RESTS AND REST SEATS, Direct And Indirect Flashcards
_____ support must be provided for a removable partial denture.
Vertical
Any components of a partial denture on the tooth surface that provides vertical support is called a?
REST
T/F
Rests Should always be located on a properly prepared tooth surface.
T
The prepared surface of an abutment to receive the rest is called a?
“REST SEAT”.
In short rests serves as (4)
to support the position of a partial denture
to resist movement towards the tissue
to transmit vertical forces to the abutment teeth
to direct those forces along the axis of the teeth.
KENNEDY CLASS III, Modification 1, maxillary arch with rest seats prepared on the lingual surface of the canine and lateral incisor and on the occlusal surfaces of the premolar and molar.
the outline form of an occlusal rest is ______ shape with apex towards the center of the occlusal surface.
ROUNDED TRIANGULAR
KENNEDY CLASS III, Modification 1, maxillary arch with rest seats prepared on the lingual surface of the canine and lateral incisor and on the occlusal surfaces of the premolar and molar.
It should be as long as it is wide, the base of the triangular shape (at the marginal ridge) should be at least _____ mm for both molar and premolars
2.5
T/F
KENNEDY CLASS III, Modification 1, maxillary arch with rest seats prepared on the lingual surface of the canine and lateral incisor and on the occlusal surfaces of the premolar and molar.
Rest seats of smaller dimensions do not provide an adequate bulk for rest.
T
KENNEDY CLASS III, Modification 1, maxillary arch with rest seats prepared on the lingual surface of the canine and lateral incisor and on the occlusal surfaces of the premolar and molar.
The marginal ridge of the abutment tooth at the site of the rest seat must be _____ to the abutment tooth at the site of the rest seat must be lowered to permit a sufficient bulk of metal for strength ad rigidity.
o Reduction of the marginal ridge of approximately ____ mm is usually necessary.
lowered
1.5
KENNEDY CLASS III, Modification 1, maxillary arch with rest seats prepared on the lingual surface of the canine and lateral incisor and on the occlusal surfaces of the premolar and molar.
The floor of the occlusal rest seat should be ___ to the marginal ridge
apical
KENNEDY CLASS III, Modification 1, maxillary arch with rest seats prepared on the lingual surface of the canine and lateral incisor and on the occlusal surfaces of the premolar and molar.
The occlusal surface should also be ____ shaped or ____.
spoon
concave
KENNEDY CLASS III, Modification 1, maxillary arch with rest seats prepared on the lingual surface of the canine and lateral incisor and on the occlusal surfaces of the premolar and molar.
The angle formed by the occlusal rest and vertical minor connector from which it originates should be _____
A degree _____ fails to transmit occlusal forces along the supporting vertical axis of the abutment tooth.
less than 90
more than 90 °
The floor of the occlusal rest should be inclined _____ from the lowered marginal ridge. Any angle less than 90 degree is acceptable as long as the preparation of the proximal surface and lowering and rounding of the marginal ridge precede completion of the rest seat itself
apically
T/F
A lingual rest is preferable than incisal rest because it is placed close to the horizontal axis of rotation of the abutment and therefore has less tendency to tip the tooth.
T
T/F
Lingual rests are more esthetically acceptable than incisal rests
T
T/F
In LINGUAL REST ON CANINES AND INCISOR TEETH
If an anterior tooth is lingually slope rather than perpendicular line the lingual rest if sometimes placed at the cingulum or just incisally to the cingulum.
T
T/ F
In LINGUAL REST ON CANINES AND INCISOR TEETH
Is Usually confined to maxillary canines that have gradual lingual incline and a prominent cingulum
T
In LINGUAL REST ON CANINES AND INCISOR TEETH
A _____-like shape which provides a positive rest seat located favorably in relation to the long axis of the tooth is formed.
saddle
The lingual rest may be placed on the surface of a [6]
- Cast veneer crown.
- A three-quarter crown.
- Inlay
- Laminate veneer
- Composite restoration
- Etched metal restoration
it is least desirable placement of rest seats previously mentioned, it may be used successfully for selected patients when the abutment is sound and when a cast restoration is not otherwise indicated.
