Introduction

Since the SARS-CoV-2 pandemic, there has been an increased awareness of the relationship of contaminated surfaces to the transmission of pathogens associated with dental care, which has highlighted the need for effective methods for cleaning and disinfection of inert surfaces¹. Dental procedures involve contact of dental equipment or instruments with the patient’s sterile tissue or mucous membranes², with these procedures being a major risk in the pathway of entry of pathogenic microbes; failure to adequately disinfect or sterilise surfaces of dental devices and equipment can lead to the transmission of infections³.

In odontology, infection control is a relevant issue to prevent the spread of diseases, so surface disinfection is a method to reduce the risk of contact with viruses and interrupt their spread⁴; therefore, it is necessary to have the knowledge of when the disinfection or sterilisation process should be performed; although both eliminate pathogens, only sterilisation eliminates endospores⁵. Disinfection and sterilisation of attachments and devices in dentistry for patient care is divided into three levels, depending on the intended use of each object: critical (contact with sterile tissue or bone: sterilisation), semi-critical (contact with mucosal membranes or non-intact skin: medium-level sterilisation or disinfection) and non-critical (contact with intact skin: medium or low-level disinfection)^{6, 7}.

Microorganisms contaminating the environmental surroundings of dental clinics represent an important source of transmission of infections associated with dental procedures. It has been reported that transmission of infections in a clinical environment is caused by endogenous microbiota residues or pathogenic bacteria from the patient⁸. When these endogenous microbiota encounter inert surfaces of dental attachments and equipment that are not adequately disinfected, they become contaminated by viruses and bacteria⁹. In dental practices, infections can be acquired through microorganisms from aerosols, water lines, blood, saliva and respiratory secretions by microorganisms from the environment, oral cavity or respiratory tract, so cleaning of surfaces in dental practices should be performed before and after each patient care^10,11.

There are desirable characteristics for a disinfectant solution: it should kill a wide variety of pathogenic microorganisms without causing the emergence of resistant forms; its action should be effective and efficient, even in the presence of organic matter. Furthermore, exposure to the disinfectant must not harm humans or the environment, be affordable, have a pleasant odour and a long shelf life⁶. The most commonly used disinfectant formulations today are quaternary ammonium compounds, which have amphoteric surfactant properties and possess positively charged polyatomic ion compounds¹². Among the most popular disinfection chemicals are hydrogen peroxide, sodium hypochlorite, quaternary ammonium compounds and glutaraldehyde⁷, although the latter gives off highly toxic vapours when used at 2%¹³.

In a dental clinic there are surfaces that are more susceptible to continuous contamination, because they are more exposed to microorganisms or involve more contact of dental staff (dental light switch, X-rays, three-way syringe tip, saliva ejector), allowing for heterogeneous microbial populations, with some opportunistic pathogens for humans; when these surfaces are touched by the hands of staff, once contaminated they are a vehicle for surface contamination¹⁴, making surface disinfection one of the mandatory infection control procedures¹⁵. Due attention to proper cleaning, disinfection and sterilisation must be ensured in routine dental practice to avoid cross-infection^13,14. Therefore, strict and proper implementation of infection control measures is essential for the safety of patients and dentists¹⁵. The aim of this study was to evaluate the antibacterial efficacy of different commercial disinfectant solutions used for three days during clinical days on different critical surfaces and dental chair attachments in a paediatric dental clinic. Total microorganisms recovered from each surface evaluated were quantified and microorganisms with pathogenic potential were identified.

Results

The results of the effect of the disinfectants evaluated on the microbial growth (evaluated in Log₁₀) per surface studied are shown in Table 2, the CFU count of the day one sample was always higher compared to the second day sample and the final sample on the third day. The efficacy of the disinfectant solutions was considered on the basis of a ≥3 Log₁₀ reduction in bacterial growth in relation to the growth of sample 1, in addition to the application time of the disinfectant solutions and the surface studied. The highest efficacy in reducing bacterial growth was observed with the application of 3% 5th generation QACs (FD 300^®) with >5 Log₁₀ reduction at the three-way syringe tip, saliva ejector converter and zero growth on the dental spitoon surface. The 5th generation QACs (Septalkan^®) evaluated was the second most effective disinfectant solution in reducing bacterial growth with a 3 to 4 Log₁₀ reduction, being particularly effective in reducing bacterial growth of the three-way syringe tip. The 0.5% NaClO had a reduction of more than 3 Log₁₀ and thus proved to be highly effective in reducing bacterial growth on cuspidor surfaces, being less effective in disinfecting the saliva ejector converter and even less effective on three-way syringe tip surfaces. ClO₂ (TwinOxide^®) showed similar efficacy to 0.5% NaClO with bacterial growth reducing effects of 3 to 4 Log₁₀ on all three surfaces tested. The 3rd generation QACs (Bactogem EQ-110^®) had the lowest reduction, with reductions between 2 and 3 Log₁₀.

