Neutral Zone In Prosthodontics part 1.ppt

Neutral zone technique in prosthodontics

1. 1
Neutral Zone In
Prosthodontics
By -Dr Vipinder Dalal

2. 2
Content
1. Introduction
2.Development and neutral zone
3.Neutral zone and denture space
4.Factor affecting the neutral zone
5.Determination of neutral zone
6.Clinical and laboratory procedures
7.The neutral zone as applied to
partial denture and overdentures
8.Conclusion
9.Bibliography

3. 3
Introduction
Iftheteetharelostdespiteallefforts
to
savethem,arestorationshouldbe
madeinsuchamannerasto
functionefficientlyandcomfortably
inharmonywiththemusclesof
stomatognathic systemandthe
tempromandibularjoints.

4. 4
In the discipline of prosthodontics
(expect in fixed prosthodontics and
implants as they get guidance from
adjacent teeth), removal appliances
(dentures, partial dentures,
maxillofacial prosthetics) are
mechanical devices and subjected to
principles of physics that is inclined
plane and lever .

5. 5
So, any removableprosthetic appliances which are
inserted into oral cavity needs position of
equilibrium during normal function , forces of
tongue (internal musculature) pressing outward
are neutralized by the forces of cheek and lips
pressing inwards.
This position of equilibrium is other named as
neutral zone and defined as-the potential space
between the lips and the cheeks on one side and
tongue on the other side ;that area or position
where forces between the tongue and cheeks and
lips are equal.
So the design of appliances should be fashioned
to work in harmony with all these muscles
actions which are commonly like swallowing
,speech and mastication etc .

6. 6
Neutral Zone
The potential space between the lips
and the cheeks on one side and
tongue on the other; that area or
position where the forces between
the tongue and cheeks or the lips are
equal.
GPT 9

7. 7
Development And Neutral zone
As each tooth erupts into position with in
its respective arch ,it is guided into narrow
zone located between horizontally directed
forces.
The outward pressure of the tongue
versus the inward pressure of the perioral
pressure musculature defines the neutral
zone.
The neutral zone determines the position
of each tooth and establishes the
dimensions of the each arch ,including the
shape and position of the alveolar
processes .

8. 9
The buccinator is a flat ,thin muscle
composed of three bands.
UPPER BAND
MIDDLE BAND
LOWER BAND

9. 10
The combined width of the three bands
covers the entire outer surface of the
dentoalveolar structures, that is the teeth,
alveolar process and gingival tissues.

10. 11
The effects of neutral zone confinement on
the dentoalveolar can also play a critical
role as a determinant of facial profile.
A restrictive perioral musculature may
prevent the dentoalveolar arches from
expanding to normal alignment with
skeletal base.
Mandibular skeletal growth may extend
the chin point forward while the dental
arches are restricted by the band of
muscles that prevent them from growing
commensurately with their skeletal base

11. 12
Variation in length and strength of the
three bands of the buccinator can further
affect the profile by controlling the axial
inclination of the anterior teeth ,especially
when combined with the variations of the
tongue size and pressure.

12. 13
A series of statements may give
perspective to an evaluation of neutral
zone considerations:
1. The teeth and their alveolar process are
the most adaptive part of the masticatory
system. They can be moved horizontally
or vertically light forces.
2. There is a neutral zone within which
muscular pressure against the dentition is
equalized from opposite directions .The
entire arch form falls within that zone of
neutral pressure.

13. 14
3. If irregularities of tooth position ,
alignment ,or contour can be corrected
within the neutral zone ,the prognosis for
long –term stability is good.
4.A problem occurs when the neutral zone
is not where we want the teeth to be.
5.A treatment decision then must allow
determination of if and how we can
change the neutral zone to orient it where
we want the teeth to be.

14. 15
Relating Malocclusion To The
Neutral Zone
The high-vaulted ,constricted maxillary
arch is a good illustration of aberrant
pressures relate to the configuration of the
dentoalveolar arches.
In the case of a patient with a high ,
narrow vault the maxillary arch is
squeezed inwardly by buccinator muscle
pressure that is unopposed by outward
tongue pressure .

