RETENTION, STABILITY & SUPPORT IN COMPLETE DENTURE.

RETENTION, STABILITY RETENTION, STABILITY

& & SUPPORTSUPPORT

IN COMPLETE IN COMPLETE DENTUREDENTURE

Specific learning objectivesSpecific learning objectives

1.Definition and importance of Retention , stability and support in complete denture.

2.Factors affecting Retention , stability and support in complete denture.

3.How to overcome common difficulties(in brief).

Factor affecting Successful denture fabrication

Biologic Factors

Physical Factors

Mechanical Factors

Retention Stability Support

Psychologic Physiologic Longevity

Comfort Comfort

Prosthesis Success

RETENTION RETENTION • It is the resistance to removal in a direction

opposite to that of insertion. (GPT)

• BOUCHER described retention as the most spectacular yet probably the least important of all complete denture objectives. This property may indeed be least important, it provides psychologic comfort to patient..

Factors affecting retention

. . Anatomical factors

. Physiological factors

. Physical factors

. Mechanical factors

. Oral& facial musculature

. Psychological effects and patient’s tolerance

ANATOMICAL FACTORSANATOMICAL FACTORS

1.Size of the denture bearing area

2.Quality of the denture bearing area

PHYSIOLOGICAL FACTORS

• Saliva- Saliva-

Quality and viscosityQuality and viscosity

The most commonly listed factors of retention include-

A) PHYSICAL FACTORS

• Adhesion

• Cohesion

• Interfacial surface tension

• Capillary attraction

• Atmospheric pressure. .

B) BIOLOGIC FACTORS

• Intimate tissue contact

• Neuromuscular control

PHYSICAL FACTORS

Adhesion

• It is the physical force involved in the attraction between unlike molecules..

Cohesion

• It is the physical attraction of like molecules for each other.

Interfacial surface tension

• It is the resistance to separation possessed by the film of liquid between two well adapted surfaces.

• Viscous tension refers to the force holding to Viscous tension refers to the force holding to parallel force together that is due to the viscosity parallel force together that is due to the viscosity of the interposed liquidof the interposed liquid

• Viscous tension is described by stefan’s law as-

• R=radius, K=viscosity of the liquid, H=thickness of the liquid, F=force, V=velocity

• Viscous tension increases proportionally to increase the viscosity of the interposed liquid and increase in surface area covered by the denture.

Capillary attraction

• It is the force that causes the surface of a liquid to become elevated or depressed when it is in contact with a solid.

Atmospheric pressure

• It is the physical factor of hydrostatic pressure due to the weight of the atmosphere on the earth’s surface.

Mechanical factors

. Undercuts

. Rotational insertion path

. Parallel walls

Biologic factors

Intimate tissue contact - It is the biologic factor that refers to the close adaptation of the denture base to the underlying soft tissues.

Neuromuscular Control– It refers to the functional forces exerted by the musculature of the patient that can affect to retention.

STABILITY

• “the resistance against horizontal movements and forces that tends to alter the relationships between the denture base and its supporting foundation in horizontal or rotatory direction.”

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

The qualities necessary to create and maintain stability are dependent upon the following factors:

Retention Diagnosis Denture base outline Size and form of basal seat. The quality of final impression. Occlusal plane. Proper location and arrangement of the

artificial teeth. Instructions and education of the patient

Diagnosis

• Diagnosis consists of planned observations to determine and evaluate the existing conditions which lead to decision making based on the condition observed.

• Examination of edentulous arches

Intra Oral Examination includes-

• Hard palate

• Soft palate

• Residual ridge height

• Ridge surface examination

• Arch form of upper and lower ridge

• Undercuts

• Ridge relationship

• Frenal attachment

• Tongue

• Saliva

• Mucosal examination

Denture base outline

• Labial flange extends from one buccal frenum to the other.

• Buccal flange extending from buccal frenum to the posterior-most part of distobuccal area.

In Maxillary Denture,

•Posterior palatal seal area.

“The soft tissue along the junction of hard and soft palate on which pressure with in physiologic limit of the tissue can be applied by a denture to aid in the retention of the denture.”

1. The anterior vibrating line is an imaginary line located at the junction of the attached tissues overlying the hard palate and the movable tissues of the immediately adjacent soft palate.

2. The posterior vibrating line is an imaginary 2. The posterior vibrating line is an imaginary line at the junction of the aponeurosis of the line at the junction of the aponeurosis of the tensor veli palatini muscle and the muscular tensor veli palatini muscle and the muscular portion of the soft palate.portion of the soft palate.

In Mandibular Denture,

• Distolingual extension of the lingual flange is the beginning of the seal area of the lower denture. Should extend downward and backward from the retromolar pad at an angle of approximately 450 .

• Level of the floor of the mouth in its normal position is about the level of internal oblique line.

• Most of the movements of tongue necessary to carry out its normal functions occurs above the mandibular teeth, but it appears that the 2mm of extension below the internal oblique ridge provides necessary seal for these movements with out the problem of overextension.

Occlusal Plane

• 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.

• Height of the occlusal rim conform to activities of tongue, cheek and corner of mouth which tend to enhance mandibular denture stability.

• An added reference check, the top of the wax rim in the region of the mandibular 1st bicuspid should never be above the corner of mouth.

An occlusal plane if too high

Forces the tongue into new position i.e. higher position

Loss of tongue accuracy.

Causes raise of floor of mouth.

Undue pressure on the border of the lingual flange

Partial loss of border seal.

An occlusal plane slightly low

Causes no problems for denture patients.

If Occlusal plane is too low

Destabilizes the denture

Proper location and arrangement of the artificial teeth –

“ARCH ARRANGEMENT”

Is used to indicate the buccolingual or buccopalatal relationship of teeth, to either the crest of the ridge or the stress bearing area.

