Purpose: To investigate the effect of silver ionised water on acid production in plaque. Methods: After injecting 0.5 mL of silver ionised water (concentration: 5 ppm) produced with the sintering coating method in the sensor part of the pH metre, plaque collected from the oral cavity by one platinum loop was mixed in. Immediately after that, a 5% sucrose solution (1 g/20 mL) was added and the pH was continuously measured for 30 minutes at 1-minute intervals (A). Similarly, silver ionised water was mixed with 5% sucrose solution in the same way as in (A) at 3 (B), 5 (C), 10 (D) and 15 minutes (E) after plaque contamination. The pH was measured at 1-minute intervals. The pH of the purified water containing no silver ionised water mixed with plaque and sugar solution at the same time was measured and used as a control. Each experiment was conducted three times, and the pH measured every minute was compared as a percentage of the pH at the beginning of the measurement (100%). Results: Analysis of variance of the repeated measurements to determine the effect of silver ionised water on the decrease in pH revealed a main effect of silver ionised water and an interaction between time and group [F (1.302,20.826) = 39.145, p < 0.01]. Multiple comparisons using Dunnett’s method showed a significant decline in the rate of decrease in pH from B to E as compared with that in the control (p < 0.01). Conclusion: Silver ionised water was found to inhibit the acid production in plaque.
Silver is a metal that has been known for a long time. It is rarely produced naturally as natural silver and is found in trace amounts in sulphide minerals such as copper, lead and zinc. Silver has long been known to have strong antibacterial [
In the dental field, the antibacterial effect of orthodontic brackets coated with silver ions [
Microorganisms in plaque on the surface of teeth are known to decompose sugar to produce acid, which demineralises the teeth. Since the lowering of pH by acid was reported by Stephan [
Silver-ion water was prepared by adding silver salt compound powder to pure water and then dissolving it. This solution was applied to the metal surface and sintered with nitrogen to form a layer containing sintered silver nitride on the metal surface. The layer was immersed in distilled water, and the silver-ion water eluted from it was used for the experiment [
The silver-ion water concentration was measured with an atomic absorption spectrophotometer (Hitachi, Ltd., Model 180-30, Japan), and 5 ppm was used. After injecting 0.5 mL of the silver ionised water in the sensor of a pH metre (LAQUA twin, Horiba, Japan) with a micropipette, the water was left for 5 minutes and when the pH of the silver ionised water stabilised owing to the influence of carbon dioxide in the air, 1 platinum loop (about 2 mg) of plaque was mixed in. Immediately after that, 50 μL of 5% sucrose solution (1 g/20mL) was added and the pH was continuously measured for 40 min at 1-min intervals (A). Similarly, sugar solution of the same concentration was added to the silver ionised water for 3 (B), 5 (C), 10 (D), and 15 minutes (E) after plaque contamination and the pH was measured for 30 minutes at 1-minute intervals. On the other hand, as a control, the plaque and sugar solution were mixed simultaneously in 0.5 mL of purified water (Ken-ei Pharmaceutical Co., Ltd., Japan) and the pH was measured. Plaque was collected from the oral cavity of experimenters who had not brushed their teeth for a day. The experiment was started at 14:00 in the laboratory.
The data obtained was expressed as a percentage of the value of pH at the beginning of the measurement as 100%, and the average value of three times was obtained. Repeated-measures analysis of variance was performed using the control and silver-ion water immersion time as factors to confirm the main effect and interaction of the rate of decrease in pH and time. Multiple comparison tests using the Dunnett’s method were conducted as subsequent tests. The SPSS Statistics 26 statistical software was used for statistical processing, and the significance probability was set at <5%.
The results are shown in the graph in
Two types of manufacturing methods have been used for silver ionised water, the conventional electrolysis method [
pharmaceutical method (zeolite) [
According to the ‘Outline of the Review of Water Quality Standards’ by the Ministry of Health, Labour and Welfare of Japan in 2003 [
As this experiment was conducted outside the oral cavity, we used relatively high silver-ion water concentrations within the safety standards. However, on the basis of the results of this experiment, we are considering conducting oral experiments with lower concentrations in the future.
The decrease in pH by the control was due to the bacteria in the plaque consuming the sugar solution, showing the so-called typical Stefan curve [
In summary, the present experiments showed that silver-ion water affected the plaque from a relatively early stage and almost stopped the acid production of plaque after 10 minutes of immersion (D).
There are several reports on the disinfection principle of silver ions. The most popular theory is that silver ions with a (+) charge adhere to the cell walls of bacteria with a (−) charge, impairing their ability to synthesize proteins and inhibiting cell division [
As the cell walls of gram-negative bacteria are thinner than those of gram- positive bacteria, the effect of silver ions is better for gram-negative bacteria. The indigenous bacteria in the oral cavity are mainly gram-positive bacillus such as Actinomyces and Corynebacterium and gram-positive coccus such as Streptococcus and Streptococcus pneumoniae [
Morishita et al. [
On the other hand, the results of a test conducted by the Japan Food Analysis Center, which investigated the effect of silver ionised water on the viable counts of oral bacteria, Prophyromonas gingivalis and Streptococcus mutans, [
These reports suggest that silver ionised water has a bactericidal activity against oral bacteria and inhibits the growth of plaque. In this experiment, acid-pro- ducing ability, which is evidence of bacterial activity, was measured directly with a pH metre and the effect of silver ionised water on oral bacteria was clarified. Pre-sleep mouthwash with silver ionised water is expected to contribute to the prevention of aspiration pneumonia in the elderly.
In this study, we found that 5-ppm silver ionised water suppressed plaque acid production and decreased the pH level.
The authors declare no conflicts of interest regarding the publication of this paper.
Morishita, S., Watanabe, S., Miyazawa, K. and Tohnai, I. (2021) Antimicrobial Effect of Silver Ionised Water Prepared with the Sintering Coating Method—Effect on Acid Production in Plaque. Health, 13, 299-305. https://doi.org/10.4236/health.2021.133024