A commonly used ingredient of prescribed mouthwash can lead to discoloured teeth and antibiotic-tolerant bacteria following long term use. Now a doctoral student at Malmö University is exploring an alternative treatment with promising results.

The best way to prevent tooth decay and periodontal disease is to brush your teeth. But for those who find it difficult to maintain good oral hygiene themselves, mouthwash can be an important supplement.
Chlorhexidine is a widely-used agent which kills bacteria in the mouth but is not optimal for preventing disease in the long term, says PhD student Olivia Aherne.

Our hope is that in the future, this solution can be used preventively against caries and periodontal disease as a supplement to tooth brushing.

Olivia Aherne

“A healthy mouth has a well-functioning ecosystem with a variety of bacteria, therefore the optimal agent is not something that kills all bacteria. We need something that can restore the healthy balance within the mouth, and the current treatment options available unfortunately do not suffice.”

Often found around the gum line, dental plaque consists of a thick coating of well attached bacteria, also known as a biofilm. To be effective, mouthwash must also reach the bacteria inside the biofilm, but the further the chlorhexidine gets in, the less concentrated it becomes.

“This means that the bacteria deep inside are exposed to the agent, but are not killed. This can lead to the bacteria developing tolerance to antimicrobial agents and even antibiotics,” says Aherne.

Together with the company CR Competence, Aherne explores an alternative solution; stabilised hypochlorous acid, which has been developed by the company Soft-Ox Solutions, whose aim is to develop products that can counter the spread of antibiotic resistance.

“In the first study, we looked at whether this solution can kill the bacteria using a similar time-frame and concentration that one would have in the mouth. We also wanted to investigate whether the solution would damage the tooth enamel.”

The tests have been done on cultured biofilms with a mixture of bacteria similar to those found in the mouth. The biofilms were left in the hypochlorous acid for five minutes and then examined by the researchers. Corresponding tests were also done with chlorhexidine.

“We could see that a significant percentage of bacteria were killed at an exceptionally low concentration of hypochlorous acid. With chlorhexidine, a much higher concentration was required to achieve the same effect. The tests on tooth erosion also showed that the hypochlorite acid did not cause damage to the enamel.

“Our hope is that in the future, this solution can be used preventively against caries and periodontal disease as a supplement to tooth brushing,” says Aherne.

The results are “promising” but what remains to be investigated is how well the solution penetrates the plaque compared to chlorhexidine. The long-term effects also need to be studied further, and in addition to that, the researchers want to understand what the bacteria's defences look like.

“In a wider perspective, it is necessary for us to find alternative ways to treat diseases caused by bacteria because we can no longer rely solely on antibiotics,” she adds.

Text: Anna Dahlbeck & Adrian Grist

More about the research and the researcher

The company SoftOx Solutions developed the solution that is being studied within the framework of the project.

"Since we are in an era of antibiotic resistance, it is central to find non-antibiotic solutions for oral hygiene. We are grateful that Olivia, together with researchers from Malmö University, is exploring whether the use of technology from SoftOx can contribute to maintaining good oral hygiene," says Magnus Mustafa Fazli, director of R&D at SoftOx Solutions.

Another partner in the project is the company CR Competence, which also sees great benefits from the collaboration.

"From our perspective, it is fun to be able to develop our own know-how together with Malmö University because we know a lot about how products behave when they are close to a surface and we know a lot about surfaces, but less about the complex world that is often on them  the movies," says Anna Stenstam, CEO at CR Competence.

The study is part of Olivia Aherne's doctoral project. You can read the study in its entirety here:

Effects of stabilized hypochlorous acid on oral biofilm bacteria