Preclinics of Conservative Dental Medicine · MU Sofia

25. Dental amalgam – clinical characteristics.

Covers dental amalgam's composition, mercury-alloy setting phases and why high-copper alloys resist creep and corrosion better than low-copper ones, with a comparison table of the three alloy types. It then describes strength, creep, corrosion and thermal behaviour, the trituration, condensation, carving and polishing steps, indications and contraindications, mercury handling, and the current EU restrictions on use.

Inside: 7 sections · 1 labelled picture · 1 table · 17 flashcards · 7 min

Topic 25 of 53 in the MU Sofia syllabus for Preclinics of Conservative Dental Medicine (Dental Medicine, Year 3). The free AceMed note covers it in 7 sections, about 915 words (7 min of reading), with 17 flashcards.

In this note

  1. Introduction
  2. Composition and types of alloy
  3. Setting reaction and phases
  4. Properties
  5. Clinical handling
  6. Indications, mercury hygiene and EU rules
  7. Key points

Introduction

Dental amalgam is mercury alloyed with a silver–tin–copper powder, condensed into the cavity while plastic and setting in the mouth. Its phase chemistry explains why modern high-copper alloys last longer, and its handling decides whether a restoration fails early.

Composition and types of alloy

Alloy powder is mixed with liquid mercury (Hg), today in pre-dosed capsules at a mercury : alloy ratio of about 1:1; the set filling contains about 40–50% Hg. Above about 55% Hg, strength falls and creep rises.

  • Silver (Ag, 40–70%): strength, less creep and corrosion; with tin forms Ag₃Sn.
  • Tin (Sn): reacts readily with mercury and slows setting, but forms the weak tin–mercury phase.
  • Copper (Cu): strength and hardness; in high-copper alloys (usually 12–30%) it binds tin and prevents γ₂.
  • Zinc (Zn, 0–2%): deoxidiser in alloy manufacture. Moisture (saliva, blood) in a zinc-containing mix causes delayed expansion (Zn + H₂O → ZnO + H₂), starting after 3–5 days and may exceed 4%: pain, protrusion, fracture.

Particles are lathe-cut (irregular filings) or spherical; spherical ones need less mercury.

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