Evaluation of the Antimicrobial Functions of N-halamine Dental Unit Waterline Tubing for One Year.

OBJECTIVES: The objective of this study was to test the biofilm-controlling properties of N-halamine antimicrobial dental unit waterline (DUWL) tubing (T) tubing, without recharging over one year, compared to a control line (C). METHODS: A simulated clinical model was used to pump ultrapure water through T and C lines at a rate of 1.4 mL/min, five minutes on, 15 minutes off, eight hours/day, five days a week. Samples of source water, effluent from T and C, and from the stagnant water in the carboy (liquid container) after bench work was completed (S2), were collected aseptically, serially diluted, and cultured on R2A agar for seven days every six weeks. SEM images of the inside surfaces of detached tubing sections were also taken. The carboy was rinsed with a 1:10 dilution of sodium hypochlorite after six months. Means of log transformed CFU values obtained in triplicate were paired by T and C lines across months for comparison by paired Student's t-tests. RESULTS: An increase in effluent and carboy bacterial counts were noted after six months, but decreased after bleach rinse of the carboy. No significant difference (p > 0.25) between T and C lines were observed; similarly, T and carboy were not significantly different (p > 0.30). SEM images showed biofilm attachment on the inside surface of C after two months, but not on T. Organisms identified in the effluent reflected those in the source carboy. CONCLUSIONS: No biofilm attachment was detected on the N-halamine test line after 12 months, indicating its antimicrobial properties were retained. Further evaluation is recommended to determine the optimal recharge interval for N-halamine DUWL tubing when ultrapure source water is used.

Remineralization of artificial enamel lesions by theobromine.

OBJECTIVE: This study investigated the remineralization potential of theobromine in comparison to a standard NaF dentifrice. METHODS: Three tooth blocks were produced from each of 30 teeth. Caries-like lesion was created on each block using acidified gel. A smaller block was cut from each block for baseline scanning electron microscopy imaging and electron-dispersive spectroscopy (EDS) analysis for surface Ca level. A tooth slice was cut from each lesion-bearing block for transverse microradiography (TMR) quantification of baseline mineral loss (Δz) and lesion depth (LD). Then baseline surface microhardness (SMH) of each lesion was measured. The three blocks from each tooth were assigned to three remineralizing agents: (1) artificial saliva; (2) artificial saliva with theobromine (0.0011 mol/l), and (3) NaF toothpaste slurry (0.0789 mol/l F). Remineralization was conducted using a pH cycling model with storage in artificial saliva. After a 28-day cycle, samples were analyzed using EDS, TMR, and SMH. Intragroup comparison of pre- and posttest data was performed using t tests (p < 0.05). Intergroup comparisons were performed by post hoc multistep comparisons (Tukey). RESULTS: SMH indicated significant (p < 0.01) remineralization only with theobromine (38 ± 32%) and toothpaste (29 ± 16%). With TMR (Δz/lD), theobromine and toothpaste exhibited significantly (p < 0.01) higher mineral gain relative to artificial saliva. With SMH and TMR, remineralization produced by theobromine and toothpaste was not significantly different. With EDS, calcium deposition was significant in all groups, but not significantly different among the groups (theobromine 13 ± 8%, toothpaste 10 ± 5%, and artificial saliva 6 ± 8%). CONCLUSION: The present study demonstrated that theobromine in an apatite-forming medium can enhance the remineralization potential of the medium.

Isolation of non-tuberculosis mycobacteria in treated dental unit waterlines.

OBJECTIVE: The purpose of the study was to investigate the presence of non-tuberculosis mycobacteria (NTM) in dental unit waterlines that were being routinely treated with an intermittent use waterline cleaner. STUDY DESIGN: The study was conducted at a hospital dentistry clinic where immunocompromised patients are seen. Water samples from two lines on one of two dental units were taken before and after routine weekend chemical treatment. Sampling was repeated on two subsequent occasions, on the same unit, at three monthly intervals. Laboratory techniques included centrifugation and membrane filtration to detect small numbers of organisms. RESULTS: Mycobacterium simiae was isolated from one of the four pre-treatment samples and from two of the four post-treatment samples. Mycobacterium mucogenicum was isolated from one of the four post-treatment samples. CONCLUSIONS: This pilot study found that NTM were present in DUWLs that were being routinely treated with an intermittent use chemical cleaner. Practitioners are urged to understand the limitations of available DUWL treatments, and to consider the use of sterile water for non-surgical, as well as surgical, treatment of immunocompromised patients.

Identification of Exophiala mesophila isolated from treated dental unit waterlines.

Members of the genus Exophiala are often difficult to identify to the species level because of their variable morphological appearances. This paper describes the methods used to identify Exophiala mesophila and provides salient differential features for distinguishing other mesophilic members of the genus.

Tuberculin skin test conversion rate in dental health care workers-results of a prospective study.

OBJECTIVES: The tuberculin skin test conversion rate over 12 months in dentists, dental hygienists, and dental assistants was assessed in 3 US-Mexico border counties of Texas in which reported tuberculosis rates were high compared with the rates for Texas and the United States. METHODS: Tuberculin skin tests were administered to 284 subjects and repeated on nonreactors 12 months later. Participants also completed self-administered questionnaires. RESULTS: The baseline positive tuberculin skin test prevalence was 4. 6%. Nonreactors were more likely to have been born in the United States (P <.001). The tuberculin skin test conversion rate over 12 months was 1.7%. CONCLUSION: Results indicate a need for heightened awareness of tuberculosis transmission and annual surveillance by dental health care workers, as recommended by the Centers for Disease Control and Prevention.

Measurement of boron isotope ratios in groundwater studies.

Boron is present at low levels in groundwater and rainfall in the UK, ranging between 2 and 200 ng ml-1. A sensitive technique has been developed using inductively coupled plasma mass spectrometry (ICP-MS) to measure boron isotope ratios at low concentrations with a precision (Sr) of between 0.1 and 0.2%. Samples were evaporated to increase elemental boron concentrations to 200 ng ml-1 and interfering matrix elements were removed by an adapted cation-exchange separation procedure. The validity of measuring boron isotopic ratios by ICP-MS at this concentration level is discussed in relation the theoretical instrument precision attainable based on counting statistics. Using the developed procedure it is possible to use ICP-MS to establish a reliable database documenting the natural variation in boron isotope compositions in aquifers and rain water in the UK. Preliminary results demonstrate a trend in boron isotopic compositions with increasing boron concentration. The method may be used to evaluate possible levels of boron pollution from anthropogenic inputs into natural aqueous systems.