STABILITY IN COMPLETE DENTURES

- MAHAK RALLI- IV/I

CONTENTS Definition Factors affecting stability Checking for stability Conclusion

DEFINITION Stability is defined as ‘the ability of a

denture to be firm, steady or constant, to resist displacement by functional stresses and not to be subjected to change of position when forces are applied.’

-GPT

It is the ability to withstand horizontal forces.

In simpler words stability is defined as “the quality of a denture to resists displacement by functional stresses.”

FACTORS AFFECTINGThe qualities necessary to create and maintain stability are dependent upon the following factors: 1. Quality of impression2. Vertical height of residual ridge3. Shape of palatal vault4. Arch form5. Quality of soft tissue covering ridge6. Mandibular lingual flange7. Occlusal plane8. Teeth arrangement9. Contour of polished surface10. Orofacial musculature

QUALITY OF THE IMPRESSION

An impression should be as accurate as possible.

The impression surface should be smooth and duplicate all the details accurately.

It should be devoid of voids and any rough surfaces

The impression should not wrap on removal

The impression should be dimensionally stable and cast should be poured as soon as possible.

VERTICAL HEIGHT OF RESIDUAL RIDGE

The residual ridge should have sufficient vertical height to obtain good stability

Highly resorbed ridges offer the least stability.

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.

QUALITY OF SOFT TISSUE COVERING THE RIDGE

The ridge should provide a firm soft tissue base with adequate submucosa to offer good stability.

Flabby tissues with excessive submucosa offer poor stability.

MANDIBULAR LINGUAL FLANGE

•Lingual slopes approach 90 degree to occlusal plane

•Effectively resists horizontal forces

•The posterior lingual flanges extends more inferiorly than anterior lingual flange

OCCLUSAL PLANE The occlusal plane should be oriented

parallel to the ridge If occlusal plane is inclined then the

sliding forces may act on the denture to reduce its stability

The occlusal plane should divide the inter-arch space equally.

The maxillary rim should be parallel anteriorly to the inter-pupillary line & posteriorly to the ala- tragus line

Plane should be parallel to the crest of residual ridge.

Occlusal surface in the region of the mandibular 1st molar are approximately 2mm below the top of retromolar pad.

TEETH ARRANGEMENT The position of the teeth and their

occlusion play an important role in the stability of the denture.

Balanced occlusion facilitates the even distribution of forces across the denture.

Absence of balanced occlusion may produce unbalanced, lever type forces on any one side of the denture leading to loss of stability.

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 displacing tendency, the ridge crest acting as a fulcrum

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 resorption pattern leads to an increase crossbite relationship

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 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

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

NEUTRAL ZONE The teeth in the denture should be

arranged in the neutral zone The neutral zone is defined as, “the

potential space between the lips and cheeks on one side and the tongue on the other. Natural or artificial teeth in this zone are subject to equal and opposite forces from the surrounding musculature.”

-GPT

CONTOUR OF POLISHED SURFACE

The polished surfaces of the denture should be harmonious with the oral structures.

They should not interfere with the action of the oral musculature.

From the cuspid to posterior aspect the denture surface slopes slightly inward creating space for buccal corridor.

The over all concept should be in terms with the neutral zone concept.

INFLUENCE OF ORO FACIAL MUSCULATURE

The geometric design should be triangular. In cross section, the upper and lower

denture should appear as two triangles that correspond to occlusal surface.

Normally, tongue should rest on the lingual flange and occlusal surface of the lower teeth- aids in stability

Occlusal harmony of opposing teeth enhance stability.

Premature contact during functional and parafunctional activities will affect the stability.

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

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

PATIENT EDUCATION

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 posteriorly and bilaterally.

CONCLUSION Stability is cited as the most significant

property in providing physiological 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

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