This document discusses factors that influence the stability of complete dentures. It defines stability as the quality of a removable prosthesis to resist displacement from functional stresses. The three main factors discussed are: 1) The relationship of the denture base to underlying tissues - Proper adaptation of the denture base to the residual ridges and surrounding tissues improves stability. 2) The relationship of the denture borders to surrounding muscles - Contouring the denture to allow free function of muscles like the buccinator and allowing muscles to help seat the denture enhances stability. 3) The relationship of opposing occlusal surfaces - Proper occlusal harmony contributes to resisting forces that could displace the dentures.

1. 1

2. Stability in complete dentures
Dr. Fateema Priyam
2nd year P G Student
Dept of Prosthodontics
2

3. Contents
 Introduction and definitions
 Factors influencing denture stability
The relationship of denture base to the
underlying tissues
The relationship of the external surface and
border to the surrounding orofacial
musculature
The relationship of the opposing occlusal
surfaces
3

4.  Patient education
 Checking of stability of dentures
 Discussion
 Summary
 References
4

5. Introduction
5

6. Success of complete denture
Retention
SupportStability
6

7. STABILITY:-
1. The quality of a removable prosthesis to be
firm, steady or constant to resist displacement
by functional horizontal or rotational stresses.
2. Resistance to horizontal displacement of
prosthesis.GPT-9
7

8.  FISH (1948) described three denture surfaces.
Tissue surface.
Polished surface.
Occlusal surface.
 All the three surfaces helps in determining
stability of the complete denture.
8

9.  The factors that contribute to stability include
ridge height and conformation, base adaptation,
residual ridge relationships, occlusal harmony,
and neuromuscular control.
9

10.  1. The relationship of the denture base to the
underlying tissues
 2. The relationship of the external surface and
border to the surrounding orofacial musculature
3. The relationship of the opposing occlusal
surfaces
10

11. The relationship of the denture
base to the underlying tissues
11

12.  Denture base adaptation
 Residual ridge anatomy
 Mandibular flange area
 Sublingual crest region
12

13. Denture base adaptation
 Maximum coverage without undue displacement
of tissue not only allows the development of a
good border seal but also provides close
adaptation of denture base with facial and lingual
slopes -improving stability.
13

14.  Boucher stipulated the following objectives of
complete denture impression
◦ Retention
◦ Stability
◦ Support
◦ Esthetic values
◦ Preservation of alveolar ridge
14

15.  He notes that stability is obtained by
incorporating the surfaces of the maxillary and
mandibular ridges, which are at right angles to
the occlusal plane.
 He further states “ maximum use of all bony
foundations where the tissues are firmly and
closely attached to the bone”
15

16. Residual ridge anatomy
 The development of stability is limited by the
anatomic variations of the patient that
determines the residual ridge height and
conformation
16

17.  Large, square, broad ridges offers a greater
resistance to lateral forces than do ovoid,
narrowed tapered ridges.
17

18.  The contacting of the labial and buccal flanges with
labial and buccal ridge slopes is one of the critical
factors contributing stability.-Friedman
 Small and rounded irregularities present on the
vertical walls of the ridges also contribute. So
alveoloplasty should be limited only to removal of
bone that would prevent fabrication of successful
prosthesis.
18

19.  The arch form – square arches tends to resist
rotation of the prosthesis better than the ovoid OR
tapered arches.
 Shape of palatal vault – stability is limited by the
length and angulations of the palatal ridge slopes.
 A steep or high arched palate enhances the stability
by providing greater area of contact and long inclines
approaching at right angle to the direction of force.
19

20. Mandibular lingual flange
 Most desirable feature of lingual slopes is that it
approaches 900 to the occlusal plane.
 Effectively resist horizontal forces.
 Although the posterior fibres of the mylohyoid
muscle attach more superiorly than anterior, they
descend nearly vertically to attach hyoid bone
20

21. 21

22.  The posterior lingual flange is usually able to be
extended inferiorly more than the anterior lingual
flange.
22
• Anteriorly, the mylohyoid muscle fibers are
directed more horizontally to communicate
with fibers of the opposite side along a
midline tendinous raphe.

