Stability in complete denture / dental implant courses by Indian dental academy

STABILITYSTABILITY
ININ
COMPLETE DENTURESCOMPLETE DENTURES
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.comwww.indiandentalacademy.com

CONTENTSCONTENTS
 IntroductionIntroduction
 DefinitionDefinition
 HistoryHistory
 Review of LiteratureReview of Literature
 Factors affecting StabilityFactors affecting Stability
 Relationship of denture base to underlying tissuesRelationship of denture base to underlying tissues
 Relationship of external surface and periphery toRelationship of external surface and periphery to
surrounding orofacial musculaturesurrounding orofacial musculature
 Relationship of opposing occlusal surfacesRelationship of opposing occlusal surfaces
 Summary and ConclusionSummary and Conclusion
ReferencesReferences

INTRODUCTIONINTRODUCTION

Biological Factors
Physical Factors
Mechanical Factors
Success of
Prosthesis
Support
Longevity
Retention
Psychological
Comfort
Stability
Physiological
Comfort

Stability is defined as “The quality of a prosthesis
to be firm, steady or constant, to resist displacement by
functional, horizontal or rotational stresses.” (GPT)
It is usually the distinguishing factor between
success and failure.

HistoryHistory
 According toAccording to Fish (1933)Fish (1933) ““ The superior fibers ofThe superior fibers of
buccinator muscles are responsible in seatingbuccinator muscles are responsible in seating
maxillary denture, middle fibers control the bolus ofmaxillary denture, middle fibers control the bolus of
the food and the inferior fibers contributes to thethe food and the inferior fibers contributes to the
mandibular denture stability”mandibular denture stability”..
 Boucher (1944)Boucher (1944) stated thatstated that “Stability is predicted“Stability is predicted
on the resistance to horizontal forces. it is developedon the resistance to horizontal forces. it is developed
in the impression technique through more definitein the impression technique through more definite
and intimate contact of labial and buccal flanges withand intimate contact of labial and buccal flanges with
there corresponding slopes and lingual flanges withthere corresponding slopes and lingual flanges with
the lingual slopes of the ridges”.the lingual slopes of the ridges”.www.indiandentalacademy.comwww.indiandentalacademy.com

 ThomasThomas ((1962) stated thatstated that “A dynamic impression“A dynamic impression
that is physiologically conformed is one of the bestthat is physiologically conformed is one of the best
means of obtaining stability in lower unfavourablemeans of obtaining stability in lower unfavourable
ridge. This impression are made by physiologicallyridge. This impression are made by physiologically
extending the denture base into prescribed areas ofextending the denture base into prescribed areas of
extension for retention and making impression ofextension for retention and making impression of
supporting tissues with various functions”.supporting tissues with various functions”.

Robert P RRobert P R (1960) stated that(1960) stated that “The form and“The form and
contour of the polished surface of the denture base iscontour of the polished surface of the denture base is
an important factor in the denture function and playsan important factor in the denture function and plays
a significant role in the complete denture stability”a significant role in the complete denture stability”
Strain C JStrain C J (1969) s(1969) stated thattated that “The polished“The polished
surface of the lower denture greatly influences thesurface of the lower denture greatly influences the
stability due to the proper adaptation of its surface tostability due to the proper adaptation of its surface to
the tongue, lips and cheeks.”the tongue, lips and cheeks.”

Lundquist (1959) conducted a clinical study involving
the EMG analysis of function of buccinator muscle and
he stated that the nature of the buccinator muscle
contraction was not able to adapt to changes in the
contours of the denture base and the denture contours
should be designed to harmonize with existing
buccinator muscle function
Jooste CH, Thomas CJ. In 1992 conducted a study on
Complete mandibular denture stability when posterior
teeth are placed over a basal tissue incline and
concluded that teeth placed over a basal tissue incline
have a destabilizing effect during complete mandibular
denture function.
Review of LiteratureReview of Literature

Ohkubo C, Hosoi T. in 1999 conducted a study on
Effect of weight change of mandibular complete
dentures on chewing and stability and concluded
that The weight of a well-fitting mandibular complete
denture did not affect jaw movements and denture
stability.
Jooste CH, Thomas CJ. In 1992 conducted a study
on “ The influence of the retromylohyoid
extension on mandibular complete denture
stability.”
He concluded that the retromylohyoid extension has
a stabilizing effect on complete mandibular
dentures.

