CLASSIC ARTICLE
The neutral zone in complete dentures
Victor E. Ber esin, DDS,
a
and Frank J. Schiesser, DDS
b
Temple University School of Dentistry, Philadelphia, Pa
The neutral-zone approach to complete denture
construction is neither new nor original but, rather, con-
stitutes the bringing together of the concepts and ideas
of many men into a viable and practical procedure.
Over the past forty years, numerous articles which
have touched upon or related to what we have termed
the ‘‘neutral-zone concept’’ have appeared in the lite-
rature. Unfortunately, the profession generally has ig-
nored these ideas, and consequently, the principles are
frequently bypassed in denture construction.
The two men who probablyhavecontributed the most
to these concepts are Wil-ford Fish
1
and Russell Tench.
2
Many others,
2-9
including Perry
10
and the Detroit Dental
Clinic Club, have helped to advance and develop both the
theoretical basis and practical procedures.
Complete dentures are primarily mechanical devices,
but since they function in the oral cavity, they must be
fashioned so that they are in harmony with normal neu-
romuscular function. All oral functions, such as speech,
mastication, swallowing, smiling, and laughing, involve
the synergistic actions of the tongue, lips, cheeks, and
floor of the mouth which are very complex and highly in-
dividual. Failure to recognize the cardinal importance of
tooth position and flange form and contour often results
in dentures which are unstable and unsatisfactory, even
though they were skillfully designed and expertly con-
structed. The coordination of complete dentures with
neuromuscular function is the foundation of successful,
stable dentures.
When all of the natural teeth have been lost, there ex-
ists within the oral cavity a void which is the potential
denture space (Fig. 1). The neutral zone is that area in
the potential denture space where the forces of the
tongue pressing outward are neutralized by forces of
the cheeks and lips pressing inward. Since these forces
are developed through muscular contraction during
the various functions of chewing, speaking, and swal-
lowing, they vary in magnitude and direction in different
individuals.
NEUTRAL ZONE
The soft tissues that form the internal and external
boundaries of the denture space exert forces which
greatly influence the stability of the dentures. The cen-
tral thesis of the neutral-zone approach to complete
dentures is to locate that area in the edentulous mouth
where the teeth should be positioned so that the forces
exerted by muscles will tend to stabilize the denture
rather than unseat it.
MUSCLE FORCES IN THE DENTAL ARCH
In the mouth of the child, the teeth erupt under the
influence of a muscular environment. This environment,
which is created by forces exerted by the tongue, cheeks,
and lips, has a definite influence upon the position of
the erupted teeth, the resultant arch form, and the
occlusion.
The dental arch is formed by the muscle forces
exerted on the teeth by the tongue, lips, and cheeks.
There is also a genetic factor which cannot be over-
looked. This inherent factor along with the muscular
forces uniquely combine their influences to determine
the final arch form and tooth position.
Generally, muscular activity and habits which develop
during childhood continue through life. After the teeth
have been lost, muscle function and activity remain
highly individual and greatly influence any complete
dentures that are placed in the mouth. It is therefore, ex-
tremely important that the teeth be placed in the mouth
with the arch form located so that it will fall within the
area compatible with muscular forces.
MUSCLE FORCES AND DENTURE
STABILITY
By thinking of the soft-tissue boundaries of the den-
ture space and of muscle function, the dentist becomes
cognizant of those forces which tend to seat or unseat
the denture. Our objective, therefore, is to recognize
and to utilize those forces resulting from muscle func-
tion so that they will have a positive influence on denture
stability. This can be accomplished only if we are aware
of the neutral zone and if we position the teeth and de-
velop the external surfaces of the denture so that all of
Read before the Academy of Denture Prosthetics, Washington, D. C.
Reprinted with permission from J Prosthet Dent 1976;36:357-67.
a
Associate Clinical Professor, Department of Prosthetic Dentistry.
b
Assistant Clinical Professor, Department of Prosthetic Dentistry.
J Prosthet Dent 2006;95:93-101.
