The antimicrobial effect of hydroxyapatite: bionic biofilm reduction

Hydroxyapatite particles have great potential in preventing dental cavities and controlling plaque. It is important and essential to use pure active substances alone, i.e. not in the toothpaste formulation, when testing their efficacy. Antimicrobial and plaque-inhibiting effects of hydroxyapatite have been proven in clinical studies; however, there has still been no evaluation of the antimicrobial action of hydroxyapatite as a pure active ingredient.

Question

How effective are the plaque-reducing and antimicrobial properties of hydroxyapatite versus chlorhexidine?

Materials and methods

Nine healthy, adult test subjects were recruited for this in-situ study. Sterilised and polished enamel samples from bovine teeth were used as the test specimens (intraorally). Once a pellicle had formed, the respective mouthwashes were used and the test slabs were worn intraorally overnight for 8 hours. The mouthwash solutions employed were pure hydroxyapatite in distilled water and a chlorhexidine digluconate solution (0.2%), along with a control without any active substance. All test subjects provided specimens with hydroxyapatite, CHX and without any use of a mouthwash for the analysis. The total cell count on the specimens (DAPI staining) and the number of live and dead bacteria (live/dead staining) were quantified using fluorescence microscopy. All the groups were compared to detect statistically significant differences (Kruskal–Wallis test).

Results

The results show that hydroxyapatite reduced the number of bacteria on the teeth to the same extent as a 0.2% CHX solution. Whilst the majority of microorganisms are killed when CHX is used, hydroxyapatite prevents them from adhering to the surface and maintains the ecological balance. The microorganisms are not killed off, thus being an innovative and modern approach to protect the teeth. Hydroxyapatite forms a protective layer on the surface of the teeth, which inhibits the formation of the bacterial biofilm, whilst the bacteria accumulate on free hydroxyapatite particles and are therefore unable to build up on the tooth surface.

Figure 1: Reduction of bacteria on the teeth (compiled according per Kensche et al., 2017).
Figure 1: Reduction of bacteria on the teeth (compiled according per Kensche et al., 2017).

Conclusion

Hydroxyapatite is highly effective in controlling the biofilm and has no effect on the ecological balance.

Figure 2: Toothpastes with hydroxylapatit help to keep the oral flora balanced (Meyer/ Enax 2018).
Figure 2: Toothpastes with hydroxylapatit help to keep the oral flora balanced (Meyer/ Enax 2018).

The published study can be read here.

Source:  Kensche, A., C. et al. Efficacy of a mouthrinse based on hydroxyapatite to reduce initial bacterial colonisation in situ. Arch Oral Biol 80, 18-26 (2017).