Download OCR Document

1
Introduction and terminology
Introduction
Terminology
INTRODUCTION
A prosthesis is the replaceme"llt of an absent part of the
human body by some artificial part, such as an eye, a
leg, or a denture. Prosthetics, then, is the art and science
of supplying artificial replacements for an absent part of
the human body.
When applied to dentistry, the term prosthetics
becomes prosthodontics and denotes the branch of
dental art and science that deals specifically with the
replacement of missing dental and oral structures.
Prosthodontics may be defined as that branch of
dentistry pertaining to the restoration and maintenance
of oral functions,
comfort, appearance, and health of the patient by the
restoration of natural teeth and/or the replacement of
missing teeth and contiguous oral and maxillofacial
tissues with artificial substitutes.
The replacement of missing teeth in a
partially edentulous arch may be accomplished by a
fixed prosthesis or by a removable prosthesis. A fixed
partial denture is not designed to be removed by the
patient (Fig. 1-1). On the other hand, a removable
partial denture is designed so that it can be
conveniently removed from the mouth and replaced by
the
patient (Fig. 1-2).
A removable partial denture may be entirely
tooth supported or may derive its support from
both the teeth and the tissues of the residual ridge. The
denture base of a tooth-supported removable partial
denture derives its support from teeth at each end of the
edentulous area(s) (Fig. 1-3). A tooth-tissue-supported
removable partial denture has at least one denture base
that extends anteriorly or posteriorly, terminating in a
denture base portion that is not tooth supported (Fig. 1-4).
Such a base extending posteriorly on a removable partial
denture qualifies the restoration as a distal extension
partial denture.
It is perhaps only natural, when beginning the study of
removable partial prosthodontics, to think primarily in
terms of fabrication of restorations. However, if students
would direct their thinking primarily to the promotion of
oral health and preservation of remaining oral structures
for patients in their care, a better perspective of the study
would be developed.
The objectives of prosthodontic treatment of
partially edentulous individuals with removable
restorations are (1) the elimination of oral disease to the
greatest extent possible; (2) the preservation of the health
and relationships of the teeth and the health of oral and
paraoral structures, which will enhance the removable
partial denture design; and (3) the restoration of oral
functions that are comfortable, esthetically pleasing, and
do not interfere with the patient's speech.
1
2
McCracken's removable partial prosthodontics
Fig. 1-1 Fixed partial dentures that restore missing
posterior teeth. Teeth bounding edentulous spaces are
used as abutments.
Fig. 1-3 Tooth-supported removable partial denture
restoring missing posterior teeth. Teeth bounding
edentulous spaces provide support, retention, and stability
for restoration.
Fig. 1-2 Clasp-type removable partial denture restoring
missing posterior teeth. Teeth bounding edentulous
spaces serve as abutments.
Fig. 1-4 Maxillary bilateral distal extension removable
partial denture restoring missing first and second molars.
Support, retention, and stability are shared by abutment
teeth and residual ridges.
Subsequent to the conscientious study of removable
partial prosthodontics in the treatment of partially
edentulous patients, success and professional satisfaction
may be more readily obtained by following these
guidelines:
1. Establish a genuine rapport with your patient to
promote trust and confidence. 2. Demonstrate
thoroughness in diagnosis and
treatment planning.
3. Make an empathic identification of prob
lems and their causes.
4. Make the patients fully aware of the corre
lation between dental and general health as
adjuncts to total well-being.
5. Explain the suggested treatment plan and
alternate plans, including time commit
ments for treatment.
6. Make the patients fully aware of their
responsibilities in the success of the treat
Chapter
1
ment by conscientious home care and periodic
recall visits.
7. Avoid an overly optimistic prognosis.
8. Plainly state anticipated compromises from
the ideal, based on inherent factors that cannot be
altered by treatment.
9. Arrive at a just fee for the proposed treatment by
taking into account the values, desires, financial
position, and other constraints of the patients.
Adjust each plan, as may be required to be in the
best interest of each patient under the given
circumstances.
10. Have the highest respect for the dignity, comfort,
and well-being of each patient at all times.
TERMINOLOGY
Familiarity with accepted prosthodontic terminology
should be acquired by the predoctoral student dentist.
