With the advent of CAD/CAM systems using Infrared or Blue Light cameras and permanent, all ceramic, metal-free inlays, onlays, veneers and crowns can be completed in about one hour. These systems, such as CEREC and E4D, require no messy impression material, no temporary that may fall off between appointments and no second visit, and they restore the teeth to original strength with biocompatible ceramic that looks and feels like real teeth.
The commonly used Vita MkII ceramic is the closest material yet to natural enamel because it has exactly the same wear rate and the same expansion and contraction rate to temperature changes as enamel.
These machines use a special, digital 3-D camera connected to a computer to make an image of a tooth or series of teeth. The shape and size of a tooth can be copied, or a tooth shape from the computer databank can be used to design the restoration. The software has many design tools to allow the dentist or technician to custom shape the 3-D image.
A block of correctly shaded ceramic is inserted into a milling unit, which creates the restoration. It is then fitted and polished, and the inside is etched and steam cleaned and then bonded permanently to the tooth. These are currently the state-of-the-art for tooth restoration in terms of biocompatibility, strength, esthetics and wear ability, as well as for conserving as much natural tooth structure as possible.
Today, most crowns are made by veneering porcelain over a cast-metal substructure. Ninety-five percent of the metal used is a silver-colored alloy containing 75 percent nickel and 2 percent beryllium. These are called non-precious alloys because there are no expensive metals in them.
There is a problem here because it is a well-known fact that nickel causes cancer. Animals are routinely given nickel to cause cancer in order for researchers to study cancer treatments!
Also, 14 percent of the world’s population is allergic to nickel, according to the World Health Organization. That is one in seven people. An easy way to check women for nickel allergy is to inquire about the type of earrings they can tolerate. If cheap earrings cause a woman’s ears to turn red, she is usually nickel sensitive.
I have seen nickel crowns cause severe gingival inflammation and bone loss. In one particular lady, the inflammation cleared up in two days after the porcelain fused to nickel crowns was removed and replaced with temporary crowns. The 2 percent beryllium in these formulas is another toxic metal I would not want in my mouth.
A healthier alternative to non-precious metals is the high-noble gold alloys. These alloys have been used for more than a century in dentistry with great results. They are strong and bond to porcelain very well. Their one drawback is the current price of gold.
Sometimes bridges that span across areas where teeth are missing can be made with a ceramic substructure called zirconia. The zirconia replaces the metal substructure in traditional porcelain fused to metal crowns and bridges and is very biocompatible and esthetic. Zirconia is strong, but it has its limitations in very long-span bridges, in which case a high-noble, gold-based alloy is the material of choice.
On molar teeth where esthetics is not as much of a concern, crowns made from high-noble gold alloys without a porcelain veneer are used in situations where people have very little vertical height to their teeth. An all-ceramic crown like a CEREC needs 2 mm of vertical clearance to ensure adequate strength. Porcelain fused to metal crowns need 1.5 mm clearance, but all gold crowns only require 1 mm since gold is malleable and ductile.
A new class of crown that uses nothing but zirconia is now on the market. These are not quite as pretty as veneering porcelain over the top, but in the case of a limited clearance of 1 mm, these are a better-looking alternative to an all-gold crown. One example of this type of crown is called BruxZir. Since these are new on the market, and we don’t have any long-term results yet, I can’t fully endorse them at this time.
Many times new products that have not been fully tested clinically come to the market. The mouth is a harsh environment with temperature changes, moisture, bacteria and other microorganisms, high loads during chewing and clenching, acids and other things a material must withstand. It must be strong, but not too hard or abrasive. It must not wear down or change color over time. And most importantly, the thing most dentists ignore, it must be biocompatible!
What good is a very durable material if it causes health problems for the patient? In the future, we will discuss this issue of biocompatibility in more detail.
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