arginine catabolism assay resulting in a 1000-fold increase in sensitivity: (i) the salivary pellet was washed and concentrated five times resulting in the removal of low density compounds interfering with the assay, (ii) the pH of the Tris-maleate buffer was increased from 6.0 to 7.5 resulting in a better conversion of arginine to ammonium and (iii) the incubation time was increased to 3 h to ensure that non-responders and salivary pellets low in cell numbers could yield detectable levels of ammonium. • Removal of a centrifuge step from the protein determination resulted in a higher protein yield improving the accuracy of the assay. • Changing from the use of the toxic, environmentally hazardous, mercury containing Nessler's reagent to a colorimetric enzyme assay achieved a safer and greener determination of ammonium concentration