FORCES ACTING ON REMOVABLE
PARTIAL DENTURES
Fibers of periodontal ligament are arranged such that their resistance to
vertical forces is much greater
than that to horizontal forces
Tissues are adapted to Tissues are adapted to receive and absorb forces receive and absorb forces within their physiological within their physiological tolerancetolerance
POSSIBLE MOVEMENTS
OF THE PARTIAL
DENTURE
I- Tissue-ward movementsI- Tissue-ward movements
II- Tissue-away movementsII- Tissue-away movements
III- Horizontal movements:III- Horizontal movements: A) Lateral movementsA) Lateral movements
B) Antero-posterior movements.B) Antero-posterior movements.
IV- Rotational movementsIV- Rotational movements
At least four possible movements of the partial dentures exist
Vertical forces acting in gingival direction tending to move the denture towards the tissues
I- Tissue-ward movementsI- Tissue-ward movements
Vertical forces acting in gingival direction tending to move the denture towards the tissues
I- Tissue-ward movementsI- Tissue-ward movements
• Mastication, Swallowing And Aimless
Tooth Contact. Biting Forces
They occur during
• P.D. should be designed to resist this movement by providing adequate supporting components
•This function of the partial denture is called
“Support”
• The Resistance to Tissue Ward Movement
Support
• Distribute the Forces Over the Supporting Sttructure
• Transferring Occlusal Stresses to the Supporting Oral Structures
Distribute the Forces Over the Supporting Structure
II- Tissue-away movementsII- Tissue-away movements
Vertical forces acting in an occlusal direction tending to displace and lift the denture from its position
Tissue-away forces occur due to
The action of muscles acting along the periphery of the denture
•This function of the partial denture is called
“Retention”
Gravity acting on upper dentures or by
sticky food adhering to the artificial teeth or to the denture base.
Resistance to movement of the denture away from its tissue foundation (resistance of a denture to dislodgment)
Retention
This Function Is Mainly Provided By:
1-Mechanical Direct Retainers, Which Engage Undercuts On Abutment Teeth
2-Attachments.
3- physiologic forces on polished surfaces of denture bases
4- physical forces on fitting surfaces of denture bases
Horizontal movementsHorizontal movements A) Lateral movementsA) Lateral movements
Horizontal forces developed when the mandible moves from side to side
during function while the teeth are in contact
Lateral movements have a
destructive effect on teeth leading to tilting, breakdown of the periodontal ligament and looseness of abutment teeth.
Bracing
to Lateral Movement of the Partial Denture
Resistance
This Function Is Mainly Provided By:
Bracing clasp arms placed at or above the survey line of the tooth.
Minor connectors in contact with axial (vertical) surfaces of abutment teeth
Proximal plates
Adequate extension of the flanges
Horizontal movementsHorizontal movements B) Antero-posterior movementsB) Antero-posterior movements
There is natural tendency for the upper denture to move forward
and for the lower to move backward.
Horizontal forces which occur during forward and backward movement of the mandible
during function while the teeth are in contact
Horizontal movementsHorizontal movements B) Antero-posterior movementsB) Antero-posterior movements
Forward movement of the upper denture could be resisted by:
Anterior natural teeth. Palatal slope. Maxillary tuberosity. The natural teeth bounding the edentulous space.
The backward movement of the lower denture could be resisted by:
The slope of the retromolar pad. The natural teeth bounding the saddle area. Proximal plates.
From:From:• Guide planesGuide planes• Bracing clasp armsBracing clasp arms
•Reciprocation I barReciprocation I bar• Lingual platesLingual plates• RestsRests• Denture basesDenture bases
Active I-barActive I-bar
ReciprocationReciprocationI-barI-bar
BRACING AND STABILITYBRACING AND STABILITY
I- Tissue-ward movementsI- Tissue-ward movements
II- Tissue-away movementsII- Tissue-away movements
III- Horizontal movements:III- Horizontal movements: A) Lateral movementsA) Lateral movements
B) Antero-posterior movements.B) Antero-posterior movements.
IV- Rotational movementsIV- Rotational movements
At least four possible movements of the partial dentures exist
IV- Rotational movementsIV- Rotational movements
Rotational movements are due to
the variation in compressibility of
supporting structures, absence of
distal abutment at one end or more
ends of denture bases, and /or
absence of occlusal rests or
clasps at any end of the base
Periodontal ligamentPeriodontal ligament(0.25mm)(0.25mm)
MucosaMucosa(2.0mm)(2.0mm)
Different Displacement Between PDL & Different Displacement Between PDL & MucosaMucosa
1-Rotation of the extension denture base around transverse fulcrum axis:
Class I Lever:
fulcrum: between E and R
E
R
Free end saddle partial denture without indirect retention
1-Rotation of the extension denture base around transverse fulcrum axis:
A) Rotation of the denture base towards the ridge around the fulcrum axis joining
the two main occlusal rests
1-Rotation of the extension denture base around transverse fulcrum axis:
B) Rotation of the denture base away from the ridge around the fulcrum axis
joining the two main occlusal rests
Class I Lever: fulcrum: between E and R R X d1= E X d2
Direction of lever arm: E opposite R
Components of Removable Partial Denture That Are Used to Reduces the Tendency for a Removable Partial Denture to or Rotate in an Occlusal Direction About the Fulcrum Axis
Indirect Retention
when force is directed against unsupported end of beam cantilever can act as first class lever Torque
on the abutment tooth
F
A rigid major connector.
Balanced contact between upper and lower teeth.
Broad base coverage
This movement is counteracted by :
Providing adequate bracing
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