15. 16
The reason for the lack of
outward tongue pressure
against the posterior arch
segments is a forward
tongue posture that
possibly developed as the
effect of inadequate
airway space.
With enlarged tonsils or
adenoids, there is no
room for the posterior
width of the tongue in its
normal position , and so
it must be postured
forward to provide an
airway.

16. 17
The forward tongue posture causes
two effects
1. It pushes the anterior teeth
forward
2.It evacuates its normal space up
in the vault , thus eliminating the
outward tongue pressure as
resistance to buccinator pressure
against the posterior teeth.

17. 18
One can correct both the narrow arch and the
anterior disharmony by changing the neutral zone
orthodontically.
Expansion of the dentoalveolar arch width at the
posterior segments creates room for the tongue to
fit up into the vault where it can direct outward
pressure against the posterior teeth to resist the
inward buccinator pressure

18. 19
As the posterior arch width is expanded,
the perioral band of muscle pulls back on
the anterior teeth thus allowing for
correction of the pointed protrusion in the
anterior segment.

19. 20
Neutral Zone And Denture Space
When all of the remaining natural teeth
are removed , there exits within the oral
cavity , void that may be called the
potential denture space.
JPD ;1976,2006

20. 21
The denture space is bounded by the
ABOVE-Maxilla and soft palate
BELOW-Mandible and floor of the
mouth
MEDIALLY-Tongue
And
EXTERNALLY-Muscles and tissue of
the lips and cheeks
Within the denture space there is an area
that has been termed the neutral zone

21. 22
The Neutral Zone is that area in the
mouth where ,during function ,the forces
of the tongue pressing outward are
neutralized by the forces of cheeks and
lips pressing inward.
The way these forces are directed against the
dentures will either help to stabilize them or will
tend to dislodge them.
These soft tissues that form the internal and
external boundaries of denture space greatly
affect and influence the stability of the dentures
and help to determine the peripheral borders
,tooth position and external contours of the
dentures

22. 23
Factors Affecting The Neutral Zone
Muscle and neutral zone
Muscle influence on development of
neutral zone
Denture surfaces and neutral zone
Direction of forces
Neutralization of forces.

23. 24
Muscle and Neutral zone
The muscle attachments and their
positions and tonus influence the border
extensions of the denture.
However ,it is the function or action of the
muscles that influences the shape and size
of neutral zone and therefore the position
teeth and flange contours.
In recent years more and more
prothodontists have recognized the
importance of these concepts.

24. 25
Boucher(1975) Stated
Formerly all teeth were placed (over the
ridge). this was done for mechanical
reasons when leverage was the big
concern.
Now , teeth are being placed in Neutral
Zonewhich in fact the zone previously
occupied by the natural teeth.
Leverage is not ignored, but a lack of
favorable leverage is counter balanced by
the controlling action of cheeks, lips and
tongue that confine the dentures.

25. 26
Thus the same forces that helped the
position the natural teeth in the
dental arches can help to maintain
the artificial teeth in their in places.
Dentures should occupy a position in
the mouth where all the forces
during function are neutralized.
Otherwise , denture stability will be
decreased proportionately to the
difference in the amount of opposing
forces.

26. 27
Muscles of the cheek
The outer limits of the neutral
zone are determined by perioral
musculature.
. Masseter
The masseter muscle has no
influence on the neutral zone.
Over extension in this area will
cause either irritation and soreness or
dislodgement of the denture

27. 28
Buccinator
The main determinant of length , strength
and position of the perioral musculature is
the buccinator muscle.
The buccinator is thin ,flat muscle
composed of three bands.
During mastication ,the buccinator helps
to place the food over the occlusal
surfaces of the teeth in coordination with
the tongue , which positions the food over
the teeth from the lingual.

28. 29
The common practice of centralization or
lingualization of occlusion, prevents buccinator
from performing its proper function in two ways.
1. Lingualization of occlusion creates a space
between the teeth and external surface of the
denture .Food tends to accumulate in this space
and it becomes more difficult for the cheek to
place food back onto the occlusal surfaces of the
teeth.
2. The space resulting from lingualization prevents
buccinator from neutralizing the lateral forces of
the tongue during function .