23.  Musculature of the floor of the mouth may also
influence the degree of intimate contact allowed.
 Any flange extension below the mylohyoid ridge
must incline medially away from the mandible to
allow for the mylohyoid muscle contraction.
23

24. 24

25. 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 the area of the anterior alveolingual
sulcus.(GPT-9)
25

26. Its coverage by denture results in
 1)Increased stability by allowing the tongue to
aid in holding the denture in place.
 2) Increased retention of the denture.
26

27.  Making the impressions with minimal pressure on
the floor of the mouth while tongue is at rest
position allows greater mobility of the underlying
muscles without denture dislodgement and
without occlusion of the sublingual gland duct.
27

28. 28

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

30. Orofacial musculature
 Both stability and retention depend upon the
relationship of polished surface and surrounding
orofacial musculature.
 The musculature can facilitate stability in two
ways????
30

31.  First, the action of certain muscle groups must
be permitted to occur without interference by the
denture base -will not dislodge the prosthesis
during function or compromise stability.
 Second, the dentist must recognize that normal
functioning of some muscle groups can be used
to enhance stability.
31

32.  The action of the levator anguli oris, depressor
anguli oris (triangularis), mentalis, mylohyoid
and genioglossus muscles can dislodge the
denture if the denture base does not provide
freedom for these muscle action.
32

33. 33

34.  Fish believed that the contours of the polished
surface provided the principal factor governing
complete denture stability.
 Robert P R (1960) stated that “The form and contour of
the polished surface of the denture base is an important factor
in the denture function and plays a significant role in the
complete denture stability”
34

35.  Strain C J (1969) stated that “The polished surface of the
lower denture greatly influences the stability due to the
proper adaptation of its surface to the tongue, lips and
cheeks.”
 The basic geometric design of denture bases
should be triangular.
 In the frontal cross section, the maxillary and
mandibular dentures should appear as two
triangles whose apexes correspond to the
occlusal surface.
35

36. 36

37.  The buccal and labial flanges of the maxillary and
mandibular dentures should be concave to
permit positive seating by the cheeks and the
lips.
37

38. 38

39.  The primary muscles of cheeks and lips are
orbicularis oris and buccinator. These muscles are
active in mastication, deglutition and speech.
 The proper contour of the denture flanges permits the
horizontally directed forces, that occur during
contraction of these muscles, to be transmitted as
vertical forces tending to seat prosthesis.
39

40.  To direct a seating action on the mandibular
denture, the tongue should rest against a lingual
flange inclined medially away from the mandible
and somewhat concave.
 The degree of inclination depends on the balance
of the muscular forces of the tongue.
40

41. Modiolus (hub of a wheel)
 The musculi cruculi modioli or modiolus and their
associated musculatures has various actions on
the denture.
 An anatomical landmark near the corner of the
mouth that is formed by the intersection of
several muscles of the cheeks and lips.
41

42.  These muscles are:-
 Orbicularis oris.
 Buccinator.
 Caninus (levator anguli oris).
 Triangularis (depressor anguli oris).
 Zygomaticus major.
 Risorius.
 Quadratus labii superioris.
 Depressor labii inferioris.
42

43. 43

44.  Because none of these muscles contains fibres
that have more than one bony attachment, they
depend on fixation of the modiolus to allow
isometric contraction.
 E.g.-contraction of the triangularis, caninus, and
zygomaticus muscles fixes the modiolus, allowing
the buccinator muscle to contract isometrically.
44

45.  This allows the buccinator muscle to tense ,
allowing it to control the food bolus on the
occlusal table.
45

46.  Isotonic contraction of the buccinator muscle in
the absence of modiolus fixation would pull the
corner of the mouth posteriorly.
 It can be fixed more anteriorly as when the word
“Hoe” is pronounced or posteriorly as in case of
“He”.
 The denture base must be contoured to permit
the modiolus to function freely.
46

47.  In the premolar region the mandibular denture
should exhibit both a shortened and narrowed
flange to permit the action that draws the
vestibule superiorly and the modiolus medially
against the dentures.
 The buccinator muscle may be divided into
superior, middle, and inferior divisions.
47

48. 48

49. 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.
49

50. Neutral zone concept
 Harmony between the polished surface of the
denture and associated musculature.
 Neutral zone is the area of potential denture
space where the forces of tongue pressing
outward are neutralized by the forces of the
cheek and lips pressing inward
50

51. 51
The Potential ‘Denture Space’
Mandibl
e

52. Importance of neutral zone:
 As the area of the impression surface decreases
(alveolar ridge resorption) less influence it has on the
denture retention and stability.
 Consequently retention and stability become more
dependent on the correct positioning of the teeth and
the contours of the external surface of the dentures.
52

53. 53
1. Those muscles which primarily dislocate the
denture during activity (Dislocating muscles),
2. Those muscles that fix the denture by
muscular pressure on the polished surfaces
(Fixing muscles).

