Neutral Zone Dentistry: Understanding the Stable Position of Teeth

NEUTRAL ZONENEUTRAL ZONE
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.comwww.indiandentalacademy.com

INTRODUCTIONINTRODUCTION
 The goal of dentistry is for patientsThe goal of dentistry is for patients
to keep all of their teeth throughoutto keep all of their teeth throughout
their lives in health and comfort. Iftheir lives in health and comfort. If
the teeth are lost despite all effortsthe teeth are lost despite all efforts
to save them, a restoration shouldto save them, a restoration should
be made in such a manner as tobe made in such a manner as to
function efficiently and comfortablyfunction efficiently and comfortably
in harmony with the muscles of thein harmony with the muscles of the
stomatognathic system and thestomatognathic system and the
temporomandibular jointstemporomandibular jointswww.indiandentalacademy.comwww.indiandentalacademy.com

 The stable position of the teeth representsThe stable position of the teeth represents
equilibrium of all the forces acting on them. Ifequilibrium of all the forces acting on them. If
that position of equilibrium namely thethat position of equilibrium namely the
neutral zone, is not found, the resultingneutral zone, is not found, the resulting
dentition will not last long and will not bedentition will not last long and will not be
esthetically pleasing and the patients use ofesthetically pleasing and the patients use of

 functional efficiency, maximumfunctional efficiency, maximum
length of use and pleasing estheticslength of use and pleasing esthetics
will not have been met.will not have been met.
 To understand the stable positionTo understand the stable position
of teeth, the concept of neutral zoneof teeth, the concept of neutral zone
is important.is important.

 Neutral ZoneNeutral Zone is defined as that areais defined as that area
in the mouth where, during function,in the mouth where, during function,
the forces of the tongue pressingthe forces of the tongue pressing
outward are neutralised by the forcesoutward are neutralised by the forces
of the cheeks and lips pressingof the cheeks and lips pressing
inwards.inwards.

FORM AND FUNCTION:FORM AND FUNCTION:
 In orthodontics and prosthodonticsIn orthodontics and prosthodontics
the basic principles of treatment arethe basic principles of treatment are
identical. They revolve around theidentical. They revolve around the
relationship between form andrelationship between form and
function..function..

 Function determines form. AbnormalFunction determines form. Abnormal
functions such as deviate swallowingfunctions such as deviate swallowing
pattern, mouth breathing and thumbpattern, mouth breathing and thumb
sucking, will modify or dictate thesucking, will modify or dictate the
form of the dental archesform of the dental arches

 It is equally true that alteration ofIt is equally true that alteration of
the form of a growing individual willthe form of a growing individual will
alter function. If the alteration ofalter function. If the alteration of
form is an improvement, there willform is an improvement, there will
be a concomitant improvement inbe a concomitant improvement in
function. Ideally, both the functionfunction. Ideally, both the function
and form should be correctedand form should be corrected
together for optimal results, and thistogether for optimal results, and this
correction should take place beforecorrection should take place before
growth has ceased.growth has ceased.www.indiandentalacademy.comwww.indiandentalacademy.com

 Prosthodontic treatment in completeProsthodontic treatment in complete
dentures is also influenced by thedentures is also influenced by the
concept that form follows function.concept that form follows function.
Complete dentures that are constructedComplete dentures that are constructed
by concepts that do not take intoby concepts that do not take into
consideration the unique functioning ofconsideration the unique functioning of
the individual patients musculature arethe individual patients musculature are
over looking this basic law of physiology.over looking this basic law of physiology.

 If form is dictated by function, thenIf form is dictated by function, then
in complete denture construction,in complete denture construction,
the operator must shape and formthe operator must shape and form
dentures to be in harmony withdentures to be in harmony with
functionfunction

 In all areas of dentistry, the ultimateIn all areas of dentistry, the ultimate
problem in maintaining the health of theproblem in maintaining the health of the
stomatognathic system throughout life isstomatognathic system throughout life is
one of harmonious pressure distribution.one of harmonious pressure distribution.
The primary function of this system is theThe primary function of this system is the
application, distribution and dissipation ofapplication, distribution and dissipation of
the pressure of the bite and of thethe pressure of the bite and of the
muscles of the lips, cheeks andmuscles of the lips, cheeks and tongue.tongue.www.indiandentalacademy.comwww.indiandentalacademy.com

 To put it more simply, the primaryTo put it more simply, the primary
function of the stomatognathic system isfunction of the stomatognathic system is
mastication.mastication.
 The prosthodontist who is unaware ofThe prosthodontist who is unaware of
the effect of muscle function will be facedthe effect of muscle function will be faced
with cases of prosthodontic relapsewith cases of prosthodontic relapse
unstable dentures.‑unstable dentures.‑

THE NEUTRAL ZONE ANDTHE NEUTRAL ZONE AND
DENTURE SPACEDENTURE SPACE
 In completely edentulous patients thereIn completely edentulous patients there
exists within the oral cavity a void thatexists within the oral cavity a void that
may be called the potential denturemay be called the potential denture
space. The denture space is bounded byspace. The denture space is bounded by
the maxilla and soft palate above, by thethe maxilla and soft palate above, by the
mandible and floor of the mouth below,mandible and floor of the mouth below,

 by the tongue, medially or internally,by the tongue, medially or internally,
and by the muscles and tissues ofand by the muscles and tissues of
the lips and cheeks laterally orthe lips and cheeks laterally or
externally. Within the denture spaceexternally. Within the denture space
there is an area that has beenthere is an area that has been
termed the neutral zone.termed the neutral zone.

 Weath (1970) has demonstrated thatWeath (1970) has demonstrated that
there is a difference in the shape ofthere is a difference in the shape of
the denture space and resultant archthe denture space and resultant arch
form at rest as compared to theform at rest as compared to the
denture space and arch formdenture space and arch form
established by function.established by function.

FACTORS AFFECTINGFACTORS AFFECTING
THE NEUTRAL ZONETHE NEUTRAL ZONE

Muscles and the neutral zone:Muscles and the neutral zone:
 Dentures should occupy a position inDentures should occupy a position in
the mouth where all the forcesthe mouth where all the forces
during function are neutralized.during function are neutralized.
Otherwise, denture stability will beOtherwise, denture stability will be
decreased proportionately todecreased proportionately to thethe
difference in the amount of thedifference in the amount of the
opposing forces.opposing forces.
 Neutral zone in complete dentures isNeutral zone in complete dentures is
in fact the zone previously occupiedin fact the zone previously occupied
by the natural teeth.by the natural teeth.www.indiandentalacademy.comwww.indiandentalacademy.com

MUSCLES OF THE CHEEKMUSCLES OF THE CHEEK
 The outer limits of the neutral zone areThe outer limits of the neutral zone are
determined by the perioral musculature.determined by the perioral musculature.
 BUCCINATORBUCCINATOR
 The main determinant of length, strengthThe main determinant of length, strength
and position of the perioral musculature is theand position of the perioral musculature is the
buccinator muscle. The buccinator is a thin, flatbuccinator muscle. The buccinator is a thin, flat
muscle composed of three bands.muscle composed of three bands.www.indiandentalacademy.comwww.indiandentalacademy.com

 The combined width of the threeThe combined width of the three
bands covers the entire outer surfacebands covers the entire outer surface
of the dento alveolar structures, thatof the dento alveolar structures, that
is the teeth, alveolar process andis the teeth, alveolar process and
gingival tissues.gingival tissues.
The upper and lower bands areThe upper and lower bands are
continuous from side to sidecontinuous from side to side
without decussation. The middlewithout decussation. The middle
band fibers decussate and joint intoband fibers decussate and joint into
the fibers of the orbicularis oristhe fibers of the orbicularis oris..

 Because the muscle fibers form aBecause the muscle fibers form a
continuous band, the size of the archcontinuous band, the size of the arch
is limited by the length of theis limited by the length of the
muscles when they are contractedmuscles when they are contracted
repetitiously. Regardless of therepetitiously. Regardless of the
reason for variations in muscle tonusreason for variations in muscle tonus
in different patients, the strength ofin different patients, the strength of
the contractile force, at the length ofthe contractile force, at the length of
the muscle during contraction, forcesthe muscle during contraction, forces
can inviolate outer limit for arch size.can inviolate outer limit for arch size.

 The effects of neutral zoneThe effects of neutral zone
confinement on the dentoalveolarconfinement on the dentoalveolar
structures can also play a critical rolestructures can also play a critical role
as a determinant of facial profile. Aas a determinant of facial profile. A
restrictive perioral musculature mayrestrictive perioral musculature may
prevent the dentoalveolar archesprevent the dentoalveolar arches
from expanding to a normalfrom expanding to a normal
alignment with the skeletal base.alignment with the skeletal base.

