minor connectors & rests

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Minor Connectors & Rests. Rola M. Shadid , BDS, MSc. Lecture Outline. Discuss functions of minor connector Discuss types of minor connectors Discuss functions of rests Discuss forms of rests & prep of rest seats. Minor Connectors. Connects components to the major connector - PowerPoint PPT Presentation

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  • Minor Connectors & RestsRola M. Shadid, BDS, MSc

  • Lecture OutlineDiscuss functions of minor connectorDiscuss types of minor connectorsDiscuss functions of restsDiscuss forms of rests & prep of rest seats

  • Minor ConnectorsConnects components to the major connectorDirect retainerIndirect retainerDenture base

  • Functions of Minor ConnectorsUnification and rigidityStress distribution *Bracing through contact with guiding planesMaintain a path of insertion via contact with guiding planes

  • Types of Minor ConnectorsEmbrasure Minor ConnectorsBetween two adjacent teeth

  • Embrasure Minor ConnectorsShould have sufficient bulk to be rigid but in the same time unobjectionable as possibleShould be located in an embrasure not be located on a convex surfaceShould be tapering toward the contact area

  • Embrasure Minor ConnectorsJoins major connector at right angles Relief placed so connector not directly on soft tissue

  • Embrasure Minor ConnectorsIt should be thickest toward the lingual surface, tapering toward the contact areaTriangular shaped in cross section

  • Embrasure Minor ConnectorsContact teeth above height of contour

    Prevents wedging & tooth mobility

  • Gridwork Minor ConnectorsConnect the denture base and teeth to the major connector

  • Gridwork Minor ConnectorsAdjacent edentulous spaces Usually connect major connector to direct retainersOpen lattice work or mesh types

  • Minor connector for mandibular distal extension base should extend posteriorly about 2/3 the length of the edentulous ridgeNever on the ascending portion of the ridge

    Gridwork Minor Connectors

  • Minor connectors for maxillary distal extension denture bases should extend the entire length of the residual ridgeGridwork Minor Connectors

  • Gridwork Minor ConnectorsMesh type FlatterPotentially more rigidLess retention for acrylic if openings are small

  • Gridwork Minor ConnectorsLattice TypePotentially superior retentionInterferes with setting of teeth, if struts are too thick Both types are acceptable if correctly designed

  • Gridwork ReliefMechanical retention of denture base resinAllows the acrylic resin to flow under the gridwork

  • Gridwork ReliefRelief wax is placed in the edentulous areas 1 mm of relief

  • Relief Under the GridworkShould begin 1.5 - 2 mm from the abutment tooth

  • Relief Under the GridworkCreates a metal to tissue contact

    Preferable since it wears lessLess porous, (hygiene)

  • Junction With Major ConnectorButt joint with slight undercut in metalMaximum bulk of the acrylic resinPrevents thin, weak edges fracturing

  • Gridwork DesignFacially just over the crest of the residual ridge

  • Position of Major Connector JunctionShould be 2 mm medial to lingual surface of denture teethEnsures bulk of resin around teeth

  • Mandibular Tissue StopsContact of metal with cast at posterior of distal extension gridworkPrevents distortion at free end during hydraulic pressure of processing

  • No Tissue Stops In MaxillaMaxillary major connector acts as a tissue stop (no relief)

  • Proximal PlatesMinor connectors originating from the gridwork in an edentulous areaBroad contact with guiding planesMay or may not terminate in an occlusal rest

  • Proximal Plates

  • Proximal PlatesShifted slightly lingually Increases rigidityEnhances reciprocationImproves estheticsOften a triangular space below the guiding plane (an undercut)

  • Proximal PlatesRigid, cannot be placed in undercutBlock-out placed in undercuts prior to waxing and casting the framework

  • Rests & Rest Seats

  • The most effective resistance can be provided if the tooth is stressed along its long axisProsthesis should engage the tooth in a manner that encourages axial loading

  • RestA rigid component of RPD resting in a recessed preparation on the occlusal, lingual or incisal surface of a tooth.Provides vertical support

  • Rest SeatPortion of a tooth prepared to receive a rest *

  • FunctionsDirect occlusal forces along long axis of abutment

  • FunctionsSUPPORT - Prevents impingement of soft tissue *Fractured abutment, no rest seat

  • FunctionsMaintains established occlusal relationships by preventing settling of the denture *

  • FunctionsMaintain components in their planned positions (maintains a clasp -tooth relationship)

  • FunctionsProvide reference for relines or impressions

  • FunctionsAct as indirect retainerPrevents rotation (Class I or II RPDs only)

