Effect of conventional mouthrinses on initial bioadhesion to enamel and dentin in situ

The study aimed to investigate the effect of a customary fluoride solution, containing sodium fluoride and amine fluoride, on initial biofilm formation on enamel and dentin in situ compared directly to chlorhexidine.

Bovine enamel and dentin specimens were mounted on maxillary splints carried by 9 subjects. After 1 min of pellicle formation, rinses with tap water (control), chlorhexidine (meridol med CHX 0.2%, GABA) and a fluoride mouthrinse (elmex, GABA) were performed for 1 min. Subsequently, the slabs were carried for another 8 h. The adherent bacteria were determined by DAPI staining, live-dead staining and determination of colony-forming units after desorption; glucan formation was visualized with concanavalin A. Additionally, energy-dispersive X-ray spectroscopy (EDX) analysis of the in situ biofilm layers was conducted, and contact angle measurements were performed. Statistical evaluation was performed by means of the Kruskal-Wallis test followed by the Mann-Whitney U test (p < 0.05).

In the control group, significantly higher amounts of adherent bacteria were detected on dentin (4.8 × 10(6) ± 5.4 × 10(6) bacteria/cm(2)) than on enamel (1.2 × 10(6) ± 1.5 × 10(6) bacteria/cm(2), DAPI). Chlorhexidine significantly reduced the amount of adherent bacteria (dentin: 2.8 × 10(5) ± 3.4 × 10(5) bacteria/cm(2); enamel: 4.2 × 10(5) ± 8.7 × 10(5) bacteria/cm(2)). Rinses with the fluoride solution also significantly reduced bacterial adherence to dentin (8.1 × 10(5) ± 1.5 × 10(6) bacteria/cm(2)). Fluoride could not be detected by EDX analysis of the biofilms. Fluoride mouthrinsing did not influence the wettability of the pellicle-covered enamel surface.

In addition to the reduction of demineralization and antibacterial effects, fluorides inhibit initial biofilm formation on dental hard tissues considerably, especially on dentin.