P3-RPD CHAPTER 10

Tooth-supported prosthesis

● Movement potential is less.

● Resistance to functional loading is provided by the teeth.

● Teeth provide efficient support → designs are less variable.

Supporting bone

○ Crown-to-root ratios

○ Crown and root morphologies

○ Tooth number and position in the arch

What are the factors in Tooth-supported prosthesis that may vary but not greatly affect the movement

Tooth-tissue-supported prosthesis

Support comes from residual ridge (remaining alveolar bone + connective tissue + mucosa

alveolar bone

highly variable form after extraction, continues to change with time.

connective tissue and mucosa

→ at risk for pressure-induced inflammatory changes

Opposing tooth position

Existence and nature of prosthesis support in opposing arch 

Potential for harmonious occlusion

Potential sources of functional force from the opposing arch affect prosthesis movement.

○ Natural teeth

○ RPDs

○ Complete dentures

Effect depends on nature of opposing occlusion:

RPDs opposing natural teeth

require greater support and stabilization because of greater functional load demands.

Occlusal relationships at maximum intercuspation

should be broadly dissipated to supporting units

2.0 mm

Tissue thickness of mucosa/mucoperiosteum

0.25-0.1mm

Tissue thickness of periodontal ligament

Class 1 and 2

What classes that has distal extention type

Class 3

What class that is a tooth-supported type

Manner of support

Impression Registration and Jw record

Indirect retention

Base material and Relining

What are the point of difference between the two main types of rpd

Primary support

Secondary support

What is the manner of support for the Distal extention type

tissues underlying the base

Primary support

abutment teeth

secondary support

All support from abutment teeth

Manner of support for tooth-supported type

Varies, because of tissue support involvement

Impression registration for Distal extention type

Different from distal extension type, depends only on tooth support

Impression registration for tootth-supported type

Required, because base may lift away from tissues due to sticky foods or tissue movement

Indirect rentention for the distal extention type

Not required, because no extension base is present Each end of base secured by direct retainer Does not rotate about a fulcrum

Indirect rentention for the tooth-supported type

Requires relining to compensate for tissue changes

relining for distal extention type

acrylic resin

base material for distal extention

Relining not required (except for hygienic, esthetic, or comfort reasons)

relining for the tooth-supported

metal bases

base material for the tooth-supported type

Movement of base under function

○ Determines occlusal efficiency of the partial denture.

○ Determines degree of torque and tipping stresses on abutment teeth.

dental implant

Negative impact of residual ridge character on occlusal support can be managed by _____, making displaceable tissue more resistant for occlusion

Anatomic form and relationship of remaining teeth + surrounding soft tissues

○ Must be recorded accurately → denture should not exert pressure beyond physiologic limits.

○ Impression material → must be removable from undercut areas without permanent distortion

■ Irreversible hydrocolloid (alginate)

■ Mercaptan rubber base (Thiokol)

■ Silicone impression materials (condensation and addition reaction)

■ Polyethers

Elastic impression materials best suited:

firm areas

used as primary stress–bearing areas.

readily displaceable tissues

should not be overloaded.

impression materials

must be capable of displacing tissue sufficiently to record the supporting form of the ridg

■ Fluid mouth-temperature wax

■ Readily flowing impression materials (rubber base, silicones, polyethers in an individual corrected tray)

■ Zinc oxide–eugenol impression paste (for extension base area only)

materials used for the suporting form

Anatomic form and relationship of remaining teeth + surrounding soft tissues

Supporting form of soft tissues underlying distal extension base

Requirements for impression registration in partial denture fabrication

○ Minimizes movement of the partial denture under function.

Maximizes support capacity of the arch

 Proper coordination of support:

rect retention

A fifth point of difference between the two main types of RPDs is in their requirements for

clasp at each enf

The tooth supported partial denture is retained and stabilized by a _____ edentulous space

Must flex during placement and removal to pass over the height of contour of teeth.

 In terminal position → clasp should be passive, flexing only when engaging undercut area to resist vertical dislodging force.

Requirements for clasps

circumferential type

bar type

Cast retentive arms generally used:

circumferential type

from clasp body, approaches undercut from occlusal direction.

bar type

arises from denture base, approaches undercut from gingival direction.

○ Displaceability of supporting soft tissues

○ Accuracy of denture base

○ Total occlusal load applied

Distal base moves tissue-ward under function, influenced by

Clasp elements in undercut area mesial to fulcrum (distal rest):

Must flex sufficiently to dissipate stresses → prevents direct leverage on abutment tooth

clasp with mesial rest

→ transmits less stress to abutment due to fulcrum change → reduces or “breaks” stress.

stress breakers

This is also called as

Stress-breakers

Wrought-wire or bar-type retentive arms:

Types of Stress Control

Wrought-wire or bar-type retentive arms:

believed by others to be more effective and simpler

Stress-breakers:

believed by some to be best at preventing leverage on abutment teeth

Wrought-wire clasp arms

flex more readily in all directions than cast half-round clasp arms → dissipate stresses better

retentive arm

Only the _____of circumferential clasp should be made of wrought meta

rigid cast elements

provide reciprocation and stabilization against lateral/torquing forces.

combination clasp

mix of cast and wrought materials in one direct retainer

terminal abutment of distal extension partial denture

when is combination clasp used

○ When mesiobuccal undercut exists but no distobuccal undercut

○ When gross tissue undercut (cervical/buccal to abutment tooth) exists

Indications for combination clasp

○ Greater flexibility than cast circumferential clasp

○ Adjustability

○ Minimum tooth contact

○ Better esthetics

○ Occasional use even in tooth-supported designs.