The frequency of pathogenic microorganisms before and after the use of disinfectants according to the selective isolates from the surfaces evaluated is shown in Table 3. It was observed that all the solutions evaluated were effective in reducing the presence of the microorganisms found (E. faecalis, KESC, P. aeruginosa, E. coli), except for the case of S. aureus (Table 3). McNemar’s tests showed that the differences were statistically significant in the reduction of E. faecalis and KESC; for S. aureus the difference represented lack of efficacy; for P. aeruginosa and E. coli a reduction was obtained in its entirety and therefore the calculation did not apply.

To compare the efficacy of the different disinfectants, a two-way repeated measures ANOVA was performed, not all groups passed the Shapiro-Wilk for normality test and Levene’s test for homoscedasticity. However, the data did pass Mauchly’s test of Sphericity (Mauchly’s W 0.977, d.f. 2, p =0.603) and were therefore considered homogeneous. For the interpretation of the multivariate contrasts, the Pillai’s trace was used, which showed significant statistical differences in the different contrasts evaluated: a) bacterial growth versus disinfectant tested (F =9.769, d.f. 4, p<0.001), b) bacterial growth versus time of sample collection from surfaces (F =116.808, p<0.001), c) the interaction of sample collection times versus disinfectant (F =4.182, p<0.001) and d) the interaction of sample collection times versus surfaces tested (F =3.769, p =0.007) (Figure 1 A-C ). Pairwise comparisons of the disinfectants showed that FD 300^® 3% and Septalkan^® were the most efficient compared to the other disinfectants evaluated. Comparison of the effect of bacterial growth reduction on the three critical surfaces showed significant difference in all groups except Septalkan^® vs. NaClO 0.5%; Septalkan^® vs. FD 300^®, and TwinOxide^® vs. Bactogem EQ-110^® (Table 4).

Figure 1 Relationship of bacterial growth versus days of sample collection (day one as baseline sample, day two and day three final sample) on the surfaces evaluated: three-way syringe tip (A) saliva ejector converter(B) dental spitoon (C). 

Discussion

The correct use of disinfectants after thorough and meticulous cleaning will prevent the risks of cross-infection in dental clinics; the proper and effective choice of disinfectant solution for dental chair surfaces and dental equipment is a key factor, as they have been reported to be a source of cross-contamination between patients, so proper disinfection is necessary^7,16. The present study compared the effect of reducing bacterial growth with five commercial disinfectants on three critical surfaces of dental chairs in a paediatric dental clinic. The first result obtained in this study showed that 5th generation 3% QACs (FD 300^®) achieved the greatest reduction of CFU at three-way syringe tip and at the ejector nozzle, and inhibited bacterial growth on the third day of evaluation in the dental spitoon. The 5th generation QACs (Septalkan^®) was the disinfectant with the second highest CFU reduction, NaClO 0.5% and ClO₂ obtained similar results, while the 3rd generation QACs (Bactogem EQ-110^®) obtained the lowest CFU reduction.

Research has shown that in dental clinics there are surfaces and equipment with a higher risk of contamination than others, as they are more frequently used, which means that their surfaces are in greater contact with the dentist and assistant, including the patient, and therefore have a higher degree of exposure to microorganisms¹⁷. In this study, we chose the dental chair cuspidor which is a source of bacteria and is in direct contact with fluids such as saliva and blood, the ejector nozzle which contributes to the reduction of aerosols generated by rotary instruments and which is normally in use during most dental treatments and the three-way syringe tip which is exposed to the operative field. Another reason why these surfaces were chosen was because the aerosols generated by the rotating equipment reach a degree of dispersion of up to 2.5 metres, so that the concentrations of microorganisms are higher when they are closer to the patient’s mouth¹⁸.

The 5th generation QACs have a broad bactericidal, fungicidal and virucidal spectrum, with excellent germicidal performance under difficult conditions¹⁹; in this study the 5th generation QACs (FD 300^®, Septalkan^®) demonstrated the highest microbial reduction values. QACs are composed of polyatomic positive ions²⁰; whereas, studies have shown that QACs are generally ineffective against polioviruses, rhinoviruses and hepatitis A²¹. Christensen et al. in their study demonstrated antibacterial activity of QACs against Pseudomonas, Salmonella and Staphylococcus but no effect against mycobacteria and polioviruses²²; although, generation, concentration and time of action will have to be considered.

