The term "crown" is used to describe the portion of your tooth that extends above the gumline - in other words, the portion of the tooth that can be seen in a healthy mouth. It is also used more colloquially to describe the dental procedure of having a prosthetic "crown" placed over a decayed, chipped, cracked, or otherwise damaged tooth.
With this dental procedure code, the prosthetic crown fitted over the tooth is made from a base of high noble metal, and then covered with a wafter-thin, porcelain veneer to enhance its cosmetic appeal. Porcelain veneers are molded perfectly to the surface of the crown through a high-heat process which fuses it to the tooth. In doing so, the process creates a crown that has excellent compression and tensile strength, while providing a cover to the underlying metal. This veneer mimics the natural translucence of your surrounding teeth. Porcelain also has the added benefit of being able to resist staining.
With regard to the crown's metal base, a crown that includes high noble metal is designated as such because at least 60% of its composition is of the noble metals gold, platinum, palladium, and silver. Of that 60%, at least 40% of that percentage needs to be gold in order to earn this distinction from the American Dental Association. Noble metals are known to interact with human tissue well, and hold up to corrosion and oxidation better than other metals. The higher the percentage of noble metals the less likely it is to corrode or oxidize.
Use of the two materials together, is done when extensive repair is needed within the "smile zone," and a full gold crown - despite its greater longevity and strength - is not preferred for cosmetic reasons. With this procedure, because the metal strengthening core is covered with porcelain that is fused to metal (FTM), you can achieve excellent cosmetic results, in addition to the durability that stems from the underlying metals.
To prepare for this type of crown, a dentist will first remove any decayed or weakened areas of the tooth, and reduce its overall shape to accommodate the crown. A mold of your bite will then be made, so the custom crown can be fabricated off-site at a dental lab. If desired, a temporary crown can be fitted until the custom crown is completed.