Advantages of combination clasp:

○ Direction and magnitude of force

○ Length of denture base lever arm(s)

○ Quality of resistance (from ridges and remaining teeth)

○ Design characteristics of partial denture

Amount of stress transferred to ridge(s) and abutment teeth depends on

○ Location of rest

○ Design of minor connector in relation to guiding plane

○ Location of retentive arm

Important design considerations

Greater surface area contact of minor connector to guiding plane

more horizontal force distribution

■ Periodontal health

■ Crown and root morphologies

■ Crown-to-root ratio

■ Bone index area (response to previous stress)

■ Location of tooth in arch

■ Relationship to other support units (length of edentulous span)

■ Opposing dentition

Considerations for abutment tooth support

■ Quality of residual ridge (bone contour, bone quality, mucosa quality)

■ Extent of ridge coverage by denture base

■ Type and accuracy of impression registration

■ Accuracy of denture base

■ Design characteristics of framework components

■ Anticipated occlusal load

Considerations for ridge support

primarily tooth supported

denture base Adjacent to abutment teeth

more tissue supported

denture base away from abutment teeth

major connectors

must be rigid → distribute forces effectively to supporting structures.

minor connectors

→ transfer functional stress to abutments via rests, and distribute effects of retainers, rests, stabilizers throughout the arch

○ Mechanical retaining elements (clasps) on abutment teeth.

○ Intimate tissue relationship of denture bases and maxillary major connectors.

Retention must resist reasonable dislodging forces. it is accomplished by

○ Avoid direct transmission of tipping/torquing forces to abutment.

○ Correct location of component parts on abutment tooth surface.

○ Provide retention against dislodging forces (consider indirect retention).

○ Compatible with undercut location, tissue contour, and esthetics.

Successful clasp design criteria

undercut

= most important factor for clasp selection that can be modifies by recontouring or restoring abutment

1. Must be supported by oral structures.

2. Must be retained against reasonable dislodging forces

All partial dentures share two requirements:

support

connectors

retainers

kennedy class III, three essential component

rest

support in class 3

stabilizing components

connectors in class 3

direct retention

retaiiners in class 3

best possible ridge support

direct retention considrations

indirect retention

Additional Design Considerations for Distal Extension Bases

1. Alveolar support of abutment teeth

2. Crown and root morphology

3. Rigidity of the RPD framework

4.. Design of occlusal rests

tooth support depends on

tooth-supported RPD

supported entirely from abutment rest

distal-extention RPD

support mainly from soft tissues + residual alveolar bone, with rest support only at abutment end.

○ Quality of residual ridge

○ Extent of ridge coverage by denture base

○ Impression registration (type & accuracy)

○ Accuracy of denture base ○ Framework design ○ Occlusal load

ridge support effectiveness will depend on

Residual ridge

→ can be improved by tissue conditioning or surgery

impression technique

maximize coverage of stress-bearing areas

denture base accurancy

→ material choice + processing technique affect stability.

occlusal load

reduced by fewer, narrower, properly shaped teeth

major connector

unites parts across the arch, must be rigid

minor connector

→ joins major connector to rests, clasps, and other parts

lingual bar

→ half-pear shape, relieved from tissues, smooth inferior border

linguoplate

■ Periodontally weakened lower anteriors

■ Excessive ridge resorption (Class I)

Shallow floor of mouth → lingual bar not possible

U-shaped palatal connector

rarely justified (poor rigidity), used only to avoid large torus

anterior-posterior palatal strap

strong, stable, and biologically sound

broad anatomic palatal connector

preferred; provides rigidity, stability, patient comfort, and may add indirect retention

○ Retain prosthesis against dislodging forces.

○ Resist displacement in horizontal plane

Function of diret retainers to the tooth-supported

intracoronal retainers

ideal, esthetic

extracoronal retainers 

widely used, economical

circumferential clasp

bar clasp

two types of extracoronal retainers

○ Must not impinge gingiva.

○ Minimal torque on abutments.

○ Engage undercut minimally but adequately.

○ Minimal bulk, tooth contac

requirements for the direct retainers

bar clasp

→ indicated when undercut near gingival margin. Avoid if: high placement needed, shallow vestibule, or large tissue undercut.

Must flex or disengage during tissue-ward movement of base → act as stress-breake

Requirements of the direct retainers for the distal extention

mechanical stress breakers

reduce leverage but compromise horizontal stabilization.

○ Must flex in multiple directions.

○ Round, tapered clasp forms are best (flexibility, minimal tooth contact, esthetics).

○ Combination clasps (cast + wrought wire) frequently used.

Clasp arms as stress-breakers:

stabilizing components

● Rigid components that resist horizontal movement.

● Minor connectors contacting vertical tooth surfaces, plus reciprocal clasp arms, act as stabilizers.

● Must be rigid but minimally bulky.

● Best located in interdental embrasures.

● Surfaces should be parallel to path of placement (surveyed).

Reciprocal clasp arm

○ Must be rigid, placed occlusally to height of contour.

○ Often require tooth reduction for placement.

○ Can be inset into crowns for better contour and strength.