JustSmile refill PAP gel syringes can be used with either of JustSmile teeth whitening kits. The refill kit contains 3 syringes the same as in JustSmile LED whitening kit.  JustSmile PAP Technology whitening gel has been designed to deliver a perfectly safe, effective whitening treatment.  JustSmile Key Ingredients * PAP - Phtalimidoperoxycaproic Acid - Actively whitens * Hydroxyapatite -Strengthens and repairs * Potassium Nitrate- Soothes and protects PAP is a new non-invasive whitening technology and is a safer and better alternative to peroxide. PAP contains a high potential of oxidation which dissolves stains that have built up on the enamel surface.