Dental crown alloys -

Categories High noble (precious), Noble (semiprecious), and Non-noble (base, nonprecious) explained. | Advantages and disadvantages of each type. | Applications/Best practices for each category of alloy.

A decision about the type of alloy used to make your dental crown must be made.

If the type of crown that will be made for your tooth has a metal component, your dentist, possibly after getting input from you, will need to make a decision about the type of dental alloy that will be used for its construction.

[Kinds of crowns that contain metal are: 1) All-metal, like the classic gold crown. 2) Porcelain-fused-to-metal (PFM, PFG and PTM crowns). With these restorations, even though the part you see is porcelain covered and white, it's been layered over a metal substructure, hence an alloy choice needs to be made.]

There are 3 basic types of alloys.

Dental alloys are classified as falling into one of 3 categories. They are: high noble (precious), noble (semiprecious) and non-noble (nonprecious).

And as you might guess, the system is based upon the alloy's composition. Both in terms of what types of metals it contains, and in what percentages.

The type of alloy chosen matters because each kind has different physical properties.

By no means are dental alloys all just alike. Instead, the composition of each has it's own unique physical characteristics, which in turn give it comparative advantages and disadvantages.

These differences can involve issues that are:

The remainder of this page explains each of the above considerations in greater detail. However, and as you'll find out below, if cost is not a factor then the alloy having the highest precious metal content typically makes the best choice.


Dental alloys - What you need to know.

Some quick background.

Contrary to what you might have thought, all dental crowns that have a metal component are made using specifically formulated dental alloys. No pure metals are ever used, not even gold.

The reason for this is because for this application, the physical properties of alloys are superior. For example:

  • Gold in pure form is too soft to give a crown good wear characteristics. (Such as resistance to wear by opposing teeth.)
  • A pure gold crown would tend to deform (distort in shape) when subjected to the forces a person creates when chewing.
  • As opposed to pure gold, base metals included in alloy formulations form oxides that enhance metal-to-porcelain bond strength.

Section references - Knosp

Dental alloy classifications - High noble, Noble, Non-noble.

Here's the classification system established by the American Dental Association (1984) that's used to categorize dental alloys.

(Since the ADA is also the organization that assigns insurance code numbers to dental procedures, this same alloy classification system is also used with them, and hence may show on your bill or insurance paperwork. Example: "D2750 crown – porcelain fused to high-noble metal.")

1) High noble alloys (Precious metal)

This group has a composition that is over 60% noble metal, of which more than 40% must be gold. The elements gold, palladium, platinum, rhodium, ruthenium, iridium and osmium are categorized as noble metals.

Examples of high noble dental alloys.
  • Product: JRVT  /  Alloy Color: Yellow  /  Composition: 77% Gold, 13% Silver, 8.5% Copper, 1.0% Palladium, Less than 1% Indium, Iridium, Zinc
  • Product: JIV-PF  /  Alloy Color: Yellow  /  Composition: 72.5% Gold, 13.5% Copper, 10.2% Silver, 2.8% Platinum, Less than 1% Indium, Iridium and Zinc.
  • Product: Noble-Cast 67  /  Alloy Color: Yellow  /  Composition: 64.0% Gold, 23.4% Silver, 3.0% Palladium, 0.1% Platinum
  • Product: Encore (White High Noble)  /  Alloy Color: Silver (white)  /  Composition: 48% Gold, 40% Palladium, 4.3% Zinc, 3.9% Tin, 3.75% Indium, 0.05% Rhenium

2) Noble alloys (Semiprecious metal)

These alloys have at least 25% noble metal content.

Examples of noble dental alloys.
  • Product: Argenco 20  /  Alloy Color: Yellow  /  Composition: 20% Gold, 20% Palladium, 40% Silver, 18% Indium, 2% Zinc, Less than 1% Iridium.
  • Product: Argelite SR+  /  Alloy Color: Silver (white)  /  Composition: 79% Palladium, 8.4% Tin, 5.0% Cobalt, 5.0% Gallium, 2.0% Gold, 0.6% Ruthenium

3) Non-noble (Nonprecious metal)

These alloys are also referred to as base metals. Their noble metal content is less than 25% (they may have none). They often contain large percentages of nickel, cobalt, chromium or beryllium.

Examples of non-precious (base) dental alloys.
  • Product: Argeloy N.P. Supreme  /  Alloy Color: Silver (white)  /  Composition: 61% Cobalt, 27% Chromium, 6% Molybdenum, 5% Tungsten, 1% Silicon, Less than 1% Manganese, Iron, Carbon
  • Product: Argeloy N.P.  /  Alloy Color: Silver (white)  /  Composition: 54.0% Nickel, 22.0% Chromium, 9.0% Molybdenum, 4.0% Iron, 4.0% Niobium, 4.0% Tantalum, 3.0 % Trace elements.

