Metal Alloy Dental Prostheses
Introduction
Metal alloy dental prostheses were the pillar of prosthetic dentistry throughout the 20th century. Made of chromium-cobalt, nickel-chromium or gold, they offer excellent mechanical strength but present significant aesthetic limits, today overcome by zirconia.
Metal alloy dental prostheses were the pillar of prosthetic dentistry throughout the 20th century. Made with chromium-cobalt, nickel-chromium alloys or noble metals such as gold, these prostheses offer excellent mechanical strength but present notable aesthetic limits.
In fixed prostheses on implants, the metal alloys were used as the internal structure (casting) on which the ceramic was applied (metal-ceramic). Today zirconia has widely replaced metals thanks to superior mechanical properties and decidedly better aesthetics.
Types of alloys
The types of dental alloys include non-noble alloys such as chromium-cobalt (the most used) and nickel-chromium (cheap but allergenic), and noble alloys such as gold (excellent biocompatibility) and palladium. Each alloy has specific characteristics of strength, cost and allergenicity.
Non-noble alloys
- Chromium-cobalt (Cr-Co): the most used, good strength, contained cost
- Nickel-chromium (Ni-Cr): cheap, but potentially allergenic (nickel)
- Iron-chromium (stainless steel): used for temporary structures
Noble alloys
- Gold (Au): excellent biocompatibility, ease of casting, high cost
- Palladium (Pd): alternative to gold, good corrosion resistance
- Silver-palladium (Ag-Pd): intermediate cost, used in the past
Advantages
The advantages of metal alloys include high mechanical strength, durability (they do not wear like resin), lost-wax casting precision, contained cost for the non-noble alloys and the reliability of a technique consolidated for decades in dentistry.
- Mechanical strength: metal alloys withstand high masticatory forces
- Durability: they do not wear like resin
- Precision: lost-wax casting guarantees good accuracy
- Contained cost (for the non-noble alloys)
- Reliability: technique consolidated for decades
Aesthetic and functional limits
The main limit is aesthetics: metal has no translucency, causes a grey halo at the gingival junction and can oxidise. Other disadvantages include high weight, thermal conductivity, possible galvanic corrosion and difficulty of repairing fractures.
The main limit of metal alloys is aesthetics. The metal:
- Does not let the light through (no translucency)
- Can cause a grey halo at the junction with the gum
- Requires a greater thickness of ceramic to be masked
- Can oxidise and discolour the surrounding gum
Other limits include:
- High weight: the alloys are heavy, especially for complete arches
- Thermal conductivity: the metal transmits hot and cold
- Galvanic corrosion: possible in the presence of other metals in the mouth
- Repair difficulty: fractures of the ceramic on metal are difficult to repair
Allergies and biocompatibility
Metal allergies, in particular nickel, cobalt and chromium, are a significant problem with symptoms such as contact stomatitis, chronic gingivitis and oral lichen planus. Zirconia is completely hypoallergenic and biocompatible, ideal for allergic patients.
Metal allergies are a significant problem in prosthetic dentistry. Nickel is the most allergenic metal, followed by cobalt and chromium. The symptoms include:
- Contact stomatitis
- Chronic gingivitis
- Oral burning sensation
- Oral lichen planus
Zirconia, on the contrary, is completely hypoallergenic and biocompatible, making it the ideal choice for patients with confirmed metal allergies.
Comparison with zirconia
Metal alloys have poor aesthetics with grey halo, high weight and possible allergies. Zirconia offers excellent aesthetics with translucency, light weight, total biocompatibility and absence of corrosion. For definitive prostheses zirconia is the superior modern choice.
| Characteristic | Metal alloy | Zirconia |
|---|---|---|
| Aesthetics | Poor (grey halo) | Excellent (translucency) |
| Strength | High | Very high |
| Weight | High | Light |
| Biocompatibility | Medium (possible allergies) | Excellent |
| Thermal conductivity | High | Low |
The Circolare d'Autore® prosthesis
- 14 teeth per arch, including all posterior molars
- Zero fake gum: the teeth emerge from the natural gum
- Zirconia + layered ceramic, with registered trademark ®
- Custom-made: every prosthesis is a unique piece designed for the patient
Discover all the details on the dedicated page: Circolare d'Autore® — the definitive prosthesis without fake gum.