54. 54
Dislocating muscles
Vestibular:
Masseter
Mentalis
Incisive Labii Infer.
Lingual:
Medial Pterygoid
Palatoglossus
Styloglossus
Mylohyoid
Fixing muscles
Vestibular:
Buccinator
Orbicularis oris
Lingual:
Genioglossus
Lingual longitudinal
Lingual vertical
Lingual transverse

55. 55

56. 56

57. Tongue
It completely fills the floor of the mouth
The lateral borders rest over the ridge which
would normally represent the occlusal surfaces
of the teeth.
The tip or apex of the tongue rests on or just
to the lingual side of the lower anterior ridge.
57

58.  As the patient becomes edentulous, the
continuous destruction of residual ridges occurs.
 Because of these changes the tongue will expand
in the space formerly occupied by the teeth.
 The position of the tongue will become
retracted.
58

59. (1) The tongue is pulled back into mouth and the
floor of the mouth is exposed.
(2) The lateral borders are either inside or
posterior to the ridge.
(3) The tip of the apex of the tongue sometimes
lies in the posterior part of the floor of the
mouth or may be withdrawn into the body of
the tongue.
59

60.  When natural teeth are present retracted tongue
position has little effect on the ordinary function
of the mouth.
 It is only when a person becomes edentulous
that a retracted tongue position becomes a
problem.
60

61.  Some authors recommend posterior extension of
the lingual flange to fill the retromylohyoid space
to permit the base of the tongue to contribute to
the neuromuscular control of the prosthesis.“’
61

62.  Inclination of the lingual flange must be designed
to guide the tongue to rest over the flange and
permit any horizontal forces generated against
the denture base to be transmitted as seating
forces.
62

63. 63

64. Relationship of opposing occlusal
surfaces
64

65.  The dentures must be free of interferences within
the functional range of movements of the
patient.
 During both functional and parafunctional
movements the occlusal surfaces should not
strike prematurely in localized areas?????
65

66. Anatomic occlusal scheme
 In maximum intercuspation, surface contact
between posterior anatomic teeth consists of
multidirectional but equalized, forces.
66

67.  But the directional forces change in eccentric
position, and there is a significant lateral force
component exerted on the denture bases
67

68. Balanced occlusion
 The bilateral, simultaneous, anterior and
posterior occlusal contact of teeth in centric and
eccentric positions. (GPT-9)
68

69.  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.
69

70.  Various philosophies have been proposed either
to provide for a fully balanced occlusion
throughout lateral and protrusive excursive
movements or to control the direction of forces
experienced during localized occlusal contact.
70

71.  Setting of anatomic or semianatomic artificial
teeth to provide excursive balance is thought to
minimize localized stress concentration and
lateral dislodging forces by ensuring multiple
points of contact to distribute functional occlusal
forces.
71

72.  To minimize dislodging forces the occlusion must
be balanced throughout the functional range of
movement of the patient.
 A balanced occlusion is limited by the
buccolingual and mesiodistal width of the
anatomic cuspal inclines.
72

73.  Some authors recommend occlusal schemes that
direct forces to minimize the unseating of the
denture during unilateral excursive tooth
contacts.
73

74. Zero degree teeth
Two dimensional/ monoplane occlusion.
 Non-anatomic teeth.
 Eliminating cusps will reduce the lateral forces.
 Balanced occlusion in eccentric relation is not a
part of the occlusal scheme
74

75.  A monoplane scheme reduces the horizontal
force components because direction of forces
between zero degree teeth in centric and
eccentric position is essentially vertical.
75

76. LINGUALIZED OCCLUSION
 Anatomic (30/330) teeth are used for the
maxillary denture. Tooth form with prominent
lingual cusps are helpful.
 Nonanatomic or semianatomic teeth are used for
the mandibular denture. Either a shallow or flat
cusp form is used.
76

77.  Maxillary lingual cusps should contact mandibular
teeth BUT the mandibular buccal cusps should
not contact the upper teeth in centric occlusion.
77

78.  The theories of lingualized occlusion provide both
a limited range of excursive balance and a
directing of forces to the lingual side of the lower
ridge during working-side contacts
78

79. 79

80.  Balancing and working contacts should occur only on
the maxillary lingual cusps.
 Protrusive balancing contacts should occur only
between the maxillary lingual cusps and the lower
teeth.
 Since in lingualized occlusion, vertical forces are
centralized on the mandibular teeth, it is proposed to
aid in stability.
80

