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Removal Partial denture Design(Part 1)Dr. Mohamed Ashour AhmedAssistant Professor of Removable Prosthodontics, Faculty of Dental Medicine, Al-Azher University

When you realize you've made a mistake, take immediate steps to correct it.RetentionReciprocationSupportIndirect RetentionRPD REQUIREMENTSBracing and StabilizationA properly constructed partial denture mustAll should be within the physiological limits of the tissues involvedRemovable Partial DentureDesignForces acting on RPD and factors that influence the magnitude of stresses transmitted to the tissues. Is the Planning of the form and extent of RPD, after studying all the factors involved Controlling the stresses by RPD

Design concepts Removable Partial Denture Design Biomechanical aspect of RPD design* Mechanical ----- related to forces and its application to object----- looseness of teeth , bone resorptionetc Removable Partial Denture Design Biomechanical aspect of RPD design

* Bio ------ pertaining to living systems-----inflammation, Caries, bone resorption.etcFORCES ACTING ON REMOVABLE PARTIAL DENTURESThe magnitude and intensity The duration The directionThe frequencyof these forces The Ability Of living tissues To Tolerate Forces Is Largely Dependent UponMaxfieldTissues are adapted to receive and absorb forces within their physiological toleranceFibers of periodontal ligament are arranged such that their resistance to vertical forces is much greater than that to horizontal forces

Class I Lever: fulcrum: between E and R R X d1= E X d2Direction of lever arm: E opposite R

Class I Lever:

fulcrum: between E and RERFree end saddle partial denture without indirect retention

Class II Lever: fulcrum at one end, Resistance R: More than E (force)Prevent rotation of the free end saddle around the fulcrum lineINDIRECT RETAINERS

Class II Lever15

Class III Lever: fulcrum at one endResistance: less than EClass III Lever: fulcrum at one end

Aker Claspa- when force is directed against unsupported end of beam cantilever can act as first class lever Torque on the abutment tooth

Fb- A cantilever design allows excessive vertical movement toward the residual ridgea

a beam supported only at one end, when force is directed against unsupported end of beam cantilever can act as first class lever Mesial rest concept for distal extension removable partial dentures

POSSIBLE MOVEMENTS OF THE PARTIAL DENTURE I- Tissue-ward movementsII- Tissue-away movementsIII- Horizontal movements: A) Lateral movements B) Antero-posterior movements.IV- Rotational movementsFour possible movements of the partial dentures exist I- Type of movement

II- Causes

III- Function of the partial denture that resist this movement

IV- Components of PD that provide this functionFour possible movements of RPDVertical forces acting in gingival direction tending to move the denture towards the tissues I- Tissue-ward movements

Control direction of forceMastication. Swallowing Parafunction.They occur duringRPD should be designed to resist this movement by providing adequate supporting components This function of the partial denture is called SupportThe Resistance to Tissue Ward MovementSupportAdequate Distribution of Forces Over the Supporting Sttructure and decrease forces/unit areaTransferring Occlusal Stresses to the Supporting Oral Structures

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 receive and absorb forces within their physiological tolerance

Periodontal ligament(0.25mm)Mucosa(2.0mm)Different Displacement Between PDL & Mucosa29The extension partial present a unique situation that it is relies upon two entirely different sources of support. The tooth represent a relatively immobile support, but the mucosa are displaceable to varying degree. This factor must be fully understood and analyzed in planning the extension base RPD. This Function Is Mainly Provided By: Properly designed supporting rests placed in rest seats, which are prepared on the abutment teeth, Broad accurately fitting denture bases in distal extension partial dentures. Rigid major connectors that are neither relieved from the tissues nor placed on inclined planes also provide support

Support is provided byDenture base.Maxillary major connectors.Rests.Rigid portions of clasps placed over the survey line.

Distribute the Forces Over the Supporting Structure

Is the Mandibular major connector play a role in support of RPD ?Lingual plate ?

34II- Tissue - away movementsVertical forces acting in an occlusal direction tending to displace and lift the denture from its position Tissue - away forces occur due toThis function of the partial denture is called RetentionThe action of muscles acting along the periphery of the denture Gravity acting on upper dentures.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

Adhesion Cohesion Interfacial surface tension. At. pressure GravityMechanicalRetentionPhysiologicalPhysicalThe physiologic molding of the tissues around the polished surfaces neuromuscular control Direct retainersIndirect R. Frictional fit Parts of the denture engaging tooth and tissue undercuts.Frictional fit Mechanical means of RetentionIndirect R. Direct retainersParts of the denture engaging tooth and tissue undercuts.ClaspsAttachmentsHave less surface area.Are bathed in saliva.Lower major connectors are relieved. The effect of physical forces is less applicable to lower dentures than upper because:contrary to upper major c. that are well adapted and their borders are beaded against the underlying tissues.4. Strong movements of the tongue

1- Mechanical Direct Retainers, Which Engage Undercuts On Abutment TeethIntracoronal (Precision attachments).Extracoronal

AttachmentsIntracoronal This Function Is Mainly Provided By: Direct RetainersExtracoronal2- physiologic forces on polished surfaces of denture bases

3- physical forces on fitting surfaces of denture bases

III - Horizontal movements A) Lateral movementsHorizontal 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.

Masticatory cycle ( frontal View)[Tear Drop appearance]BracingResistance to Lateral Movement of the Partial Denture

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

BRACINGLateral movement is resisted by: Maximum extension and coverage of the sides of the residual ridge with the denture base within the physiological limit.Rigid bracing clasp arms.Use of a continuous bar resting on the lingual surfaces of natural standing teeth (Kennedy bar).Rigid major and minor connectorsReduction of cusp angle inclination of the artificial teeth and balanced occlusion.Reduced occlusal table.Horizontal movements B) Antero-posterior movementsThere 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 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.ForceDentureResisting structuresAnteriorMaxillaryHealthy natural anterior teeth.The anterior slope of the hard palate.Clasp arms encircle a posterior tooth.The tuberosity covered by the saddle.MandibularHealthy natural anterior teeth.PosteriorMaxillaryPosterior teeth in bounded saddles.The labial saddle flange.Clasp arms on anterior tooth.MandibularPosterior teeth in bounded saddles. The steeply sloping retro molar region. Clasp arms on anterior tooth.Reciprocation It is the resistance to horizontal forces exerted on a tooth by the retentive clasp terminal during insertion and removal of the RPD, this force equal is amount, but in an opposite direction, on the opposite side of the teeth.

Palatal viewProximal viewRECIPROCATIONRECIPROCATION can be achieved by: Reciprocal clasp arms contacting the tooth prior to or at the same time the retentive tip crosses the survey line of the tooth.Parts of the major connectors.Proximal plates.We should revise cross arch resproticaon54IV- Rotational movementsRotational movements are due to the variation in compressibility of supporting structures, absence of distal abutment at one end or more ends of denture bases.absence of occlusal rests or clasps beyond the fulcrum line.Directions of rotational movementsRotation of the extension denture base around transverse fulcrum axis.

Rotation of all bases around a longitudinal axis parallel to the crest of the residual ridge.

Rotation about an imaginary perpendicular axis

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 restsB) Rotation of the denture base away from the ridge around the fulcrum axis joining the two main occlusal rests1-Rotation of the extension denture base around transverse f