PFM Restorations and Dental Metal Alloys

• Single crowns on natural teeth that have lost much of their structure or are at risk of breaking, often back teeth. When a tooth needs a crown at all is covered on dental crowns. What a metal-ceramic crown involves for the tooth, and how the treatment runs, is covered on metal-ceramic (PFM) crowns.
• Bridges that replace one or more missing teeth. Metal-ceramic has been used for decades for long bridges and under heavy loads. Bridge designs and their trade-offs are covered on dental bridges.
• Crowns and bridges on implants. A 2014 review notes that cobalt-chromium, one of the base-metal alloys, has come into use for porcelain-fused-to-metal restorations and implant frameworks².

The same kinds of alloy are also used without porcelain. A full-metal (gold alloy) crown is still an option for back teeth that do not show and for bites with very little space. Because of its appearance, it is rarely chosen.

The metal under the porcelain is an alloy, a mixture of several metals. The American Dental Association (ADA) classification, published in 2003, groups dental alloys by how much noble metal they contain³. Titanium alloys form a separate group. In dentistry, the noble metals are gold and the platinum-group metals³, such as platinum and palladium. Silver is not counted as a noble metal.

• High-noble alloys. At least 60 per cent of the alloy by weight is noble metal, and at least 40 per cent is gold.
• Noble alloys. At least 25 per cent is noble metal. Noble alloys without gold consist mostly of silver, palladium or platinum⁴.
• Predominantly base-metal alloys. Less than 25 per cent is noble metal. Nickel-chromium and cobalt-chromium are the most common³; in practice, neither contains noble metals².

Base-metal alloys came into wider use around 1980, as the price of gold rose³. A 2014 review adds that, in many countries, cobalt-chromium was increasingly used in place of nickel-chromium². The main reason it gives is concern about the toxic effects of nickel on the body² when alloys containing it are in the mouth.

Two points when you compare alloys

• Most long-term evidence comes from gold-based alloys. The authors of a 2020 study note that the traditional alloys were gold-based, and most long-term survival studies of metal-ceramic crowns are based on them⁴. The survival figures on this page are for metal-ceramic crowns as a group, or, for the 25-year series, for one high-gold alloy. They do not compare one alloy with another.
• The group alone does not tell you the composition. Each group covers many products with different compositions, so the product name and manufacturer tell your dentist more than the group does.

The material is chosen for each tooth after an examination, with X-rays where needed. The main questions are:

• How much of the tooth remains, and whether a filling, an onlay or a veneer would be enough. A crown is not the first choice for a healthy tooth whose only problem is its colour or a small flaw in its shape.
• Where the tooth is, and how much of it shows when you smile.
• Whether it is a single crown, a bridge or a restoration on an implant, and how many teeth a bridge would span.
• Your bite, and whether you clench or grind your teeth.
• How much room there is. The tooth needs enough room for both the metal and the porcelain.
• Your medical history, including any allergy to metals you know of.

Choosing the alloy is a further step. The authors of the 2020 study write that the dentist chooses the alloy together with the patient⁴, taking account of known allergies. A 2000 review advised dentists to choose alloys with the lowest release of elements (lowest corrosion)⁵. In its view, high-noble or noble alloys usually achieve this, with exceptions, so the choice should be made case by case. Cost plays a part too: a 2014 review links the wider use of cobalt-chromium to its low cost².

Ask which alloy is proposed, by group and product name. Ask too why metal-ceramic suits that tooth better than a metal-free option.

Metal-ceramic work is usually made in a dental laboratory from an impression or a digital scan of the prepared teeth. The metal framework is made first. It has traditionally been cast. A 2014 review describes computer-aided milling (CAD/CAM) and laser sintering² as newer alternatives to casting for cobalt-chromium frameworks. Porcelain is then built up on the framework in layers and fired in a furnace.

The porcelain has to bond well to the metal. The authors of a 2020 laboratory study note that insufficient bonding gives a higher risk of chipping and porcelain fracture⁴.

Knowing which alloy you received

That 2020 study, from Norway, analysed the metal in 62 metal-ceramic crowns from seven laboratories. Of these, 21 had been made by the laboratories' subcontractors abroad. Eighteen crowns came with no information, or incomplete information, about the alloy. Of the 44 crowns whose alloy was stated, 13 differed from it by more than 5 per cent by weight or contained a foreign element⁴. Large differences were more common in the imported crowns, but crowns made in Norway also differed⁴. The authors call for better quality control between laboratory and dentist⁴.

The authors point out that a dentist cannot verify the actual alloy content⁴ of a crown, so the written record of what was used matters. Ask where your restoration will be made, and ask for the names of the alloy and the porcelain in writing.

The steps below are for a crown on a natural tooth, which usually needs two or three appointments. Bridges and work on several teeth can take longer.

The figures below come from published studies, not from our own records.

