Set of 3 refill tubes. These syringes work great in clear aligners trays and custom bleaching trays. The carbamide peroxide gel is ideal for gray, brown and sensitive teeth. The gel can be used for 30 mins to several hours. It’s bleaching power remains active for up to 6 hours. For sensitive teeth, it is best to start at 30 minutes and slowly work your way up to see what your teeth will tolerate. It can also be used on single discolored teeth. Porcelain veneers can be brightened up from the gel add to the back side of the natural tooth.