However, it is unrealistic to expect a student dentist t_
memorize terms outside of a clinical environment as
an introduction to the study of removable partial
prosthodontics. Therefore this section should be
looked on as an overview of prosthodontic
terminology, as an explanation (justification) for the
choice of such terminology, and as a future reference
to be used during the initial clinical experiences with
removable partial dentures.
Significant strides have been made in prosthodontic
terminology in recent years, eliminating much
confusion created by conflicting terms.
Two glossaries, The Glossary of Prosthodontic Terms
(available to the profession through the continuing
efforts of the Academy of Prosthodontics)* and a
glossary of accepted terms in all disciplines of
dentistry, Mosby's Dental Dictionary, provide
excellent bases for dignified spoken and written
communication in prosthetic dentistry.t
'This glossary first appeared in the March 1956 issue
of The Journal of Prosthetic Dentistry (published by
MosbyYear Book, Inc., St. Louis, Mo.). The latest
reprint (ed. 7), published in 1999, may be obtained
from Mosby, Inc., 11830 Westline Industrial Drive, St.
Louis, Mo., 63146.
tZwemer D, ed: Mosby's dental dictionary, St Louis,
1998, Mosby, me.
Introduction and terminology
3
The conflicting or indefinite terms in common usage
in prosthodontics require definition and clarification.
Many of these are used synonymously; others are used
incorrectly. Although the following is not meant to be a
complete glossary of removable partial prosthodontic
terminology, some definitions are given based on
available reference material. The discussion type of
format does not lend itself to alphabetical arrangement of
defined words or terms; hopefully this creates only a
minor inconvenience to students.
The term appliance is correctly applied only to devices
(such as splints, orthodontic appliances, and space
maintainers) worn by the patient in the course of
treatment. A denture, an obturator, a fixed partial denture,
or a crown is properly called a prosthesis. The terms
prosthesis, restoration, and denture are equally acceptable
terms and are used synonymously in this book.
Stability is defined as the quality of a prosthesis to be
firm, stable, or constant and to resist displacement by
functional, horizontal, or rotational stresses. Stability
becomes more meaningful when it is thought of as the
resistance of a denture base to movement on the denturesupporting area.
Retention is spoken of as that quality inherent in the
denture that resists the vertical forces of dislodgement
(e.g., the force of gravity, the adhesiveness of foods, or
the forces associated with the opening of the jaws).
An interim, or provisional, denture is a dental
prosthesis to be used for a short time for reasons of
esthetics, mastication, occlusal support, or convenience or
for conditioning the patient to accept an artificial
substitute for missing natural teeth until a more definite
prosthetic dental treatment can be provided.
A complete denture is a dental prosthesis that replaces
all of the natural dentition and associated structures of the
maxilla or mandible. It is entirely supported by tissues
(mucous membrane, connective tissues, and underlying
bone).
An abutment is a tooth, a portion of a tooth, or that
portion of an implant that serves to support and/ or retain
a prosthesis.
The term height of contour is defined as a line
encircling a tooth, designating its greatest
4
McCracken's removable partial prosthodontics
circumference at a selected position determined by a
dental surveyor.
The term undercut, when used in reference to an
abutment tooth, is that portion of a tooth that lies
between the height of contour and the gingivae; when it
is used in reference to other oral structures, undercut
means the contour or cross section of a residual ridge or
dental arch that would prevent the placement of a
denture.
The angle of cervical convergence is an angle viewed
between a vertical rod contacting an abutment tooth and
the axial surface of the abutment. It is an apical angle
having its apex at the height of the contour of the
abutment.
Discerning this angle is important in developing uniform
retention through clasps.
Two or more vertically parallel surfaces of abutment
teeth shaped to direct a prosthesis during placement and
removal are called guiding planes. Guiding plane
surfaces are parallel to the path of the placement and
parallel to each other; however, they mayor may not face
each other. Preferably these surfaces are made parallel to
the long axes of abutment teeth.
