SDF is a clear, colourless liquid that arrests active cavitated carious lesions and remineralises demineralised enamel and dentine.36 Some products have a blue tint, but these are not available in the UK. Although licensed to treat dentine sensitivity in the UK and some other countries, it is more usually used 'off-label' to arrest carious lesions. It turns active carious lesions black; therefore, consent to treatment must be obtained and it must be handled with care as it will temporarily stain skin, mucosa and most surfaces on contact.