Stability support and retention

1. 1

2. Presented By:
Dr. shweta
2

3. Contents
 INTRODUCTION
 DEFINITIONS
 RETENTION
Historical review on retention
 FACTORS AFFECTING RETENTION
 PHYSICAL,
 BIOLOGICAL,
 MECHANICAL,
 PSYCHOLOGICAL FACTORS
 CLINICAL EVALUATION OF RETENTION
 CAUSES OF POOR RETENTION
 REVIEW OF LITERATURE
3

4.  STABILITY
 FACTORS CONTRIBUTING TO STABILITY
 REVIEW OF LITERATURE
• SUPPORT
 COMPARISION OF SUPPORT IN DENTULOUS AND
EDENTULOUS
 TYPES OF SUPPORT
 NATURE OF SUPPORTING TISSUES
 DENTURE BEARING AREAS
 METHODS TO IMPROVE SUPPORT
• Conclusion
• List of References
4

5. STABILIT
Y
SUPPOR
T

SUCCESS….
RETENTION
BIOLOGIC FACTORS
PHYSICAL FACTORS
MECHANICAL FACTORS
5
Introduction…

6. 6

7. Definitions
RETENTION
 GPT 8 That quality inherent in the dental prosthesis
acting to resist the forces of dislodgement along the
path of placement
 BOUCHER;
It’s the resistance to removal in a direction
opposite to that of its insertion.
It’s the quality in a denture that resists the forces of
gravity, the adhesiveness of foods, and the forces
associated with the opening of the jaws.
7

8. 8
STABILITY
 The quality of a removable dental prosthesis
to be firm , steady or constant to resist
displacement by functional horizontal or
rotational stresses. (GPT 8)

9. SUPPORT
• The resistance to vertical forces of
mastication and to occlusal or other forces
applied in the direction towards the basal
seat. (GPT 8).
According to Boucher,
• Support is the resistance of a denture to the
vertical components of mastication and to
occlusal or other forces applied in a direction
towards the basal seat
9

10. Retention…….
10

11. Historical review on retention
RETENTION
Fish-tissue
surface,
polished &
occlusal
surface
Craddock-
”gripping”
action of
buccinator
Schlosser &
Fish- balanced
occlusion
11

12. Factors Involved In Retention Of
Dentures
PHYSICAL
FACTORS
BIOLOGICAL
FACTORS
MECHANICAL
FACTORS
PSYCHOLOGICAL
FACTOR
∂ Adhesion
∂ Cohesion
∂ Interfacial
force
∂ Capillarity
∂ Gravity
∂ Atmospheric
pressure
∂ Saliva
∂
Intimate
tissue contact
 Border seal
 Oro-facial
musculature
 undercuts
 springs
 suction chambers
 rubber suction
discs
 magnets
 adhesives
12

13. Adhesion
 Physical force involved in the attraction of unlike
molecules
 Adhesion of saliva to the mucous membrane and
the denture base - through ionic forces between
charged salivary glycoproteins and surface
epithelium or the resin
13

14. Cohesion
 Physical attraction of like
molecules for each other
 Occurs in the layer of
saliva between the denture
base and the mucosa &
works to maintain the
integrity of the interposed
liquid.
14

15. Capillary Attraction Or Capillarity
 When there is close adoptation
between the denture base and the
mucosa … the space filled with a
thin film of saliva acts like a
capillary tube in that the liquid
seeks to increase its contact with
both the denture & the mucosal
surface.
15

16. Interfacial Force
It is the resistance to separation
of two parallel surfaces that is
separated by a film of liquid
between them. It can be
discussed by two factors
ointerfacial surface tension
oviscous tension
16

17. Interfacial Surface Tension
Interfacial surface tension results from a thin
layer of fluid that is present between two
parallel planes of a rigid material
• It is dependent on the existence of a liquid/air
interface at the terminus of the liquid/solid
contact
….. will provide less amount of retention in
mandibular denture as it is pooled with saliva.
17

