Abstract: The problem of dental hypersensitivity has posed considerable problems in dentistry for a long time; a product containing ferric oxalate has been tested recently. The desensitizer was tested on 20 teeth extracted for orthodontic reasons; the samples were analysed under SEM to check the effectiveness of dentin tubule occlusion in relation to application times. Then, the product was applied in vivo in a single layer in some patients, in a double layer in others. Subsequently, an acid solution was applied on the surface of the tooth covered with the product; pain reappeared in some patients after a single application, while no pain reappeared in those patients treated with a double layer. This means that the thickness of the desensitizer layer is very important as regards its effectiveness in time.