DENTURE BASE

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DENTURE BASE

• Dr. Waseem Bahjat MushtahaSpecialized in
  prosthodontics

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• Definition
• The denture base is that part of the RPD, which
  contacts the oral mucosa and in which the
  artificial teeth are attached.
• Requirements for an ideal denture base
• 1-Accuracy of adaptation to the tissues, with
  minimal dimensional changes.
• 2- Thermal conductivity.
• 3-Non irritant and can maintain good finish and
  polish and easily kept clean.
• 4-Low specific gravity (light in weight)
• 5-Sufficiently strong to resist fracture or
  distortion.
• 6-Esthetically acceptable.
• 7-Can be relined.
• 8-Low coast.

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• Functions
• 1 -Support artificial teeth and transfer stresses
  to the supporting structures.
• 2-Add to esthetics by reproducing natural tissue
  contour.
• 3-Stimulation of underlying tissues by the
  denture movement.
• 4-Prevent vertical and horizontal migration of
  the remaining natural teeth.
• 5-In addition, the distal extension base has the
  following

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• functions
• a-Support the broad coverage provides the best
  support with minimal load per unit area.
• b-Retention is provided by intimate contact of
  the base and palatal plates with the underlying
  tissues and by proper molding of the polished
  surface.

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Types of denture bases

• I-Acrylic denture base
• Advantages
• 1- Low specific gravity.
• 2 -Ease of relining.
• 3- Good esthetics.
• 4-Low coast.
• 5-Ease of fabrication.
• Disadvantages
• 1-Less accurate fitness and high dimensional
  changes.
• 2-No thermal conductivity.
• 3-Low strength, so it is made more thick and
  bulky.
• 4-Law abrasion resistance, so it becomes rough
  and tend to accumulate food particles and
  calcareous deposits.

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• 1I- Metallic denture bases
• Indications
• 1-For short span tooth borne denture.
• 2- When there is insufficient vertical space for
  use of resin.
• 3- When there is a deep vertical overlap of
  anterior teeth .

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• Advantages
• 1-Accuracy and dimensional stability.
• 2-High abrasion resistance.
• 3-Contributes to the health of the underlying
  tissues by its cleanliness.
• 4-Thermal conductivity may help in patient's
  acceptance to the denture.
• 5-High strength can be made in thin sections
  especially cobaltchromium and titanium alloys.
• Disadvantages
• 1-It cannot be relined.
• 2- Difficult in fabrication.
• 3-Poor esthetic.
• 4-Expensive.

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• III- Denture base resin on metal framework
  Indication
• l-For extension bases.
• 2-When denture base resin is needed to restore
  anatomic contour and esthetics.
• 3- When there is a need for relining.
• 4-For long span tooth supported saddle.

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• Design considerations
• 1-The open lattice design with large openings
  provides the greatest retention to the resin. The
  retentive mesh makes the resin packing more
  difficult and the bond between the resin and the
  metal is weak.
• 2- A relief should be provided to the metal
  framework. at the ridge area to provide a space
  to allow resin to completely surround it.
• 3-The internal and external finish lines should
  have less than 90" angle to provide mechanical
  retention for the resin.
• 4-A metal stop should be used on the extension
  base framework for stabilization of the framework
  during packing of resin

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• STRESS BREAKERS (EQUILIZERS) Definition
• It is any device that allows movement between the
  saddle unit and the retainer unit. It is used to
  reduce the lateral and tipping forces on the
  abutment teeth in the tooth- tissue borne partial
  dentures

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• Types of stress breakers
• 1-Any flexible clasp design
• that permits tissueward movement of the
  extension base with minimal leverage on the
  abutment tooth. These clasps include the wrought
  wire clasp, the RPI systems, the roach clasp and
  the C clasp. These types of clasps are commonly
  used to equitably distribute the load between the
  abutment and the ridge.
• 2- A more complicated designs include
• a- movable joints
• between the direct retainer and the denture
  base This type permits both vertical movement
  and hinge movement of the distal extension base.
  These movements prevent direct transmission of
  tipping forces to the abutment teeth during
  function. These devices include hinges, sleeves
  and cylinders, and ball and socket .
• b- A flexible connection
• between the direct retainer and the denture base
  for example split major connector

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• Advantages of stress breakers
• 1-Preservation of the abutment tooth alveolar
  support by minimizing the horizontal force
  falling on it.
• 2-Distribution of the masticatory forces between
  the abutment teeth and the residual ridge.
• 3-Physiologic stimulation of the mucosa by the
  intermittent movement of the denture base.
• 4-If relining was needed but not done the
  abutment teeth are not damaged.

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• Disadvantages
• 1-Difficult to construct and expensive.
• 2-More stresses are falling on the residual ridge
  resulting in increase bone resorption.
• 3- The effect of indirect retainer is reduced.
• 4-lt may allow food and tissue trap.
• 5-lt is liable for distortion and fracture.
• 6-It is difficult to repair.
• 7-If relining was not done when needed, excessive
  resorption of the residual ridge will occur.