FEBRUARY 2006 THE JOURNAL OF PROSTHETIC DENTISTRY 93
the forces exerted are neutralized and the denture main-
tains a state of equilibrium.
DENTURE SURFACES
The dental profession has always been concerned
with equalizing the vertical forces that are delivered by
the occlusal surfaces of the teeth and counteracted by
the vault and the ridges. It has generally ignored the im-
portance of the horizontal forces exerted on the external
surfaces of the dentures. Thus, the dental profession has
been concerned, in the main, with two surfaces—the
occlusal surface and the impression surface.
Sir Wilford Fish
1
of England has described a denture
as having three surfaces, with each surface playing an in-
dependent and important role in the over-all fit, stabil-
ity, and comfort of the denture.
We are very familiar with the impression and the
occlusal surfaces of the denture. The third surface—as
termed by Fish, ‘‘the polished surface’’—is the rest of
Fig. 1. Denture space: A, cross section of molar area; B, lateral view of incisor area. (From Beresin VE, Schiesser FJ. The neutral
zone in complete dentures. St. Louis: C. V. Mosby Co; 1973.)
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94 VOLUME 95 NUMBER 2
the denture that is not part of the other two surfaces. It is
mostly denture base material, but it also consists of those
surfaces of the teeth that are not contacting or articulat-
ing surfaces. The external or polished surface of the den-
ture is in contact with the cheeks, lips, and tongue. One
can visualize that, per square unit of area, the polished
surface can be as large as or larger than impression and
occlusal surfaces combined, depending on anatomic
structure.
INFLUENCE OF FORCES ON DENTURE
SURFACES
The greater the ridge loss, the smaller the denture
base area and the less influence the impression surface
area will have on the stability and retention of the den-
ture. As the area of the impression surface decreases
and the polished surface area increases, tooth position
and contour of the polished surface become more cri-
tical (Figs. 2 and 3). In other words, where more of
the alveolar ridge has been lost, denture stability and re-
tention are more dependent on correct position of
the teeth and contour of the external surfaces of the
dentures.
The forces exerted on the external surfaces of the
teeth and the polished surfaces are essentially horizontal.
When the occlusal surfaces of the teeth are not in con-
tact, the stability of the denture is determined by the
fit of the impression surface and the direction and mag-
nitude of forces transmitted through the polished
surfaces.
If the teeth were in contact all of the time, the pol-
ished surfaces would have relatively little effect on
denture stability. Conversely, if the teeth were never
brought into contact, the occlusal surfaces would be
relatively unimportant. In order to construct dentures
which function properly in chewing, swallowing, speak-
ing, etc., we must develop not only proper tooth posi-
tion but also the fit and contour of the polished
surfaces just as accurately and meticulously as the fit
and contour of impression and occlusal surfaces.
For example, let us examine a critical area of the lower
denture such as the anterior segment. The force of the
lower lip against the anterior surface of the denture
Fig 3. A, Cross section of favorable lower ridge. The over-all area of surface BC (impression surface) is approximately equal to
the combined area ABCD (external surface). B, Cross section of unfavorable lower ridge caused by excessive resorption. The
over-all area of surface BC (impression surface) is considerably less than the area of combined surface ABCD (external surface).
Therefore, forces exerted on external surface will have greater influence on denture stability and retention as compared to part A.
(From Beresin VE, Schiesser FJ. The neutral zone in complete dentures. St. Louis: C. V. Mosby Co; 1973.)
Fig 2. A, Cross section of a favorable upper ridge. The over-all size of surface AD (impression surface) is approximately equal
to the over-all siz e of surface ABCD (external surfa ce). B, Cross section of an unfavorable upper ridge caused by excessive
resorption. The over-all area of surface AD (impression surface) is considerably less th an the over-all area of surface ABCD
(external surface). Therefore, forces exerted on the external surface have greater influence on denture stability and retention
than do those in part A. (From Beresin VE, Schiesser FJ. The neutral zone in complete dentures. St. Louis: C. V. Mosby Co;
1973.)