18. Interfacial Viscous Tension
It refers to force holding two parallel plates
together that is due to the viscosity of the
interposed liquid. Viscous tension described by
……..
Stefan’s law:
F = (3/2)Π kr4 V/h3
 r is the radius of the plates
 k viscosity of the interposed liquid
 h thickness of liquid
 V velocity
 F force required to pull the plates apart
18

19. Atmospheric Pressure
 Atmospheric pressure is the physical
factor of hydrostatic pressure due to
the weight of the atmosphere on the
earth’s surface.
 Resist dislodging forces …dentures
have effective seal with maximum
area of coverage
19

20. Two criterias
20
Pressure
difference Vacuum(
assuming a
border seal)
The physical mechanisms of complete denture
retention Br Dent Jr, Vol 189, No 5, Sep 9, 2000
Dislodging
force
Atm
pressure
Seal
0
pressure

21. Review of literature
 Synder et al in 1945 demonstrated the effect of
reduced atmospheric
pressure on the retention of maxillary complete
dentures constructed for 7 patients
 Measurements made in a pressure chamber at 4.7
psi stimulating a 30,000 feet ascent above the earth
demonstrated a decrease in denture retention
 With a 70% decrease in atmospheric pressure, a
50% decrease in retention was noted
21

22. Review of literature
 Tyson demonstrated the role of surface tension &
atmospheric pressure in denture retention through a
series of experiments in 1967
 Confirmed the importance of a thin fluid film between
two plates in producing a pressure gradient
maintained by surface tension
 Separating force proved to be proportional to
atmospheric pressure
 Also proved that if adhesion & cohesion were the
primary retentive phenomena, separating forces
would not drastically change on immersion in water or
reduced atmospheric pressure
22

23. Gravity
 When a patient is in an upright
posture, gravity acts as a retentive
force for the mandibular denture and a
displacive force for the maxillary
denture.
 Increasing the weight of mandibular
denture may theoretically seem to
increase the retention.
23

24. Biological Factors
ORAL AND FACIAL MUSCULATURE:
o The teeth are positioned in
the “neutral zone” between
the cheeks and the tongue.
o The polished surfaces of the
dentures are properly
shaped.
24

25. For the oral and facial musculature to be
most effective in providing retention for
complete dentures, the following
conditions must be met:
25

26.  The close adaptation of denture base to the
underlying tissue
 Impression technique will determine the degree of
intimate tissue contact obtained with the tissues at
rest and during function
…….it depends on method of impression making
 Depending on the amount of pressure used
 Open mouth or close mouth technique
 Hand manipulations or functional movement
 Type of tray used
Intimate Tissue Contact
26

27. Peripheral Seal
 Reduces the distance between the future denture
and its supporting tissues.
 Skinner and chung have demonstrated that the use
of relief areas decrease the retention and
peripheral seal increases retention
MAXILLA
 Posterior palatal seal
 Buccal vestibule
 Labial vestibule
27

28. POSTERIOR PALATAL SEAL AREA
…soft tissue area at or beyond the
junction of hard and soft palate on
which pressure, within physiologic
limits, can be applied by a complete
removable dental prosthesis to aid in
its retention.
GPT-8
28

29. BUCCAL VESTIBULE
 Buccal space… varies in size and
shape – care must taken to fill entire
buccal space
 The size and shape of the distal
end of the buccal flange of the
denture must be adjusted to the
ramus and coronoid process of
mandible and to the masseter
muscle.
LABIAL VESTIBULE
The labial notch in the labial flange
of the denture must be just wide
29

30. Mandible
LABIAL VESTIBULE
The extent of denture flange in this area often is
limited by muscles that are inserted close to the
crest of the ridge …mentalis muscle is very
active in this region …
BUCCAL VESTIBULE
The denture should cover completely the buccal
shelf, despite the fact that it will rest directly on
fibres of the buccinator muscle.
POSTERIOR EXTENTION …. The denture base
should extend approx ½ to 1/3 of retromolar
30

