You can actually get porcelain fillings...inlays. Its a cosmetic feature here in the US so, its usually not covered and most dont go there. Its alot better to look at though once you see someone who might have had cavities as a child but, doesnt need to get full crowns done...the change from a silver filled mouth to a porcelian filled one is nicer.
Fillings of amalgam are still widely used here.
Crowns can be all porcelain and/or gold based with porcelain...it usually depends on the tooth to be replaced and the way in which it is being done.
The most commonly used crowns here in the US in people of and around middle age are of the gold based porcelain due to them being of the molar or incisors, one at a time.
Those who need a bridge, or few teeth, done usually have a metal base that you wont see with porcelain teeth over it and sometimes will contain a metal area to attach to other teeth, etc. It really has alot to do with whats being done, how many, and where and what works best in each area.
The really neat stuff are the surgical implants that have become more the rage here in the last 15 years or so. Like porcelain crowns the porcelains crowns need a post to be fastened to however, these screw posts are surgically implanted and the porcelain crown is made with an opposing screw post...its fascinating really.
I worked in a dental lab for way way way too long.
Oh yeah...I have one porcelain on gold crown, prolly about 5 wee fillings...I had a permanent retainer as a very young one so....its most likely I will get at least one more crown...but they're straight gosh darn it