Each 3ml syringe delivers 3-4 applications (both top and bottom teeth). Most people need 7-14 applications (once per day, 1-3 hours per application) to completely remove all stains from their teeth. This varies from person to person depending on the type and severity of stains on the teeth, as well as the length of time per application.
Keeping a white smile requires annual maintenance. Since whitening gel is less expensive when purchasing trays, we recommend that our customers purchase more gel in their original kit. Also, since shipping costs are the same, international customer are also highly recommended to purchase the 6 or 9 syringe package on their initial order. Our teeth whitening gel and desensitizing gel has a 2 year shelf-life (if refrigerated) so purchasing extra gel will ensure you are able to to keep your teeth stain-free.
See article on how much gel is needed