Scientists from the University of Plymouth found that commonly used chlorhexidine mouthwash could make saliva much more acidic and may increase the risk of tooth damage.
The research is published in Scientific Reports and was conducted by Dr. Raul Bescos et al.
In the study, the team gave a placebo mouthwash to people for seven days, followed by seven days of chlorhexidine mouthwash.
At the end of each period, they carried out an analysis of the abundance and diversity of the bacteria in the mouth—the oral microbiome—as well as measuring pH.
The researchers found using chlorhexidine mouthwash over the seven days led to a greater abundance of species within the families of Firmicutes and Proteobacteria, and fewer Bacteroidetes, TM7, and Fusobacteria.
This change was linked to an increase in acidity, seen in lower salivary pH and buffering capacity.
Overall, chlorhexidine was found to reduce microbial diversity in the mouth and may increase the risk of oral disease.
One of the primary roles of saliva is to maintain a neutral pH in the mouth, as acidity levels fluctuate as a result of eating and drinking.
If saliva pH gets too low, damage can occur to the teeth and mucosa—the tissue surrounding the teeth and on the inside of the mouth.
The study confirmed findings from previous studies indicating that chlorhexidine disrupted the ability of oral bacteria to turn nitrate into nitrite, a key molecule for reducing blood pressure.
Lower saliva and blood plasma nitrite concentrations were found after using chlorhexidine mouthwash, followed by a trend of increased systolic blood pressure.
The findings supported earlier research that showed the blood pressure-lowering effect of exercise is strongly reduced when people rinse their mouths with antibacterial mouthwash rather than water.
The team says in the face of the recent COVID-19 outbreak many dentists are now using chlorhexidine as a pre-rinse before doing dental procedures.
They urgently need more information on how it works on viruses.
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