Transcript Retention, Stability & Support in Complete Denture

RETENTION, STABILITY
&
SUPPORT
IN COMPLETE
DENTURE
Specific learning objectives
1. Definition and importance of Retention ,
stability and support in complete denture.
2. Factors affecting Retention , stability and
support in complete denture.
3. How to overcome common difficulties(in
brief).
Factor affecting Successful denture fabrication
Biologic Factors
Physical Factors
Mechanical Factors
Retention
Psychologic
Comfort
Stability
Support
Physiologic
Longevity
Comfort
Prosthesis Success
RETENTION
• It is the resistance to removal in a
direction opposite to that of insertion.
(GPT)
• BOUCHER described retention as the
most spectacular yet probably the least
important of all complete denture
objectives. This property may indeed be
least important, it provides psychologic
comfort to patient.
Factors affecting retention
. Anatomical factors
. Physiological factors
. Physical factors
. Mechanical factors
. Oral& facial musculature
. Psychological effects and patient’s
tolerance
ANATOMICAL FACTORS
1.Size of the denture bearing area
2.Quality of the denture bearing area
PHYSIOLOGICAL FACTORS
• SalivaQuality and viscosity
The most commonly listed factors of
retention includeA) PHYSICAL FACTORS
• Adhesion
• Cohesion
• Interfacial surface tension
• Capillary attraction
• Atmospheric pressure.
B) BIOLOGIC FACTORS
• Intimate tissue contact
• Neuromuscular control
PHYSICAL FACTORS
Adhesion
• It is the physical force involved in
the attraction between unlike
molecules.
Cohesion
• It is the physical attraction of like
molecules for each other.
Interfacial surface tension
• It is the resistance to separation
possessed by the film of liquid between
two well adapted surfaces.
• Viscous tension refers to the force holding to parallel
force together that is due to the viscosity of the
interposed liquid
• Viscous tension is described by stefan’s law as-
• R=radius, K=viscosity of the liquid, H=thickness of
the liquid, F=force, V=velocity
• Viscous tension increases proportionally to increase
the viscosity of the interposed liquid and increase in
surface area covered by the denture.
Capillary attraction
• It is the force that causes the surface of
a liquid to become elevated or
depressed when it is in contact with a
solid.
Atmospheric pressure
• It is the physical factor of hydrostatic
pressure due to the weight of the
atmosphere on the earth’s surface.
Mechanical factors
. Undercuts
. Rotational insertion path
. Parallel walls
Biologic factors
Intimate tissue contact - It is the biologic
factor that refers to the close
adaptation of the denture base to the
underlying soft tissues.
Neuromuscular Control– It refers to the
functional forces exerted by the
musculature of the patient that can
affect to retention.
STABILITY
• “the
resistance
against
horizontal
movements and forces that tends to alter
the relationships between the denture
base and its supporting foundation in
horizontal or rotatory direction.”
• In simpler words stability is defined as
“the quality of a denture to resists
displacement by functional stresses.”
The qualities necessary to create and
maintain stability are dependent upon the
following factors:
 Retention
 Diagnosis
 Denture base outline
 Size and form of basal seat.
 The quality of final impression.
 Occlusal plane.
 Proper location and arrangement of the
artificial teeth.
 Instructions and education of the patient
Diagnosis
• Diagnosis
consists
of
planned
observations to determine and evaluate
the existing conditions which lead to
decision making based on the condition
observed.
• Examination of edentulous arches
Intra Oral Examination includes-
• Hard palate
• Soft palate
• Residual ridge height
• Ridge surface examination
• Arch form of upper and lower ridge
• Undercuts
• Ridge relationship
• Frenal attachment
• Tongue
• Saliva
• Mucosal examination
Denture base outline
• Labial flange extends from one buccal
frenum to the other.
• Buccal flange extending from buccal
frenum to the posterior-most part of
distobuccal area.
In Maxillary Denture,
•Posterior palatal seal area.
“The soft tissue along the junction of hard and
soft palate on which pressure with in
physiologic limit of the tissue can be applied by
a denture to aid in the retention of the denture.”
1. The anterior vibrating line is an imaginary
line located at the junction of the attached
tissues overlying the hard palate and the
movable tissues of the immediately adjacent
soft palate.
2. The posterior vibrating line is an imaginary
line at the junction of the aponeurosis of the
tensor veli palatini muscle and the muscular
portion of the soft palate.
In Mandibular Denture,
• Distolingual extension of the lingual flange is
the beginning of the seal area of the lower
denture. Should extend downward and
backward from the retromolar pad at an angle
of approximately 450 .
• Level of the floor of the mouth in its normal
position is about the level of internal
oblique line.
• Most of the movements of tongue
necessary to carry out its normal functions
occurs above the mandibular teeth, but it
appears that the 2mm of extension below
the internal oblique ridge provides
necessary seal for these movements with
out the problem of overextension.
Occlusal Plane
• The maxillary rim should be parallel
anteriorly to the inter-pupillary line &
posteriorly to the ala- tragus line
• Plane should be parallel to the crest of
residual ridge.
• Occlusal surface in the region of the
mandibular 1st molar are approximately
2mm below the top of retromolar pad.
• Height of the occlusal rim conform to
activities of tongue, cheek and corner of
mouth which tend to enhance
mandibular denture stability.
• An added reference check, the top of
the wax rim in the region of the
mandibular 1st bicuspid should never be
above the corner of mouth.
An occlusal plane if too high
Forces the tongue into new position i.e. higher
position
Loss of tongue accuracy.
Causes raise of floor of mouth.
