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INTRODUCTION AND CLASSIFICATION

Terminology

Several efforts have been made to standardize dental terminology, beginning with Dr Louis Ottofy's compilation of accepted dental terms in 1923.1 This document greatly improved communication within the dental profession. As the dental profession matured, new materials and techniques were introduced. Increasing dental knowledge gave rise to recognized dental specialties, and dental terminology continued to evolve.

The greatest advance in prosthodontic terminology was made in 1956 when the Academy of Denture Prosthetics published the Glossary of Prosthodontic Terms. Since that time, the publication has been updated on a regular basis. Currently, the Glossary is published in the Journal of Prosthetic Dentistry every 2 years.

To ensure that the terminology used throughout this book will be understood by all readers, definitions of some of the most frequently encountered words are provided in this section. In addition, the terms used in this book are limited to those that are recognized as acceptable.

Branches of prosthodontics

The art or science of replacing absent body parts is termed prosthetics, and any artificial part is called a prosthesis. As applied to dentistry, the terms prosthodontics and dental prosthesis are used. Prosthodontics is the branch of dental art and science that deals with the replacement of missing teeth and oral tissues to restore and maintain oral form, function, appearance, and health. There are three major divisions of prosthodontics: fixed prosthodontics, removable prosthodontics, and maxillofacial prosthodontics (Fig 1-1). Despite the importance of dental implants, the authors of this text do not consider implantology a major division of prosthodontics. Instead, implants are considered adjuncts in fixed, removable, and maxillofacial therapy.

Fig 1-1 Branches of prosthodontics.

According to the Glossary of Prosthodontic Terms, fixed prosthodontics is the branch that deals with the replacement and/or restoration of teeth by artificial substitutes that are not readily removed from the mouth.2 This book addresses fixed prosthodontics only as it relates to removable partial dentures. The glossary defines maxillofacial prosthodontics as the branch of prosthodontics concerned with the restoration and/or replacement of stomatognathic and associated facial structures that have been affected by disease, injury, surgery, or congenital defect.2 Removable prosthodontics is devoted to replacement of missing teeth and contiguous tissues with prostheses designed to be removed by the wearer. It includes two disciplines: removable complete and removable partial prosthodontics. This book deals with the latter.

Terms related to dental prostheses

As previously noted, a prosthesis is an artificial replacement for a missing body part. A dental prosthesis is an artificial replacement of one or more teeth and/or associated structures. In clinical applications, dental prostheses may be supported by teeth, residual ridges, dental implants, or a combination thereof. Consequently, practitioners must be familiar with the associated terminology.

The terms abutment and retainer are central to a discussion of dental prostheses. An abutment is any tooth or dental implant that supports a dental prosthesis. In contrast, a retainer is the portion of a fixed or removable partial denture that attaches the prosthesis to an abutment (Fig 1-2). Hence, an abutment is part of the patient's oral cavity (eg, a tooth or implant), while a retainer is part of the prosthesis.

Fig 1-2 An abutment is any tooth or dental implant that supports a prosthesis. A retainer is the portion of the prosthesis that attaches the prosthesis to an abutment.

Traditionally, fixed partial dentures have been attached to abutments using dental cements, while removable partial dentures have been attached to abutments by other means. In removable partial denture prosthodontics, there are two principle types of retainers. They are termed extracoronal retainers and intracoronal retainers. Extracoronal retainers consist of two fingers of metal (ie, clasps) that lie on the surface of a clinical crown (Fig 1-3). One finger of metal is termed a retentive clasp, while the other is termed a reciprocal clasp. The retentive clasp is located in an undercut area of the clinical crown and resists displacement of the prosthesis away from the underlying hard and soft tissues. The reciprocal clasp is located in a non-undercut area and serves as a bracing or stabilizing element for the prosthesis. The resultant assembly is termed an extracoronal retainer because the retentive and reciprocal components lie on the external surfaces of an abutment.

Unlike extracoronal retainers, intracoronal retainers are contained entirely within the contours of a clinical crown (Fig 1-4). Consequently, the use of intracoronal retainers generally requires the fabrication of two or more specially designed, complete-coverage crowns. In most instances, retention of intracoronal removable partial dentures is dependent upon exact parallelism of the retentive assemblies. Each assembly consists of two parts, commonly termed matrix ("female") and patrix ("male"). Figure 1-5 illustrates the joining of a patrix and matrix to form a functional retentive unit. When a dislodging force is applied to the removable partial denture, binding occurs between the external walls of the patrix and the internal walls of the matrix. This binding results in retention of the prosthesis.

Fig 1-3 Components of an extracoronal retainer usually include a rest, retentive and reciprocal clasps, and a proximal plate.

Fig 1-4 An intracoronal retainer lies within the contours of the clinical crown. An intracoronal retainer consists of a matrix or "female" component (right) and a patrix or "male" component (left).

Fig 1-5 When joined, matrix and patrix components form a closely fitting retentive assembly.

Another method for categorizing removable partial dentures relates to the manner of their support. A partial denture that receives support from natural teeth at each end of the edentulous space or spaces is a tooth-supported removable partial denture (Fig 1-6). Although the denture base contacts the adjacent soft tissues, the prosthesis does not receive significant vertical support from the residual ridge.

Fig 1-6 A tooth-supported removable partial denture.

A second category of removable partial dentures includes those that extend anteriorly or posteriorly and are supported by teeth at only one end (Fig 1-7). These are called extension base removable partial dentures or tooth-tissue-supported removable partial dentures. The majority of these are distal extension removable partial dentures. Distal extension removable partial dentures are supported by teeth at the anterior aspect of the edentulous space and by tissues of the edentulous ridge posteriorly.

In certain instances, the terms interim, transitional, and treatment are applied to specific types of removable partial dentures. An interim removable partial denture is a provisional prosthesis intended to improve esthetics and function until a more definitive form of treatment can be rendered. A transitional removable partial denture may be used when loss of additional teeth is inevitable, but immediate extraction is not advisable or desirable. Artificial teeth may be added to a transitional removable partial denture as natural teeth are extracted. A transitional removable partial denture may be worn during the healing process and replaced with a definitive prosthesis when extraction sites have stabilized. A treatment denture may be used as a carrier for treatment material, as a protective covering for a surgical site, or as a matrix for soft tissue healing. In most instances, treatment dentures are used in conjunction with resilient tissue conditioners. The resultant prostheses provide cushioning effects for the underlying soft tissues and promote improved tissue health. Interim, transitional, and treatment prostheses are intended for short-term applications and should never be used for prolonged treatment. The use of such prostheses over extended periods may cause irreparable damage to a patient's remaining teeth, soft tissues, and bone.

Fig 1-7 A tooth-tissue-supported (extension base) removable partial denture.

Other terms of interest include model and cast. While cast may be used as a verb (to cast an inlay) or as an adjective (a cast framework), it is most often used as a noun to describe an accurate, positive reproduction of a maxillary or mandibular dental arch. Certain adjectives are commonly used to provide more specific meanings for the term (eg, diagnostic cast, master cast, refractory cast). The term...