This patient had a traumatic injury to her left front tooth.  A root canal had to be performed to save the tooth.  Unfortunately, teeth that have had root canals will darken over time as you can see in the before photo.  We can lighten the tooth, quite often to its original shade, by placing a bleaching agent inside the tooth in the hole where the root canal had been done.  As you can see, the results can be quite stunning.  This process will need to performed periodically unless other measures, such as a porcelain crown or laminate, is done.