Preclinics of Dental Prosthetics · MU Sofia

64. Technology of one-piece cast framework removable partial dentures – technological steps.

Walks through the technological steps for a one-piece cast framework removable partial denture, from the clinical design and mouth preparation through laboratory duplication, refractory casting, wax-up and investing. It sets out the three casts (master, refractory and duplicate stone) in a summary table, and gives the temperatures and timings for drying, beeswax dipping and casting of the cobalt-chromium alloy, with a twelve-step diagram. It ends with the finishing, fitting and delivery stages.

Inside: 4 sections · 1 labelled picture · 1 table · 13 flashcards · 2 min

Topic 64 of 75 in the MU Sofia syllabus for Preclinics of Dental Prosthetics (Dental Medicine, Year 2). The free AceMed note covers it in 4 sections, about 307 words (2 min of reading), with 13 flashcards.

In this note

  1. Introduction
  2. Requirements
  3. Three casts
  4. Technological steps

Introduction

The one-piece cast framework (clasp denture, "bugel" denture) is the classic definitive partial denture: clasps, rests, connectors and retention grids are cast together in a cobalt-chromium-molybdenum alloy. It is thin, rigid and tooth-supported, stable and retentive, and keeps the masticatory system healthy.

Requirements

  • No contact with the gingiva; thin, with no interference with the tongue.
  • Good appearance and no hindrance to speech.
  • Efficient chewing; even spread of occlusal load; prevention of periodontal damage.

Technological steps

Clinical

  1. Diagnosis and study casts; design drawn and abutment modifications planned.
  2. Mouth preparation: guide planes, rest seats, recontouring.
  3. Final impression; master cast poured.

Laboratory

  1. Design transfer and block-out: undercuts not used by clasps are filled with wax parallel to the path of insertion; relief wax under connectors and bases.
  2. Duplication: reversible hydrocolloid (agar) is heated to 100 °C, cooled to about 63 °C and poured over the master cast in a flask; cooled up to 1 hour; the mould is checked for defects.
  3. Refractory cast: investment poured in small amounts, then the rest with minimal vibration; set about 60 minutes.
  4. Drying and dipping: 82–93 °C for 30–60 minutes, then dipped in beeswax at 138–149 °C for 15 seconds for a smooth surface.
  5. Wax-up: design transferred; prefabricated plastic and wax patterns (clasps, bars, retention grids) glued on and joined with inlay wax.
  6. Spruing: sprues as thick as the pattern, attached to bulky areas, with rounded joins; single or multiple sprues.
  7. Investing in phosphate-bonded investment; burnout to eliminate the wax.
  8. Casting of cobalt-chromium (induction melting); gold alloys can be torch-melted at about 1,093 °C.
  9. Devesting (mallet, sandblasting), cutting sprues, grinding, electropolishing and polishing; ultrasonic cleaning.

Clinical again

  1. Framework try-in and adjustment.
  2. Jaw relation, teeth set in wax, try-in.
  3. Processing of the acrylic bases; delivery; instructions and recall.

The duplication step is the heart of the process: any error in the refractory cast is cast into the framework.

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