Bonding holds up fairly well first time out, however, subsequent approaches don’t adhere nearly as well. Generally speaking doing a veneer on a single front tooth can be challenging. However, it can be done by a proficient dentist working with an exceptional ceramist. I am assuming that the other teeth are unrestored.
The first rule for restoring an endodontically treated tooth is to cover all the cusps, this is to prevent subsequent fracture which can prove fatal to it in the long run. In the case you presented where there is a lot of remaining solid tooth structure I would be inclined to make a bonded ceramic onlay that covers the entire occlusal (biting) surface including a core that gets bonded to the tooth. I refer to this as a mushroom- because that’s what it looks like. I would most likely do it in e-Max because of the exceptional bond to tooth as well as the strength of the material.
The difference between a porcelain veneer and a ¾ crown is mostly a technical issue. With a peg lateral or other undersized tooth we frequently need to fill the space on the inside of the tooth to avoid unnatural contours and gaps that would be created by a veneer on the front of the tooth. Once you wrap the ceramic onto the palatal side to do this it becomes a ¾ crown. The cost should be the same.
The only way to make them right is to replace them- and yes it's not what you wanted to hear. Zirconia is popular, but unfortinately it is not very pretty most of the time. EMax is usually a better choice. Next time be sure you love them at try in before they are cemented.
The most important person in the equation is a master ceramist. In order to achieve the results you want the crown needs to be fully layered with many different enamels. Those layers are made of feldspathic porcelain. Often we will make a substructure of eMax in an appropriate base color and use it as a core. The tricky part is to get your dentist to work with someone who can handle it. A single central is one of the most challenging things to do in dentistry. My lab is in the office and I think it is really difficult to do it any other way.
