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
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
16.
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.
18.
19. Arch form
Square arches tend to resist rotation
of the prosthesis better than the other
arch forms.
20.
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
23.
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
25.
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
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
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
41.
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
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
49.
50.
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
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
61.
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
67.
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
72.
73.
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
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