29. 30
Orbicularis Oris
It exerts force against the teeth and denture
flanges which is counteracted by the tongue.
The orbicularis oris muscle and its attaching
muscles are important in denture construction in
as much as the various contributing muscles
have bony origins and their insertions are into
the modioli and orbicularis oris muscle at the
corners of the mouth.
Thus the functioning length of all these muscles
depend on the function of orbicularis oris.The
muscles that merge into the orbicularis oris are
the zygomaticus ,the quadratus labii superioris,
the caninus(levator angulioris) ,the
mentalis,buccinator,risorious and triangularis

30. 31
Three factor affect the face in
repositioning the orbicularis oris with
complete denture :
1.The thickness of the labial flanges of both
dentures
2. The anteroposterior position of the
anterior teeth
3. The amount of separation between the
mandible and the maxillae.

31. 32
Caninus(levator Anguli Oris)Muscle
It passes from below the infraorbital foramen
through the modiolus into the lower lip. This
muscle, together with other muscles, pulls the
lower lip up and in sucking and swallowing helps
to pull the lips forward, thus exerting forces on
the teeth and labial denture flange.
Risorius
Muscle inserts into the angle of mouth and retract
the corners of mouth.
Mentalis arises from incisive fossa. It turns the
lower lip outward and in contracting makes the
lower labial vestibule shallow

32. 33
Modiolus
It is located just distal
to the angle of mouth.
If the thumb is placed
inside the corner of the
mouth and the finger
outside on the
prominence ,and then
the lip and cheek are
contracted , the
modiolus feel like a
knot

33. 34
The modiolus becomes fixed every time the
buccinator muscle contracts , which is a natural
accompaniment of all chewing efforts.
The contraction of the modiolus presses the
corner of mouth against the premolars so the
occlusal table is closed in front.
Food is crushed by the premolars and molars and
does not escape the corners of the mouth unless
7
th
nerve damage has occurred
So , unless the teeth and external surface of the
denture are properly positioned and contoured by
narrowing in premolar area , the modiolus may
constantly unseat the lower denture.

34. 35
Muscle Forces In The Dental Arch
Teeth erupt into the mouth under the
influence of muscular environment.
This environment which is created by the
forces between the tongue , cheeks and
lips has a definite influence on the position
of the erupting teeth ,the resultant arch
form and occlusion.
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.

35. 36
It is , therefore , extremely
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.
This can only be accomplished through
awareness of the Neutral Zoneand by
positioning the teeth and developing the
external surfaces of the denture so that all
forces exerted are neutralized and the
denture is in a state of equilibrium.

36. 37
Denture Surfaces
The dental profession has 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 importance of
the horizontal forces exerted on the
external surfaces of the dentures
Thus ,the dental profession has been
concerned , in the main two surfaces –the
occlusal surfaces and the impression
surfaces

37. 38
Sir Wilford Fish described a denture as
having three surfaces ,with each surface
playing an independent and important role
in the over-all fit ,stability and comfort of
the denture.
JPD1976
The third surface-as termed by Fish,”the
polished the surface”-is the rest of
denture that is not part of the other two
surfaces.
It is mostly denture base material, but it
also consist of those surfaces of the teeth
that are not contacting or articulating
surfaces

38. 39
Influence Of Force On Denture
Surfaces
The greater the ridge loss, the smaller the
denture base area and less influence the
impression area will have on the stability and
retention of the denture.
As the area of the impression surface decreases
and the polished surface area increases , tooth
position and contour of the polished surface
become more critical.
The forces exerted on the external surfaces of the
teeth and the polished surfaces are essentially
horizontal.

39. 40
If teeth are not in contact ,the stability of
the denture is determined by the
impression surface and the direction and
magnitude of forces transmitted through
the polished surfaces
In order to construct dentures which
function properly in chewing ,swallowing
etc., we must develop not only proper
tooth position but also the fit and contour
of the impression and occlusal surfaces.

40. 41