Microbial contamination of retraction cords : an in vitro study

OBJECTIVE: Dental care has been particularly concerned with sterilization of instruments and materials. In this context, the methods used for infection control are essential to ensure patients’ safety. This in vitro study aimed to test gingival retraction cords taken from factory-sealed containers for the presence of contamination. Three commercial brands of retraction cords were analyzed: Retraflex, Pró-Retract, and Ultrapack. METHODS: The sample consisted of 10 1-cm segments of retraction cords of each commercial brand (n = 30). For bacterial growth analysis, 30 test tubes containing sterile brain heart infusion (BHI) as the culture medium were used. Bacterial growth was considered positive in tubes in which the BHI broth became turbid. RESULTS: Of 30 test tubes with retraction cords, six showed turbidity and were considered contaminated: three tubes with Retraflex, one tube with Pro-Retract, and two tubes with Ultrapack, accounting for 20% of the total sample. COnCLUSIOnS: The present findings showed that some retraction cords received from the manufacturers were contaminated with microorganisms. Thus, extra caution should be taken when using these materials, and further studies should be conducted.


INTRODUCTION
In dentistry, interest in infection control has increased over the years, particularly in relation to barrier precautions and instrument sterilization.Infection control is an important aspect of patient care in general, but it is particularly relevant for patients with HIV, cancer, or autoimmune diseases and transplant recipients.These patients' health may be compromised by infection with any microorganism, so the risk of pathogen transmission in dental procedures should always be considered [1].
One of the gaps in infection control is the paucity of research on dental materials supplied by the manufacturers in sealed containers [2].Some materials have shown deficiencies, and microorganisms have been identified and isolated, for example, in the powder of impression material containers [3], as well as in instruments used in endodontics [4,5] and orthodontics [6,7].
In restorative dental treatment, gingival retraction procedures are part of impression techniques [8].Although the use of retraction cords is relatively predictable, effective, and safe [9,10], it can be challenging and time-consuming, can cause bleeding and be uncomfortable for patients.Also, when inappropriately manipulated, it can lead to injury and gingival recession and delay periodontal tissue repair [11][12][13][14][15]. Several studies on the effects of gingival retraction with the use of retraction cords on periodontal health have shown that this practice causes temporary gingival inflammation [16].
In its guidelines for hospital infection control, the Brazilian Ministry of Health recommends using the Spaulding classification of inanimate objects, according to the potential risk of infection associated with the material.This classification has been widely used in dentistry, and materials are divided into three categories: critical, semicritical, and noncritical items.All critical and semicritical items should be sterilized.
Retraction cords are considered critical items [17].Therefore, because materials used for gingival retraction will be in direct contact with periodontal tissues, they must be free from contamination.However, few studies have investigated infection control and sterilization of dental materials as received from the manufacturer [2].Contamination of gingival retraction cords in particular has received scant attention in the research literature.The present in vitro study was therefore designed to test retraction cords taken from factory-sealed containers for the presence of contamination.

MATERIALS AND METHODS
This was an experimental observational study, and the tests were conducted in the Microbiology Laboratory of the Centro Universitário da Serra Gaúcha (FSG), an institution located in Caxias do Sul, southern Brazil.All materials used in this study were purchased by the authors and there are no conflicts of interest.
The sample consisted of 10 1-cm segments of retraction cords of three different commercial brands (n = 30), which were provided by the manufacturer in sealed packages.Sterile brain heart infusion (BHI) broth with no cord or any other fungal or bacterial culture was used as the negative control group.In this study, there was no positive control group.The study groups are described in Table 1.

Bacterial growth analysis
For microbiological analysis, 29.6 g of BHI broth were prepared by dilution in 800 mL of distilled water.The mixture was heated until dissolution and distributed into 30 test tubes (4 mL/tube).The tubes were then sterilized in an autoclave at 121ºC and 1 atm for 15 minutes.
The retraction cords were divided and then placed into test tubes containing sterile BHI broth, which were placed in the incubator at 35ºC for 48 hours.After this period, the medium turbidity was assessed for bacterial growth analysis.Bacterial growth was considered positive in tubes in which the BHI broth became turbid.

RESULTS
None of the control BHI broths showed turbidity, indicating absence of bacterial growth.This finding confirmed the efficacy of the method.
Of 30 test tubes with retraction cords, six showed turbidity: three tubes with Retraflex ® , one tube with Pro-Retract ® , and two tubes with Ultrapack ® , accounting for 20% of the total sample.

DISCUSSION
Concern with professional and patient safety in dental care has given rise to several studies evaluating dental materials [18][19][20][21].Some fields of dentistry have sought to assess the contamination of different materials supplied by the manufacturers in order to establish protocols of disinfection that should be adopted before their use in patients [22].
Rice et al. [2] evaluated retraction cords and irreversible hydrocolloids taken from sealed packages regarding the presence of bacterial contamination.One of the commercial brands that the authors analyzed was Ultrapak ® , which was also evaluated in the current study.Similar to the present results, they found that 5% of the cords were contaminated.
In the field of orthodontics, Purmal et al. [6] assessed four different types of orthodontic buccal tubes received in sealed containers from the manufacturer, and anaerobic

Table 1 .
Retraction cord groups