Crown Science
These days, the most technologically advanced dental crowns are made from an interesting combination of materials. Before I get into that, let’s first talk about how your teeth resist breaking in twain.
The toughest building materials have a combination of strength and flexibility. Think about wood or steel: they have strength (compressibility, tension), but because their rigidity is not infinite, they also derive durability from their ability to flex and rebound under load.
In contrast, the toughest (hardest) materials, do not flex under load. They remain rigid until they shatter completely. An everyday example: your ceramic toilet bowl.
Chewing
Natural teeth deal with this balance between flexibility and strength by using two different materials, laminated/fused together. The outer layer, the enamel, is hard like glass. It resists decades of food scraping on it, but it can fracture easily. Its tendency to fracture is, however, reduced by the underlying dentin, a bone-like material which flexes.
Replacing Teeth
Now, dentistry is attempting to mimic that lamination of enamel to dentin. On the inside of some solid porcelain crowns (a crown replaces the outside of your tooth) is a material classified as a yttria-stabilized tetragonal zirconia polycrystal—its an ultra-durable ceramic with a really cool property. Remember how we said ceramic tends to fracture? The yttria allows the material to stop cracks while they are tiny—the atomic crystal structure can switch over from one form to another.
It’s like this: imagine a table with four legs. If you stack things directly on top of the table, you can load it up with a ton of weight. However, let’s say your weight stack begins to drift, so that you’re putting an angular force on the table. The table top sliiides to one side: its legs are no longer perpendicular to the ground. Normally, the table would collapse at this point. However, your table has special reinforcements at the joints that let it drop into another stable position where the legs aren’t perpendicular (like a normal table), but resist the table falling over completely. Your special reinforcements are the yttria in that zirconia.
So, this is a no-glass, all crystal (remember the table) material used on the inside of these all-porcelain crowns. It is highly highly fracture resistant. But wait. No glass, you say? Isn’t glass the component of ceramic that gives it that nice translucency that lets dental techs make it look one heck of a lot like a natural tooth? Yes!
Now, we take a high-glass, brittle ceramic (feldspathic) and fuse it to the solid substructure. Just like the real tooth!
Comments
John
So when is this going to be available for animals? :)
Alexander Micek +1
Crowns so good, pets ask for them by name. “Meow meow 3M ESPE Lava Zirconia Crowns meow meow.”