Concept of Neutral Zone by Fish-• Neutral zone is a

potential space between lips and cheeks on one side and tongue on the other where natural or artificial teeth are subjected to equal and opposite forces from surrounding muscles.

• Centric Relation and Centric Occlusion provides stability to the denture.

• The Centric Relation and Centric Occlusion is at same position.

Education of the patient

• Every patient should be informed regarding the care & proper use of his denture.

• Failure to heed the dentist’s advice will eventually lead to damage to the supporting tissues.

• It is usually obvious to them that their failure to master their denture problem in not the fault of the dentist but rather the fault of their own inability to master the normal tongue position

SUPPORT IN COMPLETE DENTURE

• The foundation area on which a dental prosthesis rests.

• With respect to dental prosthesis, the resistance to displacement away from the basal tissue or underlying structure. (GPT-8)

• Complete denture support is “the resistance to vertical movement of the denture base towards the ridge.”

• Support counteracts the forces at right angles to the occlusal surface directed towards the ridge.

Effective support is obtained when-• The denture is extended to cover

maximum surface area without impinging on movable tissues.

• Tissues most capable of resisting resorption are selectively loaded during function.

FACTORS AFFECTING SUPPORT

• Tissues most capable of resisting vertical displacement are allowed to make firm contact with denture base during function.

• Compensation should be made for varying tissue resiliency.

SNOWSHOE PRINCIPLE

• The basic “snowshoe principle” of maximal extension is applied for support.

• It states that given a constant occlusal force, a broader denture-bearing area decreases the stress/unit area under the denture base.

• decreases tissue displacement & reduces denture-base movement.

• The initial denture support is achieved by using impression procedures that provide optimal extension & functional loading of supporting tissues.

• Long term support is obtained by directing the forces of occlusal loading towards those tissues most resistant to remodelling & resorptive changes.

MANDIBULAR ANATOMIC CONSIDERATIONS

BUCCAL SHELF AREA-• The buccal shelf is recognized as a

primary support area for the mandibular denture.

• It is usually covered by mucosa with an intervening submucous layer containing glandular connective tissue & buccinator muscle fibres.

• The muscle fibers along the shelf in a longitudinal anteroposterior direction, permitting the denture base to rest directly on a portion of the buccinator muscle without displacement.

RESIDUAL ALVEOLAR RIDGE-

• Patients exhibiting broad, square well-developed residual ridge covered by firmly bound masticatory mucosa plus a favourable intrinsic bone factor may rely on the ridges for support.

MAXILLARY ANATOMIC CONSIDERATIONS

HARD PALATE-• In the maxillae, the horizontal portion of

the hard palate lateral to the midline raphe should provide support for complete dentures.

• Keratinized masticatory mucosa overlies a distinct submucous layer everywhere but at the midline suture.

• The submucosa contains fatty tissue anterolaterally, & glandular tissue posterolaterally. This resilient layer acts as a cushion for the functional stress transmitted to the mucosa.

• Over the midline raphe, the mucosa is unyielding, & must be relieved to avoid tissue impingement.

• The relief should be minimal to permit light contact of this tissue with the denture base under masticatory loading.

RESIDUAL ALVEOLAR RIDGE

• The crest of the maxillary edentulous ridge is also important in complete denture support.

• The soft tissue is often thick, keratinized, & firmly bound to the periosteum & underlying bone.

Take home message……

• Support, stability & retention are very important features in complete denture fabrication that ensure the best possible treatment for the patient, carefully conserving what remains & replacing what is lost.

MCQsMCQs

1. Adequate retention in complete 1. Adequate retention in complete denture provides-denture provides-

a. Physiologic comforta. Physiologic comfort

b. Psychological comfortb. Psychological comfort

c. Physical comfortc. Physical comfort

d. Longivityd. Longivity

2. Which of the following factor is 2. Which of the following factor is primarily essential for longevity of primarily essential for longevity of complete denture-complete denture-

a.a.RetentionRetention

b.b.StabilityStability

c.c.SupportSupport

d.d.EstheticsEsthetics

3. The factor necessary in complete 3. The factor necessary in complete denture to be firm , stable and denture to be firm , stable and constant while resisting horizontal constant while resisting horizontal and chewing forces is-and chewing forces is-

a.a.RetentionRetention

b.b.StabilityStability

c.c.SupportSupport

d.d.EstheticsEsthetics

4. BOUCHER4. BOUCHER described which factor described which factor as the most spectacular yet as the most spectacular yet probably the least important of all probably the least important of all complete denture objectives-complete denture objectives-

a.a.RetentionRetention

b.b.StabilityStability

c.c.SupportSupport

d.d.EstheticsEsthetics

5. 5. Physical force involved in the attraction between unlike molecules is known as-

a.Cohesion

b.Adhesion

c.Surface tension

d.Capillary attraction

6. The quality to resist separation possessed by the film of liquid between two well adapted surfaces is known as-

a.Cohesion

b.Adhesion

c.Surface tension

d.Capillary attraction

7. 7. According to Stefan’s law, relation of viscous forces (F) with area of opposing surface (A) is-

a. A2

b. A3

c. 1/A2

d. 1/A3

8. 8. According to Stefan’s law, relation of viscous forces (F) with thickness of interposed medium (h)is-

a. h2

b. h3

c. 1/h2

d. 1/h3

9. Snowshoe principle is related with

a.a.RetentionRetention

b.b.StabilityStability

c.c.SupportSupport

d.d.EstheticsEsthetics

10. Neutral zone concept was given 10. Neutral zone concept was given by-by-

a. Bouchera. Boucher

b. Neilb. Neil

c. Fishc. Fish

d.Winkler.d.Winkler.