 The commonThe common practice ofpractice of
centralization, or lingualization ofcentralization, or lingualization of
occlusion, prevents the buccinatorocclusion, prevents the buccinator
from performing its proper function infrom performing its proper function in
two ways. First, lingualization oftwo ways. First, lingualization of
occlusion creates a space between theocclusion creates a space between the
cheek and the teeth and the externalcheek and the teeth and the external
surface of the denture, where foodsurface of the denture, where food
tends to accumulate and it becomestends to accumulate and it becomes
more difficult for the cheek to placemore difficult for the cheek to place
the food back onto the occlusalthe food back onto the occlusal
surfaces of the teeth.surfaces of the teeth.

 Secondly, the space resulting fromSecondly, the space resulting from
lingualization prevents the buccinatorlingualization prevents the buccinator
from neutralizing the lateral forces offrom neutralizing the lateral forces of
the tongue during function.the tongue during function.

 MASSETER:MASSETER:
 The masseter muscle has noThe masseter muscle has no
influence on the neutral zone. It onlyinfluence on the neutral zone. It only
affects the distobuccal border of theaffects the distobuccal border of the
denture.denture.

 MUSCLES OF THE LIPSMUSCLES OF THE LIPS
 Orbicularis orisOrbicularis oris : To a great extent: To a great extent
forms the lips. In function, as informs the lips. In function, as in
chewing, smiling and swallowing, itchewing, smiling and swallowing, it
exerts force against the teeth andexerts force against the teeth and
denture flanges, which isdenture flanges, which is
counteracted by the tongue.counteracted by the tongue.

 Canine muscleCanine muscle : This together with: This together with
other muscles, pulls the lower lip upother muscles, pulls the lower lip up
and in sucking and swallowing helpsand in sucking and swallowing helps
to pull the lips forward, thus exertingto pull the lips forward, thus exerting
forces on the teeth and labialforces on the teeth and labial
denture flange.denture flange.

 The greater zygomatic muscleThe greater zygomatic muscle
pulls the angle of the, mouth upwardpulls the angle of the, mouth upward
and backward.and backward.
 The risorius muscle retracts theThe risorius muscle retracts the
corner of the mouth.corner of the mouth.
 The mentalis muscle turns theThe mentalis muscle turns the
lower lip outward and in contractinglower lip outward and in contracting
makes the lower labial vestibulemakes the lower labial vestibule
shallow.shallow.

 The triangular muscle contractsThe triangular muscle contracts
during sucking to exert pressure onduring sucking to exert pressure on
the teeth and the denture flanges.the teeth and the denture flanges.

 The ModiolusThe Modiolus : Because of the: Because of the
strength and variability of movement ofstrength and variability of movement of
the area, the modiolus is extremelythe area, the modiolus is extremely
important in relation to the stability ofimportant in relation to the stability of
the lower denture. Unless the teeth andthe lower denture. Unless the teeth and
external surface of the denture areexternal surface of the denture are
properly positioned and contoured byproperly positioned and contoured by
narrowing in the premolar area, thenarrowing in the premolar area, the
modiolus may constantly unseat themodiolus may constantly unseat the
lower denture.lower denture.www.indiandentalacademy.comwww.indiandentalacademy.com

 MUSCLES OF THE TONGUEMUSCLES OF THE TONGUE
 The tongue is composed ofThe tongue is composed of
intrinsic muscles that lie within theintrinsic muscles that lie within the
tongue itself and extrinsic musclestongue itself and extrinsic muscles
that insert into the tongue.that insert into the tongue.
 The function of the extrinsicThe function of the extrinsic
muscles the styloglossus,muscles the styloglossus,
palatoglossus, hyoglossus, andpalatoglossus, hyoglossus, and
genioglossus is to move the tongue‑genioglossus is to move the tongue‑
into various positionsinto various positions

 . The tongue is capable of many. The tongue is capable of many
varied shapes and positions duringvaried shapes and positions during
speech, mastication, and swallowingspeech, mastication, and swallowing
and in all of these functions is inand in all of these functions is in
constant contact with the lingualconstant contact with the lingual
surface of the teeth, the lingualsurface of the teeth, the lingual
flange of the lower denture and theflange of the lower denture and the
palatal surface of the upper denture.palatal surface of the upper denture.

 Because of this contact, the tongueBecause of this contact, the tongue
is a dominant factor in establishingis a dominant factor in establishing
the neutral zone and therefore in thethe neutral zone and therefore in the
stability or .lack of stability of thestability or .lack of stability of the
lower denture.lower denture.

 The common practice ofThe common practice of
lingualization is probably one of thelingualization is probably one of the
greatest influencing factors in lowergreatest influencing factors in lower
denture instability, because itdenture instability, because it
violates the neutral zone andviolates the neutral zone and
encroaches on the tongue space.encroaches on the tongue space.

DENTURE SURFACESDENTURE SURFACES
 The dental profession has alwaysThe dental profession has always
been concerned with equalizing thebeen concerned with equalizing the
vertical forces that are delivered byvertical forces that are delivered by
the occlusal surfaces of the teeth andthe occlusal surfaces of the teeth and
that are counteracted by the vaultthat are counteracted by the vault
and the ridges. It has ignored theand the ridges. It has ignored the
importance of the horizontal forcesimportance of the horizontal forces
exerted on the polished or externalexerted on the polished or external
surface of the denturesurface of the denture

 Thus the dental profession has beenThus the dental profession has been
concerned mainly with two surfaces ‑concerned mainly with two surfaces ‑
the occlusal and the impressionthe occlusal and the impression
surfaces.surfaces.
 Sir Wilfred Fish in 1948 describedSir Wilfred Fish in 1948 described
a denture as having three surfaces,a denture as having three surfaces,
with each surface playing anwith each surface playing an
independent and important role inindependent and important role in
the overall fit, stability and comfortthe overall fit, stability and comfort
of the denture.of the denture.

 The first surface, the impressionThe first surface, the impression
surface, is that part of the denture insurface, is that part of the denture in
contact with the tissues and oncontact with the tissues and on
which the denture rests andwhich the denture rests and
determines retention of the denture,determines retention of the denture,
 The second surface, the occlusalThe second surface, the occlusal
surface is that area in contact withsurface is that area in contact with
the teeth, either natural or artificial,the teeth, either natural or artificial,
of the opposite jaw.of the opposite jaw.

 The stability of the denture when theThe stability of the denture when the
teeth are in contact is determined byteeth are in contact is determined by
the fit of the impression surfacethe fit of the impression surface
against the tissues and the fit of theagainst the tissues and the fit of the
occlusal surfaces against each other.occlusal surfaces against each other.

 The third surface, the polished orThe third surface, the polished or
external surface as termed by Fish,external surface as termed by Fish,
is all the rest of the denture that isis all the rest of the denture that is
not part of the other two surfaces. Itnot part of the other two surfaces. It
is mostly denture base material, butis mostly denture base material, but
it consists also of those surfaces ofit consists also of those surfaces of
the teeth that are not contacting orthe teeth that are not contacting or
articulating surfaces.articulating surfaces.

 The buccal and lingual surfaces ofThe buccal and lingual surfaces of
the posterior teeth and the labial andthe posterior teeth and the labial and
lingual surfaces of the lower anteriorlingual surfaces of the lower anterior
teeth are not part of the occlusalteeth are not part of the occlusal
surface but are part of the polishedsurface but are part of the polished
surface of the denture. The uppersurface of the denture. The upper
anterior teeth actually belong to twoanterior teeth actually belong to two
surfaces, both the occlusal and thesurfaces, both the occlusal and the
polished surfaces.polished surfaces.

 When the teeth are in contact, theWhen the teeth are in contact, the
lingual surfaces of the upper anteriorlingual surfaces of the upper anterior
teeth are part of the occlusal surface.teeth are part of the occlusal surface.
When the teeth are apart, as inWhen the teeth are apart, as in
speaking as at rest, these surfacesspeaking as at rest, these surfaces
are part of the polished surface.are part of the polished surface.

 The external surface is in contactThe external surface is in contact
with, the cheeks, lips and tongue.with, the cheeks, lips and tongue.
One can visualize that, based on aOne can visualize that, based on a
square unit of area; the externalsquare unit of area; the external
surface is as large as or larger thansurface is as large as or larger than
the impression and occlusal surfacesthe impression and occlusal surfaces
combined, depending on thecombined, depending on the
anatomic structures.anatomic structures.

INFLUENCE OF FORCES ONINFLUENCE OF FORCES ON
DENTURE SURFACESDENTURE SURFACES
 The more the ridge loss, the less theThe more the ridge loss, the less the
area of the denture base and the lessarea of the denture base and the less
the influence the impression surfacethe influence the impression surface
area will have on the stability andarea will have on the stability and
retention of the denture.retention of the denture.

 As the surface area of the impressionAs the surface area of the impression
surface decreases and the externalsurface decreases and the external
surface area increases, thesurface area increases, the
development and contour of thedevelopment and contour of the
external surface becomes moreexternal surface becomes more
critical.critical.

