Retentive Arm Material Options
Posted on 11/27/2011
Metal retentive arms are designed using two primary materials: cast metal or wrought wire.
- The cast clasp is more rigid, durable, and inflexible. It is indicated for tooth supported RPDs, or when the retentive tip releases during functional movement for distal extension RPDs, or when minimal undercut is utilized.
- The wrought wire clasp is flexible and more fragile. It is indicated in Kennedy Class I (distal extension designs) when the retentive tip of the clasps are placed forward of the axis of rotation. The axis of rotation is the imaginary line that connects the most posterior rests of a framework. For example, if the rest is designed on the distal side of the most posterior teeth, then the WW clasp is indicated as the retentive arm since it will sit forward of the axis of rotation.
Regardless of the material chosen, retentive arms should exhibit the following characteristics:
1. Uniform tapering of thickness and width.
3. Thickness of the tip should be approximately half of the thickness of the origin.
*Portions of this post were adapted from the book: Atlas of Removable Partial denture Design by Dr. Russell J. Stratton and Dr. Frank J. Wiebelt published by Quintessence Publishing Co., Inc. in 1988.
- The cast clasp is more rigid, durable, and inflexible. It is indicated for tooth supported RPDs, or when the retentive tip releases during functional movement for distal extension RPDs, or when minimal undercut is utilized.
- The wrought wire clasp is flexible and more fragile. It is indicated in Kennedy Class I (distal extension designs) when the retentive tip of the clasps are placed forward of the axis of rotation. The axis of rotation is the imaginary line that connects the most posterior rests of a framework. For example, if the rest is designed on the distal side of the most posterior teeth, then the WW clasp is indicated as the retentive arm since it will sit forward of the axis of rotation.
Regardless of the material chosen, retentive arms should exhibit the following characteristics:
1. Uniform tapering of thickness and width.
3. Thickness of the tip should be approximately half of the thickness of the origin.
*Portions of this post were adapted from the book: Atlas of Removable Partial denture Design by Dr. Russell J. Stratton and Dr. Frank J. Wiebelt published by Quintessence Publishing Co., Inc. in 1988.
