Porcelain is the only material that:-Does not change color through time
-Is not penetrated by bacteria
-Is easily washable.
-Has the most real light-reflection
For these reasons porcelain is the only recommended solution. Nowadays, there are pure-porcelain crowns (without metal). These crowns offer a superior aesthetic result at the level of the gingival margen (gum and tooth union) since there is no metal ring nor shadow to be seen.
Remember that acrylic dental crowns are used only temporaly (giving time to the constuction of the definite porcelain crown).
Acrylic crowns form bacterial niches in their microscopic organic weft, where bacteria from the normal oral flora reproduces and breeds quickly. This is not the case of porcelain crons since in its pure-minerals composition bacteria can only stay in the surface and are removed with thoothbrushing.
To create porcelain crowns is considered a true art since the aaesthetic success consists on hiding the existance of an artificial tooth in the mouth. This is why the dental technician has to copy the transparencies, shadows and tones of neighboring teeth layer by layer.
When a porcelain crown is correctly created nobody should be able to notice it. And remember that aaesthetics in dentistry aims to make the artificial to look natural, something that may seem easy but in fact has may secrets.
More about Porcelains.
Porcelain crowns and bridges