Zhang P, Xu J. in 2003 conducted a study on
retention and stability of linear occlusal complete
dentures and concluded that linear occlusal
dentures improve the performances of dentures by
enhancing their stability during mastication movement.
Hasegawa S, Sekita T, Hayakawa I. in 2003
conducted a study on Effect of denture adhesive on
stability of complete dentures and the masticatory
function and concluded that denture adhesive
contributes to reducing denture movement and so
improves chewing function.

FACTORS AFFECTING STABILITYFACTORS AFFECTING STABILITY
 Relationship of the denture base to theRelationship of the denture base to the
underlying tissues.underlying tissues.
 Relationship of the external surface and dentureRelationship of the external surface and denture
border to the surrounding oro-facialborder to the surrounding oro-facial
musculature.musculature.
 Relationship of the opposing occlusal surfaces.Relationship of the opposing occlusal surfaces.

Relationship of the Denture Base toRelationship of the Denture Base to
TissuesTissues
 Accuracy of the impression procedures.Accuracy of the impression procedures.
 Adequate extension of the denture border asAdequate extension of the denture border as
limited by the movable tissues……limited by the movable tissues……
 Nature of the overlying soft tissues…..Nature of the overlying soft tissues…..
 Ridge surface right angle to the occlusalRidge surface right angle to the occlusal
plane.plane.
 Types of underlying tissue…..Types of underlying tissue…..

Mandibular Lingual FlangeMandibular Lingual Flange
 At 90° to the occlusalAt 90° to the occlusal
plane.plane.
 Effectively resistsEffectively resists
horizontal forceshorizontal forces..

MYLOHYOID MUSCLE

Large, square, broad ridges ………
Small, rounded irregularities……..
Alveoloplasty …………
RESIDUAL RIDGE ANATOMY

ARCH FORMARCH FORM
 Square or Tapered arches ………..Square or Tapered arches ………..
SHAPE OF PALATAL VAULTSHAPE OF PALATAL VAULT
 Limited by length and angulation ofLimited by length and angulation of
palatal ridge slopespalatal ridge slopes
 Steep palatal vault……….Steep palatal vault……….

Relationship of the External Surface andRelationship of the External Surface and
Periphery to Surrounding Oro-facialPeriphery to Surrounding Oro-facial
MusculatureMusculature
Jacobson (1983) states that the orofacial musculature and
the polished surface of the denture can facilitate the
stability in two ways –
1. The action of certain muscle groups must be permitted
to occur with out interference by the denture base .
2. The normal functioning of some muscle groups is to
be recognize and can be used to enhance stability.

Fish (1933):Fish (1933): “ it is not so widely understood that“ it is not so widely understood that
the actual shape of the whole of the buccal, labialthe actual shape of the whole of the buccal, labial
and lingual surfaces can wreck the stability of aand lingual surfaces can wreck the stability of a
denture just as completely as a bad impression ordenture just as completely as a bad impression or
wrong bite.”wrong bite.”

Influence of Oro-facial MusculatureInfluence of Oro-facial Musculature
 Basic geometricBasic geometric
design –design – TriangularTriangular
 In frontal crossIn frontal cross
section ……….section ……….

Seating action by Tongue Lingual flange inclined medially

flanges concave positive seating

TONGUE
The tongue fills the floor of the mouth completely, and lateral
borders extend onto the occlusal surfaces of the mandibular
teeth.
With natural teeth
Normal Tongue position
Edentulous mouth www.indiandentalacademy.comwww.indiandentalacademy.com

Although everyone has a normal tongue position at
birth, some lose it, and as a result they acquire a
retracted tongue position.
When natural teeth are present, a retracted tongue
position has little effect on the ordinary functions of
the mouth. It is only when a person attempts to
achieve perfection in some specific function or
becomes edentulous that a retracted tongue position
becomes a problem.

Retracted tongue positions
Failure of the tongue to fill
the floor of the mouth
Lateral borders inside the
mandibular posterior teeth

Patients who have a retracted tongue position are given a
series of tongue exercises which help to strengthen the larger
muscles responsible for keeping the tongue in its normal
position.
The dentures should be removed and the exercises practiced
twice daily for periods of five to ten minutes.

Tongue exercise No. 1.
The tongue is thrust out and in rapidly.

The tongue is swung rapidly from side to side.

The tongue is fully extended and then quickly retracted.

