Dental Porcelains, With and Without Metal Substructures

Porcelain forms the basis of the very first instance of what we now term "industrial espionage" in human history, according to some sources.  Apparently, long ago porcelain manufacture was understood only by a very few Chinese artisans, and they were not inclined to give up the secret.  Europeans wanted to make porcelain themselves, though, and were very keen to figure out how.  All their attempts failed.  And then in the early 1700's a Jesuit priest, Francois Xavier d'Entrecolles, a member of the Jesuit China missions, made direct observations of the kilns of Jingdezhen and learned some of the technical knowledge of his converts.  He was able to transfer this knowledge back to Europe.  Not, of course, via the Internet, but through letters (gasp! how pre-Victorian!) and publishing in Jesuit annual reports. 

A succinct online source is: http://en.wikipedia.org/wiki/Francois_Xavier_d'Entrecolles

In dentistry, porcelains came to be highly valued as restorative materials for a number of reasons including their ability to be precisely colored, their translucency, their hardness, and the fact that they didn't stain as much in use as natural materials like ivory.  Or wood.  Or human teeth extracted from cadavers.  Yes, really.

Many artificial dental crowns today are porcelain-fused-to-metal.  This design has served us well for a long time as it combines very good esthetics and high strength.  Their strength is somewhat odd considering the vastly different properties of metal alloys and porcelains, not to mention the nature of the bond between them, but they are quite strong and fracture-resistant.

Porcelain-fused-to-metal crowns have one critical esthetic limitation, however- they can never allow a portion of the light that hits their surface to pass all the way through them.  Natural teeth reflect some light, they refract (or bend) some light within them, and yet some light also passes entirely through them.  You can easily demonstrate this by taking a small LED light like a book-reading light and shining it from behind your front teeth while standing in front of a mirror.  A lot of light will come through!

 Let's look at what this means in a practical way:

 

The tooth on the far left of the photo has a silver amalgam restoration in it that does lead to some significant graying.  There is also a composite resin restoration on the outer side which has been in service long enough to have a bit of edge wear, yet it is still a serviceable bonding.

The second tooth from the left is restored with an older porcelain-fused-to-metal crown.  It is from a technological era ("eras" change very rapidly with tech these days, so probably late 80's or so) where porcelain colors could be matched well, but properties like translucency and opacity were not as sophisticated as they are now.  Thus, the crown looks opaque in the middle third and gumline third.  Further, no incident light rays can penetrate through the crown, so it always looks different than the surrounding teeth.

The next tooth over, the second from the right, is a brand new all-porcelain crown.  Note how the surface texture, color, and translucency all precisely match the adjacent tooth on the far right, which is a totally unrestored natural tooth.  Close-up photos like this are also the ultimate test of dental esthetics; this tooth will be indistinguishable from its natural neighbors at any reasonable conversational distance. 

Note also the gum tissue at the margins of the various materials.  From the left, they are: composite resin, porcelain-to-metal crown, all porcelain crown, and natural tooth.  There is a zone of inflammation around only the tooth with the metallic substructure.  While this chronic gum inflammation does not always occur around porcelain-fused-to-metal crowns, and is a complex issue with several contributing causes, it is not entirely avoidable.  For the most part, well-contoured porcelain and composite resin materials without any metal components are highly biocompatible and do not commonly demonstrate this kind of chronic inflammatory issue.

Where indicated, all-ceramic crowns are among dentistry's finest artificial means to restore teeth that have been damaged by decay, trauma or other factors.

Comments

[Dentures Allentown]

Excellent blog, witty and informative keep up the good posting!

[Brendon Spaziani]

I like porcelain crowns because they look like real teeth, even though they aren't. Just make sure that they are strong enough to avoid chipping problems.

[Dentist Edgecliff Emergency Dentist]

Good to see more reference on dentistry.

[Fort Collins Dentist]

I prefer porcelain crowns over the others since it makes my smile more natural at all. Thanks for the article!

[cosmetic dentistry memphis]

You mention truth issue on that stuff. I think you described it in a professional way. I hope you go further in this way, with your excellent way of writing articles.