1. Stability in complete dentures is influenced by factors like residual ridge anatomy, quality of soft tissues, impression quality, occlusal planes, tooth arrangement, and contour of the polished surface. 2. Various muscles like the buccinator, orbicularis oris, and mentalis can impact denture stability if the denture borders and contours do not allow for proper function. 3. Establishing balanced occlusion is important for stability, as imbalanced forces can displace the denture during jaw movement.

1. STABILITY IN COMPLETE
DENTURES

2. Contents
 Definitions
 Factors effecting stability
 Methods to check stability
 Methods to improve stability
 Residual ridge anatomy
 Quality of soft tissue covering the ridge
 Quality of the impression
 Occlusal planes
 Arrangement of teeth
 Contour of polished surface

5. Retention Stability Support
Psychologic Physiologic Longevity
Comfort Comfort
Prosthesis Success

6. STABILITY DEFINITIONS –
GPT 8
1. That quality of maintaining a constant
character or position in the presence of
forces that threaten to disturb it; the quality
of being stable; to stand or endure
2. The quality of a removable dental
prosthesis to be firm, steady, or constant,
to resist displacement by functional
horizontal or rotational stresses
3. Resistance to horizontal displacement of a
prosthesis

7. Stability
Physiological
comfort
Prosthesis

8. Fish 1948
3 surfaces:
 Polished surface
 Occlusal surface
 Tissue surface
STABILITY

9. stability
Residual
ridge
anatomy
Quality of
soft tissue
Quality of
impression
Occlusal
planes
Teeth
arrangement
Contour of
polished
surface
Denture
base
adaptation

10. 1. Relationship of denture base to
underlying tissues

11.  Maximum coverage without undue
displacement of the tissues
 Development of good border seal
 Close adaptation of denture base
Denture base adaptation

12. Impression should be as accurate as possible
The impression surface should be smooth &
duplicate all the details accurately
The impression should not warp on removal
The impression should be dimensionally stable
& the cast should be poured as soon as
possible
Quality of the impression

13. Friedman:
 Contacting of labial and buccal flanges
with labial and buccal ridge slopes
increases stability.

14. Boucher
 Incorporating the surfaces of maxilla
and mandible which are at 90 degree
to occlusal plane improve stability.
 Maximum use of all bony foundations
where tissues are firmly and closely
attached to bone”

15. •The residual ridge should have
sufficient vertical height to obtain good
stability
•Highly resorbed ridges offer the least
stability
Vertical Height of residual
Ridges

17. Shape of palatal vault
 A steep or high arched palate
enhances the stability :
- providing greater area of contact
- long inclines approaching at right
angles to the direction of force.

19. Arch form
 Square arches tend to resist rotation
of the prosthesis better than the other
arch forms.

21. The ridge should provide a firm soft
tissue base with adequate mucosa to
offer good stability
Flabby tissues with excessive
submucosa offer poor stability

22. Mandibular lingual flange
•Lingual slopes approach 90 degree to occlusal plane
•Effectivley resists horizontal forces
•The posterior lingual flanges extends more inferiorly
than anterior lingual flange

24. •Musculature of the floor may allow influence the
degree of intimate contact allowed.
•Presence of any thin mucousa overlying the
bony ridge slopes that may require relief make
close contact impossible.
Any flanges extension beyond the mylohyoid
must extend medially away from the
mandible to allow mylohyoid muscle
contraction

26. Sublingual crescent area
The crescent shaped area on the anterior floor of the
mouth formed by the lingual wall of the mandible and
the adjacent sublingual fold. It is the area of the anterior
alveolingual sulcus (GPT-8)
Extension of the denture over the resting tissues of
the sublingual crescent area completes the border seal
Its coverage by denture results in :
Increased stability by allowing the tongue to aid in
holding the denture in place

27. Making the impression with minimal pressure
on the floor of the mouth while the tongue is at
rest position allows:
-Greater mobility of the underlying muscles
without denture dislodgement.
-Without occlusion of the sublingual gland
duct

29. 2.Relationship of external surface
and periphery to surrounding
orofacial musculature.

30. Orofacial
musclulaur
e
Polished
surface
STABILITY

31.  Polished surface should allow muscle
to function individually without any
interference which may dislodge the
denture
 Some normally functioning muscles
can aid to stabilize the denture
Proper border moulding should be
done for proper extension of the
borders

32. Dislodging muscles
 Levator anguli oris
 Depressor anguli oris
 Incisivus
 Mentalis
 Genioglossus
 Mylohyoid
If not given proper freedom to function these
muscles can dislodge the denture.Proper border
moulding ensures proper extension of these muscles

33. Fish 1933
“It is not so widely understood that the
actual shape of the whole buccal,labial
and lingual surfaces can wreck the
stability of a denture as bad as a
wrong impression”

34. Frontal cross section of denture
•Maxillary buccal flange:
Superior and lateral
•Mandibular buccal
flange:
Inferior and lateral
•Mandibular lingual
flange:
Inferior and medial
Provide vertical component to
horizontal forces

35.  The buccal and labial
flanges of the
maxillary and
mandibular dentures
 concave
 Lingual flange 
inclined and concave

36.  Primary muscles of lips and cheeks:
-Orbicularis oris
-Buccinator
Muscle
contraction
Horizontal forces
Proper contoured
flanges
Horizontal 
Vertical forces
Seating of
prosthesis

38. Modiolus (Musculi cruculi modioli
)

40.  Various actions on the denture
 None of these fibres have more than
one bony attachement
 Depend on the modiolus to allow
isometric contraction
Contraction of triangularis,caninus and
zygomaticus muscle fixes the modiolus
to allow buccinator to contract
isometrically

42.  The denture base must be contoured
to allow the modiolus to function freely
 In the premolar region the mandibular
denture:
-Shortened flange
-Narrow flange
This permits action which:
-draws vestibule superiorly
-modiolus medially against the denture

43. Buccinator muscle

44. According
to FISH
Superior
fibres
Middle
fibres
Inferior
fibres
Seat
maxillary
denture
Control
food
bolus
Denture
stability

45. Medial roll of buccinators
 Function of the medial roll:
-Forms the buccal wall of food trough
-Retrieve food that is forced into the
buccal pouch.
 This mechanism is known as
"shunting effect".