The tongue is first raised to its highest position well forward
in the mouth (left) as the sound “ee” is articulated and
dropped down (right) as the sound “yuh” is articulated.

Significance of Modiolus and
Associated Musculature
A conical prominence present near the corner of the mouth,
Intersection of several muscles of the cheeks and lips.
These include Orbicularis oris,
Triangularis,
Buccinator,
Risorius and
Zygomaticus major.

In the Premolar region
Dentures should exhibit
shortened and narrowed
flange to permit the action
that draws the vestibule
superiorly and modiolus
medially against the
dentures.
The denture base must be contoured to permit the
modiolus to function freely.

The corner of the mouth is in contact with the buccal
surface of the mandibular first bicuspid.

Significance of buccinator muscle
The buccinator is a broad band of muscle forming the entire
wall of the cheek from the corner of the mouth and passing
along the outer surface of the maxilla and mandible till it
reaches the ramus.
It can be divided into -
•Superior
•Middle
•Inferior

Schematic drawing of Buccinator musclewww.indiandentalacademy.comwww.indiandentalacademy.com

NEUTRAL ZONE

The lower denture will be unstable if –
1.It is too wide in bicuspid region.
2.If incisors are set too far labially.
3.If the molars encroach on the tongue space.
4.If buccal and lingual flanges were parallel and affect
normal functioning of buccinator and tongue muscles.
The upper and lower denture must be narrow in the bicuspid
region to avoid lifting by corners of the mouth and posterior
teeth must not encroach on the tongue space.

“The most common cause of instability of
lower denture is violation of the neutral zone by
incorrect arrangement of teeth or incorrect form
of labial and lingual angles of the polished
surface ”

Relationship of Opposing OcclusalRelationship of Opposing Occlusal
SurfacesSurfaces
Harmony between the opposing occlusal surfaces will play a
major role in the complete denture stability, regardless of the
type of posterior tooth form or occlusal scheme used. The
dentures must be free of interferences within the functional
range of movement of the patient.
Bilateral simultaneous contact of the posterior teeth in
centric relation is essential to enhance the denture stability.

Theories of OcclusionTheories of Occlusion
Balanced occlusionBalanced occlusion
Monoplane occlusionMonoplane occlusion
Lingualized occlusionLingualized occlusion

It’s the bilateral, simultaneous, anterior andIt’s the bilateral, simultaneous, anterior and
posterior occlusal contact of teeth in centric andposterior occlusal contact of teeth in centric and
eccentric position.eccentric position.
This providesThis provides
 Multiple point of contactMultiple point of contact
 Reduces localized stress concentrationReduces localized stress concentration
 Distributes functional occlusal forcesDistributes functional occlusal forces
thus ensuring stability of prosthesisthus ensuring stability of prosthesis
BALANCED OCCLUSIONBALANCED OCCLUSION

MONOPLANE OCCLUSION
•In this occlusion the teeth reduces horizontal
forces by eliminating the inclined planes.
• Positioning of these teeth slightly lingual to
mandibular ridge crest enhances denture
stability.
• These occlusion is indicated in poor ridges
which provide no resistance to lateral forces thus
minimizing horizontal forces.

LINGUALIZED OCCLUSION
The theories of lingualized occlusion provide both
a limited range of excursive balance and a directing
of forces to lingual side of the lower ridge during
working side contacts.
Such concepts may minimize horizontal stress and
enhance denture stability by controlling the leverage
induced by eccentric tooth contacts.
Recently a new tooth mold designed specifically to satisfy
the concept of lingualized occlusion (MLI) has been
introduced.

SELECTION OF TEETHSELECTION OF TEETH
 The selection of anatomic, semi-anatomic, or non-The selection of anatomic, semi-anatomic, or non-
anatomic artificial teeth depends on the occlusalanatomic artificial teeth depends on the occlusal
scheme.scheme.
 The unfavourable ridges exhibiting severe resorptionThe unfavourable ridges exhibiting severe resorption
patterns may contribute to compromised stability due topatterns may contribute to compromised stability due to
poor denture base to residual ridge relationshippoor denture base to residual ridge relationship..