  • Form of Occlusal RestRounded triangular shape with the apex toward center of occlusal surfaceAs long as it is wide

  • Occlusal Rest Seat FormBase of triangle should be one third the bucco-lingual width of the tooth *

  • Rest Seat FormSmooth flowing outline form (i.e. no sharp line angles)

  • Occlusal Rest SeatDeepest portion is central

  • Occlusal Rest SeatFloor should be apical to marginal ridge Angle formed by occlusal rest & vertical minor connector from which it originates should be less than 90

  • Positive Rest SeatsAn explorer tip will not slide off the rest seat

  • Occlusal Rest SeatDirects the occlusal forces along the long axis of the toothPrevent orthodontic movement

  • Occlusal Rest SeatFloor should be concave or spoon shaped (ball-&-socket joint)Prevents horizontal stresses & torque

  • Occlusal Rest Seat Marginal ridge must be lowered and rounded 1-1.5mmBulk of metal to prevent fracture *

  • Occlusal Rest SeatAdjacent ToothRest not flared to facial line angleLingual flared more - space for minor connector

  • Secondary Occlusal Rest *To prevent slippage of the primary rest To prevent orthodontic movement of abutment toothTo direct forces over greatest root mass of abutment

  • Extended Occlusal Rest *To minimize further tipping of the abutment

    To ensure that forces are directed down the long axis of abutment

  • Extended Occlusal RestExtends more than one half mesiodistal width of toothOne third the buccolingual width of the tooth Allow for minimum of 1 mm thickness of metalRounded with no undercuts

  • Extended Occlusal Rest (Onlay) If the abutment is severely tilted, the extended occlusal rest may take the form of an onlay to restore the occlusal plane

  • Extended Occlusal Rest (Onlay) *Provide stabilization Restore the contour & occlusion of natural tooth Directs forces down the long axis of tooth

  • Double Embrasure (Interproximal) Rest SeatAdjacent rests are used to prevent interproximal wedging by frameworkJoined rests are designed to shunt food away from contact points

  • Double Embrasure (Interproximal) Rest Seat FormFlared more dramatically on facial and lingual line angles *

  • Interproximal Rest Seat Prep.Avoid reducing or eliminating contact points of abutment teethSufficient tooth structure must be removed *Ensure all line angles are smoothed

  • Prep. For Rest SeatsRests may be placed on sound enamel or on any restoration materialRests placed on sound enamel are not conducive to caries in mouth with a low-caries index provided that good oral hygiene is maintained

  • Prep. for Rest SeatsPatient should be advised that future susceptibility to caries is not predictable and that much depends on oral hygiene and possible future changes in caries susceptibility.

  • Prep. For Rest SeatsA fluoride gel should be applied to abutment teeth following enamel recontouringIf the master cast will be fabricated from an irreversible hydrocolloid impression, application of the gel should be delayed until after impressions are made.

  • Prep. For Rest SeatsLight pressure High-speed handpiece+/- WatersprayMinimal heat is generated

  • Prep. For Rest SeatsKeep in enamelNo anesthesia

  • Prep. for Occlusal Rest SeatsThe larger round bur is used first to lower the marginal ridge and to establish the outline form of rest seatA slightly smaller round bur is then used to deepen floor of rest seatThe preparation is smoothed by polishing point

  • Prep. for Occlusal Rest SeatsWhen a small enamel defect is encountered in the preparation of an occlusal rest seat, it is usually best to ignore it until the rest preparation has been completed.

  • Prep. for Occlusal Rest SeatsWhen perforation in restoration does occur, it may be repaired, but occasionally the making of a new restoration is unavoidable.

  • Occlusal Rest Seats in CrownsOcclusal rest seats in crowns and inlays are generally made somewhat larger and deeper than those in enamel *

  • Lingual Rests on Canines & Incisor TeethA canine is much preferred over incisor *When a canine is not present, multiple rests that are spread over several incisors are preferable to the use of single incisor

  • Cingulum Rest Seat FormInverted V at junction of gingival & middle one third of tooth< 900

  • Cingulum Rest Seat Form

    Rest seat prep. broadest at most lingual aspect of canine

    As preparation approaches proximal surfaces of tooth, it is less broad than at any other areas

  • Cingulum Rest Seat FormSlightly rounded to avoid sharp line anglesTest as positive with explorer tip (floor of rest seat should be toward cingulum rather than axial wall)

  • Cingulum Rest Seat2.5 to 3 mmmesiodistal length

    2 mm labiolingual width

    1. 5 mm incisal-apical depth *

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