key: cord-0971253-8cjq50l2
authors: Schierz, Oliver; Müller, Henrik; Stingu, Catalina Suzana; Hahnel, Sebastian; Rauch, Angelika
title: Dental tray adhesives and their role as potential transmission medium for microorganisms
date: 2021-05-06
journal: Clin Exp Dent Res
DOI: 10.1002/cre2.432
sha: 77b64cd2b3d3448c8a88ab7cbc5da31fef172188
doc_id: 971253
cord_uid: 8cjq50l2

OBJECTIVES: This study aimed to evaluate the possible ability of dental impression tray adhesives to serve as a transmission medium for bacteria and fungi when reusable adhesive applicators are utilized. MATERIALS AND METHODS: Ten flasks with tray adhesive were monitored over a period of 12 weeks during clinical use for contamination with bacteria or fungi. Adhesive fluid samples were cultivated on eight different culture media. All grown colonies were identified by using mass spectrometry (MALDI‐TOF). Isolates without reliable identification were either identified by Rapid ID 32 API‐STREP V3.0 or by sequencing the 16S rRNA genes. RESULTS: After 4 weeks, bacterial growth was detected on chocolate blood agar plates in five different samples. The bacterial species were identified as Staphylococcus warnerii, Staphylococcus epidermidis, Staphylococcus pasteuri, Ralstonia insidiosa, and Alloiococcus otitidis. After 8 weeks Streptococcus oralis grew on a blood agar plate. In all samples, no fungi were identified. CONCLUSIONS: The disinfectant component of the tested tray adhesive seems to be effective. However, some bacteria survived in the flask for a clinically relevant time, which might result in a potential transmission to a new host.

For the safety of both patients and medical health care providers, infection control is a major concern in dentistry ( Cristina et al., 2009; Sabino-Silva et al., 2020) . The current COVID crisis increased the consciousness and awareness for the transmission of microorganisms. The oral microbiome is featured by a high variation and a vast diversity and contains numerous bacteria and fungi species (Renson et al., 2019) . Impression tray adhesives are commonly delivered in glass flasks featuring a plastic cap with a fixed brush (Figure 1 ). Impression tray adhesives are commonly used to retain dental impression material fixed to the impression tray, preventing deformation of the impression by partial detachment. When the brush is used on an impression tray that was not properly disinfected subsequent to the try-in procedures, both the brush and the adhesive within the flask might be contaminated by the oral microorganisms. Consequently, there is a plausible risk for transmitting oral bacteria and fungi from patient to patient. As an alternative approach, the application of the tray adhesives with a spray would be safer from a hygienic standpoint, but aerosol formation and a risk of combustion when applied near open fire are disadvantageous. Another alternative would be the use of extra vessels or single dose blisters with disposable applicators, causing higher costs and increase waste. For infection control, volatile substances like isopropanol or ethyl acetate are added to the dental tray adhesives.

A previous in-vitro study revealed no relevant growth inhibition of oral bacteria induced by these adhesives. Alginate adhesive showed the most intense bacterial growth in this study (Bensel et al., 2013) . However, due to the study design, it is possible that the disinfectant component of the adhesive did not operate effectively and volatized before the bacteria have been applied. Another study artificially contaminated suspensions of dental adhesives with three test organisms (Staphylococcus aureus, Salmonella Choleraesuis, Pseudomonas aeruginosa). In contrast to the other investigation, a significant inhibition of oral bacterial growth after 24 h was observed (Herman, 1993) . Based on the authors' knowledge, no studies have ever investigated the bacterial and fungal contamination of the liquid within the glass flasks of dental tray adhesives in clinical dental practice. The purpose of this explorative study was to measure the contamination of these adhesives under clinical conditions and to establish a qualitative screening for bacteria and fungi. The null hypothesis stated that no microorganisms can be cultivated from the liquid within the glass flasks tray adhesives. 

After two, four and 12 weeks of monitoring the flasks, no colonies could be detected on any medium. After 6 weeks of monitoring, five F I G U R E 1 Agar plate, dental tray, reusable brush, and adhesive flask F I G U R E 2 Examination procedure of the samples; MALDI-TOF = laser-desorption-ionization-time-of-flight mass spectrometry chocolate blood agar plates showed bacterial growth. In 75.0% of the samples, the bacterial species could be identified by using MALDI-TOF. The bacterial species were identified as Staphylococcus warnerii, Staphylococcus epidermidis, Staphylococcus pasteuri, Ralstonia insidiosa, and Alloiococcus otitidis. After 8 weeks of monitoring the flasks, colonies of Streptococcus oralis could be detected on a further blood agar plate. All the other samples remained negative. In total, 1.5% of all culture media (N = 400), which corresponds to six out of the 50 samples (12.0%), showed a transitional bacterial contamination (Table 1) . At all times, no fungi were detected. All positive results originated from different flasks.

The results of this longitudinal observation indicated a marginal transitional bacterial contamination of the dental tray adhesive in daily dental routine. Therefore, the null hypothesis was rejected. This observation is corroborated by other literature sources (Bensel et al., 2013; Herman, 1993) . In contrast to these studies, the present investigation was not limited to a single bacterial species. The design of the study allowed the identification of a wide range of bacteria and fungi species that potentially survive the application of a disinfectant, and could consequently be transferred to another host. The strengths of the current study include the wide variety of culture mediums and the sophisticated microbiological methods for their identification. In a most recent study growth of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Streptococcus mutans could not be inhibited (Bensel et al., 2013) . As mentioned beforehand, this is most probable due to early evaporation of the disinfectant. However, F I G U R E 3 Sample spreading path over the medium for inoculation using the cap-attached brush T A B L E 1 Positive agar probes, Roman numerals represent adhesive flask of sample origin numbered from I to X 

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