There have been many studies on the use of FW in the field of dentistry. FW has been reported to be effective as an antimicrobial mouthwash in root canal treatment [18, 19]. There are, however, no reports of its use as a gargling agent for oral care of the elderly. Our results showed that FW may be valuable in the maintenance of oral hygiene. Aspiration pneumonia is caused by a wide range of bacteria. We analyzed the effect of FW on four major causative organisms of aspiration pneumonia, and found that it had excellent bactericidal effects against all four organisms. Its bactericidal effect was equal to or greater than that of conventional mouth rinses.
Several mechanisms of action have been reported for the bactericidal effect of FW. In the guidelines published by the Society for Oral Functional Water, it is suggested that its bactericidal mechanism may be based on oxidation by hypochlorous acid . In this study, changes in the activity of SOD, which is an indicator of oxidative reactions , was used to determine whether an oxidative response occurred when the bacteria were treated with FW. We confirmed a change in SOD activity in S. aureus, one of the primary causative bacteria of aspiration pneumonia. Since treatment of Staphylococcus aureus with 100% FW killed all bacteria, five different concentrations of FW were used for treatment, and SOD was measured when the bacteria survived treatment. Treatment with 50% FW significantly increased the SOD activity, and the concentration was consistent with the concentration at which a significant bactericidal effect on Staphylococcus aureus was observed. Following treatment with 70% FW, the SOD activity tended to be higher than that of the control, despite the small number of viable bacteria. These data supported the hypothesis that the bactericidal effect of FW arises from oxidative stress.
FW produced similar or lower rates of cell death as other mouth rinses. Especially, FW showed significantly higher cell viability than the other two mouth rinses in both cell lines with high-density cultures. This observation suggests that FW is less cytotoxic than the other gargling agents. Previous reports have shown that the use of FW has no adverse effects on the human body. Morita et al. reported that mice administered FW orally experienced no physical ill effects . We envision that FW will be used for oral care of the elderly, and the fact that it is less cytotoxic than other gargling agents means that the elderly can use it safely.
The present experiment was preliminary, aiming to lay the groundwork for further clinical research, and is essentially a baseline report. However, the results suggest that FW may be more beneficial than other mouth rinses.
Chlorhexidine gluconate, which is the main component of ConCool F, is one of the most widely used mouth rinses globally [23, 24]. Most reports indicate that it is used in concentrations of 0.10–0.20% . However, the concentration used varies from country to country. In Japan, the maximum concentration used is 0.05%, due to the risk of anaphylactic shock and gingival necrosis . Further dilution is recommended; for ConCool F, the concentration after dilution is about 0.006%. CHG in Japan is diluted about 200 times more than the concentration used in other countries. It is not easy to directly quote the results of reports describing the effects of conventional chlorhexidine rinsing. Our results also show that, except for C. albicans, treatment with diluted CHG did not have an adequate bactericidal effect. FW is an aqueous solution consisting mainly of hypochlorous acid, which is purified by the electrolysis of salt water, and the possibility of gingival necrosis caused by FW is low. Although the stimulation time was short, Morita et al. also reported no gingival necrosis . In our opinion, investigations into the safety of FW should be focused on aspects other than cytotoxicity. It has been reported that common mouth rinses, such as Listerine and ConCool F used in this experiment, have a pungent taste, which can cause taste disorders [27–29]. Taste disorders can cause a wide range of problems, and reduce an individual's quality of life. . Many elderly individuals are hesitant to use gargle products under these circumstances. It is believed that taste disorders in gargling materials are mainly due to the effects of drugs . FW is produced by the electrolysis of salt water, so the risk of taste disturbance is low. FW is also used for washing food, but no taste abnormalities have been reported due to washing. However, since it can be used for cleaning food, it appears that the risk of consuming FW is insignificant.
We are currently conducting a clinical study to determine the efficacy of FW use in the elderly. The subjects are instructed to gargle three times a day for one week, and the effectiveness of the treatment is examined. Although the study is still in progress and has only been conducted on 20 subjects, none have complained of taste abnormalities due to rinsing. A few subjects were bothered by the smell of hypochlorite chlorine, but none could not gargle (data not shown). In light of the above, FW may be a gargle material that can solve the problems faced by current gargle materials.
Although FW is a beneficial rinse agent, some clinical issues need to be addressed. First, the pH of FW is low (2.2–2.7), below the critical pH, and concern has been expressed about the demineralization of the teeth due to prolonged gargling. Tooth demineralization develops due to a lack of balance with tooth remineralization [31, 32]. We believe that the demineralization of teeth can be avoided by not allowing the oral pH to become acidic for long periods of time after rinsing with FW, by restoring it to neutral at an early stage. Therefore, after gargling with FW, it is essential to restore the pH of the oral cavity to neutral by rinsing with tap water. Morita et al. reported changes in crown morphology due to FW impregnation for three weeks in an in vitro experiment . Still, no significant crown demineralization due to FW was observed in the short-term analysis. We may need to pay attention to gargling with FW in the long term.
FW has a short storage period, because it reverts to normal water after a period of time after purification , and is thus generally regarded as safe. However, this reversion indicates that the sterilizing power will be lost. FW maintains its function for one month in cold, dark storage after purification following the guidelines of the Japan Society for Oral Functional Water . Ideally, FW should be used immediately after purification, so it is not easy to distribute effective FW in the market. Therefore, it is necessary to purchase a generating device for use. We aim to use FW in the oral care of the elderly, but since it is difficult to purchase a single device for each household, it is realistic to use it only in nursing homes and dental clinics. For FW use to become widespread in general households, it is necessary to downsize the generating device, but we believe that this problem can be solved in the future.
A variety of mouth rinses are available in the market, and are used for oral care. Our results confirmed that FW had a sufficient bactericidal effect and higher safety than other gargling agents. Safety is an essential factor in the use of gargles by the elderly. We believe that FW can become a new standard for gargling agents in the oral care of the elderly.