Presentation Blocks: 03-23-2018 - Friday - 11:00 AM - 12:15 PM

Title: Time-CFU Relationship and Autoclaving Effects on Reusable Nitrous Oxide Delivery Circuitry


Arsalan Hanif (Presenter)
Midwestern University

Sheri Brownstein, Midwestern University
Lauritz Jensen, Midwestern University
Kimbal Cooper, Midwestern University
M. Teresa Pulido, Midwestern University
John Mitchell, Midwestern University


Nitrous oxide sedation offers patients an option which may ameliorate the fear of going to the dentist. Nitrous oxide is delivered to the patient through a circuitry (tubing) and a nasal mask, both of them frequently reusable. The first aim of this project was to measure the number of CFU isolated from reusable nitrous oxide delivery circuitry after different patient usage intervals. The second aim was to determine if repeated autoclave exposure altered the ability to adhere to the luminal surface of the tubing for three common microbial organisms.

Methods: Prior to patient use, two sterile sections of tubing (Henry Schein Inc, West Allis, WI) were attached to each dental chair circuitry, and usage time was recorded for each patient. The tubes were removed and sterile saline solution was added to each tube, agitated for 60 seconds, plated on Chocolate Agar (Hardy Diagnostics, Santa Maria, CA) and incubated for 48 hours to yield the total CFU count. Total CFU values were compared to minutes of patient use using non-linear regression analysis.
To evaluate the autoclave exposure effect, ¼-inch tube wedges were placed into individual pouches and randomly assigned to receive one of the following number of autoclave cycles at 270°F for 15 minutes: 0; 150; 200; and/or 250. Afterward, autoclaved samples were inoculated with one of the following organisms: Staphylococcus aureus, Neisseria mucosa or Streptococcus mutans and dry incubated for 24 hours (37°C, 100 rpm). Average number of adherent cells per tube was counted using scanning electron microscopy (SEM).

The correlation coefficient between tubing use and CFU formation was 0.18. SEM images showed increasing changes in surface texture following increasing autoclave cycles. All 3 strains of bacteria were present, regardless of the number of cycles.

No statistical relationship was found between CFU and minutes of use. Frequent autoclave exposure results in changes to the texture, but was not correlated to bacteria presence.


Poster Session

11:00 am–12:15 pm Mar 23 (US - Eastern)

CC, Hall B/C