Teeth can get discolored due to stains on the surface or by alteration of the tooth material. Discoloration may occur when the outer layer of the tooth (the enamel) is stained. This may be caused by coffee, wine, cola, tobacco, smoking. In some people discoloration may occur because of changes in inner structure of the tooth (the dentin which may become dark or get a yellow tint).
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In many people the discoloration may be age-related. This occurs due to discoloration of tooth enamel and the inner structure of the tooth –the dentin. Dentin has a naturally tendency to turn yellow over time. Rarely tooth discoloration may be due to an inborn condition called dentinogenesis imperfecta. The teeth in this disorder are discolored gray, amber or purple.