Metal Ceramic Crown
The more commonly used English abbreviations are:
- PFM (Porcelain-Fused-to-Metal),
- VMK (Veneered Metal Crown),
- CMC (Ceramic Metal Crown),
Which means the inner crown is made of metal, and the outer layer is porcelain(ceramic).
Let’s discuss the metals implanted in it
There are usually three categories:
- Precious metals
- Non-precious metals
- Pure titanium or titanium alloy
Precious metals
According to ADA (American Dental Association) standards, there are three types of precious metals:
1. (High Noble) high precious metal
(Gold, platinum, palladium) content is greater than or equal to 60% and the content of gold should be greater than 40%
2. (Noble) precious metals
(Gold, platinum, palladium) content is greater than or equal to 25%
3. (Predominantly base) Some places are called semi-precious metals
(Gold, platinum, palladium) content is less than 25%
Therefore, noble metals and precious metals contain more ferrous metals, and the inner crown will be a little golden tint.
2. Non-precious metals
Nickel-Chromium alloy: Nickel and chromium are the main components of the nickel-chromium alloy. The strength of the nickel-chromium alloy is relatively hard, and as the inner crown of the porcelain layer, it can play a very good supporting role. Since the 1970s, this metal has been widely used in the production of porcelain dental crowns because of its economy and durability.
But after doing a lot of dental crowns, I discovered that nickel is a metal that has poor bio-compatibility. What does it mean? It is placed in the human body, which may cause rejection, allergies, and other symptoms. Among the people who wear nickel-containing jewelry, 15-20% of women and 1-2% of men have allergies and have inflammation of the skin and mucous membranes. Therefore, nickel-chromium alloy porcelain crown have been eliminated in the stomatology department of regular hospitals.
Moreover, with nickle added, the crown will appear darkened in the gums after a period of use, which affects the appearance (because nickel is not an inert metal, the metal properties are more active, there will be the precipitation of metal ions) is more likely to affect your health. So now, most of the dental crowns made by factories do not contain nickle. However, the price of Ni-Cr alloy porcelain teeth is the cheapest, and it may still be done in some small clinics!
Cobalt-Chromium Porcelain Teeth: Because nickel is not so good as mentioned above, another metal is used instead, cobalt, which is more bio-compatible than nickel-chromium. The alloy is tough enough, and it is not easy to be allergic. Under normal circumstances, it will not cause the color of the gums to change, but long-term use still has the problem of discoloration of the gums.
There is no doubt that cobalt-chromium alloy porcelain has advantages. Because it does not contain harmful nickel and beryllium elements, the safe, reliable, and reasonably priced cobalt-chromium alloy has become the first choice for patients with non-precious metal porcelain repair.
Cobalt-chromium alloys have replaced nickel metal with more stable cobalt metal. In comparison, the metal is much more stable and has less harmful irritation to people. Cobalt-chromium metal is harder than nickel-chromium metal and has abrasion resistance. The binding force with porcelain powder is also better. But it is always a cheap material. It can not completely prevent bad irritation and dark gum line, and it is not the most ideal restoration material.
3. Titanium Alloy and Pure Titanium
Titanium has the best bio-compatibility among so many metals, so titanium is used for dental implants. Since it has so many advantages, why not use titanium for crowns?
1. Titanium alloy
Titanium alloy porcelain teeth, although titanium is added to the internal view, the content is usually 4%-6%. Most other metals are nickel-chromium alloy, or cobalt-chromium alloy. Therefore, it is necessary to be clear about what is inside. If only a small amount of titanium is used, it can improve toxicity and bio-compatibility, but if there is still nickel, it will not have much effect.
2. Pure titanium
Pure titanium, many reviews say that pure titanium is difficult to process, so how is it difficult to process it?
It’s mainly because:
- Titanium has poor thermal conductivity and low thermal conductivity, and heat cannot be effectively diffused during processing and production.
- Titanium has a relatively high affinity (after all, it is ranked higher in the periodic table of the elements). The phenomenon of sticking to the knife and the device is serious during processing, which easily affects the life of the device.
- Titanium has high chemical activity at high temperatures, it will react with the gas in the air, and the surface will be hardened by oxidation.
- Titanium’s elastic modulus is small, and it is prone to large deformation, spring back, and distortion during processing. The final geometry and accuracy of the molding will deviate from that made on the model. The deviation of the crown of the tooth is a few tenths of a millimeter. It may not fit in.
Pure titanium has good bio-compatibility and sufficient strength. However, because the process is more complicated, the cost is not cheap, so relatively few people use it on the market. Nowadays, more powerful zirconium dioxide inner crowns (full-ceramics) are adopted.
And last, here we go
Full-ceramic crown
As the name suggests, the entire structure is made of porcelain/ceramic without a metal inner crown, so in terms of permeability, refractive index, and transparency, it is far beyond that of a metal porcelain crown. Therefore, full-ceramic crown are more aesthetically beautiful and closer than a metal porcelain crowns. Compared with natural teeth, the price is undoubtedly higher. However, it is slightly weaker than porcelain teeth in terms of strength because there is no metal inner crown, so it is more suitable for aesthetic restoration of anterior teeth or cases of poor bite of posterior teeth.
At present, China dental outsourcing LOYAL BEAUTY’s newly developed zirconia all-ceramic crown has greatly improved its strength and has been highly praised by doctors.
full-ceramic crown has a long service life. About 65% of full-ceramic crown can be used for more than 20 years. If you take care of them, the lifespan of full-ceramic crown will be longer.
