Minor Connectors

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Minor Connectors Rests

• Rola M. Shadid, BDS, MSc

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Lecture Outline

• Discuss functions of minor connector
• Discuss types of minor connectors
• Discuss functions of rests
• Discuss forms of rests prep of rest seats

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Minor Connectors

• Connects components to the major connector
• Direct retainer
• Indirect retainer
• Denture base

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Functions of Minor Connectors

• Unification and rigidity
• Stress distribution
• Bracing through contact with guiding planes
• Maintain a path of insertion via contact with
  guiding planes

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Types of Minor Connectors

• Embrasure Minor Connectors
• Between two adjacent teeth

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Embrasure Minor Connectors

• Should have sufficient bulk to be rigid but in
  the same time unobjectionable as possible
• Should be located in an embrasure not be located
  on a convex surface
• Should be tapering toward the contact area

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Embrasure Minor Connectors

• Joins major connector at right angles
• Relief placed so connector not directly on soft
  tissue

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Embrasure Minor Connectors

• It should be thickest toward the lingual surface,
  tapering toward the contact area
• Triangular shaped in cross section

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Embrasure Minor Connectors

• Contact teeth above height of contour
• Prevents wedging tooth mobility

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Gridwork Minor Connectors

• Connect the denture base and teeth to the major
  connector

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Gridwork Minor Connectors

• Adjacent edentulous spaces
• Usually connect major connector to direct
  retainers
• Open lattice work or mesh types

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Gridwork Minor Connectors

• Minor connector for mandibular distal extension
  base should extend posteriorly about 2/3 the
  length of the edentulous ridge
• Never on the ascending portion of the ridge

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Gridwork Minor Connectors

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

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Gridwork Minor Connectors

• Mesh type
• Flatter
• Potentially more rigid
• Less retention for acrylic if openings are small

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Gridwork Minor Connectors

• Lattice Type
• Potentially superior retention
• Interferes with setting of teeth, if struts are
  too thick
• Both types are acceptable if correctly designed

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Gridwork Relief

• Mechanical retention of denture base resin
• Allows the acrylic resin to flow under the
  gridwork

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Gridwork Relief

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

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Relief Under the Gridwork

• Should begin 1.5 - 2 mm from the abutment tooth

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Relief Under the Gridwork

• Creates a metal to tissue contact
• Preferable since it wears less
• Less porous, (hygiene)

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Junction With Major Connector

• Butt joint with slight undercut in metal
• Maximum bulk of the acrylic resin
• Prevents thin, weak edges fracturing

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Gridwork Design
Facially just over the crest of the residual ridge
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Position of Major Connector Junction

• Should be 2 mm medial to lingual surface of
  denture teeth
• Ensures bulk of resin around teeth

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Mandibular Tissue Stops

• Contact of metal with cast at posterior of distal
  extension gridwork
• Prevents distortion at free end during hydraulic
  pressure of processing

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No Tissue Stops In Maxilla

• Maxillary major connector acts as a tissue stop
  (no relief)

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Proximal Plates

• Minor connectors originating from the gridwork in
  an edentulous area
• Broad contact with guiding planes
• May or may not terminate in an occlusal rest

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Proximal Plates
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Proximal Plates

• Shifted slightly lingually
• Increases rigidity
• Enhances reciprocation
• Improves esthetics
• Often a triangular space below the guiding plane
  (an undercut)

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Proximal Plates

• Rigid, cannot be placed in undercut
• Block-out placed in undercuts prior to waxing and
  casting the framework

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

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Rest

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

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Rest Seat

• Portion of a tooth prepared to receive a rest

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Functions

• Direct occlusal forces along long axis of abutment

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Functions

• SUPPORT - Prevents
• impingement of soft tissue

Fractured abutment, no rest seat
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Functions

• Maintains established occlusal relationships by
  preventing settling of the denture

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Functions

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

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Functions

• Provide reference for relines or impressions

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Functions

• Act as indirect retainer
• Prevents rotation (Class I or II RPDs only)

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Form of Occlusal Rest

• Rounded triangular shape with the apex toward
  center of occlusal surface
• As long as it is wide

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Occlusal Rest Seat Form

• Base of triangle should be one third the
  bucco-lingual width of the tooth

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Rest Seat Form

• Smooth flowing outline form (i.e. no sharp line
  angles)

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Occlusal Rest Seat

• Deepest portion is central

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Occlusal Rest Seat

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

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Positive Rest Seats

• An explorer tip will not slide off the rest seat

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Occlusal Rest Seat

• Directs the occlusal forces along the long axis
  of the tooth
• Prevent orthodontic movement

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Occlusal Rest Seat

• Floor should be concave or spoon shaped
  (ball--socket joint)
• Prevents horizontal stresses torque

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Occlusal Rest Seat

• Marginal ridge must be lowered and rounded
  1-1.5mm
• Bulk of metal to prevent fracture

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Occlusal Rest Seat

• Adjacent Tooth
• Rest not flared to facial line angle
• Lingual flared more - space for minor connector

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Secondary Occlusal Rest

• To prevent slippage of the primary rest
• To prevent orthodontic movement
• of abutment tooth
• To direct forces over greatest root mass of
  abutment

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Extended Occlusal Rest

• To minimize further tipping of the abutment
• To ensure that forces are directed down the long
  axis of abutment

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Extended Occlusal Rest

• Extends more than one half mesiodistal width of
  tooth
• One third the buccolingual width of the tooth
• Allow for minimum of 1 mm thickness of metal
• Rounded with no undercuts

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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

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Extended Occlusal Rest (Onlay)

• Provide stabilization
• Restore the contour occlusion of natural
  tooth
• Directs forces down the long axis of tooth

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Double Embrasure (Interproximal) Rest Seat

• Adjacent rests are used to prevent interproximal
  wedging by framework
• Joined rests are designed to shunt food away from
  contact points

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Double Embrasure (Interproximal) Rest Seat Form

• Flared more dramatically on facial and lingual
  line angles

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Interproximal Rest Seat Prep.

