In the past, porcelain crowns were always built upon a metal core. That was the only way they could have enough strength to withstand the tremendous biting forces that are exerted on all of your teeth. That metal core is what creates the dark blue line at the edge of many crowns.
Recent breakthroughs in adhesives, combined with the development of stronger porcelain materials, allow us to make crowns entirely out of porcelain. All-porcelain crowns maintain a translucency that makes them hard to tell from natural teeth. Without metal, the problem of a dark line at the edge of the gums is eliminated. This allows us to place the edge of the crown above the gum line, and that's healthier for your tooth and gums. When you want to improve your smile, all-porcelain crowns are a beautiful and natural looking choice.