I spoke about this with my dentist, and according to him the research and money is going to ever-greater precision and bio-compatibility. Scanning and imaging the tooth to replace is still part-art and not fully-automated yet. The scanning processes out on the market has not perfected discriminating the tooth from the surrounding tissue, so there is some manual work the dentist performs to shape the replica; there are weird artifacts here and there they shave away and/or re-shape. Bio-compatibility sounds like it is is very close: the latest materials outlast human lifespans, and is tougher than enamel, with very small populations that adversely react to the materials.
The part-art comment is certainly true. I have a 3D milled ceramic crown that was done years ago during the early days of the technology. It is absolutely great in every way, and has been since day 1. My wife went to the same dentist a few months later, another 3D milled ceramic crown. Same guy, same machine. The crown had an awful fit, was never right, and she had it replaced with a different technology within 6 months. Getting to three-9's reliability is hard for all of us.
Gold amalgams outlasted the human lifespan too. As usual, the problem is the interface: eventually, a bacterium will slip its way in between, ferment some lactose, and drop the pH, eventually dissolving away enough of the native enamel for a friend to join, and away the positive feedback loop goes.
