This is a procedure using peroxide to whiten the enamel of teeth. It can be done either in the chair for about 1 hour, or at home using custom-fitting bleaching trays. It is completely safe for tooth enamel, but sensitivity can be a short-term side effect. Pregnant or breast feeding women should delay this procedure until later. Bleaching dose not work on dental restorations. Also, it's effect may be reduced by smoking and the consumption of tea, coffee and red wine.