Rola M. Shadid, BDS, MSc
Retention
Resistance to denture removal in a
direction opposite that of its
insertion.*
Stability
Resistance of denture movement under
the effect of horizontal or rotational
forces.
Support
Resistance of movement of denture
toward the basal seat area.
The act of chewing foods
Adhesive nature of certain foods
Gravity (for upper denture) *
Surrounding musculature
Prematurities in occlusion
Primary retention is from basal
seat
Secondary retention by improving
stability & minimizing dislodging
forces
Physical means
Mechanical means
Adhesion
Cohesion
Interfacial surface tension
Atmospheric pressure
Capillary attraction
Gravity
Figure:
retention due
to
pressure
differential
between saliva
film & the air
Relationship between
the width of the
buccal channel and
resistance to flow of
saliva: (a) wide channel,
rapid flow, poor
retention; (b) narrow
channel, slow flow,
good retention.
Atmospheric pressure *
Capillary attraction
Saliva: quantity & quality *
Surface area: the larger the surface
area, the greater the retention.#
Intimacy of contact: the closer the
contact between the tissue and the
impression surface of denture, the
greater the retention.
Peripheral seal
The denture border should be shaped so
that the channel between it and the
sulcus tissues is as small as possible.
It is not possible to maintain a close
approximation between the border of a
denture and the mucosal reflection in the
sulcus at all times because the depth of
the sulcus varies during function.
The denture has to be
constructed so that
the border conforms
to the shallowest
point that the sulcus
reflection reaches
during normal
function. *
It is not possible to produce a facial seal along
the posterior border of the upper denture as it
crosses the palate. In this area, another
approach to create the smallest possible space
between denture and mucosa is adopted. A
groove known as a post-dam is cut into the
working cast so that the posterior border of
the finished denture has a raised lip which
becomes embedded a little way into the palatal
mucosa.
Right: denture poorly
retained because the
thin flanges failed to
create a facial seal and
the palatal coverage
did not make the most
of the area available.
Left: the replacement
denture corrected
these errors and as a
result had excellent
retention.
Undercuts
Overdentures attachments
Implants
Mucosal inserts
Rubber suction discs & suction
chambers (No longer used)
Magnets
Selection of path of
insertion to improve
retention by utilising
undercuts: (a) single
path of insertion to
engage labial
undercut; (b) dual
path of insertion to
engage unilateral
undercut.
Mucosal insert or implant
button: a nonreactive
metal appliance that is
affixed to the tissuebone surface of a
denture and offers
added retentive qualities
to the denture. It
consists of a base,
cervix, and head.
Rubber suction disc
& suction chamber
No longer used
because they
cause damage of
soft tissues
The surrounding musculature
Occlusal schemes
Proper patient instructions
Psychological factor
Neuromuscular control
Denture fixative
Long-term soft liners
Cheek muscles
Lips
Modiolus can cause unseating of
denture in premolar region
Tongue
Floor of the mouth
Soft palate
Masseter (affects the distobuccal
region of mandibular denture)
Neutral zone (zone of minimal
conflict)
o Explaining the central role of the tongue, lips
and cheeks in controlling the denture and
giving specific advice – such as supporting the
posterior border of the upper denture with
the tongue when incising.
o Offering advice, for example, cutting food into
smaller pieces before inserting them into the
mouth.
o Chewing on both sides of the dental arch
simultaneously
o Starting with softer ‘easier’ foods before
progressing to more challenging morsels.
As the patient
incises, the upper
denture is
controlled by the
tongue pressing
against the
posterior border.
An aid to retention, particularly under
difficult anatomical circumstances.
Come in powder, paste or sheet form,
the latter having the advantage of
staying longest between the denture and
mucosa.
 enable free, flexible margins to
extend into the anatomical defect and
engage tissue undercuts.
 can be constructed as an integral part
of the denture base or as a separate
obturator section retained on the
denture base by rare earth magnets.
Intimate contact (accuracy of fit)
Residual ridge size & contour
Residual ridge quality
Palatal vault
Neutral zone & surrounding
musculature *
Flange shape & contour: correct
contouring the external surface of
the denture base can enhance the
stabilizing potential of surrounding
musculature
Occlusal factors
Abnormal ridge relationships *
Direct bone anchorage #
Pressure from the
bolus on the
posterior part of
the lower occlusal
table, which overlies
a sloping part of the
ridge, causes the
lower denture to
slide forwards.*




Firm resilient tissue covered by
keratinized tissue & firmly
attached to underlying bone
Tissue of uniform thickness
The bone be resistant to resorption
The support areas should be at
right
angles
to
the
occlusal
surfaces
All areas of denture bearing area
should contribute to support except
relief area
Primary stress bearing areas
Greater area of coverage puts less
force per unit area (snow shoe
principle)
The
larger
surface
area
of
maxillary denture (22.96cm2) allows
a
wider
stress
distribution
compared with mandible (12.25cm2).
Surface area
Nature of supporting mucosa
Impression procedure
Accuracy of fit
Direct bone anchorage *
Retentive forces >
displacing forces
Adequate support
Stability
References:
I.
Complete Denture Prosthodontics, 1st Edition,
2006 by John Joy Manappallil, Chapter 2
II.
Basker’s Prosthetic treatment of the
edentulous patient. Fourth edition. Chapter 4.