Preclinical Prosthetic Dentistry · MU Plovdiv

80. Model cast RPD. Principles of model cast clasps construction.

Inside: 11 sections · 2 labelled pictures · 5 tables · 27 flashcards · 6 min

Topic 80 of 96 in the MU Plovdiv syllabus for Preclinical Prosthetic Dentistry (Dental Medicine, Year 2). The free AceMed note covers it in 10 sections, about 446 words (6 min of reading), with 27 flashcards.

In this note

  1. Introduction
  2. The dental surveyor
  3. Survey lines
  4. The five Ney clasps
  5. Undercut depth: the Ney gauge
  6. Other cast clasp designs
  7. Mouth preparation
  8. Static and biodynamic aspects
  9. Distally shortened and interrupted arches
  10. General principles for the body of the denture

Introduction

Cast clasps are cast in one piece with the metal framework of a partial denture. The Ney system organizes their design around the dental surveyor: each abutment is surveyed, the survey line is drawn, and the clasp type is chosen to match that line.

The dental surveyor

A surveyor (parallelometer) holds the cast on a tilting table under a vertical arm. The first surveyor was introduced in 1918, and Ney produced the first widely used instrument. It is used to:

  • Choose the path of insertion by tilting the cast.
  • Draw the survey line (height of contour) on each abutment with a carbon marker.
  • Measure undercut depth with gauges.
  • Find guide planes and block out unwanted undercuts.
  • Check parallelism of crown preparations, attachments and milled surfaces.

Undercut depth: the Ney gauge

How deep the retentive tip may go depends on how flexible the arm is:

Too deep an undercut makes the clasp overstress the tooth or deform; too shallow, and the denture won't stay in.

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