INCISAL REST & REST SEATS
Used predominantly as auxiliary rest or as an indirect retainer.
INCISAL REST & REST SEATS
It is applicable to mandibular canine; only applicable to mandibular teeth.
INCISAL REST & REST SEATS
It is applicable to mandibular canine; only applicable to mandibular teeth.
INCISAL REST & REST SEATS
Esthetically it is preferable to the three-quarter crown.
mandibular canine (INCISAL REST & REST SEATS)
T/F
Incisal rest is more likely to lead to some orthodontic movement of the tooth because of unfavorable leverage factor than is a lingual rest.
T
An incisal rest is prepared in the form of a ___ ____ at the incisal edge of an incisor.
rounded notch
In INCISAL REST & REST SEATS
The notch should be ___ both labially and lingually
beveled
An incisal rest should be approximately ____ mm wide & ____ mm deep.
2.5 mm wide
1.5 mm deep
T/F
The incisal rest should be under contoured slightly to allow labial and incisal finishing to the adjoining enamel.
FALSE
The incisal rest should be OVER contoured slightly to allow labial and incisal finishing to the adjoining enamel.
What are DIRECT RETAINERS?
(2)
INTRACORONAL RETAINER
EXTRACORONAL RETAINER
is that quality of a removable partial denture which resists the forces of gravity, the adhesiveness of foods, and the forces associated with opening the jaws.
Retention
that component of a removable partial denture used to retain and prevent dislodgement, consists of a clasp assembly or precision attachment.
Direct Retainer
retention obtained in a removable partial denture by the use of clasps or attachments that resist removal from the abutment teeth
Direct Retention
retention obtained in a removable partial denture by the use of clasps or attachments that resist removal from the abutment teeth
Direct Retention
may be cast or may be attached totally within the restored natural contours of an abutment tooth.
A. INTRACORONAL RETAINER
B. EXTRACORONAL RETAINER
A
typically composed of a prefabricated machined key
and keyway with opposing vertical parallel walls.
A. INTRACORONAL RETAINER
B. EXTRACORONAL RETAINER
A
usually regarded as an internal, precision
attachment.
A. INTRACORONAL RETAINER
B. EXTRACORONAL RETAINER
A
also known as clasp-type
A. INTRACORONAL RETAINER
B. EXTRACORONAL RETAINER
B
most commonly used retainer for RPD
A. INTRACORONAL RETAINER
B. EXTRACORONAL RETAINER
B
mechanical resistance to displacement through
components placed on or attached to the external surfaces of an abutment tooth.
EXTRACORONAL RETAINER
DIRECT RETAINERS ARE COMPOSED OF:
- Minor Connectors
- Rest
- Retentive Arm
- Non-Retentive Arm/Reciprocating Arm
- Occlusal Rest
from which clasp components originate
Minor Connectors
designed to direct stress along the long axis of the tooth.
Rest
should engage a tooth undercut. For most clasps, the retentive region is only at its terminus.
Retentive Arm
should be present on the opposite side of the tooth for stabilization and reciprocation against horizontal movement of the prosthesis (rigidity of clasp arm is essential to it’s purpose
Non-Retentive Arm/Reciprocating Arm
Function of rest and its location
support
occlusal, lingual, incisal
MINOR CONNECTOR
- Function
- Location;
stabilization
proximal surfaces extending from a prepared marginal ridge to the junction of the middle and gingival third of abutment crown.
CLASP ARMS
- Function;
- Location;
-Stabilization (reciprocation) & Retention
-middle third of crown, gingival third of crown in measured undercut.
REQUIREMENTS OF DIRECT RETAINERS
Support
Reciprocity
Bracing and Stability
Retention
Encircle more than 180 degrees.
Passivity
T/f
Rests prevent clasp from being displaced
in gingival direction.
T
Bracing arms, minor connectors
Reciprocity
- resists horizontal movement
- Rest, minor connectors , bracing arms
Bracing and Stability
T/F
passive at rest, activated only during dislodgement
T
this design is most frequently used on the side of
the arch where there is no edentulous space
Embrasure Clasp
● occlusal rests must be used to support the
embrasure portions of the clasp
● should be used with double occlusal rests.