In a description of the various components of
the partial denture, conflicting terminology must be
recognized and the preferred terms defined. A retainer is
defined as any type of clasp, attachment, device, etc.,
used for the fixation, stabilization, or retention of a
prosthesis. Thus a retainer may be either intracoronal or
extracoronal and may be used as a means of retaining
either a removable or a fixed restoration. The
term internal attachment is preferred over precision
attachment, frictional attachment, and other terms that
describe any mechanical retaining device that depenDs
on frictional resistance
between parallel walls of male and female (key and
keyway) parts. Precision attachment is objectionable
because its usage implies that all other types of retainers
are less precise in their design and fabrication.
Clasp (direct retainer) is used in conjunction
with the words retainer, arm, or clasp assembly
whenever possible. The clasp assembly will consist of a
retentive clasp arm and a reciprocal or stabilizing clasp
arm, plus any minor connectors and rests from which
they originate or with which they are associated. Bar
clasp arm is preferred over the term Roach clasp to
designate
the type of extracoronal retainer clasp arm that originates
from the base or framework, traverses soft tissue, and
approaches the tooth undercut area from a gingival
direction. In contrast, the term circumferential clasp arm is
used to designate a clasp arm that originates above the
height of contour, traverses part of the suprabulge portion
of the tooth, and approaches the tooth undercut from an
occlusal direction. Both types of clasp arms terminate in a
retentive undercut lying gingival to the height of contour,
and both provide retention by the resistance of metal to
deformation, rather than frictional resistance created by
the contact of the clasp arm
to the tooth.
A major connector is the part of a removable partial
denture that connects the components on one side of the
arch to the components on the opposite side of the arch.
A continuous bar is a component of the partial denture
framework that augments the major connector and lies on
the lingual or facial surface of several teeth. It is most
frequently used on the middle third of the lingual slope of
mandibular anterior teeth. If it is attached to the lingual
bar major connector by a thin, contoured apron, the major
connector is then designated as a linguoplate.
Any thin, broad palatal coverage that is used as a major
connector is called a palatal major connector, or if it is of
lesser width (less than 8 mm), it is called a palatal bar. A
palatal major connector may be further described
according to its anteroposterior location on the palatal surface, for example, as an anterior palatal major connector
or a posterior palatal bar. The differ
entiation between a palatal bar and a palatal strap is
somewhat subjective. As we interpret it, a palatal strap is
proportionally thinner and broader than a palatal bar. In
this textbook a palatal major connector component that is
less
than 8 mm in width is referred to as a bar. The
term anatomic replica is used to designate cast metal
palatal major connectors that duplicate the topography of
that portion of the patient's mouth. This is in keeping
with the use of descriptive terminology whenever
possible.
The term indirect retainer denotes a part of a
removable partial denture that assists the direct retainers
in preventing displacement of distal
Chapter
1
extension denture bases by resisting lever action from
the opposite side of the fulcrum line.
The term rest is used to designate any
component of the partial denture that is placed on
an abutment tooth, ideally in a prepared rest seat, so
that it limits movement of the denture in a gingival
direction and transmits functional forces to the tooth.
When a rest is placed on the occlusal surface of a
posterior tooth, it is
designated an occlusal rest. If the rest occupies a
position on the lingual surface of an anterior tooth, it is
referred to as a lingual rest. A rest placed on the incisal
edge of an anterior abutment tooth is called an incisal
rest.
Denture base is used to designate the part of
a denture (whether it is metal or is made of a resinous
material) that rests on the residual bone covered by
soft tissue and to which the teeth are attached. The
term saddle is considered objectionable terminology
when used to designate the base of a removable partial
denture.
The residual bone with its soft tissue that covers the
underlying area of the denture base is referred to as the
residual ridge or edentulous ridge. The exact character
of the soft tissue
covering may vary, but it includes the mucous
membrane and the underlying fibrous connective
tissue. The oral tissues and structures of the residual
ridge supporting a denture base are
referred to as the basal seat or denture foundation area.
Resurfacing of a denture base with new
material to make it fit the underlying tissues more
accurately is spoken of as relining. Rebasing refers to a
process that goes beyond relining and involves the
refitting of a denture by the replacement of the entire
denture base with new material without changing the
occlusal relations of the teeth.
