Thursday, September 15, 2011

CLASSIFICATION OF PARTIALLY EDENTULOUS ARCHES


CLASSIFICATION OF 
PARTIALLY EDENTULOUS ARCHES



CLASSIFICATION OF RPDs AND PARTIALLY EDENTULOUS ARCHES
INTRODUCTION
The classification of RPDs and partially edentulous arches simplifies communication and discussions. Many systems of classification have been suggested. In this post three general and widely accepted systems of classifying RPDs and partially edentulous arches will be described.
CLASSIFICATION BASED ON MAJOR CONNECTOR MATERIAL
The major connector is that part of a RPD which connects components on one side of the arch to those on the other side.  If the major connector is constructed of a cast metal alloy the RPD is termed DEFINITIVE. If the major connector is plastic, the RPD is termed INTERIM.
The Definitive RPD
Definitive RPDs are constructed after extensive diagnosis, treatment planning, and thorough preparation of the teeth and tissues for the prosthesis.  The length of service of definitive RPDs is intended to be many years (customarily 5-10 years).
CLASSIFICATION BASED ON SUPPORT
There are three types of RPDs or partially edentulous arches based on the tissue(s) which provide support.  Support is the resistance to movement of the denture toward the edentulous ridge.  RPDs maybe tooth supported, tissue supported, and toothtissue supported.  This is a simple classification system and very meaningful because the principles of RPD design depends, to a great extent, on its supporting tissue(s).
The Tooth Supported RPD
Tooth supported RPDs receive all their support from the abutment teeth.  Retention is derived from direct retainers on the abutment teeth and bracing is provided by contact of rigid components of the framework with natural teeth.  Tooth supported RPDs do not move appreciably in function.  Most tooth supported RPDs have a cast metal major connector, although sometimes it is possible to construct a tooth supported interim RPD with a plastic major connector and wrought wire rests and/or transocclusal clasps.  The principles of design of tooth supported RPDs is relatively noncontroversial and similar in many respects to the principles of design of FPDs. In lay persons vocabulary the tooth supported RPD is referred to as a "REMOVABLE BRIDGE".  This is a non professional term which should be avoided.
The Tissue Supported RPD
Tissue supported RPDs are primarily supported by the tissues (mucosa overlying bone) of the denture foundation area.  They may obtain some tooth support by contact of the denture above the height of contour of the natural teeth.  Tissue supported RPDs usually have plastic major connectors and are, therefore, usually interim RPDs.  Tissue supported RPDs will move in function because of the resiliency of the mucosa. Retention for tissue supported RPDs is customarily provided by wrought wire retentive clasp arms on selected natural teeth, contact of the plastic denture below the height of contour of the natural teeth, and by those factors which provide retention of complete dentures, i.e gravity (for mandibular RPDs), interfacial surface tension, neuromuscular control, etc.  Bracing is provided by contact of the denture with the denture bearing tissues and the natural teeth, supplemented by contact of the tongue, checks and lips with the polished surface of the denture.  The tissue supported RPD is essentially a complete denture with some remaining natural teeth.  Tissue supported RPDs have the potential to cause soft tissue damage and periodontal attachment loss and accordingly should be used for only a short period of time (one year or less) while a FPD, definitive  RPD or implant prosthesis is constructed.
The Tooth-Tissue Supported RPD
The tooth-tissue supported RPD is supported at one end by natural teeth, which essentially do not move, and at the other end by the denture bearing tissues (mucosa overlying bone) which moves because of the resiliency of the mucosa.  The design of the tooth-tissue supported RPD is one of the most controversial topics in prosthodontics.  Several philosophies with specific RPD designs or construction techniques have been suggested to compensate for the difference in support provided by the natural teeth and denture foundation tissues. This topic is discussed in a later chapter.
CLASSIFICATION BASED ON ARCH CONFIGURATION
The most widely accepted system of classification of RPDs and partially edentulous arches was proposed by Dr. Edward Kennedy in 1923. It is based on the configuration of the remaining natural teeth and edentulous spaces.  This system was further defined and expanded upon by Dr. O.C. Applegate and Dr. Jacques Fiset and will be described in this chapter and used throughout these lecture notes.
The value of the KennedyApplegate-Fiset classification system is that it is relatively simple, easy to remember, extremely comprehensive and very practical. It permits visualization of the partially edentulous arch or RPD designed for that arch.  It indicates the type of support for the RPD, which suggest certain physiologic and mechanical principles of treatment and RPD design.  There is a correlation between the basic classes and the incidence of the partially edentulous arch configurations.  It allows quick identification of the partially edentulous archs, which are difficult to treat, and that should be referred to a prosthodontist.  This system, at least the first four classes, is widely taught and generally accepted and used.  The system also simplifies communication.

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