Concentration is the highest around. I paid twice the price for half the concentration at the dentist. Syringe tip, as others have said, are too large. Had the trays made by a dentist which make for a snug fit. The fit is tight so I only have to use a small amount. Bleached my teeth whiter than the 16% in half the time only one hour! Even with this products small faults it IS the best around at half the cost! Don¿t forget to use the re-mineralizing gel to reduce the tooth ache!