Mechanical Retention: An Introduction
Posted on 11/22/2011
Of the three categories of retention outlined in previous blogs, phenomenal retention, frictional retention and mechanical retention, the latter is the most common and perhaps the most complex category. As such, we will treat mechanical retention over a series of blog posts.
Clasps, the basic form of mechanical retention, are really part of a greater unit called the "clasp assembly". The clasp assembly is composed of four elements:
1. One or two rests
2. A retentive arm
3. A reciprocating or bracing element
4. Minor connector/s
The goal of the clasp assembly is to restrict dislodgement while being totally passive when the framework is seated. This last point is critical and often neglected: clasps are not intended to support a framework; they are designed to restrict movement. Clasps should not torque the abutment during normal wear and tear (such as chewing). If the clasp is placing pressure on the abutment tooth, it will inevitably damage the abutment.
*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.
Clasps, the basic form of mechanical retention, are really part of a greater unit called the "clasp assembly". The clasp assembly is composed of four elements:
1. One or two rests
2. A retentive arm
3. A reciprocating or bracing element
4. Minor connector/s
The goal of the clasp assembly is to restrict dislodgement while being totally passive when the framework is seated. This last point is critical and often neglected: clasps are not intended to support a framework; they are designed to restrict movement. Clasps should not torque the abutment during normal wear and tear (such as chewing). If the clasp is placing pressure on the abutment tooth, it will inevitably damage the abutment.
*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.