Undue pressure on the border of the lingual flange
Partial loss of border seal.
An occlusal plane slightly low
Causes no problems for denture patients.
If Occlusal plane is too low
Destabilizes the denture
Proper location and arrangement
of the artificial teeth –
“ARCH ARRANGEMENT”
Is used to indicate the buccolingual or
buccopalatal relationship of teeth, to either
the crest of the ridge or the stress bearing
area.
Concept of Neutral Zone by Fish• Neutral zone is a
potential
space
between lips and
cheeks on one
side and tongue
on the other where
natural or artificial
teeth
are
subjected to equal
and
opposite
forces
from
surrounding
muscles.
• Centric Relation and Centric Occlusion
provides stability to the denture.
• The Centric Relation
and Centric
Occlusion is at same position.
Education of the patient
• Every patient should be informed regarding
the care & proper use of his denture.
• Failure to heed the dentist’s advice will
eventually lead to damage to the supporting
tissues.
• It is usually obvious to them that their failure
to master their denture problem in not the
fault of the dentist but rather the fault of their
own inability to master the normal tongue
position
SUPPORT IN
COMPLETE DENTURE
• The foundation area on which a dental
prosthesis rests.
• With respect to dental prosthesis, the
resistance to displacement away from
the basal tissue or underlying structure.
(GPT-8)
• Complete denture support is “the
resistance to vertical movement of
the denture base towards the
ridge.”
• Support counteracts the forces at
right angles to the occlusal surface
directed towards the ridge.
FACTORS AFFECTING
SUPPORT
Effective support is obtained when• The denture is extended to cover
maximum
surface
area
without
impinging on movable tissues.
• Tissues most capable of resisting
resorption are selectively loaded during
function.
• Tissues most capable of resisting
vertical displacement are allowed to
make firm contact with denture base
during function.
• Compensation should be made for
varying tissue resiliency.
SNOWSHOE PRINCIPLE
• The basic “snowshoe principle” of
maximal extension is applied for
support.
• It states that given a constant occlusal
force, a broader denture-bearing area
decreases the stress/unit area under
the denture base.
• decreases tissue displacement &
reduces denture-base movement.
• The initial denture support is achieved by
using impression procedures that provide
optimal extension & functional loading of
supporting tissues.
• Long term support is obtained by directing
the forces of occlusal loading towards
those tissues most resistant to remodelling
& resorptive changes.
MANDIBULAR ANATOMIC
CONSIDERATIONS
BUCCAL SHELF AREA• The buccal shelf is recognized as a
primary support area for the mandibular
denture.
• It is usually covered by mucosa with an
intervening submucous layer containing
glandular
connective
tissue
&
buccinator muscle fibres.
• The muscle fibers along the shelf in a
longitudinal anteroposterior direction,
permitting the denture base to rest
directly on a portion of the buccinator
muscle without displacement.
RESIDUAL ALVEOLAR RIDGE• Patients exhibiting broad, square welldeveloped residual ridge covered by firmly
bound masticatory mucosa plus a
favourable intrinsic bone factor may rely
on the ridges for support.
MAXILLARY ANATOMIC
CONSIDERATIONS
HARD PALATE• In the maxillae, the horizontal portion of
the hard palate lateral to the midline
raphe should provide support for
complete dentures.
• Keratinized
masticatory
mucosa
overlies a distinct submucous layer
everywhere but at the midline suture.
• The submucosa contains fatty tissue
anterolaterally, & glandular tissue
posterolaterally. This resilient layer acts
as a cushion for the functional stress
transmitted to the mucosa.
• Over the midline raphe, the mucosa is
unyielding, & must be relieved to avoid
tissue impingement.
• The relief should be minimal to permit light
contact of this tissue with the denture
base under masticatory loading.
RESIDUAL ALVEOLAR RIDGE
• The crest of the maxillary edentulous ridge
is also important in complete denture
support.
• The soft tissue is often thick, keratinized, &
firmly bound to the periosteum &
underlying bone.
Take home message……
• Support, stability & retention are very
important features in complete denture
fabrication that ensure the best possible
treatment for the patient, carefully
conserving what remains & replacing
what is lost.
MCQs
1. Adequate retention in complete
denture providesa. Physiologic comfort
b. Psychological comfort
c. Physical comfort
d. Longivity
2. Which of the following factor is
primarily essential for longevity of
complete denturea.Retention
b.Stability
c. Support
d.Esthetics
3. The factor necessary in complete
denture to be firm , stable and constant
while resisting horizontal and chewing
forces isa.Retention
b.Stability
c. Support
d.Esthetics
4. BOUCHER described which factor as
the most spectacular yet probably the
least important of all complete denture
objectivesa.Retention
b.Stability
c. Support
d.Esthetics
5. Physical force involved in the attraction
between unlike molecules is known asa.Cohesion
b.Adhesion
c.Surface tension
d.Capillary attraction
6. The quality to resist separation
possessed by the film of liquid between
two well adapted surfaces is known asa.Cohesion
b.Adhesion
c.Surface tension
d.Capillary attraction
7. According to Stefan’s law, relation of
viscous forces (F) with area of opposing
surface (A) isa. A2
b. A3
c. 1/A2
d. 1/A3
8. According to Stefan’s law, relation of
viscous forces (F) with thickness of
interposed medium (h)isa. h2
b. h3
c. 1/h2
d. 1/h3
9. Snowshoe principle is related with
a.Retention
b.Stability
c. Support
d.Esthetics
10. Neutral zone concept was given bya. Boucher
b. Neil
c. Fish
d.Winkler.