Benefits

• A long record. In a series of 2,340 single crowns from one practice, made on a high-gold alloy, 2,211 crowns were judged to be in a favourable condition when they were cemented. Of every 100 of them, about 97 were still in the mouth after 10 years and 85 after 25 years¹. This result belongs to one practice, to selected crowns and to one type of alloy. It cannot be applied to other alloys or to everyone.
• Strength from the metal. The framework allows use on back teeth and in bridges.
• Bridges. A 2026 review of 41 studies looked at metal-ceramic and all-ceramic bridges on natural teeth. After five years, about 91 in every 100 metal-ceramic bridges were in place, against about 83 of lithium disilicate glass-ceramic bridges⁶. This difference was statistically significant. The figure of about 83 is for lithium disilicate only; the review reported zirconia bridges separately. Decay at the edges and loosening were more common with all-ceramic bridges⁶.

How long single crowns last

A 2026 review estimated how many of every 100 single crowns on natural teeth would still be in place after five years. For metal-ceramic, single-piece (monolithic) zirconia and layered zirconia alike, it was about 97⁷. For single-piece lithium disilicate it was 98 to 99. These estimates cannot be applied directly to bridges or implant crowns.

Limitations

• It cannot be undone. Tissue is removed from every surface of the tooth for a crown; from then on, the tooth needs a restoration to protect it.
• Chipping of the porcelain. Fractures can occur in the porcelain layer on top. The same 2026 review found fractures and chipping significantly less common on single-piece lithium disilicate and zirconia crowns⁷ than on crowns with a porcelain layer. Small chips can sometimes be smoothed or repaired; more extensive damage may mean the crown has to be replaced.
• Effect on the tooth's nerve. The pooled results of 37 studies cover teeth that were alive at the start. These teeth then received a crown or a partial restoration, or supported a bridge. In about 5 in every 100 of these teeth, the nerve died⁸. In studies with more than ten years of follow-up, the figure was about 7 in 100. The certainty of this evidence is low. If it happens, root canal treatment is needed to keep the tooth.
• New decay. A crown does not protect the tooth beneath it from decay. New decay can develop at its edge or underneath it.
• Appearance. The metal can affect how the crown looks; see the next section.
• On implants. A crown on an implant is either cemented or screwed on; a screwed crown has an access hole for the screw. A laboratory test used 40 metal-ceramic molar crowns on implants. Those with an access hole broke under significantly lower loads⁹ than cemented crowns without one. It was a laboratory test, so it gives no rate of fracture in the mouth. A screwed crown has an advantage too. A review of 59 studies found that screw-retained restorations are more easily retrievable, so complications can be treated more easily¹⁰. Neither method was clearly better overall.

Appearance

The metal framework does not let light through. A metal-ceramic crown can look more opaque than an all-ceramic one, and a dark line may show at its edge if the gum recedes. On a front tooth, lithium disilicate or layered zirconia may match the neighbouring teeth more closely.

The shade is chosen before the restoration is made, usually with a shade guide. A review found that choosing shade by eye alone has lower accuracy and repeatability¹¹, so photographs or a measuring instrument may be used as well. If you plan to whiten your natural teeth, say so before the shade is chosen: whitening does not lighten crowns or veneers¹².

Wear of the opposing teeth

A porcelain surface, especially a rough one, can add to wear of the natural tooth it bites against. A 2024 review pooled seven small clinical studies of crowns on back teeth, followed for up to two years. Metal-ceramic and zirconia crowns caused significantly more wear than natural teeth¹³. Opposite lithium disilicate crowns, the loss of enamel differed little from the wear natural teeth cause on each other, though the estimate was imprecise. The authors call for larger trials.

After the bite is adjusted, the porcelain should be polished smooth. If you clench or grind your teeth, tell your dentist; a night guard may be recommended.

A 2026 review describes the metal alloys used in dentistry as biocompatible with the mouth, though they may rarely cause adverse reactions in susceptible people¹⁴. What the evidence says:

• Corrosion is the key property. A 2000 review called corrosion the property of a casting alloy that matters most for its effects on the body⁵. Allergy and other effects come from elements released from the alloy into the mouth. The review found little evidence that casting alloys cause harm elsewhere in the body⁵.
• Allergy is reported, but poorly documented. A 2012 systematic review of metal-ceramic crowns and bridges found reactions reported to palladium, gold, nickel and cobalt¹⁵. Few studies record them, so how often they happen is not known.
• Nickel and cobalt. The 2000 review noted that nickel and cobalt have a relatively high potential to cause allergy, but that the true risk remains undefined⁵. It advised avoiding alloys that contain them where possible. The ADA describes nickel as a common skin allergen, but notes that its effects in the mouth are rarer and less severe³.
• How often it happens is unclear. A 2026 review looked at people with metal restorations who had symptoms and were tested with skin patch tests. The studies differed widely and often lacked clinically relevant detail, so the review found it difficult to estimate how common dental metal allergy is¹⁴.
• Cobalt-chromium. A 2022 systematic review found that cobalt-chromium alloys could rarely cause sensitisation, irritation or allergic reactions¹⁶, mainly in people already allergic to cobalt or chromium. The effects reported most often were soreness, a burning feeling in the lining of the mouth, a dry mouth and redness. Few of its studies in people concerned crowns; others looked at partial dentures, braces or dental technicians. The authors call the data inconsistent.
• Beryllium and cadmium. The 2000 review advised avoiding alloys that contain beryllium or cadmium, which are known carcinogens in some chemical forms⁵. It added that such effects from dental casting alloys have not been demonstrated. Today, a metal dental material that meets the international standard ISO 22674 may contain no more than 0.02 per cent beryllium³, according to the ADA.