 In other words, where more of theIn other words, where more of the
ridge has been lost, the more theridge has been lost, the more the
denture stability and retention isdenture stability and retention is
dependent on the external surfacedependent on the external surface
than on the impression surface.than on the impression surface.
Many unstable lower dentures areMany unstable lower dentures are
caused by the external surface notcaused by the external surface not
being properly formed and the teethbeing properly formed and the teeth
not positioned in the neutral zone.not positioned in the neutral zone.

 The forces on the external surfaceThe forces on the external surface
are constantly changing inare constantly changing in
magnitude and direction duringmagnitude and direction during
swallowing, speaking andswallowing, speaking and
mastication. It is only when themastication. It is only when the
mouth is completely at rest, that themouth is completely at rest, that the
forces are constant.forces are constant.

 If a person's teeth were in contact allIf a person's teeth were in contact all
the time, the external surface wouldthe time, the external surface would
be relatively unimportant in denturebe relatively unimportant in denture
stability. Conversely if a personstability. Conversely if a person
never brought his teeth into contact,never brought his teeth into contact,
the occlusal surface would bethe occlusal surface would be
relatively unimportant and therelatively unimportant and the
stability would be dependent on, thestability would be dependent on, the
forces on the external surface asforces on the external surface as
transmitted to the impressiontransmitted to the impression
surface.surface.

 The only time teeth are in contact is,The only time teeth are in contact is,
during mastication and swallowing.during mastication and swallowing.
This means that the patient will onlyThis means that the patient will only
make tooth contact during normalmake tooth contact during normal
function. But the lips, cheeks andfunction. But the lips, cheeks and
tongue are constantly in function.tongue are constantly in function.
This stresses the significance of theThis stresses the significance of the
horizontal forces exerted by the lips,horizontal forces exerted by the lips,
cheeks and tongue.cheeks and tongue.

 In order to construct dentures thatIn order to construct dentures that
function properly not only in chewingfunction properly not only in chewing
but also in speaking and swallowing,but also in speaking and swallowing,
we must develop the fit and contourwe must develop the fit and contour
of the external surface of dentureof the external surface of denture
just as accurately and meticulouslyjust as accurately and meticulously
as the fit and contour of theas the fit and contour of the
impression surface and the occlusalimpression surface and the occlusal
surface.surface.

 The lower posterior teeth areThe lower posterior teeth are
drastically affected by the position ofdrastically affected by the position of
the tongue. If the lower posteriorthe tongue. If the lower posterior
teeth are lingualized excessively,teeth are lingualized excessively,
normal tongue function willnormal tongue function will
immediately unseat the denture. Theimmediately unseat the denture. The
tongue cannot and should not betongue cannot and should not be
restricted by the position of therestricted by the position of the
posterior teeth.posterior teeth.

MUSCLE INFLUENCE ON THEMUSCLE INFLUENCE ON THE
DEVELOPMENTDEVELOPMENT
OF THE DENTAL ARCHESOF THE DENTAL ARCHES
 Teeth erupt into the mouth underTeeth erupt into the mouth under
the influence of muscularthe influence of muscular
environment. This environmentenvironment. This environment
which is created by the, forceswhich is created by the, forces
between the tongue, cheeks and lipsbetween the tongue, cheeks and lips
has a definite influence on thehas a definite influence on the
position of the erupting teeth, theposition of the erupting teeth, the
resultant arch form and occlusion.resultant arch form and occlusion.www.indiandentalacademy.comwww.indiandentalacademy.com

 However, the muscular forces aloneHowever, the muscular forces alone
do not always determine thedo not always determine the
developing dental arch form. There isdeveloping dental arch form. There is
genetic factor which cannot begenetic factor which cannot be
overlooked. This internal factor,overlooked. This internal factor,
along with the local environmentalalong with the local environmental
forces, combines their influencesforces, combines their influences
uniquely to determine the final archuniquely to determine the final arch
form and tooth position.form and tooth position.

 It would stand to reason that whenIt would stand to reason that when
the teeth are erupting into the mouththe teeth are erupting into the mouth
during childhood and adolescence (2during childhood and adolescence (2
- 14 year group) the muscular- 14 year group) the muscular
activity and habits that develop willactivity and habits that develop will
continue through life.continue through life.

 Even after the teeth are lost, theEven after the teeth are lost, the
forces created by these habits andforces created by these habits and
actions still persist and will have aactions still persist and will have a
great influence on any complete orgreat influence on any complete or
extensive partial removableextensive partial removable
prosthesis that is placed into theprosthesis that is placed into the
mouth.mouth.

 It is therefore extremely importantIt is therefore extremely important
that the teeth be placed in that partthat the teeth be placed in that part
of the mouth and with an arch formof the mouth and with an arch form
that falls within the area formed bythat falls within the area formed by
muscular forces.muscular forces.

 Our objective is to utilise theOur objective is to utilise the
information on denture space andinformation on denture space and
muscle function so as to, position themuscle function so as to, position the
teeth and the external surfaces ofteeth and the external surfaces of
the denture that the force thethe denture that the force the
musculature exerts, instead ofmusculature exerts, instead of
having a negative influence, willhaving a negative influence, will
favourably affect the dentures andfavourably affect the dentures and
tend to seat or stabilize thetend to seat or stabilize the
dentures.dentures.

 This can be accomplished throughThis can be accomplished through
awareness of the neutral zone andawareness of the neutral zone and
by positioning the teeth andby positioning the teeth and
developing external surfaces of thedeveloping external surfaces of the
denture so that all the forces exerteddenture so that all the forces exerted
are neutralized and the denture is inare neutralized and the denture is in
a state of equilibrium.a state of equilibrium.

DIRECTION OF FORCESDIRECTION OF FORCES
 For the muscular forces to be of aFor the muscular forces to be of a
stabilizing nature, the dentures muststabilizing nature, the dentures must
be so constructed that they willbe so constructed that they will
receive these forces at the properreceive these forces at the proper
angle. Dr. Fish (1948) described theangle. Dr. Fish (1948) described the
cross section of stable dentures incross section of stable dentures in
the molar area to be triangular inthe molar area to be triangular in
shape, with the tooth being the apexshape, with the tooth being the apex
and the denture periphery the baseand the denture periphery the base
of a triangle.of a triangle.www.indiandentalacademy.comwww.indiandentalacademy.com

 A force exerted on an inclined planeA force exerted on an inclined plane
may be broken down into twomay be broken down into two
components. One component acts incomponents. One component acts in
the direction parallel to thethe direction parallel to the inclinedinclined
plane. The other component, calledplane. The other component, called
normal force, acts perpendicularly tonormal force, acts perpendicularly to
the inclined plane. If the inclinedthe inclined plane. If the inclined
planes of the external surface areplanes of the external surface are
properly fashioned and the forces areproperly fashioned and the forces are
of equal magnitude, the resultantof equal magnitude, the resultant
normal force will be in a seatingnormal force will be in a seating
directiondirection

 By the same token, if the denturesBy the same token, if the dentures
are triangular but not properlyare triangular but not properly
located within the neutral zone, thelocated within the neutral zone, the
lateral force will be unequal and notlateral force will be unequal and not
provide the equilibrium necessary forprovide the equilibrium necessary for
a stable denture. This willa stable denture. This will resultresult
either in the dislodgement of theeither in the dislodgement of the
denture or unequal pressure on thedenture or unequal pressure on the
ridge.ridge.

NEUTRALIZATION OF FORCESNEUTRALIZATION OF FORCES
 The theory of the neutralization ofThe theory of the neutralization of
forces that stabilize dentures and theforces that stabilize dentures and the
rationale involved was one of therationale involved was one of the
major contributions made bymajor contributions made by
Dr.Russel Tench and his co worker,Dr.Russel Tench and his co worker,
Dr.A.A.Cavalcarti.Dr.A.A.Cavalcarti.

 lips, cheeks and tongue in thelips, cheeks and tongue in the
passive and functioning state exertpassive and functioning state exert
forces on the natural teeth. In theforces on the natural teeth. In the
natural dentition, arch integrity andnatural dentition, arch integrity and
tooth position are maintained whentooth position are maintained when
all the forces generated by theall the forces generated by the
musculature are neutralized.musculature are neutralized.

 Any changes in the forces generatedAny changes in the forces generated
by the musculature because ofby the musculature because of
increased size, altered muscleincreased size, altered muscle
function, or abnormal habit patternsfunction, or abnormal habit patterns
will upset the equilibrium and resultwill upset the equilibrium and result
in alteration of tooth position andin alteration of tooth position and
arch form.arch form.

 If we accept the assumption that theIf we accept the assumption that the
teeth are positioned and maintainedteeth are positioned and maintained
in a neutral state by all the forcesin a neutral state by all the forces
exerted against them by theexerted against them by the
musculature, it seems reasonablemusculature, it seems reasonable
that when the dentures are made,that when the dentures are made,
the artificial teeth should be placedthe artificial teeth should be placed
in the same relative position to thein the same relative position to the
musculature as the natural teeth.musculature as the natural teeth.

