Guide · 7-minute read
Dental gold: how crowns, bridges and inlays are tested
The short answer
Nobody can tell what a crown is made of by looking at it: dental alloys run from mostly gold and platinum-group metals to base alloys with no precious metal, and colour is not a reliable guide. Only a test on exposed metal can separate them, and without an analyser many crowns cannot be identified here, so ask before you post dental work. Porcelain, tooth and cement are estimated and left out of the weight, nothing is removed before you accept an offer, and every piece gets its own line.
What dental gold is and how the alloys differ
Dental gold is the metal in crowns, bridges, inlays and onlays (fillings made of metal), and in some denture clasps and frameworks. It is never pure. Dental laboratories choose alloys for hardness, casting and resistance to corrosion in the mouth, and the recipe varies between laboratories, decades and types of work. Dental work carries no hallmark and no fineness stamp, so nothing on the piece says what it contains.
Dentistry sorts casting alloys into three families by how much of the metal is gold or platinum-group metal (platinum, palladium and their relatives). The American Dental Association's classification is the one usually quoted.
- High-noble alloy
- At least 60 per cent gold and platinum-group metals, with at least 40 per cent gold. These are the pieces most worth asking about, and the gold share still varies from one crown to the next.
- Noble alloy
- At least 25 per cent gold and platinum-group metals. Many are palladium-based and hold little gold, and many are silvery white rather than yellow.
- Predominantly base alloy
- Under 25 per cent noble metal. Most are nickel-chromium or cobalt-chromium with none at all. They look grey, but so do many palladium alloys, so colour alone cannot tell the two apart.
- Porcelain-fused-to-metal (PFM)
- A crown with a metal cap under a ceramic layer. The ceramic can weigh more than the metal, and none of it is metal.
Because the gold share differs from crown to crown, Assaypost does not quote a typical dental fineness, and does not take one on trust from a seller or a dentist. The dental gold page lists what is taken and what is not, including amalgam fillings, which contain mercury and are not handled at all.
What on a crown is not metal
A crown as it comes out of the mouth, or as a dentist hands it back in an envelope, is rarely just metal. Each part that is not metal has to be allowed for before anyone can say what the piece is. None of it is taken off before you have accepted an offer.
- Fragments of tooth are often still cemented inside a crown. Their weight is estimated and left out.
- On a porcelain-fused-to-metal crown the ceramic can outweigh the metal. It stays on, the metal under it is estimated, and the line says so.
- Cement leaves a film that adds weight and covers the surface a test would need to read. Cleaning a spot to read it needs your written consent.
- Steel or nickel-alloy posts and pins inside a crown are base metal, and they would distort a reading taken over them.
- Clasps and frameworks from partial dentures stay in the pink acrylic, and the weight of the acrylic is estimated and left out.
Everything left out appears on the item's line: what it is, how much of it was estimated and how. The same rule applies to everything else in a parcel, and the guide to stones, clasps and what is not metal covers it.
Hygiene, and what happens to a crown when it arrives
Dental work has been in a mouth. Rinse each piece in warm water, dry it and seal it in a small zip bag before packing. Do not try to remove porcelain or tooth yourself: it needs the right tools and a way to catch the fragments, and it does not need doing before an offer.
- Weighed as it arrivedEach piece is weighed on its own. What is taken to be tooth, cement or ceramic is estimated, left out and written on the line as an estimate.
- Nothing taken offNothing is cleaned, chipped or scraped. Cement, tooth and ceramic stay where they are, unless you agree in writing to one small spot being cleaned so that it can be read.
- Checked, and the limits written downEach piece is examined on its own; where several are clearly alike, the line says which were checked together. Every check made goes on the line with where it was made, and so does anything that could not be established.
How dental gold is tested, and why XRF struggles with small pieces
The usual first test for a crown is X-ray fluorescence (XRF). No analyser is in use here yet, so XRF is not available, and without it the alloy of most crowns cannot be established here. XRF does not mark the piece, and it reads only a thin surface layer, a matter of microns that varies with the metal and the instrument. On a flat, clean, uniform sample it gives a consistent reading. A crown is none of those things.
- A crown may offer only a few square millimetres of clean metal, and small or thin samples give less certain readings than a bar or a chain.
- XRF expects the sample to fill its measuring window. A curved crown wall leaves gaps, which weaken the signal and can skew the result.
- Years in the mouth can change the surface layer, and cement blocks a reading altogether, so a surface result may not match the alloy beneath.
- Bridges are joined with solder of a different composition. A reading taken on a joint describes the solder, not the crown.
- Metal under a ceramic layer cannot be read through it. Only exposed metal can be tested.
So where an analyser is used, a crown should be read in more than one place, every spot recorded, and the result written beside its limits. Density does not help on porcelain-bonded pieces, because the ceramic makes the result meaningless.
Where a crown cannot be identified, the honest answer is to say so. It is then either priced conservatively, with the limits written on the offer, or left out of the offer and returned at our cost, and the offer says which; you can also ask for it back before any offer is made. An assay of melted metal would settle it, but no arrangement with a laboratory exists, so Assaypost cannot offer one. The XRF guide and the testing page explain the methods in more detail.
What a test settles on a crown, and what it leaves open
Where an analyser is available, a test on a crown does one job well: it shows which of the three families the piece belongs to. That is less than sellers hope for, and a great deal more than a guess.
