Electrical impedance — a new parameter for oral mucosal irritation tests

The potential for dental materials to irritate human oral mucosal membranes was assessed by an electrical impedance technique. A small electrode at the site of irritation on the inside of the cheek and a large electrode on the outside of the cheek were used. Skin impedance was reduced by inundation with ECG-gel. An irritation index was formed by calculating the quotient between the impedance absolute value at 20 kHz and the impedance value at 1 MHz. Electrical impedance technology was found to be more sensitive than traditional visual registration of mucosal reactions. Two series of experiments were performed in which special appliances were constructed to ensure duplicate measurements on the small area of exposed buccal mucosa. Liquid samples elicited differentiated fast response, which was insignificantly influenced by mechanical factors. The mechanical irritation induced by merely the shape of a solid specimen prevents detection of slight mucosal irritation from potentially leaking substances.