 . The term "relative position" rather. The term "relative position" rather
than exact position" is used becausethan exact position" is used because
age, tonus, ridge resorption andage, tonus, ridge resorption and
other factors may modify or alter theother factors may modify or alter the
denture space and neutral zone sodenture space and neutral zone so
that the artificial teeth, should notthat the artificial teeth, should not
necessarily be in the exact samenecessarily be in the exact same
position as the natural teeth.position as the natural teeth.

 If the teeth are placed too farIf the teeth are placed too far
lingually in the molar region, theylingually in the molar region, they
will encroach on the tongue space.will encroach on the tongue space.
Dr.Mayskens estimates that if theDr.Mayskens estimates that if the
sizes of the mandibular teeth are toosizes of the mandibular teeth are too
large or if the posterior teeth are setlarge or if the posterior teeth are set
1 mm lingually, the tongue is1 mm lingually, the tongue is
deprived of approximately 1000deprived of approximately 1000
cubic mm of functional space. Thiscubic mm of functional space. This
can force the tongue into ancan force the tongue into an
abnormal retracted position.abnormal retracted position.

 In summary, the neutral zoneIn summary, the neutral zone
philosophy is based on the conceptphilosophy is based on the concept
that for each individual patient therethat for each individual patient there
exists within the denture space aexists within the denture space a
specific area where the function ofspecific area where the function of
the musculature will not unseat thethe musculature will not unseat the
denture, and at the same time wheredenture, and at the same time where
the forces generated by the tonguethe forces generated by the tongue
are neutralized by the forcesare neutralized by the forces
generated by the lips and cheeksgenerated by the lips and cheeks
Furthermore, denture stability is asFurthermore, denture stability is as
much or more influenced by toothmuch or more influenced by tooth
position and flange contour as byposition and flange contour as by
any other factors.any other factors.

 In other words, we should not beIn other words, we should not be
'dogmatic and insist that the tooth'dogmatic and insist that the tooth
should always be placed over theshould always be placed over the
crest of the ridge, or lingual to thecrest of the ridge, or lingual to the
ridge or buccal to the ridge.ridge or buccal to the ridge.
Placement of the teeth should bePlacement of the teeth should be
detected by the musculature and willdetected by the musculature and will
vary for different patients.vary for different patients.

DETERMINATION OF THEDETERMINATION OF THE
NEUTRAL ZONENEUTRAL ZONE
DIAGNOSIS AND TREATMENTDIAGNOSIS AND TREATMENT
PLANNINGPLANNING
 Success in complete dentureSuccess in complete denture
prosthetics is frequently dependentprosthetics is frequently dependent
on what is done prior to theon what is done prior to the
construction of the dentures as muchconstruction of the dentures as much
as or more than on the skill andas or more than on the skill and
meticulous care utilized in the actualmeticulous care utilized in the actual
construction of dentures.construction of dentures.

 Examination, diagnosis, andExamination, diagnosis, and
treatment planning for completetreatment planning for complete
dentures should be as meticulousdentures should be as meticulous
and detailed as for any other branchand detailed as for any other branch
of dentistry.of dentistry.
 After a proper examination andAfter a proper examination and
preparation of diagnostic casts we gopreparation of diagnostic casts we go
in for the treatment proper.in for the treatment proper.

Reversed Sequence inReversed Sequence in
Denture ConstructionDenture Construction

 First, the bases are very carefullyFirst, the bases are very carefully
adjusted in the mouth to be sureadjusted in the mouth to be sure
that they are not overextended andthat they are not overextended and
that they, are stable during mouththat they, are stable during mouth
opening, swallowing and speaking.opening, swallowing and speaking.

 Then modelling compound instead ofThen modelling compound instead of
wax, is used to fabricate occlusionwax, is used to fabricate occlusion
rims. These rims which are mouldedrims. These rims which are moulded
by muscle function, locate theby muscle function, locate the
patients neutral zone,.patients neutral zone,.

 After tentative vertical dimensionAfter tentative vertical dimension
and centric relation are `established,and centric relation are `established,
the final impressions are made withthe final impressions are made with
a closed mouth procedure. Onlya closed mouth procedure. Only
then, when the final impression isthen, when the final impression is
completed, are the verticalcompleted, are the vertical
dimension and centric relationdimension and centric relation
refined and finalized.refined and finalized.

DIAGNOSING THE LOWERDIAGNOSING THE LOWER
DENTURE PROBLEMDENTURE PROBLEM
 The premise behind the rationale isThe premise behind the rationale is
that, in our thinking and procedures,that, in our thinking and procedures,
we should separate the denture basewe should separate the denture base
from that which rests on the denturefrom that which rests on the denture
base - the body of the denture. Withbase - the body of the denture. With
the neutral zone approach, thethe neutral zone approach, the
impression surface is called the baseimpression surface is called the base
and the polished surface is called theand the polished surface is called the
'body' of the denture.'body' of the denture.

 Once the operator begins to think inOnce the operator begins to think in
terms of first creating a stable, baseterms of first creating a stable, base
and then placing on that base, teethand then placing on that base, teeth
and flange contours that will notand flange contours that will not
unseat the denture base, theunseat the denture base, the
problem and its solution becomeproblem and its solution become
apparent and comparatively simpleapparent and comparatively simple
to solve.to solve.

EFFECT OF VERTICAL ANDEFFECT OF VERTICAL AND
HORIZONTAL FORCESHORIZONTAL FORCES

 The borders of the dentureThe borders of the denture
 The body of the denture consists ofThe body of the denture consists of
the external or polished surface andthe external or polished surface and
the labial, buccal and lingual surfacesthe labial, buccal and lingual surfaces
of the teethof the teeth
The occlusal surfaces and incisal edgesThe occlusal surfaces and incisal edges
of the tooth on a dentureof the tooth on a denture

IDENTIFYING CAUSES OFIDENTIFYING CAUSES OF
INSTABILITYINSTABILITY

 First, an acrylic base is constructed,First, an acrylic base is constructed,

 If we now place on this stable baseIf we now place on this stable base
the body of the denture,the body of the denture,

 We now have an upper and lowerWe now have an upper and lower
base and body. If we instruct the‑base and body. If we instruct the‑
patient to bring the jaws togetherpatient to bring the jaws together
and the denture bases are dislodged,and the denture bases are dislodged,
it can only be caused by theit can only be caused by the
occlusion and the occlusion should beocclusion and the occlusion should be
corrected.corrected.

CLINICAL AND LABORATORYCLINICAL AND LABORATORY
PROCEDURESPROCEDURES

PRIMARY IMPRESSIONS ANDPRIMARY IMPRESSIONS AND
CONSTRUCTION OF ACRYLICCONSTRUCTION OF ACRYLIC
TRAYSTRAYS

SELECTION OF STOCK TRAYS

SHAPING THE TRAYS

Fingers
in
crisscross
position
& close
the lips
around
the
fingers,
seal off
the air, &
draw in
as if
sucking
through
a straw &
then
swallow

The
patient is
instructed
to seal off
the air by
closing
the lips
around
the
operator’s
finger &
to suck &
swallow
vigorously
.

CONSTRUCTION OF THECONSTRUCTION OF THE
ACRYLIC BASEACRYLIC BASE

CREATING STABLE BASESCREATING STABLE BASES

 Stability of base is tested by 2Stability of base is tested by 2
methodsmethods
 1 base in patient’s mouth &1 base in patient’s mouth &
operator’s fingers are placed onoperator’s fingers are placed on
bicuspid area to firmly seat the basebicuspid area to firmly seat the base
If squishing sound is heard as the baseIf squishing sound is heard as the base
is seated or eases up or pops upis seated or eases up or pops up

 2 ask the patient to open wide, purse2 ask the patient to open wide, purse
the lips as in sucking, wet the lips &the lips as in sucking, wet the lips &
speak normally if any unstabilityspeak normally if any unstability
observed by the operator or theobserved by the operator or the
patient himselfpatient himself

 Methods for locating areas ofMethods for locating areas of
overextension of the baseoverextension of the base
 visual observation or eyeballingvisual observation or eyeballing
 use of disclosing materialuse of disclosing material

visual observation or eyeballingvisual observation or eyeballing

use of disclosing materialuse of disclosing material

 Mandibular- 6 sectionsMandibular- 6 sections
1 labial or buccal1 labial or buccal
open widely several times, thenopen widely several times, then
purse the lips as in sucking, & thenpurse the lips as in sucking, & then
swallow vigorously base is removedswallow vigorously base is removed
and examined.and examined.
at least 1-2mm thickness ofat least 1-2mm thickness of
disclosing wax, smooth & roundeddisclosing wax, smooth & rounded
should be seen.should be seen.

