There are two types of professional teeth whitening that cosmetic dentists offer their patients. One is "take home tray bleaching", where the dentist makes custom trays that deliver the bleaching gel onto the teeth for a period of 30 min to all night, depending on which type of bleaching gel the dentist feels will give you the best result. The over night technique often used a carbamide peroxide bleaching material that was more dilute and was used while one sleeps, generally kept in the mouth for 4-7 hours. Discus Dental's "nite white" is an example of this.
The shorter acting material is used in trays for 30-60 minutes. Discus Dental's "day white" is an example of that material, and is generally hydrogen peroxide based, rather than carbamide peroxide based.
The second type is done in the dental office and is often called "deep bleaching" or "power bleaching". Some even use a light to activate the bleaching gel more. An example of this is the Discus/Phillips "Zoom" bleaching treatment.
Costs can vary depending on which material and technique the dentist uses. Some offices offer tray bleaching free to new patients or others having a considerable amount of cosmetic dentistry (porcelain veneers, porcelain crowns or bonding). Others may charge $100-$800, depending again, on which technique the dentist and patient choose to use.