To describe an impression and the resulting cast of
the supporting form of the edentulous ridge, the terms
functional impression and
functional ridge form are used. These terms
have been accepted as meaning the form of the
edentulous ridge when it is supporting a denture base.
It is artificially created by means of a specially
molded (individualized) impression
tray or an impression material, or both, that
displaces those tissues that can be readily
displaced and that would be incapable of
Introduction and terminology
5
rendering support to the denture base when it is supporting
functional load. Firm areas are not displaced because of
the flow characteristics of the impression material, thus
the tissues are
recorded more nearly in the form they will
assume when supporting a functional load. In contrast, the
static form of the edentulous ridge, as often recorded in a
soft impression material such as hydrocolloid or metallic
oxide impression paste, is referred to as the anatomic ridge
form and results when an impression tray is uniformly
relieved. This is the surface form of the edentulous ridge
when at rest or when not supporting a functional load.
Perhaps no other terms in prosthodontics
have been associated with more controversy
than have centric jaw relation and centric occlusion.
All confusion could be terminated by acceptance of one
definition of centric relation and one definition of centric
occlusion and then
using these respective positions as references for other
horizontal locations of the mandible or other
relationships of opposing teeth. The consensus
definitions in the seventh edition of The Glossary of
Prosthodontic Terms, however, consider centric
occlusion and centric relation to be terms in transition.
To minimize confusion during this transition, the
following definitions,
which are given in this glossary, are selected as
meaningful:
centric occlusion: The occlusion of opposing teeth when
the mandible is in centric relation. This mayor may not
coincide with the maximum intercuspation position.
maximum intercuspation: The complete intercuspation
of the opposing teeth independent of condylar
position.
centric relation: A maxillomandibular relationship in
which the condyles articulate with the thinnest
avascular portion of their respective disks, with the
complex in the anterior-superior position against the
slopes of the articular eminences. This position is
independent of tooth contact. This position is clinically
discernible when the mandible is directed superiorly
and anteriorly. It is restricted to a purely rotary
movement about a transverse horizontal axis. This
term previously referred to the most posterior relation
of the mandible to the maxilla
at the established vertical dimension of occlusion.
maxillomandibular relationship: Any spatial relationship
of the maxilla to the mandible; anyone of the many
relations of the mandible to the maxillae.
6
McCracken's removable partial prosthodontics
maxillomandibular relationship record: A registration of
any positional relationship of the mandible to the
maxillae. These records may be made at any vertical,
horizontal, or lateral orientation.
For complete dentures, centric occlusion is the
occlusion that should be made to coincide with centric
relation for that particular patient. In an adjustment of
natural occlusion the objective may be to establish
harmony between centric relation and centric occlusion.
With removable partial dentures the objective is to make
the artificial occlusion coincide and be in harmony with
the remaining natural occlusion. Ideally the natural
occlusion will have been adjusted to harmonious contact
in centric relation and be free of eccentric interference
before occlusal relationships are established on the
partial denture.
Balanced occlusion is a term that describes the
contact of opposing teeth. It is defined as the
simultaneous contacting of maxillary and man
dibular teeth on the right and left in the anterior and
posterior occlusal areas in centric or any eccentric
position within the functional range.
Functional occlusal registration is sufficiently
descriptive and is used to designate a dynamic
registration of opposing dentition rather than the
recording of a static relationship of one jaw to another.
While centric position is found somewhere in a
functional occlusal registration, eccentric positions are
also recorded, and the created occlusion is made to
harmonize with all the gliding and chewing _ovements
that the patient is capable of making.
The word cast may be used as an infinitive (to cast)
or as an adjective (cast framework, or cast metal base).
Cast is used most frequently in this text as a noun to
designate a positive reproduction of a maxillary or
mandibular dental arch made from an impression of that
arch. It is further designated according to the purpose
for which it is made, such as diagnostic cast, master
cast, or investment cast. An investment cast also may be
referred to as a refractory cast because it is
compounded to withstand high temperatures
without disintegrating and, incidentally, to perform
certain functions relative to the burnout and expansion
of the mold. A refractory investment is an investment
material that can with
stand the high temperatures of casting or soldering.
Plaster of Paris and artificial stone also may be
considered investment if either is used to invest any part
of a dental restoration for processing.