 2 lingual2 lingual
swallow vigorously several times,swallow vigorously several times,
wet the lips with the tongue & andwet the lips with the tongue & and
count from 1 to 10count from 1 to 10

 Retromylohyoid fossaRetromylohyoid fossa
lingual to retromolarpad andlingual to retromolarpad and
posterior to mylohyoid ridge-posterior to mylohyoid ridge-
undercut areaundercut area

 Maxillary- 4 sections (excluding posteriorMaxillary- 4 sections (excluding posterior
border)border)
frequently under extended area infrequently under extended area in
maxillary base is around the tuberosity inmaxillary base is around the tuberosity in
the buccal space area.the buccal space area.
functional movements –opening wide,functional movements –opening wide,
pursing the lips as in sucking, bringing thepursing the lips as in sucking, bringing the
upper lip down, swallowing & moving theupper lip down, swallowing & moving the
upper jaw from side to side (thickness ofupper jaw from side to side (thickness of
flange over tuberosity to be sure that theflange over tuberosity to be sure that the
coronoid process of the mandible doesnotcoronoid process of the mandible doesnot
dislodge the upperbase.dislodge the upperbase.

Locating the posterior borderLocating the posterior border
 Posterior border should terminate atPosterior border should terminate at
the flexion line between the movablethe flexion line between the movable
& nonmovable tissue of the palate.& nonmovable tissue of the palate.
vibrating line/blowdown linevibrating line/blowdown line
3 marks should be made after drying3 marks should be made after drying
one on each hamular notch & third inone on each hamular notch & third in
the midline at flexion line.the midline at flexion line.

LOCATING THE NEUTRAL ZONELOCATING THE NEUTRAL ZONE
AND PLANE OF OCCLUSIONAND PLANE OF OCCLUSION
 Materials:Materials:
 Locating the neutral zone for theLocating the neutral zone for the
lower denture is one of the mostlower denture is one of the most
important factors in achievingimportant factors in achieving
stability of the lower denture. Tostability of the lower denture. To
locate the neutral zone and form thelocate the neutral zone and form the
body of the denture, if is necessarybody of the denture, if is necessary
to use materials that can be mouldedto use materials that can be moulded
by the horizontal forces of theby the horizontal forces of the
tongue, lips and cheeks.tongue, lips and cheeks.www.indiandentalacademy.comwww.indiandentalacademy.com

 Buchman, Gelb, Lott and Levin, andBuchman, Gelb, Lott and Levin, and
Russell have described the use ofRussell have described the use of
waxes in locating the neutral zone.waxes in locating the neutral zone.
 Kline of France has advocated theKline of France has advocated the
use of self curing acrylic to form ause of self curing acrylic to form a
'piezograph', which is his term for'piezograph', which is his term for
the registration of the neutral zone.the registration of the neutral zone.
 Health of England has, forHealth of England has, for
experimental purposes used a gelexperimental purposes used a gel
that is a polymer of dimethylthat is a polymer of dimethyl
silocane filled with 17% calciumsilocane filled with 17% calcium
silicate.silicate.

 TenchTench has suggested the use ofhas suggested the use of
modelling compound, whichmodelling compound, which hashas
worked well. Korr's low fusing grayworked well. Korr's low fusing gray
and green compound is best suitedand green compound is best suited
for this purpose. It permits thefor this purpose. It permits the
patient to mold the compound intopatient to mold the compound into
the neutral zone with the leastthe neutral zone with the least
amount of time and effort.amount of time and effort.

FOR THE LOWER ARCHFOR THE LOWER ARCH

ESTABLISHING THE 0CCLUSALESTABLISHING THE 0CCLUSAL
PLANEPLANE
 In the natural dentition, the lowerIn the natural dentition, the lower
occlusal plane runs from the incisalocclusal plane runs from the incisal
edges of the lower anterior teethedges of the lower anterior teeth
through the tips of the cusps of thethrough the tips of the cusps of the
posterior teeth to a pointposterior teeth to a point
approximately two thirds of theapproximately two thirds of the
height of the retromolar padheight of the retromolar pad

 To locate the occlusal plane, placeTo locate the occlusal plane, place
the rim back into the mouth and usethe rim back into the mouth and use
a sharp pointed pencil to mark thea sharp pointed pencil to mark the
commisures of the lip and the heightcommisures of the lip and the height
of the lower lip at rest. These threeof the lower lip at rest. These three
points are connected by a line that ispoints are connected by a line that is
continued on each side to a pointcontinued on each side to a point
one half to two thirds the height ofone half to two thirds the height of
the retromolar pad. The excessthe retromolar pad. The excess
compound is trimmed to this line.compound is trimmed to this line.

 To further check the correctness ofTo further check the correctness of
the height of the occlusal plane,the height of the occlusal plane,
observe its relationship to the lateralobserve its relationship to the lateral
borders of the tongue. With theborders of the tongue. With the
tongue at rest, the height of thetongue at rest, the height of the
occlusal plane should be 1 2 mm‑occlusal plane should be 1 2 mm‑
below the greatest convexity of thebelow the greatest convexity of the
lateral borders of the tongue. Iflateral borders of the tongue. If
necessary, the compound rim cannecessary, the compound rim can
be, modified by reduction orbe, modified by reduction or
addition.addition.

TESTING THE STABILITY OFTESTING THE STABILITY OF
THE LOWER OCCLUSION RIMTHE LOWER OCCLUSION RIM
 The lower occlusion rims is placedThe lower occlusion rims is placed
back into the patient’s mouth andback into the patient’s mouth and
checked for stability by having thechecked for stability by having the
patient open wide, wet the lips withpatient open wide, wet the lips with
the tongue, count from 1 to 100, andthe tongue, count from 1 to 100, and
say exaggerated "oh" "ahs" andsay exaggerated "oh" "ahs" and
"ees"."ees".

 The next procedure is to test theThe next procedure is to test the
outer edge of the rim with the tip ofouter edge of the rim with the tip of
the index finger in the bicuspid andthe index finger in the bicuspid and
incisor regions. If pressure on theincisor regions. If pressure on the
outer edges causes the opposite sideouter edges causes the opposite side
of the rim to lift up, then the rimof the rim to lift up, then the rim
must be narrowed from the labial ormust be narrowed from the labial or
buccal to where the vertical pressurebuccal to where the vertical pressure
will not cause the rim to tilt.will not cause the rim to tilt.

 This will occur where there has beenThis will occur where there has been
extensive ridge resorption and whereextensive ridge resorption and where
the residual ridge is narrowthe residual ridge is narrow
buccolingually and labio-lingually. Ifbuccolingually and labio-lingually. If
this is not corrected and the teeththis is not corrected and the teeth
placed at this position, then theplaced at this position, then the
vertical forces as in mastication willvertical forces as in mastication will
tilt the denture.tilt the denture.

 The final test is to have the patientThe final test is to have the patient
speak, swallow, wet the lips andspeak, swallow, wet the lips and
open wide without the rim moving oropen wide without the rim moving or
being dislodged. We have thereforebeing dislodged. We have therefore
created a tray or base that is notcreated a tray or base that is not
dislodged by muscle function anddislodged by muscle function and
have placed on it a body that is alsohave placed on it a body that is also
not displaced by muscle function.not displaced by muscle function.

FOR THE UPPER ARCHFOR THE UPPER ARCH
 The tray is firmly seated, and withThe tray is firmly seated, and with
the operator's fingers out of thethe operator's fingers out of the
mouth, the patient is instructed tomouth, the patient is instructed to
suck and swallow.suck and swallow.

 A line is scribed about 2 mm belowA line is scribed about 2 mm below
the upper lip at rest and thethe upper lip at rest and the
compound is trimmed to this line.compound is trimmed to this line.
The excess in the posterior is cutThe excess in the posterior is cut
away parallel to the ridge. The upperaway parallel to the ridge. The upper
rim is now tentatively completed andrim is now tentatively completed and
will be further modified whenwill be further modified when
determining vertical dimension anddetermining vertical dimension and
registering centric relation.registering centric relation.

VERTICAL DIMENSION:VERTICAL DIMENSION:

FINAL IMPRESSIONSFINAL IMPRESSIONS
 The advantage with the use of a closedThe advantage with the use of a closed
mouth technique are:mouth technique are:
A more accurate functional molding ofA more accurate functional molding of
the borders can be obtained, especially inthe borders can be obtained, especially in
the lower arch.the lower arch.
By having the patient to close gentlyBy having the patient to close gently
and swallow, there is more evenand swallow, there is more even
distribution of pressure and impressiondistribution of pressure and impression
material with less likelihood of excessivematerial with less likelihood of excessive
pressure in one area or another.pressure in one area or another.

 TECHNIQUE :TECHNIQUE :
 With the procedure to beWith the procedure to be
described, two impression pastes ofdescribed, two impression pastes of
contrasting colors are used. This iscontrasting colors are used. This is
called a color coded impression‑called a color coded impression‑
procedure, the purpose of which is toprocedure, the purpose of which is to
locate areas of tissue displacement.locate areas of tissue displacement.
The impression trays and the twoThe impression trays and the two
zinc oxide eugenol paste should be ofzinc oxide eugenol paste should be of
three different colors.three different colors.