81. Maxillary and mandibular tooth
position
 The arch curvature should correspond to curvature of
alveolar ridge, facial contour and maxillary lip
position.
 Anterior and posterior teeth should be arranged as
close as possible to the position once occupied by the
natural teeth, with only slight modifications made to
improve leverages and esthetics
81

82.  Mandibular anterior teeth should be in harmony
with the maxillary anterior tooth position.
 Errors in maxillary tooth position will be
transferred to the mandibular arch.
82

83. OCCLUSAL PLANE
 A mandibular occlusal plane that is too high can
result in reduced stability.
1.Lateral tilting forces directed against the teeth
are magnified as the plane is raised.
2.The mandibular denture needs to be controlled
by the musculature of the tongue, lips, and
cheeks.
83

84.  An elevated occlusal table prevents the tongue
from reaching over the food table into the buccal
vestibule.
 A raised mandibular occlusal plane is usually
present when the vertical dimension of occlusion
is increased excessively.
84

85.  The best stability is obtained when the occlusal
plane is parallel to and evenly divided between
the ridges.
85

86.  If the occlusal plane is tipped???
 If the occlusal plane is lower in molar area, there
will be a tendency for upper denture to be
displaced posteriorly and lower denture
anteriorly.
86

87. Patient education
 Patients must be advised that chewing is not
random but an intentional and selective
activity.
 The eating skills must be slowly developed
and refined
87

88.  How to eat with dentures is a skill that has to be
learned
 Basically chewing with dentures is more
methodical than with natural teeth.
 Patients must be instructed to divide the normal
spoonful of food into half and place each half
posteriorly and bilaterally
88

89. Checking stability of the denture
 Pressure is applied with the ball of the finger in
the premolar-molar regions of each side
alternatively. This pressure must be at right
angle to the occlusal surface.
 If pressure on one side causes the denture to tilt
and raise on the other side, it indicates that the
teeth on the side on which the pressure was
applied are outside the ridge.
89

90. Improving denture stability
Over dentures
 Dentures get more ridge support, this enhances
the retention of the denture and ultimately
stability gets improved.
 Rate of resorption of residual ridge decreases.
 tooth supported
Implant supported
90

91.  Prospective clinical evaluation of mandubular
implant overdentures part-I -retention stability
and tissue responses.
David R.Burns,et al
J Prosthet Dent 1995;73(4): 354-63
91

92.  17 subjects with preexisting conventional
complete dentures were evaluated.
 Two implants were placed bilaterally in the
anterior mandible.
 The conventional dentures were modified, and
the retention stability, and tissue response for
conventional dentures were compared (cross
over experimental study)
92

93.  The study showed superior statistics of implants
as an treatment alternative to increase stability
than ridge augmentation or vestibular extension
procedures.
93

94. Discussion
94

95. Summary
 Stability prevents anterio-posterior shunting of
the denture base .
 It has been cited as the most significant property
in providing physiology comfort to the patient.
 Denture instability adversely affect retention &
support and results in deleterious forces on the
edentulous ridge during function and
parafunction.
95

96. References
Journal references:
 T.E.Jacobson , A.J Krol “A contemporary review of
the factors involved in complete dentures part II:
stability” J Prosthet Dent 1983;49:165-172.
 Corwin R. Wright , “Evaluation of the factors
necessary to develop stability in complete dentures”
J Prosthet Dent 1966;16:414-30.
reprint J Prosthet Dent 2004;92:509-18
96

97.  Brill N , Tryde G, Cantor R, The dynamic nature of
the lower denture. J Prosthet Dent 1956, 15:401-
417
 Ross L Taylor, The stability of complete dentures.
Aust Dent Journal 1962; 7(2): 145-154.
 Becker C M, Swoope C C , Gucker A D,
Lingualized occlusion for removable prosthodontics
J prosthet Dent 1973;38: 601-608
97

98.  Krishna Prasad D, B Rajendra prasad, Enhancing
stability: A review of various occlusal schemes in
complete denture prosthesis. NUJHS 2013;
3(2):105-112.
 C H Jooste, C J Thomas, The influence of
retromylohyoid extension on mandibular complete
denture stability . Int J Prosthodont 1992; 5 : 34-
38.
98

99.  Textbook reference:
1) Zarb Bolender, Prosthodontic Treatment for
Edentulous Patients ,2004,12 Ed,Mosby Inc
2) Winkler ,Essentials of Complete Denture
Prosthodontics 1996,2nd Ed,AITBS Publishers.
3) Heartwell,Syllabus of Complete
Dentures,1992,4th Ed,Varghese Publishing
House.
4) Glossory of prosthodontics -9
99

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