31. For the denture to be
successful, the flange
must be made parallel to
the mylohyoid ridge when
it is contracted.
If the lingual flange is
properly shaped and
extended , it will provide
border seal and guide
the tongue to rest on top
31
LINGUAL BORDER
Mandible
Mandible
Mandible
 Mylohyoid Ridge
– Palpate
• If prominent, may need relief
 Mylohyoid muscle
• Raises floor of mouth
• Differences between rest and
activity
• Affects length of flanges

 Mylohyoid Ridge
Mylohyoid Ridge
–
– Palpate
Palpate
•
• If prominent, may need relief
If prominent, may need relief

 Mylohyoid muscle
Mylohyoid muscle
•
• Raises floor of mouth
Raises floor of mouth
•
• Differences between rest and
Differences between rest and
activity
activity
•
• Affects length of flanges
Affects length of flanges

32. 32
The denture border should extend
posteriorly to contact the retromylohyoid
curtain

33. TONGUE
Base of the tongue – serve as an
emergency retentive force
Rises up at the back and presses
against distal border of the –
maxillary denture
33

34. Mechanical Factors
UNDERCUTS
 Undercuts act as mechanical
locking system in retention of
denture.
34

35.  Unilateral undercuts
are utilized for
denture retention.
 Bilateral undercuts
can be used for
retention as long as
they are not severe.
 when present on both
sides, one side of
undercut is surgically
removed.
35

36. Springs
 made of coiled stainless steel
or gold-plated base metal
…their ends attached to
swivels in the premolar areas
on both sides of the upper and
lower dentures.
 as soon as they are released
the dentures are forced apart
by the action of the springs
and held in place.
36
Fauchard 1678- 1761 introduced
springs

37. Disadvantages of springs
 Constant pressure causes
excessive resorption
 The inner surfaces of the cheeks
frequently become sore from
frictional contact with the springs.
 Lateral movements of mandible
restricted and hence efficiency of
the dentures is impaired.
 Mucous membrane can not
tolerate constant pressure.
 unhygienic
37

38.  A relief chamber with definite
margins is created on the palatal
side of the denture
 When the denture is inserted, a
partial vacuum is created in this
chamber by sucking and
swallowing action
DISADVANTAGE
Irritation and proliferation of
tissues in to the chamber
Suction Chambers
38

39. Rubber Suction Discs:
 They consist of a rubber disc which is
buttoned on to a stud sunk into the
fitting surface of the denture.
 The partial vacuum created within the
perimeter of this disc holds the upper
denture suspended from the hard
palate.
DISADVANTAGES:
 Due to the swelling and spreading of
the rubber disc they are not self-
limiting in action
 unhygienic. Damage to soft
39

40. Mucosal Inserts
 These are small mushroom shaped metal
appliances attached to the tissue side of the
maxillary denture . When the denture is
inserted in to the mouth , these studs insert in
to specially prepared receptor sites within the
mucosa.
40

41. Magnets:

 In 1971, Javid - extra-oral & intra-
oral prosthesis joined with
magnets
 In 1979, Moghadam et al –
described a simple technique for
use of magnets in overdentures
 Use of small steel magnets
beneath the molar and premolar
teeth have been advocated.
 They are arranged such that
similar poles oppose each other.
41

42. Adhesives
 Denture adhesive refers to
nontoxic, soluble material (powder,
liquid, cream) that is applied to the
tissue surface of the denture to
enhance denture retention, stability
and performance.
42

43. Mechanism of action:
The adhesives increase retention by optimizing
interfacial forces by-
 Increasing the adhesive and cohesive
properties and viscosity of the saliva between
denture base and underlying tissue.
 Eliminating voids between the denture base and
its basal seat
43

44. Psychological Factors
 The patients ability and
willingness to accept and learn to
use the dentures ultimately
determines the degree of success
of clinical treatment
 Helping a patient to adapt to
complete denture can be one of
the most difficult but also one of
the most rewarding aspects of
clinical dentistry.
44