LOWER SECONDARYLOWER SECONDARY
IMPRESSION:IMPRESSION:
 The material is mixed and placedThe material is mixed and placed
evenly over the lower tray and theevenly over the lower tray and the
tray is placed carefully in the mouth.tray is placed carefully in the mouth.
Slight pressure is applied with theSlight pressure is applied with the
forefingers in the bicuspid area untilforefingers in the bicuspid area until
the paste is seen to exude from thethe paste is seen to exude from the
tray around the peripheries.tray around the peripheries.

 The upper rim, which has been lubricated,The upper rim, which has been lubricated,
is placed into the mouth, and the patientis placed into the mouth, and the patient
is guided into a hinge closure andis guided into a hinge closure and
instructed not to exert any pressure afterinstructed not to exert any pressure after
light contact is made. After the initiallight contact is made. After the initial
contact, the patient is directed to swallowcontact, the patient is directed to swallow
and remain closed. In about 30 seconds,and remain closed. In about 30 seconds,
the patient is asked to open and wet thethe patient is asked to open and wet the
corners of the mouth with the tongue,corners of the mouth with the tongue,
purse the lips, such in as drawing throughpurse the lips, such in as drawing through
a straw and then close and swallow again.a straw and then close and swallow again.
At no time should excessive pressure beAt no time should excessive pressure be
applied.applied.

 When material has set, the lower rimWhen material has set, the lower rim
and tray are removed from theand tray are removed from the
mouth and inspected. If there aremouth and inspected. If there are
areas of the tray showing throughareas of the tray showing through
the impression material, it indicatesthe impression material, it indicates
areas of excessive pressure that willareas of excessive pressure that will
cause tissue displacement. Thesecause tissue displacement. These
areas are relieved to a minimumareas are relieved to a minimum
depth of 0.5 mm.depth of 0.5 mm.

 The impression material covering theThe impression material covering the
peripheris is cut away with a sharpperipheris is cut away with a sharp
knife to prevent excessive pressureknife to prevent excessive pressure
that will cause tissue displacement.that will cause tissue displacement.
These areas are relieved to aThese areas are relieved to a
minimum depth of 0.5 mm. Theminimum depth of 0.5 mm. The
impression material covering theimpression material covering the
peripheris is cut away with a sharpperipheris is cut away with a sharp
knife to prevent excessive build up ofknife to prevent excessive build up of
the borders, which would result inthe borders, which would result in
overextension when theoverextension when the
corrective impression is made.‑corrective impression is made.‑

 The tray is now ready for a secondThe tray is now ready for a second
impression. The material of choice isimpression. The material of choice is
Krex, which is white soft thin, freeKrex, which is white soft thin, free
flowing and of a contrasting color toflowing and of a contrasting color to
the zinc oxide eugenol used. Thethe zinc oxide eugenol used. The
Krex is mixed evenly and spreadKrex is mixed evenly and spread
over the entire tray and borders andover the entire tray and borders and
the procedure as mentioned before isthe procedure as mentioned before is
repeated. After it is set the tray isrepeated. After it is set the tray is
removed and the impression isremoved and the impression is
checked for defects.checked for defects.

Upper impression:Upper impression:
 Prior to the making of the upperPrior to the making of the upper
impression, several holes are drilledimpression, several holes are drilled
in the ruage area. The zinc oxidein the ruage area. The zinc oxide
impression paste is mixed and placedimpression paste is mixed and placed
over the trayover the tray and borders. The trayand borders. The tray
is carried into the mouth andis carried into the mouth and
centered over the ridges.centered over the ridges.

 The anterior part of the tray isThe anterior part of the tray is
seated with a light pressure toseated with a light pressure to
position it properly. With the foreposition it properly. With the fore
finger applying pressure in the molarfinger applying pressure in the molar
area, the posterior part is seatedarea, the posterior part is seated
until the material starts to flow outuntil the material starts to flow out
from the posterior border.from the posterior border.

 The completed lower impression isThe completed lower impression is
inserted into the mouth and theinserted into the mouth and the
patient is guided into a hingepatient is guided into a hinge
closure, avoiding excessive pressure.closure, avoiding excessive pressure.
The patient is instructed to swallowThe patient is instructed to swallow
and remain closed. In 30 secondsand remain closed. In 30 seconds
the patient is directed to open thethe patient is directed to open the
mouth, move the jaw from side tomouth, move the jaw from side to
side, purse the lips as in sucking,side, purse the lips as in sucking,
bring the upper lip down hard, and‑bring the upper lip down hard, and‑
then swallows and close withoutthen swallows and close without
pressure‑pressure‑

 . When the material has set the tray. When the material has set the tray
is removed and the impression isis removed and the impression is
inspected for pressure areas.inspected for pressure areas.
 If pressure areas are present,If pressure areas are present,
Krex is used for correctiveKrex is used for corrective
impression and the above procedureimpression and the above procedure
is carried out to get a correctedis carried out to get a corrected
impression.impression.

Centric relationCentric relation
 The centric relation is recorded withThe centric relation is recorded with
the same completed final impressionthe same completed final impression
trays and compound rims.trays and compound rims.
 After the vertical relation isAfter the vertical relation is
rechecked and corrected for anyrechecked and corrected for any
changes occuring after the finalchanges occuring after the final
impression making the centricimpression making the centric
relation is recorded by the check biterelation is recorded by the check bite
procedure or the nick and notchprocedure or the nick and notch
method.method.

 After the centric relation is recordedAfter the centric relation is recorded
a facebow recording is made. Aftera facebow recording is made. After
this the facebow assemblage, upperthis the facebow assemblage, upper
and lower final impressions, andand lower final impressions, and
occlusion rims are now ready to beocclusion rims are now ready to be
sent to the laboratory.sent to the laboratory.

LABORATORY PROCEDURESLABORATORY PROCEDURES

FABRICATION OF TONGUE, LIPFABRICATION OF TONGUE, LIP
AND CHEEK MATRICESAND CHEEK MATRICES

SELECTION ANDSELECTION AND
ARRANGEMENT OF ANTERIORARRANGEMENT OF ANTERIOR
TEETHTEETH
 The neutral zone developed by eachThe neutral zone developed by each
individual patient is usually not aindividual patient is usually not a
narrow restricted area and thereforenarrow restricted area and therefore
permits some latitude for positioningpermits some latitude for positioning
of the anterior teeth to obtainof the anterior teeth to obtain
adequate lip support for optimumadequate lip support for optimum
facial appearance.facial appearance.

 This is especially true, with theThis is especially true, with the
upper neutral zone, since it is notupper neutral zone, since it is not
nearly as critical for denture stabilitynearly as critical for denture stability
as is the lower neutral zone.as is the lower neutral zone.
 After the shade, shape, size andAfter the shade, shape, size and
tooth material are selected thetooth material are selected the
arrangement of the anterior teetharrangement of the anterior teeth
are done.are done.

SELECTION AND POSITIONINGSELECTION AND POSITIONING
OF POSTERIOR TEETHOF POSTERIOR TEETH
 With the neutral zone concept, eitherWith the neutral zone concept, either
anatomic or non anatomic forms cananatomic or non anatomic forms can
be used. The neutral zone onlybe used. The neutral zone only
indicates the labiolingual orindicates the labiolingual or
buccolingual position of the teeth.buccolingual position of the teeth.
The occlusal forms of the teeth to beThe occlusal forms of the teeth to be
used are essentially the operator'sused are essentially the operator's
choice.choice.

 After selection of the proper size,After selection of the proper size,
occlusal morphology and material ofocclusal morphology and material of
the posterior teeth to be used, we gothe posterior teeth to be used, we go
in for the positioning or arrangementin for the positioning or arrangement
of teeth. The following is a step byof teeth. The following is a step by
step sequence for arrangement ofstep sequence for arrangement of
anterior and posterior teethanterior and posterior teeth
 The lower anterior teeth are set toThe lower anterior teeth are set to
the height of the labial matrix and tothe height of the labial matrix and to
the labial limit of the neutral zone.the labial limit of the neutral zone.

 The upper anterior teeth are setThe upper anterior teeth are set
against the labial limits of the upperagainst the labial limits of the upper
matrix.matrix.
 The lower posterior teeth are setThe lower posterior teeth are set
against the tongue matrix and‑against the tongue matrix and‑
against the template occlusally.against the template occlusally.
 The upper posterior teeth are set, toThe upper posterior teeth are set, to
the buccal limits of the neutral zone.the buccal limits of the neutral zone.

 The matrices are removed, and theThe matrices are removed, and the
upper bow of the articulator is closedupper bow of the articulator is closed
in order to evaluate the relationshipin order to evaluate the relationship
of the upper and lower posteriorof the upper and lower posterior
teeth.teeth.
 The upper posterior teeth will haveThe upper posterior teeth will have
to be rearranged to assure maximumto be rearranged to assure maximum
contact with the lower posteriorcontact with the lower posterior
teeth.teeth.

