Dental Materials · MU Plovdiv

75. Investment materials. Refractory components and binder.

Inside: 10 sections · 3 labelled pictures · 3 tables · 25 flashcards · 5 min

Topic 75 of 85 in the MU Plovdiv syllabus for Dental Materials (Dental Medicine, Year 1). The free AceMed note covers it in 9 sections, about 536 words (5 min of reading), with 25 flashcards.

In this note

  1. Introduction
  2. Requirements
  3. Why expansion is so important
  4. Not limiting the expansion
  5. Components
  6. The three types
  7. Expansion of each type
  8. Handling
  9. Other uses

Introduction

Casting investment materials, or refractory investments, are auxiliary materials used to make metal and ceramic restorations by the lost wax technique. They form the heat-resistant mold into which molten metal is cast.

Requirements

  1. Fluid when mixed: a low-viscosity suspension that tightly surrounds the finest details of the wax.
  2. Fine-grained: for a smooth casting. Fine investment painted onto the wax improves this further.
  3. Strong: it must not break or crumble under the pressure of the flowing metal.
  4. Refractory: it must not melt or break down at the casting temperature.
  5. Chemically inert: if it reacts with the alloy, deposits form, and grinding them off loses detail.
  6. Porous: gases in the mold must escape through the pores, or the casting will be incomplete.
  7. Expandable: its expansion must make up for the shrinkage of the alloy.
  8. Heat-conductive: so that the mold expands evenly and the casting does not distort.
  9. Easy to break away after cooling.

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