Teeth whitening is the procedure and process of lightening the color of human teeth. The chemical degradation of the chromogens within or on the tooth is termed as bleaching. Whitening is often desirable when teeth become yellowed over time for a number of reasons, and can be achieved by changing the intrinsic or extrinsic color of the tooth enamel. The chemical degradation of the chromogens within or on the tooth is called as bleaching.