 The upper and lower posterior teethThe upper and lower posterior teeth
are checked for the buccal andare checked for the buccal and
lingual relationship to each other.lingual relationship to each other.
 In order to avoid an edge to edgeIn order to avoid an edge to edge
relationship which might lead torelationship which might lead to
check biting, the lower posteriorcheck biting, the lower posterior
teeth may be moved buccally withinteeth may be moved buccally within
the neutral zone, resulting in athe neutral zone, resulting in a
cross bite relationship.‑cross bite relationship.‑

THE TRIAL DENTURETHE TRIAL DENTURE
 The purpose of the trial denture is toThe purpose of the trial denture is to
check thecheck the following.following.
 Stability and retention of the basesStability and retention of the bases
 Vertical dimensionVertical dimension
 PhoneticsPhonetics
 Centric relationCentric relation
 EstheticsEsthetics

PREPARATION OF THE TRIALPREPARATION OF THE TRIAL
DENTURE FOR INVESTINGDENTURE FOR INVESTING
 The laboratory procedures forThe laboratory procedures for
investing, packing and processing ofinvesting, packing and processing of
dentures when using the neutraldentures when using the neutral
zone technique is generally the samezone technique is generally the same
as for conventional dentures.as for conventional dentures.
However, because of the materialsHowever, because of the materials
used for the external impressions, itused for the external impressions, it
is necessary to be especially carefulis necessary to be especially careful
in some of the procedures.in some of the procedures.

 Great care must be taken to be sureGreat care must be taken to be sure
that none of the external impressionthat none of the external impression
material has flowed under the basesmaterial has flowed under the bases
of the trial denture.of the trial denture.
 When zinc oxide eugenol paste hasWhen zinc oxide eugenol paste has
been used for the externalbeen used for the external
impression, the flasks should not beimpression, the flasks should not be
allowed to remain in the boil out tank‑allowed to remain in the boil out tank‑
for more than 5 minutes, becausefor more than 5 minutes, because
the zinc oxide eugenol paste willthe zinc oxide eugenol paste will
liquefy and attack the stone,liquefy and attack the stone,
resulting in a bleached appearance toresulting in a bleached appearance to
the processed acrylic.the processed acrylic.

 After processing the dentures areAfter processing the dentures are
remount on the articulator. Occlusalremount on the articulator. Occlusal
discrepancies are checked for withdiscrepancies are checked for with
the template and carbon paper. Theythe template and carbon paper. They
are corrected, the dentures areare corrected, the dentures are
finished, polished and insertion isfinished, polished and insertion is
done.done.

 A clinical remounting is done and theA clinical remounting is done and the
dentures are inserted and checkeddentures are inserted and checked
for any discrepancies. The patient isfor any discrepancies. The patient is
given post insertion instructionsgiven post insertion instructions
which are similar to that ofwhich are similar to that of
conventional complete dentures.conventional complete dentures.

CONCLUSIONCONCLUSION
 In summary, the neutral zoneIn summary, the neutral zone
philosophy is based on the concept‑philosophy is based on the concept‑
exists within, the denture space, aexists within, the denture space, a
denture, and at the same time wheredenture, and at the same time where
the forces generated by the tonguethe forces generated by the tongue
are neutralized by the forcesare neutralized by the forces
generated by the lips arid cheeks.generated by the lips arid cheeks.

 Furthermore, denture stability is asFurthermore, denture stability is as
much or more influenced by toothmuch or more influenced by tooth
position and flange contour as to anyposition and flange contour as to any
other factor.other factor.
 In other words, we should not beIn other words, we should not be
dogmatic and insist that the teethdogmatic and insist that the teeth
should always be placed over theshould always be placed over the
crest of the ridge,or lingual to thecrest of the ridge,or lingual to the
ridge or buccal to the ridge!ridge or buccal to the ridge!
Placement of the teeth should bePlacement of the teeth should be
dictated by the musculature and willdictated by the musculature and will
vary forvary for different patients.different patients.

REFERENCESREFERENCES
 Beresin VE, Schiesser FJ.Beresin VE, Schiesser FJ. The neutralThe neutral
zone in complete dentureszone in complete dentures.. J ProsthetJ Prosthet
Dent. 1976 Oct;36(4):35667.Dent. 1976 Oct;36(4):35667.
Neutral zone approach for dentureNeutral zone approach for denture
fabrication for a partial glossectomyfabrication for a partial glossectomy
patient: a clinical report.patient: a clinical report. :: J Prosthet Dent.J Prosthet Dent.
2000 Oct;84(4):39032000 Oct;84(4):3903
 Bocage M, Lehrhaupt J.Bocage M, Lehrhaupt J. Lingual flangeLingual flange
design in complete denturesdesign in complete dentures. :. : J ProsthetJ Prosthet
Dent. 1977 May;37(5):499506Dent. 1977 May;37(5):499506

 Walsh JF, Walsh T.Walsh JF, Walsh T. MuscleformedMuscleformed
complete mandibular denturescomplete mandibular dentures. :. : JJ
Prosthet Dent. 1976 Mar;35(3):2548.Prosthet Dent. 1976 Mar;35(3):2548.

Orstavik JS, Floystrand F.Orstavik JS, Floystrand F. Retention ofRetention of
complete maxillary dentures related tocomplete maxillary dentures related to
soft tissue function . Acta Odontol Scand.soft tissue function . Acta Odontol Scand.
1984 Oct;42(5):31320.1984 Oct;42(5):31320.
 Niedermeier W, Hofmann M.Niedermeier W, Hofmann M. The effectThe effect
of the arrangement of the artificial sets ofof the arrangement of the artificial sets of
teeth on the physical stability of totalteeth on the physical stability of total
prothesesprotheses .. Dtsch Zahnarztl Z. 1979Dtsch Zahnarztl Z. 1979
Aug;34(8):6168.Aug;34(8):6168.

 Demirel F, Oktemer M.Demirel F, Oktemer M. The relationsThe relations
between alveolar ridge and the teethbetween alveolar ridge and the teeth
located in neutral zone.located in neutral zone. :: J Marmara UnivJ Marmara Univ
Dent Fac. 1996 Sep;2(23):5626.Dent Fac. 1996 Sep;2(23):5626.

Suenaga K, Sato T, Nishigawa G,Suenaga K, Sato T, Nishigawa G,
Minagi SMinagi S. Relationship between size of. Relationship between size of
denture foundation area and resorption ofdenture foundation area and resorption of
alveolar ridge in the edentulousalveolar ridge in the edentulous
mandible.mandible. :: J Oral Rehabil. 1997J Oral Rehabil. 1997
Apr;24(4):3159.Apr;24(4):3159.
 www.indiandentalacademy.comwww.indiandentalacademy.com

 Khamis M, Razek A, Abdalla F.Khamis M, Razek A, Abdalla F.
Twodimensional study of the neutralTwodimensional study of the neutral
zone at different occlusal verticalzone at different occlusal vertical
heightsheights.. J Prosthet Dent. 1981J Prosthet Dent. 1981
Nov;46(5):4849.Nov;46(5):4849.

Alfano SG, Leupold RJ.Alfano SG, Leupold RJ. Using theUsing the
neutral zone to obtainneutral zone to obtain
maxillomandibular relationshipmaxillomandibular relationship
records for complete denturerecords for complete denture
patientspatients. :. : J Prosthet Dent. 2001J Prosthet Dent. 2001
Jun;85(6):6213.Jun;85(6):6213.

REVIEW OF LITERATUREREVIEW OF LITERATURE
 Beresin VE, Schiesser FJBeresin VE, Schiesser FJ. In 1976. In 1976
concluded that the neutralzoneconcluded that the neutralzone
philosophy is based upon the conceptphilosophy is based upon the concept
exists within the denture space aexists within the denture space a
denture and where forces generateddenture and where forces generated
by the tongue are neutralized by theby the tongue are neutralized by the
forces generated by the lips andforces generated by the lips and
cheeks.cheeks.

 Walsh JF, Walsh T.Walsh JF, Walsh T. in 1976in 1976
presented a method whereby apresented a method whereby a
patient's musculature is used topatient's musculature is used to
indicate the position of the teeth andindicate the position of the teeth and
to develop the shape and thicknessto develop the shape and thickness
of the denture base. Of 30 patientsof the denture base. Of 30 patients
tested, 28 experienced improvedtested, 28 experienced improved
stability of their lower dentures.stability of their lower dentures.

 Bocage M, Lehrhaupt J.Bocage M, Lehrhaupt J. in 1977in 1977
concluded that the lingual designconcluded that the lingual design
advocated for complete lower denturesadvocated for complete lower dentures
involves no changes in current conceptsinvolves no changes in current concepts
regarding minimumpressure, functionalregarding minimumpressure, functional
impression techniques. The sublingualimpression techniques. The sublingual
horizontal extension suggested is placed inhorizontal extension suggested is placed in
a biologically acceptable fashion bya biologically acceptable fashion by
increasing the area of the denture, whichincreasing the area of the denture, which
enhances retention and stability.enhances retention and stability.

