What are all-metal crowns?
Just as their name implies, this type of crown has a construction that's 100% metal.
The classic all-metal is the "gold" crown, however, they can also be made using silver-colored metals too ("white gold").
What type of metal is used?
Crowns aren't made out of pure metals because none has the ideal physical properties required for dental applications (good strength, resistance to tarnish and corrosion, wear resistance and characteristics that make it easy for the lab technician to fabricate the restoration and the dentist to adjust it).
What is used is some type of dental alloy (a blend of metals). One that's been engineered so its physical properties approach the ideal.
That means your "gold" dental crown isn't 24 karat (pure gold). In fact, the "precious" yellow-gold alloys used to make all-metal dental crowns usually only run about 15 to 20 karat. (See below for more details.)
Advantages of all-metal / gold crowns.
Opting for an all-metal crown can make an excellent choice, if you don't mind the fact that it's not tooth-colored. Here's why:
a) Superior strength.
Due to their 100% metal construction, there's no type of crown that's stronger than an all-metal one. (That can be said no matter what type of dental alloy has been used to make it.)
Failure due to breaking is an extremely rare event. In comparison, that's a real possibility with an聽all-ceramiccrown. Or in the case of a聽porcelain-fused-to-metal聽one (PFM), a significant portion of its porcelain covering may fracture off thus resulting in restoration failure.
b) Superior longevity.
Due to their single-component construction and the great strength and durability characteristics they possess, no other type of dental crown can be expected to provide more lasting service than an all-metal one.
That doesn't mean that other types of crowns can't provide lasting service too. But in terms of predictability (what type of things might go wrong and how often these events occur), an all-metal crown is the safest bet possible.
c) Good biocompatibility.
In terms of how your crown might affect you or your mouth, all-metal crowns generally offer good biocompatibility.
Minimal wear to opposing teeth.
The wear coefficient of dental alloys is typically similar to tooth enamel. That's good because it means that restorations made using them won't cause excessive wear on the teeth they bite against.
The specific metal used may matter. - As rules of thumb, "gold" (high-noble, see below) alloys typically are "kind" to teeth in this manner. Possibly base-metal alloys are comparatively more abrasive to opposing teeth. (Yin 2004) [page references]
Keeping in mind how many decades a person's teeth might be in perpetual contact with the crown opposing them, this might be a significant point to consider. Especially in the case where they have a habit of clenching or grinding their teeth.
In comparison to all-metals, porcelain-surface crowns that have not been polished or glazed appropriately (a failure on your dentist's part) are likely to cause tooth wear, possibly significantly so.
Beyond that, due to the wide range of ceramics that can be used to make tooth-colored crowns, no other hard and fast rules can be stated. Studies do suggest however that some types of ceramics are kinder or gentler to opposing dentition than others, possibly on the same order as high-noble dental alloys. (Yin 2004)
While possible, it's relatively rare for a person to have an allergic sensitivity to a crown that's been made using a "gold" (high-noble) dental alloy. This same statement cannot be made for base-metal ones (see below).
In cases where potential complications with a metal allergy are a concern, placing an all-ceramic dental crown can sidestep this issue entirely.