If you have, or suspect, a metal allergy

• Before treatment, tell your dentist about any metal allergy you know of, or any reaction to metal you have had.
• Ask for the full composition of any alloy proposed. An alloy without the metal you react to can then be chosen, or a metal-free option. Under ISO and ADA standards, an alloy sold as "nickel free" must be labelled as containing less than 0.1 per cent nickel³.
• If soreness, burning or redness appears around a metal restoration, see your dentist. Symptoms like these are not specific to allergy. Because the treatment is to remove the metal, the 2026 review stresses establishing that the metal is the cause before treatment¹⁴.

Reactions to titanium, the metal used for most implants, are covered on titanium.

For single crowns on natural teeth, five-year survival is close across metal-ceramic, zirconia and lithium disilicate (see "Benefits and limitations" above). The choice depends on where the tooth is, how much of it remains, your bite and what you expect of its appearance.

• Zirconia has no metal alloy or metal framework. Depending on the type, it is used on front and back teeth, in bridges and on implants. Patients often call it "zirconium"; its types and limits are explained on zirconium (zirconia).
• Lithium disilicate glass ceramic has no metal framework and lets more light through. It is used for single crowns, veneers and partial restorations. As a bridge material it did less well in studies than metal-ceramic (see above). Its properties are explained on lithium disilicate glass ceramic.
• How the ceramics fit together, from feldspathic porcelain to zirconia, is set out on porcelain and dental ceramics.
• Options other than a crown. A filling or a partial restoration (inlay, onlay) keeps more of the healthy tooth than a full crown.

On an implant, a metal-free crown or abutment is still fixed to an implant that is usually titanium.

Daily cleaning matters most where the crown meets the gum, because new decay can start at its edge.

• Brush twice a day with a fluoride toothpaste.
• Clean every day where the crown meets the gum, and under bridges; use interdental brushes or bridge floss.
• If you clench or grind your teeth, wear the night guard your dentist recommends.
• Keep up regular check-ups, usually with your own dentist in the UK.

When to see a dentist

• The crown or bridge feels loose or comes off (keep it, and do not glue it back yourself)
• The porcelain cracks, chips or feels rough
• Sensitivity that does not settle, or keeps getting worse
• Pain when you bite, or the crown feels high when you bite
• Swelling, bleeding or discharge from the gum around the crown

If pain keeps increasing, or you have facial swelling or a high temperature, see a dentist without waiting for the clinic's reply. In England, if you have no dentist or cannot get an emergency appointment, the NHS says to call 111 or use 111 online¹⁷. Elsewhere in the UK, check the urgent dental care route where you live.

Emergencies. With a suspected dental abscess, the NHS says the following need urgent medical help¹⁷. In the UK, call 999 or go to A&E.

• It is hard to breathe, speak, swallow or open your mouth
• A swollen or painful eye, or sudden problems with your eyesight
• A lot of swelling inside your mouth

Ask for these details in writing before treatment.

• Whether each crown or bridge will be metal-ceramic, and which alloy group: high-noble, noble or base metal.
• The alloy's product name and manufacturer, and whether it contains nickel, especially if you have a metal allergy.
• The porcelain used, and where the restoration will be made.
• The written terms if a crown chips, breaks or comes loose after you are home: whom you contact, and who pays for repair and travel.

Bring home for your UK dentist a written record: the teeth treated, the alloy and its manufacturer, the porcelain, the shade and the laboratory. For work on implants, add the implant system and the part and lot (batch) numbers. In Turkey, the health tourism regulation entitles international patients, on request, to free copies of the records of the materials used, the tests and the imaging¹⁸.

Aftercare. Problems after you return are usually first seen by your own dentist in the UK. The General Dental Council suggests speaking to your own dentist¹⁹ before you consider treatment abroad; ask whether they will see you afterwards. The NHS website for England says the NHS is not liable for negligence or failure of treatment²⁰ when you have treatment abroad. It also says that most travel insurance policies will not cover you for planned treatment abroad²⁰. Scotland, Wales and Northern Ireland run their own health services, with their own rules, which this page does not cover; if you live there, ask your dentist.

Your choice. These crowns and bridges, and the metal-free alternatives, are also available from UK dentists, who can give you an independent opinion. You can say no, or ask to stop, at any stage. Once a tooth has been prepared, that step cannot be undone.

The GDC and NHS questions to ask before treatment abroad are listed on our page about metal-ceramic (PFM) crowns.