Wit HP AutoMixx 35% Hydrogen Peroxide In-Office Automix Whitening Refill Kit: 1 x 2g Syringe, 2 Applicator Tips. Syringe yields up to 4 smile line applications on both arches. Single application per session: the product may be kept from 40 to 50 minutes in contact with teeth. Remaining content can be stored and used later. Contains calcium: to keep enamel integrity during the whitening process. Gel has excellent, easy to handle viscosity.