What Happens to a Veneer over Time?

Most porcelain veneers nowadays are made from porcelain that is as strong as, or stronger, than your natural tooth.  The bonding agents we use are the best they've ever been.  That being said, the weakest part of any restoration is the cement bond where the restoration (veneer, crown, filling) and the tooth meet.  As that breaks down over time, the veneer or crown could debond and either fracture or fall off, although this is quite rare.  I would always choose to prepare for a veneer over a crown as there is so much more conservation of tooth structure with a veneer prep so when it needs to be replaced in the future, you will have more tooth structure to work with. 

Everything has a life expectancy and can break and wear down. It is important to know that, but what can you do about it? I feel like it is best most of the time to conserve tooth structure and doing a crown doesn't do that. If the veneer is going to remove a significant amount of tooth structure then a 3/4 crown or full crown may be acceptable too. The only reason to do a full crown is if they are not confident about the bond and need the mechanical retention it offers, or that the bite is in a spot where the porcelain of a veneer risks being damaged. 

10 years is a good guess, but nobody knows for sure. If the veneer is bonded to a lot of enamel that can increase it's odds of lasting long.

The strength of the porcelain between a veneer and a crown is no different. The remaining tooth structure left after the trauma will determine how much coverage should be needed. Veneers have been on my patients teeth since the mid 80's. The average life of a veneer is 10 – 15 years. With proper care, a veneer can last indefinitely. Patient follow through as well as strict adherence to care instructions is a must! This would include no nail biting, consistent wearing of a night guard and proper home dental care. Twice yearly exams can monitor this.