Cast is the preferred dental term, which should
always imply that it is an accurate reproduction of the
tissues being studied or on which a restoration may be
fabricated. Any cast that is admittedly inaccurate is
unacceptable in modern dentistry because of the
availability of excellent impression and cast materials.
The word cast is preferable to the term model, which
should be used only to designate a reproduction for
display or demonstration purposes. A model of a dental
arch or any portion thereof may be made of durable and
attractive material. It need not be an accurate
reproduction but should be a reasonable facsimile of the
original. It is frequently made of tooth- and tissuecolored acrylic resin.
Use of the term mold is also incorrect when referring to a
reproduction of a dental arch or a portion thereof. The word
mold is used to indicate either the cavity into which a casting
is made or the shape of an artificial tooth.
A wax pattern is converted to a casting by the
elimination of the pattern by heat, leaving a mold into
which the molten metal is forced by centrifugal force or
other means. Casting is therefore used most frequently as
a noun, meaning a metal object shaped by being poured
into a mold to harden. It is used primarily to designate
the cast metal framework of a partial denture but also
may be used to describe a molded metal denture base,
which is actually cast into a mold.
Dental stones are used to form an artificial stone
reproduction from an impression, and they are used as an
investment or for mounting purposes. All dental stones
are gypsum products. Use of the word stone in dentistry
should be applied only to those gypsum materials that are
employed for their hardness, accuracy, or abrasion
resistance.
A dental cast surveyor is an instrument used to
determine the relative parallelism of two or more axial
surfaces of teeth or other parts of a cast of a dental arch.
This instrument is used to locate and delineate the
contours and relative
Chapter I
positions of abutment teeth and associated structures.
The word wrought, when used to describe an
alloy, means worked into shape by rolling,
forging, or extrusion. Mechanical treatment of an
alloy has two primary objectives. One objective
is to obtain a desired form for use-for example,
wires, bands, bars, and sheets. Another objective is to
enhance certain mechanical properties that are
unsatisfactory in a cast alloy.
The terms canine (tooth) and premolar
(tooth) are used to designate those teeth commonly
called cuspid and bicuspid teeth. Denton gives these
chief arguments for the use of the word canine: "(1) it
is the term used in other sciences, and (2) other terms
in standard usage can be understood only in relation to
canine tooth: canine eminence, canine muscle, canine
fossa." For the use of premolar, he gives the following
arguments: "(1) the term bicuspid is not descriptive of
all teeth of that class, and (2) the acceptance of
premolar makes uniform the terminology of dentistry
and comparative dental anatomy."*
Some controversy exists over the use of the terms
x-ray, radiograph, and roentgenogram in
dentistry. The American Academy of Oral
Roentgenology has indicated its preference for the use
of the term roentgenogram, at the same time
admitting that it may leave much to be
'From Denton GB: The vocabulary of dentistry and
oral science, Chicago, 1958, Anerican Dental
Association.
Introduction and terminology
7
desired as descriptive terminology. Examination of several
recent textbooks on dental subjects finds usage divided
between all three terms.
However, in deference to the terminology preferred by the
American Academy of Oral Roentgenology, the terms
roentgenogram,
roentgenographic
survey,
and
roentgenographic interpretation are used herein.
Use of the term acrylic as a noun is avoided. Instead it
is used only as an adjective, such as acrylic resin. The
word plastic may be used either as an adjective or a noun;
in the latter sense it refers to any of various substances
that
harden and retain their shape after being
molded. The term resin is used broadly for
substances named according to their chemical
composition, physical structure, and means for activation
or curing, such as acrylic resin.
Retention, in terms of complete dentures, should be
considered a denture base to soft tissue relationship. In
removable partial prosthodontics, we speak in terms of
direct and indirect retention. Direct retention is the retention obtained in a removable partial denture by
the use of attachments or direct retainers (clasps)
that resist the displacement or removal of the
partial denture from the abutment teeth.
The terms defined in this chapter were selected to
establish clarity in this text. The Nomenclature
Committee of the Academy of Prosthodontics is to be
commended for their efforts in compiling a current
glossary that may be used for guidance in prosthodontic
terminology.