What the checks on a crown establish
| Check | What it settles | What it still leaves open |
|---|---|---|
| Magnet | A piece that pulls has steel in it, usually a post or a pin | Many base dental alloys do not pull, so a crown that ignores a magnet can still contain no precious metal |
| Weight, less the estimated tooth and cement | Roughly how much of what arrived is metal | Nothing about which metals they are |
| XRF on exposed metal, where an analyser is available | Which elements are present, and roughly in what proportion | Whether the surface matches the body, on a worn or soldered piece |
| Further readings in other places | Whether the first reading was typical or sat on a joint | The metal under a bonded ceramic layer, which cannot be read through |
| Assay of melted metal | The composition, within the laboratory's stated uncertainty | Not available here: no arrangement with a laboratory exists |
The practical point for a seller: two crowns from the same mouth in the same decade can be a high-noble alloy and a base alloy, and look alike in an envelope. Anything said about them before they are tested describes the envelope, not the crowns.
If you do send dental work, send it with the rest of the box rather than on its own. It gets the same written list, and one offer covers the lot (everything you send together), as selling gold by post describes.
Seller risks and exceptions
- A single figure for all dental gold. One fineness for every crown, given without testing, is a guess or an average, and an average means the high-noble crowns pay for the base-alloy ones. Ask what was established for each piece.
- Weighing with the tooth still in. Tooth and cement can add a good deal to a crown's weight. Any weight that does not allow for them includes the tooth.
- Palladium-based crowns. Some noble alloys are mostly palladium with very little gold. Palladium is a precious metal in its own right; see the platinum and palladium page.
- Throwing out grey crowns. Grey does not always mean base metal, because many palladium alloys are grey or white too. Keep them with the rest and ask.
- Very small pieces. A single inlay may weigh under half a gram. It is examined in the same way, but any result is less certain at that size, and the line says so.
- Amalgam. Silver-coloured fillings contain mercury, and amalgam is not taken, tested or handled, so leave it out of the parcel. Dental practices must have amalgam waste, including teeth containing it, handled by an authorised waste business (Article 10(6) of Regulation (EU) 2017/852 on mercury, as it applies in the UK).
When not to use the scrap route
Dental gold rarely has a value above its metal, with two exceptions
Gold teeth set into antique jewellery, or into traditional jewellery from other cultures, belong to that object, and we would flag such a piece before any offer so you could show it to a specialist or an auction house. And a large quantity, such as a dental laboratory clear-out, is better settled by an assay of the melted metal than by checks on each piece. No arrangement with a laboratory exists here, so a lot that size may do better with a refiner who offers one.
For ordinary crowns and bridges from one person's dental history, the question is whether whoever receives them can establish what each piece is and shows you the result. A photograph cannot establish a dental alloy, and without an analyser examination here may not settle it either, so ask before you post dental work. Send photographs on WhatsApp to 07369 296063, or ring or text that number (6am to 10pm, seven days); the photo estimate page explains what to photograph.
Questions sellers ask
What proportion of a dental crown is gold?
There is no single answer, and anyone who gives you one is guessing. High-noble alloys are at least 40 per cent gold, noble alloys can hold very little, and base alloys usually hold none. The recipe differs between laboratories, and only a test on exposed metal comes close to settling it for a particular crown, with the limits of a surface reading stated beside it.
Do I need to get the tooth out of the crown before sending it?
No, and please do not try. Rinse it, dry it and seal it in a small bag. Tooth, cement and porcelain stay where they are until you have accepted an offer. Their weight is estimated and written on the line for that piece, and they come off afterwards, with the right tools.
Is a porcelain crown worth anything?
Only for its metal cap, if it has one. An all-ceramic crown has no metal in it at all. A porcelain-fused-to-metal crown has a metal cap under the ceramic, and that cap is what is assessed, with the ceramic left in place and its weight estimated.
Why can XRF give an uncertain reading on a crown?
XRF reads only a thin surface layer and expects a flat sample that fills its window. A crown is small, curved, sometimes altered at the surface after years in the mouth, and sometimes joined with solder of a different alloy. That is why a crown should be read in more than one place, with the limits of each result written beside it.
How do I know a gold-coloured crown is not a base alloy?
Often you cannot. Colour is a poor guide: some gold-coloured crowns are base metal, and many valuable palladium alloys are grey or white. A magnet is little help, because many base dental alloys do not pull. Only a test on exposed metal can settle it, and until then nothing about the crown is known.
Is it worth sending photographs of dental work first?
Yes, though expect less from them than for jewellery. Pictures show roughly how much tooth and ceramic is still attached, and whether a piece is set into jewellery. Colour is only a first clue, so a photograph cannot establish the alloy, and nothing should be thrown away on looks alone.
An envelope of crowns from the dentist?
Tip them out on white paper and photograph them together. A person writes back about what they appear to be. Some alloys look alike in a photograph, and the reply says when that is so.
Nothing is sold until you say yes. Say no and everything comes back by tracked, signed-for post at our cost.
No WhatsApp? Call or text 07369 296063, 6am to 10pm, seven days a week.
Nothing is assumed
Two crowns that look alike can be quite different alloys. Every piece is weighed and checked for its metal before an offer is made, and the methods used are listed on the offer. Porcelain is not counted as metal.