• Avoid reducing or eliminating contact points of
  abutment teeth
• Sufficient tooth structure must be removed
• Ensure all line angles are smoothed

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Prep. For Rest Seats

• Rests may be placed on sound enamel or on any
  restoration material
• Rests placed on sound enamel are not conducive to
  caries in mouth with a low-caries index provided
  that good oral hygiene is maintained

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Prep. for Rest Seats

• Patient 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.

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Prep. For Rest Seats

• A fluoride gel should be applied to abutment
  teeth following enamel recontouring
• If the master cast will be fabricated from an
  irreversible hydrocolloid impression, application
  of the gel should be delayed until after
  impressions are made.

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Prep. For Rest Seats

• Light pressure
• High-speed handpiece
• /- Waterspray
• Minimal heat is generated

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Prep. For Rest Seats

• Keep in enamel
• No anesthesia

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Prep. for Occlusal Rest Seats

• The larger round bur is used first to lower the
  marginal ridge and to establish the outline form
  of rest seat
• A slightly smaller round bur is then used to
  deepen floor of rest seat
• The preparation is smoothed by polishing point

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Prep. for Occlusal Rest Seats

• When 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.

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Prep. for Occlusal Rest Seats

• When perforation in restoration does occur, it
  may be repaired, but occasionally the making of a
  new restoration is unavoidable.

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Occlusal Rest Seats in Crowns

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

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Lingual Rests on Canines Incisor Teeth

• A 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

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Cingulum Rest Seat Form

• Inverted V at junction of gingival middle one
  third of tooth
• lt 900

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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

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Cingulum Rest Seat Form

• Slightly rounded to avoid sharp line angles
• Test as positive with explorer tip (floor of
• rest seat should be toward cingulum rather
  than
• axial wall)

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Cingulum Rest Seat

• 2.5 to 3 mm
• mesiodistal length
• 2 mm
• labiolingual width
• 1. 5 mm
• incisal-apical depth

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Correct Preparation
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Preparation Too High
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Preparation Too Low
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Cingulum Rest Prep.

• Do not create an enamel undercut
• Cylindrical bur along the long axis of the tooth

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Maxillary Cingulum Rest Seats

• Avoid opposing occlusion

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Maxillary Cingulum Rest Seats

• 1.5 - 2.0 mm clearance for metal
• Check with articulated models

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Cingulum Rest Seat Placement

• Place in sound tooth structure
• Not on amalgam restorations
• If cingulun not prominent or large pulp
• Use different tooth
• Composite restoration
• Onlay or crown
• Bonded rest seat

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Bonded Rest Seat

• Cast chromium-cobalt alloy rest seat forms
• Attached to lingual surfaces of anterior teeth by
  use of composite resin cements with acid-etched
  tooth prep.

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Ball (Round) Lingual Rest

• Mesial of the canine teeth when typical cingulum
  rest contraindicated
• Large restoration
• Lack of clearance
• with the opposing teeth
• Poor cingulum

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Ball (Round) Lingual Rest

• Spoon shaped, similar to occlusal rest seat
• More difficult due to the incline of the lingual
  surface
• Easily incorporated into crowns

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Ball (Round) Lingual Rests

• Rest seats prep. in
• -tooth surface if sufficient
  enamel thickness exists
• -restorations placed in teeth where
  enamel thickness is inadequate
• More conservative than cingulum lingual rest seats

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Incisal Rest

• The least desirable placement of a rest seat
• Incisal rests are used predominantly as
• - Auxiliary rests
• - Indirect retainers

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Incisal Rest
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Lingual Rest Preferable to Incisal Rest

• Lingual rest placed nearer horizontal axis of
  rotation (tipping axis) of abutment
• - Less tendency to tip the tooth
• More esthetically acceptable than incisal rest

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Incisal rest

• More applicable to mandibular canine
• -Definite support with little loss of
• tooth structure
• -Little display of metal

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Incisal Rest Prep.

• 2. 5 mm wide
• 1. 5 mm deep

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Incisal Rest Prep.

• Rounded notch at the incisal angle with the
  deepest portion apical to the incisal edge
• The notch should be beveled labially lingually

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Multiple Incisal Rests

• Take advantage of natural incisal faceting.
• Tooth morphology does not permit other designs.
• Can restore defective or abraded tooth anatomy.
• Provide stabilization.
• May restore or provide anterior guidance.

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References

• 1. McCrackens Removable Prosthodontics, 11th
  Edition 2005 by McGivney GP, Carr AB. Chapter 5
  and 6
• 2. Dalhousie continual education