Section references - Anusavice
Alloy compositions taken from manufacturer's information.


Why does it matter which alloy is used to make your crown?

There are several reasons why it's important. Some of them affect you directly. Others will be more of a concern to your dentist, or the dental laboratory that makes your crown.

a) Costs - High noble metal alloys are more expensive.

Some of the predominant noble metals contained in dental alloys are gold, platinum and palladium. And just as you'd expect, the greater the percentage of these metals that an alloy contains, the more expensive it will be.

  • With restorations where the actual amount (weight) of metal they contain is relatively small, the price difference between using a high-noble or base-metal alloy might be very minor.

    (As examples, the metal component of a porcelain-fused-to-metal crown for a lower incisor or upper lateral incisor might be relatively minimal.)

  • But in the case where an all-metal restoration is made for a large tooth (like a molar, and especially one that's lost a lot of tooth structure), the cost difference might be significant enough to affect your decision.

(Here's more information about dental crown costs.)

b) Dental plan and insurance policy limitations.

If there's a third party involved in paying a part of your bill, you might check to see if there are any limitations as to the type of metal that can be used for crowns.

Possible restrictions.

The policy might state that they do not cover the cost of high noble alloys. Or the level of coverage (in terms of your out-of-pocket expenses) might vary according to which type is used.

(Here's more information about insurance coverage for dental crowns.)

Picture of a deep-yellow gold dental crown.

This gold crown has a yellow color.

c) Color - Dental alloys can be white or yellow.

As you might have noticed in our tables above, dental alloys are either gold or silver ("white") in color.

This factor is due to the metal's composition. As an interesting note, even alloys whose major single component is in fact gold may still have a white coloration ("white" gold).

Considerations.
  • Some dentists feel that using a yellow-colored alloy with PFM crowns gives the restoration's porcelain a warmer, more natural look.
  • If you're having an all-metal crown placed, you may have a big preference as to its color (deep yellow, yellow, pale yellow or white).

Section references - Knosp

d) Some people have metal allergies.

Some of the metals included in the formulation of dental alloys used for crown fabrication have been shown to trigger an allergic reaction with some patients. Nickel, chromium, palladium and cobalt have all been implicated.

  • It's estimated that 10 to 20% of females have an allergic response to nickel. The incidence rate for men is lower, possibly as low as 5%.
  • Sensitivity to palladium generally runs about 1/3rd that of nickel. But those who are are almost always allergic to nickel too. (We've found conflicting sources as to whether the reverse is true.)
  • The allergic response experienced is typically benign. But its associated itching can affect the person's quality of life. Besides just the mouth, other parts of the person's body may be affected too.
  • In cases where a question about metal sensitivity exists, prior to restoration construction a dermatological patch test can be used to evaluate the patient's status.

Section references - Sakaguchi, Zhang, Knosp

Alloy alternatives do exist.

If the metal that triggers the response can be identified, an alternative alloy can usually be found.

  • Base (non-noble) alloys, as opposed to noble or high-noble ones, are typically associated with a larger release of nickel, chromium, and cobalt ions, and thus their use may be indicated.
  • While palladium is found in many high-noble formulations, some palladium-free products do exist (see table above). Additionally, some of these formulations don't contain any of the other metals commonly associated with allergies either.

 

e) The physical properties of the alloy are an important consideration.

Some dentists and dental laboratories have a set opinion about which grades of dental alloys they will even consider working with. A part of this reasoning may be because their primary goal is simply getting the job done right, the first time.

They know that any difficulties or problems that crop up will just end up costing them money. So, if choosing a certain type of alloy makes getting a positive result more likely, then that's the one they'll want to work with.

Picture of a porcelain-fused-to-metal dental crown.

A porcelain-fused-to-metal dental crown.

The advantages of precious dental alloys.

High noble alloys constitute the "gold standard" of dental metals. (All others are compared to them.) And dentists and dental technicians generally much prefer working with them, especially those that have a high gold content, because:

  • They are the easiest to cast (the process by which metal crowns are made) and polish.
  • Restorations made using high-nobles are known for their accurate fit on their tooth. But also, this grade of alloy is relatively malleable so the fit of the restoration can be adjusted if needed.
  • High noble alloys generally offer the most predictable bond with porcelain, a factor that can influence porcelain-fused-to-metal crown longevity.
  • The noble metals these alloys contain give them superior corrosion resistance.

Section references - Anusavice, Sakaguchi

Which type of alloy should you choose for your dental crown?

As mentioned above, assuming that cost is not a factor, opting for a high noble dental alloy makes the best choice.

 
 
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