BIOCERAMICS
30,000 years of ceramics!
Did you know that the oldest ceramic piece ever discovered is the Venus of Dolní Věstonice which has been dated to approximately 30,000 years ago! Most incredibly, scientists have discovered the fingerprint of a young child on the piece
Ceramics is ultimately a catch-all term for the process of taking inorganic materials like clays, silicates, and other more sophisticated oxides, and heating them up through very high temperatures into a new solid form. This firing process sinks energy into the atomic structures of the materials which allows them to form new bonds, creating a much stronger lattice structure. Take a look at the picture below. On the left if the powdered form of Zirconium Oxide (ZrO2). Through the firing process, the powder was transformed into the crucibles you see on the right. The heat process loosens the atomic bonds of the powder, creating a kind of slurry that can be formed into various shapes. Once cool, the new material is ready to use.
Fired at
2700˚C / 4892˚F
What are Ceramics Exactly?
Zirconium Oxide
ZrO2
Zirconia Crucibles
ZrO2
How are Bioceramics Different?
Bioceramics are simply one specific kind of ceramics, sort of like how a Saint Bernard is one kind of dog. The important difference is that Bioceramics interact with the body where appropriate, and don't interact where we don't want them to. This is key to the concept of biocompatibility. We want to limit the negative interactions of every single thing that enters your body, especially something as long-term as a dental implant. Zirconia is inert, titanium is not and the ceramic version of titanium is just not strong enough to endure.
So What is the Difference Between Zirconium, Zirconia, and Zircon
All of these names sound really similar, so it certainly can be a bit confusing. We describe them below in increasing complexity, from a singular atom to a mineral. We've even included pictures to help clear things up! Hopefully!
-
Zirconium: Zirconium is simply an element like you've seen on the Periodic Element Tables back in chemistry class. Zr is the symbol for Zirconium. Zirconium easily combines with other elements to create more sophisticated molecules with very different properties.
-
Zirconia: Zirconia, or more specifically Zirconium Oxide (ZrO2), is the molecule that makes up the ceramics that we use in the dental field. You can see from the diagram that the ceramic matrix is made of only two elements: Zirconium (Zr) and two Oxygen molecules (O2). You can actually see from the diagram how the arrangement of the two atoms creates an incredibly strong molecular arrangement. It is one of the strongest ceramic molecules in existence.
-
Zircon: Zircon is technically called Zirconium (IV) Silicate (ZrSiO4). Zircon is actually a mineral that can be mined for either zircon dust or as a semi-precious gemstone. Zircon gemstones come in so many different colors because of the open lattice work of the zircon matrix allows for a wide array of other elements to be trapped, thus causing color differentials.
Why Zirconium is a Metal, but Zirconia is Not
Elemental Zirconium is chemically defined as a transition metal, just like Titanium. Transition metals are essentially metals but they have the higher capacity of absorbing elements like Oxygen and creating oxide bonds. Let’s use copper as an example. Copper is a transition metal with one of the most famous oxidation states in all of chemistry: Look at the Statue of Liberty!
That green layer is the oxidation layer, and all transition metals are able to create new chemical states like that. It does not take much to change a metal to a non-metal; for Zirconium, it just takes two oxygen atoms. Further down you can see how those two oxygen atoms completely transforms Zirconium into Zirconia!
Does the Oxide (O2) Part of Zirconia Make that Much Difference?
Absolutely! One of the curious parts of chemistry is how small differences in chemical compounds can completely and fundamentally transform it. My favorite Chemistry lesson about this involved the chemical carvone. There are two versions of carvone. There is R-Carvone (R stands for right-handed), and S-Carvone (S stands for sinistral, or left-handed). Below are the two versions of Carvone. You can see that they are exact mirror images of each other, but they have very different effects on us. R-Carvone gives us spearmint flavor while S-Carvone gives us dill flavors.
R-Carvone
vs
S-Carvone
The point of this example is to show you that even when a compound has the exact same structure but differs only in orientation, the effects can be very different. So, what happens when completely new elements are mixed together? First, below is what pure elemental zirconium and titanium look like.
Elemental Zirconium
Elemental Titanium
Now let's add two Oxygen (O2) atoms to each element and see what we get. See below:
Zirconium Oxide
Titanium Oxide
Now that is a transformation! What was clearly a metal has been completely reconstituted into a white powder, and all it took was two oxygen atoms. Specifically, what is created is a zirconium oxide ZrO2 (Zirconia) powder and a titanium oxide (Titania) powder. From there, with enough heat and pressure, these oxides can be transformed into their ceramic forms like the crucibles at the top of the page.
Why Ceramic Zirconia is Better than Ceramic Titania for Dental Implants?
