The whitening solutions purchased over the counter at the drug stores are not as effective. They are a diluted, weaker version than used in the dental office. The difference is that there is no professional monitoring or maintenance with a product sold over the counter, thus the concentrations cannot by law be as strong for fear of harm to a consumer. The solutions used by the dentist are of stronger percentages and concentrations, and are routinely monitored by the dentist and office. While these in-office solutions are not harmful to the teeth or gum tissue, if monitored and used properly, they render a far more profound and longer lasting result.