Dental bonding is done by placing tooth-like material onto the tooth to build it up and/or to alter its shape. Over time the bonded portion of a tooth will change color as compared to the natural, un-bonded portion of the tooth. The bonding is an ultra-conservative way to restore a tooth and is completed in one visit.
The disadvantage being that bonding it will discolor over time, and is more prone to breakage than a veneer.