Download - Stability in complete dentures
STABILITY IN COMPLETE
DENTURES
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
Retention Stability Support
Psychologic Physiologic Longevity
Comfort Comfort
Prosthesis Success
STABILITY DEFINITIONS –
GPT 81. 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
Stability
Physiological comfort
Prosthesis
Fish 1948
3 surfaces:
Polished surface
Occlusal surface
Tissue surface
STABILITY
stabilityResidual
ridge anatomy
Quality of soft tissue
Quality of impression
Occlusalplanes
Teeth arrangement
Contour of polished surface
Denture base
adaptation
1. Relationship of denture base to
underlying tissues
Maximum coverage without undue
displacement of the tissues
Development of good border seal
Close adaptation of denture base
Denture base adaptation
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
Friedman:
Contacting of labial and buccal flanges
with labial and buccal ridge slopes
increases stability.
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”
•The residual ridge should have
sufficient vertical height to obtain good
stability
•Highly resorbed ridges offer the least
stability
Vertical Height of residual
Ridges
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.
Arch form
Square arches tend to resist rotation
of the prosthesis better than the other
arch forms.
The ridge should provide a firm soft
tissue base with adequate mucosa to
offer good stability
Flabby tissues with excessive
submucosa offer poor stability
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
•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 mylohyoidmust extend medially away from the mandible to allow mylohyoid muscle contraction
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
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
2.Relationship of external surface
and periphery to surrounding
orofacial musculature.
Orofacialmusclulaur
e
Polished surface
STABILITY
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
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
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”
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
The buccal and labial
flanges of the
maxillary and
mandibular dentures
concave
Lingual flange
inclined and concave
Primary muscles of lips and cheeks:
-Orbicularis oris
-BuccinatorMuscle
contraction
Horizontal forces
Proper contoured flanges
Horizontal Vertical forces
Seating of prosthesis
Modiolus (Musculi cruculi modioli
)
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 modiolusto allow buccinator to contract isometrically
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
Buccinator muscle
According to FISH
Superior fibres
Middle fibres
Inferior fibres
Seat
maxillary
denture
Control
food
bolus
Denture
stability
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".
Middle fibers:
-contract and controlling food bolus
Inferior fibres:
-Relax to form pouch to store food until
needed to form another bolus
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 buccinatormuscle function
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
Tongue
As the patient becomes edentulous,the continous destruction of residual ridges occurs.
Because of these changes the toungewill expand in spaces formerly occupied by the teeth
This occurs partially due to growth of tounge known as Proptosis lingualis
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
3.Relationship to opposing
occlusal surfaces.
Balanced occlusion
The bilateral simultaneous,anterior
and posterior occlusal contacts of
teeth in centric and eccentric
positions.-GPT 8
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
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.
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.
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
Maxillary anterior tooth
position The arch curvature should correspond
to:
- curvature of alveolar ridge
- facial contour
- Maxillary lip position
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
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
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.
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
Maxillary posterior tooth position
Natural posterior maxillary teeth have
a buccal inclination and the
mandibular teeth have a normal
lingual axis inclination
The normal residual ridge resorptionpattern leads to an increase crossbiterelation 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
In such cases the working side occlusal
pressure causes a displacing tendency
because the line of force is buccal to the
fulcrum
Mandibular posterior teeth
The buccal cusps and fossae of the
mandibular posterior teeth should lie
directly over crest of the ridge
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
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
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.
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
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
Preprosthetic surgeries
Over dentures
Soft liners
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
Though to fabricate perfectly stable
denture may not be truly possible we
should still try to achieve the
maximum stability as possible