Embrasure Clasp
Indication
- tilted abutments
- most posterior abutments
- usually mesially/ lingually tilted mandibular
molars.
Ring Clasp
it is used when a proximal undercut cannot
be approached by undercut means
Ring Clasp
should always be used with a supporting strut on the non-retentive side, with or without an auxiliary occlusal rest on the
opposite marginal ridge.
Ring Clasp
Design
- clasp approaches undercut from edentulous area and engages undercut opposite to edentulous space.
Circumferential/Akers clasp
correct form of this clasp has only one retentive clasp arm, opposed by a non-retentive reciprocal arm on the opposite side.
Circumferential/Akers clasp
Indication
- Tooth supported partial denture
Circumferential/Akers clasp
Contraindication
- They cannot be used for distal extension cases as they engage the mesiobuccal undercut.
Circumferential/Akers clasp
Hairpin Clasp
Reverse Action Clasp
A simple circlet clasp in which the retentive arm
loops back to engage an undercut apical to the
point of origin.
Reverse Action Clasp
used when a distofacial undercut is present
adjacent to the edentulous space
Reverse Action Clasp
Consists of:
- retentive arm arising from one side of the tooth
Half and half clasp
- a reciprocal arm arising from the other direction on the opposite side of the tooth.
- two minor connectors
Half and half clasp
Indications
- Usually, it is used with isolated premolars and molars bounded and free end partial dentures
Half and half clasp
A circumferential clasp which extends to neighboring teeth in order to provide increased splinting and stabilizing and to engage a more favorable undercut.
Extended Arm Clasp
Indication
- used when the undercut on the tooth near the edentulous area is poor, while that on the adjacent tooth is suitable.
Extended Arm Clasp
Advantages
- The clasp has splinting action
- Distributes lateral load over the two teeth.
Extended Arm Clasp
Best Esthetics
Infrabulge Arm Clasps
I-bar most common
- minimal contact w/ tooth surface so no
food accumulation
- minimal show of metal
- same function as other clasps
Infrabulge Arm Clasps
Engages 0.01 inch undercut
Provides unilateral bracing
Infrabulge Arm Clasps
“Y”, “T”, modified “T” and “U” less useful.
Infrabulge Arm Clasps
● modification of the ring clasp with the same advantages and apparently no disadvantages
● difficult to justify it’s use.
Back-action Clasp
simply two opposing circumferential clasps joined at the terminal end of the two reciprocal arms.
Multiple Clasp
used when additional retention and stabilization are needed, usually on tooth-supported partial dentures.
Multiple Clasp
may be used for multiple clasping in instances in which the partial denture replaces an entire half ot the dental arch.
Multiple Clasp
R- REST (always mesial)
P - ________ (distal)
I - ____(buccal)
PROXIMAL PLATE
I-BAR
During function, proximal plate and I-bar clasp move in ______ direction - disengaging tooth
mesiogingival
When tissue undercuts begin from 3 mm away from the gingival margin, an ____ clasp is used no matter how deep the facial surface tissue under cut.
RPI
R - REST (always_____)
P - PROXIMAL PLATE (distal)
A - _________ARM ( always wrought wire)
mesial
AKER’S RETENTIVE
this distributes more functional load to edentulous ridge.
R- REST (always mesial)
P - PROXIMAL PLATE (distal)
I - I-BAR (buccal)
Indications:
- in distal extension cases, as it provides a stress releasing action.
- when tissue undercuts are not severe
- when esthetic is important
R- REST (always mesial)
P - PROXIMAL PLATE (distal)
I - I-BAR (buccal)
in distal extension RPDs present with
shallow vestibule or severe tissue undercut.
R - REST (always mesial)
P - PROXIMAL PLATE (distal)
A - AKER’S RETENTIVE ARM ( always wrought wire)
when tissue undercuts begin less than 3 mm from the gingival margin and are more than 1 mm in depth, an ____ may be used.
RPA
