It is not a compliment when someone tells you have nice crowns. First of all it should not be obvious that they are not your natural teeth

Aesthetic crowns should not stick out as being man made. Zirconia, a white metal allows even single crowns to blend in with your natural dentition.  Where possible they should be single

and not connected  to their neighbouing crown.

Zirconia is an aesthetic material and not suitable for back teeth molars or premolars