Chlorhexidine mouthwash is used as an antiseptic to reduce gum disease, prevent plaque buildup, and to slow the development of tartar (chalky deposits). Chlorhexidine is a positively charged molecule that can bind to negatively charged microbial cell walls to interfere with the microorganism’s equilibrium. At lower concentrations, chlorhexidine is bacteriostatic by way of causing leakage of low molecular weight substances from the microbial cell and inhibiting reproduction. At higher concentrations, chlorhexidine is bactericidal by precipitating the cytoplasmic contents of the microbial cell through adsorption to the negatively charged cell wall. [1], [2]
While its use is associated with tooth staining, the exact mechanism of this side effect is not completely understood. Current hypotheses suggest the staining is due to anionic dietary chemogens (e.g., from tea, coffee, tannins from wine) that adsorb to chlorhexidine cations. Because this is closely linked with chlorhexidine’s mechanism of action, lack of staining is likely to indicate a lack of efficacy and teeth staining can be expected with very low concentration rinses. [1], [2]
A 2017 Cochrane review and meta-analysis studied the use of chlorhexidine mouthwash and the incidence of teeth staining. While chlorhexidine can reduce plaque build-up for the first weeks or months of use, it can lead to tooth staining or tartar buildup when used for longer than four weeks. A review of 51 randomized controlled trials included people brushing their teeth, either with or without using floss, and professional tooth cleaning during chlorhexidine use. Results found a large increase in extrinsic tooth staining after 3-6 weeks of chlorhexidine use. This effect continued to increase in participants using chlorhexidine mouthwash after 7-12 weeks and after 6 months. Chlorhexidine concentrations studied in the papers discussing tooth staining ranged from 0.06% to 0.2%. The authors conclude that chlorhexidine mouthwash causes tooth staining, which requires polishing carried out by a dental professional, after four weeks or longer of use. [2]
A 2019 systematic review and meta-analysis evaluated whether chlorhexidine mouthwash with an anti-discoloration system is effective in preventing extrinsic tooth surface discoloration without sacrificing efficacy. Thirteen randomized studies were identified for this meta-analysis. For non-brushing studies, there was a significant difference in staining scores between chlorhexidine mouthwash with anti-discoloration systems and normal chlorhexidine. However, when studies involved toothbrushing, there was no difference in staining between the two formulations of chlorhexidine. Studies between the two formulations found no differences in efficacy in terms of plaque scores and gingival inflammation. [3]
An in vitro study assessing the role of saliva in chlorhexidine-induced tooth staining used tea as the staining agent and hydroxyapatite as mimicking teeth. Various combinations of tea, chlorhexidine and parotide saliva were used to investigate different substances binding to hydroxyapatite by performing sodium dodecyl sulfate–polyacrylamide gel electrophoresis with Coomassie Brilliant Blue (R250). While tea interacted with several salivary proteins including proline-rich proteins and histamines, chlorhexidine did not bind to salivary proteins. Additionally, the combination of tea and chlorhexidine increased binding of both agents to hydroxyapatite. The authors suggested that a possible mechanism of stain promotion by chlorhexidine could be through accelerating formation of acquired pellicle and the accumulation of tea and chlorhexidine onto tooth surfaces. [4]