46.  Middle fibers:
-contract and controlling food bolus
 Inferior fibres:
-Relax to form pouch to store food until
needed to form another bolus

47. Clinical significance
 Extension of concave denture base into
this pouch allows cheek to lie over flange
 Electromyography:
-Buccinator muscle contraction cannot
adapt to changes in contour of denture
base
-Denture contours should be designed to
harmonize with existing buccinator
muscle function

48. Neutral zone
 The potential space between the lips
and cheeks on one side and the
tongue on the other; that area or
position where the forces between the
tongue and cheeks or lips are equal

51. Tongue
 As the patient becomes
edentulous,the continous destruction
of residual ridges occurs.
 Because of these changes the tounge
will expand in spaces formerly
occupied by the teeth
 This occurs partially due to growth of
tounge known as Proptosis lingualis

52.  A small narrow tongue contributes to
the ease of impression making but
jeopardized the lingual seal for
mandibluar dentures
 An extremely large tounge poses
additional problems during impression
making and impairs denture stability

53. 3.Relationship to opposing
occlusal surfaces.

54. Balanced occlusion
 The bilateral simultaneous,anterior
and posterior occlusal contacts of
teeth in centric and eccentric
positions.-GPT 8

55.  Establishing a balanced occlusion is key
to maintaining stability and in turn the
border seal.
 Lower dentures are particularly
vulnerable to instability as a result of
poor retention.
 Here the occlusal table should be
designed to provide optimum load
distribution in order to seat the denture

56.  The patients with balanced occlusion
do not upset the normal static,stable
and retentive position
 Absence of occlusal balance will result
in leverage of the denture during
mandibular movement,compromising
stability.

57. Lingualized occlusion
 Balancing and working contacts
should occur only on maxillary lingual
cusps.
 In lingualized occlusion,the vertical
forces are centralized on the
mandibular teeth,it is proposed to aid
in stability.

58. Tooth position
 Anterior and posterior teeth should be
arranged as close as possible to the
position once occupied by the natural
teeth
 Modifications can be made to improve
aesthetics and leverage

59. Maxillary anterior tooth
position
 The arch curvature should correspond
to:
- curvature of alveolar ridge
- facial contour
- Maxillary lip position

60.  Arranging the teeth in to a square arch
form on a tapering ovoid residual ridge
causes canines to be labial to crest of
the maxillary ridge than the incisors

62.  This results in bicuspids being more
buccal to the ridge than they should be.
 Working side occlusal pressure produces
a diplacing tendency, the ridge crest acting
as a fulcrum

63.  The labial axial inclination of the natural anterior
tooth places the incisal edge labial to the centre
of rotation of the tooth.
 If prosthetic tooth is placed exactly in the same
position as the natural crown it will be labial to
the ridge support
 Incisal pressure causes a displacing torque.

64. Mandibular anterior tooth
position
 It should be in harmony with the
maxillary anterior tooth
 Errors in maxillary tooth position will
be transferred to the mandibular arch
 For maximum stability overbite should
be as minimum as possible

65. Maxillary posterior tooth position
 Natural posterior maxillary teeth have
a buccal inclination and the
mandibular teeth have a normal
lingual axis inclination

66.  The normal residual ridge resorption
pattern leads to an increase crossbite
relation ship
 Tendency to avoid cross bite
arrangement results in placing the
maxillary teeth in buccal position or
mandibular teeth in lingual to desired
position
 Results in impaired stability

68.  In such cases the working side occlusal
pressure causes a displacing tendency
because the line of force is buccal to the
fulcrum

69. Mandibular posterior teeth
 The buccal cusps and fossae of the
mandibular posterior teeth should lie
directly over crest of the ridge

70.  If placed more buccally, the working side
occlusal pressure causes a displacing tendency
because the line of force is buccal to the
fulcrum
 If placed lingually tongue will displace the
denture

71. Occlusal plane
The occlusal plane should be oriented
parallel to the ridge
If the occlusal plane is inclined, then the
sliding forces may act on the denture &
reduce its stability
The occlusal plane should divide the
interarch space equally

74. Patient education
 Eating:
 Eating skill must be slowly developed
and refined
 Initially patient should have soft diet
 Patient should be instructed to divide
normal spoonful of food into half and
place each half posterioirly and
bilaterally.

75. Checking the stability
 Pressure is applied with the ball of
finger in premolar and molar region of
each side alternatively
 Pressure must be at right angle to
occlusal surface.
 if pressure on one side causes the
denture to tilt and raise on other side it
indicates that the teeth on the side to
which pressure is applied are outside
the ridge

76. Maximizing stability
 Maximum coverage of denture bearing area
within physiological limits
 Understanding muscle actions
 Neutral zone
 Correct occlusal plane and teeth position
 Patient education
 Denture modifications
 Denture adhesives

77.  Preprosthetic surgeries
 Over dentures
 Soft liners

78. CONCLUSION
 Stability is cited as the most significant
property in providing physioloical
comfort to the patient.
 It is important to know the factors
affecting stability
 The main factors cited were the
occlusal tissue and polished surfaces

79.  Though to fabricate perfectly stable
denture may not be truly possible we
should still try to achieve the
maximum stability as possible