45. SURGICAL METHODS TO
AUGMENT RETENTON
 Vestibuloplasty
 Ridge augmentation procedure
 Implants
 Pre-prosthetic surgery
aims at providing a good
healthy surface for the
insertion of dentures
Surgical Methods:
45

46.  Prospective clinical evaluation of
mandubular implant overdentures part-
I retention stability and tissue
responses
DR Burns et al
JPD1995;73
 The study shown superior statistics of
implants as an treatment alternatative to
increase stability than ridge
augmentation or vestibular extension
procedures.
46

47. Clinical Evaluation Of Retention
47
Maxillary denture
denture is grasped
by the incisors and
pulled downward
between thumb and
forefinger
Placing fingers on the
palatal surface and
pulling forward
Checked by pulling downward with two
fingers

48. Mandibular dentures
The retention of the lower
denture is assessed by
gently pushing posteriorly
against the facial surfaces
of the mandibular incisors.
The denture should not
become dislodged.
48

49. Causes of poor retention
 When opening wide mouth
 Over / under extension
 Tight lips
 Tongue cramp
 Lack of peripheral seal
 Lack of saliva
 When coughing or sneezing
 Normal… due to sudden rise of soft palate
 Technical fault
 Inherent polymerisation shrinkage
 In denture that is in use for more than a year
 When attempting to whistle
 Overextension / thick labial flanges
 Disruption of seal
49

50. Factors important in complete
denture retention
 Surface tension
 Viscosity
 Base adaptation
 Border seal
 Seating force
 Soft tissue
50

51. Viscosity
 Rheology of saliva & where its viscosity
is located is important
 As viscosity of saliva is many times that of air,
separation is more difficult when fluid fills the
space between the denture & tissue
51

52. Base adaptation
 Single most important criteria for denture
retention
 Measure of the fit determines the size of the gap
between the mucosa and the fitting surface,
which in turn controls flow of saliva
Seating force
52
Firm seating force should be applied as this
aids in retention of the denture
Immediate effect of this…
1. Results in a thin film of saliva
2. Also tends to expel air which does not
contribute to retention

53. Soft tissue
Soft tissue
compliance
is important
when
dentures are
first inserted
In the
medium
term soft
tissue
remodeling
In the long term,
resorption &
remodeling of hard
tissue may exceed
the adaptive capacity
of overlying soft
tissues
53

54. STABILITY
54

55. Stability
 FACTORS CONTRIBUTING TO STABILITY
 DIAGNOSIS
 RELATIONSHIP OF DENTURE BASE TO
UNDERLYING TISSUES
 RELATIONSHIP OF EXTERNAL SURFACE AND
PERIPHERY TO SURROUNDING ORO FACIAL
MUSCULATURE
 RELATIONSHIP OF OPPOSING OCCLUSAL
SURFACES
 PATIENT EDUCATION
55

56. Diagnosis
56

57. Relationship Of Denture Base To Underlying Tissues
Denture base adaptation
 A properly formed denture base outline
develops a seal that can be maintained
during most of the normal oral functions
 Depends on impression procedures
• Extend all over the basal seat within the
limits of health and function of tissues…
• SNOW SHOE PRINCIPLE
57

58.  SNOWSHOEEFFECT
 The ability of a denture to distribute forces over wide
areas due to an increase in the denture- base area
 Stability is compromised-
 Inflammed tissues
 Distorted or displaced tissues
 Hyperplastic tissues
58

59. Residual ridge anatomy
 Large, broad, square ridges offer a greater resistance to lateral forces
than do small, narrow, tapered ridges
Arch form – square and taper arch tend to resist rotation
than ovoid arch
Palatal vault
59

60. Relationship Of The External Surfaces And
Periphery To The Surrounding Oro-facial
Musculature
 Muscle action on denture…. Vertical or lateral
dislodging forces . .such as actions of levator
anguli oris, incisivus, depressor anguli oris,
mentalis, mylohyoid, and genioglossus
The following factos will be considerd ,
• The external surface of the denture
• Influence of oro-facial musculature
• Modiolus and associated structures
• The neutral zone
60

