According to the American Dental Association:
There’s no reason to put up with gaps in your teeth that are stained, badly shaped or crooked. Today, a veneer placed on top of your teeth can correct nature’s mistake or the results of an injury and help you to have a beautiful smile.

After

Before

After

Before

Dental veneers are wafer-thin, custom-made shells of tooth-colored materials designed to cover the front surface of teeth to improve your appearance. The shells are bonded to the font of the teeth changing their color, shape and size or length.

According to www.WebMD.com, some of the top reasons for having veneers are:

• Teeth that are discolored – because of root canal treatment, stains from tetracycline or other drugs, excessive fluoride or other causes, or the presence of large resin fillings that have discolored the tooth
• Teeth that are worn down
• Teeth that are chipped or broken
• Teeth that are misaligned, uneven or irregularly shaped (for example, have craters or bulges in them)
• Teeth with gaps between them (to close the space between these teeth)