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FEBRUARY 2006 95
and the anterior teeth will cause the denture to rise un-
less the teeth and flange are properly positioned and
contoured. When the mouth is closed, the denture
may remain stable. However, as soon as the mouth
opens, the lower lip is like an elastic band pressing
against the anterior flange and teeth. The wider the
mouth is opened, the tighter the band (Fig. 4).
The influence of the lip on stability of the lower den-
ture becomes more critical as resorption of the ridge
increases or as the patient ages (Fig. 5). Lammie
5
has
shown that as the alveolar ridge resorbs, the ridge crest
falls below the origin of the mentalis muscle. As a result,
the muscle attachment folds over the alveolar ridge and
comes to rest on the superior surface of the ridge crest.
The result is a posterior positioning of the neutral zone
and, with it, the need to place the lower anterior teeth
further lingually than had been the position of the natu-
ral teeth (Fig. 6).
Fig 4. A, Cross section of mouth in repose. No unfavorable forces are external surfaces by the lips and cheeks. B, As the mouth
opens, the denture comes under the influence of horizontal forces from the lips. C, With the mouth wide open, maximum hor-
izontal forces are exerted on the labial and buccal external surfaces of the teeth and flanges. The distance AB when the mouth is
open (below) is less than the distance AB when the mouth is at rest (above). (From Beresin VE, Schiesser FJ. The neutral zone in
complete dentures. St. Louis: C. V. Mosby Co; 1973.)
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It seems obvious that if we do not determine the neu-
tral zone and. as a result, the teeth and flanges are not
properly positioned and contoured, the force of pressure
from the lower lip may constantly unseat the lower
denture.
REVERSED SEQUENCE IN DENTURE
CONSTRUCTION
The usual sequence for complete dentures is to make
primary impressions, construct individual trays, make fi-
nal impressions, and then fabricate stabilized bases.
Occlusion rims or other devices are used to establish
the occlusal vertical dimension and centric relation.
With the neutral-zone approach to complete dentures,
the procedure is reversed. Individual trays are con-
structed first. These trays are very carefully adjusted in
the mouth to be sure that they are not overextended
and remain stable during opening, swallowing, and
speaking. Next, modeling compound is used to fabricate
occlusion rims. These rims, which are molded by muscle
function, locate the patient’s neutral zone (Fig. 7). After
a tentative vertical dimension and centric relation have
been established, the final impressions are made with a
closed-mouth procedure. Only when the final impres-
sions are completed are the occlusal vertical dimension
and centric relation finally determined.
BASE AND BODY OF THE DENTURE
It is important to understand the rationale behind the
reversal of the usual steps in complete denture construc-
tion. The premise is that we should separate the denture
base from the body of the denture.
With the neutral-zone concept, the impression sur-
face is called the ‘‘base’’ and the polished surface is called
the ‘‘body’’ of the denture. In the past, we did not orient
our thinking in this direction, and as a result, we were
less aware of the problems and their solutions.
Once the dentist begins to think of first creating a sta-
ble base and then placing teeth and flange contours that
will not unseat it, the problems become apparent and are
comparatively simple to solve.
The following example illustrates this important
point. We all have had the experience of inserting a lower
denture which moves upward as soon as the patient
opens his mouth or starts to speak. The first assumption
is usually that the denture is overextended so that the
Fig 5. A, Cross section of a favorable lower anterior ridge. The dislodging forces exerted on the denture by the lower lip are
resisted by the ridge. B, Cross section o f unfavorable lower anterior ridge. The dislodging forces exerted on the denture by
the lower lip cannot be counter-acted by the unfavorable ridge. Therefore, tooth position becomes much more critical. (From
Beresin VE, Schiesser FJ. The neutral zone in complete dentures. St. Louis: C. V. Mosby Co; 1973.)
Fig 6. Broken line indicates original position of natural lower
anterior teeth. Solid outline indicates proper position of ante-
rior denture teeth to avoid dislodging forces of the lip. (From
Beresin VE , Schiesser FJ. The neutral zone in complete den-
tures. St. Louis: C. V. Mosby Co; 1973.)
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FEBRUARY 2006 97