Tooth Position and Occlusal PlaneTooth Position and Occlusal Plane
Anterior teeth:Anterior teeth:
The anterior teeth arrangementThe anterior teeth arrangement
must fulfill certain functional asmust fulfill certain functional as
well as esthetic requirements.well as esthetic requirements.
 The lower anteriors if placedThe lower anteriors if placed
far forward of the remainingfar forward of the remaining
alveolar ridge, the orbicularisalveolar ridge, the orbicularis
oris muscle will lift the loweroris muscle will lift the lower
denture when it contacts.denture when it contacts.

Boucher (1960) stated thatBoucher (1960) stated that “The only correct position of a tooth“The only correct position of a tooth
is the one in which, it was placed by the natureis the one in which, it was placed by the nature.”.”
In general the lower anteriors teeth should not be set furtherIn general the lower anteriors teeth should not be set further
forward than a plane perpendicular to the mucobuccal fold.forward than a plane perpendicular to the mucobuccal fold.

Posterior teeth:
The posterior teeth bear the functional burden for the
occlusion. By their proper arrangement they serve to aid in
retention and stability and preserve the health of masticatory
tissues.
The buccolingual position of the lower posterior teeth is
determined by the needs of retention and stability.

If they are located buccal to ridge…….
If the teeth arranged too far lingually…….

Significance of Occlusal Plane
• The anterior height ……
•The posterior height ………

•The laterally tilting forces directed against the teeth are
magnified and the muscular support from the tongue will be
obliterated.
• forces the tongue into a higher position which raise the floor of
the mouth and creating undue pressure on the border of the
lingual flange resulting in a partial loss of the border seal.
Can result in
Reduced Stability
Mandibular occlusal plane set too high
Reasons

Ridge relationship and denture stability
•Excessive amount of interridge space
•Small amount of interridge space.
Ridges that are not parallel to each other will cause the
movement of the denture bases when the teeth are occluded
because of unfavourable distribution of the forces.
The anteroposterior and lateral ridge relationship will also
influence the stability of the denture. The amount of resorption
which occur when the natural teeth are removed will affect
these relationships –
•Maxillary ridge resorption
•Mandibular ridge resorption

Jacobson (1983) stated that “Stability is a problem in
prognathic and retrognathic patients. The Class III patients
frequently displays a lower arch anterior to the upper arch in
centric relation. Sufficient mandibular occlusion must be developed
so that contact against the maxillary denture extends posteriorly
more than half the distance from the incisive papilla to the hamular
notch without this contact the maxillary denture would tip
anterosuperiorly, traumatizing the maxillary anterior ridge and
loosening the maxillary denture”.

Assessment of StabilityAssessment of Stability
To check the stability put two fingers on either side of
the quadrant and light pressure is applied alternatively
on each side. This pressure must be directed at right
angle to the occlusal surface. if pressure on one side
causes the denture to tilt and rise from the ridge on the
other side then the denture is not stable.

The factors of stability involve the tissue,The factors of stability involve the tissue,
occlusal and polished surfaces of theocclusal and polished surfaces of the
denture. Care must be taken in thedenture. Care must be taken in the
development of all three of thesedevelopment of all three of these
surfaces to ensure optimal stability ofsurfaces to ensure optimal stability of
the final prosthesisthe final prosthesis.
CONCLUSION

REFERENCES
1. Zarb - Bolender : Prosthodontic treatment for edentulous
patients. Twelfth edition, 2004.
2. Jacobson T.E. : Contemporary review of factors involved
in the complete dentures. J. Prosthet. Dent. 49: 165,
1983.
3. Corwin R.Wright, :Evaluation of factors necessary to
develop stability in mandibular dentures. J. Prosthet. Dent.
92:509-518,2004
4. Arthur R.F. : Complete denture stability related to tooth
position. J. Prosthet. Dent. 1961; 11: 1031-1037.
5. Strain C.J. : Establishing stability for mandibular complete
denture. J. Prosthet. Dent. 21: 359, 1969.
6. Victor E. and Frank J. :The neutral zone in complete
dentures, J. Prosthet. Dent. 1976;36 :356-365

7.Victor E. and Frank J. :The neutral zone in complete
dentures, J. Prosthet. Dent. 1976;36 :356-365
8.Rahn and Heartwell : Textbook of complete denture, 5th
edition, 1993.
9.Sharry J.J. : Complete denture prosthodontics, 1968.
10.Thomas E. :Stabilizing lower dentures on unfavourable
ridges. J. Prosthet. Dent. 12: 420-424, 1962.
11.H.R.B. Fenn :Clinical dental prosthodontics, 1st edition,
1986.
.

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