61. External surface of the denture
 Fish… “the shape of buccal, labial and lingual
surfaces can wreck the stability as completely as
a bad impression or a wrong bite”
61

62. 62
Buccal flange of
maxillary denture
should slope up and
out from the occlusal
surface of the teeth
Buccal flanges of
mandibular should slope
down and out
When buccinater
muscle contracts it
will tend to retain
dentures
Lingual surfaces of the lingual
flange should slope towards the
centre of the mouth so that the
tongue can fit against them and
perfect the border seal in
lingual side of the denture

63. Influence of oro-facial musculature
• The basic geometric design of
denture bases should be triangular
•Maxillary buccal flange….laterally and
superiorly
•Mandibular buccal flange….laterally
and inferiorly……and
•its lingual flange..medially and
inferiorly
63

64. Modiolus and associated musculature
 Tendinous node near corner of mouth formed
by intersection of several muscles of cheeks
and lips
64

65.  The buccinator muscle may be divided in to
superior, middle, and inferior divisions.
65

66. According to
Fish,
Superior fibers
acts to seat the
maxillary
denture.
Middle fibres
controls the
bolus of food.
The inferior
fibres
contributes to
mandibular
denture
stability.
66

67.  While the middle fibres contract,
controlling the bolus, the inferior fibres
relax to form a pouch capable of storing
food until needed to form another bolus.
 Extension of a concave denture base
into this pouch allows the cheek to lie
over the flange.
67

68. Action of some other muscles.
Dislocating
muscles
Fixing
muscles
vestibular Masseter
Mentalis
Depressor labii
inferioris
Buccinator
Orbicularis oris
lingual Internal pterigoid
Palatoglossus
Styloglossus
mylohyoid
Genioglossus
Intrinsic
muscles of
tongue
JPD1965;15:401-417
68

69.  The three structures …..
 .
medial roll of
the
buccinator
muscle
tongue teeth
69
JPD
2004;92;509-
518

70. THE NEUTRAL ZONE (NZ)
 Area or position where the
forces between tongue and
cheeks or lips are neutralised
Fish… 1931
 Tissues … functionally mold
entire polished surface
 Teeth should be placed within
NZ for better stability
70

71. Relationship Of The Opposing Occlusal
Surfaces
 Dentures should be free
of interferences – within
functional range of
movements of patients
 Premature contacts –
uneven stresss
 Bilateral balanced
occlusion
….simultaneous and
smooth glinding
contacts
71

72. Occlusal Plane
 The occlusal surfaces in the
region of the mandibular molars
are approximately two millimeters
below the top of the retromolar
pads
 Anteriorly – interpupillary line/
corner of mouth
 Posteriorly – camper’s plane /
anterior 2/3rd of retromolar pad &
lateral border of tongue
72

73.  The influence of the retromylohyoid extension on
mandibular complete denture stability.
 The contribution of retromylohyoid extension in complete
mandibular impression was tested in six individuals by
means of cineradiography and placement of metal marker.
 It was concluded that the retromylohyoid extension has a
stabilizing effect on mandibular complete denture.
73
C.H.Jooste, C.J. Thomas
IJP1992;5:34-38

74. 74
Myloc system
The surface of a lower
denture facing the
tongue is fitted with
small bars shaped like
wings. These wings lay
underneath the tongue
providing stability of the
denture-mandible
Prim Dent Care 1999 Oct ;6(4):135-9

75. Myloflex Dentures
 . It incorporates a positional memory insert and
an extended flange that takes advantage of the
undercut available in the submandibular fossa.
75
J Am Dent Assoc 1959 Jul ;59(1):88-95

76. SUPPORT
76

77. complete denture support is the resistance to vertical
movement of the denture base towards the ridge
Factors responsible for support are
 Size and consistency of tissues.
 Patients general health and resistance.
 Force developed by supporting muscles.
 Severity and location of past periodontal
diseases.
 Length of edentulousness.
Support
77
According to jacobson and
krol,

