57. Clasps. Cast clasps as retainers - “Ney” system.
Explains how Ney cast clasps are designed around the dental surveyor, starting with the surveyor's uses for path of insertion, survey lines and undercut blocking. It then covers the three survey line types and the matching clasp for each, followed by the five numbered Ney clasps with their designs and indications. The note also gives the Ney gauge undercut depths for different alloys and arms, and briefly lists other cast clasp designs such as E-type, G-type, divided Roach and RPI.
Topic 57 of 75 in the MU Sofia syllabus for Preclinics of Dental Prosthetics (Dental Medicine, Year 2). The free AceMed note covers it in 6 sections, about 199 words (3 min of reading), with 13 flashcards.
In this note
Introduction
The dental surveyor
Survey lines
The five Ney clasps
Undercut depth: the Ney gauge
Other cast clasp designs
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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