Tooth whitening can be done by a variety of methods using hydrogen peroxide or carbamide peroxide in differing concentrations. In-office whitening is the easiest and fastest way. Three appointments for one hour each are made approximately one week apart. The most color change is seen in the first appointment and the subsequent appointments help stabilize the color change. Custom trays can be made in the office and tooth whitening gel dipensed into them at home for two weeks for noticeable effects. Professional strength whitening strips are available and can be used for three weeks for noticeable effects. Color changes are affected by coffee, tea, colas, and smoking. Whitening can be repeated as necessary. Surface hardness of teeth is not affected by whitening. Any tooth sensitivity can be reversed by decreasing exposure time to the whitening agents.