This patient probably fell when he was about one year old and caused some trauma to the two permanent front teeth that were developing under his gum.  This type of corrective procedure can be done in a single visit by removing the discolored enamel and replacing it with tooth-colored filling material.  In the after photo, the teeth were still very dry from the procedure, so the whitish splotches stand out, but once the teeth were wetted for a while, the color blended really well and the patient was extremely happy.