RETENTION, STABILITY

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RETENTION, STABILITY SUPPORT IN COMPLETE
DENTURE
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Specific learning objectives

• Definition and importance of Retention ,
  stability and support in complete denture.
• Factors affecting Retention , stability and
  support in complete denture.
• How to overcome common difficulties(in brief).

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Factor affecting Successful denture fabrication
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Biologic Factors Physical Factors
Mechanical Factors Retention
Stability Support Psychologic
Physiologic Longevity Comfort
Comfort Prosthesis Success
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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.

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Factors affecting retention

• . Anatomical factors
• . Physiological factors
• . Physical factors
• . Mechanical factors
• . Oral facial musculature
• . Psychological effects and patients tolerance

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ANATOMICAL FACTORS

• 1.Size of the denture bearing area
• 2.Quality of the denture bearing area

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PHYSIOLOGICAL FACTORS

• Saliva-
• Quality and viscosity

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• The most commonly listed factors of retention
  include-
• A) PHYSICAL FACTORS
• Adhesion
• Cohesion
• Interfacial surface tension
• Capillary attraction
• Atmospheric pressure.

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• B) BIOLOGIC FACTORS
• Intimate tissue contact
• Neuromuscular control

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PHYSICAL FACTORS

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

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

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

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• Viscous tension refers to the force holding to
  parallel force together that is due to the
  viscosity of the interposed liquid
• Viscous tension is described by stefans law as-
• Rradius, Kviscosity of the liquid, Hthickness
  of the liquid, Fforce, Vvelocity
• Viscous tension increases proportionally to
  increase the viscosity of the interposed liquid
  and increase in surface area covered by the
  denture.

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• 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.

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• Atmospheric pressure
• It is the physical factor of hydrostatic pressure
  due to the weight of the atmosphere on the
  earths surface.

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Mechanical factors

• . Undercuts
• . Rotational insertion path
• . Parallel walls

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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.

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

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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.

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

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• 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

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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

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• Intra Oral Examination includes-
• Hard palate
• Soft palate
• Residual ridge height
• Ridge surface examination
• Arch form of upper and lower ridge

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• Undercuts
• Ridge relationship
• Frenal attachment
• Tongue
• Saliva
• Mucosal examination

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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.

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• 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.

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• 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
  line at the junction of the aponeurosis of the
  tensor veli palatini muscle and the muscular
  portion of the soft palate.

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• 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 .

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• 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.

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Occlusal Plane

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

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• 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.

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• 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.

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• 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.

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• An occlusal plane slightly low
• Causes no problems for denture patients.

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• If Occlusal plane is too low
• Destabilizes the denture

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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.

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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.

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• Centric Relation and Centric Occlusion provides
  stability to the denture.
• The Centric Relation and Centric Occlusion is
  at same position.

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Education of the patient

• Every patient should be informed regarding the
  care proper use of his denture.
• Failure to heed the dentists 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

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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)

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• 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.

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FACTORS AFFECTING SUPPORT

• 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.

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• 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.

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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.

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• 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.

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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.

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• 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.

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• 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.

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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.

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

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• 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.

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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.

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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.

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MCQs

• 1. Adequate retention in complete denture
  provides-
• a. Physiologic comfort
• b. Psychological comfort
• c. Physical comfort
• d. Longivity

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• 2. Which of the following factor is primarily
  essential for longevity of complete denture-
• Retention
• Stability
• Support
• Esthetics

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

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• 4. BOUCHER described which factor as the most
  spectacular yet probably the least important of
  all complete denture objectives-
• Retention
• Stability
• Support
• Esthetics

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• 5. Physical force involved in the attraction
  between unlike molecules is known as-
• Cohesion
• Adhesion
• Surface tension
• Capillary attraction

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• 6. The quality to resist separation possessed by
  the film of liquid between two well adapted
  surfaces is known as-
• Cohesion
• Adhesion
• Surface tension
• Capillary attraction

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• 7. According to Stefans law, relation of viscous
  forces (F) with area of opposing surface (A) is-
• a. A2
• b. A3
• c. 1/A2
• d. 1/A3

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• 8. According to Stefans law, relation of viscous
  forces (F) with thickness of interposed medium
  (h)is-
• a. h2
• b. h3
• c. 1/h2
• d. 1/h3

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• 9. Snowshoe principle is related with
• Retention
• Stability
• Support
• Esthetics

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• 10. Neutral zone concept was given by-
• a. Boucher
• b. Neil
• c. Fish
• d.Winkler.