In vivo and in vitro irritation testing of low concentrations of hydrofluoric acid

Acidic fluorides are proposed for the treatment of dental erosion. The aim of this study was to examine the irritation properties of dilute hydrofluoric acid (HF) solutions for potential use in the oral cavity.

Hen's egg test-chorioallantoic membrane (HET-CAM): The CAM was accessed by careful dissection through the egg shell (n=36, 6 eggs/test solution) and exposed to 300 µl of the HF solutions (0.05%, 0.10%, 0.20%, and 1.0%) under macroscope examination over the course of 5 min. Mean time-to-coagulation and average irritation score were recorded based on appearance of hemorrhage, coagulation, and lysis of the blood vessels in the membrane. Mouse skin test: 60 male mice were randomly divided into 10 groups of 6 animals each (control, 0.05%, 0.10%, 0.20%, and 1.0% HF), shaved on the back, exposed to test solution, and euthanized after 2 h or 24 h. Skin samples were evaluated by light microscopy, scoring epithelial leukocyte infiltration, vascular congestion, and edema.

HET-CAM: 0.05% HF was slightly irritant, 0.1% HF moderately irritant, 0.2% and 1% HF strongly irritant. 0.1-1% HF solutions were severely irritating on the eye. Mouse skin test: HF concentration was significantly correlated with tissue response, and 24-h exposure to 1% HF solution showed focal erosion of the epithelium and marked localized subepithelial leukocyte infiltration.

The results of the studies suggest that accidental exposure of soft tissues to solutions containing more than 0.2% HF may be harmful.