The 0.5% NaClO has demonstrated sufficient effectiveness for cleaning dental clinic workstation surfaces, and is considered one of the most widely used disinfectants worldwide^23,24. The results of this study demonstrated lower efficacy of 0.5% NaClO than the QACs disinfectants; nevertheless, it demonstrated better efficacy in reducing microorganisms from the dental spitoon than from the three-way syringe tip and ejector nozzle. ClO₂ had a very similar effect to 0.05% NaClO, both are used to disinfect inanimate surfaces and one of their main advantages is that ClO₂is non-corrosive^25,26. Biocides containing chlorine are used for surface decontamination, in the form of hypochlorite, are cheap and easy to produce. ClO₂ is a highly oxidative biocide manufactured for water disinfection; with a disinfectant activity less influenced by pH resulting in trace by-products that are not very harmful, unlike conventional treatments with other chlorinated compounds^27,28. Patel et al. demonstrated that ClO₂ is effective against S. aureus, P. aeruginosa, S. mutans, Candida albicans, Bacillus subtilis, Mycobacterium tuberculosis, Mycobacterium avium subsp. avium and Hepatitis B virus²⁹. In this study, the disinfectant evaluated TwinOxide^® consists of 0.3% stabilised ClO₂ with a ClO₂ purity of more than 99% and a stability of more than thirty days according to its instructions and without by-products or residues such as free chlorine or chlorite, it kills bacteria, fungi, yeasts, viruses and spores, making it an alternative for contact disinfection of surfaces and equipment³⁰.

Finally, the disinfectant with the lowest action was 3rd generation QACs; despite its increased biocidal activity and higher detergency versus 1st and 2nd generation quaternary ammoniums, in this study it was the disinfectant with the lowest efficacy in bacterial reduction in the three-way syringe tip, cuspidor and ejector nozzle.

The second result of this study showed the basal presence of P. aeruginosa, S. aureus, E. faecalis, E. coli and Klebsiella-Enterobacter-Serratia-Citrobacter complex, KESC, and after the disinfection protocol applying the evaluated solutions, P. aeruginosa and E. coli were completely eliminated. A statistically significant reduction of E. faecalis and KESC was obtained, though, in the case of S. aureus, the results obtained did not show a statistically significant reduction. Various studies have reported that some bacteria that can cause risks of infections linked to dental practice are S. pneumoniae, Mycobacterium tuberculosis, Klebsiella pneumoniae, E. coli, Legionella pneumophila and P. aeruginosa³¹, in our study we identified P. aeruginosa and the KESC complex of these bacteria. Other studies have reported that one of the most contaminated surfaces is the dental spitoon with a high number of CFU, which coincides with the result obtained in this study, while other studies have identified other microorganisms such as Klebsiella pneumoniae, Shigella sonnei y Staphylococcus aureus¹⁸.

The third result of this study demonstrated the efficacy of the disinfectants, as significant statistical differences were determined in bacterial growth versus the disinfectants evaluated, showing that 5th generation QACs significantly reduces bacterial growth versus NaClO, ClO₂ and 3rd generation QACs. A difference was determined between the microbial growth obtained between the initial sample and the final sample, which means that the longer and more consistent the application, the greater the efficacy. Finally, a significant difference was demonstrated in the interaction of the times (basal and final) versus the disinfectant and the surfaces, which means that as the working days of the paediatric dental clinic went by and the greater the number of applications of the disinfectants on the surfaces evaluated in the dental units, there was a greater reduction in bacterial growth.

Future long-term studies of other critical surfaces in dental clinics should be conducted and other types of disinfectants available for medical use should be evaluated. It is recommended that dental clinic staff be trained to perform disinfection procedures, and follow previously established standardised disinfection protocols, as well as the proper use of barriers in clinical procedures^32,33.

Conclusions

The implementation of a cleaning and disinfection protocol applied between each patient during three days of working days in a paediatric dental clinic proved to be effective in reducing CFU isolated from three critical surfaces in the dental units: three-way syringe tip, saliva ejector converter and cuspidor. The 5th generation QACs Septalkan^® and FD 300^® were the most effective, followed by ClO₂ (TwinOxide^®) and 0.5% NaClO. The 3rd generation QACs was insufficient to reduce the isolated microbial count. Bacterial growth decreased with all disinfectants evaluated as the evaluation periods elapsed on the three critical surfaces evaluated in the dental units.