Hello, Thanks for writing in. Since your teeth are discoloured,you have to initially get your teeth cleaned by a dentist. Then depending on the severity of discolouration existing after teeth cleaning has done,you can go for bleaching/veneering /porcelain crown as per your dentist s advice. Chewing gum cannot give a permanent whitening at all. Always maintain good oral hygiene. Brush and floss your teeth daily. Use soft-interdental toothbrush to clean your teeth. Take care.