The main reason is that ceramic titania is nowhere near strong enough to withstand the normal day to day biting forces of the mouth, so nobody actually makes ceramic titania implants. However, ceramic titania is used as a whitening element in things like powdered sugar donuts and paint; and, as we’ll discuss a bit later, as a coating for titanium implants themselves
Ultimately, Zirconia is the only choice since it is the strongest bioceramic there is. Zirconia is already widely adopted as a material for molar crowns due to it's unparalleled strength and durability. Zirconia crowns and restorations are about as strong as they come, but they have historically been a bit too white and solid colored to look natural. Technology has improved the aesthetics of the restorations a lot and are even being used for anterior restorations now.
Titanium Implant Coatings and Problems with Them
Titanium implants are obviously made from Titanium, but they all require a special coating of either Titania or some other bioceramic. Titanium itself does not integrate well which is why a bioceramic coating is necessary. Again, Titanium by itself does not integrate in bone well, so why use it? Because of all of the metals, it was the easiest to get a bioceramic coating to attach to, and thirty years ago when Titanium implants came to market, there were no alternatives.
Ok, that’s all well and good, but what happens if there is damage to the outer layer of the Titanium implant? Won’t the Titanium be exposed and leech out? Yes. Yes it will.
So how can the outer layer of a titanium implant get damaged? Easy. The implant process itself puts intense strain on the coating since it is literally being screwed into the bone and the bioceramic layer is being scraped against the bone the entire time the implant is being screwed into place.
In fact, it is even more likely to occur when you learn that the implant manufacturers have to prepare the implant surface to make it rough. This ‘roughness’ is important to give the bone and tissue something to grab onto during the integration process. Too smooth and there is nothing for the bone to attach to; too rough and the frictional forces due to torquing the implant in the bone can sheer off the oxidation layer. Since most Titanium implant manufacturers don't care about Titanium being shorn off, the surface is prepped, considerably.
Issues and Side-Effects of Free Roaming Titanium Particles
If the sheering force on the Titanium implant's oxidation layer wasn't bad enough, oxygen, heat, pH, bacteria, acidic liquids and fluoride can all degrade the oxide layer even more, exposing the implant site to even more Titanium particles. Again, this Titanium oxide layer is very, very thin, and it does not take a great deal of interference to strip some of it, exposing the raw Titanium underneath.
With the raw Titanium exposed to the gums and the highly vascular oral cavities, Titanium ions can, and do, get distributed throughout the body ending up in organs like your lungs, kidneys, and liver. If you are one of those people who is allergic to Titanium, you really don't want the inflammation that goes along with it occurring in your organs. Another issue that we commonly see is degradation of bone around the actual dental implant site. Enough bone loss and the Titanium implant won't hold. With enough bone loss, no implant of any kind will hold.
So Quick Question. What is Cubic Zirconia Then?
Chemistry is fun! So this is yet another form of Zirconia! Cubic Zirconia has a bit of a bad rap since you have the entire multi-billion dollar diamond industry doing everything they can to try and convince you to pay thousands of dollars for a gemstone. Here are some Zircon gemstones.
Regardless, Cubic Zirconia has a slightly different chemical makeup versus our Zirconia implants, and it is heated for a bit longer during the crystallization stage. And, if you're still wondering why Cubic Zirconia isn't used in implants, it's as hard as our implants, but it's more brittle and the biting action would ultimately cause cracking. Cubic Zirconia is meant to be sparkly, not withstand a biting force.
Though both ceramics and metals have similar uses, especially in households, these two materials are very different. Below are some of the major ways in which Ceramics and Metals are different:
-
Electrical conductivity. Electrical conductivity refers to a material’s ability to carry electric current. Metals have high electrical conductivity, while ceramics are poor conductors of electricity. Ceramics are good insulators.
-
Thermal conductivity. Thermal conductivity refers to a material’s ability to conduct heat. For example, metals are good heat conductors and will therefore transfer heat. On the other hand, ceramics are poor heat conductors.
-
Corrosion. Corrosion is the process of destroying, damaging, or weakening slowly by chemical action. Corrosion is a problem for metals, while ceramics are corrosion-resistant.
-
Workability. Metals are malleable and ductile, meaning that they can quickly be hammered into shape without breaking. On the other hand, ceramic is hard and breaks easily when subjected to stress.
-
Tensile strength. Tensile strength is a material’s ability to withstand a pulling force. The tensile strength of metals is high and will therefore not break when subjected to tensile force. Dental ceramics are almost never subject to a pulling force. Ceramics are good at the compression force of eating, especially the advanced ceramics used in our dental implants.
-
Plasticity. Plasticity is the ability to be easily shaped. For example, metals can easily be shaped or molded, while ceramic can only be made into shapes through molds.