 Niedermeier W, Hofmann M.Niedermeier W, Hofmann M. inin
1979 demonstrated the effect of1979 demonstrated the effect of
masticatory forces within and outsidemasticatory forces within and outside
the stable stressbearing areas of thethe stable stressbearing areas of the
complete upper denture on thecomplete upper denture on the
pressure gradient and the flow ofpressure gradient and the flow of
saliva into the space under thesaliva into the space under the
prosthesis and showed thatprosthesis and showed that
masticatory stress within the stablemasticatory stress within the stable
area led to aarea led to a

 continual increase in pressure in the spacecontinual increase in pressure in the space
under the prosthesis. Masticatory forceunder the prosthesis. Masticatory force
outside the stable area led to a decreaseoutside the stable area led to a decrease
in pressure and an equalization ofin pressure and an equalization of
pressure in this space as well aspressure in this space as well as
dislocation and tilting of the completedislocation and tilting of the complete
denture. Due to masticatory force outsidedenture. Due to masticatory force outside
the stable area, the shape of the ridgethe stable area, the shape of the ridge
influences the stability of the completeinfluences the stability of the complete
denture.denture.

 Khamis M, Razek A, Abdalla F.Khamis M, Razek A, Abdalla F. inin
1981 developed a new technique to1981 developed a new technique to
locate the neutral zone. The neutrallocate the neutral zone. The neutral
zone was studied on two groups ofzone was studied on two groups of
patients with prominent or flatpatients with prominent or flat
residual alveolar ridges. The neutralresidual alveolar ridges. The neutral
zone was determined for eachzone was determined for each
patient at three vertical heights. Itpatient at three vertical heights. It
was studied both vertically andwas studied both vertically and
horizontallyhorizontally

 The width of the neutral zone wasThe width of the neutral zone was
measured at different regions with thesemeasured at different regions with these
conclusions: 1. The width of the neutralconclusions: 1. The width of the neutral
zone is minimum at the level of thezone is minimum at the level of the
occlusal plane and increases gradually asocclusal plane and increases gradually as
it goes up and down. 2. The width of theit goes up and down. 2. The width of the
neutral zone is also minimum at theneutral zone is also minimum at the
posterior (molar) region and increasesposterior (molar) region and increases
gradually toward the anterior.gradually toward the anterior.

 3. There is no significant difference3. There is no significant difference
in the width of the neutral zone inin the width of the neutral zone in
patients with prominent or flatpatients with prominent or flat
alveolar ridges. 4. The width of thealveolar ridges. 4. The width of the
neutral zone increases as the verticalneutral zone increases as the vertical
dimension of occlusion increases anddimension of occlusion increases and
decreases as the vertical dimensiondecreases as the vertical dimension
of occlusion decreases.of occlusion decreases.

 Orstavik JS, Floystrand F.Orstavik JS, Floystrand F. in 1984in 1984
investigated the influence of freeinvestigated the influence of free
tongue, lip, and cheek function ontongue, lip, and cheek function on
the retention of complete maxillarythe retention of complete maxillary
dentures. Test dentures weredentures. Test dentures were
designed with full palatal coveragedesigned with full palatal coverage
and functionally determined filling inand functionally determined filling in
of the vestibular sulcus.of the vestibular sulcus.

 The front teeth were arrangedThe front teeth were arranged
primarily to meet cosmeticprimarily to meet cosmetic
demandsthat is, anterior to the topdemandsthat is, anterior to the top
of the residual alveolar ridge.of the residual alveolar ridge.
Retention was measured asRetention was measured as
resistance to dislodgementresistance to dislodgement
provoking loads applied vertically toprovoking loads applied vertically to
the incisive edge of the centralthe incisive edge of the central
incisors, using a miniature bite forceincisors, using a miniature bite force
recorder.recorder. www.indiandentalacademy.comwww.indiandentalacademy.com

 All the participants were able to load theirAll the participants were able to load their
front teeth with 35 N or more without lossfront teeth with 35 N or more without loss
of retention. None of them experiencedof retention. None of them experienced
denture dislodgement provided thedenture dislodgement provided the
tongue, lips, and cheeks wee allowed totongue, lips, and cheeks wee allowed to
act freely. If the peripheral soft tissuesact freely. If the peripheral soft tissues
were separated from the vestibularwere separated from the vestibular
denture flange, no obvious effect ondenture flange, no obvious effect on
denture retention could be detected.denture retention could be detected.
Physically preventing the tongue fromPhysically preventing the tongue from
pressing against the posterior part of thepressing against the posterior part of the
denture reduced the retentiondenture reduced the retention
significantly.significantly.

 Measurements of anterior loadsMeasurements of anterior loads
tolerated after stepwise reductions oftolerated after stepwise reductions of
the denture extension indicated thatthe denture extension indicated that
the tongue acted primarily bythe tongue acted primarily by
pressure against the tuber regions.pressure against the tuber regions.
Tongue pressure against the centralTongue pressure against the central
parts of the palate and lip or cheekparts of the palate and lip or cheek
pressure against the vestibularpressure against the vestibular
flange seemed to be of lessflange seemed to be of less
importance.importance.

 Demirel F, Oktemer M.Demirel F, Oktemer M. in 1996 definedin 1996 defined
the neutral zone as the area where thethe neutral zone as the area where the
forces of the tongue pressing outward areforces of the tongue pressing outward are
neutralized by the forces of the cheeksneutralized by the forces of the cheeks
and lips pressing inward. In this studyand lips pressing inward. In this study
records of neutral zones of 30 edentulousrecords of neutral zones of 30 edentulous
patients were used to establish thepatients were used to establish the
relation between teeth arrangementrelation between teeth arrangement
according to neutral zone principles andaccording to neutral zone principles and
teeth arrangement according to crest ofteeth arrangement according to crest of
ridge.ridge.

 These 30 patients were classifiedThese 30 patients were classified
according to their ages, edentulousaccording to their ages, edentulous
periods and denture experience. Theperiods and denture experience. The
results have shown that the lower molarsresults have shown that the lower molars
were positioned a little bit closer to lingualwere positioned a little bit closer to lingual
with respect to crest of ridge; premolarswith respect to crest of ridge; premolars
were positioned either close to crest ofwere positioned either close to crest of
ridge or they were coincided on it. In theridge or they were coincided on it. In the
anterior zone, the teeth were inanterior zone, the teeth were in
accordance with known principles ofaccordance with known principles of
positioned of anatomic landmarks.positioned of anatomic landmarks.

 Suenaga K, Sato T, Nishigawa G,Suenaga K, Sato T, Nishigawa G,
Minagi S.Minagi S. in 1997 investigated thein 1997 investigated the
relationship between the size of therelationship between the size of the
denture foundation area and thedenture foundation area and the
resorption of the alveolar ridge. Theresorption of the alveolar ridge. The
denture foundation area wasdenture foundation area was
recorded using a modellingrecorded using a modelling
compound impression technique withcompound impression technique with
border moulding.border moulding.

 Both sides of each edentulousBoth sides of each edentulous
mandible were examined separately,mandible were examined separately,
making a total of 110 experimentalmaking a total of 110 experimental
sides in the study. On a stone castsides in the study. On a stone cast
made from each impression, the sizemade from each impression, the size
of of the superficial dentureof of the superficial denture
foundation area and of the projectedfoundation area and of the projected
denture foundation area on thedenture foundation area on the
tentative plane of occlusion of eachtentative plane of occlusion of each
anatomical zone were measured.anatomical zone were measured.

 The vertical height of the alveolar ridge atThe vertical height of the alveolar ridge at
the lateral incisor and first molar regionthe lateral incisor and first molar region
was also evaluated. The size of thewas also evaluated. The size of the
superficial denture foundation area in thesuperficial denture foundation area in the
anterolingual and posterolingual zonesanterolingual and posterolingual zones
showed no significant correlation with theshowed no significant correlation with the
degree of alveolar ridge resorption. Thedegree of alveolar ridge resorption. The
size of the projected denture foundationsize of the projected denture foundation
area on the tentative plane of occlusion inarea on the tentative plane of occlusion in
the anterior section showed negativethe anterior section showed negative
significant correlation with the degree ofsignificant correlation with the degree of
alveolar ridge resorption.alveolar ridge resorption.

 Alfano SG, Leupold RJ.Alfano SG, Leupold RJ. In 2001In 2001
presented a technique for obtainingpresented a technique for obtaining
maxillomandibular registration formaxillomandibular registration for
complete denture patients.. Thecomplete denture patients.. The
maxillary rim is formed with the usemaxillary rim is formed with the use
of conventional techniques. Theof conventional techniques. The
mandibular rim is made frommandibular rim is made from
modeling plastic impressionmodeling plastic impression
compound on a record base formedcompound on a record base formed
by the patient into the neutral zone.by the patient into the neutral zone.

Neutral Zone Dentistry: Understanding the Stable Position of Teeth

Neutral Zone Dentistry: Understanding the Stable Position of Teeth

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Neutral Zone Dentistry: Understanding the Stable Position of Teeth