78. Mechanisms of Complete Denture
Support:
 basic problem ..…edentulous --artificial
replacements are attached to the
supporting bone
 Masticatory loads:
 natural teeth : 44 lb (20 kg)
 complete dentures : 13-16 lb (6-8 kg)
 Mucosa Support :
 Mean Denture Bearing Area
 Maxilla: 22.96 cm²
 Mandible : 12.15 cm²
78

79. Anatomy of supporting structures
 The foundation for dentures is
made up of bone of the hard
palate and residual ridge,
covered by mucous membrane.
1. Mucous Membrane:
 The mucosa is formed by stratified
squamous epithelium which often is
keratinised,
 submucosa …. connective tissue
that varies in character from dense
to loose areolar tissue and also
varies considerably in thickness….
79

80. 2. Hard Palate :
 palatine bone form the
foundation for the hard palate
and provide considerable
support for the denture.
 It is covered by soft tissue of
varying thickness, even though
the epithelium is keratinized
throughout.
80

81. 3. Soft Tissues
 The presence of keratinized firmly bound mucosa permits
the tissue to better resist stress.
 Keratin is a scleroprotein present in the stratum corneum
….. protects the vital underlying epithelial layers.
 Resilient submucosa permits moderate compressibility
with out much impingement of the mucosa between
denture base and bone.
81

82. 4. Bone Factor
 pressure tension concept …..destruction or
preservation of the bone of the residual ridge.
 pressure stimulates resorption and tension
maintains the integrity or causes the deposition
of bone.
 the area of muscle attachment, tends to preserve
the quality of bone.
 Cortical bone is more resistant to resorption than
cancellous or medullary bone.
82

83. Based on the clinical and histological impressions the dentist
can categorise the denture bearing areas in to;
83

84. A high or V-shaped palate only provides secondary
support.
The flat or U shaped palate provides excellent
support
84

85. Methods To Improve Support
SURGICAL METHODS
 Surgical removal of
pendulous tissues.
 Surgical reduction of
sharp or spiny
mandibular ridges.
 Surgical enlargement
of ridge.
 Flabby ridge.
 Implants.
NON SURGICAL
METHODS:
 Occlusal and vertical
dimension correction
of old prosthesis.
 Good nutrition.
 Conditioning of
patients musculature.
85

86. “Technique itself is merely the
practical application of principles, and
if the principles are unsound, the most
elaborate and painstaking technique
certainly is doomed to fail.”
- Bohannan
86

87. References…
87
 Boucher’s prosthodontic treatment for edentulous patients - 11th edition
 Complete denture prosthodontics, 2nd edition, John j. Sharry
 Impressions for complete dentures, Bernard Levin
 Problems and solutions in complete denture prosthodontics, David J.
Lamb
 Essentials in complete denture prosthodontics, 2nd edition, Sheldon
Winkler.
 A contemporary review of the factors involved in complete denture
retention, stability, and support. Part 1: retention T. E. Jacobson, A.J.
Krol. JPD 1983, 49:5-15.

88. 88
 T.E. JACOBSON and J. KROLL :A contemporary review of the factors involved
in the complete dentures. J PROSTHET DENT 49:2,1983.
 A contemporary review of the factors involved in complete dentures. Part 3
support. J P D 1983; 49(3) ; 306- 313
 FRIEDMAN.S.: Edentulous impression procedures for maximum retention
and stability. J PROSTHET DENT 7:14,1957.
 BECKER C.M et.al, :Lingualized occlusion for removable prosthodontics. J
PROSTHET DENT 38:601,1977.
 The physical mechanisms of complete denture retention Br Dent Jr, Vol 189,
No 5, Sep 9, 2000
 Skinner E W, Chung P. The effect of surface contact in the retention of a den
-J Prosthet Dent 1951; 1: 229-235
 JPD1965;15:401-417

89. 89 Thank you