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